US2901892A - Secondary refrigerant and apparatus for circulating the same - Google Patents

Description

J. E. WOODS Filed March '7, 1956 SECONDARY REFRIGERANT AND APPARATUS FOR CIRCULATING THE SAME IN V EN TOR.

JOHN wooos ATTORNEYS OE O$ R DRY ICE PRESSURE GENERATOR PRESSURE REGULATING VALVE OOOLANT COOLING TUBES Sept. 1, 1959 E a; I! E MIXING VALVE atent Patented Sept. 1, 1959 SECONDARY REFRIGERANT AND APPARATUS FOR CIRCULATING THE SANIE John E. Woods, Cohasset, Mass, assignor to Standard- Thomson Corporation, Waltham, Mass, a corporation of Delaware Application March 7, 1956, Serial No. 570,094

4 Claims. (Cl. 62-86) The present invention relates to secondary refrigerants for cooling systems, such refrigerants being of the brine type, that is, maintaining the liquid state throughout the circulation cycle. More particularly, the invention is concerned with such refrigerants for cooling systems operated by direct application of gas pressure thereto.

This application is a continuation-in-part of my copending application Serial No. 322,676, filed November 26, 1952, now Pat. No. 2,760,345.

The principal object of the present invention is to provide a circulating liquid coolant (or brine) for a system of the general type described in the abovementioned application, wherein circulating pressure for the coolant is supplied by sublimation of a quantity of Dry Ice. By means of a float valve chamber, the circulating pressure is applied intermittently to the coolant to cause it to circulate, first through coolant cooling tubes disposed in a heat exchange relation to a body of Dry Ice, and then through cooling tubes disposed in the space to be cooled.

In such a system, it is clear that certain sections of the circulating liquid system are cooled to temperatures below the freezing point of water, whereby any water accidently entrapped in the pipes would turn to ice and tend to clog the system and impede the flow of coolant. This is especially undesirable in a low pressure circulating system such as that described. It is accordingly a further and important object of the invention to provide a suitable coolant in which such water entering the circulating system is miscible, thereby preventing such clogging.

A further object is to provide a circulating coolant that has a high flash point. It is of course obvious that the coolant must also have a sufliciently low viscosity to permit flow at low operating temperatures created by the presence of a large body of Dry Ice.

With the above and other objects in view, the features of the invention include the use of ethylene glycol monoethyl ether, having the formula C H OCH CH OH and commonly sold under the trade name Cellosolve, as the circulating coolant. The features of Cellosolve include a relatively high flash point of 135 F., and low viscosity at the operating temperatures experienced in the above-described system. Also, I have found that water is miscible in Cellosolve, with the result that leakage thereof into the system does not give rise to blockage, as would be the case if such water were allowed to collect and freeze at some point in the system.

The above and other features of the invention will be. more clearly understood from the following description of a preferred embodiment of a coolant system adapted to use a coolant according to this invention as the circulating liquid therein.

The drawing illustrates a preferred embodiment of a Dry Ice cooling system for installation in a truck trailer or railroad box car, said system incorporating the coolant according to this invention. This system may also be used, of course, in a stationary installation.

As heretofore mentioned, Dry Ice, preferably in the block form, is used for cooling the liquid coolant prior to its entry into the space cooling tubes. This Dry Ice isloaded through an opening at the top having a cover 2 into a Dry Ice bunker 3, which may be constructed as shown in my above-mentioned application, with a number of cooling tubes at the bottom disposed in parallel fashion between headers connected into the coolant circulating system. An atmosphere vent 4 prevents the building up of pressure in the bunker.

The properties desirable in a coolant suitable for use in a system of this type include, in addition to the miscibility of water therein, a high flash point and low viscosity at operating temperatures. The former property reduces the hazards incident to the use of a combustible substance under extremes of ambient temperature and in the possible presence of sparks, as in a railroad installation. The latter property tends to eliminate sluggishness in the circulation. Accordingly, I preferably use one of the lower alkyl ethers of lower alkylene glycols, such as ethylene glycol monoethyl ether, namely Cellosolve as previously stated. This liquid is used in a substantially pure form, that is, undiluted with Water.

Dry Ice for generating the circulating pressure, also preferably in the block form, is loaded into a Dry Ice pressure generator through an outside cover 5 and an opening having a gas tight cover 6. The pressure generator may be constructed as shown in my above-mentioned copending application, being provided with a second, or double bottom, which may be made of sheet metal welded to the side walls to provide an exchanger through which the coolant may be circulated prior to its entry into the coolant cooling tubes. The heat exchanger may be provided with one or more partition walls, whereby the flow path is of any desired length, or the heat exchanger may be constructed in any other desired manner readily permitting the flow of heat from the coolant into the space above.

