US2061776A - Refrigeration - Google Patents

Description

Nov. 24, 1936. E. RICE, JYR v 2,061,776

REFRIGERAT ION Original Filed July 7, 1933- 2 Sheets-Sheet l l 2 sheets-sheet 2 Original Filed July 7, 1935 Patented Nov. 24, 111936 UNITED.. STATI-s PATENT 2,061,176 aEFRIGERA'iIoN Edward Rice, Jr., Croton-on-Hudson, N. yY., assignor to International Carbonio,v Inc., Wilmington, Del., a corporation of Delaware original application July 7, 1933, serial "Nn.

679,435. Divided and this application 'November 3, 1934, Serial N0. 751,392

' 14 Claims. (Cl. 62-91.5)

'This application is a division of my applica` tion for patent filed July '7, 1933, Serial No. 679,435, now matured into Patent Number 1,980,089, issued November 6, 1934.

This invention relates to improvements in refrigerating methods and apparatus for use with solid refrigerants, such as solid carbon dioxide, water ice, brine icefetc.

The invention described and claimed herein resides in a novel way of forming and using a solid metallic heat conductor for transferring heat to a solid refrigerant from air flowing from the refrigerated space or area; wherein the said conductor consists of a thick heavily: finned metal plate which forms --the bottom and a side.

sections of the conductor are preferably, but not necessarily always, metallically joined together.

In operation the air from the refrigerated space circulates through the open-ended ducts, heat is y absorbed from the air by the large exposed surfaces of the finned conductor and is transferred bythe metal tothe solid refrigerant, which is maintained by gravity in contact, or in suitable conductive relation with the conductor. The air from the refrigerated space is caused to circulate downwardly and out through the back part'of the ducts by natural thermo. convection or'by a power driven fan or blower; or circulation in the reverse direction may be set up by the fan or blower. The conductor forming the bottom of the refrigerant-containing 4space may be inclined slightly toward the vertical conductor wall so that a higher temperature solid refrigerant such as water ice will tend to gravitate continuously against the vertical conductor wall to facilitate heat transfer to the refrigerant.

This novel construction ofthe conductor makes yit possible to provide refrigerating apparatus for trucks, railway cars and containers, and storage compartments, wherein the greatest pos= sible area of constant heatabsorbng surfaces may be provided with the smallest allowable size of bunker and quantity of solid refrigerant; and whereby the most eicient thermo-circulation of air in the refrigerated space and the greatest possible rate of heat transfer to the solid refrigerant may be maintained. This invention provides refrigerating apparatus, for use with solid refrigerants, which is much more efcient than anything previously known for cooling compartments such as truck bodies into which there is a large heat leakage through door openings, or for cooling down at a maximum rate such products as fruits and vegetables which are frequently loaded into the refrigerated space at a high temperature.

An object of the invention is to provide a means for transferring heat to a solid refrigerant at a. higher rate than provided in previously known methods, the refrigerant being used in the usual and ordinary processes of refrigerated storage and transportation of ,perishable foodstuffs.

Another object is'to provide a means for transferring heat to small quantities of a solid refrigerant at the same rate as to comparatively large quantities, the refrigerant being used in the usual and ordinary processes of refrigerated storage -andA transportation of perishable foodstuffs with the result thatv approximately constant refrigerating temperatures can be maintained substantially as long as any of the refrigerant remains.

Another object is to provide a means for transferring heat to small quantities of asolid refrigerant at the same rate as to comparatively large quantities, the refrigerant being'used for cooling a uid such as air or water, thus making it possible to use smaller quantities of the re` frigerant than heretofore for a desired rate of heat transfer and to maintain ythe same rate'of heat transfer substantially as long as any of the refrigerant remains.

Another object is to provide a means for maincient surface in heat exchange relation with the refrigerated area or mass, and with sumcient heat transfer capacity or cross section to pick up and transfer to the refrigerant the maximum amount of heat as required to effect the desired refrigeration.

More specifically an object is to provide a solid metallic heat conductor of the above characteristics for use with low temperature solid refrigerants, such as solid CO2 and brine ice, in combination with means for controlling and regulating-(A) The heat transfer to the conductor fromV the refrigerated area (B) The heat transfer from the conductor to the refrigerant-or a combination of these means-for the purpose of regulating the temperature of the refrigerated area.

