US3374640A

US3374640A - Liquid gas refrigeration system

Info

Publication number: US3374640A
Application number: US520254A
Authority: US
Inventors: Harold L Boese
Original assignee: Boese Corp
Current assignee: Boese Corp
Priority date: 1966-01-12
Filing date: 1966-01-12
Publication date: 1968-03-26
Anticipated expiration: 1985-03-26

Description

March 26, 1968 H. L. BOESE 3,374,640

LIQUID GAS REFRIGERATION SYSTEM Filed Jan. 12, 1966 Fig.|

INVENTOR Harold L. Boese BY 75% wad ATTORNEY United States Patent 3,374,640 LIQUID GAS REFRIGERATION SYSTEM Harold L. Boese, Duncanville, Tex., assignor to Boese Corporation, Dallas, Tex., a corporation of Texas Filed Jan. 12, 1966, Ser. No. 520,254 22 Claims. (CI. 6252) ABSTRACT OF THE DISCLOSURE This invention relates to a refrigeration system utilizing a liquid gas as a cold reservoir. A vaporizer is employed to convert the liquid gas to a vapor in which form it is passed through a set of cooling coils across which a ventilator forces a flow of air. The vaporizer is disposed remote from the air flow to prevent erratic operation, and in a preferred embodiment, the volumes of the vaporizer and cooling coils are substantially equal to equalize the vapor pressures Within the system.

It is commonly known that conventional refrigeration and air conditioning systems which utilize compressors are complex, expensive and require considerable maintenance. Conventional systems which do not use a compressor, such as gas air conditioners employing the heat pump effect, are also expensive for other reasons. Moreover, both of these types of systems comprise a relatively large amount of hardware and parts. Thus it is apparent that an air conditioning or refrigeration system in which the initial cost is low, which is economic to operate and which is greatly simplified in terms of the amount of equipment and parts used, has many advantages over more conventional systems.

Several attempts have been made to provide a simplitied and inexpensive system to replace the more conventional compressor type and gas-heat pump type systems by using an available cold reservoir, such as Dry Ice or liquid gas. However, none of these systems have met with any degree of success for one or more reasons, as evidenced by the lack of commercially available units. Suffice it to say that a system that uses Dry Ice as a cold reservoir is impractical because of the volumes required for storage, the fact that conduction to or from the cold reservoir takes place by means of carbon dioxide in the gaseous form, which is a poor conductor, and the fact that no means have been devised to conserve the Dry Ice. Insofar as liquid gas reservoir systems are concerned, no effective system has been devised that provides the degree of cooling required in conjunction with a sufiicient conservation of the liquid gas. Moreover, no such liquid gas system has been devised that provides the necessary degree of control both as to temperature of the volume or space to be refrigerated and as to the use of the liquid gas itself.

The use of a liquid gas for refrigeration purposes is desirable, however, because of its now availability in commerial quantities at low cost, its large gas to liquid volume ratio for providing storage in a small space in the liquid form and the very low temperature of the gas in the liquid form. Be this as it may, liquid gas is difficult to handle and control by virtue of the latter two characteristics just noted. A few observations regarding the desirable features which a refrigeration system which uses a liquid gas reservoir will be informative when taken in conjunction with the problems of controlling the liquid gas.

Use of any liquid gas dictates that the vapor necessarily derived therefrom must eventually be discharged. It is not desirable to discharge this vapor directly into the space to be refrigerated for cooling purposes or otherwise, since there is inherently poor circulation of the vapor for cooling purposes and it is normally undesirable to fill this space with this vapor. Moreover, use of the vapor in the manner for cooling is inherently inefiicient in terms of the quantity of liquid gas used. If the vapor is discharged into the space, a vent means must be provided to relieve the pressure build-up, thus creating an air conditioning leak. Even in circumstances Where it is not objectionable to discharge the vapor into this space, a suitable circulation means should be provided for forcing a flow of air across a set of coils which are cooled by the liquid gas vapor.

