US1843026A - Heat transfer system and method - Google Patents

Description

Jan. 26, 1932. F. B. HQNT 1,843,026

HEAT TRANSFER SYSTEM AND METHOD Filed July 17, 1930 2 Sheets-Sheet l f; 5 &

i N INVENTOR.

flan/Ell 16.155005 H aa A TTORNE Y.

Jan. 26, 1932. F. B. HUNT Y mm TRANSFER SYSTEM AND METHOD '2 Sheets-Sheet 2 Filed July 17, 1930.

#fii 4435/ 1/);71/1 J/ 10/ 1 /71 1/ .2 1/7 1/1 a J j/ /z/ INV ENTOR flan/E'khfl/Yanf BY 4WCLM ATTORNEY Patented Jan. 26, 1932 i UNITED STATES PATENT OFFICE FRANKLIN B. HUNT, or omcaeo, ILLINOIS, ASSIGNOR '1'0 DRYICE EQUIPMENT conronA'rIon, 01 NEW YORK, N; Y., A. CORPORATION or DELAWARE HEAT TRANSFER srs'rm AND mmnon Application filed lTuly 17,

My present invention is shown as embodied 1n systems primarily devised for transfer of heat from a region or'space to-be niaintamed at a desired refrigerant temperature to a re-.

: frigerant source, and includes means whereby a very intense, that is to say, low temperature refrigerant may be used for refrigeration at a -much higher temperature, the preferred refrigerant'being solidified carbon dioxide in a various forms, compounds and mixtures, no-

tably approximately pure carbon dioxide, at approximately 110 below zero F. However, various features of. the invention are applicable to variouslower temperature refrigsubstantially below the boiling point of the heat transfer medium.

The heat transfer medium will be selected as preferred. In general, a higher boiling point medium may be employed where the desired refrigerating temperature is relatively high or the heat leaks to be refrigerated 1 againstare relatively small, but its freezing point shouldbe below the temperature of the condenser. The specific medium selected may be any of those known totheart, forinstance, sulphur dioxide (S ,ammonia (NH ,carbon dioxide (CO methyl chloride (CH) 501, propane (C l-I etc." i

The systems shown herein include control of temperature of the refrigerated space by having the heat absorbing-coil or evaporator part of the circuit flooded, not flooded, or partly flooded, either (0,) by locatingsaid evaporator in gravity flow relation to thecondenser and employing a thermostatically operated .v'alve between the coil and the condenser to control, permit or prevent flow-of the-condenserliquid from said condenser into said eya'po'rating coil; or (b) to effect the same control of gravity flow by-moving 1930. Serial No. 468,601.

vapor coil above or below the level 0 the liquid ilrtlie-condenser; or by locating the coil at or above the level of the condenser and providing, a lift line in the form of a small capacity boiler exposed tothe heat of the refrigerated space in such relation that part of the liquid in said lift coil will be evaporated, the incipient bubbling thus produced serving to decrease the specific gravity the of the liquid in the lift line so that it is unbalanced and forced upward by the cold liquid in the condenser and, when the boiling becomes pronounced, the bubbles of vapor will exercise a pronounced air lift effect so that when proportioned and designed to suit the conditions, the main evaporator will be properly charged or flooded with liquid. This will occur when temperatures in the refrigerated-space are too high. Consequently, such liquid flooded into the evaporator will rapidly absorb heat from the refrigerated space, and the resultant boiling of the liquid will maintain the evaporator at constant or controlled temperature according to the internal pressure on the system.

In order to effect further control, said pressure within the system may be prede termined and automatically adjusted by v means of a pressure valve in the llne between the evaporator and the condenser whereby when the internal pressure becomes too low by reason of fall of temperature in the refrigerated space, the return flow of vapor to the condenser will be blocked.

My invention also includes a specific improved arrangement of condenser with referen'ceto solid carbon dioxide as the refrigerant, whereby the rate of heat transfer to the condenser is reduced so that other things .beingequal the temperature of the condenser itself may be substantially higher than that of the solid carbon dioxide refrigerant. This may be of advantage with any .of the above mentioned heat transfer liquids since' has been condensed, is unnecessary.

