US 3783633 A
Refrigeration apparatus utilizing solid carbon dioxide as a refrigerant comprising a pair of refrigeration compartments, a solid carbon dioxide hopper defined by a pair of hollow condensers arranged in the shape of a V for cooling a circulating heat-exchange fluid. A pair of evaporators vertically below the hopper define a chimney between compartments for the circulation of air being cooled. A blower may be used to control air circulation.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Glynn et al.
[ CO REFRIGERATION SYSTEM  Inventors: Emmett P. Glynn, Lemont; Howard- L. Hsu, Hickory Hills, both of 111.
 Assignee: Liquid Carbonic Corporaiton, Chicago, Ill.
22 Filed: Aug. 11, 1972 [21 Appl. No.: 279,968
Related U.S. Application Data  Division of Ser. No. 66,961, Aug. 26, 1970, Pat. No.
 U.S. Cl......- 62/168, 62/384  Int. Cl. F25d 3/12 58 Field of Search 24 6 12 387, 388, 119
[5 6] References Cited UNITED STATES PATENTS 2,010,431- 8/1935 Hulse 62/384 1 Jan. 8, 1974 2,055,994 9/1936 Baker 62/384 2,125,888 8/1938 Cordrey 62/387 2,187,569 1/1940 Henney 62/384 Primary ExaminerMe yer Perlin Attorney-William H. Anderson et al. I
57 ABSTRACT Refrigeration apparatusutilizing solid carbon dioxide 9 as a refrigerant comprising a pair of refrigeration compartments, a solid carbon dioxide hopper defined by a pair of hollow condensers arranged in the shape of a V for cooling a circulating heat-exchange fluid. A pair of evaporators vertically below the hopper define a chimney between compartments for the circulation of air being cooled. A blower may be used to control air circulation.
4 Claims, 2 Drawing Figures 1 C02 REFRIGERATION'SYSTEM This application is a division of patent'application Ser. No. 66,961, filed Aug. 26, 1970 now US. Pat. No.
This invention relates to cooling systems, and more particularly to cooling systems which are particularly suited for employing solid carbon dioxide as a refrigerant.
Solid carbon dioxide is an excellent expendable refrigerant because it is relatively inexpensive and has a very high cooling capacity per unit of weight and volume. Because of its .relatively low freezing point (109.6F.), there are advantages to using carbon dioxide in an indirect refrigeration system rather than employing it to directly cool particular products. As a result, systems have been developed using solid carbon dioxide to cool an intermediate heat-exchange liquid, for example, methylene chloride, having a low freezing point which in turn is used to absorb heat from the product being refrigerated Low-freezing liquid solutions of relatively high percentages of methanol in water have also been employed as heatexchange liquids. Systems using other subcooled intermediate liquid eutectics of relatively high heat capacities have been used fairly extensively in truck refrigeration and have also found applications in railroad car refrigeration. Improved cooling systems employing such intermediate heat-exchange liquids which are particularly adapted for use with solid carbon dioxide are still desired.
It is an object of the present invention to provide an improved cooling system using an intermediate heatexchange fluid that is particularly designed to employ solid carbon dioxide as the refrigeration source. Another objectof the invention is to provide a cooling system for effectively controlling the release of the inherent refrigeration value of solid carbon dioxide, which system is simple in construction and contains few moving parts, thereby assuring good reliability in operation. A further object of the invention is to provide a cooling system employing solid carbon dioxide which isparticularly adaptable for use in portable apparatus and which has the capability to operate with substantial independence of environmental conditions.
These and other objects of the invention will be apparent from the following detailed description of several systems embodying various features of the invention when read in conjunction with the accompanying drawings wherein: Y
FIG. 1 is a front elevation view, with portions broken away, of apparatus incorporating acooling system designed for operation with solid carbon dioxide and embodying various features of the invention; and
FIG. 2 is an enlarged sectional view of the apparatus shown in FIG. 1 taken generally along the lines 22.
Shown in FIGS. 1 and 2 is a refrigeration apparatus I 11 in the form of a cart having a chassis or enclosure 13 which is mounted on four wheels 15 to make it easily transportable. A pair of refrigeration compartments 17 are arranged generally side-by-side in the cart. The walls of the chassis are suitably insulated, and access to each compartment 17 is provided by a suitably insulated, vertically hinged door 19. The illustrated apparatus 11 is designed for good service, and each compartment 17 has a plurality of cantilever brackets 21 mounted therewithin on the respective outer walls. The
I brackets 21 are used to support food trays at spaced vertical locations within the compartments 17.