Another specific object is to provide a solid metallic heat conductor of the above characteristics which is commercially practicable in refrigerated storage and transportation of perishable foodstuffs, and which can be constructed o1' cheap available metals such as aluminum or copper; which can be easily made of bent or welded plates or cast or extruded forms of such metals; and which provides the necessary heat-absorbing and heat-emitting surfaces and heat transfer capacities without interfering with the usual and ordinary practices in construction of refrigerated storage and transportation units using solid refrigerants, suchA as household refrigerators, ice cream cabinets, motor truck bodies, R/R cars and containers, etc.

Figure 1 is a vertical section of a refrigerated compartment embodying my invention; Figs. 2 and 3 showing the bunker section of Fig. 1 in modified forms;

Figs. 4, 5 and 6 are diagrammatic sectional views of refrigerating units constructed according to my invention; and

Figs. 7 and 8 show cross sections of a solid metallic heat conductor suitable for use in the refrigerating apparatus illustrated in Figs. 1 to 6, inclusive.

During the past two summers I have designed and had constructed and commercially used a variety of improved forms of refrigerating apparatus for the storage and transportation of .perishable foods, ice cream etc. which employ as'the source of refrigeration solid refrigerants `such as solid carbon dioxide, water ice, or brine ice in combination with an extended solid metallic heat conductor which is chilled either by direct contact with the solid refrigerant or by some other uniform or controlled heat exchange relationship with the refrigerant.

I'he characteristics of thismetallic heat conductor must be such that (a) it forms a principal path of heat transfer between the refrigerated area or mass and the solid refrigerant-(b) it has a surface area in suitable heat exchange relationship with the space or mass refrigerated, this surface area being sufficiently extended to provide the number of square feet of heat absorbing surface required to absorb the heat removed from the refrigerated area, at the temperature differential ranges-used in any given apparatus between the conductor surface and the refrigerated area-(c) that it has a minimum cross sectional mass at any particular point suflicient to conduct in the direction of the solid I differential ranges used in any given apparatus between theheat absorbing conductor surfaces and the conductor surfaces exposed to the solid refrigerant-(d) it has a surface area in suitable heat exchange relationship with the solid refrigerant, this surface always being smaller thanvthe surface exposed to and absorbing heat from the refrigerated area.

This general method of using solid refrigerantsy is fully disclosed and claimed in my pending application Serial No. 467,999, filed July 14, 1930, and various forms of apparatus for carrying out the method are there described. In this application I Wish to disclose more specifically the principles of this method of refrigeration, to describe in more detail the characteristics of the solid metallic heat conductor which is the essence and concrete embodiment of the invention, and to claim improved forms of the conductor and ways of using it.

The use of this metallic conductor conforms to the usual and well known principles of heat yabsorption and emission by, and transfer through, a solidhhomogeneous material. For instance a certain number of heat units per hour are to be absorbed to maintain the required temperature in a household refrigerator, say equal to the meltage of one pound of water ice per hour. lIn using water ice for this purpose which melts at 32 F. a metallic conductor of copper or aluminum can be chilled to an average temperature of say 36 to 44 F. by-direct contact with asurface of the ice. This conductor can in turn chill the air of the refrigerator to say anaverage of 47 F. in an 7 room. To accomplish this approximately 144 B. t. u.s per hour must be transferred from. the

air of the refrigerator to the ice, or suficient to melt one pound of ice per hour. Where air circulates by natural convection over a cooling surface under these conditions approximately 11/2 B. t. u.s per hour per F. differential between the air and the cooling surface, per square foot of cooling surface can be absorbed. Therefore about fifteen square feet of chilled conductor surface is exposed to the air atan average temperature of 40 F., thusabsorbing approximately 15 square ft. x 11/2 B. t. u.s per hour x 7 F. differential-157 B. t. u.s per hourthis meets condition (b) above. Next a surface area of the 'conductor must be in direct contact (in the present instance) with the ice. This surface need be only a fraction. of the lsurface absorbing heat from the air;' anda in this fact lies the great practical advantage in this method of refrigeration, as well as one of the principal objects of v the invention, as it permits satisfactory refrigeration with small amounts of solid refrigerant. There is no exact physical data covering this heat transfer from the metal to a solid refrigerant but experimental observation shows that it is from fty to several hundred times as much per unit area per degree difference in temperature as from the air to the conductor surface. For instance with a sufficiently thick conductor, say of aluminum, fifteen square inches of water ice contact with the conductor can absorb the heat that is picked up from the air by fifteen square feet of conductor surface exposed to con- -vection currents in the form of ns-this corresponds to condition (d) above.