I operativeness of my apparatus depends mainly on the heat absorbed by the boiling -modifications Fig. 8 is a detail view of condenser contained in Fig. 1.

In Fig. 1 the refrigerated space 1 is shown as enclosed by heat insulating casing which may comprise exterior and interior gas-tight shells 2 with intervening heat insulating ma:

terial 3 enclosing,preferably at a high level therein, a refrigerant container 4 WhlCh may be charged with refrigerant such as solid carbondioxide 5 by removing the hatch 6.

The insulation' i may be very heavy so that only a negligible amount of heat can be absorbed throu h the walls thereof, directly from the re rigerated space, but it is only necessary that this insulation be sufficient so that the refrigerant'efi'ect thus directly exerted upon the refrigerated space 1 will be at all times insufiicient to keep the temperature of the refrigerating space 1 down to the desired maximum. That'is to say, so long as such direct refrigeration is insufficient, the control of the exact desired temperature will reside in my heat transfer system which I will now describe.

The heat transfer circuit comprises a condenser 7, fromthe bottom of which the condensed liquid flows through pipe 8 into the refrigerated space, thence upward through an accelerating heat absorbing coil 9 and through pipe 10 into the top of a boiler 11.

The liquid gravitates to the bottom of this boiler and the vapor therefrom escapes through pipe 12, control valve 13 and pipe 14 back to the condenser 7. While the liquid may be any known or desired liquid such as those above mentioned, we may assume for present purposes that sulphur dioxide (S0 is used. The amount of liquid charged into the system should 'be such that even when I the amount of liquid contained in the condenser 7 and coil 9 is a maximum, there will still be some liquid left in the bottom of the evaporator 11.

The liquid in evaporator 11 is exposed to the atmosphere in the refrigerated space 1 and, absorbing heat from the latter, will evaporate sufiiciently to generate a pressure in the system corresponding to the saturation pressure of sulphur dioxide for .that temperature. The vapor in the condenser -7 will of course be at the same pressure as in 11,:

but being in contact with the cold surfaces of the condenser .7 condense, thereby 'phur dioxide will boil at the same rate that the condenser 7 can condense it. The boiling off of the liquid removes some of the heat from the evaporator 11 and lowers the temperature in the refrigerated space 1. The coil and condenser will now come to equilib- 'rium for this lower temperature in space 1; the temperature of the evaporator will drop and correspondingly the pressure in the entire system will drop. 1

It is thus evident that the functioning oi the system is governed in accordance with its internal pressure and an important feature oi the particular system shown in thisFig. 1 is providing the valve 13 between the evaporator 11 and condenser 7, which may be used to control this pressure, preferably automatically. When the valve is open, the above described cycle of boiling in the evaporator 11 and condensing in the condenser 7 continues unmodified, but if the valve be closed, the vapor escaping from the evaporator cannot flow through its normal path to the condenser and the pressure automatically rises. the result being that the boiling point of the liquid in the system is raised above the temperature of evaporator 11. Ofcourse, the rise of pressure takes effect as a back pressure through coil 9, but this has no other eifeci than to force part of the liquid in that coil back into the condenser. Boiling being thus prevented, the rate of heat absorption in coil 11 is greatly decreased, thereby permitting the temperature in spacel to rise. While such a valve could be operated by hand 01 thermostatically, the present preferred arrangement is one in which the valve automatically opens upon rise of pressure, therebypermitting vapor again to flow into the condenser an closes on fall of pressure cuttin off such flow. The means diagrammatical y indicated for this purpose is a metallic bellows 15, the exterior of which is exposed to atmospheric pressure through vent 16, and the interior of 'which is exposed to the interior pressure of the system through inlet 17. The normal position of the valve is controlled by balance between an interior spring 18 and exterior spring 19 and may be set to operate at desired internal pressures by an adjusting screw 20, whereby the exterior spring 19 may be 31-: under greater or less nitial pressure ten g toclose. the valve'13. It will be noted. that the inlet to theev'aporator 11 is at a point above the normal level ofli'quid in the system and no liquid would normall flow by gravity from the condenser mosphere in the refrigerated space 1, but it I may be arranged in the walls the refrigerator or partly or wholly outside the same.

