CN110254340B - Portable liquid nitrogen-based refrigeration system for transporting refrigerated goods - Google Patents

Portable liquid nitrogen-based refrigeration system for transporting refrigerated goods Download PDF

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CN110254340B
CN110254340B CN201810504018.3A CN201810504018A CN110254340B CN 110254340 B CN110254340 B CN 110254340B CN 201810504018 A CN201810504018 A CN 201810504018A CN 110254340 B CN110254340 B CN 110254340B
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cold
air
temperature
cooling
liquid nitrogen
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CN110254340A (en
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普拉森特·卡尔
卢普·高希
萨里什·戈文德·基兰科
安基特·蒂瓦里
海孟德·库默·帕特尔
哈利巴西·S·沃拉
拉蒂普·库默·库什
皮尤什·萨克塞纳
苏雷斯·钱德拉·潘迪达
迪帕克·库默·阿扎里
阿布希雪克·贾恩
拉克什曼·辛格
L·阿拉基利斯沃米
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Yuan Zinengmishubu
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Yuan Zinengmishubu
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60H—ARRANGEMENTS OF HEATING, COOLING, VENTILATING OR OTHER AIR-TREATING DEVICES SPECIALLY ADAPTED FOR PASSENGER OR GOODS SPACES OF VEHICLES
    • B60H1/00—Heating, cooling or ventilating [HVAC] devices
    • B60H1/32—Cooling devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60P—VEHICLES ADAPTED FOR LOAD TRANSPORTATION OR TO TRANSPORT, TO CARRY, OR TO COMPRISE SPECIAL LOADS OR OBJECTS
    • B60P3/00—Vehicles adapted to transport, to carry or to comprise special loads or objects
    • B60P3/20—Refrigerated goods vehicles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
    • F25D3/10—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid air

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Transportation (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)

Abstract

The present invention relates to a liquid nitrogen based refrigeration system for storing and transporting perishable goods/food at controlled temperature and humidity levels. The present invention provides for the storage and transportation of goods that require a controlled temperature to be maintained in the range of-50 ℃ to +20 ℃ within a vacuum insulated cold room. The system maintains temperature and humidity levels within the cold cabin by means of a specially designed cryogenic flywheel unit that includes a water-ethanol heat exchanger and ammonia-based Loop Heat Pipes (LHP) for cooling air and storing refrigerated goods. The modular skid supports four/eight such cold pods having LNs 2 Storage container, circulation pump/fan and battery. The skid is designed so that it can be supported on a truck, trolley, rail wagon, ship or as a stand-alone stationary system, and all four/eight cold compartments supported on the skid have independent temperature and humidity control units so that each compartment can be maintained at different temperature and humidity levels independently of the other compartments.

Description

Portable liquid nitrogen-based refrigeration system for transporting refrigerated goods
Technical Field
The invention relates to the use of Liquid Nitrogen (LN) 2 ) As a cooling source to refrigerate and transport perishable goods, such as food, vegetables, fruits, medical products, fish, meat, and the like, at controlled temperature and humidity levels to extend their useful life. The present invention provides flexibility in operation and provides a single common solution for storing and transporting goods requiring controlled temperatures of about 0 ℃ (up to +20 ℃) and goods requiring refrigeration temperatures up to-50 ℃ (the same configuration can provide this wide range-50 ℃ to +20 ℃) in an efficient manner without any mechanical changes to the configuration. More specifically, the present invention provides a reliable, efficient and cost effective way to maintain temperature and humidity levels inside cargo-carrying containers called cold boxes by means of Loop Heat Pipes (LHP) and specially designed cryogenic flywheel units with water-ethanol heat exchangers for the dual purpose of storing refrigerated goods and cooling air. A specially designed modular skid supports four/eight such cold tanks and their temperature and humidity control units, LN2 storage containers, circulation pumps/fans, and batteries for powering the circulation pumps/fans. The skid is designed so that it can be supported on any truck, trolley, rail wagon, or can be considered a free standing fixture system. All four/eight cold compartments with independent temperature and humidity control units supported on the skid blocks can be maintained at different temperature and humidity levels, providing storage flexibility. The invention also relates to a cold box design suitable for use in a temperature and humidity control unit and also for reducing heat leakage to a storagePerishable material of the deposit, and use of emission N 2 The vapor protects and rapidly reduces the temperature of the cold compartment of the system. Briefly, the present invention proposes a modular skid having a cold box for storing and transporting perishable items and a specially developed temperature and humidity control unit that can maintain a wide range of temperatures and desired humidity levels by means of LHP and a specially designed cryogenic flywheel that includes an alcohol-water heat exchanger using LN2 as a cooling source and has inherent advantages of operational flexibility, rapid cool down, simpler and more economical operation, etc.
Background
The present invention relates to methods and apparatus for transporting refrigerated food or other goods in a transportable refrigeration skid in an efficient controlled environment in a storage space (i.e., under controlled temperature and humidity conditions appropriate for a given food or goods). Such skid blocks carry an environmentally controlled rectangular/cylindrical chamber (known as a cold box) for storing items such as fruits, vegetables, pharmaceuticals and other such items requiring appropriately controlled conditions, primarily temperature and humidity using liquid nitrogen as the primary source of refrigeration. This skid performs all the functions of the REEFER, but is more robust (typically for bad road conditions), provides operational flexibility and controls the overall environment (both temperature and humidity), which is not possible with each conventional refrigerated vehicle (only some of them have this facility). The skid is likely to integrate with the cold chain that is being established in india and many developing countries, thereby replacing traditional refrigerated vehicles.
It is common practice to transport food or goods in mechanical refrigerated trucks to a refrigerator, a market or a shop. Mechanical refrigerated trucks carry sufficient food to serve multiple markets or stores. When parking a vehicle, a person must enter the truck storage space and discharge a quantity of selected food or cargo. In general, the cooling systems for such trucks are typical mechanical compressor based systems, comprising an evaporator and a condenser. Not only is such a system more costly to operate, but such a system is prone to mechanical failure (failure frequency may be higher for poor road conditions), which in turn may negatively impact the quality of the food. Furthermore, the refrigerant circulating in such systems may contaminate the atmosphere if it leaks. The refrigeration unit is driven by a diesel engine which in any case pollutes the environment.
Cooling systems for a few vehicles using liquid nitrogen as the primary cooling source are known, using hybrid systems, i.e. liquid nitrogen in combination with a compressor-based system, or liquid nitrogen alone. These liquid nitrogen systems, however, primarily utilize a cold nitrogen spray in the refrigerated space and are therefore cooled by direct introduction of liquid nitrogen. The atmosphere will therefore contain an excess of gaseous nitrogen and will not be breathable, thereby constituting a safety risk for the staff due to oxygen deprivation. Examples of refrigerated vehicles utilizing liquid nitrogen (direct injection of liquid nitrogen or indirect cooling of air in a heat exchanger) can be found in U.S. patent nos. 4,060,400, 6,345,509B1 and 3,464,222 and soviet patent No. 1,204,888.
In us patent No. 4,060,400, the refrigerator mentioned in the semi-trailer for transporting frozen food products has an automated cooling apparatus that includes both a compressor-based system and a cryogenic system. This arrangement has certain risks associated with it due to the direct injection of liquid nitrogen, and there are also disadvantages of compressor-based systems as described above.
This is the fact that: the liquid nitrogen based system is much more advantageous than the conventional mechanical compressor based system because it rapidly lowers the temperature of the storage space of the refrigerated vehicle from near room temperature after frequent door openings or initially.
In soviet patent No. 1,204,888, liquid nitrogen is fed into an open tray along the inside wall of the refrigerator body. The liquid nitrogen evaporates in the pallet causing a cold vapor of gaseous nitrogen to leave the pallet and fill the space in the trailer, thereby cooling the transported cargo. This system requires additional safety measures for ensuring a breathable atmosphere, as well as measures for safe and effective refrigeration while the door is open.
Us patent No. 3,464,222 describes a refrigerated vehicle using liquid nitrogen in which the liquid is directed through an injection pipe arrangement and simultaneously through an evaporator arrangement. As the liquid nitrogen flows through the evaporator unit, it is converted to gaseous nitrogen which is used to drive a fan to draw air into the space to effect environmental control. Thus, when liquid nitrogen is injected in the space, air is sucked into the space. However, there is still a serious safety risk due to the high level of nitrogen in the air.
Priori knowledge:
this a priori knowledge is limited to two categories of refrigerated vehicles (refrigerated vehicles) which are:
A. there are refrigerated vehicles consisting of large thermally insulated (with PUFs, extruded polystyrene, etc.) compartments that are cooled by a refrigerator based on a vapor compression cycle.
B. A recent area being developed is refrigerated vehicles that utilize liquid nitrogen for cooling, but the process is quite different. For example, they do not allow for active control of humidity, etc. They also do not provide such a large temperature range. Where liquid nitrogen is injected to reduce the temperature in a conventional refrigerated vehicle, thereby constituting a safety risk for the workers who will enter the refrigerated area because of the high percentage of nitrogen in the containers.
The proposed invention is completely different in terms of operating principle, cooling scheme and construction.
Disadvantages associated with the processes/devices known hitherto:
disadvantages of prior knowledge in this field are:
a. the entire refrigerated vehicle is maintained at the same temperature and ambient conditions and therefore the same items must be stored throughout the refrigerated vehicle. There is no flexibility. Some refrigerated vehicles at best provide a partition so that different items can be stored in different compartments, but mixing does occur.
b. There are several dynamic components and therefore poor road conditions are a big problem, especially in the case of suburban roads.
c. Refrigerated vehicles are cooled by conventional refrigeration systems based on vapor compression cycles and have frequent maintenance problems when used in rough road conditions.
d. Because of the problem of backhaul cost, the operation cost is high and the utilization rate is low.
e. The use of diesel fuel and refrigerant can lead to environmental degradation.
f. A major problem is also the high operating costs of the refrigerated vehicle, since conventional refrigerated vehicles as well as liquid nitrogen based refrigerated vehicles (which use PUF to insulate the cargo compartment) suffer from high heat leakage.
