US 1980089 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
NOV. 6, E, RlCE, JR 1,980,089
REFRIGERATION 5 Sheets-Sheet l Filed July 7, 1933 v af. ff
Nov. 6, 1934. E RICE, JR 1,980,089
REFRIGERATION Filed July '7, 1933 3 Sheets-Sheet 2 Nov. 6, 1934., E, MCE, JR 1,980,089
` REFRIGERATION Filed July 7, 1933 i 5 Sheets-,Sheet 5 'I'.'IIIIIIIL l a, J J ffy. 9.
Patented lNov. A(A5, 1934 -NTED STATES P A'rrlvr I OFFICE 1,980,089 REFRIGERATION Edward Rice, Jr., NewYork, N. Y. Application July 7, 1933, serial No. 679,435 c claims.' (ci. ca -91.5)
This invention relates to improvements in refrigerating methods and apparatus for use with solid refrigerants, such as solid carbon dioxide, water ice, brine ice, jetc.
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 the result that 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'a solid refrigerant at the same rate as to comparativelylarge quantities, the refrigerant being -used for cooling a iiuid such as air or Water, thus making it possibleto use smaller quantities of the refrigerant than heretofore for a desired rate of Aheat transfer and to maintain the same rate of heat transfer substantially as' long as any V`of the refrigerant remains.
Another object is to provide a means for maintaining substantially constant temperatures in the refrigeration of perishablefoodstuis within a range of approximately 0 F. to 50 F. when using solid refrigerants, such as solid CO2 or brine ice of a considerably lower temperature than that required in the refrigerating process.
More specifically an object is to provide a ,solid metallic heat conductor between the area or mass to be refrigerated and the solid refrigerant with sumcient surface in a uniform or controlled heat exchange relation with the refrigerant, with suflicient surface in heat exchange relation with the refrigerated area or mass, and with sumcient heat transfer capacity vor cross section to pick up and transfer to the refrigerant the maximum The heat transfer Aalong the conductor-or af combination of these meansfor the purpose of regulatingthe temperature of the refrigeratedv area,
Another specific object isvto provide a solid metallic heat conductor `of the above character- 4isticsvvhich is commercially practicable in refrigerated storage and transportation of perishable foodstuffs, and which can be constructed of cheap available metalssuch 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 heatabsorbing and heat-emitting surfaces and heat transfer capacities without interfering withthe usual and ordinary practices in construction of refrigerated storage and transportation units using solid re'frigerants, such as househol refrigerators, ice cream cabinets, motor truck bodies, railroad cars and containers, etc.
Figures 1 to 4, inclusive, and la are diagrammatic vertical sectional views of a refrigerated compartment incorporating various embodiments of my invention, and y Figs. 5 to '14, inclusive, are respectively di- 80 agrammatic fragmentary sectional views illustrat- Q ing other modications within the Scope of my invention. i
During the past two summers I have designed and had constructed and commercially used a V variety of improved forms of refrigerating apparatus for the storage and transportation f perishable foods, ice cream etc. which employ as the source of refrigeration solid refrigerants such as solid carbon dioxide, waterice, or brine 9c ice in combination with an extended solid metallic heat' conductor which is chilled either by direct -contact with the solid refrigerant or4 by 4some other uniform or controlled heat exchange relationship with the refrigerant.V r 95 The characteristics of this metallic heat conductor must be such that (11,)b it forms a prin- `cip'al path of heat transfer between the refrigthe solid refrigerant the heat absorbed by the surface extended beyond that point, at the temperature differential ranges used-in any given apparatus between the heat 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 solidrefrigerant, this surface always being smaller than the surface exposed to and ab-l sorbing heat from therefrigerated area.A
This general method of using solid refrigerants is fully disclosed and claimed in my pending application Serial #467,999, filed July 14, 1930, and various forms of apparatus forfcarrying out the method are there described. In thisy 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 imprpved forms of the conductor and ways of using it; I .y
The use of this metallic conductor conforms to the usual and well known principles of heatabsorption and emission by, and transfer through, a solid homogeneous material. For intemperature say of 36"to 44 F. by direct contact with ay surface of the ice. This conductor can in turn chill the air of the refrigerator to say an average of 47 F. in an 80 room. To accomplish this approximately 144 B.y t. u.s vper hour must be transferred from the air of the refrigerator to the ice, or sufficient to melt` one pound of ice per hour. Where air circulates by `condition A(d) above.