Because of the tremendous pressures developed when liquid gas is converted to a vapor, it will be apparent that controlling the vapor and thus the temperature of the space to be refrigerated, presents unusual problems, both engineering and otherwise. Consequently, an efiicient vaporizer is necessary to provide an effective control over the gas in both the liquid and vapor forms, which also implies an effective efliciency control. Moreover, an effective control over the vapor, or rate at which it is derived from the source of liquid gas, also implies an effective temperature control of the space to be refrigerated. In the provision of an effective and controllable vaporizer, it is also undesirable that the vaporizer be situated in any substantial heat exchange relation with the flow of air that is forced across the cooling coils for circulation, since this would be a factor causing at least a partial loss of control over the vaporization process. There are other considerations that must be taken into account in the use of a liquid gas reservoir to provide an effective refrigeration system, but the above noted factors are of prime consideration.

The present invention has as a broad object thereof the provision of an air conditioning or refrigeration system which utilizes a liquid gas reservoir, wherein the system is both economical in cost and in operation. Further, it is another object to provide such a system that has application to virtually all air conditioning and refrigeration needs. Accordingly, the present invention provides a system utilizing a reservoir of liquid gas in which vapor is derived from the gas at a controlled rate and passed through a set of coils across which air within the space to be refrigerated is forced to provide the necessary refrigeration. Preferably, liquid nitrogen is used because of its commercially available quantities at low price, its low temperature in the liquid state and its large gas to liquid volume ratio. The conservation of the liquid gas is of primary importance in providing for economical operation while still providing for all the cooling power that is needed. To effect this, the system employs a vaporizer for the liquid gas that controls the amount of vapor used in accordance with the volume and cooling requirements of the cooling coils.

Another object is to utilize, to the greatest degree possible, the liquid gas and vapor therefrom for additional functions other than for its cooling effect, While providing a system in which the refrigeration can be controlled as desired. When a liquid gas is enclosed, a considerable vapor pressure will develop which, if not used for refrigeration, must be released. In most refrigeration applications, the system will cool the space to be refrigerated to a temperature below which it is not desirable to cool, in which case, the system'is cut back to control the space at this temperature. This means that less vapor from the liquid gas is needed for refrigeration, and consequently, this vapor is available for other useful work. Moreover, it has been found that there is quite often more available vapor from the liquid gas than is required for the refrigeration function. To utilize this additional vapor, the invention also provides, in an embodiment thereof, a completely automatic and self-contained system in which the vapor from the liquid gas is also used as a power source for operating other parts of the system in addition to its refrigeration functionl Specifically, an air driven ventilating fan means is employed which operates from the pressure of the vapor derived from the liquid gas. Moreover, the system, in another embodiment, is automatic in that various fiow rates of the liquid gas and vapor therefrom are controlled by valve means in response to the temperature of the space to be cooled. In addition, a gas storage means is provided in communication with the liquid gas reservoir to relieve the vapor pressure therefrom for later use to perform useful work other than refrigeration.

- Many other objects, features and advantages will become readily apparent from the following detailed description of the invention when taken in conjunction with the 7 appended claims and attached drawing, wherein:

FIGURE 1 is a schematic diagram of a preferred embodiment of the refrigeration system of the invention; and

FIGURE 2 is'anelevational view in section of an air drivenv motor adapted for operation from a source of pressurized vapor from a liquid gas.

The system, as shown in FIGURE 1, comprises a container for containing a quantity'of a liquid gas, which container is comprised of any suitable material, such as metal, and which is suspended within an insulated outer container 12 and insulated therefrom by a vacuum space 14. Container 12 is any suitable vacuum type container having insulated walls, wherein a preferred insulation for .the wallsis pearlite aggregate having an ASTM specification of C--57T, although any other suitable insulation can be used. A pipe is provided to the reservoir 7 and communicates with the vacuum space between the inner and outer containers for pulling a vacuum within the space by any suitable vacuum means or pump (not shown) through a pipe 36 connected to pipe 40 through'a hand valve 38 and a suitable vacuum gauge 42 provided in line 40 to monitor the vacuum. Line 40 is sealed within the outer container by a vacuum seal. Another pipe or conduit 24 communicates with the cold reservoir and passes through the outer container by a vacuum seal and into the interior of the inner container, also by a vacuum seal. This conduit extends down near the bottom of the inner container and is open on that end, and serves the dual purposes of filling the inner container with the liquid gas and drawing off liquid gas from the reservoir for use as a refrigerant. Connected in communication with this con- .duit is a fill pipe 20 by means of another hand valve 22.

