US2636357A - Refrigerating apparatus - Google Patents

Description

April 28, 1953 Filed Oct. 8, 1949 J. E. WOODS REFRIGERATING APPARATUS 3 Sheets-Sheet l 'IIIIIIIIllllll/III(III.\-

Patented Apr. 28, 1953 REFRIGERATING APPARATUS John E. Woods, Cohasset, Mass., assignor to Standard-Thomson Corporation, Boston, Mass, a corporation of Delaware 1 Application October 8 1949, Serial No. 1203M 11 Claims.

The present invention relates to refrigerating apparatus and more particularly to refrigerating apparatus useful with Dry Ice or solid carbon dioxide as the primary refrigerating medium.-

The use of solid carbon dioxide for refrigeration in conjunction with a circulating cooling medium has been proposed. For some types of service, as in freight car cooling, it is desirable to avoid the use of motors, pumps, or other moving elements. that the Dry Ice be used not only for cooling the circulating medium but also for applying the pressure to circulate it through the cooling system. Such apparatus has appeared to offer promise for freight car service but in practice it has not proved satisfactory.

The use of the same Dry Ice for both the pressure and cooling functions has certain disadvantages which are pointed out in the Brunsing Patent 2,450,713, granted October 5, 1948, which describes a system of utilizin two separate bodies of Dry Ice, namely, a large body for cooling the circulating medium and a smaller body in a pressure container for generating the pressure to be applied to the circulating medium. However, the apparatus described in the Brunsing patent has not proved to be satisfactory in practice.

In any type of Dry Ice cooling system some difiiculty has been experienced in maintaining a proper temperature control. The most difiicult controls are required by certain perishable foods for-which a relatively narrow temperature'range must be maintained. For example, in the case of certain fresh vegetables a range between about 33 and 38 F. is required, since a drop of temperature below 32 may cause freezing while an increase above 38 may result in spoilage. One method of control which has been proposed is that of varying the pressure of the carbon dioxide on the circulating medium in accordance with the temperature desired. This has been found undependable because of the uncertainty of gas control valves at low temperatures and particularly because of the possibility of the valve beingheld open by the presence of a small piece of dirt; in such a case the pressure will be applied continuously and thereby result in over-cooling of the contents of the car.

Another difficulty encountered in operation of the BlLlllSilig apparatus is stalling of the equipment under some conditions. This has been found to be due to the fact that the circulating system must be maintained within a fairly narrowrange'of pressures and that under conditions of low outside temperature it-is possible for'the To that end it has beensuggested pressure chamber to'be cooled to such an extent that the Dry Ice willnot generate a sumcient pressure to circulate the'cooling'liquid. This con dition can arise if the freight car, after going through a cold belt where the system has not been required to circulate the cooling medium I for aconsiderable period, enters a Warm belt where refrigeration is called for; under such conditionsit has been found that the car may warm up above the safe refrigeration point while the pressure system remains stalled at a low temperature.

Since the freight car refrigeration service may.

be such as to require the car to remain unattended for long periods, it is essential that the apparatusbe of utmost simplicity and reliability. To this end it is the object of the present invention to provide improvements in a refrigerating system, with particular views toward maintenance of proper temperature control and assurance against any possibility of stalling. It is a further object to insure safe operation of the system, even in the event of failure of the thermostatic control apparatus.

With these objects in View one of the principrl features of the invention comprises the use of multiple cooling coils for the space to be refrigerated, whereby there are preferably provided atleast two coils, each of which has the coolingmedium circulated therethrough by gas pressure and each of which is provided with an independent thermostatic control. The thermostatic con-- trol'devices are arranged to fail safe whereby in the event of a rupture of the bulb or bellows the circulating valve will close'and thereby shut off circulation to its associated cooling coil. Since the refrigeration required for maintenance of a low temperature is less than that required to establish it, the loss of'refrigerating effect in a portion of the system is not serious, because the remaining coils will maintain refrigeration for a sufficient period. This is to be distinguished from a control in which failure will result in continued circulation of the refrigerant, which would result in excessive cooling and possible freezing of the contents of the car, and rapid depletion of the Dry Ice supply.

