US2641110A - Method and system for refrigeration of railroad cars - Google Patents

Description

R. D. PIKE 2,641,110

METHOD AND SYSTEM FOR REFRIGERATION 0F RAILROAD CARS June 9, 1953 5 sheets-sheet 1 Filed Aug. l0, 1950 5 Sheets-Sheet 2 R. D. PIKE |,i IIN: .l.l In. Qlillll June 9, 1953 Filed Aug. 1o, 195o IN1/EN TOR. ROBERT D. lo/KE Arran/sys June 9, 1953 R. D. PIKE 2,641,110

METHOD AND SYSTEM FOR REFRIGERATION OF' RAILROAD CARS Filed Aug. 10

uNKr-:n TEMPERATURE 'F 1950 5 Sheets-Sheet 3 I I I I I I I I NUMBERS INDICATE LB NH4 NO3` PER IOO LB ICE I I I 2O O 5 IO I5 2O 25 50 35 LB NA CL PEE |00 LB ICE INVENTOR. R085@ T D. P//IE ATTORNEYS Patented June 9, 195g METHOD AND SYSTEM FOR REFRIGERA- TION F RAILROAD CARS Robert D. Pike, Greenwich, Conn.

Application August 110, 1950, Serial No. 178,603

17 Claims.

This invention is directed to an improvement in method and apparatus for refrigerating the storage compartment of a railroad refrigerator car.

Another object of the present invention is to provide a more economical and eiiicient refrigeration system in a railroad refrigerator car wherein the refrigerants are disposed solely in the ceiling of the car and wherein substantially the entire horizontal door area of the car is available for lading purposes in contrast to those refrigerator cars wherein vertically extending end bunkers sometimes occupy more than ten percent of the available lading area.

Another object of this invention is to utilize in eflicient and economical manner the refrigerant properties of a eutecti-c mixture of sodium chloride, ammonium nitrate or other melting point depressants, and ice disposed in spaced overhead tanks.

Other objects and advantages of my invention will become apparent from the following description of .a preferred form of the invention, reference being made to the accompanying drawings wherein Fig. l is a longitudinal section of my refrigerator car taken along the middle of the car;

Fig. 2 is a fragmentary plan View taken on the line 2-2 of Fig. 3;

Fig. 3 is a View in section taken substantially on the line 3-3 of Fig. 1, but on a larger Yscale;

Fig. 4 is a fragmentary View in section taken on the line 4 4 of Fig. 1, but on a larger scale;

Fig. 5 is a chart showing tank temperatures with various mixtures of water ice, sodium chloride and ammonium nitrate;

Fig. `t is a fragmentary View in section taken on the line t-t-of Fig.V 1; and

Fig. 7 is a fragmentary view in section taken on the line T-l' of Fig. 1.

In United States Letters Patent No. 2,501,141, there is shown a refrigerated railroad car suits able for the transportation of frozen foods or the like at uniform and predetermined low tem-V peratures. The storage compartment of the car there shown was spaced from the inner surfaces of the car to provide air passageways therebe`- tween. A positive circulation of air was provided to effect a symmetrical pattern of transverse and longitudinal, peripheral flow lof air about the storage compartment in cooperative heat transferrelationship vvith a plurality-of low temperature refrigerant bunkers.

in Patent No. 2,501,141, the circulating .air contacts in heat exchange relationship ,end refrigerants of Water ice and salt mixture. The

end refrigerants in the embodiment shown were air permeable ice beds having interstices providing numerous air passages through the bed and giving large surface areas for transfer or" heat from air to ice to allow for the transfer of the latent heat of melting. The circulating air also contacts overhead tanks containing Dry Ice or low temperature eutectic brine mixtures in heat exchange relationship of predetermined character.

Through the use vof the invention hereinafter described, I am able to reduce very considerably the cost of transcontinental shipment of refrigerated food and the like by (-1) increasing the amount of lading area and the eiliciency of the refrigerant system, (2) proportionately reducing the cost of refrigerants, and (3) by providing in the system a exibility of temperature range relative to refrigerant used heretofore unachieved.