Object of the Invention
The primary object of the present invention is directed to providing a portable liquid nitrogen based refrigeration system for transporting refrigerated goods that maintains a desired temperature for the goods/food loaded in a cold room loaded on a transportable skid, with or without humidity control of the refrigerated storage space, by using a new cooling scheme that utilizes liquid nitrogen as the primary refrigeration source.
Another object of the present invention is directed to providing such a portable liquid nitrogen-based refrigeration system for transporting refrigerated goods wherein a vacuum insulated double-walled tank for storage and a vacuum insulated transmission line are used to prevent heat transfer into/out of the system.
Yet another object of the present invention is directed to providing such a portable liquid nitrogen based refrigeration system for transporting refrigerated goods wherein a plurality of cold compartments with associated cooling units and liquid nitrogen containers may be suitably stacked in skid-mounted blocks with wheels for ease of handling, suitably stacked within standard containers placed on trucks/trailers or railroad trucks and the like for transport.
Yet another object of the present invention is directed to providing such a portable liquid nitrogen-based refrigeration system for transporting refrigerated goods wherein the temperature and humidity of the individual cold compartments can be independently controlled/maintained to transport different food items requiring different environments during transport, which food items are stored in different chambers while also conserving the consumption of liquid nitrogen.
Yet another object of the present invention is directed to providing such a portable liquid nitrogen-based refrigeration system for transporting refrigerated cargo wherein the temperature and humidity set points required for the different materials to be transported can be provided in a PLC and associated electronic control system which controls the flow of liquid nitrogen/nitrogen vapor and gas streams into the compartment in accordance with the set points to maintain the environment within the compartment.
Yet another object of the present invention is directed to providing such a portable liquid nitrogen based refrigeration system for transporting refrigerated goods wherein the system employs a primary heat exchanger that exchanges heat with liquid nitrogen acting as a cold source using an alcohol-water solution of selected concentration to maintain the temperature of the storage space within the range of-50 ℃ to 20 ℃ for the food/non-food items being stored.
Yet another object of the present invention is directed to providing such a portable liquid nitrogen-based refrigeration system for transporting refrigerated goods wherein the purpose of humidity control is accomplished by placing loop heat pipes in communication with a primary heat exchanger as needed for the goods to be stored/transported.
A further object of the present invention relates to providing said portable liquid nitrogen-based refrigeration system for the transport of refrigerated goods, wherein minimum dynamic components are involved and thus a longer service life and less maintenance of the equipment are ensured even in bad road conditions, in particular in the case of suburban roads.
Disclosure of Invention
A basic aspect of the present invention is directed to providing a portable liquid nitrogen-based refrigeration system for transporting refrigerated cargo comprising:
at least one temperature controlled cold housing/cold bin defining a refrigerated storage space having an inlet for fresh cold air and an outlet for recycled air exhausted from the cold housing/cold bin;
an alcohol-water heat exchanger having a reservoir of ethanol water solution cooperatively disposed with respect to fresh/recirculated air entering the cold housing from the recirculated air outlet;
a cooling source comprising liquid nitrogen, the cooling source being operatively connected to the alcohol-water heat exchanger to freeze an aqueous ethanol solution to a desired controlled cryogenic temperature;
a PLC controller for monitoring storage conditions within the cold housing/cold bin and regulating the entry of the temperature controlled fresh/recirculated air after contacting the alcohol-water heat exchanger as a temperature controlled cold air stream flowing forward into the storage space of the cold housing/cold bin to maintain a set temperature inside the storage space of the cold housing/cold bin and to exhaust recirculated air out as a return air stream flowing from the cold housing/cold bin.
Another aspect of the invention relates to a portable liquid nitrogen based refrigeration system in which the temperature controlled fresh/recirculated air is also humidity controlled, comprising involving a loop heat pipe exchanger cooperating with the alcohol-water heat exchanger, the loop heat pipe exchanger comprising a pre-cooling (evaporator) section and a re-heating (condenser) section and a cooperating solenoid valve for controlled re-heating of air flowing on a loop connecting the tubes of both the pre-cooling and re-heating sections.
Yet another aspect of the invention relates to a portable liquid nitrogen based refrigeration system wherein each of said cold housings/cold compartments is provided with a respective cryogenic flywheel/cooling unit comprising a heat exchanger unit with or without a circulating Loop Heat Pipe (LHP), a fan/blower for controlled circulation of fresh air supply intake and return air exhaust, said heat exchanger unit and said fan/blower being respectively operatively connected to solenoid valves controlled by a PLC.
Yet another aspect of the invention relates to a portable refrigeration system based on liquid nitrogen, optionally operating lines for directing at least a portion of the return air stream from the storage space of a cold room through the alcohol-water heat exchanger where it is cooled again to a set temperature and fed to contact the aqueous ethanol solution, such that it freezes the solution at-40 ℃ to-100 ℃ as required.
Another aspect of the invention relates to a portable liquid nitrogen based refrigeration system including each of said cold enclosures/cold compartments having a coordinated nitrogen vapor supply into said enclosure/compartment for forwarding nitrogen vapor generated after heat exchange of liquid nitrogen in said heat exchanger for utilizing residual refrigeration in said nitrogen vapor to cool said cold enclosures/cold compartments.
Yet another aspect of the invention relates to the portable liquid nitrogen based refrigeration system wherein the coordinated nitrogen vapor supply into each of the enclosures/cold compartments includes a liquid nitrogen delivery line inside the cold enclosure/cold compartment wall connected to the main liquid nitrogen supply line into the heat exchanger, each of the cold enclosure/cold compartments is housed within a cold enclosure/cold compartment delivery enclosure for transport and the nitrogen vapor is released into the cold enclosure/cold compartment delivery enclosure after cooling the respective cold enclosure/cold compartment.
Another aspect of the invention relates to a portable liquid nitrogen-based refrigeration system comprising: an ammonia-based loop heat pipe exchanger in combination with the alcohol-water heat exchanger, the system having a pre-cooling section and a reheat section that pre-cools a return air stream before cooling in the heat exchanger and re-heats after cooling in the heat exchanger to achieve a desired set humidity and temperature in a controlled manner, preferably the ammonia-based loop heat pipe is placed around a main heat exchanger in the cryogenic flywheel/cooling chamber such that it first sub-cools incoming air to the main heat exchanger and then re-heats the air in the condenser section of the LHP, which condenser section together with the heat exchanger provides a facility that addresses both dehumidification and cooling simultaneously, the facility being assisted by a solenoid valve provided to control the flow of liquid nitrogen in the system,
a blower to maintain air flow in the cold box and exhaust fan to facilitate return of air from the cold box after cooling the cold box,
a cryogenic flywheel/cooling chamber with a damper to draw in air from the atmosphere and maintain freshness of the air; self-pressurized liquid nitrogen vacuum insulated container comprising safety devices including pressure reducing valves and pressure regulating valves, and the control of the flow is performed by an electronic system controlled by a PLC.
Another aspect of the invention relates to a portable liquid nitrogen-based refrigeration system comprising: a plurality of said temperature controlled cold shells/pods, each being a vacuum insulated double walled shell/pod defining a plurality of refrigerated storage spaces;
each of said storage spaces having a respective said alcohol-water heat exchanger for controlling independent cooling of the respective storage space;
the PLC controller independently monitoring the storage conditions inside each of the cold enclosures/cold compartments and regulating the admission of fresh/recirculated air flowing in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside each of the storage spaces in the range of-50 ℃ to room temperature (20 ℃) and to exhaust recirculated air from each of the cold enclosures/cold compartments independently of each other to allow for variable conditions required to store goods/items in the respective storage spaces.
Another aspect of the invention relates to a portable liquid nitrogen-based refrigeration system comprising: a plurality of vacuum insulated temperature controlled cold shells/cold boxes based on various shapes and configurations, each cold shell/cold box having a base operably connected to self-pressurizing Liquid Nitrogen (LN) 2 ) A self-contained cooling unit/cryogenic flywheel of supply container, valve box with other auxiliary systems and controller unit, said cold housing/cold bin being portable and loadable onto a trailer/truck to achieve the desired portability of refrigerated goods/items; and
a PLC controller for monitoring storage conditions inside the cold housing/cold box and regulating the intake of fresh/recirculated air flowing in contacting the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to exhaust recirculated air from the cold housing/cold box.
Another aspect of the invention relates to a portable liquid nitrogen-based refrigeration system comprising: install more on sled dress pieceIndividual cold boxes with their self-contained cooling units/cryogenic flywheels, from LNs mounted on the same skid 2 The vessel feeds all of said cryogenic flywheel on the cold pods simultaneously in a controlled manner involving the valve box and controller unit, each of said cold pods being independently and individually loaded/unloaded from the skid as and if required, without affecting the operation/performance of the other pods.
Yet another aspect of the present invention relates to a portable liquid nitrogen-based refrigeration system suitable for both temperature and humidity control, comprising: a cooling unit/cryogenic flywheel of the cold room comprising said heat exchanger, a surrounding ammonia loop heat pipe, a fan/blower for air circulation, a shutter with a damper for controlling the supply of fresh air and the discharge of return air, respectively, and a solenoid valve controlled by a PLC;
PLC controlling LN in transmission line 2 Flow to properly cool the heat exchanger unit to a set temperature, then the cold nitrogen vapor flows through coils wound on an inner vessel before escaping to the atmosphere during initial cooling of the system, or is vented directly to the atmosphere, depending on the temperature of the inner wall of the cold box sensed by a temperature sensor and maintained by controlling the flow through a solenoid valve under control of the PLC;
the PLC is further adapted to control the humidity inside the storage space of the cold cabin and achieve the desired set points (temperature and humidity) by: controlling the temperature of the heat exchanger unit, controlling the reheating in the LHP by means of a solenoid valve, and by controlling the intermittent operation of the fan/blower as required;
said Programmable Logic Controller (PLC), preferably HMI (human machine interface) device, capable of setting the temperature and humidity requirements of the different compartments, so as to trigger the different flow control valves according to the set points specified by the user;
a conduit for conveying return air to the front end of the LHP for recirculation of air to the front end of the LHP and to the heat exchanger unit in order to maintain a desired temperature and humidity.