A rupture disk 8 is also preferably constructed into the wall of the pressure generator. This places an absolute limit on the pressure in the generator regardless of any failure of the valves or other parts of the circulating system, and in the embodiment described I have found that a disk which ruptures at about 15 psi. is normally quite satisfactory.

A pair of relief valves 10 connect the space above the sublimating CO in the pressure generator through a hand valve 12 to a main pressure line 14. The relief valves are provided with vents 15 and adjusted to hold the pressure in the line 14 at a substantially constant value above atmospheric, as explained in my abovementioned application. They are connected in parallel to insure continuous application of pressure to the line 14 in case one of them should become plugged with frost. The line 14 is connected with a pressure regulating valve, which is fully described in my above-mentioned application, and with a coolant reservoir and float valve chamber, the latter being connected through a four-Way valve 16. The valve 16, as well as the other parts of the float valve chamber and coolant reservoir are fully described in my above-mentioned copending application, and their operation is briefly as follows.

Warm coolant returning from the space cooling tubes over a line 18 is vented into the float valve chamber. Within the chamber is a float 20 slidably mounted on a fixed spindle 22 having slots through which are projected a pair of lugs 24 and 26, secured to a valve stem 27.

While the coolant rises in the chamber, the valve stem 28 is connected with the space above the liquid in the chamber, and the pressure line 14 is disconnected from the chamber. In some instances the vent 28 may become plugged with frost. To avoid this possibility, it is preferably connected to the space above the Dry Ice in the bunker as shown in the drawing, since this space is at atmospheric pressure, but at a considerably reduced temperature. It is also devoid of moisture by reason of the high concentration of CO caused by the gastight lining, hereinafter more fully described. At this time the pressure for circulating the coolant is provided by the connection of the line 14 with the space above the liquid in the coolant reservoir.

While the liquid is flowing into the float valve chamber as above described, it is prevented from flowing downward through a pipe 30 into the coolant reservoir by reason of the pressure differential between the valve chamber and the coolant reservoir holding a check valve 32 closed. Also, liquid is prevented from flowing in the reverse or upward direction through the pipe 30' by reason of the check valve.

Eventually, the float reaches the lug 24 and moves the valve stem upward, thereby disconnecting the atmosphere vent 28 from the space above the valve chamber, and connecting the pressure line 14 therewith. This stops the circulation of brine through the system by removing the pressure dilferential previously existing between the line 14 and the line 18. Since the spaces above the liquid in the valve chamber and coolant reservoir are now at the same pressure, namely, that of the line 14, the liquid in the valve chamber flows by gravity through the pipe 30 into the coolant reservoir until the float 20 strikes the lug 26, thereby giving the valve stem a downward movement, and re-establishing the initial conditions.

Thus, except for the periods in which the liquid in the valve chamber is being removed into the coolant reservoir, a circulating pressure diiferential is continuously applied to the coolant, which flows through a line 34 to the pressure regulating valve.

The pressure regulating valve provides means for dividing the flow from the pipe 34 between a line 36 and a line 38 according to the pressure in the line 14, which is connected to the valve by a line 40. Details of construction of this valve are fully described and illustrated in my above-mentioned application.

Thus a certain amount of the coolant is directed from the pressure regulating valve through the line 38 and directly to the coolant cooling tubes, and the remaining coolant is directed through the line 34 to the pressure regulating heat exchanger, from which it passes through a check valve 76, which prevents any tendency to thermal siphonic back flow, and enters the coolant cooling tubes. Upon leaving the cooling tubes, the coolant passes through a line 78 to parallel-connected space cooling tubes, preferably mounted at the ceiling above the space 79 to be cooled in the manner fully shown and described in my above-mentioned application. Upon leaving the space cooling tubes the coolant may pass through one or more of three parallel-connected paths to the line 18, from which it is emptied into the float valve chamber. The above-described parallel connections are intended as safety measures against the plugging or failure of any part of the apparatus in the space to be cooled. However, as previously mentioned, any plugging that is likely to arise would in most cases be caused by foreign matter or products of corrosion that might become lodged in the circulating system, such matter not including water that enters the system and becomes mixed with the Cellosolve. Hand valves provide means for isolating the parts of the apparatus most likely to fail during operation. These precautions have been dictated in part by the extremely high cost of cargo shipped under refrigeration in railroad car installations. The system is normally operated with a hand valve 80 closed, so that the returning coolant must pass through one or both of two temperature-regulated valves 81, compensated to eliminate the effect of pressure variations, these valves providing means for controlling the rate at which the returning brine fills the float valve chamber. Thus the temperature-regulated valves 81 provide means for regulating the rate of repetition of the flow cycle.

In my above-mentioned application, it is recognized that certain heat exchange relationships exist between the.

