WO1994012836A1 - Self-contained cooler/freezer apparatus - Google Patents

Self-contained cooler/freezer apparatus Download PDF

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Publication number
WO1994012836A1
WO1994012836A1 PCT/US1993/011142 US9311142W WO9412836A1 WO 1994012836 A1 WO1994012836 A1 WO 1994012836A1 US 9311142 W US9311142 W US 9311142W WO 9412836 A1 WO9412836 A1 WO 9412836A1
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WO
WIPO (PCT)
Prior art keywords
carbon dioxide
container
insulated container
temperature
self
Prior art date
Application number
PCT/US1993/011142
Other languages
French (fr)
Inventor
Anthony Bartilucci
Original Assignee
Grumman Aerospace Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Grumman Aerospace Corporation filed Critical Grumman Aerospace Corporation
Priority to AU56702/94A priority Critical patent/AU5670294A/en
Publication of WO1994012836A1 publication Critical patent/WO1994012836A1/en

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25DREFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D3/00Devices using other cold materials; Devices using cold-storage bodies
    • F25D3/12Devices using other cold materials; Devices using cold-storage bodies using solidified gases, e.g. carbon-dioxide snow
    • F25D3/125Movable containers
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25DREFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00Arrangement or mounting of control or safety devices
    • F25D29/001Arrangement or mounting of control or safety devices for cryogenic fluid systems