With a given surface exposed to the air and a certain amount of,ice available for minimum contact with the conductor then condition (c) by providing a necessary area of chilled surface, and to get the heat out of the conductor to the solid refrigerant, by providing an area of the conductor in uniform or controlled heat exchange relationship with the refrigerant, it is necessary to make the conductor sufficiently thick to transfer the maximum amount of heat to be taken out of any given refrigerated space or mass to effect the desired refrigeration under the most adverse conditions of actual use. This thickness is determined for the minimum temperature differential that it is feasible to use between the points where the heat enters and leaves the conductor, or between any two points along the conductor path. The rate per hour for this form Yof heat transfer is established for all the available metals and can be easily ascertained in the usual physics handbooks. Brieiiy for any given metal -it varies directly as the cross section and temperature differential used. For instance, other features being equal, approximately twice as much heat will be transferred per hour by an aluminum plate 1/4" thick as by one 1/8" thick for the same temperature differential; or approximately the same amount of heat will be transferred per hour by conductor plates, other factors being equal, made of l" copper, 1/4" aluminum, or iron. It is to be expected that these rules can notv be very reliable for overall temperature differentials of less than 2 or 3 F. or morethan 20 to' 30; or for excessively long distances, say over 6 orv 8 feet; or for excessively thin or thick conductors, say a co-nductive capacity of less than fg" of aluminum or over 1/2" of copper. But the conductor can always be constructed with enough surface and .sufficiently thick to take care of extreme conditions of use, and once constructed its heat transfer properties do not change. And experimental observation and wide commercial use show that-for the commonly available solid refrigerants such as water ice, brine ice and solid CO2; and for the cheaply available metals such as aluminum and copper,`and to a lesser extent iron; and for ordinary commercial purposes in which it is common to use solid refrigerant; such asthe transportation and storage of perishable foodstuffs-it is possible to construct refrigerating apparatus on the principles described above that is a great improvement over anything previously known in the art for usewith solid refrigerants.

In eiect such apparatus provides a new means of transferring energy or power in the form of heat, and greatly enlarges the entire field of use for solid refrgerants as a class, as well as providing a means of temperature control in the .use of solid CO2, often called dry ice, the newvvolume and surface of a solid refrigerant when heat is applied, have made it inevitable that -an excessive amount of the refrigerant had to be provided to supply sufficient surface to/ take up the required amounts of heat; and that there has been a steady rise in refrigerating temperatures due to the reduction in the heat absorbing surfaes of the refrigerant.

r the heat transfer to the refrigerant has been through the walls of a refrigerant container or support in contact with the refrigerant,

theheat reachingv the ice at the area of contact-which in some cases provided a constant surface of the refrigerant itself direct for heat absorption, but which resulted in such small surfaces being available for that purpose that either very limited refrigeration was secured or such large containers had to beused as to be commercially impracticable. When necessary to segregate the ice metal containers were often used, usually of galvanized iron, but the functi-on of the metal was altogether asa convenient material for constructing the containers and segregating the ice to control meltage, etc. and not as disclosed-above to forman extended thick walled metal conductor of heat to the ice. The metal of the containers on which the ice rested acted to slow up heat transfer from the air to taken from the refrigerated space'or mass be.

passed through the conductor, but only as stated in condition (a) above that it provide a princi-l pal path of heat transfer; although in usual practice most of the heat is thus transferred. It is sufficient that the fixed heat absorbing surface and transfer capacity provided by the conductor be large enough to take up the minimum amount of heat necessary to maintain a useful temperature when the volume of the refrigerant is considerably reduced-say to 5% or 10% of the bunker capacity. There will always be some heat get into the bunker space, and to the ice surface exposed there, through the walls of the bunker no matter how well insulated; and there may at times be some direct circulation of air from the refrigerated space, or around it, over the refrigerant as well as over the chilled conductor surfaces. In ythe absence of any regulalfrom a full bunker down to 5% to 10% capacity.

There-must be always a substantial conductor with a heat absorbing surface extended away from contact with the ice, and a heat transfer capacity for keeping the maximum temperatures permissible. This additional partial circulation over'the refrigerant of the convection currents of the refrigerated space can be controlled by means of thermostatically operated valves and thus become a. temperature controlling feature and as the refrigerant volume is reduced the valve can open to permit the necessary additional heat transfer directly from the circulating air to the surface of -the solid CO2 thus maintaining approximately constant refrigerant temperatures.

