US2026353A - Method and apparatus for refrigerating with solid refrigerants - Google Patents

Description

Demo 31, 1935. 1 w. e. MAYER 2&265'553 METHOD AND APPARATUS FOR REFRIGERATING WITH SOLID REFRIGERANTS Filed June 9, 1932 5 Sheets-Sheet 1 emu-noon 0000a WWNEESES INVENTOR 3% $6M. A g m, aflzw w' Dec. 31, 1935. w G MAYER 2,026,353

I METHOD AND APPARATUS FOR REFRIGERATING WITH SOLID REFRIGERANTS Filed June 9, 1932 5 Sheets-Sheet 2 WITNESSES Dec. 31, 1935. w. e. MAYER 2,026,353

METHOD AND APPARATUS FOR REFRIG-ERATING WITH SOLID REFRIGERANTS.

Filed June 9, 1952 3 Sheets-Sheet 3 R O T N E v m h fi a 0 a 7 e. 6 4

' wn'nsssts ifiQM ideal refrigerant,

Patented Dec. 31, 1935 UNITED STATES] PATE NT] OFFICE I A'rmewun SOLID nnmreaaanrs William G. Mayer, Pittsburgh, Pa. Application June 9, 1932, Serial No. mass 5, Claims.

This invention relates to refrigeration, and particularly to the refrigeration of vehicles by means of solid carbon dioxide. 4

Ordinary water ice as a refrigerant for vehicles, such as trucks, carrying perishable materials, e. g. foodstuffs, is not satisfactory for various reasons. Chief arn ong these are the bulk and weight of ice and b rme which must be carried, and the rather limited cooling effect and refrigeration period available.- Also, the refrigerating effect is quite restricted.

The advantages of solid carbon dioxide, e. g., in the form of so-called snow or ice, are well known. Its temperature is about ll5 F., and it does not melt, but sublimes. It thus provides greater refrigerating possibilities than water ice,

A further object is to provide an apparatus for refrigerating with solid carbon dioxide, which is I compact, of sturdy and inexpensive construction,

eflicient in operation, adapted for the practice of v the method embodied in the invention, and which in a particular embodiment eliminates contact of ing partition of metal 'of high'thermal conductivity to solid carbon dioxide refrigerant in heatexchanging contact with the other side of the partition. Most suitably the partition consti-, tutes a wall of a container enclosing the refrigand it eliminates the collection of liquid with'its erant, and its exterior presents td the chamber attendant disadvantages. In general 1 pound of solid carbon dioxide is capable of the same refrigerating efi'ect as about 15 pounds of water ice. Thus lower temperatures, with better preserva tion of foodstuffs, are possible, and pay loads and route lengths may be increased. Furthermore, solid carbon dioxide does not require the brines needed with water ice, so that this source of non-pay weight, and the corrosion due to brine, are eliminated. v These properties render solid carbon dioxide an particularly for vehicular transportation of perishables. However, it is substantially more expensive weight-for-weight than water ice; gaseous carbon dioxide formed on evaporation may exert an injurious effect on some foods; and its u'serequires some measure of temperature control, since otherwise foods refrigerated with it may be frozen; Therefore, trucks and similar vehicles using'carbon dioxide refrigerant must be adapted to prevent undue evaporation of the carbon dioxide and contact of the gas with its load, as well as providing for temperature control. The constructions, whether vehicular or stationary, available. heretofore have not ciency' of refrigeration because the cool gas is retained for further heat absorption. The refrigerating efllciency may be, and preferably is, further increased by relieving the excess CO2 gas into the insulation of the enclosing walls of the refrigerated chamber. In circulating through the insulation the gas absorbs further amounts of heat, so that it approaches atmospheric temperature before finally reaching the atmosphere.

This aflords utilization of substantially the entire capability of the carbon dioxide to absorb heat; furthermore the transfer of heat from the frigerated chamber is minimized.

, atmosphere through the enclosing walls of the re- The invention is further predicated upon my I discovery" that by restrlcting the heat transfer substantially to the partition, or wall, with which the refrigerant is in contact, evaporation of the refrigerant will be confined primarily to the face in contact with the container wall, so that the refrigerant will continuously present substansuit particular needs, which utilizes the major tially constant refrigerating area. This affords proportion of the heat absorbing capacity of the refrigerant material, is economical, applicable constancy of heat transfer, with consequent uniformity of refrigerating effect and improved efliciency. Also in accordance with the invention regulation of the rate of heat transfer between,

I the chamber and the refrigerant to maintain the chamber at a desired temperature, is accomplished by interposing resistance to thermal conduction between the refrigerant and the heat exchanging partition.