A V-shaped hopper 23is arranged centrally of the upper portion of the chassis 13, and access to the hopper 23 for supplying solid carbon dioxide is provided by an upper hinged door 25. The hopper 23 is formed by a pair of hollow condenser plates 27 arranged at an acute angle to each other. The V-shape of the hopper 23 has been found to assure that good heat transfer is achieved between discrete carbon dioxide nuggets (with which the hopper 23 is preferably filled) and the fluid in the condenser plates 27 which form the bottom walls of the hopper. Nuggets are short cylinders of dense solid carbon dioxide that can be handled like other particulate materials. The undersurface of the V- shaped hopper 23 also serves to smoothly direct the circulation of air either entering or leaving the refrigeration compartments 17. v
The two refrigeration compartments 17 are spaced apart to provide a vertical chimney 29'therebetween, which chimney is generally defined by a pair of vertical evaporator plates 31. These two evaporator plates 31 also respectively define the inner boundary of each refrigeration compartment 17 and as such constitute the inner side wall of each compartment. The lower end of each of the evaporators 31 is spaced a given distance above the bottom of the chassis 13 to provide lower circulation openings 33. Likewise, the upper end of each evaporator. 31 is spaced a desired distance below the inclined undersurface of the hopper 23 to provide upper openings 35. The upper and lower openings 35 and 33 at the top' and the bottom of the evaporator plates 31 facilitate the circulation of air through the chimney 29 and the two refrigeration compartments 17.
Heat transfer to the cold evaporator plates 31 cools the air adjacent both surfaces of each of the evaporator plates. The more dense, cooler air gravitates downward in the chimney 29 and flows out through the lower openings 33 into the bottom of the refrigeration compartments 17. When the food or other material in the compartments 17 is at the desired temperature, wanning of the air is via heat flow into the cart 11 through the outer walls of the chassis 13. Such heat input warms the air adjacent the inner wall surfaces of the refrigeration compartments 17'and causes an uplift of the less dense air adjacent these locations, thus establishing a natural convection flow upward along the walls of the refrigeration compartment 17. Overall circulation is achieved as this warmer air at the top of the compartments 17 is drawn through the upper openings 35 into the chimney 29 and downward along the evaporator plates 31 to replace the descending cooled column of air.
In many cases, this natural convection flow will be sufficient to accomplish a rapid enough cool-down of the natural convection. Performance is improved both from the standpoint of more rapid cool-down and from the standpoint of more uniformity of temperature throughout the refrigeration compartments 17. Normally, the upper portions of the refrigeration compartments are more difficult to maintain in the same narrow temperature range with the lower portions thereof. It is believed that the splitting of the upward moving column of air by the undersurfaces of the inclined walls of the hopper 23 at the top of the chimney 29 causes an effective spreading of the cool air throughout the upper portions of the refrigeration compartments 17.
More particularly, the apparatus employs a completely closed system of an intermediate heat-exchange liquid, preferably a Freon. Freons, or polyhalogenated flurocarbons as they are sometimes called, are short chain paraffin hydrocarbons which have been substituted with one atom of fluorine and at least another atom of halogen, which may be fluorine, chlorine or bromine. Freons are well known for their use as heatexchange fluids, and a particular Freon is generally chosen having physical properties which best complement the overall characteristics of the system, includ ing the desired temperature range to be maintained in the refrigeration compartment 17 and the temperature of the refrigerant source. In general, when solid carbon dioxide is used as the source of refrigeration and it is desired to maintain a temperature in the neighborhood of 40F. in the refrigeration compartment 17, the preferred Freons are Freon 12, Freon 21, and Freon 11.
In the illustrated apparatus 11, the condenser plates 27 which are disposed in the V-shape arrangement extend from the front wall 39 to the rear wall 41 of the chassis 13 and constitute the hopper 23. If desired to increase its volumetric capacity, the upper portions of the condensers might be made vertical and not substantially detract from the effect gained by having the lower surfaces inclined. The condensers 27 are hollow in their interior and have an upper surface resembling that of a waffle to provide extended surface area for heat transfer purposes. The hollow plates 27 serve in the illustrated system as a reservoir for the freon that is being condensed. The undersurfaces of the condenser plates are covered with insulation 43 to provide a good thermal barrier between them and the refrigeration compartments 17. To achieve the desired advantages from the V-shaped arrangement, each of the condenser plates 27 should be disposed at an angle between about and about 40 to the vertical. This arrangement has been found to both produce the desired flow-directing effect from the undersurface and to produce excellent heat-transfer on the interior plate surfaces as a result of the effect to gravity forcing the solid CO nuggets downward against the plate surfaces and the particular angle of contact preventing bridging of the nuggets in the hopper.