Another conduit 30 communicates with the interior of the reservoir and is passed through the walls of the inner and outer containers, as shown, by vacuum seals. This conduit has, as one purpose, the provision of a tank exhaust means and is connected through a pressure gauge 32, a safety, pop-off valve 34and through a hand valve 28 to pipe 26, the latter of which is open to the atmosphere.

pipe 20 while

hand valves

22 and 28 are open, all as will be explained below. An extension of conduit 24 is connected through a hand valve 52 and a solenoid valve 54 to a set of coils'56 wound around the inner container 10 in heat conduction relationship therewith, whereby another extension 58 connected to the bottom of the'set of coils is connectedto one side of another solenoid valve 60. The other side of valve 60 is connected into a vaporas a cooling fluid.

Another pipe '68 communicates with the interior of enclosure 62 of the vaporizer and is connected to the input of a set of cooling coils across which air is forced to coolthe space to be refrigerated. The output of the cool-' ing coils 70 is then connectedto communicate with a gas storage tank 78 by means of apipe 72 connected at one side to another solenoid valve 74 and pipe '76 connected at the other side of the solenoid valve and into the storage tank. The storage tank, to be further explained, is adapted to store the cold vapor passing through the cooling coils for acting as a power source for driving an air or gas driven motor. A suitable pressure gauge and safety, pop-off valve 82 is provided to the storage tank for monitoring the pressure and maintaining it at a safe level. A ventilating fan and motor- 86 is used to draw air across the cooling coils for circulating the cold air within the space to be refrigerated. In the preferred embodiment, the ventilating fan and motor comprises an air driven motor specially adapted for use with a cold gas as will be explained in conjunctionwith FIGURE 2,

' and is connected to the top of the storage tank by means of a conduit 84 passing through a pressure valve 85 and another solenoid valve 83. Valve 85 serves to automatical- 'above a predetermined minimum and to maintain't'he pressure of the vapor in the top of the inner reservoir tank 10 below a predetermined maximum. This is not just for safety purposes in so far as the reservoir tank is concerned, but allows a sufiicient pressure to be maintained within the storage tank for providing the required power for the system. To effect such a pressure distribution, the

inner reservoir tank 10 and the storage tank 78 are con solenoid valve 60 by means of another cross-coupling 98.

All of the solenoid valves mentioned are thermostatically operated in the preferred embodiment of the invention for automatic control. One means for accomplishing this, as shown in FIGURE 1, comprises a thermostat located in heat conduction relationship with the cooling 'coils 70 to monitor the temperature thereof, wherein the temperature of the cooling coils is proportional to the temperature of the volume or space to be refrigerated.

. Thermostat 100, in one embodiment, is a conventional,

The inner container 10 is filled with the liquid gas through a temperature operated off-on switch connected at one side 7 to a battery or voltage source 106 through electrical connection 102 and at the other side by connection 104 to one terminal each of the four

solenoids

74, 54, 60 and 92 through

electrical connections

112, 116, and 124, respectively. The other side of the battery or voltage source is connected to the other terminals of the

solenoids

74, 54, 60 and 92 by means of

electrical connections

110, 114, 118 and 122, respectively. It will be remarked at this time that, in the particular embodiment shown and for the particular operation to be described, solenoid 92 is normally open, whereas each of

solenoids

54, 60 and 74 are normally closed. {That is to say, solenoid'92 can be spring biased to an open condition which closes only upon the application thereto of a suitable voltage to close it, wherein the solenoid valve opens again when the voltage signal is removed. In contrast to this, the operation of the other solenoids are the opposite. Moreover, solenoid 83, although connected to a different thermostat control, is also normally open. i