Definitions

  • the present invention relates to a self-contained cooler/freezer apparatus, and more particularly, to a self-contained cooler/freezer apparatus which utilizes solid carbon dioxide in the form of blocks or snow to maintain a predetermined temperature within the apparatus.
  • such a container is designed to carry either frozen foods or foods that must be maintained at high but still refrigerated temperatures, such as for example .0 degrees Fahrenheit.
  • portable refrigeration devices designed to maintain or preserve perishable commodities at a given temperature for a given period of time. These refrigeration devices utilize various means to maintain the commodities at a given temperature, including compressed gas refrigeration systems, liquid cooled refrigeration systems, and solid cooled refrigeration systems.
  • U.S. Patent No. 3,633,381 discloses a portable refrigerator
  • a stored compressed gas such as carbon dioxide
  • the evaporator comprises a serpentine
  • the temperature of the evaporated medium is lower than the ambient temperature of the interior of the container comprising the storage portion of the refrigerator which is cooled thereby.
  • the gas passing through the evaporator may be exhausted into the interior of the container whereby the cooler air which is next to the evaporator medium is circulated throughout the interior of the container.
  • U.S. Patent No. 3,961,925 discloses a portable self-contained refrigerated storage and transportation container for preserving perishable commodities, and includes an insulated storage chamber for the perishable commodities.
  • a recirculating liquid cooling system is provided within the container and includes conduit and nozzle means disposed within the storage chamber and adapted to spray a liquid coolant, such as chilled brine, directly onto the perishable commodities to maintain them at a uniform cooled temperature.
  • the sprayed liquid coolant is collected in the bottom portion of the storage chamber.
  • a closed refrigeration system is also
  • the container provided within the container and includes heat exchange means disposed within the bottom portion of the storage chamber for cooling the sprayed liquid coolant which has collected there.
  • a solid carbon dioxide cooling container In U.S. Patent No. 4,502,293, there is disclosed a solid carbon dioxide cooling container.
  • the container includes an insulated top, bottom, opposite sides and opposite end walls.
  • An upstanding transverse insulated hollow housing is mounted within the container adjacent one end thereof and a carbon dioxide snow cabinet constructed from a "good" heat transfer material is disposed within the housing with opposing wall portions of the cabinet and housing passing exteriorly about the cabinet.
  • a heat insulative horizontal baffle is mounted within the container spaced below the top wall and extends between the sidewalls thereof. The baffle defines a cooled air passage beneath the top wall extending lengthwise of the container.
  • the airflow passage includes an outlet end adjacent and in at least reasonably closed communication with the end of the cooled air passage adjacent the aforementioned one container end wall and an inlet end opening outwardly of the housing into the interior of the container below the baffle.
  • the end of the cooled air passage adjacent the other container end wall opens into the interior of the container and a thermostatically controllable air pump structure is provided to effect airflow inwardly of the inlet of the airflow passage, through the airflow passage and into the cooled air passage.
  • a structure is provided for spray discharging of liquid carbon dioxide into the interior of the upper portion of the cabinet and into the airflow passage at points spaced in order to form carbon dioxide snow thereon.
  • U.S. Patent No. 4,276,752 discloses a refrigerated cargo container which utilizes solid carbon dioxide as a cooling medium.
  • the refrigerated cargo container comprises a bunker which is filled with solid carbon dioxide or dry ice, a heat exchanger which is in thermal contact with the solid carbon dioxide, a fan, and ducts for circulating carbon dioxide gas through the container. Warm gas from the container's interior and the cargo contained therein rises to the top of the container due to the natural convective flow of gas in the container.
  • This warm gas enters the heat exchanger and causes the solid carbon dioxide to sublime.
  • the heat exchanger is cooled, and as warm gas passes over this cooled heat exchanger that gas is likewise cooled.
  • a fan can be installed to increase the flow of warm gas from the interior of the container to the heat exchanger.
  • a damper means is located in the duct carrying cold gas from the heat exchanger to control the amount of cool gas entering the container.
  • a control means may also be installed to control the operation of the fans based on temperature differentials.
  • the present invention is directed to a self-contained cooler/freezer apparatus for holding and preserving items which need to be stored at refrigerated or below freezing
  • the apparatus comprises an insulated container, a coolant compartment for holding solid carbon dioxide, commonly referred to as dry ice, and a temperature control device for maintaining the temperature within the insulated container at a predetermined value.
  • a first portion of the insulated container is adapted to hold the items which need to be stored at refrigerated or below frozen temperatures, and a second portion is adapted to form the coolant compartment for holding the dry ice.
  • the first portion of the insulated container and the coolant compartment are thermally isolated from each other by an insulated shelf to prevent heat transfer therebetween.
  • both the first portion of the insulated container and the coolant compartment are
  • the temperature control device comprises at least one temperature sensing device, such as a thermocouple, mounted within the first portion of the insulated container, a thermostatic controller for setting the desired temperature, and a device, such as a fan, for circulating gaseous carbon dioxide from the first portion of the insulated container and the items contained therein to the coolant compartment.
  • the gaseous carbon dioxide is formed by the sublimation of the dry ice contained within the coolant
  • the circulating gaseous carbon dioxide absorbs the heat load of the first portion of the insulated container and rejects it to the dry ice contained within the coolant compartment.
  • a pressure relief valve located in the first portion of the insulated container vents carbon dioxide gas to the external environment when the pressure within the first portion of the insulated container exceeds a predetermined safe threshold value.
  • the items to be shipped are loaded into the first portion of the insulated container and a predetermined quantity of dry ice, in block or snow form, is loaded into the coolant compartment.
  • a predetermined quantity of dry ice in block or snow form