The evaporator plates 31 each have a hollow center section 45 having both surfaces of generally waffle-like design. As seen in FIG. 2, a peripheral flange portion 47 surrounds the center section 45 and extends from the front wall 39 to the rear wall 41 of the cart chassis 11. The evaporators 31 are suitably mounted, as by thermally-insulating brackets (not shown), in a manner to minimize heat conduction between the cart walls and the evaporator plates. Accordingly, the evaporator plates 31 define the inner boundaries of the two refrigeration compartments l7, and their location serves to create the desirable convection flow of air within the compartments that establishes the desired uniformity of temperature.
Freon liquid condenses in the condensers 27 and flows downward through a tee 49 into a line that contains a modulating valve 51. The liquid stream passing through the valve 51 flows downward through an insulated pipe 52 to a location near the bottom of the cart where it enters another tee member 53 and is split into a pair of lines 55 which lead to inlets at the respective bottoms of the evaporators 31. Because the tee member 53 is located at a position below the evaporator plates 31, the amount of liquid Freon in both evaporators is equalized because the fluid interconnection equalizes the hydraulic head in both. In the evaporators 31, the cooled liquid freon slowly vaporizes, absorbing heat from the air adjacent the surfaces of the evaporator plates. If one of the refrigeration compartments should be subjected to a greater heat load than the other, automatic compensation is provided via the hydraulic head equalization. The warmer vapor exits from outlets at the top of the evaporator plates 31 and flows through conduits 57 which lead to inlets near the upper ends of the condenser plates 27. Heat transfer from the warm vapor to the cold solid carbon dioxide nuggets, which have a surface temperature of about I 10F., rapidly takes place and the Freon vapor is reliquified. In the illustrated embodiment, a temperature sensor 59 is located near the rear of the lefthand refrigeration compartment 17 which is connected to the modulating valve 51. In response to the temperature read by the sensor 59, the valve 51 either slightly opens or closes to adjust the rate of flow of freon'through the valve downward through the line 52 and into the bottom of the evaporator plates 31 to cause the temperature of the compartments 17 to approach the desired temperature. The rate of flow through the valve 51 will likely vary depending upon the temperature of the liquid leaving the condensers 27. It has been found that the angular disposition of the walls of the hopper 23 assures good heat transfer to the solid CO nuggets even when the apparatus 11 has been in use for some time and less than half of the expendable CO nuggets remain in the hopper. The angular disposition assures, with the assistance of gravity, the prevention of bridging of the nuggets in the hopper and provides good heat transfer near the bottom ofthe condenser plates 27 where the liquid Freon is at its coolest before leaving the condensers for another circuit through the closed loop system.
It should be understood that the cantilever arms 21 are preferably relatively narrow in width and therefore leave ample space between the arms at each vertical level for the circulation of air in the refrigeration compartments 17. Of course, when food trays or the like are supported in the compartments, the region for circulation is somewhat restricted. However, the size of the compartments 17 is preferably proportioned to be substantially larger than the trays which will be accommodated therewithin so that there accordingly is space remaining for air circulation between the peripheries of the food trays and the walls of the enclosure 13. As a result, natural convection flow is created as the air is cooled adjacent the evaporator plates 31 and descends to the bottom of the cart chassis. This effect is particularly pronounced in the chimney where there is minimal outer wall surface for heat inflow and where the pair of spaced evaporator plates 31 define the major portion of the boundary. The cool descending column of air in the chimney flows through the lower openings 33 under the evaporator plates into the refrigerator compartments 17 where it displaces the air therein which is slowly being warmed. The heat flow into the cart 11 is through the walls of the enclosure and the upward convection currents are located generally about three sides of the tray peripheries adjacent the inner wall surfaces of the enclosure 13. The warm air enters the top of the chimney 29 through the upper openings 35 where it is smoothly directed downward by the undersurfaces of the hopper 23.