Yet another aspect of the present invention relates to a portable liquid nitrogen-based refrigeration system suitable for temperature control only, comprising a cold compartment and an associated cooling unit for maintaining a desired temperature within the storage space of the cold compartment;
said cooling unit of the cold box comprises a heat exchanger, a fan/blower for air circulation, a shutter with damper for controlling the supply of fresh air and the discharge of return air, respectively, and a solenoid valve controlled by a PLC controlling a LN 2 Flow in the transfer line to properly cool the heat exchanger unit to a set temperature, then LN 2 Flowing through a similar flow path, said PLC also providing for controlling said temperature inside said storage space of the cold box and achieving said desired set temperature by controlling the temperature of the heat exchanger unit and by controlling the intermittent operation of the fan/blower as required;
a duct for conveying return air to a forward end of the heat exchanger unit for cooling and recirculation.
Yet another aspect of the invention relates to a portable liquid nitrogen based refrigeration system wherein the cooling unit of the cold compartment comprises a LHP with solenoid valves on individual cooling circuits for controlling reheating, a heat exchanger and solenoid valves on the liquid nitrogen inlet line and outlet nitrogen vapor line, a fan/blower and a duct, and a shutter with damper for supply of fresh air and discharge of return air respectively;
the PLC control is adapted to pass the mixed air flow through the LHP and the heat exchanger after appropriate supply of fresh air and discharge of return air, after which the air flow with controlled temperature and humidity is supplied to the storage space of the cold compartment and the air after heat and humidity exchange in the cold compartment is returned as a return flow to the cooling unit.
Another aspect of the invention relates to a portable liquid nitrogen-based refrigeration system that includes a LHP having a pre-cooling (evaporator) section and a reheating (condenser) section and a solenoid valve (for controlled reheating of air flowing through the LHP on a circuit of tubes connecting both the pre-cooling and reheating sections),
the LHP may operate as an air-to-air heat exchanger to utilize heat transferred during re-heating to pre-cool the incoming air stream in the pre-cooling section, thereby increasing efficiency.
Yet another aspect of the invention relates to a portable liquid nitrogen based refrigeration system comprising a heat exchanger comprising a C-shaped aqueous ethanol circuit fitted with a system for LN 2 A flowing coil/serpentine and a finned connecting channel for efficient heat exchange of the aqueous ethanol solution with the air stream,
the aqueous ethanol solution is filled inside the C-shaped circuit and the connecting channel by an operative connection, and can be discharged through the connection when necessary,
the LN 2 Flows through the electromagnetic valve, passes through the coil pipe/the coiled pipe, exchanges heat with the ethanol water solution filled in the C-shaped loop and the connecting channel,
output N 2 The vapor involves cooling the inner walls of the cold box through coils wound on the inner vessel of the cold box or venting to the atmosphere as needed.
Yet another aspect of the invention relates to a portable liquid nitrogen based refrigeration system wherein the skid includes a vacuum insulated cold chamber, a self contained cooling unit/cryogenic flywheel, commercial self pressurized Liquid Nitrogen (LN) 2 ) A container and a valve box and a controller unit with other auxiliary systems, the skid blocks being loaded in an enclosed cargo container including any trailer/truck or rail wagon, and wherein the output vapor is vented around the skid blocks within the outer enclosed cargo container after transferring cold to the cabin to act as a shielding gas and trap heat leaking into the system, thereby utilizing the cold available in the output vapor.
Another aspect of the invention relates to a method for conservatively utilizing liquid nitrogen as a cooling source for conditioning a refrigerated space, including a portable refrigerated space for transporting refrigerated goods, comprising:
controlling the temperature difference between the liquid nitrogen and the desired cooling environment of the storage space by controlling the use of the liquid nitrogen in a manner that divides the cooling range and promotes cooling
i) Providing an intermediate energy reservoir for the coolant, which involves using liquid nitrogen as a cooling source in an alcohol-water heat exchanger having a reservoir for aqueous ethanol;
ii) controlled freezing of the aqueous ethanol solution to achieve a desired controlled low temperature, which involves a controlled supply of pressurized liquid nitrogen;
iii) A PLC-based control to monitor the aqueous ethanol solution for the required controlled freezing to achieve the desired controlled cryogenic temperature and to supply liquid nitrogen at a desired controlled rate, thereby providing a liquid nitrogen-based cooling source.
Yet another aspect of the present invention relates to a method for conditioning a refrigerated space with liquid nitrogen economized as a cooling source, comprising: generating controlled cool air for conditioning a refrigerated space by allowing ambient air to contact through the alcohol-water heat exchanger with a reservoir of the chilled aqueous ethanol solution; and effecting a desired heat exchange and intermittently or continuously circulating the thus generated cold air in the refrigerated space in accordance with a desired set temperature in the storage space.
A further aspect of the invention relates to a method for conditioning a refrigerated space with liquid nitrogen as a cooling source in an economical manner, wherein liquid nitrogen is passed through the alcohol-water heat exchanger via a co-located line, so that after exchanging heat, the cold nitrogen vapour in the line extends to the storage space and is further used for cooling the storage space in order to effect a rapid drop in temperature and in turn, because this carries away heat entering as thermal radiation from the outer container, the inner container also functions as a heat shield.
Another aspect of the invention relates to a process wherein for controlled cooling of the aqueous ethanol solution to a desired controlled low temperature in the range of-40 ℃ to-100 ℃ under ambient conditions, a nitrogen supply in the range of-150 ℃ to-180 ℃ is involved.
Yet another aspect of the present invention relates to a method for refrigerating a storage space, comprising:
providing a portable liquid nitrogen-based refrigeration system including a cold shell/cold bin-based storage space;
providing entry of fresh cold air and exit of recycled air out of the cold housing/compartment;
providing the intermediate energy reservoir of coolant, which involves using liquid nitrogen as a cooling source in an alcohol-water heat exchanger having an aqueous ethanol reservoir disposed relative to the entry of the temperature controlled air into the cold housing;
supplying liquid nitrogen operatively connected to the alcohol-water heat exchanger to freeze the aqueous ethanol solution to a desired controlled cryogenic temperature;
engaging a PLC controller to monitor storage conditions inside the cold housing/cold bin and regulate the intake of incoming cold air in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to cause a supply of circulating air to enter/exit the cold housing/cold bin.
Yet another aspect of the invention relates to a method wherein the initial cooling step of the system comprises:
loading each hold with cargo and feeding the required temperature and humidity set points into the PLC, whereby the PLC will start pressurizing LN2 in the storage vessel and maintain a constant pressure inside the vessel during flow of LN2 in the alcohol-water heat exchanger;
allowing the vapour of the vaporized nitrogen generated after the cold energy has been transferred to the alcohol-water mixture to flow through a coil brazed on the outer surface of the inner container of the cold compartment and promoting the lowering of the temperature of said compartment to said set point specified by said user,
venting the output vapor after transferring cold to the cabin around a skid in an outer container of the truck such that the output vapor acts as a shielding gas and traps heat leaking into the cabin, further contributing to the process savings;
once LN is used 2 With the alcohol-water heat exchanger filled and the tank already cooled by the outgoing vapor, air circulation will begin, which will cool the waterThe temperature within the cabin, with or without the required humidity control, is maintained within the specified range;
said air flow is optionally intermittent in nature, depending on the ambient temperature and said set point specified by said user; and
the LN2 supply is stopped once the desired temperature of the alcohol-water heat exchanger (-40 ℃ to-100 ℃) is reached and the supply is resumed again when the temperature of the alcohol-water heat exchanger is no longer able to maintain temperature and humidity.
Another aspect of the invention relates to a method wherein the step of maintaining a desired environment after initial cooling of the system comprises:
after the temperature of the wall of the cold bay has reached the desired temperature set by the user, the N2 vapor is bypassed to avoid any further cooling of the bay, and optionally the N2 vapor is bypassed to a skid/container carrying cargo to reduce the effective heat load of the system, the bypass valve is controlled using a PLC depending on the temperature of the wall of the bay and the status of the N2 supply monitored by the PLC, so that when the cold stored in the alcohol-water heat exchanger is insufficient to maintain the required temperature and humidity levels, the LN2 supply is again activated to cool the alcohol-water heat exchanger, whereby both the LN2 supply and the air flow are effectively intermittent, or can be substantially continuous as required by the conditions to be maintained and determined by the set point specified by the user in the PLC.
Yet another aspect of the invention relates to a method comprising a humidity control step comprising:
moist hot (specific humidity) fresh outdoor air is mixed in proportion to the type of food stored with warm circulating air returned from the refrigerator, and humidity is maintained by operating a solenoid valve on the refrigerant circuit surrounding the loop heat pipe under active control of the PLC.
Yet another aspect of the invention relates to a method wherein
The mixed air is pre-cooled to a desired condition in a pre-cooling section surrounding the controllable loop heat pipe, and then the air is further cooled by means of a heat exchanger to a temperature below the required condition, at which point the air may be too cold and too saturated to be supplied to the storage space and provide set air conditions in the storage space, which air is then dehumidified in a re-heating section of the LHP and brought to final set conditions before being delivered to said storage space. A pre-cooling section of the LHP is connected upstream of the main heat exchanger unit and a reheat section of the LHP is connected downstream of said main heat exchanger unit for following such a method.