The apparatus embodied in the invention comprises a chamber for containing the materials to berefrigerated, preferably one having its enclosing walls insulated with a material permeable by gas. The refrigerant is enclosed within a container havinga heat exchangingsurface of metal of high thermal conductivity exposed to the chamber, and advantageously the container is associated with the top, or roof, of the chamber, with its bottom supporting the refrig-. erant. Preferably the container is provided externally with a large heat exchanging surface, as by providing it with a plurality of fins or ribs. For most purposes the container is constructed to 1 prevent leakage of substantial amounts of gaseous carbon dioxide into the chamber, and most suitably to maintain the evaporated CO2 gas under pressure, means being provided to relieve excess gas according to circumstances.

, Although the exposed wallsof the container may act together as a heat exchanging partition, it is preferred, for reasons presently to be explained, to so construct the container as to restrict the heat transfer substantially to the heat exchanging partition, e. g. the bottom wall. In such case the remaining exposed walls are insulated from the refrigerant,,but most advantageously they act to assist in absorbing heat from the container, and to transfer it to-the heat exchanging wall.

The invention is particularly adapted for use with trucks and other vehicles and for purposes of further illustration will be so described, although it will be understood that it is not restricted thereto and may be applied to other uses.

In the accompanying drawings Fig. 1 is a fragmentary side elevation, partly in section, of a truck body showing one embodiment of the invention; Fig. 2 an enlarged horizontal view, partly in section, of the refrigerant container taken on line 11-11, Fig. 1; Fig. 3 a perspective view of the container shown in Figs. 1 and 2; Fig. 4 a perspective view of an insulating pad for use in the practice of the invention; Fig. 5 a bottom plan view of another form of refrigerant container illustrating the preferred embodiment of the inbetween walls 2 is filled with suitable heat ins'ulating material 4, preferably one permeable by gas, such as the fibrous insulators now commonly used for instance Kapok or Balsa wool), As shown in Fig. 1, a refrigerant container 5 is mountedin ahatchway formed in the roof of the truck body. Container 5 comprises a base plate 5, which supports a cake I of solid carbon dioxide within the-container, and which is connected to vertically positioned side plates 8.

Plates 6 and 8 are formed from a metal of good thermal conductivity, such as aluminum or its light alloys. dimensions of the container are such as to accom- Advantageously the cross sectional modate the standard cakes of solid carbon dioxide, or multiples or uniform fractions thereof. The container is suspended from the side walls 9 of the hatchway, and in the embodiment shown the container is constructed and is fitted 5 into the hatchwaysnugly to prevent leakage of substantial amounts of ,gas into the compartment.-

Base plate 6 is preferably provided with means for increasing its normal heat radiating capacity, and this may be accomplished by connecting to one or both sides of the base plate sheet metal corrugated to form V-shaped fins. As shown in Figs. 1 and 2, the lower side of the base plate is provided with corrugated sheets ll forming ribs which extend entirely across the lower side of the base plate, the latter extending laterally from the sides 8 toincrease the heat-exchanging surface. The lateral projections of plate 6 are provided' on the upperv surface with similar corru- 20 gated sheets l2, as shown particularly in Fig. 2. This construction provides channels for circulation of air over the heat radiating surfaces, so as to increase the rate of heat transfer. Such air circulation may be increased by perforating 25 corrugated sheets II and I! as at l3 and by cutting slots l4 through the sheets and plate 6.

The construction thus provided is adapted to efiiciently refrigerate the compartment. In most instances regulation of temperature is desirable, 30

, mize CO2 consumption. Such control may be effected by vertical adjustment of the container 35 in the hatchway, or of the refrigerant in the container, or both. The containerposition may be adjusted by moving it up or down in the hatchway, a plurality of horizontal rows of screw holes l5, Fig. 3, beingprovided in walls 8for 40 that purpose.

Further control of rate of heat, transfer is afforded by interposing'thermal resistance under the refrigerant. The pad shown in Fig. 4 forms a particularly suitable means of doing this. It comprises a hollow box-like structure I 6 formed of metal,the interior being reinforced by corrugated sheet metal II to resist crushing of the walls by the refrigerant cakes.- The heat insu-.- lating eifect may be increased by making the box gas tight to provide dead air space. Being formed:from-metal and being in full contact with cake I such pads afford direct heat transferring contact between the refrigerant and base plate 6, while they reduce the rate of heat transfer.