Depending upon a number of considerations, such as the type of material to be refrigerated, the temperature to be maintained in the refrigerator compartments 17, the desired time within which it is desired that equilibrium temperature should be reached after loading the hopper with CO nuggets and the environment within which the cart will be used, the amount of circulation that is achieved by natural convection may be sufficient. However, should a more rapid cool-down of material be desired, for example, or should greater uniformity of temperature be desired within the refrigeration compartments than is accomplished, the blower unit 37 is located in association with the central chimney. To retain the portability of the cart 11, the blower is preferably battery-powered. The blower 37 could be employed to merely assist the convection flow and thereby increase the draft down the chimney and out through the lower openings 33 into the bottom of the respective refrigeration compartments 17. However, it has been surprisingly found that even more effective cooling is achieved if the blower 37 is directed upwardly so as to reverse what would otherwise be the natural convection pattern within the enclosure 13. The upward moving column of cool air in the chimney 29 is split into two halves when it reaches the undersurfaces of the hopper 23, and the angular inclination of these surfaces effectively and efficiently directs the cooled air outward and across the upper portions of the refrigeration compartments 17. From these upper locations, the circulation is downward past the peripheries of the tray and then back into the chimney 29 through the lower openings 33 adjacent the location of the blower. 1 One example of a refrigeration cart 1 l is constructed and operated which incorporates various features of the invention. The cart 11 incorporates two side-byside refrigeration compartments 17 each measuring approximately 22 inches wide by about 53 inches high by 25 inches deep. Each compartment 17 is adapted to hold food trays each of which is about 17.5 inches by 21 inches.
A V-shaped hopper 23 is provided having an upper insulated access door 25 in the top wall of the chassis l3, and approximately pounds of solid CO nuggets are used to fill the hopper. The hopper 23 is defined by the upper surfaces of two' condenser plates 27 each measuring approximately 11 inches by 19 inches and each having a waffle upper surface design. Suitable flanges at each end of the condensers 27 extend to the walls of the cart enclosure 13 and support the condenscrs by appropriate attachment thereto. Located below the condenser plates 27 are a pair of parallel evaporator plates 31, which are vertically disposed and are spaced approximately 7 inches apart. The evaporator plates 31 individually measure about 22 inches by 24 6 inches and have central sections 45 of waffle surface design about 20 inches by 22 inches in dimension.
A closed freon loop system is employed similar to that shown in FIGS. 1 and 2 of the drawings and contains approximately 3.5 lbs. of Freon-l2. A modulating valve 51 is employed which is regulated by a temperature sensor 59 located generally centrally of the lefthand refrigeration compartment 17 at a position approximately 15' inches below the top of the compartment and 10 inches forward of the rear wall 41. The temperature sensor 59 is suitably supported from the underside of one of the brackets 21 that support the food trays. One-half inch thick foamed styrene insulation is provided at the undersurfaces of each of the condenser plates 27.
The system is set to achieve a temperature of 40 plus or minus 5F. in the refrigeration compartments 17. Starting with the cart 11 at an ambient temperature of F. and using only natural convection, the system cools to below 45F. in twenty minutes and maintains this temperature for over 4 hours on the original load of CO nuggets. Starting from an ambient temperature of about F., it is found that cool-down to or below 45F. occurs in less than 30 minutes, which is considered to be excellent performance.
Various of the features of the invention are set forth in the claims that follow.
What is claimed is:
1. Refrigeration apparatus utilizing solid carbon dioxide as a refrigerant, which apparatus comprises means defining a pair of insulated refrigeration compartments designed for maintaining temperatures below ambient temperature, hopper means for holding a quantity of solid carbon dioxide, said hopper means being at least partially defined by a pair of hollow units arranged in the shape of a V which serve as condensers for a circulating heat-exchange fluid, said hopper means being located at an upper location generally between said compartments, a pair of generally planar evaporators which are vertically disposed below said hopper means and respectively positioned at a boundary of one of said refrigerated compartments, first conduit means connecting outlet means from said condensersto an inlet into each of said evaporators, second conduit means connecting outlets from said evaporators to inlets to said condensers, valve means associated with said first conduit means for regulating the flow of fluid into said evaporator means, and temperature sensing means for controlling said valve means to achieve desired temperatures in said refrigerated compartments.
2. Apparatus in accordance with claim 1 wherein said evaporators are spaced apart to provide a chimney therebetween, said V-shaped hopper means being disposed at the top of said chimney, said evaporators being spaced below said hopper means and above the bottom wall of said compartments to respectively provide upper and lower openings for the circulation of air therethrough, the undersurfaces of said V-shapedhopper serving to direct the smooth flow of air between the upper portions of said compartments and said chimney.
3. Apparatus in accordance with claim 2 wherein fan means is located in association with said chimney, which fan means is adapted to establish an upward moving column of air in said chimney which creates a forced circulation of air throughout said pair of refrigeration compartments.
4. Apparatus in accordance with claim 1 wherein said pair of hollow units forming said V-shaped hopper means are each disposed at an angle between about 20 degrees and 40 degrees to the vertical.