natural convectionover 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 cool-- ing surface can be absorbed. Therefore about fifteen square feet of chilled conductor. surface is exposed to the air at an average' temperature vof 40 F., thus absorbing approximately 15 sq. ft. x 11/2 B. t. u.s per hour x 7 F. differential-"- 157 B. t.l u.s per hour-this meets condition (b) Next a surface area of Athe conductor do not change.
tact with the conductor then condition jc) above becomes an absolutely essential consideration in constructing a conductor for use in this method of refrigeration. After means are provided to get the heat into the metal conductor, by providing a necessary area of chilled surface, and to get the heat out of theconductor to the solid refrigerant,vby 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 mostV adverse conditions of actual use. This thickness is determinedv 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 of heat transfer is established for all the available metals and can be easily ascertainedin the usual physics handbooks. Briefly for any given metal it var ies 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"I thick for the same temperature differential? or ap-f proximately the same amount of heat will be transferred per.hour by conductor. plates, other factors being equal, made of V3" copper, 1/4'. alum num, or 1%" iron. It is to be expected that these rules can not be very reliable for voverall temperature differentials of less than 2 or 3 F. or more than 20'o to 30; or for excessively long distances, say over 6 or 8 feet; or for excessively thinor thick conductors,say a conductive capaciis thick 'to take care of extreme conditions of use,
and once constructed its heat transfer properties4 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 refrigerants, such as the transportation and storage of perishable foodstus--it' is must be in direCt'COIltaCi (in the present npossible to construct refrigeratingapparatuson a fraction of the Asurface absorbing heat from the air; and in this fact lies the great practical advantage`j in vthis method -of refrigeration, as well as one of the principal objects of the inven` tion, as it permits satisfactory refrigeration with small amounts of solid refrigerant. There is no exact physical data covering this heat transfer stance) with the ice. This Surface-need be Only. the principles described above that is a great improvement over anything previouslyknownin the art for use-with solid refrigerants. L
In effect suchapparatus provides a new' means of transferring energy orpower in the form of heat, and greatly enlarges the entire field of use for solid refrigerants as a class, as welllas providing a means of temperature control in the from the metal tofa solid refrigerant but experi- )use of solid CO2, often called dry ice, the newly mental observation shows that it is from fty to several hundred times as much perunit 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 byfifteen square feet of conductor surface exposed to convection currents inthe' form of fins-this corresponds to With a given surf "ce exposed tothe air ar developed solid refrigerant which is now coming into such wide commercial use.
Heretofore the transfer of heat to solid` refrigerants has been either- "From the air or other fluid or mass to be cooled directly to the surface of the ice. Here the inexorable laws of physics, governing heat transfer have made it inevitable'that an excessive amountA of the refrigeranthad to be provided to supply 75 certain amount of ice available for minimum con- Osufficient surface to take up the required amounts '150 of heat; and that. there has been a steady rise in refrigerating temperatures due to the reduction in the heat absorbing surfaces of the refrigerant.
Or the heat transfer to the refrigerant has been through the walls of a refrigerant container or support in contact with the refrigerant, the heat reaching the ic'e at the area of contactwhich in some cases provided a constant surface of the refrigerant itself direct for heat absorption, butV which resulted in such small surfaces being available for that purpose that either lvery limited refrigeration was secured or such large containers had to be used asfto be commercially impracticable. When necessary to segregate the ice metal containers wereoften used, usually of galvanized `iron, but the function of the metal was altogether as a convenient material for constructing the containers and segregating the ice to control meltage, etc. and not as disclosed above to form an extended thick walled metalconductor 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 the refrigerant,l not to vfacilitate it,
-and no heat in any useful amount Wasabsorbed by the'metal beyond the actual point of contact with the ice. The thinner the metal was in con# tact with the ice the more rapid the heat transfer; whereas in the extended metal conductor method described above the thicker the metal the more rapid the transfer. f
In .constructing refrigerating apparatus for solid refrigerants using this solid metallic heat conductor it is not necessary that all the heat taken from the refrigerated space or mass be passed through the conductor, but only as stated in condition (a) above that it provide a principal path of heat transfer; although in usual practice most of the heat is thus transferred.
l It is sufficient that the fixed heat absorbing sur- .exposed there, through the walls of the bunker no matter how well insulated.