This fact that all the heat need not pass through the conductor to obtain the benefits of this invention often permits a cheaper and easier construction. For instance in the household refrigerant described above using water ice, a simple aluminum n assembly'r placed vertically on one side of the ice compartment will provide 15 sq. ft. of constant heat absorbing surface whereas 100 1b. block of water ice used in the ordinary way would present about 7% sq. ft. of surface at rst which would steadily diminish, reaching approximately 21/2 sq. ft. at 25 lbs. If'the conductor is loosely fitted with a 1 or 2 inch opening over the top then air can flow over the -ice as well as the conductor. When vfirst iced there would be 15 sq. ft. of conductor exposed for heat absorption plus 'l1/2 sq.- ft. of ice surface or a total of 221/2 sq. ft. At 25 lb. of ice there would be 15 sq. ft. of conductor surface plus 21/2 sq. ft.`

of ice surface or a total of 171/2 sq. ift-quite sufficient to maintain temperatures, which the 21/2 sq. ft. surface of the 25 lbs. of lice alone cannot possibly do.

Besides being able to transfer heat to small amounts of solid refrigerants at a rate before unequalled in similar refrigerating apparatus, one of the principal advantages of this conductor method of using solid refrigerants is that it makes possible a controlled use of solid refrigerants such as solid CO2 which sublimes at a temperature far below those required for ordinary refrigeration purposes, or such as a brine ice that can be 'made so as to melt from minus 6 degrees to about minus 30 degrees F. As explained above the number of sq. ft. of heat absorbing conductor surface and the difference in temperature of this surface below. that of the refrigerated space determines the amount of heat absorbed per hour-and thus the effective refrigerating temperatures. Obviously with a very cold refrigerant, like solid CO2 at minus 110 degrees F., a small conductor surface could be -`chilled to a very low temperature and theoretically produce the same results as a much larger surface at a higher temperature. But in practice a difference in temperature of more than 8 or l0 degrees F. between the conductor surface fand the air temperature of the refrigerated space does not result in a comparative increase in heat transfer from the air; and in most cases there is sufficient moisture in the air to cause considerable frosting of the low temperature surface which steadily cuts down heat transfer. Therefore it is preferable to use as far as possible a large surface high temperature conductor with a low temperature refrigerant like solid C02.

This large surface chilled a few degrees below the ordinarily required refrigerating temperatures, which range between degrees and 50 degrees F., can only be secured when using solid CO2 as the refrigerant by means of some intermediate heat transfer agent such as a circulating gas or liquid, or such as a suitably formed good heat conducting metal.

tively small surfaces of the refrigerant to meet most refrigerating means. Heat transfer by a circulating liquid such as alcohol or in freezing brine can transfer a considerable amount of heat As mentioned above heat transfer to the refrigerant by a gas, including air,

to a small surface of the solid CO2 especially when forced circulation is used, but as a principal means of heat transfer for refrigeration purposes such a system is not the subject of th'is application. A combination of circulating gas and liquid in the form' of a condensible refrigerant such as methyl chloride, etc. can also be used as a heat transfer means, but that also is not the subject of this application. The only remaining convenient means for providing the required heat transfer agent is'the use of a solid good heat conducting metal which can provide the necessary heat absorbing surface and transfer capacity, which can provide the necessary function of transferring heat at a comparatively high rate to a small surface of the refrigerant, and which permits of using means to control the rate of heat iiow from the refrigerated area to the refrigerant via the conductor in order to regulate the temperature of the refrigerated area. Various forms of such a solid metallic heat conductor for use with solid refrigfrom the refrigerated 4area to the conductor.

When the refrigerated area consists of an enclosed space in which a fluid circulates by convection, such as air, water or a non-freezing liquid, and the conductor is of such a form that a wall can be set up to form a confined space in which the fluid can flow past the conductor, then a convenient way of control is to establish manually or thermostatically operated valves in this confined passage which restrict, or at times shutoff entirely, the flow over the conductor as may be desired, thus limiting the amount of heat that has access to the conductor and so regulating the temperature of the refrigerated area. When it is impossible to set up this confined convection passage because of the nature of the refrigerated area, or when the character of the conductor permits, it is sometimes convenient to control the heat transfer to the conductor by placing predetermined amounts of insulation on the exposed surface of the conductor Where it is extended away from contact with the refrigerant and does not form an integral part of the refrigerant containing bunker space.