The phenomenon of stalling which has been previously mentioned has been found to be due to the influence of the large body of Dry Ice used for cooling, said body being in necessary proximity to the Dry Ice pressure tank. The temperature in the pressure tank must be suf 'ficient to genrate the required circulating pressure, usually in the neighborhood of 5 or 6 pounds per square inch. The temperature in the pressure tank is determined by the balance between the heat radiated to the cooler Dry Ice storage space and the heat absorbed from the car itself. Under conditions of prolonged inactivity as in the passage of the car through a cold belt, the heat balance is upset to the extent that the Dry Ice in the pressure tank may assumesubstam tially the temperature of the larger body of Dry Ice used for cooling purposes. It has been found that when this condition is established, the pressure is lost and may not be regained for an eX- tended period after the car enters a warmer belt. According to the present invention, means are provided to accelerate the; ahsorptien of. heat by the Dry Ice in the pressure tank from the warmer parts of the car in relationtothe. heat radiated or conducted from the pressme tanlrto the Dry Ice bunker. This is preferably accomplished either by the use or a radiator through which a part oithe circulating medium, is passed by the thermo-siphonic action, or by, the use of. insulation between the bunker; and the. pres ure. tank, or both.

In the accompanying drawings illustrating what is nowconsidered' the. preferred form of the invention Fig. l is a diagrammatic View showing. the Dry Ice cooling storage space, the pressure tank, and. associated parts: Fig. 2 is a sectional; elevation of. the preferred form of float valve and float or collecting chamber; Fig. 3 is a diagram illustrating the heat absorption apparatus for theprevention of stalling; and 4 is a diagram of one of the thermostatic ccntrol units.

In the system shownin Fig. 1 the freight car is indicatedin diagrammatic outline. The car has at one end a cooling space ordinarily of the type used as an ice bunker, completely separated from the rest of the car by the wall 4. In this space is a series of cooling pipes or coil's' 6 connected with headers 8. A considerable quantity of Dry Ice is carried inthe space directly above the coils. Contained within the tubes and headers is a circulating cooling medium which may be an alcohol, an ethylene glycol mixture or any suitable material having a suficientiy low freezing point sothat it remains fluid at any temperatures encountered ina Dry Ice system. In many instances this material is referred to as brine even though it maycontain no salt.

"The storage space in which the DryIce is contained may be referred to as the Dry Ice cool ing storage space or the Dry-Ice bunker. This bunker may contain several thousand pounds of Dry Ice which is in intimate heat exchange relation with the cooling coils.

Immediately beside the Dry Ice bunker is a container :2 which is referred to as the Dry Ice pressure tank. This container holds a relatively small quantity of Dry Ice which is used as a means of generating pressure for the circulating medium.

A tank for the circulating medium is also provided. This tank is divided into two sections, namely, a float chamber 15 at the too and a pressure chamber is at the bottom. The float chamber (6 receives the returned warm refrigerant from the system and the pressure chamber I8 is the tank from which the refrigerant is started on its cooling cycle.

The compartment 30 above the float c am er M contains valves and piping to be describedlater in connection with Fig. 2. p

A pipe 2b connects the bottom of the chamber 18 with one of. the headers 8 of the; coolingcoils.

, chamber if; has mounted therein a float valve including a float member 32 which is free to slide upand down on av tube 34. At the top the valve. is provided; with a casing including two poppet valves 38 and as having suitable seats whereby the, valve 238 is closed when the valve il is open and vice versa. A pipe 152 runs from thetop- Qf the float chamber into the side of the casing 35 adjacent to the valve 69, which controls a. vent to the atmosphere indicated at 3 1. A pipe 15. leads, from, the pressure generating tank:

to the-top of. the casing 36 and a, secondpipe 46'.

leads from below theval'ye 3,8; into thetop oi the. float. chamber; It, With the parts in the position shown in Fig. 2, the float" chamber is vented to atmosphere and the pressure from the pre sure tank is not communicated to the floatchamber, being closed on: at the valve 33; When the float rises su cientiy; however, to engage a pin 5% on the valve stem 52 the latter is" lifted,

thereby closing valve it and opening valve 385. This closes the vent to atmosphere and applies the carbon dioxide pressure to the float chamber. A pipe containing a check valve 55; runs from the neat chamber 5 6 into the pressure chamber Hi.

It will be seen, therefore, that with the float down the float chamber it is at atmospheric pressure. Since the pressure chamber H3 is always at full pressure by reason of the permanent connection 29 between the Dry Ice container 12 and the chamber it, there is a differential pressure between chambers 18 and 15 which causes the circulation of the cooling medium through coils 53 pipe 22 ceiling coils 25, control valves and pipe 23- to the heat chamber it. When a sufficient amount of cooling medium has circulated to cause the float to rise, thereby closing valve- 4'9- and opening valve 38, the pressure is applied to the float chamber, thereby equalizing the pressures in the twochambers, allowing theliquid' to flow by. gravityinto the lower chamber i8; When the float drops to the bottom, it restores the valves to their initial positions and causes the circulation to resume. It will be understood that the circulation is free to take place only'when the thermostatic control valves are open.