  • heat entering through the walls of the insulated container is transferred to the dry ice thereby causing sublimation to occur and carbon dioxide gas to form.
  • the dry ice contained within the coolant compartment will continuously generate a quantity of cold gaseous carbon dioxide.
  • the cold gaseous carbon dioxide is circulated around the container via channels or ducts in the sidewalls forming the insulated container, thereby cooling the first portion of the insulated container and the items contained therein.
  • the temperature within the first portion of the insulated container is maintained at the predetermined value by the temperature control device.
  • Thermocouples mounted on the walls of the first portion of the insulated container monitor the temperature of the gaseous carbon dioxide and are connected to the thermostatic control device which is set to a predetermined temperature.
  • the thermostatic control device actuates the fan which circulates the cold gaseous carbon dioxide around the insulated container. The fan is stopped when the desired temperature is achieved.
  • the self-contained cooler/freezer apparatus of the present invention utilizes a simple control system and the very high cooling capacity of dry ice, which is approximately 247 BTU/LB, to permit maintenance of desired product temperature over a wide range of external ambient temperatures for long periods of time.
  • dry ice as the coolant
  • temperatures ranging from sub-zero to 70 degrees Fahrenheit can be maintained for periods exceeding four days.
  • a simplistic temperature control system circulates cold gaseous carbon dioxide, formed from the sublimation of the dry ice, as needed to accurately maintain the temperature within the insulated container and of the items contained therein at a
  • the fan duty cycle will be proportionately higher.
  • the circulating gaseous carbon dioxide absorbs the heat from the first portion and rejects in to the dry ice in the coolant compartment causing increased sublimation to occur and creating additional gaseous carbon dioxide at a temperature of approximately of -109 degrees
  • the self-contained cooler/freezer apparatus of the present invention is designed in s ⁇ ch a manner, and constructed from materials such that the apparatus is inexpensive to operate and environmentally safe.
  • the materials used in the construction of the apparatus are lightweight, accordingly, the apparatus can be utilized in applications requiring lightweight refrigeration/freezer units.
  • Typical applications for the present invention are in the air freight, cargo ship or overland cross-country shipping of perishable commodities, vendor carts, hand-held ice chests, camping ice chests, or large stationary installations.
  • FIG. 1 is a diagrammatic representation of the self-contained cooler/freezer apparatus of the present
  • Figure 2 is a schematic view of the internal structure of the self-contained cooler/freezer apparatus of the present invention.
  • Figure 3 is a schematic view of an alternate embodiment of the internal structure of the self-contained cooler/freezer apparatus of the present invention.
  • the present invention is directed to a self-contained cooler/freezer apparatus or container for holding and
  • FIG. 1 there is shown a diagrammatic representation of the cooler/freezer apparatus 100.
  • the apparatus 1.00 comprises an insulated container 10,
  • the walls 16, 18, 20 and 22 as well as the top 12, base 14 and access door 24 are constructed from inner and outer hard shells 26 and 28 with a high
  • a first portion of the inner volume of the insulated container (not shown) is utilized to store the items or products, while a second portion (not shown), which is much smaller in volume than the first portion, houses a coolant compartment in which the material used as the refrigerant/coolant is stored.
  • part of the temperature control means is also stored within the second portion.
  • Mounted to the front wall 22, above the access door 24 is a compartment for holding a battery 32 which supplies power for operation of the temperature control means, and a thermostatic controller 36.
  • a pressure relief valve 34 which vents the first portion of the inner volume.
  • FIG 2 there is shown a schematic view of the internal structure of the cooler/freezer apparatus 100.
  • the walls 16, 18, 20 and 22, the top 12, the base 14, and the access door 24 are constructed from inner and outer hard shells 26 and 28 with a high resistance insulating material 30 sandwiched
  • the inner and outer shells 26 and 28 are formed from any suitably rigid material, such as fiberglass, aluminum, or stainless steel, which is capable of withstanding various structural loading.
  • the insulating material 30 represents an important design choice in that heat energy transfer into or out of the insulated container 10 must be limited.
  • the coolant compartment 38 is formed by the placement of a shelf 40 between the pair of sidewalls 16 and 18 and fit tightly between the rear wall 20 and the front wall 22.
  • the shelf 40 is formed from the same material as the walls 16, 18, 20 and 22, the top 12, the base 14, and the access door 24. It is essential that the shelf 40 is insulated and that no gaps exist between the coolant compartment 38 and the first portion 42 of the insulated container 10. If the coolant compartment 38 is not fully thermally isolated from the first portion 42 of the insulated container 10, excessive heat transfer may opcur between the two portions, thereby resulting in a loss of temperature control, especially at high end temperatures i.e. greater than 50 degrees Fahrenheit.
  • the base 14 comprises ridges 44 upon which the items or commodities 46 are placed. These ridges 44 allow for circulation of the coolant gas, which is carbon dioxide, thereby providing for better heat energy transfer.
  • the inner shell 28 of each of the side walls 16 and 18 and the rear wall 20, is corrugated (not shown) so that the items 46 are not placed directly against the side walls 16 and 18 or rear wall 20, thereby allowing for the free circulation of carbon dioxide gas between the walls 16, 18, and 20 and the items.
  • a gas duct 48 is positioned within the insulation 30 and directly behind the inner shell 28. The gas duct 48 runs almost the entire length of the side wall 18, extending from the coolant compartment 38 to the bottom of the first portion 42 of the insulated container 10.
  • At the upper end of the gas duct 48 is a vent or opening through which cold gaseous carbon dioxide, indicated by the arrows 11, enters for
  • gas duct 48 At the lower end of the gas duct 48 is a second vent or opening through which the cold gaseous carbon dioxide exits, indicated by the arrows 13, and circulates through the first portion 42 of the insulated container 10, indicated by the arrows 15, absorbing heat energy.
  • One or several gas ducts can be placed within the side wall 18. The number of gas ducts and the size of the gas duct(s) can vary and is basically an engineering choice based on container size and design heat loads.
  • a second gas duct 50 is positioned within the insulation 30 and directly behind the inner shell 28. This gas duct 50 is much shorter in length than the other gas duct 48, extending from the coolant
