MXPA95001755A - Cryogenic system for temperature control - Google Patents

Abstract

A cryogenic cooling system for transport vehicles. The cooling system includes an evaporator fed with liquid CO2 from a filling tank. A gas-driven pump circulates liquid CO2. A gas-driven pump circulates liquid CO2 from the filling tank to the evaporator. The working fluid is supplied to the gas pump from the evaporator in the form of C gas

Description

* "CRYOGENIC SYSTEM FOR TEMPERATURE CONTROL" INVENTORS: BERNARD DE LANGAVANT. NORMAND MASSE. JEAN OACQUES DE LANGAVANT NATIONALITY: NORTH AMERICAN CITIZENS RESIDENCE: 642 DOLLARD BOULEVARD, OUTREMONT, QUEBEC H2V 3G3 E.U.A. 108 TOUSSAINT ROCHON, STREET, REAOHARNOIS, QUEBEC J6N 3N1 E.U.A. 222 CHICOINE STREET, DORION QUEBEC J7V 1Y8 E.U.A.

OWNER: FRIDEV REFRIGERATION SYSTEMS INC.

NATIONALITY: NORTH AMERICAN SOCIETY RESIDENCY: 1 WATERMAN STREET, STAMBERT, QUEBEC J4P 1R7 E.U.A. > t FIELD OF THE INVENTION The present invention relates to the art of controlling the temperature in an isolated closed space and, more particularly, to a cryogenic cooling system that is capable of maintaining a comparatively stable temperature within an isolated closed space. The cooling system is particularly suitable for use in vehicles designed to transport refrigerated products. Vehicles such as trailers and railways designed for the transportation of perishable goods rely mostly on forced convection mechanical systems to maintain low temperature conditions in the cargo area. The refrigeration units that operate under the principle of forced convection include an evaporator in the front wall of the loading area, in which a refrigerant flows that converts from liquid to gas in a way that absorbs the thermal energy and therefore decreases the room temperature. A fan mounted behind the evaporator creates a cold air stream with which it is intended to establish uniform temperature conditions by circulating air continuously in the cargo area. For reasons of simplicity in installation, mechanical refrigeration by means of forced air convection has become the standard for transport vehicles. Still, this approach to temperature control has some major drawbacks. Perhaps, the most serious drawbacks are the lack of flexibility and the inability to ensure uniform temperature conditions. For example, products that are located in close proximity to the evaporator unit may be supercooled while products that are stored farther away from the evaporator are subcooled. In addition, the forced circulation of air maintained in the cargo area has the undesirable effect of consuming the moisture of the products that are stored in the cargo area at an accelerated rate. This is particularly harmful for unpackaged meat and for fish products which are very sensitive to drying. In an attempt to overcome the drawbacks associated with mechanical forced convection systems, the industry has developed cryogenic cooling units that absorb thermal energy by causing liquid cryogen such as CO2 to evaporate within the cargo area. In contrast to the mechanical units equipped with a compressor, the cryogen in gaseous state, after carrying out its cooling function, is discarded in the atmosphere instead of being re-liquified so as to carry out repeated cooling cycles. Systems for cooling generally fall into two categories. The first is the injection method which is used mainly for the pre-cooling of an area for cargo. The liquid cryogen, kept under pressure, is sprayed directly in the area for charging at atmospheric pressure. Immediately, dry snow and cryogenic vapors are formed. While dry snow sublimates, it absorbs heat at the rate of 246 thermal units (Btu) per pound (for CO2) • Cryogen injection is characterized by the ability to cause rapid thermal reduction. This is suitable for transporting frozen products that can sustain very low temperatures. By contrast, fresh or partially frozen products that can be damaged at very low temperatures can not be transported safely in refrigerated vehicles of this type. The crude cryogen injection system described above can be significantly refined by modulating the injectors so that they deliver liquid cryogen within the cargo area at a controlled rate precisely in accordance with the requirements for heat absorption. This method, known as temporary injection, achieves much better temperature control and can be used to transport frozen products as long as they are not sensitive to excessive CO2 concentration, or to dryness. It also has to be noted that the liquid cryogen released in the charging area has the effect of consuming the oxygen content of the cooled enclosed space to a point where humans can no longer breathe properly and as a result, special procedures for charging are required to limit the risks of respiratory injuries. For example, the products that must be transported are always loaded in the cargo area without performing any pre-cooling so as to maintain the oxygen content at safe levels. The cryogen injection is effected only after the loading procedure has been completed and the cargo area has been sealed. It will be apparent that the exposure of chilled or frozen products to room temperature during the charging process is undesirable, particularly for products that are subject to rapid deterioration or decomposition when exposed to ambient temperatures. Cryogenic cooling systems that fall under the second category make use of an evaporator in which a cryogen fluid flows before being discarded into the atmosphere. The cryogen gas is subjected to a phase change from liquid to gas in the evaporator, thereby absorbing a large amount of heat so as to produce the desired cooling effect. The rate of absorption of the temperature is usually controlled by means of the regulation of the pree in the evaporator. At a lower pree, the cryogenic liquid evaporates at a rapid rate by this means absorbing significant amounts of thermal energy. In contrast, an increase in pree reduces the rate of evaporation of the cryogen to, in this way, decrease the absorption of heat by the system. The thermodynamic activity that takes place inside the evaporator is not a continuous process because only a finite amount of cryogenic liquid can be stored in the evaporator. When the cryogenic liquid has been consumed, a replenishment cycle must be carried out. This is achieved by establishing a liquid course between the evaporator and a reservoir. The cryogenic liquid is kept in the reservoir under pree (in the order of 300 pounds per square inch (psi)) and as a consequence, a natural transfer of fluid to the vacuum evaporator occurs only if the pree inside the evaporator is carried at a pree lower than the reservoir pree. Once the evaporator has been filled with cryogenic liquid, the liquid communication with the reserve tank is finished and the evaporator resumes its normal operation. During the replenishment cycle of the evaporator, the heat absorption process required to maintain a constant temperature in the cargo area is severely affected because the operator has no control over the process of evaporation of the cryogenic liquid which translates into variations of undesirable temperatures. When the heat absorption requirements are high, the cryogenic liquid is consumed at an accelerated rate which shortens the time interval between the replenishment cycles. The disturbances in temperature can become significant enough to break down the sensitive products. Although cryogenic cooling systems based on evaporator technology can maintain a relatively stable temperature, these can not effectively regulate the atmospheric water vapor content (relative humidity) in the cargo area. This quantity is an important factor in the prevention of dehydration of fresh products. It is known that the temperature differential between the evaporator and the ambient temperature in the charging area affects the humidity level. The higher the temperature differential, the lower the relative humidity. Accordingly, the cooling procedures that are usually carried out with the evaporator operating at a high temperature differential must be carried out with great care to avoid drying the sensitive products. In conclusion, the cooling systems based on the evaporation of cryogenic liquid are by far superior to the traditional mechanical refrigeration units, although these suffer from inconveniences which should still be considered to provide refrigerated vehicles that can truly provide optimal conditions to preserve delicate products of decomposition over long periods of time.