Referring now to the drawings, l have shown one form-of my invention embodied in a railroad car IIJ adapted to transport frozen foods or the like in the desired temperature range from about 0 F.5 F. with certain refrigerant mixtures, or in other ranges with other refrigerants.

The car l- .comprises a top Il, sides B2, ends I3 and bottom I4, all of the car walls being insulated in a suitable-manner. The storage area or compartment proper of the car extends substantially the entire length and width of the car. The usual loading doorways I5 are provided in the sides I2.

The floor 20 of the storage compartment may be formed of fioor racks comprised of planks 2| six to eight inches wide mounted on suitable supports 22 which space the rack about six inches above the bottom I4 of the car thereby forming an air chamber 23 between the iioor 251 and bottom I 4. The planks may be Aspaced an inch or two apart to provide air communication between the storage compartment and air chamber 23.

The ends IS `and the `sides i8' of the storage compartment are formed by securing plywood panels or boards to nailing studs (not shown) attached to the inner surfaces of the car, thus providing together with the floor 2G, a storage compartment shell Within the confines of the car.

The ends i6 of the storage compartment are preferably spaced about 5 to 6 inches from the inner surfaces of the car ends i3, thereby forming a ,vertically extending end i'lue 26 -that is in communication with air chamber Z3 as shown in Fig. 1. The side walls llt of the compartment are also spaced from the inner surfaces of the car sides ("2 to provide side wall nues 28 about an inch wide as shown in Figs. 4 and 6. These flues 28 are similarly in communication with air chamber 23 as may be seen in Fig. 6. These side wall fines 28 are disposed in the wall portion of the car located between the dotted lines shown in Fig. 1.

Beneath the compartment floor near the ends of the car are provided fans 30 which are activated by the car axle through connections not shown. There is no spacing between the planks which make up the oor rack in the portion of the latter' which extends from the fans to the compartment end I6. Between the fans the air chamber 23 is in communication with the sidewall ues 2S as shown in Fig. 6.

Beneath the roof of the car at spaced intervals a plurality of overhead refrigerant tanks 36, 38, 40 are provided, the disposition of which is shown in Figs. 1 and 2. Each of' these tanks is comprised of an open sheet metal container 3I secured to the top of the car by appropriate means as by brackets 32, with the opening of the tanks being in alignment with `a pair of hatches 33. The container structures of the tanks extend substantially transversely of the car as is apparent in Fig. 2 and they may be supported at opposite ends by bracket and angle iron assembly or other suitable means.

On the bottom plates of the various tanks are provided metal tansfer ns 34 welded to the tanks, and being preferably about 11/2 deep, and on 3" centers. These ns extend transversely of the length of the car on the centermost pair of tanks 36 and on the intermediate pair of tanks 38. The fins may be omitted for a short distance 39 at the center, as indicated in Fig. 4. The bottom plates of the end tanks 40 are provided with similar fins, except that, as indicated in Fig. 1 and 3, these ns extend parallel to the longitudinal axis of the car.

Disposed beneath the overhead tanks are drip boards or sub-ceiling panels 42 and 42a, as shown in Figs. l, 3 and 4. It will be noted that the drip boards extend to and are secured upon the upper ends of the side wall panels I8 of the storage compartment. The drip boards 42 slope toward the car ends so that any moisture which may accumulate will, upon melting, flow down through the car end flues 26 and be discharged from the car in suitable manner so as not to wet the goods in the compartment. These drip boards 42 preferably extend under the first encountered intermediate tanks 38, although they may be terminated short thereof, extending only so far as the inner edges of the end tanks 40. Beneath the centermost tanks 36 the drip boards 42a preferably slope from the car center toward each side so that ice which may accumulate on them or beneath the tanks will, upon melting drain into side wall flue openings 28 as described hereinafter.