At least one temperature controlled cold housing/cold bin defining a refrigerated storage space having an inlet for fresh air and an outlet for recycled air exhausted from the cold housing/cold bin;
an alcohol-water heat exchanger having a reservoir of ethanol water solution cooperatively disposed with respect to controlled fresh air entry into the cold housing;
a cooling source comprising liquid nitrogen, the cooling source being operatively connected to the alcohol-water heat exchanger to freeze an aqueous ethanol solution to a desired controlled cryogenic temperature;
a PLC controller for monitoring storage conditions inside the cold housing/cold bin and regulating the intake of fresh air and recirculated air flowing in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to exhaust recirculated air from the cold housing/cold bin.
Yet another aspect of the invention relates to a method comprising the step of providing a specific environment in said storage space maintained under controlled cooling of produce, said specific environment comprising a nitrogen or ethylene environment (for fruit ripening) during transport/sea, an inert gas environment for corrosion sensitive produce, etc.
The above and other objects and advantages of the invention are described in more detail below with reference to the following non-limiting illustrative figures.
Drawings
Fig. 1a depicts a trailer with a cold room loaded along the length of the vehicle.
Fig. 1b depicts the situation where the cold box is loaded perpendicular to the length of the trailer.
FIG. 1c part number 102: and (4) conveying skid-mounted blocks of the cold chamber.
FIG. 2 shows a description from LN 2 The nitrogen of the vessel is simultaneously flowed to a schematic block diagram of the individual self-contained cooling units (of the cold box) through vacuum insulated heat transfer lines.
Fig. 3 shows a detailed description of a type a cold box and associated cooling units for maintaining a desired temperature and humidity inside the storage space of the cold box.
Fig. 4 shows a detailed description of a type B cold cabin and associated cooling units for maintaining a desired temperature inside the storage space of the cold cabin.
Figure 5a depicts the components inside the cooling unit of a type a cold box, including the LHP and solenoid valves on the individual cooling circuits for controlling the reheating.
Figure 5b shows an isometric view of the LHP and components of the main heat exchanger unit indicating that the precooling (evaporator) section, the reheating (condenser) section and the loop pipe connecting the precooling and reheating sections of the LHP are deployed and the solenoid valve mounted on the loop pipe. Figure 5c depicts the main heat exchanger unit.
Fig. 6 shows a cooling scheme or unit with humidity control (as given in fig. 5 (a) for a type a cold box application).
Figure 7 shows a psychrometric chart illustrating the state points of a cooling cycle/scheme operating controllably around an LHP with preheat and reheat coils.
Figure 8 shows a psychrometric chart illustrating the process during maintenance of a dehumidified environment.
Fig. 9 shows a psychrometric chart of a process for humidifying a cargo storage space.
Fig. 10 shows a logic or flow diagram to illustrate how the PLC operates/activates the various required control parameters based on the set points (temperature, humidity) selected for the cold box.
Detailed description of preferred embodiments of the invention with reference to the accompanying drawings
In the present invention, refrigerated goods/food to be transported are loaded in a plurality of double-walled vacuum insulated containers (called cold pods) which are in turn loaded on transportable self-contained skid blocks along with self-pressurized liquid nitrogen containers and other ancillary equipment. This skid is transported by any truck/trailer within the uninsulated cargo container and the same cargo container on the truck/trailer can be used to transport the uninsulated cargo by removing the skid. The primary aspect of the present invention relates to maintaining a desired temperature with/without humidity in a refrigerated storage space for goods/food loaded in a cold compartment on a transportable skid by using a new cooling scheme that utilizes liquid nitrogen as a primary source of refrigeration.
This cooling scheme effectively utilizes liquid nitrogen to cool the intermediate reservoir (aqueous ethanol solution) and the heat exchanger, referred to as the main heat exchanger unit, to a suitably low temperature. The unit is the main part of a 'low-temperature flywheel', which consists of a main heat exchanger, a centrifugal pump/blower, a damper and a loop type heat pipe.
A return air stream from the storage space of the cold cabin is blown onto the main heat exchanger unit where it is cooled to a set temperature. This cold air flow is then supplied to the storage space loaded with food/goods, where it exchanges heat to maintain the required temperature and returns as a return air flow to the cooling unit. The air moves in a closed loop.
A cooling unit for stored goods/food requiring strict humidity control and temperature has a controlled loop heat pipe exchanger (LHP) surrounding the main heat exchanger unit. The LHP has pre-cool and reheat sections to pre-cool the return air stream before it is cooled in the main heat exchanger unit and to reheat it after it has been cooled in the main heat exchanger unit in a controlled manner to achieve the desired set humidity and temperature. Precooling the return air stream with the LHP bypasses the main heat exchanger unit's excess sensible cooling capacity, which saves the amount of liquid nitrogen used to maintain the low temperature of the main heat exchanger unit for maintaining humidity. However, the LHP is an alternative device that will be used in refrigerated vehicles that require humidity control. The flexibility of this solution is characterized by the following features: if the LHP is removed, the system can still operate, but maintain temperature and not humidity. This supply scheme is retained since not all cargo requires humidity control. Two types of systems are shown in fig. 3 and 4, respectively.
Two configurations of a refrigerated truck/trailer are depicted in fig. 1a and 1 b. Fig. 1a depicts a trailer with a cold box loaded along the length of the vehicle, while fig. 1b depicts the cold box loaded perpendicular to the length of the trailer (i.e., laterally). 101 is a cab that will just have a screen for displaying the set temperature and the current temperature in the cold room. A skid 102 (shown in the figure list as a single figure 1 c) comprising a vacuum insulated cold box 103, a self-contained cooling unit (refrigeration unit, i.e. cryogenic flywheel) 104, commercial self-pressurized Liquid Nitrogen (LN) is loaded (by means of wheels) onto the trailer/truck 2 ) A container 105 and a valve box with other auxiliary systems and a controller unit 106. This skid 102 can be loaded into any typical uninsulated cargo container on any truck/trailer. The skid 102 is a separate unit and can be loaded/unloaded on a road truck/trailer/trolley or rail wagon of appropriate size by means of wheels 107 at the bottom of the same skid.
The cold box 103 as shown in fig. 1a and 1b is a vacuum insulated double-walled cylindrical/rectangular container with a front compartment containing LN as the main refrigeration source 2 A driven refrigeration/cooling unit 104. Four/eight such cold pods 103 and their self-contained cooling units 104 are mounted on skid 102. From LNs mounted on the same skid in a controlled manner by means of a valve box and controller unit 106 2 The container 105 feeds all four/eight cooling units, i.e. the cryogenic flywheel 104 on the cold box 103, simultaneously. The cold bay 103 can also be loaded/unloaded from the skid 102 separately as and if desired without affecting the operation/performance of the other bays.
FIG. 2 shows a description from LN 2 Nitrogen from vessel 201 (105 in FIGS. 1a-1 b) flows simultaneously to individual self-contained chills (of cold box 208) via vacuum insulated transfer line 207A schematic block diagram of unit 210, the flow of nitrogen being controlled by a Programmable Logic Controller (PLC) 204. LN 2 The self-pressurizing unit 202 on the vessel 201 is also controlled by the PLC 204 so that it is on line with the LN 2 During supply to cooling unit 210 at LN 2 A suitable pressure is maintained in the vessel 201 to avoid causing overpressure by venting nitrogen to atmosphere via vent line 213. The nitrogen gas supplied through the transmission line 207 is used in the corresponding cooling unit 210 to maintain a desired temperature and/or humidity level inside the storage space 209, and then discharged to the atmosphere through 211.
The cooling scheme and cold box are shown in fig. 3 and 4.
A cooling scheme consisting of an ethanol-based heat exchanger and Loop Heat Pipes (LHP) has been proposed to maintain the temperature and humidity levels within the storage space of the cold box. Two alternative cold box configurations have been proposed for this purpose:
1.A model cold box: comprising an alcohol-based heat exchanger and a Loop Heat Pipe (LHP) for applications requiring humidification as well as dehumidification.
Model 2.B cold box: containing an ethanol-based heat exchanger, is only used for applications requiring only temperature control and no humidity control.
Fig. 3 shows a detailed description of a type a cold box and associated cooling units for maintaining a desired temperature and humidity at the storage space 209 portion of the cold box. The cooling unit 210 of the cold box (i.e., the cryogenic flywheel) consists of: a main heat exchanger unit 308 (also shown in fig. 5), a surrounding Loop Heat Pipe (LHP) 309, a fan/blower 304 for air circulation, louvers 306 and 307 with dampers for controlling the supply of fresh air and the discharge of return air, respectively, and solenoid valves controlled by PLC 204. PLC controlled LNs in transmission line 301 (207 in FIG. 2) 2 The flow appropriately cools the primary heat exchanger unit 308 to a set temperature, then the cold nitrogen vapor flows through coils 310 wound on an inner vessel before escaping into the atmosphere during initial cooling of the system, or is discharged directly into the atmosphere, depending on what is sensed by the temperature sensor and by corresponding control through the electromagnet by means of the PLC 204The flow of valves 302 and 303 maintain the temperature of the inner walls of the cold box. The PLC 204 also controls the temperature and humidity within the storage space of the cold box and achieves the desired set points (temperature and humidity) by: the temperature of the main heat exchanger unit 308 is controlled, the reheating in the LHP 309 is controlled (by means of solenoid valve 311), and by controlling the intermittent operation of the fan/blower 304 as required. 305 shows the conduits for delivering return air to the front end of the LHP 309 for recirculation to maintain the required temperature and humidity.
Fig. 4 shows a detailed description of a type B cold box and associated cooling units for maintaining a desired temperature inside the storage space 209 of the cold box. The cooling unit 210 of the cold box consists of: a main heat exchanger unit 407 (also shown in fig. 5 c), a fan/blower 406 for air circulation, shutters 404 and 405 with dampers for controlling the supply of fresh air and the discharge of return air, respectively, and solenoid valves controlled by PLC 204. LNs in transmission line 401 (207 in FIG. 2) controlled by PLC 2 The flow appropriately cools the main heat exchanger unit 407 to the set temperature, followed by LN 2 A similar flow path is followed as described in fig. 3. The PLC 204 also controls the temperature within the storage space of the cold box and achieves the desired set temperature by: the temperature of the main heat exchanger unit 407 is controlled and by controlling the intermittent operation of the fan/blower 406 as required. 408 shows a conduit for conveying return air to the front end of the main heat exchanger unit 407 for cooling and recirculation.