OBJECTIVES AND SUMMARY OF THE INVENTION One object of the invention is a cryogenic cooling system which is capable of maintaining a very stable temperature in a closed space. Another object of the invention is a cooling system capable of controlling the temperature in a closed space without this causing a significant desiccation of the product. Other objects of the invention will become apparent as long as the description is developed.

According to the embodiment that is widely described herein, the invention provides a system for cooling a closed space, comprising: an evaporator for receiving cryogenic liquid (for the purpose of this specification cryogen is used to designate a substance which, when in the liquid phase, boils at less than -30 ° C at atmospheric pressure, such as CO2, hydrogen, helium, methane, nitrogen, oxygen, air, etc.) the cryogenic liquid capable of absorbing thermal energy so as to produce a cooling effect when subjected to a phase change from liquid to gas in said evaporator; - a container for intermediate filling in fluid communication with said evaporator to supply cryogenic liquid to said evaporator; - a storage container in fluid communication with said container for intermediate filling to supply cryogenic liquid to said container for filling in medium; - first valve means in a first fluid course established between said evaporator and said container for intermediate filling, said first valve means are able to selectively assume an open position and a closed position, in said open position said first valve means allow the Cryogenic fluid transfer between said container for intermediate filling and. said evaporator, in said closed position said first valve means terminates said fluid course; - a second valve means in a second fluid course established between said intermediate filling container and said reserve container, said second valve means being able to selectively assume an open condition and a closed condition, in said open condition and said second means of valves allow the transfer of cryogenic liquid from said reservoir container to said container for intermediate filling, in said closed condition said second valve means terminates said second fluid course, wherein said first and second valve means allow isolating said evaporator from said reserve container during: a) the transfer of the cryogenic liquid between said intermediate filling container and said reserve container; and b) the transfer of the cryogenic liquid between said container for intermediate filling and said evaporator. In a preferred embodiment, the intermediate filling container communicates with the evaporator through a conduit incorporating a pump for transferring the cryogenic liquid from the intermediate filling vessel to the evaporator. During normal operation of the system when the evaporator provides a heat absorbing activity, the pump goes into operation continuously to replenish the cryogenic liquid that is being gradually evaporated. A return line connects the evaporator back to the intermediate fill vessel to return the overflow of cryogenic liquid without evaporation. Since this line also carries a significant amount of cryogenic liquid in the gaseous state, a separator surrounded by gas is incorporated in the course of the return line. The cryogenic fluid passes through the gas / liquid separator so that only the liquid fraction of the fluid exiting from the evaporator will be returned to the tank. The gas fraction is ventilated at a controlled rate to regulate the pressure and temperature in the evaporator and, in this way, the rate of heat absorption by the cryogenic fluid. When the intermediate filling vessel is emptied of cryogenic liquid, a replenishment cycle is initiated which consists in establishing a liquid communication between the intermediate filling vessel and a supply of cryogenic liquid contained in a reserve recirculator. During this replenishment cycle, the valves in the feed line and the gas / liquid return line between the evaporator and the intermediate filling vessel are closed, thereby isolating the evaporator from the reservoir vessel. When the replenishment cycle is complete, the dual-line fluid communication between the intermediate filling vessel and the evaporator is re-established by opening the valves while the line connecting the reserve vessel to the intermediate filling vessel is closed. It will be apparent that the intermediate filling vessel acts as a stabilizer that absorbs disturbances to the system that occur during the replenishment cycle. As a result, the pressure in the evaporator can be better controlled, and this means the reduction of temperature disturbances in the enclosed space. According to the widely described embodiment, the invention also provides a system for cooling a closed space, comprising: a supply container for the storage of cryogenic liquid; - an evaporator in a fluid communication relationship with said supply vessel for receiving the cryogenic liquid, said evaporator having a heat acquisition surface through which the thermal energy of the closed space is absorbed by the cryogenic liquid that is subjected to a phase change in said liquid to gas evaporator so that a cooling activity is carried out, said heat acquisition surface has a selectively variable surface area, thereby enabling controlling an absorption rate of heat by said evaporator. Generally speaking, the temperature inside the closed space is controlled by regulating the amount of heat extracted from the enclosed space per unit of time. The prior art cryogenic cooling systems based on the evaporator approach control the rate of heat transfer by varying the differential between the evaporator temperature and the temperature in the enclosed space. In contrast, the cooling system according to the invention provides an additional temperature control lever which is the surface area of the heat acquisition surface. This feature allows heat to be absorbed at a rapid rate and at a comparatively low temperature differential through the use of a larger heat acquisition area. This leaves the temperature differential as a control lever to adjust the rate of moisture consumption; The larger the temperature differential, the more water vapor is extracted from the air. In a more preferred embodiment, the evaporator is made of modules that can be progressively placed in line so as to expand the heat acquisition surface. A fluid course joins the evaporator modules to allow cryogenic liquid to circulate through them. The intermodular valves control the flow of cryogenic liquid so that the number of active numbers is fixed at each given point in time during the operation of the system. According to the embodiment and widely described herein, the invention also provides a cryogenic cooling system, comprising: an evaporator for receiving cryogenic liquid, the cryogenic liquid is capable of absorbing thermal energy so as to produce an effect of cooling upon being subjected to a phase change from liquid to gas in said evaporator - a supply container for storing cryogenic liquid, said supply container being in fluid communication with said evaporator to supply cryogenic liquid to said evaporator; - a pump in a fluid course between said evaporator and said supply container to cause the transfer of cryogenic liquid from said supply container to said evaporator; - a turbine in a driving relation with said pump; and - an expulsion duct for supplying cryogenic gas discharged from said evaporator to said turbine, by this means driving said turbine and causing said pump to operate. The regenerative pump operated with the working fluid discharged from the evaporator has the advantage of transferring the liquid from the supply vessel, such as the intermediate filling vessel to the evaporator without any external energy input. In addition, the output through the pump is automatically modulated according to the rate of consumption of cryogenic liquid by the evaporator. When the evaporator is being operated close to the total capacity, the larger volume of cryogenic gas being discharged drives the pump faster so that more cryogenic liquid is transferred to the evaporator. In contrast, at a lower utilization capacity, the flow rate of the cryogenic liquid by means of the pump is reduced since less working fluid is available. In a more preferred mode, the turbine is connected directly to the axis of the pump so that it is imparted to this rotating mechanical power of the energy of the gas exhaust stream. In a possible variant, the drive ratio between the turbine and the pump is established through the means of an electric motor generator / system. More specifically, the turbine drives the generator so that it produces electrical energy which in turn is used to power the electric motor of the pump.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS - Figure 1 is a flow chart of a cryogenic temperature control system constructed in accordance with the present invention; - Figure 2 is a plan view of an evaporator panel; - Figure 3 is a vertical cross-sectional view of an evaporator panel shown connected to the roof structure of the closed space in refrigeration; - Figure 4 illustrates a plurality of evaporator panels coupler together to form an evaporator module; - Figure 5 is a vertical cross-sectional view of the closed space in the refrigerator illustrating the arrangement of the evaporator modules, which also show with arrows the air currents passing between the evaporation modules; - Figures 6a and 6b illustrate an alternative arrangement of evaporator modules - Figure 7 is a schematic view of the evaporator distributor illustrating the network of conduits and control valves that regulate the flow of cryogenic liquid towards the individual evaporator modules; - Figure 8 is a block diagram of an electronic controller and the associated sensors to control the operation of the cryogenic cooling system; and - Figures 9a to 9d are flowcharts of the program stored in the memory of the controller which is invoked to control the various functions of the cooling system.