Dry Ice pressure generator and the Dry Ice bunker and coolant reservoir and related parts. Accordingly, I provide a pressure regulating heat exchanger in the floor of the pressure generator, and controlled means for diverting the flow of warm coolant into the exchanger to provide extremely close control over the net heat flow into the generator. This control is effected by the pressure in the main line 14 through the line 40 as described above and in my above-mentioned application. I also preferably provide insulation 82 as described in my abovementioned application to reduce the out-flow of heat to the body of Dry Ice above the coolant cooling tubes, so as to effectively isolate the generator from this source of heat loss. Enough of the warm coolant passing through the lines 34 is diverted to the heat exchanger to provide the necessary circulating pressure.

The presence of gaseous CO in the system affects the condition of the load and the operation of the system either by escaping into the space to be cooled or by settling to the bottom of the apparatus, being heavier than air, thus drawing air into the system at the top of the apparatus and allowing it to condense on the cooling tubes. This creates a form of heat insulation which is commonly experienced with ordinary household refrigerators, and which necessitates periodic defrosting.

Accordingly, I provide a gas tight lining 87 on the inside of Walls of the Dry Ice bunker 3, as shown in the drawing. This lining is preferably made of sheet metal such as aluminum, the pieces of which are preferably welded to each other, and welded or otherwise sealed to the tubes or vents leading to the outside. In this manner I may exclude the CO gas generated in the apparatus from the space to be cooled. I may also permit a controlled quantity of the gas to escape into the cargo space 79 through a tube 88 and a hand operated valve 90. I also prevent the continuous flow of moisture-laden air into the bunker, and substantially eliminate the formation of snow or other condensate on the coolant cooling tubes.

It should be noted that while the concentration of CO within the lining will be high, the pressure cannot go up by reason of the vent 4 leading to the outside at the top.

From the foregoing description, it will be appreciated that the described system operates at relatively low gas pressures, and that accordingly obstructions to the flow of coolant should be prevented from forming in operation. If water enters the system, the Cellosolve therein provides the very important advantage of mixing with the water, thus preventing the latter from collecting at bends or constrictions in the system and forming ice blocksi. Yet, even after dissolving an appreciable quantity of Water, the Cellosolve maintains the essential properties of a low viscosity coolant. I have found that the use of this coolant in a system such as that herein described affords much better over-all operation of the system than would be afforded by the use of any of the commonlyused brine solutions.

It will be understood that, while the invention has been described with reference to its application in a particular form of coolant circulating system, it also contemplates other comparable systems utilizing a circulating brine, such comparable systems being of such forms other than that here described as should occur to one skilled in the art after a reading of the foregoing specification.

Having thus described the invention, I claim:

1. A process for transmitting heat including the steps of applying superatmospheric gas pressure to a body of ethylene glycol monoethyl ether to circulate it in a circuit including a reservoir, a heat exchanger provided with a primary coolant, a heat exchanger in a space to be cooled and a collection chamber elevated from the reservoir and vented to atmosphere, and thereafter applying said gas pressure to the chamber to allow gravity flow from the chamber to the reservoir.

2. A process for transmitting heat including the steps of applying superatmospheric gas pressure at less than 15 p.s.i. to a body of ethylene glycol monoethyl ether to circulate it in a circuit including a reservoir, a heat exchanger provided with a primary coolant, a heat exchanger in a space to be cooled and a collection chamber elevated from the reservoir and vented to atmosphere, and thereafter applying said gas pressure to the chamber to allow gravity flow from the chamber to the reservoir.

3. A process for transmitting heat including the steps of applying superatmospheric gas pressure to a body of ethylene glycol monoethyl ether to circulate it in a circuit including a reservoir, a heat exchanger provided with a primary coolant, a heat exchanger in a space to be cooled and a collection chamber elevated from the reservoir, provided with a float and vented to atmosphere, and applying said gas pressure when the float reaches a predetermined level to allow gravity flow from the chamber to the reservoir.

4. A process for transmitting heat including the steps of applying superatmospheric gas pressure to a body of ethylene glycol monoethyl ether to circulate it in a circuit including a reservoir, a heat exchanger provided with a primary coolant, a heat exchanger in a space to be cooled, and a collection chamber elevated from the reservoir, provided with a float and vented to atmosphere, and applying said gas pressure to the chamber when the float reaches a predetermined upper level to allow gravity flow from the chamber to the reservoir, and reventing said chamber to atmosphere to repeat said first-mentioned step when the float reaches a predetermined lower level.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,289 Beebe Oct. 17, 1939 2,225,774 Flosdorf Dec. 24, 1940 2,379,249 Muskat June 26, 1945 2,450,713 Brunsing Oct. 5, 1948 2,636,357 Woods Apr. 28, 1953

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