I- have found that.p'articular advantages attend the retention under pressure in the container of the gaseous CO2 which is formed as the solid refrigerant evaporates in absorbing heat from the compartment. To this end the container and its associated parts are constructed to maintain 'the gas under a desiredpressure. For this purpose hatchway cover i0 is maintained by any suitable means in gas-tight relationship with the hatchway. For example to each side of the cover there is connected 2. spring latch [8 which engages a catch I! mounted on side wall 9. The latches press the cover against a gasket 20 interposed between the cover and the top of the hatchway.

Excess pressure is relieved through an outwardly opening adjustable relief valve indicated schematically at 2|, a number of types of which are available. Because the CO: gas formed in the container is quite cold it is preferred to relieve it into insulation 4, soas to obtain additional refrigerating effect. Thus valve 2| opens into the insulation space between side walls 2 so that-the gas circulates through insulation 4, thus cooling the compartment walls and minimizing heat transfer to. the chamber from the atmosphere. In order to permit free circulation through the insulation body structural members, such as indicated at 22, are provided with holes 23 as need be. The gas finally escapesto the atmosphere through the cracks in the body walls.

The refrigerating unit thus provided possesses numerous advantages, among which are its compactness, the slight weight of the container and refrigerant needed to equal the refrigerating effect of large volumes and weights of water ice, and the ability to prevent contact of foodstuffs with gaseous CO2. y

Especially great advantages flow from the effi- "ciency of the unit, which arises from a number of factors. In the first place, the, heat transfer is directly from the chamber through the heat exchanging wall to the refrigerant. This is augmented by presenting a large heat absorbing surface to the chamber, and by having the refrigerant cake in full contact with the other side of the exchanging wall, 1. e. having a flat surface of refrigerant entirely contacting the plane surfaced base. I

Further efficiency is derived from the ability to regulate the rate of heat transfer, so that the refrigerant .is not used needlessly, and so that therefrigeration is optimum for the particular materials being cooled. i Thus if the heat exchanging surface is too great for the refrigeration-desired, the container may be moved heat transfer, and vice versa. A similar result is obtained 'by the use of thermal resistance between the plate and cake 1. described are-especially desirable, as they maintain metallic and full contact between the plate and the refrigerant, and merely reduce the rate of heat-transfer to the base and the area of upwardly in. the hatchway, to reduce the rate' of refrigerant exposed to the side walls. Both means of adjustment may be used,. for example to roughly approximate the desired temperature by varying the container position, and completing the regulation by the.use of pads. Actual tests have shown-that in this manner desired temperatures in the range from 40 F. below zero to- 15 F. above zero can. be maintained satisfactorily;

formation of CO: gas, and this is used in two ways to appreciably augment-the refrigerating effect. is available for further absorption of heat, and it represses evaporation thereof, thus decreasing the consumption of solid carbon dioxide. In

general, retention of the gas at pressures of from about 5 to 15 pounds persquare inch affords satisfactory results. Second, ancillary cooling is obtained through release of gas to the enclosing'tvalls when the pressure within the container buil'ds'up to a point where it exceeds the .pressure for which the relief valve is set. -The cool gas circulates through the insulation around the enclosing'walls, and this may be, and adt eousl is, enhanced b sealing the linings van ag y y ofI sumciently'to permit brackets 4| to be swung of the inside and outside walls, and roof, of the vehicle body, so as to compel the gas to flowover The pads Absorption of heat from'the' chambercauses By retaining the gas under pressure it and this furtherreduces refrigerant consump tion, so that substantially the full refrigerating power .of. the CO: is thereby utilized. In addition, this circulation of gas through the enclosing walls serves the useful function of keeping the. insulation dry, the-gas flow preventing entry, or at least accumulation, of atmospheric moisture. I

vIn caseinsulation 4 is not;a fibrous or loose and gas permeable material, .-'the relief valve may open to the atmosphere, or where meat and the like goods, which are improved, or; whose value is not deteriorated, by carbon dioxide gas,

are carried the valve-may open directly into the compartment, if desired.