DESCRIPTION OF A PREFERRED MODALITY The present invention provides a cryogenic cooling system that is particularly suitable for transport vehicles such as refrigerated straight body trucks, trailers, rail cars, ISO or domestic containers for intermodal transport, among others. With reference to Figure 1, the cryogenic cooling system comprises an evaporator 10 which is designed to absorb thermal energy within the cooled cooled space so as to produce the desired cooling effect. In essence, the cryogenic liquid, such as CO2, is subjected to evaporation as a result of the heat of the environment. This phase change from liquid to gas produces a thermal absorption. The cryogenic fluid is discharged from the evaporator through the ejection line 14 into a separating vessel 12. The cryogenic fluid that flows from the evaporator 10 includes a larger gas fraction and a smaller liquid fraction, i.e., unvaporated cryogenic liquid. The purpose of recirculating separator 12 is to divide these fractions under the effect of gravity. More particularly, the unvaccinated liquid flows to the bottom of the container while the gas is directed through line 16 to a vent valve 18. The liquid in the separator vessel 12 is returned to a container for intermediate filling 22 under the effect of gravity through the valve 20. The intermediate filling container 22 supplies cryogenic liquid to the evaporator 10 through the fixed course that comprises the valve 24, the pump 26, the valve 28 and finally the supply line 29. Valves 24 and 28 are three-way devices for controlling the flow of cryogenic liquid from two different points. More particularly, in a first position, the valve 24 establishes a liquid communication between the intermediate filling container 22 and the pump 26. In a second mode of operation, the cryogenic liquid can flow from a reserve container 34 to a pump 26 but, it is prevented from reaching the filling tank 22 through the valve 24. Similarly, the valve 28, in a first mode of operation, allows the cryogenic liquid to pass through the pump 26 to the evaporator 10 through the feed line 29. In a second mode of operation, the feed line 29 is closed and the flow from the pump 26 is redirected to the intermediate fill tank 22. The valve system described above allows the selectively connecting the intermediate filling vessel 22 to the reserve vessel that constitutes the main supply of cryogenic liquid. This connection is established only when the intermediate filling container 22 is empty and needs to be refilled with cryogenic liquid. Between replenishment cycles, the cryogenic fluid flows from the intermediate filling vessel 22, through the valve 24, the pump 26, the valve 28, the evaporator 10 and is then returned to the intermediate filling vessel 22 through the return line 14, the separator 12 and the valve 20. The reservoir 34, the intermediate filling vessel 22, the separation vessel 12, and all connecting lines are properly insulated to prevent undesired evaporation of the liquid fluid. During a refueling cycle, the valve action events below are carried out simultaneously: a) the valve 20 closes to terminate the liquid course between the evaporator 10 and the intermediate filling vessel in the fluid return line cryogenic; b) the valve 24 is changed to the second mode of operation so that the cryogenic liquid of the reserve tank 34 occupies the pump 26; c) the valve 28 is changed to the "second mode of operation, by this means closing the feed line 29 and allowing the cryogenic liquid from the pump 26 to enter the intermediate filling container 22; and d) a valve 33 is changed to open a line for degassing between the intermediate filling container 22 and the storage container 34. The degassing line 31 is opened inside the reservoir 34 on the surface of the liquid body to allow the gaseous medium in the intermediate filling vessel 22 balancing the pressure with the gaseous medium within the reservoir 34. When the intermediate filling vessel has received a predetermined charge of cryogenic liquid, the valves 24 and 28 are repositioned in their original positions so that the pump 26 directs the cryogenic liquid to the evaporator 10. Valve 33 is closed and valve 20 is open to resume the normal operation of the evaporator 10. During the refueling procedure, the filling container acts essentially as a stabilization zone preventing direct communication between the reservoir 34 and the evaporator 10. It must be appreciated that the pressure in the reservoir 34 can be very different from the pressure in the evaporator 10. As a result, any direct communication between these components can significantly disturb the heat absorption activity of the evaporator and also cause excessive stress in the pump 26 since it can be subject to a very large pressure differential. In contrast, the intermediate filling container allows maintaining a controlled level of pressure inside the evaporator 10 during the refueling cycle. Although the cryogenic liquid is not supplied to the evaporator at this point, the heat absorption activity is maintained because at least some of the cryogenic liquid remains inside the evaporator and continues to convert to its gas phase. The replenishment cycle is initiated by observing the cryogenic liquid level within the intermediate fill vessel 22. This information is provided by means of a pair of level switches which generate signals to notify the system controller when the Cryogenic liquid level has reached a high level or a low level. This feature will be described in detail later. The gaseous fraction of the cryogenic fluid leaving the separating vessel is directed towards a ventilation valve 18 that precisely regulates the rate at which the gas is released from the system to, in turn, control the pressure in the evaporator 10. Data there is a direct relationship between the pressure in the evaporator 10 and the temperature of the cryogenic liquid, it is possible to adjust the rate of heat absorption by means of controlling the pressure of the evaporator. The gas released from the vent valve 18 is still at a considerable pressure and instead of being discharged into the atmosphere, the cooling system according to the invention makes use of the energy contained in the gas stream to energize the components that are necessary for the operation of the system. More particularly, the vent valve discharges the gas released from the evaporator into a pressure-stabilizing vessel 36 which stores the liquid medium before it is used to drive the pump 26, a generator 40 and a fan 42. The pump 26 it always receives priority because, as discussed above, it plays an important role in the transfer of liquid oxygen from the reservoir 34 to the intermediate filling tank 22 and to continuously supply the evaporator 10. The hierarchy of the components supplied from the pressure stabilizer tank is determined based on the operating pressure. The pump 26 is supplied with low pressure gas from the pressure reducer 28 which opens at a pressure in the order of 20 pounds per square inch (PSI). The gas stream drives a turbine (which is not shown in the illustrations) directly connected to the axis of the pump to impart a rotational movement to it. The gas expelled from the turbine is directed through the ducts (which are not shown in the illustrations) under the floor of the enclosed space, previously to be discarded in the atmosphere, so that any capacity for the absorption of heat remaining in the "gas is used to form a barrier to heat infiltration." The turbines (which are not shown in the illustrations) which activate the generator 40 and the fan 42 are supplied from a high pressure reducer 44 set to about 100 PSI By means of this arrangement, the generator 40 and the fan 42 are allowed to operate only when the pressure in the stabilization vessel pressure 36 has reached or exceeds 100. PSI Below this level, gas is reserved for the operation of pump 26. The purpose of generator 40 is to recharge the battery (not shown in the illustrations) that supplies electrical energy to the electronic controls of the system; generator 40 receives priority before fan 42. The purpose of the fan is to create an air stream within the cargo area so that high heat points are eliminated. The fan can be beneficial for some perishable products that can be heated during transport. The fan is of a type described in U.S. Patent No. 4,986,086 issued January 22, 1991. The subject which is the subject of this patent is incorporated herein by reference. Similar to the pump 26, the ejection stream from the generator 40 and the fan 42 is transported through the ducts below the floor of the enclosed space. As previously mentioned, it is important that the transfer of the cryogenic liquid from the reservoir 34 to the intermediate filling vessel 22 will be completed as quickly as possible because during the replenishment cycle, the absorption of heat by means of the evaporator 10 can be limited If the heat absorption is limited, only a small amount of gas is discharged from the evaporator which may not be sufficient to actuate the pump 26, especially when the pressure stabilization tank 36 has been previously emptied. For this reason, the cooling system according to the invention provides a pressure amplification circuit that supplies cryogenic gas directly from the reservoir 34 (assuming that it is always under sufficient pressure). The amplifier circuit includes a reducer 46 which adjusts the pressure of the cryogenic gas to about 110 PSI and a reducer 48 which also adjusts this pressure by decreasing it to about 18 • PSI and joins the line that supplies the working pressure to the pump 26. In this manner, if no gas is available from the pressure stabilizing vessel, the gas coming from the reservoir 34 will drive the pump 26 during the liquid transfer cycle. Either way, if gas is available from the pressure stabilization tank 36, it will take precedence at high temperature (20 PSI vs. 18 PSI). Accordingly, no gas will flow through the amplification line. Similarly, if the battery has a low voltage, the generator 40 is activated by the pressure of the reservoir vessel 34 through the line 41. The cooling system according to the invention also incorporates a section for pre-cooling. cooling that uses direct cryogenic liquid injection. A mouthpiece 200 directly supplied from the reservoir 34 releases a temporary spray of cryogenic liquid in the closed space. The flow of cryogenic liquid is controlled by means of a valve 202. The rapid cooling effect produced by evaporation / sublimation of the cryogenic liquid is very effective in reducing the temperature of the structure of the closed space, such as the walls, the floor and roof, which has a significant thermal inertia. Without the precooling the evaporator 10 will require a longer period of time to bring the temperature in the closed space to the desired set point. The nozzle 200 is also used as a cooling accelerator if the heat absorption capacity of the evaporator 10 is insufficient for the extreme temperature differential between the indoor and outdoor generators. The structure of the evaporator 10 will now be described in detail in connection with figures 2 to 7. The evaporator 10 is made from individual sections 50 which are assembled together in modules which can be selectively actuated to control the rate of absorption heat of the evaporator. An evaporation section 50 is shown in Figure 2. It is made of a solid sheet of aluminum having a thickness of 1.8 millimeters (mm) with a continuous tube circuit 52 which is an integral part of the sheet and through which the cryogenic fluid can pass. This plate type heat exchanger is manufactured by Algoods, a dion of Alean Aluminum Ltd. under the brand name Roll-Bond. Each evaporation section 50 is eight feet long by one foot wide. The longitudinal ends 54 of the evaporator section are bent downwards for better rigidity. Four parallel tubes 52 extend in a parallel relationship along the panel. At both ends of the section, the tubes are mixed in a pair of connecting tubes 56 that allow joining together several evaporation sections. As shown in Figure 4, several parallel sections 50 are serially joined together in a row to form an evaporator module 58. At one end of the row the connection tubes 56 are joined at 60 to close the fluid circuit. Therefore, a double tube circuit is created. The cryogenic liquid will leave just after the point where it entered the circuit after having absorbed the heat collected by the evaporator module. In a more preferred embodiment, eight of said evaporator modules are suspended from the ceiling of the enclosed space. This feature is shown in more detail in Figures 5 and 3. The evaporator modules are mounted obliquely, slightly overlapping each other so that they condense the liquid that will slide down and collect it in the gutters 62, instead of descending. The positioning of the evaporation module as shown in Figure 5 allows an excellent rise of the heated air towards the evaporator along the side walls of the enclosed space. The hot air then moves over the modules 58 and is then cooled by the cryogenic liquid in evaporation. The cold air then descends between the indual modules 58. In Figure 5, the modules 58 extend along the longitudinal axis of the closed space under cooling. Figure 6a shows a variant where the modules are in a pattern of multiple domes and these do not overlap one another. Figure 6b shows a further variant with superimposed modules placed in a simple dome configuration. Figure 7 illustrates the arrangement of the distributor of the evaporation module conduits and the operation of the associated valves, which allow controlling the extension of the heat acquisition surface of the evaporator. In the illustration, eight evaporation modules are shown, designated by reference numerals 58a through 58h. The cryogenic liquid feed line 29 is connected to a first distribution node 64 which supplies the modules 58b and 58g. Downstream of the stream of the node 64 three additional distribution nodes are provided which are referred by means of the numerals 66, 68 and 70 which supply the pairs of evaporation modules 58c and 58f, 58a and 58d and 58e, respectively. The valves for inter-node isolation 72, 74 and 76 control the flow of the cryogenic liquid towards the various evaporation modules. Figure 8 is a flow chart of the electronic controller that controls the operation of various system components to maintain the temperature and relative humidity as close as possible to a predetermined set point. The electronic controller 80 includes a central processing unit (CPU) 82 of known construction. A CPU available by Intel under the designation 80C5EFB has been found satisfactory. A memory 84 for storing data and program instructions communicates with the CPU 82 via a bus 86. A serial interface 86 allows the controller 80 to acquire data from the various sensors and output signals to the various components controlled by means of the system.