Opposite the ends of the centermost and intermediate pair of tanks 36 and 38 are openings 44 into the side wall fiue area 28 which are substantially equal in length to the full width of the tanks along the length of the car as shown in Figs. 2 and 4. In addition to these openings, I preferably provide two smaller openings 46 into the side wall lues in the region of the doors I on both sides of the car, and also opemngs 48 of about the same size as those in the door region into the side wall flues, the latter openings being located intermediate the tanks 38 and 40 as shown in Fig. 2. These openings 44, 46, and 48, taken together, are suicient in size to handle the volume of air flow necessary for the predetermined proper circulation of the car at a velocity through them which will be adequate to evenly distribute the flow of air into the side wall flues as Will be described further hereinafter.

Between the insulated end walls I3 of the car and the outer ends of the end tanks 40, and between the side walls of these tanks and the inside of the insulated walls I2 of the car are provided spaces or flues 5D and 52 respectively. Similarly, there are provided spaces or nues 54 between the ends of the tanks 36 and 38 and the side walls I2 of the car. The provision of these flues 50, 52 and 54 permits the circulating `air to contact the maximum surface area of the tank for heat transfer purposes.

Interconnecting the tanks 36, 38, and 4D, and extending from the centermost tanks 36 longitudinally to the ends of the car, as shown in Figs. 1 and 2, are a plurality of overflow pipes 56 and 56a adapted to drain brine accumulating in the center tank 36 through the pipes 56 to the tanks 38 and finally through pipes 56a. to end tanks 40. Overilows drains 56D lead from the end tanks 40 vertically down through the end flues 26 so that the brine may eventually be drained out of the car through a suitable connection not shown in detail.

For effective and economical operation of my invention in the transportation of frozen foods l for example which are preferably maintained at a temperature of not over 5 F. or even lower, approximating 0 F., I prefer to provide refrigerants of the following kind in the tanks. The end bunkers 40 and intermediate bunkers 38 are filled through the hatches with the eutectic mixture of water ice and salt, namely pounds of ice to 30 pounds of salt. This mixture in itself gives a brine temperature of about 5 F. The center bunkers 36 are filled with a eutectic mixture of sodium chloride, 30 pounds, and ammonium nitrate, 15 pounds, to each 100 pounds of ice, thereby establishing in these bunkers a temperature of about -15 F. This temperature'will be explained by reference to the chart in Fig. 5.

The air circulation pattern of the car may now be easily explained in view of the description of the car structure set forth above. The fans 30 draw air from the air chamber 23 toward each end of the oar in divergent streams and direct the air longitudinally beneath the compartment floor into the end flues 26 and upwardly into contact with the outer surfaces of end tanks 40. The air substantially envelops the ends and sides of these tanks through the flues 50 and 52, with the major part of the air being constrained by the drip boards 42 to flow in heat transfer relation with the bottom plates and heat transfer ns of the tanks. The then convergently directed air streams at each end of the car are channeled by means of the drip boards 42 into contact with the overflow pipes 56a, against the side walls of the next tanks 38, and beneath these tanks into contact with the heat transfer ns and bottom plates of the tanks, and between the drip boards and the tank bottoms.

From the air streams between the end tanks 40 and the tanks 38 I preferably introduce about 15% of the total stream into the side wall openings 48 leading into the side wall ues. It will be noted that the openings 48 are located at a position which will lead the air through the side wall fiues into the fan inlets. About twice this amount of air is diverted into the larger openings 44 disposed adjacent the ends of the bunk'- ers 38.

The balance of the converging air streams next contact the overflow pipes 56 and then come into heat exchange relationship with the tanks 36 as was described in connection with tanks 38. A similar amount of the streams is diverted into the openings d adjacent the ends of these tanks 36. The balance of the air streams is diverted into the openings 46 in the region of the door by the time it reaches the center of the car. Some air, of course, may be deflected into the storage compartment.