. The operation of this system, including the various features thereof, will now be described. The reservoir tank is initially, filled With alliquid gas for operation. To accomplish this,

hand valves

22 and 28 are opened and hand valve 52 is closed. It will be assumed, of course, that a vacuum has already been established between the inner and outer containers of the reservoirqA liquid gas is then pumped through connection into the interior of inner tank 10, and the fumes or vapor resulting from the filling of the tank are permitted to exhaust through conduit 30 and out connection 26 through open valve 28. If the exhaust path is not provided, it would be very difficult, if not impossible, to fill the tank to the desired quantity. Hand valve 52 is maintained closed during this time so that vapor pressure within the top of the inner tank 10 will not force the liquid gas back up through the system prior to the time that operation is desired. The vapor within the top of the reservoir tank, however, can travel through cross-connection 96 and conduits 94 and 90 down into the storage tank, since valve 92 is normally open. There is no objection to this since the purpose of the storage tank is to store vapor at all times. The vapor can not enter into the vaporizer through solenoid 60 at this time as the latter is close-d. Once the reservoir has been filled to the desired quantity of liquid gas,

solenoid valves

22 and 28 are closed and solenoid valve 52 opened. The system can then be left in this condition for a predetermined period of time to permit vapor to pass into the storage tank 78 through conduit 90 until a predetermined pressure is attained. At this time, the system can be actuated by closing a main switch 105 connected between the battery and thermostat 100 to actuate

solenoid valves

74, 54, 60 and 92 in response to the temperature of the cooling coils.

The temperature of the cooling coils will initially be at a relatively high temperature, thus causing normally open solenoid 92 to close and normally closed

solenoids

54, 60 and 74 to open. The pressure established within the inner tank 10 as a result of vapor boiling from the liquid gas Will force the liquid gas by perculator action up through conduit 24, through hand valve-52 and solenoid 54 and down through the length of conduit 56 forming a coil about the inner reservoir tank in heat conducting relationship therewith. The passage of liquid gas through coil 56 acts as an additional thermal shield for the reservoir, whereby it should be understood that conduit 56 is not absolutely necessary and can be obviated if desire-d. The liquid gas passes through conduit 58 and open solenoid 60 into the vaporizer, wherein the liquid gas is vaporized or atomized as it passes through holes 66. The gas, now in a vapor form, passes into the cooling coils 70 through conduit 68 and on into storage tank 78 through open solenoid valve 74. The vapor pressure from storage tank 78 causes the ventilating fan 86 to be driven by the passage of the vapor therethrough. By this means, air is drawn across the cooling coils to cool the space to be refrigerated. As the temperature of the air of the space to be refrigerated drops and as the temperature of the cooling coils drops in accordance therewith, thermostat 100 will open at a predetermined temperature to close

solenoid valves

54, 60 and 74 and to open solenoid valve 92. This is the temperature at which sufiicient cooling is provided so that a continued drop in temperature is not desired. However, it is important to maintain circulation of the air within the space to be cooled, and thus the ventilating fan 86 continues to run. This is provided by the pressure from'the storage tank 78. Furthermore, since liquid gas is no longer being derived from the reservoir at this time, it is necessary to relieve the vapor pressure within the top of the inner tank. Moreover, the pressure within the storage tank 78 will tend to drop as it is not being supplied through the cooling coils. To provide a stabilization between the two tanks, the vapor passes from the liquid gas reservoir through cross-connection 96 and down into the storage tank through open solenoid valve 92. Thus a continuous source of pressure is provided for running the ventilating motor 86.

Cross-connection 98 is provided between the top of the reservoir tank and the input to the vaporizer to further relieve the pressure from the liquid reservoir when solenoid valve 92 is closed, so that an excessive amount of pressure will not build up within the liquid reservoir when the system is circulating the liquid gas. That is to say, -a release path is provided should the pressure within storage tank 78 tend to exceed a maximum during operation of the system. Pressure valve is provided in conduit 84 to maintain a constant flow rate of vapor through motor 86. This pressure valve is of any suitable design and is automatic in that it opens and closes according to the pressure applied thereto from storage tank 78.