  • the suction end of the dual fans 52 are directed towards the first portion 42 of the insulated
  • the dual suction fans 52 serve two purposes. One purpose is to draw in warmer gaseous carbon dioxide
  • the second purpose is to circulate the cold gaseous carbon dioxide formed by the sublimation of dry ice 54, placed within the coolant compartment 38, into the first portion 42 of the insulated container 10 via the gas duct 48 in order to lower the temperature within the first portion 42 of the insulated container 10.
  • the warmer gaseous carbon dioxide drawn in from the first portion of the container 10 is cooled in two ways. First, as it passes over the dry ice 54 as indicated by the arrows 21, and secondly, as it mixes with the sublimated gas continuously being generated in the coolant compartment 38.
  • the dual fans 52 are powered by the high energy battery 32 shown in Figure 1, and are
  • thermostatic controller 36 which is also powered by the high energy battery 32.
  • dry ice 54 in either block or snow form, is loaded into the fully insulated coolant compartment 38.
  • Dry ice has an extremely high cooling capacity on the order of 247 BTU/LB; accordingly, the dry ice 54 provides a highly weight-efficient heat sink.
  • the required amount of dry ice can be calculated as a function of its own cooling capacity.
  • a sufficient amount of dry ice surface area is left exposed for forced convection heat transfer to occur from the internal gaseous carbon dioxide environment; namely, the warm gaseous carbon dioxide drawn from the first portion 42 of the insulated container 10.
  • the items 46 to be shipped are then loaded into the first portion 42 of the insulated container 10.
  • heat energy is transferred into the insulated container 10 from the ambient environment when the access door 24 is open to load the items 46, through the insulated container 10 itself, and from the heat contained within the items 46, thereby causing
  • the coolant compartment 38 contains a quantity of cold, approximately -109 degrees Fahrenheit, gaseous carbon dioxide.
  • the pressure relief valve 34 shown in Figure 1 which is connected to the first portion 42 of the insulated container 10 will actuate or open to the ambient environment when the pressure within the first portion 42 of the insulated container 10 rises above a
  • the pressure relief valve 34 is connected to the first portion 42 of the insulated container 10 as opposed to the coolant compartment 38 because it is more beneficial from the energy standpoint to vent warmer gaseous carbon dioxide into the external environment than it is to vent cold gaseous carbon dioxide.
  • Circulation of the cold gaseous dioxide is caused by the operation of the dual fans 52 mounted in the lower portion of the gas duct 50.
  • Each fan is operable to supply a
  • the dual fans 52 must create an airflow velocity sufficient to reject the heat energy within the first portion 42 of the insulated container 10 to the dry ice 54 in order to maintain the desired temperature within the insulated container 10.
  • the dual fans 52 must create an airflow velocity sufficient to reject the heat energy within the first portion 42 of the insulated container 10 to the dry ice 54 in order to maintain the desired temperature within the insulated container 10.
  • the dual fans 52 are controlled by the thermostatic controller 36 (shown in Figure 1).
  • Thermocouples 56 and 58 are mounted on the side walls 16 and 18 within the first portion 42 of the insulated container 10. The exact placement and number of thermocouples can vary. To more closely reflect the item thermal response, the thermocouples 56 and 58 can be embedded in heat conductive materials such as small aluminum blocks, painted black, and mounted on the inner shell 28 of the
  • thermocouples 56 and 58 are used as a measure of the average radiant and convective environment within the first portion 42 of the insulated container 10 and generate an electrical signal proportional to this temperature.
  • the electrical signals are supplied to the thermostatic controller 36 wherein a comparison is made between the electrical signals and the predetermined temperature setting. If the temperature within the first portion 42 of the insulated container 10 is above the preset level, the dual fans 52 are activated and cold gaseous carbon dioxide is circulated throughout the first portion 42 of the insulated container 10 thereby reducing the temperature
  • the dual fans 52 remain idle.
  • the inertial thermocouples 56 and 58 respond slowly, thereby more closely reflecting the actual item temperature within the first portion 42 of the insulated container 10. It is noted that
  • thermocouples exposed to the ambient carbon dioxide environment could also be used, but not as effectively.
  • FIG. 3 there is shown a schematic view of an alternate embodiment of the internal structure of the cooler/freezer apparatus 100.
  • the walls 16, 18, 20, and 22, the top 12, the base 14, and the access door 24 are constructed from inner and outer hard shells 26 and 28 with a high resistance insulating material 30 sandwiched therebetween.
  • the coolant compartment 38 is placed at the bottom portion of the insulated container 10, whereas in the previous embodiment, the coolant compartment 38 is placed in the upper portion of the insulated container 10.
  • the coolant compartment 38 is formed by the placement of a shelf 60 between the pair of sidewalls 16 and 18 and fit tightly between the rear wall 20 and the front wall 22.
  • the shelf 60 is formed from the same materials as the walls 16, 18, 20, and 22, the top 12, the base 14, and the access door 24; however, the top of the shelf 40 comprises ridges 62 upon which the items or commodities 46 are placed.
  • the ridges 62 which were on the base 14 in the previous
  • embodiments serve the same purpose; namely, providing gaps for circulation of the gaseous carbon dioxide.
  • a gas duct 64 is positioned within the insulation 30 and directly behind the inner shell 28.
  • the gas duct 64 runs a short length of the side wall 18, extending from the bottom of the first portion 42 of the insulated container 10 to the coolant compartment 38.
  • a vent or opening At the upper end of the gas duct 64 is a vent or opening through which warmer gaseous carbon dioxide from the first portion 42 of the insulated container 10, indicated by the arrows 23, enters for transport to the coolant compartment 38.
  • a second vent or opening through which the warmer gaseous carbon dioxide exits into the coolant
  • a secpnd gas duct 66 is positioned within the
  • This second gas duct 66 runs the entire length of the side wall 16.
  • the coolant compartment 38 can hold dry ice in snow form or in block form on a support shelf 68.
  • the support shelf 68 can be formed from any material capable of supporting heavy loads.
  • a fan 70 mounted within the coolant compartment 38 draws cold gaseous carbon dioxide formed by the mixing of warmer gaseous carbon dioxide drawn in from the first portion 42 of the insulated container 10 with the continuously