(B) Ways for controlling the heat transfer from the conductor to the refrigerant. This forms probably the best method of controlling the temperature of the desirable large heat-absorbing conductor surface chilled only a few degrees below the refrigerated area, when using low temperature solid refrigerants like solid carbon dioxide.f This method operates by controlling the spaced relation of the conductor and the solid refrigerant. When the ice is hard down on the bare conductor, a maximum heat flow results, and consequently the lowest refrigerating temperatures for a given apparatus. If the ice is held more than AU from the conductor, there is not much effective heat transfer. However, from the point of contact to about 1A," away from the conductor provides a region where the surface of the solid CO2 can be held in a, controlled heat exchange relationship with the conductor by which the temperature of the chilled conductor, and, therefore, the refrigerating temperatures, can be varied at will. lThe first break in the direct contact of the ice with the conductor will result in a marked resistance to the heat ow; and every change of a fraction of an inch toward or away from the conductor will speed up or retard the heat flow correspondingly. This action is in accordance with the ordinary physical laws of heat flow already referred to. Heat is accumulated by the conductor land brought by it to that part of its surface opposing the ice surface. The amount of this Iheat taken up by the ice varies directly as the temperature.

differential between the surface of the ice and the conductor surface opposed to it; this differential in turn being largely determined by the distance between the ice and conductor and the substance .filling this space. These last two factors are easily varied duringV the operation of a given refrigerating apparatus, and, therefore, provide a most eflicient means for regulating the refrigerating temperatures. The first factor,/or temperature differential, changes asa result of the variation of thel other two factors and so need only be regarded as a corollary indication of what has taken place.

Thus it is the nature and amount -of the substance between the ice and the conductor that governs in this method of temperature control.

The rate of heat transfer varies with the substance. Also the, rate will vary with the thickness or distance between the ice and the conductorthe further apart the less heat transmitted, and vice versa. `The substance can bev of any convenient character, preferably a solid, or a uid like air or CO2 gas, or a non-freezing liquid, or a combination of substances, depending on the means used for varying the amount of the substances. The substance may be:

(1) Asolid Iin unit form such as sheets of paper, compressed board like cardboard or 3/8 thick pieces of pressed wood, or sheets of metal. These may be put into place tothe required thickness when putting the ice into the bunker and changed by lifting out and replacing the ice; or

raised. In operation this formcan function by alternately lowering the ice hard down to take up the heat ata higher rate than required and then raising the ice far enough away to take less heat than required, the action being controlled by a thermostat and resulting in the average heat ow required. Here the substance forming the resistance to the heat flow is a solid or a fluid (CO2 gas and air) or a. varying combination of the two. Or as -is more usual, this form can function by having the supporting trol by hand-operated mechanical elevating means. The spaced support for the ice can also means, under thermostatic control-from the refrigerated space, take a stable position, holding the ice in approximately uniform heat-exchange relation with the conductor changing slightly from time to time to meet changing conditions in the refrigerated space, etc. Or this stable position may be achieved without thermostatic contake the form of a hollow chamber between the ice and the conductor which is filled, or partially lled, with a non-freezing liquid, suchy as alcohol,

'from the refrigerated space, to permit the ice to melt more rapidly at these vpoints and the whole ice mass to be lowered nearer the conductor, thus increasing the rate 0f heat flow as necessary to keep the conductor chilled to the required temperature. Any conveniently controlled source of heat may be used for this purpose including electrically heated resistance wires fixed to the supporting insulated areas; or a uid, such as air or alcohol circulating in a closed pipe system which picks up heat from the refrigerated space, or outside it, and discharges this heat to lthe ice through that part of the system on which the ice .is supported, namely the insulatedsmall areas,

having a thermostatic valve located in the system; or heat may be taken up from the solid metalliciconductor or from-th`e air of the refrigerated space Aby a miniature solid metallic conductor system and transferred as required to the support areas in any of the ways used in the principal heat transfer for refrigerating purposes; or heat may be supplied as required to the insulating supporting areas from the controlled inter-action of suitable chemicals. This way of regulating the heat-resisting space between the ice and the conductor uses principally a gas and air-filled space and a balanced condition such as is described above, although it may also operate by the alternate hard on and off action also described above. This method is based on a fact I have discovered that solid CO2 when supported on small insulated areas over a metallic conductor which is a source of heat will not melt down over the supporting areas and approach the conductor so long as the supports are colder than the conductor surface opposed to the ice.