A pressure regulating valve 54 is connected to the line at the top of the casing 36. This may be of any standard form and serves to maintain the pressure in the tank at any desired value, preferably in the neighborhood of 5 pounds per square inch.

The control valves 26 have already been mentioned. Each valve comprises a bellowsoperated valve compensated for atmospheric pressure and operated through a. suitable capillary with a temperature. responsive bulb 56, the bulbs 58 being disposed in suitable positions with.- in the car. As shown in Fig. 4, each valve 26 has a casing enclosing a bellows, 51, the bulb and easing being. charged with a fluid capable, of generating a vapor pressure, which is Super atmo pher c. at the central, temp ature Bison an increase in temperature the increased pressure moves a valve member 58 off its seat 59 against the spring 60. There is provided a compensating bellows 6| sensitive to atmospheric pressure in a manner described below. The bellows Bl compensates for such variations in pressure as may be occasioned by the passage of the car at different altitudes. When the temperature in the car is sufiiciently low, the valve 58 closes, thereby cutting off circulation of brine through the system. The control temperature may be manually adjusted by varying the spring tension by a hand knob 62.

Another bellows 63 surrounds and encloses the spring 60. The bellows 6| and 63' are secured to a fixed plate 64, and both are evacuated. The

exterior of bellows 6| is acted upon by the pres-' sure of the circulating refrigerant which is always at a substantially constant gage pressure,

namely about 5 lbs. per square inch. Hence the bellows and spring combination 6t, 6! compensates for changes in atmospheric pressures.

The temperature sensitive bellows 5'!- is enclosed in a casing 64', while the valve and compensator parts are enclosed in a casing 65. The casings are closed by rubber diaphragms 66 and 6! attached to the valve spindle, the two diaphragms being of equal areas in order that no unbalanced pressures will be applied to the valve.

It will be observed that if the bulb 56 or bellows 51 of either valve 26 fails, the internalpressure is reduced to atmospheric, thereby closing the valve under the action of the spring. This prevents dangerous overcooling of the car. Since failure of both units is unlikely, sufiicient refrigeration to maintain the temperature will be permitted through the other valve. The system may thus be said to fail safe.

To provide a safeguard against holding open of the thermostatic valves 26 in the refrigerant lines, a separate thermostatically controlled valve 68 (see Fig. 2) is inserted in the line carrying the carbon dioxide from the pressure tank l2 to the top of the casing 36. The valve 68 has a bulb 69 located in the car near the bulbs 56. In case either of the valves 26 in the refrigerant lines should become jammed in the open position, as by the presence of dirt on the seat, thus causing the temperature to fall below the desired level, the valve 68 operates to shut off the flow of carbon dioxide. The valve 68 may in fact be placed in the line 29 as indicated at a: in Fig. 1, or at any of the three points marked a: in Fig. 2 since closure of any such line will prevent either application of pressure to the chambers, or venting of the float chamber. The valve 68 is,preferably set for a temperature slightly lower than the valves 26, so that it acts as an overriding safety control to prevent overcooling.

The present invention also has provision to prevent stalling. It has been mentioned that the apparatus tends to stall, particularly if the car has been traveling through a cold belt, so that cycling of the brine has not been called for over a long period. The reason for stalling was not evident, but it was discovered to be due to the fact that the relatively small amount of Dry Ice in the pressure container 12 becomes overcooled by its proximity to the large body of Dry Ice on coils 6, and hence is incapable of generating pressure sufiicient to circulate the refrigerant. Under normal conditions, the temperature of the Dry Ice in the container I2 is maintained sufficiently high by absorption of heat from the refrigerant in the chamber l8 and from other sources, but under extreme cold conditions, such heat absorption is insufiicient to maintain a balance against the heat lost to the large body of Dry Ice in the bunker 4. After the Dry Ice in l2 has become overcooled it recovers only very slowly, even after a warm belt is reached, so that the refrigeration is lost for considerable time.