The average velocity of air in all of the openings into the side wall flues is made high enough so as to insure a substantially equal velocity in each, which in turn insures an even distribution of the iiow from one end of the car to the other. It will be noted that the iiow of air in heat transfer relation with the bottom plates of the center and intermediate tanks is a combination of iiow across the heat transfer fins and along them transversely to the openings into the sidewall iiues, which insures a high coeflicient of heat transfer expressed as B. t. u./s. f./hr./F. difference between the air and the surfaces. In addition, both sides of the tanks come into efficient heat transfer relation with the moving air and with the plurality of overflow pipes 56, 56a. These pipes add a not inconsiderable additional surface for heat transfer.

Thus, substantially all of the circulating air passes through the openings into the side wall flues, and from these into the air chamber 23 beneath the floor of the compartment, then back into the fan inlets for recirculation over the same path as just described.

The result of this circulation is to effect a highly efficient transfer of heat from the air into the refrigerants in the top tanks and to substantially completely envelope the goods with this chilled air. Thus, almost all of the heat which flows into the car from the outside is brought into the circulating air and conveyed in it to the refrigerants without there being any` opportunity for the heat to flow directly into the goods within the storage compartment. The shielding air streams follow a course along the length of the car toward the center, with simultaneous ydiversions of the air into the side Wall lues and vertically down to the air chamber 23 beneath the compartment floor and then move divergently toward the fan inlets which are near the ends of the car.

Considering now the use of the refrigerants in the tanks, it will be clear that as the ice in the mixture in the center bunkersr 36 melts, the brine will flow through the overflow pipes toward the opposite ends of the cars and into the intermediate tanks 38. By the use of a plurality of overflow pipes 56, the strong ammonium nitrate brine from the center tanks is evenly distributed and thoroughly mixed in the adjacent tanks 38. Because no ammonium nitrate is added directly to these latter tanks, the concentration of ammonium nitrate in the brine which flows out through the plurality of overflow pipes 56a will be lower than in the pipes 56, and will be, in turn, uniformly mixed in the end tanks 40, giving a slight further rise in temperature of the brine in these end tanks as compared with the tanks 38.

Thus the overflow of the brine from the center most tanks 36 into and through the tanks 38 and 40 provides a diminishing concentration of ammonium. nitrate,y but this. concentration.1 nevertheless, is vsuicient inupractice to reduce 'the term perature in the end tanks 40 Ato about -12"`F which, as indicated by the chart in Fig. 5, necessitates about ve pounds of ammonium nitrate per pounds of ice, with thirty pounds of salt. This is substantially the composition of the brine which drains from the car through the overiiow pipes 56h, which is economical in the use of ammonium nitrate and which gives an average temperature to the heat transfer surfaces of all of the top tanks of about 13 F.

The active circulation of the air which has been described hereinabove in contact with the heat transfer surfaces of the tanks, in View of the .fact that the average temperature of the brine in these `tanks may be maintained, by the means described, at approximately 13 F. makes it possible to deliver frozen foods after transcontinental hauling in the summer season from this car at about 0 F. or less.

It is believed that .the combination of center, intermediate and end overhead tanks having a diminishing temperature from the center to the end, together with a forced circulation of air in series from the end toward the center in heat transfer relation with the tanks, is broadly new in the refrigeration art. By means of my invention there is established in the car a low, uniform temperature in the goods even in the hottest summer weather.

Other refrigerant mixtures can be used in the tanks than the combination described above, and many of the novel features of my invention can be achieved thereby except that the temperature of the goods upon delivery will vary from the temperature range above given. For example, if all of the tanks are filled with eutectic mixture of sodium chloride and water ice, the refrigeration of the car will be equally effective except that the temperature of the goods will range at from 5 to 8 F. upon delivery. Similarly, if it is desired to utilize the car of my invention for transportation of perishables, which should not be held at temperatures much, if any, below 34 F., I may supply water ice alone to all of the top bunkers.