These two bzjoad ways, which I have described under A and B above, of controlling the refrigerating temperature when using solid CO2 as a refrigerant in combinationwiththe solid metallic conductor are all involved in the general principle of setting up a conductor resistance in the path .of heat ow formed by the conductora principle which is disclosed in my pending application Serial No. 467,999, led July 14, 1930. ,A more detailed description is included in this application and various improved means which I have developed for, carrying out the principle are now claimed."

The more complete disclosure in this application both of the principles of the solidmetallic conductor and of the conductor resistance is made for the purpose of providing a basis for the wider use of the invention. There are illustrated herewith, and claims are made for, a few of the .particular forms and improvements which are embodied in actual refrigerating apparatus used at the present time. But I do not wish to limit myself to theseA specific designs as almostevery commercial use of a solid refrigerant for the refrigerated storage or transportation of perishable foodstuffs, or other refrigerating purposes, calls for a different design and a differentway of applying the principles of the invention. There are always different refrigeratingtemperatures to be considered, different rates of heat transfer, different forms of storage spcaes and different forms of solid refrigerants and bunker capacities-and the conductor must be constructed accordingly.

The attached drawings illustrate various preferred forms of the solid metallic conductor used with various solid refrigerants, also various preferred means for controlling the rate 0f heat transfer from the refrigerated space to the refrigerant via the conductor, all of which embody advances madesince the filing of my application Serial No. 467,999, filed July 14, 1930.

Figures 1 vto 3 inclusive show a conductor arrangement =for storage compartments, railroad containers, and truck bodies where a strong air circulation is required and to meet the widest range of uses, particularly where a warm lading must be cooled down quickly. Here the conductor 3 is in the form of a thick walled plate forming the bottom and one side of the ice compartment. The plate carries heavy fins closely spaced, formed integrally with the plate and of the same metal, to obtain the largest possible amount of heat absorbing surface. The bottom conductor wall is slanted toward the side to keep the ice in contact with both when desired. Fig. A1 shows ay vertical section of such an apv paratus arranged for water ice or brine ice. The numeral I indicates the conventional insulated I casing surrounding a refrigerated compartment, 2 being the enclosed space to be refrigerated, while 4 indicates the solidvrefrigerant in contact with the bottom and side walls of the bunker formed by the metallic conductor 3. An insulated bafrle 25 forms an open ended duct in which the air can 'circulate by natural convection over the conductor surfaces. Sheet metal 26 is bent around in this passage to guide the air and catch the condensation. A valve 21 can be used when desired to regulate the air ow. At 28 are shown holes through the conductor to permit draining oi the meltage. Fig. 2 shows the ice compartment of Fig. 1 arranged for air circulation over the ice at the same time as over the ns. 'Ihis is sometimes desirable. to obtain a maximum circulation when first cooling down a warm lading with water ice or brine ice. A wire mesh screen at 29 and 29a permits this air circulation over the ice. Fig. 3 shows the ice compartment of Fig. 1 arranged for use with dry ie. The movable insulation 24 is shifted across to a position between the ice and the vertical conductor wall in order to force the principal heat exchange between the conductor and the ice down to the bottom surface of the ice where it cank be controlled by conductor resistance 5.

Figures 4-6 inclusive show vertical sections of conductor refrigerating units which can conveniently be built separately from the refrigerated compartment, and can be bolted into place in any desired position. Figure 4 corresponds exactly to the ice compartment and conductor construction just described under Fig. 1; a metal sheet for guiding the air being shown at 30, and a drain pipe at 3l. Fig. 5 shows the same unit tted with an electric driven fan 32 by which the air can be made to circulate in either direction and a higher rate of heat transfer from the air to the ns obtained. Fig. 6 shows the same type of unit constructionfadapted for dry ice and with the addition of a" gas outlet 33 whereby the CO2 gas can be piped to the outside of the refrigerated compartment when desirable.

Figures 7 and 8 show a convenient preferable form of aluminum nned conductor, manufactured by the extrusion process. The back 6l is made sufficiently thick to handle the required amount of heat the required distance. The ns 62 can provide any required amount of heat absorbing surface. The sections are cut to the specified length and joined together by the male and female joints shown at 63 and 64. In Fig. 8 the ns 62` are shownribbed to give the greatest possible amount of heat absorbing surface for a given amount of metal. Thousands of extruded aluminum fins of this form have been used with great success commercially in apparatus designed by the applicant for use with solid refrigerants and under the principles described in this application.