The previous method of building ice cream delivery truck bodies for use with solid carbon d ioxide-as compared with similar truckV bodi'es now built with a solid metallic heat conductor constructed on the principles described above `forms an excellent illustration of the old case/ of transferring heat directly to the surface of the ice by air circulation or directly through the wall of a metallic ice container at the area, Where it is in contact with the refrigerante-as compared with the new way disclosed in the present invenlv tion. Formerly the insulated ice cream truck compartment included a dry ice bunker in the top back corner made of light galvanized iron with an access hatch through the roof and a galfI vanized double wall inner lining of the compartment built integrally with the galvanized bunker forming a l inch hollow space completely sur` rounding the storage compartment, in which CO2 gas and air from the bunker circulated. There was no direct air and gas access or circulation between the bunker and the storage space. Heat coming in through the walls of the compartment or through the door was absorbed either through the inner lining Wall by the cold CO2 gas or air, which was thus caused to circulate by natural convection over the ice in the bunker, o r it was absorbed by the contacting surface of thel ice through the part of the bunker wallfon which the ice rested. Although the compartment usedl only or 40 lbs. of ice per day at the most yet vthe bunker usually had a capacity over 100 or 150 lbs. in an effort to get enough ice surface for circulating currents to contact to insure refrigeration as"/the ice melted, and the surface decreased, and'to secureincreased heat absorbing ice contact'area with the bottom of the bunker. In a storage compartment about 31/2 ft. X 5 ft. x
2% ft. high this bunker provided, when rst loaded with 100 lbs. of I/dry ice, vapproximately 7 sq. ft. of ice surfacev exposed to,fthe gas and air circulation and 2 sq. ft. in direct contact with the bottom of the bunker. J C
In operation the transfer of heat by the closed gas and air circulation to the ice surface was very linefficient; and the heat transfer across the bot-- tom of the bunker to the contacting ice was con-A ned to such a small intensely cold area exposed to the storage compartment that there was considerable frosting. This, combined with a steadily diminishing ice surface, say a total of 21/2 sq. ft. at 20 lbs. of ice, resulted in a slowly rising temperature, as well as unsatisfactory temperatures even when first iced. Although idely used as the lbest type available at the time these trucks never provided a means of using solid 'CO2 efficiently or to its full possibilities as a refrigerant.
In comparison trucks recently put'on the market with a solid metallic heat conductor, or heat transfer agent, between the dry ice and the Stor--v age compartment constructed as shown in this application have proved entirely satisfactory for holding icecream and other frozen foods in the hottest weather. Using the same insulationA and general storage compartment construction as before the method and means of transferring heat to the ice'is radically different. The entire top' inner wall of the compartment is made of` a copper or aluminum plate suiciently thick to maintain-the required chilled surfaces.
partment of the size mentioned above copper 1/8 inch thick or aluminum A1A; inch' thick forming lthe 4top wall will provide enough conductive capacity' and exposed surface to put the closed compartment to minus 40 degrees F. if required, or
easilyrmaintained zero under the hardest operat- Y ing conditions of heat, door openings, etc.` down to the last 2 or 3 lbs. of ice. This compares with a low of from 0 degrees to 15 degrees F. for the older types of trucks with approximately 20- degrees F. on hot days--too high for ice cream or proper holding of any frozen foods. In the new conductor type the dry ice restsin a small insulated s pace on top of the conductor plate, either directly on the plate to give maximum refrigeration for a given size and capacity of conductor, 'or in a controlled-spaced-distance from the plate whereby the heat transferto the ice is slowed up and controlled for the purpose offregulating theA temperatures in the refrigerating compartment to meet various working conditions.