Figure 5a shows the components inside the cooling unit of a type a cold room, including the LHP 501 and solenoid valves 510 on the individual cooling circuits for controlling the reheat, the primary heat exchanger 502 and solenoid valves on the liquid nitrogen inlet line 511 and the outlet nitrogen vapor line 512, the fans/blowers 503 and 504 and the duct 505, and the shutters 506 and 507 with dampers for the supply of fresh air and the discharge of return air, respectively. After appropriate supply of inlet fresh air and exhaust return air, a mixed air stream 508 is passed through LHP 501 and main heat exchanger unit 502. Thereafter, an air stream 509a having a controlled temperature and humidity is supplied to the storage space of the cold box,and the air after exchanging heat and humidity in the cold box is returned to the cooling unit as return stream 509 b. Figure 5b shows an isometric view of the assembly of LHP 501 with main heat exchanger unit 502. The LHP 501 comprises a pre-cooling (evaporator) section 516 and a reheating (condenser) section 517 and a solenoid valve 510 on a circuit connecting the pipes of the pre-cooling and reheating sections (for controlled reheating of the air flowing over the LHP). The LHP acts as an air-to-air heat exchanger to utilize the heat transferred during re-heating to pre-cool the incoming air stream 508 at the pre-cooling section, thereby increasing efficiency. FIG. 5C depicts a main heat exchanger unit 502 consisting of a C-shaped aqueous ethanol circuit 513 fitted with a heat exchanger for LN 2 A flow coil/serpentine 514 and finned connecting channels 515 for efficient heat exchange of the aqueous ethanol solution with the air stream. The aqueous ethanol solution fills the C-loop and the connecting channel via connection 518 and can be drained off as needed via connection 519. LN flowing through solenoid valve 511 2 Passes through the coil/serpentine 514 to exchange heat with the aqueous ethanol solution filled in the C-circuit 513 and the connecting passage 515. Then N of output 2 The vapor 512 is used to cool the inner walls of the cold box or is vented to the atmosphere as described above in fig. 3. The cooling scheme and valve arrangement of the cooling unit for the type B cold box would be similar to a type a cold box that does not include the LHP without the need for strict humidity control.
The process is briefly described as follows:
products from farms that are transported refrigerated, refrigerated products or pharmaceutical products must be packed into cylindrical/rectangular crates when transportation is required. Once loaded into the crate, the goods must be loaded into the cold box. Cargo requiring different temperatures must be loaded in different compartments. Once all crates are loaded in the cabin, the temperature and humidity requirements of the different cabins must be fed into a Programmable Logic Controller (PLC). The PLC will trigger different flow control valves according to the set point specified by the user.
Once all inputs are entered by the user feed, the PLC will maintain the desired temperature and humidity levels and no further input from the user is required.
Step I: initial cooling of the system:
once the compartments are filled with cargo and the desired temperature and humidity set points are fed into the PLC, the PLC will begin to pressurize the LN2 in the storage container. The PLC has been programmed to maintain a constant pressure within the vessel during the flow of LN2 in the alcohol-water heat exchanger. The vapor that evaporates after transferring the cold to the alcohol-water mixture will flow through the coils brazed on the outer surface of the vessel inside the cold chamber and thereby help to lower the temperature of each chamber to the set point specified by the user. This will help to quickly bring down the system temperature and take advantage of the cold available in the output vapor. The vapors output after transferring cold to the cabin will be vented around the skid in the outer container of the truck. Thus, the vapor acts as a shielding gas and traps heat leaking into the compartments, which helps to maintain the desired temperature. Once the alcohol-water heat exchanger is filled by using LN2 and the tank has been cooled by the outgoing vapor, air circulation will begin, which will help maintain the temperature and humidity inside the cold tank within the specified ranges. The air flow may be intermittent in nature, depending on the ambient temperature and the set point specified by the user. The LN2 supply may be stopped once the desired temperature of the alcohol-water heat exchanger (-40 ℃ to-100 ℃) is reached, and will be resumed again when the temperature of the alcohol-water heat exchanger is no longer able to maintain temperature and humidity. The consumption of LN2 will be higher during the initial cooling period as it must lower the temperature of the bulkhead and the loaded food/cargo.
Step II: maintain the desired environment after initial cooling of the system:
after the temperature of the wall of the cold chamber has reached the desired temperature set by the user, the cold N2 vapor used to exchange heat with the wall of the cold chamber, if it continues to flow, will cause the cold chamber to be subcooled, which is not desired. Accordingly, measures have been taken to bypass the N2 vapor directly to the container of the truck that houses the skid blocks and the bays and to reduce the effective thermal load of the system. The bypass valve will be controlled according to the temperature of the bulkhead. When the N2 supply is disconnected, the bypass problem will not exist, and the cooling of the bulkhead will also result from the flow of cool air.
Once the cold stored in the alcohol-water heat exchanger is insufficient to maintain the desired temperature and humidity levels, the LN2 supply will start again to cool the alcohol-water heat exchanger. Thus, both LN2 supply and air flow may be intermittent or continuous in nature, as required by the conditions to be maintained, and will be determined by user-specified set points.
Humidity control
A cooling scheme or unit with humidity control (as given in fig. 5 (a) for a type a cold box application) is shown in fig. 6 and 7.
The hot humid fresh outdoor air (1) is mixed proportionally with the recirculated air (5) returning from the refrigerated storage space (the ratio depends on the type of food being stored). The enthalpy-wet measurement process is shown in fig. 2. The mixed air (2) is pre-cooled to a condition (2') in a pre-cooling section of a surrounding controlled Loop Heat Pipe (LHP). The air at (2') is then further cooled and dehumidified by the main cooling coil (main heat exchanger unit) to reach condition (3). The air at this time may be too cold and supersaturated to be supplied to the storage space. In order to provide set air conditions in the storage space, this air is reheated in a reheating section of the LHP before being delivered to the storage space (4). The pre-cooling section of the LHP is connected upstream of a main heat exchanger unit (which is the main cooling coil) and the reheat section of the LHP is connected downstream of said main heat exchanger unit.
For example, assume that the conditions of the air leaving the main cooling coil (main heat exchanger unit) are about 5 ℃ to 6 ℃ and 100% relative humidity, and the air supply required in the storage space is about 14 ℃ to 16 ℃ and 60% relative humidity. Thus, after the cooling air stream from the main heat exchanger unit is reheated in the reheat section of the LHP, the final conditions will be achieved without additional cost. The heat and moisture can be absorbed by the air in the storage space and leave as return air (5) which is warmer and more humid (higher than humidity) than when the air first entered. A suitable proportion of the return air is recirculated and mixed with the incoming fresh ambient air and will be returned to the storage space again by the cooling unit. A proportional amount of air will be discharged to the environment. Energy must be supplied to the main cooling coil (Δ h coil) for cooling and dehumidification and to the reheat coil (Δ h reheat) in order to bring the air to set conditions before supplying it to the storage space. However, the energy recovered from pre-cooling (Δ h pre-cooling) is used to offset the reheat (Δ h reheat) load, resulting in lower energy requirements.
This act of precooling the return air stream with the LHP bypasses the excess sensible cooling capacity of the main heat exchanger unit, which saves the amount of liquid nitrogen used to maintain the low temperature of the main heat exchanger unit for maintaining humidity.
By mounting solenoid valves on the refrigerant circuit surrounding the loop heat pipes, it is possible to control the amount of refrigerant flow in the individual circuits between the pre-cooling and re-heating sections of the LHP, and thus effectively control the amount of re-heating applied to the air stream.
Example (c):
in this example, the case has been described where two different transport conditions are to be maintained in the cold room, one with a humidified environment and the other with a dehumidified environment. The test takes into account the following two conditions:
1. storing the pumpkin at 12 ℃ and 70% relative humidity, and
2. storing tomatoes at 0 ℃ and 90% relative humidity
Case I: storing the squash at 12 ℃ and 70% RH:
the environmental conditions were assumed to be 30 ℃ and 60% RH, and the above temperature and humidity levels had to be maintained inside the cold box. Therefore, in order to cool the air to the required temperature and maintain the required RH level by means of the above described cooling scheme for the type a cold box, the following steps are followed.
Suppose that:
1. assume that the leak-in heat per bin is about 100W and the cargo has been pre-cooled to a set temperature.
2. Assuming that 2 c of subcooled air is used to maintain the required temperature, i.e. a temperature of 12 c inside the cold box, 10 c of chilled air flow will be used.
3. For this case, it is also assumed that 10% of the fresh air is fed in and 10% of the recirculated air is discharged. However, as the supply and discharge amounts of air vary, the operation of the respective components will change accordingly.
Fig. 8 shows the enthalpy-moisture measurement process for this case. The following points are first marked on the chart:
1. environmental conditions are as follows: 30 ℃ and 60% RH (point E)
2. Storage conditions: 12 ℃ and 70% RH (point A)
3. Air inlet conditions are as follows: 10 ℃ and 80% RH (point B)
4. Ethanol-based heat exchanger conditions: 0 deg.C (Point G)
The following procedure must be performed in order to maintain the required storage conditions corresponding to point a:
1. process B to A: maintaining temperature and humidity in storage space
2. Processes A to C: mixing 10% fresh air with recirculated air
3. Process C to D: cooling air flow in evaporator of LHP
4. Procedures D to F: cooling an air stream in an ethanol-based heat exchanger
5. Procedures F to B: reheating air at a condenser section of an LHP to maintain a desired humidity
Process control logic and sequence:
1. the pre-cooled goods are first loaded into the cold room and then the user will set the temperature and humidity levels required for the stored goods, in this case pumpkin.
2. The user must also input the fresh air recirculation required for the stored cargo (the PLC can also be programmed with default values for temperature, humidity and fresh air recirculation required for common fruits and vegetables).