The preferred embodiment of the invention is illustrated in Figs. 5 to 8, according to which the refrigerant container is ,-mounted wholly within the chamber to be refrigerated. In this,

embodiment. the container comprises a shell, or 20 box-like structure, advantageously of cast construction, having a base 25, side walls 26, and a top 21. The container is providedwith a-door, for introducing refrigerant; preferably it forms one end of the container, the opposite end be- 25 ing closed by a wall 26a continuous with side walls 26. The. container isattached in any suitable manner to the top of the chamber to be refrigerated, for example by lag screws 210, Fig.

6. Solid carbon dioxide refrigerant Ia rests in 30 complete contact with bottom wall 25, as in the fins, or ribs, 28 and 35 hereinabove, and the door is arranged to be 40 gas tight under the pressures used. Various constructions may be used for this purpose, but I have found, that, in general, the pressure within the container tends to cause leakage around the periphery ofthe door unless it is of very 45 heavy section, or "unless it is designed to prevent its being sprung by the pressure within the container. A door construction which has been found to be satisfactory is illustrated. in Figs. 7 and 8. As 50 there shown the door comprises a peripheral flange 3| conforming to the end of the container,

and an integrally. formed body portion 32 which i is bowed outwardly, as seen in Fig. 8. This shape resists'deformation by interior pressure, but to further reinforce it the door isprovided interiorly with longitudinal ribs 35.

:The door is hinged to swing at bottom wan 25 of the container by hinge-connections 350; Figs. 5 and 8,.and it, is clamped in closed position by a cross yoke 36 held pivotally by a pin 3! ma U-b'racket 38 integral with and project- 'ing from the face of the door. The door is forced into sealing relationship with a gasket 39 surrounding the container by application of pressure to the ends of yoke 36 through pressure screws 4|! which move in threadedU-shaped bracket members I pivotally connected by pins 42 to bosses 43 cast integrally at the sides of the container. 'To-remove the door, screwsv 40 are backed laterally, thus freeing the yoke andjdoon Prior.

to opening the door the gas pressure is relieved through a hand operated blow-of! valve 44 pass- [5 ing through a boss formed on one side of the container.

The container just described may be used to effect refrigeration of the chamber within which it is mounted, e. g. a truck body, by transfer of heat from the chamber through the bottom and side walls of the container, as in the preceding embodiment But where heat is transferred freely through all sides of the container, as in prior units, the solid refrigerant diminishes in size in all of its dimensions. This decreases the area of contact of the refrigerant with the container wall, and may result in decreasing rate of heat transfer. i

In a further aspect of the invention I have found that adequate and uniform refrigeration may be obtained by substantially restricting heat transfer to the wall of the container with which the refrigerant is in contact, which I have found maintains substantially constant contact area between the refrigerant cake and the heat exchanging partition. This is' accomplished, as shown in perishable materials.

Fig. 6, by mounting an inner liner 45 of wood or other material of low heat conductivity within the container to form a space between itand the side walls and top. This space is lagged with a heat insulator 46, suclpas cork or the like. The door is likewise. insulated by a panel 460 of suitable wood. To increase the area of theheat exchanging surface, to provide adequate refrigerating effect for all conditions, the sides and ends of the container are provided with fins 41 cast integrally with the container. These fins act chiefly to augment the absorption of heat, which they transfer to the base, for the insulation of thetop, side and end walls prevents direct transfer of heat from them to the refrigerant. It is preferred that the total exposed area of the container, i. e. the surface area of the fins plus the surface area of the walls between the bases of the fins, be at least equal to the area of the roof plus half the area of the enclosing walls, as this gives the most satisfactory results for most purposes.

It thus appears that in the preferred embodiment fin sides of the container act to absorb heat and transfer it through a single side to the refrigerant, which is insulated on fin sides, and further that the enclosing walls are refrigerated on fin sides by the evaporated gas. Tests of a refrigerant container constructed in'this manner have shown that in actual service cake Ia diminishes in size primarily in its horizontal dimension.