Finally, the controller 80 also includes an input / output unit (1/0) 88 which includes a keyboard and a unit for deployment that allow the operator to modify the adjustment options of the system, monitor the execution of the program, etc. Four sensors are provided to notify the controller 80 of the occurrence of various events and of the magnitude of certain physical quantities so that the appropriate action can be taken so that the environmental conditions in the enclosed space are as close as possible. possible to the set point. An internal temperature sensor 90 measures the temperature of the room in the closed space under cooling. The information generated by means of the sensor is used by the controller 80 to calculate a differential between the set point of the temperature and the actual temperature in the closed space. Based on the magnitude of this differential, the controller will readjust the configuration options of the system so that the error in the temperature is reduced as much as possible. A pressure sensor of the evaporator 92 observes the pressure in the evaporator 10. This data is used by the controller to determine the temperature of the cryogenic liquid and the rate of evaporation of the cryogenic liquid, therefore the rate at which the heat is absorbed from the space closed. A temperature sensor on the outside 91 measures the external temperature. This information is used by the controller to set the initial heat absorption capacity of the evaporator 10. A wall temperature sensor 93 provides information on the temperature of the structure that forms the cooled enclosed space. The signal generated by the sensor 93 is mainly used to control the duration of the pre-cooling cycle, as will be described later. Based on the information generated by means of the sensors 90 to 93, the controller 80 generates an output signal to the ventilation valve 18 for regulating the pressure inside the evaporator. More preferably, the valve 18 is pulse modulated to regulate with a high level of precision the amount of gas that is allowed to escape from the evaporator. In short, the vent valve is openly repeated at very short time intervals. By adjusting the duration of these time intervals (modulation of pulse duration) a very precise pressure control can be carried out in the evaporator. In a variant, the valve can be kept open for intervals of constant time duration, but by varying the pulse rate, i.e. the number of valve openings per unit of time, the rate of gas flow that is allowed to escape from the evaporator is regulated. A valve available from H. D. Baumann Assoc. Ltd. under the brand name Baumann has been found satisfactory. The low-level cryogenic liquid and high-level cryogenic liquid sensors 94, 96 mounted on the intermediate filling container 22 to provide information on the level of cryogenic liquid stored in that container. The information generated by means of these sensors is used to control the replenishment procedure, in the manner that will be described hereinafter. The interface 86 also generates output signals to the valves 20, 33, 24, 28 to control the replenishment cycle of the intermediate fill container 22, as will be described in greater detail later. The interface 86 also controls the valves 72, 74 and 76 of the evaporator 10 which determines the number of currently active evaporation modules. Figures 9a to 9d provide a flow chart of the program program that controls the operation of the cryogenic cooling system. In an initialization step 98, the program performs a certain number of basic operations such as resetting counters to initial values, locating in memory the starting address of the data acquisition blocks and loading the interruption vectors, among others. In step 100, the internal temperature set point (TSET) is reached. This is achieved by waiting for a certain period of time for the operator to enter a value. Specifying a new TSET is achieved either through the keyboard or the 1/0 88 unit or through the serial 86 interface using an external computer connected to the controller 80. If after a predetermined wait a new TSET has not been introduced , the program will initialize itself by loading from memory the last value of TSET that has been used. Similarly, the program initializes at step 102 the desired relative humidity level by means of waiting for an input, and if that entry does not occur the previous moisture value is used. Prior to pre-cooling, step 400 initiates processing (see Figure 4d) to determine the initial configuration of the evaporator, i.e., the number of pairs of active modules. In step 402 the outside temperature (OTEM) is determined by observing the output of the sensor 91. Based on the value of TSET and OTEM the program calculates the temperature differential TD and the number of pairs of evaporation modules that must be placed in operation. The contents of the reference table are reproduced below: INITIAL NUMBER OF MODULES If TSET is above 28 ° F and TD < 25 ° F - 2 modules If TSET is above 28 ° F and 25 ° F < TD < 40 ° F -4 modules If TSET is above 28 ° F and 40 ° F < TD < 60 ° F -6 modules If TSET is above 28 ° F and TD > 60 ° F -8 modules If TSET equals 28 ° F or less -8 modules In step 406 the isolation valves 72, 74 and 76 are operated to configure the evaporator 10 according to the number of modules selected from the reference table. The execution of the program then jumps to step 104 where the controller 80 determines the maximum range within which the pressure may fluctuate in the evaporator 10 to help maintain the humidity at the set level. This calculation can be done by means of: a) reading the moisture level selected in step 102 (HH, MH, LH or frozen); b) compare the current humidity level with the set point; and c) consulting a reference table stored in the memory 84 to determine the limits of the pressure range according to the desired humidity level. The limits of the pressure range are defined by the variables (PMAX and PMIN) that are +/- X PSI from a mean PSET value based on TSET. The magnitude of the variable X is inversely proportional to the moisture error value. The content of the reference table is read for the frozen products in the following manner: PMIN -25 and PMAX +25 for HH or High Moisture PMIN -50 and PMAX +50 for MH or Medium Moisture PMIN -75 and PMAX +75 for LH or Low Moisture and frozen products.