Abstract

A self-contained cooler/freezer apparatus for carrying items (46) in a frozen or refrigerated environment. The apparatus comprises an insulated container (10) which is divided into two portions. The first portion (42) is where the items are stored. The second portion (38) houses a coolant compartment for storing a solid coolant, namely, solid carbon dioxide or dry ice (54). Within a short period of time, the dry ice starts to sublimate, thereby forming cold gaseous carbon dioxide which fills the volume of the apparatus. A fan (52) is used to circulate the gaseous carbon dioxide throughout the insulated container thereby removing heat from the first portion and rejecting it to the dry ice in the coolant compartment, thereby cooling the first portion of the insulated container. The cold gaseous carbon dioxide is circulated throughout the insulated container via gas ducts located within the walls of the insulated container. A thermostatic controller (56) actuates the fan based upon temperature readings from thermocouples located within the first portion of the insulated container. A pressure relief valve (34) is positioned within the insulated container to prevent the pressure within the insulated container from building beyond a maximum value.

Description

SELF-CONTAINED COOLER/FREEZER APPARATUS
The present invention relates to a self-contained cooler/freezer apparatus, and more particularly, to a self-contained cooler/freezer apparatus which utilizes solid carbon dioxide in the form of blocks or snow to maintain a predetermined temperature within the apparatus.
Many shipping and trucking lines use refrigerated containers to carry perishable commodities over long
distances. Typically, such a container is designed to carry either frozen foods or foods that must be maintained at high but still refrigerated temperatures, such as for example .0 degrees Fahrenheit. There exists a multitude of portable refrigeration devices designed to maintain or preserve perishable commodities at a given temperature for a given period of time. These refrigeration devices utilize various means to maintain the commodities at a given temperature, including compressed gas refrigeration systems, liquid cooled refrigeration systems, and solid cooled refrigeration systems.
An example of a refrigeration system employing compressed gas is set forth in U.S. Patent No. 3,633,381. U.S. Patent No. 3,633,381 discloses a portable refrigerator
employing an open cycle system. A stored compressed gas, such as carbon dioxide, is passed from a storage container through an evaporator. The evaporator comprises a serpentine
passageway for the gas in a surrounding medium such as water, which is maintained frozen due to the passage of the expanding compressed gas through the coiled passageway. The temperature of the evaporated medium is lower than the ambient temperature of the interior of the container comprising the storage portion of the refrigerator which is cooled thereby. The gas passing through the evaporator may be exhausted into the interior of the container whereby the cooler air which is next to the evaporator medium is circulated throughout the interior of the container.
U.S. Patent No. 3,961,925 discloses a portable self-contained refrigerated storage and transportation container for preserving perishable commodities, and includes an insulated storage chamber for the perishable commodities. A recirculating liquid cooling system is provided within the container and includes conduit and nozzle means disposed within the storage chamber and adapted to spray a liquid coolant, such as chilled brine, directly onto the perishable commodities to maintain them at a uniform cooled temperature. The sprayed liquid coolant is collected in the bottom portion of the storage chamber. A closed refrigeration system is also
provided within the container and includes heat exchange means disposed within the bottom portion of the storage chamber for cooling the sprayed liquid coolant which has collected there.
In U.S. Patent No. 4,502,293, there is disclosed a solid carbon dioxide cooling container. The container includes an insulated top, bottom, opposite sides and opposite end walls. An upstanding transverse insulated hollow housing is mounted within the container adjacent one end thereof and a carbon dioxide snow cabinet constructed from a "good" heat transfer material is disposed within the housing with opposing wall portions of the cabinet and housing passing exteriorly about the cabinet. A heat insulative horizontal baffle is mounted within the container spaced below the top wall and extends between the sidewalls thereof. The baffle defines a cooled air passage beneath the top wall extending lengthwise of the container. The airflow passage includes an outlet end adjacent and in at least reasonably closed communication with the end of the cooled air passage adjacent the aforementioned one container end wall and an inlet end opening outwardly of the housing into the interior of the container below the baffle. The end of the cooled air passage adjacent the other container end wall opens into the interior of the container and a thermostatically controllable air pump structure is provided to effect airflow inwardly of the inlet of the airflow passage, through the airflow passage and into the cooled air passage. In addition, a structure is provided for spray discharging of liquid carbon dioxide into the interior of the upper portion of the cabinet and into the airflow passage at points spaced in order to form carbon dioxide snow thereon.
The above described patents are representative of the various systems available for preserving perishable items.
Each of these systems offers varying degrees of cooling
capacity, temperature control and temperature control system simplicity. However, none of the above described systems alone offers a self-contained cooler/freezer apparatus which provides a high cooling capacity and a highly accurate and simplistic temperature control system. U.S. Patent No. 4,276,752 discloses a refrigerated cargo container which utilizes solid carbon dioxide as a cooling medium. The refrigerated cargo container comprises a bunker which is filled with solid carbon dioxide or dry ice, a heat exchanger which is in thermal contact with the solid carbon dioxide, a fan, and ducts for circulating carbon dioxide gas through the container. Warm gas from the container's interior and the cargo contained therein rises to the top of the container due to the natural convective flow of gas in the container. This warm gas enters the heat exchanger and causes the solid carbon dioxide to sublime. As the coolant sublimes, the heat exchanger is cooled, and as warm gas passes over this cooled heat exchanger that gas is likewise cooled. A fan can be installed to increase the flow of warm gas from the interior of the container to the heat exchanger. A damper means is located in the duct carrying cold gas from the heat exchanger to control the amount of cool gas entering the container. A control means may also be installed to control the operation of the fans based on temperature differentials.
The above described patent utilizes natural convection of gas within the container in conjunction with a heat
exchanger to provide a flow of cooling gas. A fan and damper means are utilized to augment air flow and partially control the circulation of the cooling gas. However, the use of a heat exchanger in direct contact with the dry ice causes pockets of carbon dioxide gas to form as the dry ice
sublimates. These pockets create a large thermal resistance between the warmed gas and the dry ice heat sink, thereby limiting the heat rejection capability of the system. Limiting the heat rejection capability prevents the maintenance of lower temperatures within the cargo container. Additionally, in relying on natural convection, there is a diminished ability to accurately control and maintain the temperature within the container. Finally, the use of a heat exchanger adds
unneccessary complication to the overall system.
The present invention is directed to a self-contained cooler/freezer apparatus for holding and preserving items which need to be stored at refrigerated or below freezing
temperatures. The apparatus comprises an insulated container, a coolant compartment for holding solid carbon dioxide, commonly referred to as dry ice, and a temperature control device for maintaining the temperature within the insulated container at a predetermined value. A first portion of the insulated container is adapted to hold the items which need to be stored at refrigerated or below frozen temperatures, and a second portion is adapted to form the coolant compartment for holding the dry ice. The first portion of the insulated container and the coolant compartment are thermally isolated from each other by an insulated shelf to prevent heat transfer therebetween. In addition, both the first portion of the insulated container and the coolant compartment are
unpressurized. However, one can design the apparatus utilizing pressurized compartments. The temperature control device comprises at least one temperature sensing device, such as a thermocouple, mounted within the first portion of the insulated container, a thermostatic controller for setting the desired temperature, and a device, such as a fan, for circulating gaseous carbon dioxide from the first portion of the insulated container and the items contained therein to the coolant compartment. The gaseous carbon dioxide is formed by the sublimation of the dry ice contained within the coolant
compartment. The circulating gaseous carbon dioxide absorbs the heat load of the first portion of the insulated container and rejects it to the dry ice contained within the coolant compartment. A pressure relief valve located in the first portion of the insulated container vents carbon dioxide gas to the external environment when the pressure within the first portion of the insulated container exceeds a predetermined safe threshold value.