That is, the area of contact with base 25 remains substantially constant, the cake gradually decreasing in height without materially diminish ing in horizontal cross sectional area. Thus restriction of heat transfer substantially to the contact surface maintains a substantially uniform area of contact between the cake and bottom.

and provides practically constant heat exchanging conditions. v

The retention of CO2 gas under pressure redoor is advantageously positioned facing the door of the truck body, so that the refrigerant may be readily introduced into the container. I

The invention thus provides for adequate and efficient refrigeration of chambers containing The apparatus provided 5 by the invention and used in the practice of its method requires but a small amount of space in the refrigeration compartment. This provides greater refrigerating space, and consequently larger pay loads. Furthermore, as the unit is relatively small, and is preferably constructed from a light metal, lighter trucks can be used, which decreases the initial vehicle cost and its upkeep, and also increases the area of the district that can be served by a single vehicle. The corrosion due to the use of water ice is eliminated. The refrigeration is improved, being uniform and otherwise more desirable than that with water ice. Substantial economies attend the use of evaporated gas in the manner described, because this utilizes as completely as is economically possible the heat absorbing capacity'of the refrigerant. Other advantages will be understood by those skilled in the art.

Actual experience with units embodying the invention has clearly demonstrated its utility, both in efiecting quick cooling of the chamber,

and maintaining adequate refrigeration, and in providing economy of refrigerant. The value of circulating the gas through the enclosing walls is 3 shown in part by the fact that frost may, and does, appear on the ceiling and walls for a substantial distance from the unit, or container. This shows the gas to be very cold as it leaves thecontainerfand that this factor substantially 5 reduces the transfer of heat'to the chamber from the atmosphere, and that in turn reduces solid CO: consumption.

The invention is not restricted to use with trucks, but is applicable to other vehicles, such as 40 railway or freight cars, and also to stationary refrigeration, as of cabinets and permanent and fixed refrigerating installations.

This application is a continuation in part of my copending application Serial No. 534,721, filed May 4, 1931.

. According to the provisions of the patent statutes, I have explained the principle and construction-of my invention and have illustrated and described what I now consider to represent its best embodiment. However,'I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A bunker for solid carbon dioxide refrigerant comprising a metallic container having top, bottom and side walls of a metal of high thermal conductivity associated in gas-tight relation, said bottom wall being ribbed to provide a total exposed heat exchanging area .at least equal to the area of the roof and one-half the side walls of the chamber to be refrigerated, one of said container walls providing an aperture for introduction of said carbon dioxide, and a closure for 5 said aperture comprising an outwardly bowed member, a yoke adapted to press said member into gas-tight relation with the sides of the aperture,

and releasable means associated with said container cooperating with the yoke to effect closure. 2. A bunker for solid carbon dioxide refriger-- ant comprising a metallic container having top, bottom and side walls of a metal of high thermal conductivity associated in gas-tight relation, the bottom wall being ribbed to provide a total ex- 15 posed heat exchanging surface equal at least to the area of the roof plus one-half the side wall area of the chamber to be refrigerated, one of said container walls having an aperture for introduction of said carbon dioxide, and a closure for said aperture comprising an outwardly bowed plate member, a yoke adapted to press said member into gas-tight relation with the sides of the aperture, and releasable means associated with said container coperating with the yoke to efiect closure, and an outwardly opening relief valve associated with a wall of said container for retaining C02 gas therein under predetermined pressure.

3. A bunker for solid carbon dioxide refrigerant comprising a metallic container having a top wall for association with the roof of the chamber to be refrigerated, a bottom wall and side walls, said walls being formed of metal of high thermal conductivity associated in gas-tight relation with one another and one of the side walls providing an aperture for introduction of refrigerant, said side walls being interiorly insulated, and a closure for said aperture comprising an outwardly bowed plate member, a bowed yoke adapted to press said closure into gas-tight relation with the sides of the aperture, and releasable means associated with the container cooperating with the yoke to effect closure.

4; A bunker for solid carbon dioxide refrigerant comprising a metallic container having a top wall for' association with the roof of the cham- 5 ber to be refrigerated, side walls, and a bottom wall ribbed exteriorly to provide a total exposed heat exchanging area at least equal to the area of the roof plus one-half the area of the side walls of the chamber to be refrigerated, said container being formed of metal of high thermal conductivity and the walls-being associated in gas-tight relation with one another with one side wall providing an aperture for introduction of refrigerant, said container side walls being interiorly insu- .lated, and a closure for said aperture comprising an outwardly bowed plate member, a bowed yoke adapted to press said closure into gas-tight relation with the sides of the container, and releasable means associated with the container 00- operating with the yoke to efiect closure.'

5. A bunker for solid carbon dioxide refrigerant according toclaim 4, and an outwardly opening relief valve associated with one of the container walls for retaining C02 gas'therein under predetermined pressure.

WILLIAM G. MAYER.

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