Vto the ice, with the exception of that comingdirectly through the top of the ice bunker hatch, arrives through `the medium of the solid metallic heat conductor to one surface of the ice. The heat coming in through the roof, outside that through the bunker hatch, is absorbed by the con- 1 ductor plate and taken to the ice before it can reach the storage compartment. The heat coming through the side walls, floor, door and by means of goods storedin the compartment, is transferred by convection and radiation to the conductor plateformingthe inner ceiling and enters along through the plate to the ice. For more severe conditions or for use with brine ice at 6 F. the conductor plate can be thickened and bent down to form part of the vertical side walls as Well as the top. The conductor can take an infinite variety of forms, thicknesses, etc., the one described immediately above being a convenient and successful application to ice cream truck construction. y
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 conductormethod of using solidrefrigerants is that it makes possible a controlled use of solid refrigerants such as solid CO2 which sublimes at a temperature far below those requiredfor ordinary refrigeration purposes, or such as a brine ice that can be made so asto melt from minus 6 degrees to about minus 30 degrees F. As explained above the number of sq. ft. of heat absorbi g conductor surface and the difference in temperature of this surface below that of the refrigerated space determines the amount of heat absorbed lper hour-and thus the effective-refrigerating temperatures. vObviously with a very cold refrigerant, like solid CO2 at minus 110 degrees F., a small conductor surface couldbe '5 does not result in a comparative increase in heat chilled to a very low temperature'and theoreti callyfproduce the same results as a much larger surface at a higher temperature. But in practice-"adiiference in temperature. of more than 8 "or 10 degrees F. between the conductor surface and the air temperature of the refrigerated space transfer from the'ar; and in most cases there is suicient 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 alarge surface high temperature conductor with a low temperature refrigerant like solid CO2. I
This 'large surface chilled a few degrees' below the ordinarily required refrigerating temperatures, which range between 0 degrees and 50 degrees F., can only -be secured when using solid CO2 as 'the refrigerant vby means of some inter.- mediate heat transfer agent such asa circulating gas or liquid, orsuch as a suitablyformed good heat conducting metal. As mentioned above heat transfer to the refrigerant by a gas, including air', is not always satisfactory, and can not be maintained at a suiciently high rate to the comparatively small surfaces of the refrigerant to meet most refrigerating means. -Heat transfer by a circulating liquid such as Lalcohol or in` means to control the rate of h eat flow from the y 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 refrigerants such as solid CO2 are included in the subject matter of this application, and various means, in combination with the conductor, for controlling the heat flow from the-refrigerated area to the solid refrigerant via ,the conductor are included in the claims.y
These various means, as include:
(A)v Ways for controlling the heat transfer from the refrigerated area to the conductor. When the refrigerated area consists of an enclosedspace 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 fluidcanflow past the conductor, then a convenient way of control is to establish manually or thermostatically operated valves in indicated above, I
this confined passage which restrict, or at timesV shut off 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 notform an integral part of the refrigerant containing bunker space. (B) Ways for controlling the heat transfe from the conductor to the refrigerant. This forms probably the best method of controlling the temperature of .the desirable large heat-ab-.f sorbing conductor surface chilled only a few degrees below the refrigerated area, when using low temperature solid refrigerants like solid carbon dioxide. This method operates by controlling the spaced relation of the conductor and th'e solid refrigerant.l When the ice is hard down on the bare conductor, a maximum heat ow results, and `consequently the lowest refrigerating temperatures for a given apparatus. If the ice is held more than 3A" from the-conductor, there is not much effective heat transfer. However, from the point of contact to about 1/2 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. The first break in the direct contact of the ice with the conductor will result in a marked resistance to the heat flow; 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 referredV to. Heat is accu-A during the operation of a given refrigeratingv ap- -paratus, and, therefore, provide a most eicient means for regulating the refrigerating temperatures.- The rst factor, or temperature differential, changes as a result of the variation of the 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 conductor-,the further apart the less heat transmitted, and vice versa. The substance canA be of any convenient character, preferably a solid, or a fluid 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) A solid in unit form.,such as sheets of paper, compressed board like cardboard or lAgt thick pieces of pressed wood, or sheets of metal; These may be put into place to the required thickness when putting the ice into the bunker and changed by lifting out and replacing the ice.