According to the present invention, a proper balance is maintained between heat loss and gain,

first by the use of radiating means, and second by heat insulation between the Dry Ice bunker and the container [2. One form of radiation is the coil 1 (see Fig. 3) located in the body of the refrigerated space and connected to the pressure chamber H3 at two points of difierent liquid level. The coil absorbs heat from the surroundings. By thermo-siphon effect this heat is transmitted to the refrigerant in the pressure chamber l8. Another form of radiating apparatus is a metal fin, rod or pipe 12 extending downwardly from the chamber l8 through the floor of the car, whereby the lower end is exposed to the outside temperature. The refrigerant in the pressure chamber I8 is thus kept suificiently warm to provide heat, by conduction and radiation, to the Dry Ice pressure tank l2. While some heat is thus furnished by the coil 10, a balance is maintained by reducing the loss of heat by insulation i l, between the bunker and the pressure tank l2. It has been found that in some cases a proper balance can be maintained by either the coil 10 or the insulation M alone. The pressure chamber I8 is raised somewhat above the level of the cooling pipes 6. The difference in level prevents the fluid in the pressure chamber from losing heat by convection to the fluid in the coils in the bunker. The heat thus retained in the chamber I8 helps to maintain the temperature in the Dry Ice pressure tank l2 at a level sufficiently high to prevent stalling.

Having thus described the invention, I claim:

1. A. refrigerating system comprising a circulatin system for a refrigerant, means for maintaining a supply of Dry Ice in heat-exchange relationship with the refrigerant, a pressure tank for a sup-ply of Dry Ice to apply circulating pressure to the refrigerant, the two supplies of Dry Ice being adjacent to each other, and means for accelerating absorption of heat into the pressure tank in relation to the heat transferred between the pressure tank and the heat-exchange supply of Dry Ice in order to prevent stalling by reduction of pressure, said means including a pressure chamber in heat exchangerelation to the pressure tank for warm refrigerant, and a heat pickup coil connected to the pressure chamber to permit the transfer of heat to the pressure chamber by thermo-siphonic flow of refrigerant.

2. A refrigerating system comprising two parallel-connected cooling coils, means utilizing Dry Ice to cool and circulate a liquid refrigerant through the coils, and valves responsive to the temperature ofthe cooled space to control the passage of liquid refrigerant through the coils in-- dependently, each valve including a temperaturesensitive pressure device producing a superatmospheric pressure at the control temperature, a member for variably impeding the flow of liquid being urged to open by the pressure of said device, and resisting means urging the member to close, whereby rupture of the pressure device al lows the resisting means to close the valve to prevent over cooling.

access;

3. A refrigerating system comprising two par allel-connected cooling coils, a circulating Systein for passing a liquid refrigerant through the coils, a, container for a body of Dry Ice to cool the liquid. refrigerant, a pressure tank to hold a. supply of Dry Ice to apply circulating pressure to: the liquid refrigerant, and valve responsive; to.

the temperature of the cooled space to control.

the passage of liquid refrigerant through the-coils independently, each valve including a. temperature-sensitive pressure device producing a superatmospheric pressure at the. control temperature,

a member for variably impeding the flow of liquid.

being urged to open. by the pressure of said device, and resisting. means urging the member to; close, whereby rupture of the. pressure. device. allows. the resisting means to close. the valve, to

prevent over cooling.

i. A refrigerating system comprising two parallel-connected cooling coils, means utilizing Dry Ice to cool and circulate a liquid refrigerant through the coils, valves responsive-to the.

temperature of the cooled, space to control the vice, and resisting means urging the membe to 2 close, whereby rupture of the pressure device allows the resisting means to close the valve to prevent over cooling, and an overriding thermostatic control toprevent the application of circulating pressuratothe liquid refrigerant when the temperature of the cooled space reaches a fixed value lower than the control temperature,

. 5.. A refrigerating system comprising two par, duel-connected cooling coils, a. circulating system for passing a liquid refrigerant through the. coils, a container for abQd-y of. Dry Ice. to cool the liquid. refrigerant, a pressure. tank to hold a supply of Dry Ice to apply circulatin pressure to the liquid refrigerant, and an overriding thermostatic control to prevent the application of cir- 1 culating pressure, to the liquid refrigerant when the temperature of the cooled space reaches a fixed value lower than the control temperature.

6. A refrigerating system comprising two parallel-connected cooling coils, a circulating system for passing a liquid refrigerant through the coils, a container for a body of. Dry Ice to cool the liquid refrigerant, a pressure tank to hold a supply of Dry Ice to apply circulating pressure to.

the liquid refrigerant, a float chamber having a valve to control flOW of the refrigerant and a vent valve for carbon dioxide, and valves responsive to the temperature of the cooled space to control passage of liquid refrigerant through the coils independently, each valve including a temperature-sensitive pressure device producing a superatmospheric pressure at the control temperaturea member for variably impeding the flow of liquid being urged to open by the pressure of said device, and resisting means urging the member to close, whereby rupture of the pressure device allows the resisting means to close the valve to prevent over cooling.