Example In understanding the principles and operation of my invention, the following illustration may be helpful. This example refers to the application of my invention to a superinsulated car with 6-7" insulation and having an overall length of 45 1". There are four intermediate top tanks, 31%" wide (along the length of the car) and 8 6" long (across the car) by about 1'1" deep, and one end top tank on each end, 48 wide (along the length of the car) by about 8 6 long, and having a depth of about 11". In an average transcontinental crossing in the summer with time in transit under load of about 183 hours, the consumption of Water ice en route will be about '28,700 lbs. in order to deliver the goods at about 0 F. in the car of my invention.

The following table summarizes the consumption of refrigerants en route and discardedat the end:

Average temperature brine inltop taiilsend top tanks 12 F., two center top tanks -15 13 F. Average temperature air circulating in heat transfer contact with surface of top tanks -4. 16 F Average temperature difference between outside air and air inside car 78.6 F. Total flow of heat into car, B. t. u./ hr 14, 100

Heat estimated as passing directly into refrigerants through the roof of the car, B. t. u.'/hr Heat which must pass through plate surfaces of tanks,

14,1oo-2,o3o, B. i. 11./hr 12, 07o Areas available for heat transfer: Bottom plates of intermediate tanks, in-

cluding heat transfer fins 180. 85 s. f. Side plates 45. 3 s. f. Bottom plates end tanks with heat transier ns 135. 6 s. f. Area side and end plates 33. s. f.

`Total Temperature difference between brine and circulating air, 13-4.176= v 84 F.

Heat transfer coefficient, B. t. u./s. f./hr./ F.,

394.85X8.84 `"'f v Velocity of air entering openings into side wall flues, feet/ second .-5 7 z... 14.7

Pressure corresponding inches water gage, m .0510

Thepressure imparted by the fans at train speed of 31.4 M. P. H., is about .21" W. G. The fans therefore produce sufficient pressure in their outlets to circulate the air and Vto provide the velocity of entrance'into'A thev tops of the side wall fiues. At the same time, the velocity of en trance into the side wall flues is high enough to distribute the ow'of the air to the center of the car and thence back under the floor racks to thefan inlets;

I wish it to be understood that I do not confine myself to the precise details herein set forth in the preferred means of carrying out my ind vention as it is apparent that many changes and variations may be made by those skilled in the simultaneously passing the streams into a plu# rality of heat exchange zones wherein progressively diminishing temperatures chill the air,

and diverting successive predetermined portions I of the convergent air streams transversely and peripherally whereby substantially all the air of each stream is thus peripherally distributed prior to convergence. Y

2. In a method of refrigerating the storage compartment of a refrigerator car wherein air is drawn transversely about the side wall periphery of the storage compartment, then withdrawn to each end of the car in divergent streams, and circulated vertically about the ends of thecar, the steps comprising directing the thus circulated air streams convergently above the storage compartment and simultaneously passing the streams into a plurality of heat exchange zones of progressively diminishing temperatures to chill the air, and drawing off, transversely and peripherally, predetermined portions from the convergent air streams at spaced intervals whereby each stream is thus substantially distributed peripherally prior to convergence.

3. In a method of maintaining substantially at a predetermined temperature the storage compartment of a double-shell type refrigerator car having the compartment spaced by interconnecting air passageways from the inner surfaces of the outer shell and having'refrigerants disposed in overhead tanks beneath the roof of the car adjacent the storage compartment, the outer surfaces ofthe refrigerant tanks being in heat exchange relationship with air flowing through said passageways, wherein air is drawn in symmetrical patterns about the sidewall periphery of the storage space, then withdrawn to each end of the car in divergent streams, and circulated vertically about the ends` of the car in A 'symmetrical patterns, the steps comprising directing the thus circulated air streams con-v vergently above the storage compartment and simultaneously vpassing the streams into a plurality' of heat exchange "zones of progressively diminishing temperatures to chill the air, and drawing off transversely and peripherally predetermined portions from' the convergent air streams at spaced intervals whereby each stream is thus substantially distributed peripherally prior to convergence. Y