PLC will sense temperature and humidity inside the cold chamber and will start to act on LN 2 The vessel is pressurized.
PLC will start to make LN 2 Flows through the ethanol-based heat exchanger and the vaporized nitrogen vapor, after passing through the heat exchanger, will be forced through the coils wound on the inner vessel of the cold box.
5. If the internal container of the cold box is lowered to the temperature level required by the stored cargo, the PLC will bypass the nitrogen vapor stream directly to the atmosphere rather than flowing it through the coils wound on the internal container of the cold box.
6. Once the temperature of the heat exchanger drops to a significant level (already programmed in the PLC), the PLC will signal the blower to start the air flow.
The plc will activate/adjust the motorized damper/shutter to maintain 10% fresh air recirculation.
8. The air will be forced through the evaporator section of the LHP, the ethanol-based heat exchanger, and the condenser section of the LHP, respectively, to achieve the desired temperature and humidity levels (point B).
9. The air leaving the cold box (point a) will mix with fresh air from the atmosphere and reach point C.
10. The air from point C will first be cooled in the evaporator section of the LHP (processes C to D)
11. The air will be further cooled in the main heat exchanger unit to point F (processes D to F)
12. The air will then be reheated in the condenser section of the LHP (procedures F to B)
13. The cycle F-B-ase:Sub>A-C-D will continue until the desired temperature and humidity level is maintained inside the cold box. During this process, the PLC will continuously monitor the temperature and humidity levels within the cold chamber. Based on these inputs, the PLC will attempt to maintain the air cycle F-B-A-C-D.
PLC will control LN 2 Valves in the loop and LHP to control temperature and humidity, respectively.
15. Once the temperature of the ethanol-based heat exchanger has reached the set temperature programmed in the PLC (cargo-based set temperature), the PLC will operate the valve to stop the flow of LN2 and will release the pressurization of the LN2 tank.
The plc will operate the blower in on/off mode to maintain the required conditions.
17. Since the ethanol-based heat exchanger has an energy reservoir in it, this process will last for a period of time, depending on the storage conditions set by the user. However, once the heat exchanger temperature is above a certain value, the PLC will return to point 3 above and follow the same process again.
Case II: storing tomatoes at 0 ℃ and 90% RH:
the ambient conditions were assumed to be 30 ℃ and 60% RH as described above, and the required temperature and humidity levels had to be maintained inside the cold box. Therefore, the air must be cooled to the required temperature and maintain the required RH level by means of the above-described cooling scheme. There are two types of cold tanks, one with LHP and the other without LHP. The type a cold box with LHP will follow the same procedure as mentioned in case I to maintain the required temperature and humidity levels. However, for a type B cold box, there is no humidity control, but the desired temperature set by the user will be maintained. However, while maintaining a temperature lower than ambient temperature, a humidity level of 90 to 100% is maintained by default. A small ultrasonic humidifier may also be used in some cases to maintain the desired humidity.
Suppose that: it is assumed that similar to the case I, since the compartments storing the goods will be similar:
1. assume that the leak-in heat per bin is about 100W and the cargo has been pre-cooled to a set temperature.
2. Assuming that 2 c of subcooled air is used to maintain the required temperature, i.e. 10 c inside the cold box, 8 c of chilled air flow is used.
3. For this case, it is also assumed that 10% of the fresh air is fed in and 10% of the recirculated air is discharged. However, as the supply and discharge amounts of air vary, the operation of the respective components will change accordingly.
Figure 9 shows the psychrometric chart for this case. The following points are first marked:
1. point A: storage conditions 10 ℃ and 90% RH
2. Point B: intake conditions of 8 ℃ and 100% RH
3. Point E: environmental conditions 30 ℃ and 60% RH
4. Point G: 0 ℃ of ethanol heat exchanger
The following procedure will have to be followed to maintain the required storage conditions:
1. process B to A: maintaining desired conditions in a storage space
2. Processes A to C: mixing recirculated air with fresh air
3. Process C to D: cooling air flow in heat exchanger
Process control logic and sequence:
1. the pre-cooled cargo is first stored inside the cold box and the user will input the desired temperature of the stored cargo.
2. The user will also input the fresh air recirculation required for the stored cargo (the PLC can also be programmed with default values for temperature and fresh air recirculation required for common fruits and vegetables).
The plc will sense the temperature and humidity level inside the cold box (to increase the humidity level, an ultrasonic humidifier will be used) and will start pressurizing the LN2 tank.
4. Once the LN2 tank is pressurized, the PLC will begin flowing LN2 through the ethanol-based heat exchanger.
The PLC will also sense the temperature of the inner container of the cold box and if the temperature of the inner container is higher than the set temperature of the cargo, the PLC will direct the nitrogen vapor generated after heat exchange with the ethanol solution through the coil wound on the inner container of the cold box. Otherwise, the PLC would vent the nitrogen vapor directly to the atmosphere.
6. Once the temperature of the heat exchanger drops to a significant level (already programmed in the PLC), the PLC will signal the blower to start the air flow.
The plc will activate/adjust the motorized damper/shutter to maintain 10% fresh air recirculation.
8. The air will be cooled (to point B) by heat exchange with an ethanol-based heat exchanger (processes C to B).
9. The cooled air will then maintain the desired temperature in the cold room (processes B to a).
10. Based on feedback obtained by the PLC through the hygrometer, an ultrasonic humidifier will sometimes be used to increase the humidity level within the cabin.
11. Once the temperature of the heat exchanger is maintained at the desired temperature, the flow of LN2 will be stopped by the PLC and the pressurization of the vessel will be released.
The plc will control the blower in on/off mode to control the desired temperature inside the cold box.
13. Since the heat exchanger also has a hot reservoir based on an ethanol solution, this cooling process will last for a period of time, depending on storage and environmental conditions.
14. When the temperature of the ethanol-based heat exchanger rises above a certain limit (programmed in the PLC), the flow of LN2 will be started again and the steps following step 3 will be followed again.
Thus, by means of the above-described process and its sequence, different temperatures and humidity levels can be maintained within the cold chamber. For type a cold boxes we have a humidity control that can control the humidity precisely, but for type B cold boxes we can only use an ultrasonic humidifier to increase the humidity. Both types of cabins have their own set of applications. Furthermore, the use of LHP in type a cold pods also reduces heat waste and makes the process more economical (since no heaters are used for reheating).
FIG. 10 shows a logic or flow diagram to illustrate how the PLC operates/activates various required control parameters, such as liquid nitrogen flow, fresh and return air flow, vent, etc., based on selected set points (temperature, humidity) for the cold boxes carrying different refrigerated goods requiring different storage environment conditions during transport, as described below:
the following inputs are considered for the operation of one cold box 208:
the temperature of the cold box ST1=10 ℃; relative humidity SHd =60%
The PLC will first sense the set conditions of the cold box 208 and the temperature RHxT1 of the primary heat exchanger unit 308. The PLC has been programmed so that the set average temperature of the main heat exchanger unit is about 40 ℃ lower than the set temperature in the cold box 208. Thus, the set temperatures of the heat exchangers are:
SHxT1= ST1-40 (in case of temperature in ° c)
PLC [ number 1 ]]The sensed temperature of the heat exchanger (RHxT 1) will then be compared with the set temperature (SHxT 1) derived as above.Based on this comparison, if the sensed temperature RHxT1 is greater than the set temperature SHxT1 of the primary heat exchanger, the PLC will initiate a warm-up of LN 2 Pressurization of the container 201. The PLC will also sense LN 2 The pressure in the vessel and the pressurizing valve will be controlled so that the pressure in the vessel is within the allowable set limits in the PLC.
Is connecting LN 2 After the vessel is pressurized to a set point (SP 1) programmed into the PLC during programming, the PLC will operate the LNs accordingly 2 Flow valve to activate LN 2 Of the flow of (c). LN (N) 2 Will cool the aqueous ethanol solution in the main heat exchanger to the set point (SHxT 1). Once the temperature of the main heat exchanger has reached the set point (SHxT 1), the PLC will turn off the LN 2 Flow valve to stop LN 2 The flow of (c). Once LN is completed 2 The PLC will also turn on the LN 2 The exhaust valve of the container 201.
PLC [ number 2] will sense the temperature of cold compartment 208 (RT 1) and if RT1 is greater than set temperature ST1, PLC will initiate air circulation to cool 208. The PLC will also sense the relative humidity (RHd 1) in the cold chamber 208 and compare it to the set humidity (SHd). Based on the humidity change, the PLC will control the operation of the solenoid valves of the LHP loop to adjust humidification and dehumidification. Once the temperature in 208 reaches the set temperature ST1, the PLC will stop the operation of the LHP and air circulation for humidification and dehumidification.
The field test results are as follows:
the scaled-down cold box test with 95kg apples was run for 5 hours with the result that about 4.10 litres of liquid nitrogen was consumed when maintaining a temperature of 2 degrees celsius. The apples were initially cold and at a temperature of 4 ℃ and reached 2 ℃ in a refrigerator car. (as is well known in the relevant art, refrigerated trucks transport refrigerated goods, but they are not used to pre-cool goods.
Specific protocols were used during the experiments. The ambient temperature was 32 ℃. The preset conditions of 2 +1 ℃ are maintained as the ideal tolerance range for apples. Once the temperature rises to 3 ℃, the fan that transfers cold to the cold box is started and the temperature is reduced to 1 ℃. At this time, the fan is automatically stopped due to feedback from the temperature sensor. When the heat remains leaking, the fan is then started again when appropriate, after which the temperature rises again to 3 ℃. This discontinuous operation of the fan also saves power. The relative humidity of the environment is 50% and the system maintains the relative humidity at 90%.
Using 190 liters of LN 2 A Dewar flask. The evaporation was measured using a rotameter to measure the amount of nitrogen vapor released. The standard conversion factor for measuring evaporation was taken to be 700 liters of vapor equal to 1 liter of LN 2 . The solution of measuring vapour is used instead of the method using a level sensor, since the level sensor will not give the correct value for a moving vehicle, wherein the liquid inside the vehicle is continuously moving inside the vehicle due to the motion.