The items to be shipped are loaded into the first portion of the insulated container and a predetermined quantity of dry ice, in block or snow form, is loaded into the coolant compartment. Within a short period of time, heat entering through the walls of the insulated container is transferred to the dry ice thereby causing sublimation to occur and carbon dioxide gas to form. Given that the temperature at which sublimation occurs at one atmosphere pressure is approximately -109 degrees Fahrenheit, the dry ice contained within the coolant compartment will continuously generate a quantity of cold gaseous carbon dioxide. When needed, the cold gaseous carbon dioxide is circulated around the container via channels or ducts in the sidewalls forming the insulated container, thereby cooling the first portion of the insulated container and the items contained therein. The temperature within the first portion of the insulated container is maintained at the predetermined value by the temperature control device.
Thermocouples mounted on the walls of the first portion of the insulated container monitor the temperature of the gaseous carbon dioxide and are connected to the thermostatic control device which is set to a predetermined temperature. When the temperature rises above the predetermined value, as measured by the thermocouples, the thermostatic control device actuates the fan which circulates the cold gaseous carbon dioxide around the insulated container. The fan is stopped when the desired temperature is achieved.
The self-contained cooler/freezer apparatus of the present invention utilizes a simple control system and the very high cooling capacity of dry ice, which is approximately 247 BTU/LB, to permit maintenance of desired product temperature over a wide range of external ambient temperatures for long periods of time. In utilizing dry ice as the coolant,
temperatures ranging from sub-zero to 70 degrees Fahrenheit can be maintained for periods exceeding four days. A simplistic temperature control system circulates cold gaseous carbon dioxide, formed from the sublimation of the dry ice, as needed to accurately maintain the temperature within the insulated container and of the items contained therein at a
constant value. It is noted that for environmental conditions resulting in high heat loads to the items within the first portion of the insulated container, the fan duty cycle will be proportionately higher. The circulating gaseous carbon dioxide absorbs the heat from the first portion and rejects in to the dry ice in the coolant compartment causing increased sublimation to occur and creating additional gaseous carbon dioxide at a temperature of approximately of -109 degrees
Fahrenheit.
The self-contained cooler/freezer apparatus of the present invention is designed in sυch a manner, and constructed from materials such that the apparatus is inexpensive to operate and environmentally safe. In addition, the materials used in the construction of the apparatus are lightweight, accordingly, the apparatus can be utilized in applications requiring lightweight refrigeration/freezer units. Typical applications for the present invention are in the air freight, cargo ship or overland cross-country shipping of perishable commodities, vendor carts, hand-held ice chests, camping ice chests, or large stationary installations.
Figure 1 is a diagrammatic representation of the self-contained cooler/freezer apparatus of the present
invention.
Figure 2 is a schematic view of the internal structure of the self-contained cooler/freezer apparatus of the present invention.
Figure 3 is a schematic view of an alternate embodiment of the internal structure of the self-contained cooler/freezer apparatus of the present invention.
The present invention is directed to a self-contained cooler/freezer apparatus or container for holding and
preserving items which need to be stored at refrigerated or below freezing temperatures. Referring to Figure 1, there is shown a diagrammatic representation of the cooler/freezer apparatus 100. The apparatus 1.00 comprises an insulated container 10,
rectangular in shape, having a top 12, a base 14, a pair of side walls 16 and 18, a rear wall 20, and a front wall 22 with an access doorway and door 24. The walls 16, 18, 20 and 22 as well as the top 12, base 14 and access door 24 are constructed from inner and outer hard shells 26 and 28 with a high
resistance insulating material 30 sandwiched therebetween. A first portion of the inner volume of the insulated container (not shown) is utilized to store the items or products, while a second portion (not shown), which is much smaller in volume than the first portion, houses a coolant compartment in which the material used as the refrigerant/coolant is stored. In addition, part of the temperature control means is also stored within the second portion. Mounted to the front wall 22, above the access door 24 is a compartment for holding a battery 32 which supplies power for operation of the temperature control means, and a thermostatic controller 36. Also mounted within the front wall 22 is a pressure relief valve 34 which vents the first portion of the inner volume. A detailed description of each of the components or elements mentioned above as well as a description of operation of the apparatus 100 is given in subsequent sections.
Turning to Figure 2, there is shown a schematic view of the internal structure of the cooler/freezer apparatus 100. As discussed in the proceeding paragraph, the walls 16, 18, 20 and 22, the top 12, the base 14, and the access door 24 are constructed from inner and outer hard shells 26 and 28 with a high resistance insulating material 30 sandwiched
therebetween. The inner and outer shells 26 and 28 are formed from any suitably rigid material, such as fiberglass, aluminum, or stainless steel, which is capable of withstanding various structural loading. The insulating material 30 represents an important design choice in that heat energy transfer into or out of the insulated container 10 must be limited. A
polyurethane insulation provides one such suitable design choice. Other materials will obviously suggest themselves to those skilled in the art. The coolant compartment 38 is formed by the placement of a shelf 40 between the pair of sidewalls 16 and 18 and fit tightly between the rear wall 20 and the front wall 22. The shelf 40 is formed from the same material as the walls 16, 18, 20 and 22, the top 12, the base 14, and the access door 24. It is essential that the shelf 40 is insulated and that no gaps exist between the coolant compartment 38 and the first portion 42 of the insulated container 10. If the coolant compartment 38 is not fully thermally isolated from the first portion 42 of the insulated container 10, excessive heat transfer may opcur between the two portions, thereby resulting in a loss of temperature control, especially at high end temperatures i.e. greater than 50 degrees Fahrenheit.
The base 14 comprises ridges 44 upon which the items or commodities 46 are placed. These ridges 44 allow for circulation of the coolant gas, which is carbon dioxide, thereby providing for better heat energy transfer. The inner shell 28 of each of the side walls 16 and 18 and the rear wall 20, is corrugated (not shown) so that the items 46 are not placed directly against the side walls 16 and 18 or rear wall 20, thereby allowing for the free circulation of carbon dioxide gas between the walls 16, 18, and 20 and the items. In one side wall 18, a gas duct 48 is positioned within the insulation 30 and directly behind the inner shell 28. The gas duct 48 runs almost the entire length of the side wall 18, extending from the coolant compartment 38 to the bottom of the first portion 42 of the insulated container 10. At the upper end of the gas duct 48 is a vent or opening through which cold gaseous carbon dioxide, indicated by the arrows 11, enters for
transport to the first portion 42 of the insulated container 10. At the lower end of the gas duct 48 is a second vent or opening through which the cold gaseous carbon dioxide exits, indicated by the arrows 13, and circulates through the first portion 42 of the insulated container 10, indicated by the arrows 15, absorbing heat energy. One or several gas ducts can be placed within the side wall 18. The number of gas ducts and the size of the gas duct(s) can vary and is basically an engineering choice based on container size and design heat loads. In the other side wall 16, a second gas duct 50 is positioned within the insulation 30 and directly behind the inner shell 28. This gas duct 50 is much shorter in length than the other gas duct 48, extending from the coolant
compartment 38 to just inside the first portion 42 of the insulated container 10. At the lower end of the gas duct 50 is an opening in which dual fans 52 are mounted. It should be noted that only a single fan can be utilized just as
effectively as two. The suction end of the dual fans 52 are directed towards the first portion 42 of the insulated
container 10. The dual suction fans 52 serve two purposes. One purpose is to draw in warmer gaseous carbon dioxide
circulating throughout the first portion 42 of the insulated container 10, indicated by the arrows 17, and direct it through the gas duct 50 and out through a vent in the upper portion of the gas duct 50 into the coolant compartment 38, as indicated by the arrows 19. The second purpose is to circulate the cold gaseous carbon dioxide formed by the sublimation of dry ice 54, placed within the coolant compartment 38, into the first portion 42 of the insulated container 10 via the gas duct 48 in order to lower the temperature within the first portion 42 of the insulated container 10. In addition, the warmer gaseous carbon dioxide drawn in from the first portion of the container 10 is cooled in two ways. First, as it passes over the dry ice 54 as indicated by the arrows 21, and secondly, as it mixes with the sublimated gas continuously being generated in the coolant compartment 38. The dual fans 52 are powered by the high energy battery 32 shown in Figure 1, and are