The heat operates first to decrease the specific gravity of the liquid in this coil, up to the boiling point thereof; and thereafter will cause incipient bubbling and ultimately boiling of the liquid in said coil to whatever extent .may be necessary to decrease the specific gravity of the liquid to a point where the cold, heavy liquid remaining in the condenser will overbalance the light liquid in 9. and force some of the mixture to flow'into the evaporator 11.

It will be noted that in thus functioning, the lift coil 9 is thermostatic in so much as the warmer it gets, the more effective it-will be in lifting liquid and supplying it to the evaporator.

A special feature of the system shown in Fig. l is the peculiar form of condenser and means for conducting heat therefrom into intimate and sure heat exchange relation with the solid carbon dioxide. In the form shown in Fig. 1, and more in detail in Fig. 8, the condenser consists of two plates, 27, 28,

held parallel by spacer framing strip 29 affording a con enser interspace 30 which is rendered gas-proof under. any pressure that may be exerted in the system by welding the plates to the spacer. As shown in Fig. 8, the spacer is preferably formed with an inclined bottom so that all liquid may be drained therefrom through pipe 8. The rear plate, 28, of the condenser is integral with a horizontal plate 28a extending laterally over the bottom of the bunker, so that the solid carbon dioxide 5 rests on said plate.

:- With such an arrangement, the heat from the condenser reaches the solid carbon dioxide mainly by conduction through the all metal path aiforded by 28a, and the amount of heat absorbed depends on the area of contact. of the refrigerant block 5 with said plate.

Consequently, said block 5 may be 'evapo-' rated down tov a thin slab before there is any -substantial decrease in the refrigerating effect which it exerts on the condenser. The

heat conveyed from the condenser to the refrigerant may be stillfurther limited to that which flows through the all metal path by"ap-' plying a layer 31 of compressed cork or other heat insulating material over the face of condenser plate 30, between it and the refrigerant 5.

'Ihe carbon dioxide gas evolved incontainer 4 maintains the latter full of pure cold which has a remarkable insulating effect 5:?! further limits leak of heat to the solid responding to drop below the desired temperature.

"if desired, or ma be returned to the bunker.

Other-modifie systems in accordance with my present invention are illustrated in Figs. 2 to 7 inclusive. In these figures, parts corig. 1 are represented by the same reference 11 merals, distinction between figures being'pr served by the use of dif ferent exponen for the numerals of each figure.

In Fig. 2, the space laxis to be cooled to, and maintained at, some definite temperature considerably higher than the temperature of the source of refrigeration which is con tainedin 4a and which may be very cold brine, solid carbon dioxide, liquid air or the lik For a specific case, one may assume that the refrigerant is solid carbon dioxide which evaporates at 'a temperature of 11 0 F. and that space 1a is to be cooled to a temperature of 40 F.

The condenser 7 a is indicated as a coil in refrigerant compartment 4a so that if vapor of some volatile liquid is introduced therein, its latent heat will be removed, thereby condensing it to liquid. This condenseris connected by pipe 8a with the evaporator 11a which is in the refrigerated space 1a and is at a lower level so that liquid from the condenser 7 a will drain by gravity into the top of said evaporator and the lower end ofthe latter is connected by pipe 12a with the top of condenser 7a. Drainage of liquid is controlled from the condenser into the evaporator by 'a valve 13a, which isdiagrammatlcally indicated as controlled by a thermostatic above the desired temperature and to close said valve when the temperature tends to In operationwe may assume that the condenser 7 a is filled with sulphur dioxide; thati bunker 4a contains solid carbon dioxide; and that space 1a is at a temperature of 70. Since the bulb F is adjusted to open valve 13a at40, a