It is important to note that the cooling system does not perform an active humidity control function, - it merely controls the rate at which water vapor is extracted from the air or from the products (going into freezing and condensing in the evaporator) . In other words, no incoming steam input is made to raise the humidity level and the only action the system can take is to limit the amount of water vapor condensed in the evaporator so that it is reduced as much as possible excessive drying. An example can help illustrate this point. Assume that products that do not release moisture are charged in the refrigerated enclosed space that is at 75% relative humidity. If the operator sets the humidity setting to HH the system will not be able to reduce the moisture error value beyond the original 20%. Either way, by controlling the temperature differential between the evaporator and the temperature in the enclosed space, the system can prevent the error value from increasing further. When the desired humidity level is very high, the evaporator will be operated within a more restricted pressure range so as to limit the evaporator / closed space temperature differential. As mentioned above, a high temperature differential increases the rate of water vapor condensation and freezing in the evaporator, thus causing faster moisture consumption. In contrast, under conditions of reduced temperature differential the removal of moisture still occurs, but at a much slower pace. However, when the moisture error value is low, a higher operating pressure range is permissible. The value of the PSET variable which is the average value at which the evaporator is originally set is determined based on the TSET temperature setting. The following table is used for this purpose: Set Point Initial Setting Point C? 2 Pressure Temperature Liquid PSET Equivalent Indoor TSET in ° F Initial in PSI Temperature in ° F 37 435 Maximum permissible 24 36 430 Minimum permissible 23 34 420 22 32 410 21 28 390 18 24 370 14 20 350 11 16 330 7 12 310 4 8 290 0 4 270 0 250 - 4 230 - 13 - 8 210 - 17 - 10 200 - 20 In step 300, the program initiates a pre-cooling procedure (see Figure 9e) After observing in step 302 the temperature of the wall of the closed space with the sensor 93 (TWALL), a comparison is made with the point Fixed (TSET). Yes TWALL >; TSET valve 202 is open to spray cryogenic liquid in the closed space for 10 seconds every 30 seconds. The TWALL of temperature is measured repeatedly and the cycle for opening and closing of valve 202 is activated until TWALL is equal to TSET. Then proceed with the injection for 3 seconds every 30 seconds until the internal temperature observed by the sensor 90 is equal to TSET. This completes the pre-cooling procedure. In step 106, a reading of the internal temperature (ITEM) is made by observing the signal produced by the sensor 90. ITEM is subtracted from TSET in step 108 to determine an error value (Delta) which is the differential between the set point of the temperature and the internal temperature of the closed space. In decision step 110 the magnitude of Delta is evaluated. If it exceeds 0.5 ° F, the pressure in the evaporator is reduced so that the rate of heat absorption increases (when ITEM is smaller than TSET). When Delta is negative, i.e. TSET < ITEM by 0.5 ° F, the pressure in the evaporator is increased to reduce the rate at which the closed space is emptied of heat. The corrected pressure (CPSET) in the evaporator is determined by adding or subtracting, from the current pressure setting, as the case may be, N psi, where N is proportional to the temperature error and varies in the range of 3 psi to 20 psi. The variation of 5 psi corresponds to an adjustment of 1 ° F. The pressure correction is increased from one pass of the program to another so that the overall correction can be extended well beyond the 20 psi limit for each step. In decision step 114, the program determines whether CPSET is between the specified range PMIN and PMAX set according to the desired level of relative humidity in the cooled enclosed space. In the affirmative case, the program calculates in step 116 a new pulse width according to which the vent valve 18 must be put into operation to achieve the reach of CPSET. The maximum pressure of 435 PSI and the minimum pressure of 200 PSI are accepted by the program. Once these pressures are passed, it is immediately considered as reaching a PMAX or a PMIN. On the other hand, if the CPSET is outside the PMAX and PMIN range, the program will open or close (depending on the sign of the correction) one of the valves 72, 74 or 76 so that it increases or de-creeds in one the number of pairs of active evaporation modules. This action has the effect of expanding or reducing the heat acquisition surface of the evaporator to, in turn, control the rate of heat absorption while maintaining the CPSET within the range of PMIN and PMAX.