controlled by the thermostatic controller 36 which is also powered by the high energy battery 32.
In operation, dry ice 54, in either block or snow form, is loaded into the fully insulated coolant compartment 38. Dry ice has an extremely high cooling capacity on the order of 247 BTU/LB; accordingly, the dry ice 54 provides a highly weight-efficient heat sink. Once the desired
temperature and the weight of the perishable items is known, then the required amount of dry ice can be calculated as a function of its own cooling capacity. A sufficient amount of dry ice surface area is left exposed for forced convection heat transfer to occur from the internal gaseous carbon dioxide environment; namely, the warm gaseous carbon dioxide drawn from the first portion 42 of the insulated container 10. The items 46 to be shipped are then loaded into the first portion 42 of the insulated container 10. Within a short period of time heat energy is transferred into the insulated container 10 from the ambient environment when the access door 24 is open to load the items 46, through the insulated container 10 itself, and from the heat contained within the items 46, thereby causing
sublimation of the dry ice 54 within the coolant compartment 38. Given that the temperature at which sublimation occurs at one atmosphere pressure at the surface of the dry ice 54 is approximately -109 degrees Fahrenheit, the coolant compartment 38 contains a quantity of cold, approximately -109 degrees Fahrenheit, gaseous carbon dioxide. When the thermostatically controlled dual fans 52 are actuated the cold gas is circulated to and through the first portion 42 of the insulated container 10 via gas ducts 48 and 50 to maintain the temperature at the desired level. As a precautionary measure, the pressure relief valve 34 (shown in Figure 1) which is connected to the first portion 42 of the insulated container 10 will actuate or open to the ambient environment when the pressure within the first portion 42 of the insulated container 10 rises above a
predetermined level, for example 1 psig. The pressure relief valve 34 is connected to the first portion 42 of the insulated container 10 as opposed to the coolant compartment 38 because it is more beneficial from the energy standpoint to vent warmer gaseous carbon dioxide into the external environment than it is to vent cold gaseous carbon dioxide.
Circulation of the cold gaseous dioxide is caused by the operation of the dual fans 52 mounted in the lower portion of the gas duct 50. Each fan is operable to supply a
sufficient flow rate of gaseous carbon dioxide. The dual fans 52 must create an airflow velocity sufficient to reject the heat energy within the first portion 42 of the insulated container 10 to the dry ice 54 in order to maintain the desired temperature within the insulated container 10. However, there exists a tradeoff between more accurate control of the
temperature and achieving lower temperatures. The lower the capacity of the dual fans 52, the more uniform the temperature profile within the first portion 42 of the insulated container 10, whereas the higher the capacity of the dual fans 52 the lower the temperatures. This is easily explained in that the lower the capacity of the dual fans 52, the longer the fans will be on during any cooling cycle. During periods in which the fans are activated, better mixing of the carbon dioxide in the first portion 42 of the insulated container 10 results in small temperature gradients within the first portion 42 of the insulated container 10. Variable speed fans can be employed to achieve both the desirable results of minimum first portion temperature gradients as well as lower first portion 42
temperature level control.
The dual fans 52 are controlled by the thermostatic controller 36 (shown in Figure 1). Thermocouples 56 and 58 are mounted on the side walls 16 and 18 within the first portion 42 of the insulated container 10. The exact placement and number of thermocouples can vary. To more closely reflect the item thermal response, the thermocouples 56 and 58 can be embedded in heat conductive materials such as small aluminum blocks, painted black, and mounted on the inner shell 28 of the
sidewalls 16 and 18. Utilized in this manner, the
thermocouples 56 and 58 are used as a measure of the average radiant and convective environment within the first portion 42 of the insulated container 10 and generate an electrical signal proportional to this temperature. The electrical signals are supplied to the thermostatic controller 36 wherein a comparison is made between the electrical signals and the predetermined temperature setting. If the temperature within the first portion 42 of the insulated container 10 is above the preset level, the dual fans 52 are activated and cold gaseous carbon dioxide is circulated throughout the first portion 42 of the insulated container 10 thereby reducing the temperature
therein. If on the other hand, the temperature is below the preset level, the dual fans 52 remain idle. The inertial thermocouples 56 and 58 respond slowly, thereby more closely reflecting the actual item temperature within the first portion 42 of the insulated container 10. It is noted that
thermocouples exposed to the ambient carbon dioxide environment could also be used, but not as effectively.
The simple controls featured in this design, together with the high cooling capacity of dry ice permits the
maintenance of desired product temperatures, for example, sub-zero temperatures, -40 degrees Fahrenheit, up to 70 degrees Fahrenheit for many days of transport over a wide range or external ambient temperatures.
Referring to Figure 3, there is shown a schematic view of an alternate embodiment of the internal structure of the cooler/freezer apparatus 100. As in the embodiment of Figure 2, the walls 16, 18, 20, and 22, the top 12, the base 14, and the access door 24 are constructed from inner and outer hard shells 26 and 28 with a high resistance insulating material 30 sandwiched therebetween. The coolant compartment 38, however, is placed at the bottom portion of the insulated container 10, whereas in the previous embodiment, the coolant compartment 38 is placed in the upper portion of the insulated container 10. The coolant compartment 38 is formed by the placement of a shelf 60 between the pair of sidewalls 16 and 18 and fit tightly between the rear wall 20 and the front wall 22. Once again the shelf 60 is formed from the same materials as the walls 16, 18, 20, and 22, the top 12, the base 14, and the access door 24; however, the top of the shelf 40 comprises ridges 62 upon which the items or commodities 46 are placed. The ridges 62 which were on the base 14 in the previous
embodiment serve the same purpose; namely, providing gaps for circulation of the gaseous carbon dioxide.
In one side wall 18, a gas duct 64 is positioned within the insulation 30 and directly behind the inner shell 28. The gas duct 64 runs a short length of the side wall 18, extending from the bottom of the first portion 42 of the insulated container 10 to the coolant compartment 38. At the upper end of the gas duct 64 is a vent or opening through which warmer gaseous carbon dioxide from the first portion 42 of the insulated container 10, indicated by the arrows 23, enters for transport to the coolant compartment 38. At the lower end of the gas duct 64 is a second vent or opening through which the warmer gaseous carbon dioxide exits into the coolant
compartment 38, indicated by the arrows 25. In the other side wall 16, a secpnd gas duct 66 is positioned within the
insulation 30 and directly behind the inner shell 28. This second gas duct 66 runs the entire length of the side wall 16. At the lower end of the gas duct 66 is a vent or opening in which cold gaseous carbon dioxide exits the coolant compartment 38, indicated by the arrows 27, for transport to the first portion 42 of the insulated container 10. At the upper end of the gas duct 66 is a second vent or opening through which the cold gaseous carbon dioxide exits, indicated by the arrows 29, and circulates through the first portion 42 of the insulated container 10 absorbing heat energy.
The coolant compartment 38 can hold dry ice in snow form or in block form on a support shelf 68. The support shelf 68 can be formed from any material capable of supporting heavy loads. A fan 70 mounted within the coolant compartment 38 draws cold gaseous carbon dioxide formed by the mixing of warmer gaseous carbon dioxide drawn in from the first portion 42 of the insulated container 10 with the continuously
sublimated gaseous carbon dioxide, and expells it into the gas duct 66 where it is circulated into the first portion 42 of the insulated container 10. Since carbon dioxide is a heavier gas, it naturally circulates within the first portion 42 of the insulated container 10 in a downward direction as indicated by the arrows 31. The basic operation of the apparatus 100 is substantially identical to that as previously described in relation to the device shown in Figure 2.
Although shown and described is what are believed to be the most practical and preferred embodiments, it is apparent that departures from specific methods and designs described and shown will suggest themselves to those skilled in the art and may be used without departing from the spirit and scope of the invention. The present invention is not restricted to the particular constructions described and illustrated, but should be constructed to cohere with all modifications that may fall within the scope of the appended claims.