liquid in 7a is free to flow into coil 11a. The warm atmosphere around 11a vaporizesthe liquid and the vapor flows through ipe 12a to the condenser .7 a where its heat 0 vaporization is removed and it becomes liquid. This liquid drains into coil 11a, where'it is again vapprized, thereby removing more heat from space 1a. This cycle continues until the desired temperature (40 F.) is reached in space 1a, whereupon the thermostatic bulb closes valve 13a, so that liquid sulphur dioxide can no longer flow from 7a to 11a and refrigerating of space 1a is arrested. As soon as the temperature starts to rise, the bulb again opens valve 13a and the cycle of the sulphur dioxide through the system is resumed and continues until the temperature is again, lowered to the point where the bulb F will again close the valve 130. Thus, as long as there is refrigerant in bunker 4a sufficient to condense the sulphur dioxide vapor, space 10 will be maintained at F. although the temperature of the refrigerant is about 110 F. Similarly, the valve 130: can 'be adjusted for other temperatures such as and flow to condenser 7a, thus preventing any rise of pressure such as operates to discon tinue the boiling in Fig. 1 where the valve is between the evaporator and the condenser. The control valve is, and in all systems may be, the well known type of snap-action valve now employed in mechanical refrigerators the'characteristic ofwhich is that it remains wide open until a predetermined low pressure is reached and, having reached this low pres-- sure and having closed, it remains closed until a predetermined high pressure is reached.

In Fig. 2, .the evaporator 11a has to be at a low level in order to insure gravity drainage of liquid into it from the condenser 7a and this is frequentlyundesirable because the bottom of the refrigerator naturally tendsto be the coldest part thereof and unless the heat is absorbed in the upper warmer part of the atmosphere, the convection currents will not be sufficient tomaintain reasonable uniformity of temperature between the top and the bottom of said space. However, the system shown in Fig. 2 may be made to operate with the coil in the upper part. of the re-. frigerated space by providing an air lift pipe 96, which operates on the principle described in connection with the coil 9 of Fig. 1, that is to say, if the system is filled with liquid to the liquid through the distance a; plus 3 when-' height indicated by the dotted llne w, the part of it in9b being exposed to the heat in the upper part of the refrigerated space 1?), will cause incipient boiling suflicient to lift ever the thermostatic valve 136 is open, Ob-

' viously, said, valve 131) can be located in the return conduit 126 if desired, in which case M vapor formed in 116 after the'valve is closed will be cut oil from condenser 7 b and can only take effect as back pressure raising the level of the liquid in the condenser 7 1). Obviously, such a-valve can be located anywhere in the exterior part of the circuit in or between the .condenser outlet 86 and the condenser inlet 12b. e I I I The evaporator coil may be modified'in several ways without changing the basic principle of operation. I In Fig. 4,- coil 110 is supposed to be the same as coil 11b of Fig. 3, but it is provided with short circuiting pipes 1110, 11m, to afford short paths for vapor return from different parts of the coil so that the vapor will not tend to lift the liquid back towards its source. I

In Fig. 5, I have shown means whereby the liquid-may be raised to an evaporator coil lid, located at any desired height. This is accomplished by one or anydesired number of loops 11y, 112, connected in parallel to the low level drainage pipe 8d of condenser 7d and re-entering the raiser pipe 9d at asub- I stantially higher level.- In this waya desired amount of the cold liquid, may be heated enough to lift it to the required height. The

heat and the absorbing capacity of these loopsmay be such-as to cause practicall all of the frosting to occur onsaidloops, l eaving the evaporator coil 11d, free from frost 'or alternately frosted and defrosted, in cases where the refrigerant temperature in 1d is at or above the freezing point of water.

If it is necessary or desirable to elevate the evaporator 11d, to a level as high or high- ;er than that shown in Fig. 5, additional lifting effect for the liquid in 9a may be obtained by using as many loops, with as much heat absorbing surface as may be necessary to give proper air lift? for the liquid, in any particular case. If a thermostatic valve is used, it can be placed'either in evaporator coil 11d or in the loops themselves.