Vaporizer 62 plays a very important functional role in the operation of the system. It will be noted that in the preferred embodiment shown, the liquid gas is converted to a vapor primarily by an atomization process rather than by heating the liquid gas, although heating does play a part. The vaporizer is at a higher temperature than the liquid gas itself, and thus the higher heat does aid the atomization process. However, the heat transferred to the vaporizer from its surroundings is substantially constant, so as not to vary the rate of vapor formation that is controlled. It is highly undesirable that the vaporizer be situated within the air flow created by ventilator 86, since this will effect the control and cause substantially greater heating of the vapor and its rate of creation. This, of course, is because of the heat exchange relation that would exist between the vaporizer and the high velocity air stream. It is much more desirable to have the liquid gas vaporized at as low a temperature as possible, transfer the vapor to the cooling coils, and effect all the necessary refrigeration of the space by an air flow across the coils. Since the vapor flow through the coils must be stopped from time to time to maintain the exact temperature control desired, means must be provided to perform this function, and this is effected by the solenoid valve 60'. It will be remarked that pressure within the vaporizer will exceed the pressure within the reservoir tank because of the higher temperature. If valve 60- were disposed between the vaporizer and the cooling coils in conduit 68, the increased pressure would back up into the reservoir tank when the valve is closed. Consequently, a tremendous rush of vapor, and even the liquid gas itself, would be pushed through the cooling coils when the valve is reopened because of the pressures involved. The liquid gas would not have time to become vaporized because of the velocity with which it would travel from the reservoir tank to the coils. Consequently an excessive amount of liquid gas would be used and wasted, in addition to an almost complete loss of temperature control and regulation. By situating valve 60 between the reservoir and vaporizer, the increased pressure is blocked within the vaporizer and not allowed to back up into the reservoir. In effect then, the flow of liquid gas itself is directly controlled to effect an indirect control over the flow of vapor. The system just described is capable of continuous operation for a considerable length of time before it becomes necessary to replenish the liquid nitrogen (or other gas) supply. Liquid nitrogen is preferred because of its commercial availability at low cost of about four cents (4c) per pound, its large gas to liquid expansion ratio and its low temperature of 320 F. in the liquid state. To illustrate the capacity of the system, and typical operating temperature and pressures, as one example only, a liquid nitrogen reservoir tank having a capacity to hold 97 pounds of liquid nitrogen when full is typical for refrigerating a refrigeration truck. The vapor pressure on the top is maintained at about 100 pounds per square inch pressure absolute. Similarly, the vapor storage tank is also maintained at about 100 pounds per square inch pressure and thus it will be seen that the storage tank acts as a pressure equalizer for the reservoir tank. It will be apparent that all the liquid nitrogen within the reservoir above the bottom of outlet conduit 24 will eventually be used. For safety purposes, the safety valves 34 and 82 are set to discharge at a pressure of about pounds per squire inch.

The volume of the vaporizer 62 is preferably equal to 7 the total interior volume of cooling coils 70, although diiferent volumes can be used. Should the volume of the vaporizer be larger than that of the cooling coils, a

layer of vapor pressure will exist in the vaporizer, thus causing the cooling coils to be operated at a lower tem perature than the vaporizer because of the increased vapor flow rate therethrough. Thermostat 100 is normally set at 40 F. for refrigeration purposes (the air or space being refrigerated being at a higher temperature),

maintain the proper refrigeration temperature in a refrigerated truck van of dimensions 40 ft. x 7.5 ft. x 7 ft., with a depletion rate of the liquid nitrogen of no greater than one pound per hour.