Step 120 terminates the temperature control routine. The program then continues with a processing path that controls the supply cycle of the intermediate filling container 22. More particularly, in step 122 a reading of the sensor 94 is made to determine whether the level of cryogenic liquid in the container 22 is found. at the level at which the replenishment cycle should be initiated. If in fact the filling container 22 is low in cryogenic liquid, the valves 24 and 28 are connected to establish a fluid course between the reservoir 34, the valve 24, the pump 26, the valve 28 and the container for filling intermediate 22. In these positions of the valves, the supply line is closed and the fluid course between the filling container 22 and the valve 24 is also closed. At the same time, the valve 20 is closed and the valve for degassing 33 is open. As a result of this sequence of operation, the pump 26 absorbs liquid from the reservoir 34 and fills the container for intermediate filling 22. At the same time, the evaporator 10 is completely isolated from the remnant of the system so as to avoid Altering the pressure inside it. In the processing step 124, the program observes the output of the sensor 96. This sensor will notify the controller 80 when the level of cryogenic liquid in the filling tank has reached an upper limit. If the container 22 has not yet been filled, the program returns to step 124 to observe the sensor 96 again. This cycle is repeated until the container 22 has been filled. At this point, the valve 33 is closed, the valve 20 is open and the valves 24 and 28 are repositioned in their original positions and therefore establish a communicative relationship between the intermediate filling container 22 and the evaporator 10. The execution of the program then returns to step 106 to effect the new pass of the temperature control routine. The valves used in the cryogenic cooling system described above are preferably electrically actuated gas driven devices. The advantage of these valves is that they can be actuated by means of the ascension of cryogenic gas at any suitable point in the circuit. The only thing that is required is a weak electric current generated from the controller 80 to operate the valve. These valves are well known to the man skilled in the art and do not need to be described in more detail. It may also be provided to provide the cooling system as described above with a small heating unit to provide heat when the outside temperature falls below the set point. A unit for diesel heating has been found satisfactory. The heated air is preferably evenly distributed in the area for loading through ducts in the walls and the floor. It can also be envisaged to provide a thermopile generator (a component manufactured by Global Thermopile Canada, which has been found satisfactory) to generate electricity from the thermal energy in the hot air stream. Electric power is supplied to the controller 80 which can also be constructed to regulate the operation of the heating unit. The system for cryogenic pre-cooling as described above can also be conveniently used as an amplifier to further cool the enclosed space when the heat absorption requirements are high. The logic of the program in the control can recognize a situation when the evaporator is operating at full capacity, and then the injection of cryogenic liquid into the closed space begins if the temperature should be lowered. This amplification function is suitable when transporting frozen products which are not susceptible to direct contact with the cryogenic liquid. The present invention should not be construed in any limiting manner since refinements and variations are possible without departing from the spirit of the invention. The scope of the invention is defined in the appended clauses and their technical equivalents.