In Fig. 6, I have shown how two differentcompartments, 1m, 1 can be refrigerated at different temperatures by separate evaporators 11c and 11 connected in parallel with the same refrigerant condenser 7e. While any'ofthe herein described systems can be thus connected to a single source, by the use of lifting-loops or coils where these are necessary, the specific form here shown is Where one of the evaporators 'isbelow thelevel of the condenser and in this case-the condensed liquid in 86 passes through branch pipes 8f and 9;, each' provided with an outwardly opening check valve 8g, 9g, while the vapor returns areconnected with 12 by pipe 12/,

12a, respectively. 129 will contain a stand:

ard control valve 13, which may be of the type shown in F ig. 1, while 12f will be controlled by snap action control valve 13!; such as described in connection with Fig. 2.

Thus, there aretwo heat absorbing systems operating independently-from the same condenser 70. When the compartment-1y reaches a desired temperature, say10,- valve 13 will operate to discontinue evaporationin evaporator 11c. Likewise when 11f pm.

. being indicated in Fig. 7 where the condenser 7a has'a reservoir 7 o to assist in determining liquid in the system will be normally;

The above noted tendency of the lift line to respond thermostatically to the temperature in the refrigerated space may be utilized as the sole thermostatic control factor of the system, one arrangement for such purpose a definite normal level for liquid in the condenser while the evaporator lln is,- located wholly above said level so as normally to contain no liquid. In this case the drainage pipe 8% drains directly into a loop 110, which exposes enough heat absorbing area in the refrigerated space 1n so that the liquid is warmed above the frosting point by the time it reaches the lift coil 9n. Normally, the cold liquid flows to the bottom leg of the coil 110 and as it becomes heated risesinto the lift coil 91, the shunt pipe 80 having little or no effect on'this natural thermocirculation' of the liquid. However, when bubblingand upflow of liquid becomes copious, 80 may come into action to supply liquid directly to the lift coil, 9%. The coil 110' may have such heat absorbing capacity as vto warm the liq uid above the frost point, when the refrigerant temperature in In 'is substantially above.

32 -F., otherwise there may be frost on lift coil 9n, but the functioning will be upon the same principle as where there is no frost formation. That is to say, the main evapomtor lln, being above the normal level of the dry and they only boiling that occurs will e in the loop 110 and lift coil 9n. Whenever this becomes excessive, however, the liquid will progressively invade the evaporator lln and the heat absorption and transfer will be increased accordingly.

Iclaim:

1. A method of refrigeration which includes evaporating a liquid by heat absorbed in a region to be cooled; conducting resulting vapor in operative relation to the refrigerant,

, to recondense the same to liquid, said recondensation taking place in. one portion of a condenser while the heat is conducted to the refrigerant in a different portion of the com denser through a comparatively thick metallic path; conductingthe liquid back to the region to be cooled in continuous circuit; and

controlling evaporation to control the temperature in therefrigerated region by controlling fiow of fluid between the evaporator and the condenser.

2. A- method of refrigeration which includes evaporating a liquid by heat'absorbed in a region to be cooled; conducting resultingvapor in operative relation to the refrigerant, to recondense the same to liquid, said recondensation taking place in one portion of'a condenser while the heat is conducted to therefrigerant in a diflferent portion of the condenser through a comparatively thick metallic path conducting the liquid back to the in a region to be cooled; conducting resulting vapor in operative relation to the refrigerant; to recondense the same to liquid, sa1d recondensation taking place in one portion of a-condenser while the heat is conducted to the refrigerant in a different portion of the condenser through a comparatively thick metallic path; conducting the liquid back to the region to' be cooled in continuous circuit; and

controlling evaporation to control the temperature in the refrigerated region by causing decrease of pressure in the system to cut off return of the vapor to the condenser.