The system, as shown in FIGURE 1, can also be used to air condition the cab of a truck, for example, or heat the cab as desired. To efiect this, another set of cooling coils 130 is provided across which a flow of air is forced by a ventilator 133 within the cab. To provide the cooling for the coils 130, a conduit 131 is connected to the outlet conduit 88 of motor 86 through a three-way valve 87. Valve 87, when turned as shown, connects

conduits

88 and 131, but when turned 90 from that shown connects conduit 88 with an atmosphere exhause pipe 89 and shuts off conduit 131. The latter valve position is used when no heating or air conditioning to the cab is desired. A pipe 132 connects the outlet of coils 130 to ventilator 133 for operation, the latter also being a gas driven motor and fan' combination. The vapor is then discharged to the atmosphere through pipe 134.

For purposes of heating, a conduit 138 connects a set of heating coils 137 wound about the truck muffler or other exhaust means 136 in communication with the outlet conduit from the storage tank, as shown, through another solenoid valve 139. The other side of the heating coils is connected in communication with conduit 84 preceding the input to motor 86 by means of conduit 140.

each of solenoid valves 83 and 139 through electrical connections 146 and .148, respectively, and the other thermostat terminal 144 is connected to one side of battery 106.

Theother terminals

145 and 147 of solenoid valves 83 and 139 are connected to the other side of the battery.

When thermostat 142 registers above a predetermined maximum temperature, solenoid valve 139 is closed, and valve 83 is open, thus allowing the cold vapor from the storage tank (which is suitably insulated) to pass directly to motor 86 and into coils 130. If the temperature registered by thermostat 142 falls below a predetermined minimum, valve 83 Will be closed and valve 139 opened, thus directing the vapor from the storage tank through the heating coils 137 before it passes through motor 86 and coils 130. It will be apparent that cold vapor passing through coils 130 will be at a higher temperature than when the vapor passes through coils 70, primarily because of the heating effect on the vapor in the latter. However, this is desirable since it is normally not desired to refrigerate the cab of the truck to the degree that the van is refrigerated. Even so, the vapor temperature is more than adquately low to provide all the cab refrigeration required. In so far as the heating of the cab is concerned, it will be apparent that the vapor from the storage tank provides a readily available medium for transferring heat 8 from the exhaust means 136 to coils 130. Without this vapor supply, an air intake system, or water system, would be required.

An elevational view in section of an air driven motor adapted for use with the system as the ventilating means is shown in FIGURE 2. It will be remarked that a conventional air driven motor cannot be used with this system because of the low temperature of the vapor that is used to drive it, although suitable modifications can be made to adapt it for this use. The motor comprises a housing 150 which defines a central, cylindrical cavity 151 having a cylindrical wall surface 152. The housing is mounted on a base 154 for mounting the motor. A cylindrical rotor 156 is provided which is mounted eccentric of the central axis of the housing on an axle 158 mounted at either end in conventional bearings (not shown). A set of

vanes

160, 162, 1-68 and 170 are provided within the rotor, which vanes are elongated and substantially coextensive with the length of the rotor along the axis thereof and mounted within suitable channels.

Vanes

160 and 162 are each spring-biased outwardly by springs 165 and 166, respectively, which springs bear against the inner ends of the vanes and bear against the opposite ends of a pusher rod 164 at the other ends. The pusher rod is free to move along the line connecting the two vanes as required by the pressure exerted by the springs. The outer ends of the vanes are curved to provide a smooth interface with the inner surface 152 of the motor housing. Vanes 168 and 170 are similarly mounted on the opposite ends of another pusher rod 172 through springs 173 and 174, respectively, wherein this pusher rod is also free to move along the line connecting the two vanes as determined by the spring pressures. The pusher rods 164 and 172 are nonintersecting for obvious reasons.

A first channel or cavity is provided in the motor housing at one side of the rotor and communicates with a pipe or conduit 184, so that air or other gas may be supplied through the pipe to the intake 180 of the motor. Similarly, another channel or cavity 182 is provided at the other side of the rotor and communicates with another pipe 186. This motor, as appears from the drawing,

can be driven in either direction with pipe 184 being used as the input and pipe 186 used as the output, or vice versa. Assuming that air under pressure is applied through pipe 184, the-air pushes against the vanes to cause the rotor to turn in a counter clockwise direction as viewed in FIGURE 2. The rotor is mounted eccentric to the axis of the motor housing so that a pressure differential or build up will be created as the rotor rotates to compress the air on the right side of the rotor when turning in a and the vanes are dissimilar, and consequently have different thermal coeflicients of expansion and contraction.