Claims

WHAT WE CLAIM IS:
1. A self-contained cooler/freezer apparatus for holding and preserving items which need to be stored at refrigerated or frozen temperatures, comprising a container having an insulated shell and an access doorway and door, a first portion of said container being adapted to hold said items; a coolant compartment constructed within a second portion of said container and insulated from said first portion for holding carbon dioxide in solid form; and temperature control means for maintaining the temperature within the first portion of said
container at a predetermined value, said temperature control means having means for setting the temperature at said predetermined value, at least one temperature sensing device mounted within said first portion of said container, and means for circulating gaseous carbon dioxide formed by the sublimation of said carbon solid dioxide throughout said container.
2. The self-contained cooler/freezer apparatus according to Claim 1, further comprising a pressure relief valve mounted in said first portion of said container, said pressure relief valve being operable to maintain the pressure within said container below a predetermined maximum value.
3. The self-contained cooler/freezer apparatus according to Claim 1 or 2, wherein said container is substantially rectangular in shape and comprises first and second side walls, a pair of end walls, one of said pair of end walls having said access doorway and door mounted therein, a top, and a base, said first and second side walls, said pair of end walls, said top, and said base each being formed from an inner and outer shell with an insulative material sandwiched therebetween.
4. The self-contained cooler/freezer apparatus according to Claim 3, wherein said first side wall comprises a first gas duct, having vents at each end thereof, mounted therein and extending from said coolant compartment to said base of said container, and said second side wall comprises a second gas duct, having vents at each end thereof, mounted therein and extending from said coolant compartment to just inside said first portion of said container, said second gas duct having said means for circulating mounted therein, said first and second gas ducts being operable to circulate said gaseous carbon dioxide.
5. The self-contained cooler/freezer apparatus according to Claim 3 or 4, wherein said inner shells of said first and second side walls comprise corrugations for preventing low temperature contact damage to said items and for providing increased circulation of said gaseous carbon dioxide.
6. The self-contained cooler/freezer apparatus according to any one of Claims 3 to 5, wherein said coolant compartment is formed by the mounting of a shelf between said first and second side walls in the upper region of said container, said shelf being constructed from an inner and outer shell with an insulative material sandwiched therebetween.
7. The self-contained cooler/freezer apparatus according to any one of the preceding claims, wherein said means for setting the temperature is a thermostatic controller which is responsive to said at least one temperature sensing device, said thermostatic controller being operable to control said means for circulating.
8. The self-contained cooler/freezer apparatus according to any one of the preceding claims, wherein said at least one temperature sensing device is a
thermocouple, said thermocouple is disposed within a heat conductive material for providing a thermal inertia thereby more closely reflecting the temperature of said items.
9. The self-contained cooler/freezer apparatus according to any one of the preceding claims, wherein said means for circulating comprises at least one fan operable to circulate said gaseous carbon dioxide at a predetermined rate.
10. The self-contained cooler/freezer apparatus according to Claim 9, further comprising a battery for supplying power to said at least one fan and said thermostatic controller.
11. The self-contained cooler/freezer apparatus according to any one of Claims 3 to 10, wherein said base comprises ridges formed on its inner shell for providing increased circulation of said gaseous carbon dioxide.
12. The self-contained cooler/freezer apparatus according to any one of the preceding claims, wherein said inner and outer shells are formed from aluminum, and said insulative material being a
polyurethane insulation.
13. The self-contained cooler/freezer apparatus according to any one of Claims 1 to 11, wherein said inner and outer shells are formed from fiberglass, and said insulative material being a polyurethane
insulation.
14. The self-contained cooler/freezer apparatus according to any one of the preceding claims, wherein said coolant compartment comprises a rack for holding said carbon dioxide.
15. A method for holding and preserving items which need to be stored at refrigerated or frozen
temperatures, said method comprising the steps of:
(a) positioning said items within a first portion of an insulated container;
(b) loading solid carbon dioxide into a coolant compartment within a second portion of said insulated container;
(c) controlling and maintaining the temperature within said first portion of said insulated container by circulating gaseous carbon dioxide formed by the sublimation of said solid carbon dioxide throughout said insulated container.
16. The method for holding and preserving items according to Claim 15, wherein said step of
controlling and maintaining the temperature comprises the steps of:
(a) measuring the temperature within said first portion of said insulated container;
(b) comparing the measured temperature with a predetermined temperature value; and
(c) actuating at least one fan to circulate said sublimed gaseous carbon dioxide if the temperature within said first portion of said insulated container is above said predetermined temperature.
17. The method for holding and preserving items according to Claim 16, wherein said at least one fan draws in warmer gaseous carbon dioxide from said first portion of said insulated container and forces it to pass over said solid carbon dioxide thereby cooling said carbon dioxide gas and mixing it with said sublimed gaseous carbon dioxide for circulation into said first portion of said insulated container.
18. The method for holding and preserving items according to Claim 15 or 16, wherein said at least one fan draws sublimed gaseous carbon dioxide from said coolant compartment and circulates it to said first portion of said insulated container and forces warmer gaseous carbon dioxide within said first portion of said insulated container to pass over said solid carbon dioxide thereby cooling it and mixing it with said sublimed gaseous carbon dioxide.
PCT/US1993/011142 1992-11-20 1993-11-16 Self-contained cooler/freezer apparatus WO1994012836A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU56702/94A AU5670294A (en) 1992-11-20 1993-11-16 Self-contained cooler/freezer apparatus

Applications Claiming Priority (2)

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US97976692A 1992-11-20 1992-11-20
US979,766 1992-11-20

Publications (1)

Publication Number Publication Date
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AU (1) AU5670294A (en)
MX (1) MX9307230A (en)
WO (1) WO1994012836A1 (en)

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EP2873937A1 (en) * 2013-11-13 2015-05-20 ACP Belgium N.V. Warehouse system for products storage and transport at low temperature

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CN102635987B (en) * 2012-04-28 2015-01-14 青岛大学 Auxiliary refrigerating system of semitight heat capacity variable refrigerating plant
GB201301494D0 (en) 2013-01-28 2013-03-13 True Energy Ltd Refrigeration apparatus
CN105556224B (en) 2013-07-23 2019-10-11 确保冷藏有限公司 Refrigerating plant and method
EP3341665A4 (en) 2015-09-11 2019-05-01 The Sure Chill Company Limited Portable refrigeration apparatus
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Also Published As

Publication number Publication date
AU5670294A (en) 1994-06-22
MX9307230A (en) 1994-05-31
CN1097505A (en) 1995-01-18

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