4. A method of refri eration which includes evaporating a liquid by heat absorbed in a region to be cooled; conducting resulting vapor in operative relation to the refrigerant, to recondense the same to liquid, said recondensation taking place'in' one orti'on of a condenser while the heat is 0011 noted. to the refrigerant in a different portion of the condenser through a comparatively thick metallic path; conducting the liquid back to the region to be cooled in continuous circuit; and

ing changes of pressure in the system due to changes of temperature in the refrigerated space to control return flow of the vapor to the condenser, I

5. A method of refrigeration which include's evaporating a liquid by heat absorbed in a region to be cooled conducting resulting vapor in operative relation to the refrigerant, to recondense the same to liquid, saidrecondensation taking place in one ortion of a condenser while the heat is con noted to the refrigerant in a different portion of the condenser through a comparatively thick metallic path; conducting the liquid back to the region to be cooled in continuous circuit; and controlling evaporation to control the temperature in the refrigerated region by utilizingchanges of pressure in the system due to changes of temperature in the refrigerated [space to cut off flow of the vapor to the coning vapor in operative relation to the refrigerant, to recondense the same to liquid;

conducting the liquid back to the region tobe cooled in continuous circuit; and controlling evaporation to control the temperature in the refrigerated region by locating the inlet to the vaporative portion of the circuit at a level higher than the normal level of condensed liquid in the circuit and utilizing heat ab-- sorbed from the refrigerated space by the liquid in its path from condenser to the evap orator to warm and partially vaporize the liquid to lift it above said normal level a distance sufficient to cause the liquid to'over- 4 densed liquid in the circuit and utilizing heat absorbed from the refrigerated space by the liquid in its path from condenser to the evaporator to warm and partially vaporize the liquid to lift it above said normal level a distance suflicient to cause the liquid .to overflow into the evaporator or to not overflow,

according as the amount of heat so absorbed is greater or less.

8. The method of modifying the refrigerative effect of solid carbon dioxide on a condenser that has a condenser portion and a plate extending therefrom which includes conducting the heat from the condenser through an all-metal path including said metal plate and upon which the solid carbon dioxide is supported.

9. A closed circuit refrigerating system including an evaporator for boiling a liquid by heat absorbed in a region to be cooled; a

conduit conducting resulting vapor to a condenser in operative relation to a refrigerant, thereby recondensing the same to liquid, sa id recondensation taking place in one portion of the condenser while the heating is conducted to the refrigerant in a different portion of the condenser through a comparatively thick inetallic path; a return conduit for conduct ing the liquid back to the region to be cooled,

in continuous circuit; and means for controlling the temperature which includes valve means for controlling, permitting or preventing flow of fiuid in said circuit.

it A'closed circuit refrigerating system including an evaporator for boiling a liquid by heat absorbed in a region to be cooled; a

conduit conducting resulting vapor to a con-'v denser in operative relation to a refrigerant,

recondensation taking place'in one portion thereby recondensing the same to liquid, said" i of the condenser while the heating is conducted to the refrigerant in a different portion of the condenser through a comparatively thickmetallic path; a return conduit for conducting the liquid back to the region to be cooled, in continuous circuit; and means for controlling the. temperature which includes valve means for preventing return fiowof the vapor to the condensenf 11. A closed circuit refrigerating system by heat absorbed in a region to be cooled; a conduit conducting resulting vapor to a condenser in operative relation to a refrigerant,

thereby recondensing the same to liquid, said recondensation taking place in one portion of the condenser while the heating is conducted to-the refrigerant in a different portion of the condenser through a comparatively thick metallic path; a return conduit for conducting the liquid back to theregion to be cooled, in continuous circuit; and means for controlling the tcmperature which includes automatic valve means utilizing decrease of pressure in the system to cut off return of the vapor to the condenser.

12. A closed circuit refriger ting system including an evaporator for boi ing a liquid by heat absorbed in aregion to be cooled; a conduit conducting resulting vapor to a condenser in operative. relation to a refrigerant, thereby recondensing the same to liquid, said recondensatio'n taking place in one portionof the condenser while the heating is conducted to the refrigerant in a different portion of the condenser through a comparatively thick metallic Path; a return conduit for conducting the liquid back to the region to be cooled, in continuous circuit; and

means for controlling the temperature which includes automatic valve means utilizing changes of pressure in the systemv due to changes of. temperature in the refrigerated space to control return flow of the vapor to the condenser.