I claim: l. .In refrigerating apparatus, cooled by a solid refrigerant such as water ice, brine ice, or solid carbon dioxide, a solid metallic heat conductor presenting surfaces for heat absorption from the refrigerated space or material of greater area than the surfaces of the conductor presented in the refrigerantcontaining space for heat transfer to the refrigerant; the capacity of said conductor to transmit heat along in the direction of the refrigerant from the said surfaces presented for heat absorption being sufficient, by reason of its thickness in cross section, to maintain the said heat-absorbing surface areas at `a lower temperature than that of the refrigerated space or material; said conductorbeing formed of a plate of a good heat-conducting metal which forms the bottom and a side wall of the refrigerant-containing space, presenting a substantially flat surface in the refrigerant-containing space for heat transfer directly to the solid refrigerant, said plate having finned bottom and side surfaces for absorption of heat derived from the refrigerated space; and a' continuous baille embracing said finned surfaces and having openings at both ends whereby air from the refrigerated space may circulate in contact with the heat-absorbing surfaces of the conductor.

2. In refrigerating apparatus, cooled by a solid refrigerant, a compartment adapted to contain thel material to be refrigerated; a refrigerantcontaining bunker within said compartment; a solid metallic heat conductor of a good conducting metal forming the bottom and a side wall of the said bunker and having heat-absorbing metal ns on the outside surface of' said bottom and side walls, the said bottom wall forming a support for the solid refrigerant; and a continuous baille embracing said nned surfaces and having openings at both ends whereby air from the refrigerated compartment maycirculate in contact withthe finned heat-absorbing surfaces of the conductor.

3. A refrigerating unit for use with solid refrigerants comprising a refrigerant containing bunker and means for continuously draining same; a solid metallic heat conductor of good heat-conducting metal forming the bottom and a side wall of the said bunker and having heatabsorbing metal vfins on the outside surface of said bottom and side Walls, the said bottom wall forming a support for the solid refrigerant; 'and acontinuous baile embracing said finned surfaces and having openings at both ends whereby air from the space to be refrigerated may circulate in contact with the finned heat-absorbing surfaces of the conductor.

4. A refrigerating unit for use with solid refrigerants comprising. a refrigerant containing bunker and means for continuously draining same; a solid metallic heat conductor of good heat-conducting metal forming the bottom and a side wall of the said bunker and having a nned outside surface, the said bottom wall forming a support for the solid refrigerant; and a continuous baiile embracing said finned surfaces and having openings at both ends whereby air from the space to be refrigerated may circulate in concontinuous baiile embracing said finned surfaces andhaving openings at both ends whereby air from the space to be refrigerated may circulate in contact with the finned heat-absorbing surfaces of the conductor, together with a valve for controlling the air circulation over the said finned surfaces.

6. A refrigerating unit for4 use with solid refrigerants comprising a refrigerant containing bunker and means for continuously draining same; a solid metallic heat conductor of good heat-conducting metal forming the bottom and a side wall of the said bunker and having finned outside surfaces, the said bottom wall forming a support for the solid refrigerant; and a continuous bafe embracing said finned surfaces and having openings at both ends whereby air from the space to be refrigerated may circulate in contact with the finned heat-absorbing surfaces of the conductor, together with means located between the solid refrigerant and the metallic conductor to restrict and control heat transfer;

ous baille embracing said finned surfaces and having openings at both ends whereby air from the space to be refrigerated may circulate in contact with the finned heat-absorbing surfaces of the conductor, together with openings at the top and bottom of said bunker through which air from the space to be refrigerated may circulate in direct contact With the solid refrigerant.

8. A refrigerating unit for use with solid refrigerants comprising a refrigerant containing A bunker and means for continuously draining same;'a solid metallic heat conductor of good side wall of the said bunker and having a finned outside surface, the said bottom wall forming a support for the solid refrigerant; and a continuous baffle embracing said finned surfaces and having openings at both ends whereby air from the space to be refrigerated may circulate in contact with the finned heat-absorbing surfaces of the conductor, the said finned metallic conductor being formed of cast or extruded sections assembled by means of male and female joints along their lateral edges.