'Even if the rotor and vanes are comprised of the same metal, the tolerances that would have to be maintained would be too severe because of the relatively large thermal coefficients of expansion of most metals. To eliminate this problem, the rotor and vanes are manufactured of the same material which has a very low coeificient of thermal expansion and contraction. In the preferred embodiment, both the rotor and vanes are comprised of Teflon, which is commonly known and is a trade name of the Du Pont Company. This material, in addition to having a low thermal coefiicient of expansion and contraction, is well adapted for the use to which it is applied in the rotor.

Consequently, the motor cannot freeze up even at the low temperatures involved.

Many modifications and substitutions of the invention will undoubtedly become apparent when taken in conjuction with the preceding description thereof. However, it is intended that all such modifications and substitutions that fall within the true scope of the invention be included therein, and that the invention be limited only as defined in the appended claims.

What is claimed is:

1. A refrigeration system comprising:

(a) a source of liquid gas,

(b) a set of cooling coils through which vapor from said liquid gas passes,

(c) a ventilator for forcing a flow of air within a space to be cooled across said cooling coils, and

(d) a vaporizer situated in substantially non-heat exchange relation With said flow of air and said space to be cooled connecting said source of liquid gas with said set of cooling coils for supplying said set of cooling coils with a flow of vapor from said liquid gas therethrough.

2. A refrigeration system according to claim 1 including an enclosed container for containing said liquid gas under vapor pressure, and a conduit connecting said source of liquid gas with said vaporizer having an open end communicating with the interior of said container beneath the liquid level of said liquid gas and arranged so that liquid gas is freed therethrough against the force of gravity by said vapor pressure.

3. A refrigeration system according to claim 2 wherein said vaporizer comprises an enclosed space which communicates with said set of cooling coils and an atomizer coupled to said conduit and disposed within said enclosed space through which said liquid gas passes and is converted to a vapor.

4. A refrigeration system according to claim 1 wherein said ventilator comprises a gas driven ventilating fan means communicating with the outlet of said set of cooling coils for being driven by the vapor passing through said set of cooling coils.

5. A refrigeration system according to claim 3 wherein the interior volume of said enclosed space is substantially equal to the interior volume of said set of cooling coils.

6. A refrigeration system according to claim 1 wherein said liquid gas comprises nitrogen.

7. A refrigeration system according to claim 2 wherein at least a part of said conduit is disposed in heat exchange relation with said container.

8. A refrigeration system according to claim 1 including control means disposed intermediate said source of liquid gas and said vaporizer for regulating the flow of liquid gas to said vaporizer.

9. A refrigeration system according to claim 4 including a gas storage tank disposed intermediate and in communicating relationship with said set of cooling coils and said ventilating fan means.

10. A refrigeration system comprising:

(a) a container for containing a liquid gas,

(b) a vaporizer for converting liquid gas to a vapor,

(c) a first conduit having an open end communicating with the interior of said container beneath the liquid level at which said liquid gas is to be maintained and communicating at the other end with said vaporizer, through which liquid gas is forced by the vapor pressure created in the top of said container,

(cl) a set of coils communicating at an inlet thereof with said vaporizer through which said vapor passes,

(e) a gas storage tank,

(f) a second conduit connecting the outlet of said set of coils with said gas storage tank for containing the vapor passing through said set of coils,

(g) a third conduit connecting the top of said liquid gas container with said storage tank,

(h) a gas driven ventilating fan means communicating with said gas storage tank for being driven by the vapor contained within said storage tank for forcing a flow of air within a space to be cooled across said cooling coils,

(i) first, second and third controllable valve means disposed within said first, said second and said third conduits, respectively, and

(j) control means connected to said first, said second and said third valves responsive to the temperature of said set of coils for controlling said first, said second and said third valves means.