4. The method of refrigerating the storage compartment of a refrigerator car having the compartment spaced by air passageways from the inner surfaces of theends, side walls, roof and bottom of the car, the air passageways being in communication vwith the compartment, and having refrigerants disposed in overhead tanks beneath the car roof and adjacent the storage compartment, the outervsurfaces of the refrigerant tanks being inl heat exchange relation with air flowing through the said air passageways, which comprises: drawing air transversely in symmetrical patterns about the side Wall periphery of the storage compartment; withdrawing said peripherally circulated air to each end of the car in divergent streams; circulating the longitudinally directed air streams vertically about the ends of the car in symmetrical patterns into heat exchange relationship with a ceiling refrigerant disposed, at the ends of the car; directing the chilled air convergently above the storage compartment; diverting a portion of the chilled air laterally and peripherally into the side wall air passageways; passing the balance of the convergent air streams into heat exchange relationship with an inwardly disposed ceiling refrigerant of lower temperature than said first mentioned refrigerant and diverting another portion of said further chilled air laterally and peripherally of thestorage compartment.

5. The method of refrigerating the storage compartment of av refrigerator car havingthe compartment spacedby air passageways from the inner surfaces of the ends, side walls,roof and bottom of the car, the said air passageways interconnecting the compartment and car, Vand having refrigerants disposed in the overhead tanks beneath the car roof and adjacent the storage compartment, the outer surfaces of the refrigerant tanks vbeing in heat exchange relation with air flowing through the said air passageways, which comprises: causing air to flow in symmetrical patterns about the side wall periph-` ery of the storage compartment through the air passageways; directing said peripherally circulated air to each end of the car in divergent streams; circulating the longitudinally directed air streams vertically about the ends of the car in symmetrical patterns into heat exchangerela- 9 tionship with a firstv overhead refrigerant disposed at the ends of the car; directing the chilled air convergently above the storage compartment and concurrently diverting a portion of the chilled air laterally and peripherally into the side wall air passageways; passing the balance of the convergent air streams into heat exchange relationship with a plurality of inwardly disposed overhead refrigerante of progressively diminishing temperature lower than the temperature of said first mentioned refrigerant and concurrently diverting other portions of said further chilled air laterally and peripherally of the storage compartment; and recirculatingl the entire iiow of chilled air thus peripherally distributed about the storage compartment whereby recirculated air dissipates to the refrigerants heat conducted into the car from the outside atmosphere.

6. A railroad refrigerator car comprising: a storage compartment, the compartment being spaced by air passageways from the'inner surfaces ofthe ends, side walls, roof and bottom of the car, the air passageways being interconnected and being in communication with the upper portion of the compartment, a plurality of tanks containingr low temperature eutectic brine refrigerant disposed beneath the car roof and adjacent the storage compartment, the outer surfaces of the refrigerant tanks being in heat exchange relationship with the Vair flowing through said passageways, pipe drains interconnecting the tanks in series from the centermost tanks to each end of the car whereby brine melted in the centermost tanks will flow outwardly to the ends of the car through tanks intermediate thereto; and air impelling means disposed in communication with the air passageway for forcing divergent streams of air toward the opposite ends of the car and through the said passageways.

7. A. double-shell type refrigerator car com,- prisng a storage compartment spaced by air passageways from the inner surfaces of the ends, side walls, roof and bottom ofthe car, the air passageways being interconnected and being in communication with the upper portion of the compartment, air impelling means for circulating streams of air about the periphery of the compartment through the air passageways, overhead tanks spaced apart longitudinally containing eutectic brine mixture refrigerants disposed f beneath the roof of the car adjacent the storage compartment, and pipe drains interconnecting the centermost tank `on each side of the middle of the car with the tanks intermediate the ends whereby brinev melted in the centermostvtanks will iiow outwardly to the ends of the car through the tanks intermediate thereto.