13. A closed circuit refrigerating system including an evaporator for boiling a liquid by heat absorbed in a region to be cooled; a conduit conducting resulting vapor to a condenser in operative relation to a refrigerant, thereby recondensing the same to liquid, said recondensation taking place in one portion of the condenser while the heating is conducted to the refrigerant in a different portion of the condenser through a comparatively thick netallic path; a return conduit for conducting the liquid back to the region to-be cooled, in continuous circuit; and means for controlling the temperature which includes automatic valve means operating to cut off new of the vapor to :the condenser'when the temperature falls below. predetermined minimum and topermit flow to the condenser when the temperature rises above a predetermined maximum.

.14. 'A closed circuit refrigerating system including an evaporator for boiling a liquid including an evaporator for boiling a liquid i by heat absorbed in a region to be cooled; a

conduit conducting resulting vapor to .a condenser in operative relation to a refrigerant,

thereby recondensing the same toliquid; a return conduit for conducting the liquid back to the reglon to be cooled, 1n continuous c rcuit, the inlet-to the-evaporator being at a level higher than the normal levelof'condensed liquid in the system and the liquid,

including an evaporator for boiling a liquid by heat absorbed in a region to'becooled; a-

conduit conducting resulting vapor to a condenser in operative relation to a refrigerant, thereby recondensing the'same to liquid; areturn conduit for conducting the liquid back to the region to be cooled, incontinuous circuit, the inlet to the evaporator being at a level higher than the normallevel of condensed liquid in the system and the liquid supply conduit tothe evaporator being de- Signed and located to absorb heat-from the refrigerated space to Warm and partially vaporize the liquid to lift it above said normal level a distance sufficient to cause the liquid to overflow into the evaporator ornot to overflow, according as the amount of heat so absorbed is greater orless.

"- 16. Refrigerating apparatus, including a closed circuit through a condenser in heat transfer relation to a refrigerated. source, a discharge conduitfor liquid therefrom. an evaporator in the refrigerated space into wh ch said conduitdischarges, a return conduit for vapor from the evaporator to the condenser, the inlet of the evaporator being, at a level above the normal level of liquid in a the condenser and the liquid discharge conduit from the condenser to the evaporator having in shunt thereon an auxiliary conduit exposed to heat from or varying with the temperature of refrigerated space and of heat absorbing capacity suflicient to cause partial boiling of liquid therein to lift the liquid in said discharge conduit above the level oftl e liquid in the condenserand discharge it into the evaporator.

17. Refrigerating apparatus, including a closed circuit through a condenser in heat transfer relation to a refri erant source, a discharge conduit for liquid therefrom, an evaporator in the refrigerated space into which said conduitdischarges, areturn conduit for vapor from the evaporator to the condenser, designed and operating to maintain above freezing temperatures in the refrigerated space, the liquid discharge conduit from the condenser exposed to heat from the atmosphere of the space to be refrigerated and of heat absorbing capacity sufiicientto Warm the liquid above frostcollecting temperature before it enters the evaporator.

18.,Refrigerating apparatus, including a' closed circuit through a condenser in heat transfer relation'to a refrigerantsource, a discharge conduit for liquid therefrom. an evaporator in the refrigerated space into which said conduit diseharges,-'a return couduit for vapor from the evaporatorto the condenser, said latter conduit having a low level loop exposed to the atmosphere of the space to berefrigerated and of heat absorbing capacity sufficient vtoflsubstantially warm the liquid before it enters the evaporator.

19, Refrigerating apparatus, including an outer heat-insulating casing provided with an inner g'as-tight shell forming an interspace for circulation of carbon dioxide gas between it and the outer casing; a" container for solid carbon dioxide in the upperportion of saidchamber, arranged for overflow of gas therefrom into said interspace and provided with v heavy heat insulation between it and the chamber to be refrigerated, thereby minimizing 'dlrect heat transfer; a metali'condenser therein having its'inlet' at a relatively high level and its outlet at a-lower level and having a transverse integral extension upon which SOllCllfiBd carbon dioxide refrigerant is supported, thereby affording an all metal pathfortransfer ofheat from the condenser't'othe refrigerant; a-"discharge conduit from the lower portion of the condenser extending into the refrigerated space, an evaporator in the refrigerated spaceinto which said conduit discharges, a return conduit closing aclosed circuit return for vapor fromthe evaporator to the condenser, ,and means for controllingthe rate of evaporation in the evaporator by and in accordance with the temperature of the refrigerated chamber.