or (2) A suiciently rigid piece of material may be used to support the ice and this material in turn raised and lowered in relation to the conductor by any `convenient mechanical elevating means operated by hand, or by automatic power applied by the action of a thermostat located in the refrigerated space. In this form the maximum heat ow can occur when the movable support means is in its lowest position, and a diminishing heat flow results as the ice is raised. In
operation this form can function lby alternatelyv having the supporting means, under thermostatic control from the refrigerated space, takev a stable position, holding the ice in approximately uniform heat-exchange relation with the con-` ductor changing slightly from time to time to meet changing conditions in the refrigerated space, etc. Or this stable position may be achieved without thermostatic control by handoperated mechanical elevating means. The spaced support for the ice can also take the form of Ia hollow chamber between the ice yand the conductor which is filled, or partially filled; with a non-freezing liquid, such as alcohol, the levelv of the liquid being regulated by a thermostatically controlled feed.l When it is full of liquid, maximum heat transfer results. Wheny the liquid is lowered,'the gas lled space above the liquid gives added resistance to the heat flow.
or (3) Relatively(A small ice supporting can be set up on the conductor whereit is opposed to the ice surface, well insulated against heat flowfrom the conductor, and sumcient heat, applied .to these areas under thermostatic control from the refrigerated space, to permit the ice to melt more rapidly at these points and the whole'V ipe mass to'be lowered nearer the conductor, thus increasing the rate of heatl flow as necessary ,tof
keep the conductor chilled Ato the required temperature. Any conveniently controlled source of heat may be used for this purpose including electrically heated resistancewires xed'to the supporting insulated areas; or a huid, suchfas air or alcohol'circulating in a closed `pipesysteln d which picks up heat from the' refrigerated space, or outside it, and dischargesthis heat to the vice through ,that part of the system on which thelc'e is supported, namely the insulated small areas,
having a thermostatic valve located in the, sys?" tem; or heat may be taken up from the solid metallic conductor or from the `air of the refrigerated space by a miniature solid metallic conductor system and transferred as required to the support areas in any of the ways useNdVinthe principal heat transfer forv refrigerating purposes; or heat may be supplied as required to theinsulating supporting areas from the controlled interaction of suitable chemicals. This way of regu- -lating the heat-resistingspace between the .ice
and the conductor uses principally a gas and airfilled space and a balanced condition such as is described above, although it may also operate scribed above. This method is based on a fact I have discovered that solid CO2 when supported on small insulated areas over a` metallic conductor point beyond its pointhof contact with the refrigf erant in order to form a. controlled resistance to the heat flow similar to the resistance-between the ice and the conductor described above in para-A graph B. The break must be so located. and sufflciently great as to cut down the heat flow below the minimum required for refrigeration purposes andthe controlling means for closing this break must be adequate to increase the heat flow to the maximum requirements. For instance a break of, one-half inch or oneinch may be provided and the break mechanically adjusted or closed by hand or thermostatically controlled means, or a suitable separate heat-conducting means automatically moved into place as required. l One way f regulating the heat ow across the break, or resistance interposed in the conductor itself, is to provide a short length of flexible metallic heat conductor which is moved in and out of contact with the conductor, preferably being fastened permanently to 'one side of the break and ,moved by thermostatically controlled means in and out of contact with the other side, or maintained in a balanced heat-exchange position with the conductor on the other side of the break. Such a. flexible metallic conductor section can be formed from a iiexible at copper cable made up of small i 110 by the alternate hard on and off action also demore consistently because the flexible part can.
be pressed up hard against the rigid part of the woven copper wires and which is thick enough to possess in eHect the heat transfer capacity of the conductor itself and still have considerable exibility of movement. rllhis form is desirable as there is of necessity considerable resistance to .heat ow across any break in the conductor and the mending of the break should be over as large an area as possible to cut down this resistance sumciently. In'using copper and aluminum for the conductor in solid'sheet or casting form, andY also using thel same form for connecting the break, lit is very hard to make this contact accurately and consistently over a suiiicient area because of the tendency of the metals to warp, but if the nexible section as described i-s interposed, a larger area of close contact can be maintained conductor to overcome the surface irregularities and other causes of resistance to heat flow. This is` an invaluable feature because the rst small break-in the contact of the two metallic faces sets up a large resistance to the heat flow, just as the rst break between the solid refrigerant and the metal conductor also does.l
These three broad ways, which I have described under A, B and C above, of controlling the refrigerating temperature when using solid CO2 as a refrigerant in combination with the 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 conductor--a principle which is disclosed in my pending application Serial No. 467,999, filed July 14, 1930.