11. A refrigeration system according to claim 10 wherein said control means causes said third valve means to close when said first and said second valve means are caused to be opened thereby, and vice versa.

12. A refrigeration system according to claim 10 wherein said first and said second valve means are normally closed and said third valve means is normally open, and said control means causes said first and said second valve means to open and said third valve means to close when the temperature of said set of coils exceeds a predetermined minimum, whereby said third conduit provides a path for the flow of vapor from said liquid gas container to said storage tank when said first and said second valve means are closed and said third valve means is open to maintain the vapor pressure within said liquid gas container below a predetermined maximum and said vapor pressure within said storage tank above a predetermined minimum.

13. A refrigeration system according to claim 12 including a fourth conduit connecting said storage tank with said ventilating fan means, and fourth valve means disposed within said fourth conduit for maintaining the flow rate of vapor to said ventilating fan means substantially constant.

14. A refrigeration system according to claim 13 wherein each of said first and said second valve means comprises a normally closed solenoid valve, said third valve means comprises a normally open solenoid valve, said fourth valve means comprises a pressure regulator, and said control means comprises a source of electrical power for operating said first, said second and said third valve means and thermostat means for connecting said source of electrical power thereto when the temperature of said set of coils exceeds said predetermined minimum.

15. A refrigeration system according to claim 10 including a fourth conduit connecting the top of said liquid gas container with said first conduit.

16. A refrigeration system according to claim 10 including a fourth conduit connecting said third conduit with said first conduit, wherein said first valve means is disposed within said first conduit between the interconnection of said first and said fourth conduits and said vaporizer, and said third valve means is disposed within said third conduit between the interconnection of said third and said fourth conduits and said storage tank.

17. A refrigeration system according to claim 1 including an additional set of cooling coils, means for passing the vapor passing through said first mentioned set of coils through said additional set of coils, and an additional ventilator for forcing a flow of air across said additional set of cooling coils.

18. A refrigeration system according to claim 10 including an additional set of coils communicating at an inlet thereof with the outlet of said ventilating fan means through which said vapor passing through said ventilating fan means passes, and an additional gas driven ventilator fan means communicating with the outlet of said additional set of cooling coils for being driven by said vapor for forcing a flow of air across said additional set of cooling coils.

19. A refrigeration system according to claim 10 including an additional set of coils, a fourth conduit connecting said gas storage tank with an input of said ventilating fan means to provide said communication therefor, a fifth conduit connecting an outlet of said ventilating fan means with an inlet to said additional set of coils through which said vapor passing through said ventilating fan means passes, a sixth conduit having an inlet and an outlet and adapted to' be disposed in heat conducting relationship with a source of heat interconnected at both said inlet and said outlet thereof with one of said fourth and said fifth conduits,'means for controllably directing said vapor which passes through said additional set of coils through said sixth conduit, and additional gas driven ventilating fan'means communicating with the outlet of said additional set of coils for being driven by said vapor for forcing a flow of air across said additional set of coils.

20. A refrigeration system according to claim 19 wherein said means for controllably directing said vapor through said sixth conduit comprises a fourth controllable valve means disposed within said sixth conduit and a fifth controllable valve means disposed in said one of said fourth and said fifth conduits between said inlet and said outlet of said sixth conduit.

12 7 21. A refrigeration system according to claim 1 wherein said vapor passing through said set of cooling coils is discharged remote to said space to be cooled.

22. A refrigeration system according to claim 10 wherein said vapor passing through said ventilating fan means is discharged remote to said space to be cooled.

, I References Cited UNITED STATES PATENTS 1,905,811 4/1933 Culver 62440 2,718,766 9/1955 Imperatore et al. 62-434 2,943,459 7/1960 Rind 6252 r 3,058,317 10/1962 Putman 62-52 3,092,976 6/1963 Tafreshi 6298 3,191,395 6/1965 Maher et al. 62--52 3,241,329 3/1966 Fritch et al. 62-52 3,255,597 6/1966 Carter 62-239 3,271,970 9/1966 Berner 62-419 LLOYD L. KING, Primary Examiner.