This almost matches the laboratory test data, only increasing by 10%. This increase is due to additional evaporation caused by the vibration. At an average speed of 45 km/h, this reflects a transportation cost of 0.9 lux per tonne per km/h, taking into account the effect of the scaling down of the cold box. Since the diameter of the cold box for the test run is half of the actual diameter envisaged, scaling down forms the picture. In this case, although the storage amount is quadrupled, the actual heat leak-in increases by less than twice. Much lower than the market price of 2.0 to 2.5 lux per kilometre per ton. Laboratory and test run data demonstrate the advantages of this system. The industrial applicability of this system will be economically beneficial and environmentally friendly due to the use of nitrogen as a cooling source.
Thus, by the present invention, it is possible to provide a liquid nitrogen based refrigeration system for storing and transporting perishable goods/food at controlled temperature and humidity levels, wherein separate temperature and humidity control units are provided such that each compartment can be maintained at different temperature and humidity levels independently of the other compartments to selectively store and transport goods that require a controlled temperature maintained within the vacuum insulated cold compartment in the range of-50 ℃ to +20 ℃. The system maintains temperature and humidity levels within the cold compartment by means of ammonia-based Loop Heat Pipes (LHP) and a specially designed cryogenic flywheel unit having a dual purpose water-ethanol heat exchanger for storing the chilled contents and cooling air. The modular skid design enables loading on a truck, cart, rail wagon, ship, or as a stand-alone stationary system comprising four/eight cold compartments supported on the skid, such that each compartment can be maintained at different temperature and humidity levels independent of the other compartments.

Claims (25)

1.A portable liquid nitrogen-based refrigeration system for transporting refrigerated goods, comprising:
at least one temperature controlled cold housing or cold compartment defining a refrigerated storage space having an inlet for fresh cold air and an outlet for recycled air exhausted from the cold housing or cold compartment, and a cooling unit associated with the cold housing or cold compartment for maintaining a desired temperature inside the storage space of the cold compartment; a duct for conveying return air to a forward end of the heat exchanger unit for cooling and recirculation;
the cooling unit comprises an alcohol-water heat exchanger having a reservoir of an aqueous ethanol solution cooperatively disposed with respect to fresh air entering the cold housing from the recycled air outlet or cooperatively disposed with respect to fresh air and recycled air entering the cold housing from the recycled air outlet;
a cooling source comprising liquid nitrogen, the cooling source being operatively connected to the alcohol-water heat exchanger to freeze an aqueous ethanol solution to a desired controlled cryogenic temperature;
a PLC controller for monitoring storage conditions inside the cold housing or cold room and adjusting the entry of temperature controlled fresh air or fresh air and recirculated air after contacting the alcohol-water heat exchanger as a temperature controlled cold air stream flowing forward into the storage space of the cold housing or cold room to maintain a set cooling temperature inside the storage space of the cold housing or cold room and to exhaust recirculated air out as a return air stream flowing out of the cold housing or cold room;
said cooling unit of the cold box comprises a heat exchanger, a fan or blower for air circulation, a shutter with damper for controlling the supply of fresh air and the discharge of return air respectively, and a solenoid valve controlled by said PLC controller which controls the flow of liquid nitrogen in the transmission line to properly cool the heat exchanger unit to a set temperature, and then the liquid nitrogen flows through a similar flow path, said PLC controller also providing for controlling the temperature inside the storage space of the cold box and achieving the desired set temperature by controlling the temperature of the heat exchanger unit and by controlling the intermittent operation of the fan or blower as required.
2. The liquid nitrogen-based portable refrigeration system of claim 1, wherein the temperature-controlled fresh air or fresh air and recirculated air is also humidity-controlled, comprising involving a loop heat pipe exchanger in cooperation with the alcohol-water heat exchanger, the loop heat pipe exchanger comprising a pre-cooling section and a reheat section and a cooperative solenoid valve for controlled reheat of air flowing over a loop of pipes connecting both the pre-cooling section and the reheat section.
3. The portable liquid nitrogen-based refrigeration system of claim 2,
wherein each of said cold housings or cold compartments is provided with a respective cryogenic flywheel or cooling unit comprising a heat exchanger unit with or without a circulating loop heat pipe, a fan or blower for controlled circulation of fresh air supply intake and return air exhaust, said heat exchanger unit and said fan or blower being respectively operatively connected to a solenoid valve controlled by said PLC controller.
4. The portable liquid nitrogen-based refrigeration system of any one of claims 1 or 2, further comprising an operating line for directing at least a portion of the return air stream from a storage space of a cold compartment through the alcohol-water heat exchanger where the return air stream is again cooled to a set temperature and the liquid nitrogen is supplied to contact the aqueous ethanol solution such that the liquid nitrogen freezes the aqueous ethanol solution at-40 ℃ to-100 ℃.
5. A portable liquid nitrogen based refrigeration system according to either one of claims 1 or 2 including each said cold housing or cold chamber having a coordinated nitrogen vapor supply into said cold housing or cold chamber for forwarding nitrogen vapor generated after heat exchange of liquid nitrogen in said heat exchanger to utilize residual cold in said nitrogen vapor for cooling said cold housing or cold chamber.
6. The portable liquid nitrogen-based refrigeration system of claim 5, wherein the coordinated nitrogen vapor supply into each of the cold shells or cold compartments includes a nitrogen vapor delivery line inside the cold shell or cold compartment wall that is connected to a main supply line of liquid nitrogen into the heat exchanger, each of the cold shells or cold compartments is contained within a cold shell or cold compartment delivery shell for transport, and after cooling the respective cold shell or cold compartment, the nitrogen vapor is released into the cold shell or cold compartment delivery shell.
7. A portable liquid nitrogen based refrigeration system according to claim 3 including an ammonia based loop heat pipe exchanger in combination with the alcohol-water heat exchanger, the system having a pre-cooling section and a reheat section that pre-cools and re-heats the return air stream after cooling in the heat exchanger in a controlled manner to achieve the desired set humidity and temperature;
the ammonia-based loop heat pipe is placed around the primary heat exchanger in the cryogenic flywheel or cooling chamber such that it first subcools the incoming air to the primary heat exchanger and then reheats the air in the reheat section of the loop heat pipe, which along with the heat exchanger provides a means to address both dehumidification and cooling, assisted by a solenoid valve provided to control the flow of liquid nitrogen in the system,
a blower to maintain air flow in the cold box and exhaust fan to facilitate return of air from the cold box after cooling the cold box,
a low temperature flywheel or cooling chamber with a damper, which is used for sucking air from the atmosphere and maintaining the freshness of the air; a self-pressurized liquid nitrogen vacuum insulated container comprising a safety device comprising a pressure reducing valve and a pressure regulating valve, and the control of the flow is performed by an electronic system controlled by the PLC controller.
8. The portable liquid nitrogen-based refrigeration system of any one of claims 1 or 2, comprising
A plurality of said temperature controlled cold shells or cold compartments each being a vacuum insulated double walled cold shell or cold compartment defining a plurality of refrigerated storage spaces;
each of said storage spaces having a respective said alcohol-water heat exchanger for controlling independent cooling of the respective storage space;
the PLC controller independently monitoring the storage conditions inside each of the cold enclosures or cold compartments and regulating the intake of fresh air or fresh air and recirculated air flowing in contact with the alcohol-water heat exchanger to maintain the set cooling temperature inside each of the storage spaces within the range of-50 ℃ to 20 ℃ and to exhaust recirculated air from each of the cold enclosures or cold compartments independently of each other to allow for variable conditions required to store goods or items in the respective storage spaces.
9. A portable liquid nitrogen based refrigeration system as defined in any one of claims 1 or 2 including a plurality of vacuum insulated temperature controlled cold housings or cold compartments based on various shapes and configurations, each cold housing or cold compartment having a self-contained cooling unit or cryogenic flywheel operatively connected to a self-pressurized liquid nitrogen supply container, a valve box with other auxiliary systems and a controller unit, said cold housings or cold compartments being portable and loadable on a trailer or truck to achieve a desired portability of refrigerated goods/items; and
a PLC controller for monitoring storage conditions inside the cold housing or cold box and regulating the intake of fresh air or fresh air and recirculated air flowing in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to exhaust recirculated air from the cold housing or cold box.
10. The portable liquid nitrogen-based refrigeration system of any one of claims 1 or 2, comprising
A plurality of cold boxes mounted on the skid blocks, said cold boxes having their self-contained cooling units or cryogenic flywheels, all said cryogenic flywheels on the cold boxes being simultaneously supplied in a controlled manner involving a valve box and a controller unit from a liquid nitrogen container mounted on the same skid block, each said cold box being independently and individually loaded or unloaded from the skid block as and if required without affecting the operation and performance of the other cold boxes.
11. The portable liquid nitrogen-based refrigeration system of any one of claims 1 or 2, said system being adapted for both temperature and humidity control, said portable refrigeration system comprising
A cooling unit or low temperature flywheel of the cold box comprising the heat exchanger, a surrounding ammonia loop heat pipe, a fan or blower for air circulation, a shutter with damper for controlling the supply of fresh air and the discharge of return air, respectively, and a solenoid valve controlled by the PLC controller;
the PLC controller controlling the flow of liquid nitrogen in the transmission line to properly cool the heat exchanger unit to a set temperature, then the cold nitrogen vapor flows through coils wound on an inner vessel before escaping into the atmosphere during initial cooling of the system, or is discharged directly into the atmosphere, depending on the temperature of the inner wall of the cold chamber sensed by the temperature sensor and maintained by controlling the flow through a solenoid valve under the control of the PLC controller;
the PLC controller is further adapted to control the humidity inside the storage space of the cold box and achieve a desired set point by: controlling the temperature of the heat exchanger unit, controlling reheating in the loop heat pipe by means of a solenoid valve, and by controlling intermittent operation of a fan or blower as needed;
the PLC controller, HMI device, which is able to set the temperature and humidity requirements of the different compartments in order to trigger the different flow control valves according to the set points specified by the user;
a conduit for conveying return air to the front end of the loop heat pipe to recirculate air to the front end of the loop heat pipe and the heat exchanger unit in order to maintain a desired temperature and humidity.