myself to these specific designs as almost every 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 different way of applying the principles of the invention. There are always different refrigerating temperatures to be considered, different rates of heat transfer,
ferred forms of the solid metallic conductor used with various solid refrigerants, alsovarious pre-Q,
ferred means for controlling the rate of heat transfer from the refrigerated space to the re-V frigerant via the conductor, all of which embody advances made since the ling of my application Serial No. 467,999, filed Ju'ly14, 1930.
Figures 1 to 4, inclusive, and la-show designs particularly adapted for use of dry ice or brine ice in large storage compartments or in truck.
bodies and "railway containers; In Fig. 1, the conventional insulated casing is indicated by the reference numeral 1, this casing embracing the storage compartment 2. 3 is a metallic conducl tor formed preferably of a single sheet of vcopper recense or aluminum, which in the present instance forms the effective upper wall surface of the refrigerated compartment.. For use with dry ice, this conductor may be of ML" aluminum or 1/8" copper. As illustrated, the conductor 3 also forms the bottom wall of the refrigerant compartment 4, and 4a indicates a mass of thesolid refrigerant supported on the conductor. The refrigerant can rest directly on the conduct-or, as shown in Fig. l, or it can be held in a controlled spacedrelation with the conductor by any suitable form of conductor resistance, such for example as indicated at 5 in Fig. 4. The conductor resistance 5 interposedbetween the refrigerant and the conductor regulates the temperature of the extended heat-absorbing surfaces of the conductor, and
.hence the temperature of the refrigerated space.
While it is preferred to form the conductor of a single continuous sheet, the conductor may be fabricated by welding or otherwise securing relatively small sections together. If so fabricated, however, it is most important that the thickness or cross section is never decreased'as the point of heat transfer with the refrigerant is appreached, as this would form a bottle neck through which the passageof heat would be restricted. Also it is preferable not to make any joints in the conductor except "by welding,vv since if for example two parts of a copper conductor were soldered together, there would be a large .drop of temperature across the joint because solder is a much poorer heat conductorthan copper. In this form'of refrigerated container almost `,100% of the heat abstracted from the refrigerated space reaches the lower surfaces of the refrigerant through the conductor; also the heat \coming through the hottest wall of the compartment, namely, the roof, is absorbed by the conductor without reaching the inside of the refrigerated compartment.' Sometimes for convenience of construction, the conductor plate may be dropped down ,a few inches from the ceiling. This construction is illustrated in Figure la ,wherein the corresponding parts arel designated by the same reference numerals used in Figure land 1n the subsequent Figures 2, 3, and 4.
Fig. 2 shows the same general construction as illustrated in Fig. l modified to adapt it more particularly for use with brine ice. In this case the conductor plate is turned down the sides ofthe `insulated compartment to alford a more extended heat-absorbing surface and the conductor prefl-erably should be thickened to the extent of about 50% on account of the higher temperature of the refrigerant. Since the construction in the embodiments of my invention illustrated in Fig. 2 and also in Figs. 3 and l is essentially the same as that illustrated in Fig. l, the corresponding parts are designated by the same reference numerals.
In the embodiment illustrated in Fig. 3, Ihave provided the conductor 3 with a hinged flap 3a permitting insertion of the refrigerant in the compartment 4 from the inside of the refrigerated compartment 2.
y Fig." 4 illustrates a compartment adapted when l which may drip down from the conductor plate when the higher refrigerating temperatures are used. In operation, when the storage compartment and its contents are cooled down to a steady state, the circulating air goes up at the ends and down the center, as indicated by the arrows. However, during the cooling-down operation, the circulation as shown is reversed. This apparatus will operate at frozen temperatures with dry ice directly on the conductor, or at above freezing using dry ice with a conductor resistance 5 as shown, or with brine ice in direct contact with the conductor. l
Figs. 5 to 14, inclusive, illustrate various forms of conductor resistance used for regulating the rate of heat transfer from the refrigerated space to dry ice via the extended metallic conductor.