8. A double-shell type refrigerator car comprising a storage compartment spaced by air passageways from the inner surfaces of the ends, side walls, roof and bottom of the car, the air passageways being interconnected and being in communication with the upper portion of the compartment, air impelling means for circulating streams of air about the periphery of the ccmpartment through the air passageways, overhead tanks spaced apart longitudinally containing eutectic brine mixture refrigerants disposed beneath the roof of the car adjacent the storage compartment, and pipe drains interconnecting the centermost tank on each side of the middle of the car with the tanks intermediate the ends whereby brine melted in the centermost tanks will flow outwardly to the ends of the car through the tanks intermediate thereto, the temperatures- `most tank on each side of the longitudinal center of the car with the tanks longitudinally outwardthereof, said' center-most tanks containing a eutecti'c mixture of sodium chloride, ammonium nitrate and ice, and said outward tanks containing aeutectic mixture of water ice and salt, whereby as iceI ini the centermost tanks melts the resultant brine containing a eutectic concentration of ammonium nitra-te fiows outwardly to the ends of the" car through the outward tanks and thereby distributes an effective concentration of ammonium nitrate to the outer tanks, and air impelling means for circulating streams of air about the longitudinal and transverse periphery of the compartment through the air passageways and in heat exchange contact with the surfaces of said tanks.

l0. The method of refrigerating the storage space of a refrigerator car having the said space separated by air passageways from the inner surfaces of the ends` of thev car, from the inner surfaces of the side wallsl and from the bottom and r-oof, the said passageways being interconnected with the said storage space, the car having refrigerants disposed in overhead tanks beneath the roof, the outer surfaces of which are in heat exchange relation with air flowing through the said passageways, such flow of air being induced by a fan' actuated by the running gear of the car, which comprises: causing air to fiow through thev passageways between storage space and the inside walls of the car, further causing such air to flow to each end of the car, circulating said streamsvertically about the ends of the car in heat, exchange relationship with a first refrigerant inl overhead tanks at the ends of the car beneath the roof; directing the chilled air above the storage compartment, diverting said chilled air into the side wall flues between the storage compartment and the inner side walls of the car while causing a portion thereof to pass in direct heat exchange relationship with a plurality of centerwardly disposed refrigerants in overhead tanks of progressively diminishingtemperature lower than the temperature of the refrigerant in the said end overhead tanks, and recirculating the entire ow of chilled air passing through the side wall ilues whereby the said recirculatedair dissipates to the refrigerante the heat conducted into the car from the outside atmosphere.

11. .A double shell type refrigerator car system, comprising a storage compartment spaced by air passageways from the inner surfaces of the car, a plurality of overhead tanks extending transversely of the car and spaced apart longitudinally of the car containing heat transfer fins on their surfaces, and pipe drains connecting the centermost tank on each side of the longitudinal center of the car with the tanks longitudinally outward thereof, saidl centermost tanks being supplied with an eutectic mixture of sodium chloride, ammonium nitrate and water ice, and said outward tanks being supplied with an eutectic mixture of water ice and salt, whereby as the ice in the centermosttanks melts, the resultant brine conthe said outer tanks, and air impelling means for circulating streams of air about the storage compartment and in heat exchange contact with the surfaces of the said tanks and the said heat transfer fins.

12. A double shell type refrigerator car system, comprising a storage compartment spaced by air passageways from the inner surfaces of the car, a plurality of overhead tanks extending transversely of the car and spaced apart longitudinally of the car, and pipe drains connecting the centermost tank on each side of the longitudinal center of the car with the tanks longitudinally outward thereof, said centermost tanks being supplied with an eutectic mixture of sodium chloride, ammonium nitrate and water ice, and said outward tanks being supplied with an eutectic mixture of water ice and salt, whereby as the ice in the centermost tanks melts, the resultant brine containing a eutectic concentration of ammonium nitrate flows outwardly to the ends of the car through the outward tanks, thereby distributing an effective concentration of ammonium nitrate to the said outer tanks and substantially lowering the temperature in the outward tanks, and air impelling means for circulating streams of air about the storage compartment and in heat exchange contact with the surfaces of the said tanks, said air first contacting the outermost tanks containing the brine of highest temperature, and lastly contacting the centermost tanks containing the brine of lowest temperature.