20. Refrigerating apparatus, including an .outer heat-insulating casing provided with an inner gas-tight shell-forming an interspace for circulation of carbon" dioxide gas between it and the outer casing; a container for 'solid carbon dioxide in'the upper portion of said chamber,'arranged for joverfiow of.

gas therefrom into said interspace and pro-' vided with heavy heat insulation between it and the chamber to be refrigerated, thereby minimizing direct heat trans fer; a metal 011-.

denser therein having its inlet at a relatively higlrlevel and its, outlet at'a lower level and having a transverse integral extensionupon vvhich solidified carbon dioxide refrigerant is supported, thereby affording an all metal path for transfer of heat from the condenser to the refrigerant and heat insulating ma terial interposed laterally between the solid carbon dioxide and the condenser to minimize direct. transfer of heat; a discharge conduit from the lower portion of the condenser ex;

' tending into the refrigerated space, an evaporator in the refrigerated space intowhich said conduit discharges, a return conduit closing a closed circuit return for vapor from the evaporator to the condenser, and means for controlling the rate of evaporation in the evaporator by'and-in accordance with the temperature of the refrigerated chamber.

21. Refrigerating apparatus, including an insulating casing, a container for solid carbon dioxide provided with heavy heat insulation, thereby minimizing direct heat transfer to the exterior, a metal heat exchange device for circulation of a fluid to be cooled which includes a condenser portion and a transverse metal plate extending therefrom and being within said container upon which the solidifiedcarbon dioxide refrigerant is supported, thereby affording an all metal path for transfer of heat from the heat exchange device to refrigerant to recondense the same to liquid,-

said recondensation taking place in one portion of a condenser while the heat is conducted to the refrigerant in a dilferent portion of the condenser through a comparatively thick metallic path, conducting the liquid back to the regions tobe cooled in separate circuits, and controlling evaporation to control the temperatures in the refrigerated regions by controlling flow of fluid between the 'evap'orators and the condenser.

23. method of refrigeration which in.- cludes evaporating a liquid by heat absorbed in a region to be cooled, conducting resulting vapor in operative relation-to the refrigerarranged so that the solid carbon dioxide is in heat conducting relationship therewith whereby heat is absorbed mainly by conduction through said solid portion.

' 25, An apparatus for refrigerating with solid carbon dioxide which comprises an outer container, 2, solid carbon dioxide chamber within said container, a fluid condenser having a hollow portion for condensing the fluid and a fluid inlet and outlet communication with said hollow portion and a solid portion extending therefrom, said solid-portion being arranged to support the solid carbon dioxide, whereby heat is absorbed mainly by conduction through said solid portion.

' Signed at Chicago, in the county of Cook, and State of Illinois, this 23rd day of June,

FRANKLIN B. HUNT.

ant, to recondense the same to liquid, said recondensation taking place in one portion of a condenser while the heat is conducted to the refrigerant in a different portion of the condenser through a comparatively thick me tallic path, conducting the liquid back to the region to be cooled in continuous circuit, controlling evaporation to control the temperatures in the refrigerated region by preventing return flow-of the vapor to the condenser;

and maintaining the rate of condensation substantially uniform by interposlng suitable insulationv between said condensing portion and the refrigerant, thus preventing substantially all direct heat absorption therebetween. 24. An apparatus for refrigerating with solid carbon dioxide which comprises an outer container, a solid carbon dioxide chamber within said container, a fluid condenser having a hollow port-ion for condensing the fluidand a fluid inlet and outlet communication with said hollow portion and a solid portion extending therefrom, said solid portion being

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