In Fig. 5, the spaced relation, or thickness of conductor resistance, between the conductor 3 and ice 4 is regulated by means of a vlever 37 which is pivoted at the point 38. The ice is supported on the metal plate 35 preferably of the same material as the conductor 3 previously delscribed, and this plate is`raised or lowered .by
means of the lever 3'7 which may be operated in any convenient manner. The' conductor resistance is ,formed by the plate 35 in combination with the gas-lled space 36. It will be noted that in Figs. 5 to 14, inclusive, I have usedfthe same reference numerals to indicate directly corresponding functional elements.
In Fig. 6 a support for the ice is formed by the hollow tube 39 which is insulated at Y40 from the conductor 3. Tube 39 is lled with a nonfreezing fluid, such as alcohol, and forms a closed circulating system. Incorporated in the down leg of this system is valve 41 operated by a conventional thermostatc bellows 42, which in turn isresponsive to the temperature of the refrigerated space through bulb 43. In operation when the refrigerating temperatures are higher than\ desired the valve 41 remains open, the liquid circulates in the direction of the arrows, the portion of the tube supporting the ice becomes warmer melting that portion of the ice resting on the tube and allowing the remaining portions of the bottom surface of the ice to approach the conductor 3. This action results in an increasedchilling of the conductor, a lowering consequently of the refrigerating temperatures and ultimately a closing of the valve 41 when these temperatures go below the thermostat setting. The ice resting on the tube then ceases to melt so rapidly because the tube is insulated from the warmer conductor and the ice begins to melt back from the conductor proper. The spaced relation, or conductor resistance, between the ice and conductor is thus increased, the refrigerating temperatures gradually go up and the cycle is repeated. Any convenient means under thermostatic control may be used to heat the insulated ice support, the one described being only one of several preferred forms. Y.. v Figs. 7 to 11 inclusive show various ways of introducing the controlled conductor resistance in the path of the metallic conductor itself.as distinguished from its location between the ice and the conductor. In Fig. '7 the continuity of the metal conductor is broken by the gap 3". This gap is closed by the plate 3 hinged on one side to the conductor 44. Theplate is caused to swing in and out of contact with the conductor surfaces on either side of the gap by means of the conventional therrnostatic bellows 42,which in turn is responsive to the temperature of the refrigerated When the tem,
vto 11 goes through exactly the same operation.
In Fig. 8 the gap is closed by a loosely packed springy material 3 such'fas copper ribbons or shavings. When compressed by the bellows 42 an increased heat'transfer takes place because of the greater density and hence conductivity of the material. When the pressure is released the particles spring apart and the heat transfer lessens. A large coiled spring 46 can be imbedded in the particles to assist in separating them. In Fig. 9 a variation of the make and break plate of Fig 7 is shown. A pair of plates 3'- hinged at 44 are forced in and out of contact with the conductor 3 by action of the bellows 42 working through the member 45 which slides in contact with plates 3'. A spring 46 helps maintain this contact. In Fig. 10 the break is closed by a section of iiexible 'conductor preferably made of woven copper wire. It is secured firmly to the fixed conductor on one side of the break, and is moved into contact on the other side of the bellows. In Fig. 11
the same exible 'conductor section is used in slightly different form and location. 'I'he bellows action is applied by lever 47 which is pivoterd at 48.