Claims (19)

NOVELTY OF THE INVENTION Having described the invention, it is considered as a novelty, and therefore it is claimed as established in the following: CLAUSES

1. A cooling system for an isolated enclosed space comprising: a main isolated reserve tank for storing cryogen in liquid phase, in sufficient quantity to supply the cooling system with an appropriate fuel autonomy. - an evaporator thermally coupled to the ceiling of said closed space, said evaporator containing cryogen in liquid and gaseous phases, the heat of this closed space is transferred to said evaporator by natural convection which causes the cryogen inside it to be converted from said liquid phase up to said gaseous phase which increases the pressure inside said evaporator; - a ventilation means coupled to said evaporator, said ventilation means being able to release sufficient liquid cryogen from said evaporator to maintain the pressure inside it at the precise level required to ensure adequate temperature of the cryogen and in doing so maintain the space closed said at the desired temperature; - a liquid transfer medium which allows the transfer of the liquid cryogen from said main isolated reserve tank to the said evaporator as required and which provides liquid cryogen to the said evaporator at the pressure level required to ensure adequate temperature and heat absorption capacity of said evaporator; - a means for gas distribution which has the gaseous cryogen evacuated from the evaporator through said ventilation means to activate several air motors which energize a liquid transfer pump, an electric generator and a fan, in this order , depending on the amount of available gaseous cryogen; - an electronic controller, with an appropriate program, which controls said ventilation means, liquid transfer means, and gas distribution means to operate as required, and maintain adequate pressures within said evaporator and the various said means, using data collected by means of temperature, pressure, humidity and CO2 sensors, and sending signals to electronic solenoids that activate pneumatic valves; said cooling system can maintain a closed space at a temperature as low as -20 ° F or as high as +45 ° F while the outdoor temperature rises as high as + 120 ° F; said cooling system can modulate the heat absorption capacity of said evaporator to obtain adequate cooling with an appropriate level of humidity; said cooling system can operate each component without any external source of energy other than the energy contained within the cryogen gas.

2. A cooling system as defined in Clause 1, in which said evaporator comprises a plurality of evaporation units for receiving liquid cryogen within a pipe network housed within Roll-bond aluminum plates interconnected together and a separating means at the outlet end of said evaporator to ensure the separation of the cryogen in said liquid and gaseous phases, said evaporation units are manufactured in the form of panels, positioned in a partial overlap relationship and are arranged obliquely to allow the drained from the condensers towards predetermined areas of said enclosed space.

3. A cooling system as defined in Clause 2, in which each of said evaporation units is equipped with an isolation valve that controls the supply of liquid cryogen to the individual evaporation units. The control means that regulate the operation of each of said isolation valves allows a selected number of said evaporation units to receive liquid cryogen and in doing so increases or decreases the heat absorption capacity of said evaporator.

4. A cooling system as defined in Clause 3, in which the electronic controller said, using data collected by means of said temperature, pressure and humidity sensors, determines the number of said isolation valves that must be opened to obtain a evaporator with a heat absorption capacity that allows the said vent to maintain the appropriate temperature differential (TD) between the temperature of the liquid cryogen and the temperature set point within said enclosed space for the desired humidity level within said closed space.

5. A cooling system as defined in Clause 1, wherein said means for transferring liquids comprises: - a filling tank in a fluid communication with an inlet end of said evaporator that allows the transfer of liquid cryogen between these, also in fluid communication with said separation means at the exit end of said evaporator which ensures the separation of the cryogen in said liquid and gas phases, and furthermore in fluid communication with said main reserve tank which supplies the liquid cryogen to said filling tank; - first valve means in a fluid course between said filling tank and said evaporator for controlling the flow of liquid cryogen between said evaporator and said filling tank; - second valve means in a fluid course between said main isolated reserve tank and said tank for filling to control the transfer of liquid cryogen between them; - third means of valves in a fluid course between said separator and said tank for filling to control the flow of cryogen between said separator and said tank for filling; - valve half-rooms in a fluid course between said tank for filling and gas side of said main isolated reserve tank to equalize the pressure of the cryogen in gas phase while said isolated main reserve tanks supply liquid cryogen to said tank for filling the said electronic controller with the appropriate program constitutes means for: a) maintaining said first valve means in an open condition when said filling tank supplies liquid cryogen to said evaporator; b) maintaining said second valve means and fourth valve means in a closed condition to prevent a fluid communicative relationship between said main isolated reserve tank and said filling tank when said filling tank supplies the liquid cryogen to said evaporator, thereby means maintaining said main isolated reserve tank of said evaporator during the process of heat absorption; c) maintaining said third valve means in an open condition when said fourth valve means are in a closed position, by this means keeping said separator in communication with said tank for filling during the heat absorption process to allow the overflow of liquid cryogen return to the tank for filling; the said electronic controller similarly constitutes means for: d) maintaining said first and third valve means in a closed position when said second and fourth valve means are in an open condition, thereby isolating said evaporator and said separator when said tank for filling is being replenished with liquid cryogen from said main isolated reserve tank.

6. A cooling system as defined in Clause 5, but making use of three-way valve means to replace said first valve means and said second valve means; - first means of three-way valves that establish a fluid course between said tank for filling and said evaporator while keeping the fluid course between said filling tank and said isolated reserve tank and vice versa; second valve means that establish a fluid course between said main isolated reserve tank and said filling tank while keeping the fluid course between said tank for filling and said evaporator, and vice versa; similarly said third valve means and said fourth valve means are connected together so that, when said third valve means are open, they automatically close said fourth valve means, and vice versa.

7. A cooling system as defined in Clause 6, comprising a gas-driven pump in the fluid course between said first three-way valve means and said second valve means for transferring the liquid cryogen either from said tank for filling to the said evaporator or from the main isolated backup tank to the said fill tank depending on how the said electronic controller opens or closes said three-way valve means and said third and fourth valve means; - two liquid level sensing means comprising maximum level and minimum level switches mounted inside the said filling tank that give the required signals to said electronic controller to make the exchange of the various valve means. As a consequence, said liquid transfer means provide the evaporator with said liquid cryogen at the precise pressure level required to ensure the proper heat absorption capacity to said evaporator, regardless of the pressure in the main liquid cryogen reservoir tank, and allows the transfer of the liquid from the main isolated reserve tank to the said evaporator as required, regardless of the pressure in said evaporator.