13. A double shell type refrigerator car system, comprising a storage compartment spaced by air passageways from the inner surfaces of the car, a plurality of overhead tanks extending transversely of the car and spaced apart longitudinally of the car, and pipe drains connecting the centermost tanks on each side of the longitudinal center of the car with the tanks longitudinally outward thereof, said centermost tanks being supplied with an eutectic mixture of sodium chloride, ammonium nitrate and water ice, and said outward tanks being supplied with an eutectic mixture of water ice and salt, whereby as the ice in the centermost tanks melts, the resultant brine containing an eutectic concentration of ammonium nitrate flows outwardly to the ends of the car through the outward tanks, thereby distributing an effective concentration of ammonium nitrate to the said outer tanks, whereby temperature of the brine in the centermost tanks is lower than in the outermost tanks, and air impelling means for circulating streams of air about the storage compartment and in heat exchange contact with the surfaces of the said tanks, said air first contacting the outermost tanks containing the brine of highest temperature, and lastly contacting the centermost tanks containing the brine of lowest temperature, the surfaces of said tanks being provided with heat transfer fins in contact with the circulating air to increase heat transfer.

14. The method of cooling air in a closed compartment having a plurality of interconnecting low temperature liquid refrigerant tanks of differential temperatures comprising drawing a continuous ilow of air about the inner surfaces of the compartment, thereby gathering into the circulating air now heat conducted into the compartment from the outside, directing the air flow successively first into heat exchange 'contact-with the higher temperature refrigerant tank and then with the lower temperature refrigerant tank, thereby supplementing the cooling effect of said first heat exchange contact, and concurrently drawing melted brine from the refrigerant tank of lower temperature into and through the tank of higher temperature, thereby maintaining a balanced differential temperature relationship therebetween.

15. In a method of cooling air to a temperature of 0 F. or less in a closed compartment having a plurality of brine refrigerant tanks of differential temperatures wherein the higher temperature refrigerant is water ice and the other lrefrigerant is provided with a eutectic mixture of water ice and a melting point depressant, the tanks being interconnected by pipe drains, the steps comprising directing a forced circulation of air successively into heat exchange contact first with the refrigerant of higher temperature and then with the refrigerant of lower temperature, and draining melted brine from the lower temperature refrigerant into and through the higher temperature refrigerant.

16. In a method of cooling air to a temperature of about 0 F. in a closed compartment having a plurality of brine refrigerant tanks of differential temperatures wherein the lower temperature refrigerant is provided with a eutectic mixture of ammonium nitrate, salt and water ice, and the other refrigerant being provided with a eutectic mixture of salt and water ice, the tanks being interconnected by pipe drains, the steps comprising directing a forced circulation of air successively into heat exchange contact with the refrigerant of higher temperature and then with the refrigerant of lower temperature, and drawing the melted brine from the lower temperature refrigerant into and through the higher temperature refrigerant.

17. The method of cooling air to a temperature of 0 F. or less in a closed compartment having a plurality of interconnected brine refrigerant tanks wherein the tank of lowest temperature is provided with a eutectic mixture of ammonium nitrate, salt and water ice which melts at 15 F. and the other tanks being provided with a eutectic mixture of salt and water ice which melts at .-5" F., the steps comprising directing a forced circulation of air successively into heat exchange contact first with the tanks of higher temperature and then with the tanks of lower temperature, and draining melted brine from the tank of lower temperature successively through the other tanks thereby reducing the temperature in the tanks of higher temperature and lower concentration of ammonium nitrate to about -12 F. while providing an average temperature of the brine in all of the tanks of about 13 F., with consumption of not more than about 5% ammonium nitrate on ice.

ROBERT D. PIKE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,219,570 McCoy Mar. 20, 1917 1,344,057 Moore June 22, 1920 1,421,913 Collins July 4, 1922 2,324,749 Wieden July 20, 1943 2,331,002 Small Oct. 5, 1943 2,501,141 Plummer Mar. 21, 1950

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