Figs. 12 and 13 `show the use of a liquid confined in the conductive path, the level of which controls the heat transfer rate. The liquid level in turn is controlled by the usualthermostaticallyoperated bellows. In Fig. 12 a. conductor resistance 5 is provided between the ice and the conductor in the form of a hollow metal pad filled with alcohol. The pad is connected with a bellows 51 the two forming aclosed fluid system containing a fixed amount of alcohol just enough to completely fill the pad when the bellows is contracted.v A second bellows 42 operates under thermostatic' control from the refrigerated space as previously described to contract and expand bellows 51-containing the alcohol. When the temperature of the refrigerated space goes up bellows 42 expands, bellows 51 contracts and pad 5 is filled with liquid permitting a maximum heat transfer. As the temperature drops bellows 42 contracts, bellows y 51 expands and the liquid 49 in the pad drops Fig. 14 shows a denite break in the conductor path Where the heat transfer across the break is v vprincipally by radiationbetw'een two relatively large opposing surfaces of the conductor. In this apparatus the heat transfer across the break is regulated by means of a series of thin polished bright metal plates 52 arranged on pivots 53 to swing like the leaves of a shutter from a horizontal to a vertical position. When they are in a horizontal position the maximum heat transfer will take place between the opposing faces of the conductor and the refrigerating temperatures will be lowest. When in a vertical position the amount of radiated heat transfer will be cut down by reection from the bright surfaces and the temperatures will be higher in the refrigerated space. The action of the shutters can be controlled by any convenient known mechanical means,y operated by hand or thermostatically under control from the refrigerated space.
1. In refrigeratin'g 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 thev surfaces of the conductor presented in the refrigerant-containing 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 or cross section, to maintain the said heatabsorbing surface areas at a lower temperature vthan that of the refrigerated space or material;
said heat-absorbing surface areas being formed by a substantially horizontal thick metal plate located at the top of the refrigerated space, and the solid refrigerant being supported by a portion only of said solid metallic conductor.
2. 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 refrigerant-containing 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 suicient, by reason of its thickness or cross section, to maintain the said heat-absorbing surface areas at a lower` temperaturevthan that of the refrigerated space or material; said heat-absorbing surface areas being formed by a substantially horizontal thick metal plate located at the top of the refrigerated space,
. and the solid refrigerant being'supported by a portion only of said solid metallic conductor, to-
gether with means for access to the refrigerantcontaining space through a wall of the refrigerated space, or from within the refrigerated space through the said conductor plate.
3. In refrigerating apparatus, cooled bya 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 vthan the surfaces of the conductor presented in the refrigerant-containing space for heat transfer to the refrigerant; the capacity'of said con.
plate located at the top of the refrigerated space, and the solid refrigerant being supported by a portion' only of said solid metallic conductor, together with a wall vertically spaced below the said heat-absorbing surface areas of the conductor plate to form an open-ended duct through which air from the refrigerated` space may circulate `in contact with the said heat-'absorbing surface areas.
4. In refrigerating apparatus, cooled by a solid refrigerant such as water ice, brine ice, or solid carbon dioxide, a solid metallic heat conductor presenting surfacesl for heat absorption from the refrigerated space or material of greater area than the `surfaces of the conductor presented in the refrigerant-containing 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 or cross section, to maintain the said heat-absorbing surface areas at a lower temperature than that of the refrigerated space or material; said heat-absorbing surface areas being formed by a substantially horizontal thick metal plate located at the top of the refrigerated space, and the solid refrigerant being supported by a portion only of said solid metallic conductor, together with means for controlling and regulating the transfer yof heat from the refrigerated space or material to the solid refrigerant, said means being located between the metallic conductor and the solid refrigerant.
5. 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 refrigerant-containing space for heat transfer tothe refrigerant; the capacity ofsaid 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-V orcrossl section, to maintain the said heat-absorbing surface areas at a lower temperaterial; said heat absorbing surface areas being formed by a substantially horizontal thick metal plate located at the top of the refrigerated-space, and the solid refrigerant being supported by a portion only ofl said solid metallic conductor, together with means for controlling and 'regulating the transfer of heat along the metallic conductor in the direction of the refrigerant from the saidv heat-absorbing surface areas, said means being y formed by a break in the metallic continuity of the conductor, and means for varying the heat ow across said break.
6. In refrigerating apparatus cooled by a solidv refrigerant, a space adapted to contain the material vto be refrigerated, a solid metallic conductor located at the top of said'space', and a refrigerant containing bunker located above a portion only of said conductor, the said conductor being formed by a substantially horizontal plate vwhich forms the principal path of heat Atransfer be-` tween said space and the solidA refrigerant. f. EDWARD RICE,v Jn.'