8. A cooling system as defined in Clause 1, wherein said gas distribution means comprise: - a pressure stabilization tank which receives all of the cryogen gas passing through said ventilation means, said -The pressure stabilization tank is equipped with a safety valve adjusted to 175 PSI; - a sealing valve means for bypass in a fluid course between said pressure stabilizing tank and said air motor of said liquid transfer pump using cryogen gas reduced to 20 PSI; - a back pressure regulating means and a generator coil valve means in a fluid course between said pressure stabilization tank and said air motor of said electric generator using cryogen in gas escaping from said pressure stabilization tank when the pressure rises above 100 PSI; - a second back pressure regulating means in a fluid course between said pressure stabilizing tank and said air motor of said fan using cryogen in gas escaping from said pressure stabilization tank when the pressure rises above 150 PSI; - a network of cavities under the aluminum floor of the said enclosed space that gathers all the exhaust gas from the said three air motors before it is released into the atmosphere and acts as a cold barrier for the coming heat infiltration from below said closed space. Said said distribution means supply working fluid in the form of gaseous cryogen to said air motors without making use of the pressurized gaseous cryogen stored inside said main isolated reserve tank. Consequently, no energy contained in said main isolated reserve tank is wasted by the operation of the system outside of the cooling function. Priority is given to said liquid transfer pump which operates as soon as a pressure of 20 PSI exists in said pressure stabilization tank, then said electric generator is activated when the pressure in said pressure stabilization tank is increased by above 100 PSI and if the battery needs recharging. If not the generator coil valve means will direct the excess gas to the fluid course connected to said air motor of said fan which is normally used when the pressure in said pressure stabilization tank rises above 150 PSI.

9. A cooling system as defined in Clause 8, which further comprises an amplifying means for the gas distribution means when not enough cryogen gas is generated by the heat absorption of the said evaporator. The said amplification means comprise: a fluid course reduced to 110 PSI connected to the gas side of said main isolated reserve tank; - a shut-off valve means for pre-filling in the fluid course reduced to 110 PSI coming from said insulated reserve tank and in addition it is reduced to 18 PSI. This said sealing valve means for pre-filling supplies cryogen in gas to said air motor of said liquid transfer pump if there is not enough gas available for the air motor from said pressure stabilization tank to operate in accordance with the program of the said electronic controller; - a valve means in the fluid course reduced to 110 PSI coming from said main isolated backup tank and opening the communication with the said coil valve means of the generator which supplies the said air motor with said electric generator of the said air motor of said fan if the electronic controller specifically requests it. This said valve means opens only if there is a real need to recharge the battery because of insufficient heat absorption of said evaporator or if there is a need for a particular type of air turbulence within said closed space.

10. A cooling system as defined in Clause 1, in which said electronic controller is informed by the operator through a digital keypad of the temperature setpoint, the desired humidity level and the required CO2 concentration. inside the closed space. The said electronic controller immediately decides the required mode of operation, the number of said isolation valves that must be opened and the pressure that must be maintained in said evaporator, and with the appropriate program, monitors each action or reaction of the system there. onwards.

11. A cooling system as defined in Clause 10, in which the original temperature within said closed space is decreased very rapidly to the set point before the perishable products are introduced into said closed space. This mode of operation called pre-cooling is obtained by direct injection of the cryogen concurrently with the absorption of heat generated by said evaporator. The said liquid cryogen injection is performed by means of a temporary opening and closing (10 seconds every 30 seconds) of a valve means called Coldspray in a fluid course between the main isolated reserve tank and the enclosed space until the temperature within the walls of said closed space has reached the temperature set point established by said operator. Then the internal temperature is progressively stabilized to the set point by means of a short injection of liquid cryogen (3 seconds every 30 seconds) if and when required. Thereafter, the system is in its normal operating mode and the said electronic controller adjusts the pressure set point of the said vent and the opening and closing of said isolation valves within precise limits to maintain the temperature and the appropriate humidity levels without the injection of the liquid cryogen.

12. A cooling system as defined in the Clause 11, but wherein the electronic controller is activated by a half-switch after closing of the doors to ensure a rapid recovery of the temperature by temporary injections of liquid cryogen by means of said Coldspray means until the temperature setpoint is reached again within said closed space. This mode of operation called re-cooling comes automatically after closing the doors. While the doors are open, said same switch means stops any possible injection of the liquid cryogen into said closed space so that the personnel is not bothered during the loading of said closed space, and temporarily stops any adjustment in the pressure or- in the temperature until the doors are closed.

13. A cooling system as defined in Clause 11, but where the electronic controller activates said Coldspray means to respond to the demands of said CO2 concentration sensor • The temporali-zador that opens or closes said Coldspray it does now only 1% seconds every 30 seconds until the proper concentration is reached. If the 'CO2 concentration is set to "0", the said Coldspray will never open after the pre-cooling mode is completed even after the doors are opened as described in Clause 12.

14. A cooling system as defined in Clause 11, but wherein the electronic controller activates said Coldspray means as an amplifier when the temperature of the cryogen inside said evaporator can not be brought sufficiently low to absorb the entire requirement of heat absorption. This will only happen when the transported product is frozen or sub-frozen and the outside temperature is extremely high.

15. A cooling system as defined in Clause 1, but which includes a small diesel burner heater to allow the transportation of perishable products when the outside temperature is lower than the selected temperature set point for the loading area. Said diesel burner heater circulates glycol within a network of pipes located within the network of cavities under the aluminum floor of said enclosed space at the base or the walls of said enclosed space protected by appropriate fastening bands. . Said diesel burner heater is equipped with a thermopile which produces enough electricity not only to operate its own circulation pump and the ignition shutter, but also to recharge the battery and operate small electric ventilators.

16. A cooling system as defined in Clause 1, wherein the said main reserve tanks are located under the floor of the fence in an in-obstructive placement allowing maximum load for the vehicle.

17. A cooling system as defined in Clause 1, but where the said main reserve tank is remote to allow the supply of cryogen to several separate cooling systems. For the intermodal application, said first reserve tank would be a container tank loaded in the center of an articulated platform with all containers connected to the container tank by means of flexible tubing, small reserve to be transported in the chassis at each end of the trip , which would be provided on the roof of each container.

18. A cooling system as defined in Clause 15, but which is used for multi-temperature applications, in which the Coldsink is maintained at the refrigerated temperature and the pressure for the refrigeration compartment, and in which the Coldspray ensures the appropriate temperature in the frozen compartment, the heating system is only installed in the refrigeration compartment.

19. A cooling system as defined in Clause 15, but installed inside the walls of a tank for the transportation of liquids which must be maintained at a precise temperature, this allows the operation of the system without any external power supply for operate the cooling or heating systems. IN WITNESS WHEREOVER, I have signed the above description and claims of novelty of the invention, as attorney in charge of FRIDEV - REFRIGERATION SYSTEMS INC., In Mexico City, Republic of Mexico on April 11, 1995.