7. A refrigerating system comprising a circulating system for a liquid refrigerant, a con- &

pressure chamber maintaining a separate heat exchange relationship with the pressure tank and having a pressure connection therewith, saidohamher collecting returned warm refrigerant from the circulating systemand applying circulating pressure to the refrigerant, said heat exchange relationships. being relatively adjusted, whereby the. rate of heat flow from the returned refrigerant in the pressure chamber to the-pres sure tank exceeds the rate of heat flow fromthe pressure tank tothe container. over the range. of operating conditions for the system.

8. A refrigerating system comprising a circulating system for a liquid refrigerant, a. containerfora; supply of DryIce to cool the refrigerant, a pressure tank for a. supply of Dry Icetoi apply circulating pressure to the refrigerant, the two supplies of Dry Ice; being adjacent to, each other, a body of insulating material sepa-- rating said supplies to establish a definite heat exchange relationship between said supplies, and a pressure chamber maintaining a separate heat exchange relationship with; thepressure tank and having; a pressure connection; there. with, said chamber collecting returned warm-refrigerant from the circulating system and apply ing circulating pressure to the refrigerant, said heat exchange relationships being relatively adjusted, whereby the rate of heat flow from the. returned refrigerant in the pressure chamberv to the pressure tank exceeds the rate of heat flow from the pressure tank to the container over the: rangev of operating conditions for the system.

9. A refrigerating system comprising a circu-- lating system for a liquid refrigerant, a container for a supply of Dry Ice to cool the refrigerant, a pressure. tank: for a supply of dry ice to applycirculatin pressure to the refrigerant, the two. supplies of DryIce; beingiacent to each other, a body of insulating material separating said; supplies to establish a definite heat exchange relationship between said supplies, float valve. means for controlling cyclic circulation of the refrigerant, and a pressure chamber maintaining a separate heat exchange relationshi with the pressure tank and having a pressure connection therewith, said chamber collecting returned warm refrigerant from the circulating system and applying circulatin pressure. to the refrigerant, said heat exchange relationships being relatively adjusted, whereby the rate of heat flow from" the returned refrigerant in the pressure chamber to the pressure tank exceeds the rate of heat flow from the pressure tank to the container over the range of operating conditions for the system.

10. A. refrigerating system comprising a circulating system for a liquid refrigerant, a container for a supply of Dry Ice to cool the refrigerant, a pressure tank for, a supply of Dry Ice to. apply circulatin pressure. to. the. refrigerant, the two supplies of Dry Ice being in heat exchange relationship with each other, a pressure chamber maintaining. a separate heat exchange relationship with the pressure tank and having a pressure connection therewith, said chamber collecting returned warm refrigerant from the circulating system and applying circulating pressure to the refrigerant, and means for conducting added heat to the returned reiris rant in the, chamber.- from. the siun'oundings, said heat exchange relationships being relative.- ly" adjusted; wherebythe rate of. heat flow from the. returned. refrigerant:.mztheipressure chem her to the pressure tank exceeds the rate of heat flow from the pressure tank to the container over the range of operating conditions for the system.

11. A refrigerating system comprising a circulating system for a liquid refrigerant, a container for a supply of Dry Ice to cool the refrigerant, a pressure tank for a supply of Dry Ice to apply circulating pressure to the refrigerant, the two supplies of Dry Ice being adjacent to each other, a body of insulating material separating said supplies to establish a definite heat exchange relationship between said supplies, a pressure chamber maintaining a separate heat exchange relationship with the pressure tank and having a pressure connection therewith, said chamber collecting returned warm refrigerant from the circulating system and applying circulating pressure to the refrigerant, and means for conducting added heat to the returned refrigerant in the chamber from the surroundings, said heat exchange relation- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,155,484 Gottlieb Apr. 25, 1939 2,168,157 Crago Aug. 1, 1939 2,176,289 Beebe Oct. 17, 1939 2,214,055 I-Ienney Sept. 10, 1940 2,287,492 Brown June 23, 1941-2 2,440,098 Keller Apr. 20, 1948 2,450,713 Brunsing Oct. 5, 1948 FOREIGN PATENTS Number Country Date 522,507 Great Britain June 19, 1940

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