12. The portable liquid nitrogen based refrigeration system of claim 11, wherein the cooling unit of a cold compartment comprises loop heat pipes with solenoid valves on separate cooling circuits for controlling reheating, heat exchangers, and solenoid valves on liquid nitrogen inlet and outlet nitrogen vapor lines, fans or blowers and conduits, and shutters with dampers for supply of fresh air and discharge of return air, respectively;
the PLC controller controls the heat exchanger adapted to achieve a proper supply of fresh air and discharge of return air, the mixed air flow passing through the loop heat pipes and the heat exchanger, after which the air flow with controlled temperature and humidity is supplied to the storage space of the cold compartment, and the air after exchanging heat and humidity in the cold compartment is returned as a return flow to the cooling unit.
13. The portable liquid nitrogen-based refrigeration system of any one of claims 1 or 2, comprising a loop heat pipe having a pre-cooling section and a reheat section and a solenoid valve for controlled reheating of air flowing through the loop heat pipe on a loop of pipe connecting both the pre-cooling section and the reheat section;
the loop heat pipe may operate as an air-to-air heat exchanger to utilize heat transferred during reheating to pre-cool an incoming airflow in a pre-cooling section, thereby increasing efficiency.
14. The portable liquid nitrogen based refrigeration system of any one of claims 1 or 2, comprising a heat exchanger comprising a C-shaped aqueous ethanol circuit fitted with coils or coils for liquid nitrogen flow and finned connecting channels for efficient heat exchange of aqueous ethanol with an air stream,
the aqueous ethanol solution is filled inside the C-shaped circuit and the connecting channel by an operative connection, and can be discharged by a connection when necessary,
the liquid nitrogen flows through the electromagnetic valve and passes through the coil pipe or the coiled pipe to exchange heat with the ethanol water solution filled in the C-shaped loop and the connecting channel,
outputting nitrogen vapor involves cooling the inner walls of the cold box through coils wound around the inner vessel of the cold box or venting to the atmosphere as needed.
15. A portable liquid nitrogen based refrigeration system according to claim 12 including a skid comprising a vacuum insulated cold box, a self contained cooling unit or cryogenic flywheel, a commercial self pressurized liquid nitrogen container and valve box and a controller unit with other auxiliary systems, said skid being loaded in an enclosed cargo container including a trailer or truck or railway truck and wherein said output nitrogen vapor after transfer of refrigeration to the vacuum insulated cold box is vented around the skid in the outer enclosed cargo container to act as a protective gas and trap heat leaking into the system, thereby utilizing the available refrigeration in the output nitrogen vapor.
16. A method for conserving the use of liquid nitrogen as a cooling source to condition a refrigerated space including a portable refrigerated space for transporting refrigerated goods as applied to the portable liquid nitrogen based refrigeration system of any one of claims 1 to 15, the method comprising:
controlling the temperature difference between the liquid nitrogen and the desired cooling environment of the storage space by controlling the use of the liquid nitrogen in a manner that divides the cooling range and promotes cooling
i) Providing an intermediate energy reservoir for coolant, which involves using liquid nitrogen as a cooling source in an alcohol-water heat exchanger with an aqueous ethanol reservoir;
ii) controlled freezing of the aqueous ethanol solution to achieve a desired controlled low temperature, which involves a controlled supply of pressurized liquid nitrogen;
iii) Based on the control of the PLC controller to monitor the aqueous ethanol solution for a desired controlled freezing to achieve a desired controlled low temperature, and to supply liquid nitrogen at a desired controlled rate, thereby providing a liquid nitrogen-based cooling source.
17. The method for conserving conditioning a refrigerated space using liquid nitrogen as a cooling source according to claim 16, the method comprising: generating controlled cool air for conditioning a refrigerated space by allowing ambient air to contact through the alcohol-water heat exchanger with a reservoir of the ethanol water solution; and effecting a desired heat exchange and intermittently or continuously circulating the thus generated cold air in the refrigerated space in accordance with a desired set temperature in the storage space.
18. Method for conditioning a refrigerated space sparing the use of liquid nitrogen as a cooling source according to any of claims 16 or 17, wherein liquid nitrogen is passed through the alcohol-water heat exchanger via a cooperatively arranged line, so that after exchanging heat, the cold nitrogen vapour in the line extends to the storage space and is further used for cooling the storage space in order to carry out a rapid drop in temperature and in turn because this takes away heat entering as thermal radiation from the outer container, so that the inner container also acts as a heat shield.
19. The process as claimed in any one of claims 16 or 17, wherein for controlled cooling of the aqueous ethanol solution to a desired controlled low temperature in the range of-40 ℃ to-100 ℃ under ambient conditions, a nitrogen supply in the range of-150 ℃ to-180 ℃ is involved.
20. The method of any one of claims 16 or 17, for refrigerating a storage space, the method comprising:
providing a portable liquid nitrogen-based refrigeration system according to any one of claims 1 to 15, comprising a cold housing or cold compartment-based storage space;
providing entry of fresh cold air and exit of recycled air from the cold housing or cold box;
providing the intermediate energy reservoir of coolant, which involves using liquid nitrogen as a cooling source in an alcohol-water heat exchanger having an aqueous ethanol reservoir disposed relative to the entry of temperature controlled air into the cold housing;
supplying liquid nitrogen operatively connected to the alcohol-water heat exchanger, to freeze the aqueous ethanol solution to a desired controlled low temperature;
engaging the PLC controller to monitor storage conditions inside the cold housing or cold compartment and regulate the intake of cold air flowing in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to cause a supply of circulating air to enter or exit the cold housing or cold compartment.
21. The method of claim 20, wherein the initial cooling step of the system comprises:
loading each bay with cargo and feeding the required temperature and humidity set points into the PLC controller, whereby the PLC controller will begin pressurizing liquid nitrogen in a storage vessel and maintain a constant pressure inside the vessel during the flow of liquid nitrogen in the alcohol-water heat exchanger;
allowing the vapour of the vaporized nitrogen generated after the cold energy has been transferred to the alcohol-water mixture to flow through a coil brazed on the outer surface of the inner container of the cold box and promoting the lowering of the temperature of said cold box to said set point specified by the user,
venting the output vapor after transferring the cold to the cold compartment around a skid in an outer container of the truck such that the output vapor acts as a shielding gas and traps heat leaking into the cold compartment;
once the alcohol-water heat exchanger is charged with liquid nitrogen and the cold compartment has been cooled by the output vapor, air circulation will begin, which maintains the temperature within the cold compartment, with or without the required humidity control, within the range specified by the set point;
said air flow is optionally intermittent in nature, depending on the ambient temperature and said set point specified by said user; and
the supply of liquid nitrogen is stopped once the desired temperature of the alcohol-water heat exchanger is reached, which is-40 ℃ to-100 ℃, and is resumed again when the temperature of the alcohol-water heat exchanger is no longer able to maintain the temperature and humidity.
22. The method of claim 21, wherein maintaining a desired environment after initial cooling of the system comprises:
after the temperature of the inner wall of the cold box has reached the desired temperature set by the user, the nitrogen vapour is bypassed to avoid any further cooling of the cold box and optionally to a skid or container carrying cargo to reduce the effective heat load of the system, the solenoid valve is controlled using the PLC controller in dependence on the temperature of the inner wall of the cold box and the status of the nitrogen supply monitored by the PLC controller so that when the cold stored in the alcohol-water heat exchanger is insufficient to maintain the required temperature and humidity levels, the liquid nitrogen supply is again activated to cool the alcohol-water heat exchanger whereby both the liquid nitrogen supply and the air flow are effectively intermittent or can be substantially continuous as required in dependence on the conditions to be maintained and determined by the set point specified by the user in the PLC controller.
23. The method of any one of claims 16 or 17, comprising a humidity control step comprising:
the moist hot fresh outdoor air is mixed proportionally with the warm circulating air returned from the refrigerator depending on the type of food being stored, and humidity is maintained by operating a solenoid valve on the refrigerant circuit surrounding the loop heat pipe under active control of the PLC controller.
24. The method of claim 23, wherein
Pre-cooling the mixed air to a desired condition in a pre-cooling section surrounding the controllable loop heat pipe, and then further cooling the air by means of a heat exchanger to a temperature below the required condition, at which time the air may be too cold and too saturated to be supplied to the storage space and provide set air conditions in the storage space, which air is then dehumidified in a reheating section of the loop heat pipe and achieves the final set conditions before being delivered to the storage space; a pre-cooling section of a loop heat pipe is connected upstream of a main heat exchanger unit and a reheat section of a loop heat pipe is connected downstream of the main heat exchanger unit for following such a method;
at least one temperature controlled cold housing or compartment defining a refrigerated storage space having an inlet for fresh air and an outlet for recycled air exhausted from the cold housing or compartment;
an alcohol-water heat exchanger having a reservoir of ethanol water solution cooperatively disposed with respect to controlled fresh air intake into the cold housing;
a cooling source comprising liquid nitrogen, the cooling source being operatively connected to the alcohol-water heat exchanger to freeze an aqueous ethanol solution to a desired controlled cryogenic temperature;
the PLC controller for monitoring storage conditions inside the cold housing or cold compartment and regulating the intake of fresh air and recirculated air flowing in contact with the alcohol-water heat exchanger to maintain a set cooling temperature inside the storage space and to exhaust recirculated air from the cold housing or cold compartment.
25. The method of any one of claims 16 or 17, including the step of providing a specific environment in the storage space maintained under controlled cooling of the product, the specific environment including a nitrogen or ethylene environment during transport or shipping, an inert gas environment for corrosion sensitive products.
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