9. In refrigerating apparatuscooled by a solid refrigerant such as water ice, brine ice, or solid carbon dioxide, a solid metallic heat conductor presenting extended surfaces for heat absorption from the space or material to be cooled of 'greater area than the surfaces of the conductor presented inv the refrigerant-containing space for heat transfer to the refrigerant; the capacity of the said conductor to transmit he'at along in the direction of the refrigerant from-the said surfaces presented for heat absorption being suicient, by reason of its thickness or mass, to maintain the said heat-absorbing surface areas at an effective refrigerating temperature lower than that of the space or material to be cooled, whereby the said heat-absorbing surfaces are adapted to absorb a major amount of the heat transmitted by said conductor; the solid refrigerant being maintained in direct contact with the said conductorand the said extended heat-absorbing surfaces being formed by fins metallically joinedto the remaining portions of the conductor; together with a wall cooperating with the said extended heat-absorbing surfaces to form open-endedv ducts through which air may flow `from the refrigerated space in contact with said surfaces, and mechanically-operated means, such as a blower or fan, to accelerate the flow of .air through said ducts.

10. In refrigerating apparatus, cooled by a solid refrigerant such as water ice, brine ice, or solid,l carbon dioxide, a solid metallic heat conductor presenting extended surfaces for heat absorption from the space or material to be cooled of greater area than the surfaces of the conductor presented inthe refrigerant-containing space for heattransfer to the refrigerant; the capacity of the said conductor to transmit heat along in the direction of the refrigerant from the said surfaces reason of its thickness or mass, to maintain the said heat-absorbing surface areas at an effective refrigerating temperature lower than that of the space or material to be cooled, whereby the said heat-absorbing surfaces are adapted to absorb heat transmitted by said conductor; the solid refrigerant being4 maintained in heat-conductive relation with the said conductor; and the said extended heat-absorbing surfaces being formed by fins metallically joined to the remaining portions -vof the conuductor; together with a wall cooperating with the said extended heat-absorbing surfaces to form open-endedducts through which air may flow from the refrigerated space in contact with said surfaces, and mechanically-operated means to vaccelerate the flow of air through said ducts.

11. In refrigerating apparatus.- cooled by a solid refrigerant such as Water ice, brine ice, or solid carbon dioxide, a solid metallic heat conductor presenting extended vsurfaces for heat absorption from the space or material to be cooled of greater area than the surfaces of the conductor presented in the Vrefrigerant-co'ntaining spacev for heat transfer to' the refrigerant; the capacity of the said conductor to transmit heat along'in the direction of the refrigerant from the said surfaces presented for heat absorption being sufficient, by reason of its thickness or mass, to maintain the said heat-absorbing surface areas at an effective refrigerating temperature lower than that of the space or material to be cooled, and means for circulating a fluid surfaces. Q

12. In refrigerating apparatus, cooled by a solid refrigerant such as water ice, brine ice, or solid carbon dioxide, a solid metallic heat conductor presenting extended surfaces for heat absorption from the space or material to be cooled of greater area than the surfaces of the conductor presented in thel refrigerant-containing space for heat transfer to the refrigerant; the capacity of the said conductor to transmit heat along in the direction of the refrigerant from the said surfaces presented lfor heat absorption being sufcient, by reason 'of its thickness or mass, to maintain the said heat-absorbing surface areas at an effective refrigerating temperature lower than that of the space or material to be cooled, and mechanically operated means for circulating a fluid to be cooled over said extended portions.

13. In refrigerating apparatus, cooled by ay from the said surfaces presented for heat ab`V 2,061,778 in the space to be refrigerated over said extended sorption being sufficient, by reason of its thickness or mass, to maintain the said heat-absorbing surface areas at an effective refrigerating temperature lower than that of the space or material to be cooled, whereby the said heat-absorbing surfaces are adapted to absorb a major amount of the heat transmitted by said conductor; the solid refrigerant being maintained in direct contact with the said conductor; and mechanically operated means for circulating a fluid to be cooled over said extended surfaces.

14. A method of refrigeratingwhich comprises transferring heat from a space to be cooled by absorbing heat from said space on an extended portion of a solid metallic heat conductor which is in heat-conductive relation with a solid refrigerant and which has a capacity to transmit heat along in the direction of the solid refrigerant from the surface exposed for heat absorption sufficient,l by reason of its thickness with respect to the heat conductivity of the metal from which it is formed and the area of the extended surface exposed for heat absorption to maintain said heat absorbing surface at an effective refrigeratving temperature lower than that of the space to be cooled, and setting up a secondary heat transfer from the space to be cooled to the solid refrigerant by thermal circulation of air from `said space directly over the solid refrigerant.

EDWARD RICE, JR.

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