US 3662561 A
Apparatus for use in a cryogenic gas cooling system for conditioning liquid cryogenic gas prior to introducing the same to an evaporator where the conditioned gas is vaporized, and an improved cryogenic gas cooling system utilizing the conditioning apparatus to provide a more efficient cooling system and to provide improved temperature control of a space to be cooled.
Description (OCR text may contain errors)
United States Patent Schroeder 1 May 16, 1972 541 COOLING APPARATUS 3,106,070 10/1963 Harper ..62/514  Inventor: Michael J. Sch er, Carromon Tex 3,491,547 1/1970 Watkins ..62/514  Assignee: Veskol, lnc., Garland, Tex. Primary ExaminerWilliam J. Wye Filed: y 1970 Attorney-James D. W1llborn  Appl. No.: 59,643  ABSTRACT Apparatus for use in a cryogenic gas cooling system for condi-  U.S. Cl ..62/119, 62/52, 62/53, tioning liquid cryogenic gas prior to introducing the same to 62/514, 62/208, 62/212, 62/217, 62/56 an evaporator where the conditioned gas is vaporized, and an [51 Int. Cl ..F25d 15/00 improved cryogenic gas cooling system utilizing the condition-  Field of Search ..62/52, 53, 514 A, 514, 208, ing apparatus to provide a more efficient cooling system and 62/209, 212, 217,45, 119 to provide improved temperature control of a space to be cooled.  References Cited 10 Claims, 4 Drawing Figures UNITED STATES PATENTS 3,046,751 7/1962 Gardner ..62/52 POWER SUPPLY PATENTAAEDHAY 16 I972 INVENTOR MICHAEL J. SCHROED ER ATTORNEY COOLING APPARATUS This invention relates to air-conditioning and refrigeration systems and, more particularly, to air-conditioning and refrigeration systems utilizing cryogenic gases.
Air-conditioning and refrigeration systems are known which operate to cool a defined space by vaporizing cryogenic or super-cooled liquid gas, such as liquid nitrogen, through an evaporative coil and thereafter disposing of the vaporized liquid gas into the atmosphere or, where the cooled space contains only vegetable produce or the like, into the defined space. Ventilating means are utilized in a conventional manner and are arranged with respect to the evaporative coils such that air is circulated across the coils and through the defined space to provide the cooling desired.
While cryogenic cooling systems appear to have substantial utility for cooling applications where there is little or no power available for driving compressors, such as would be required in the well known closed-loop, recirculating type of air-conditioning or refrigeration system in use today, they have not come into common use. I
The cost of certain cryogenic gases, for instance liquid nitrogen, has been reduced to a point where if the gas is used efficiently, then the cost of operating a cryogenic cooling system is within the means of high-volume consumers. Boat, aircraft, and automobile owners can utilize this type of cooling system without wasting valuable engine power driving compressors. Known cryogenic cooling systems do not operate efficiently because of two basic reasons: inefficient utilization of the coil surfaces and surging" in the coil.
In a cryogenic cooling system, the cryogenic gas is stored in a liquid state, and in order to improve the safety of the system, the liquid gas is stored at a low-pressure. In the past, the liquid gas has been allowed to flow directly into the evaporative coils as the cooling demand is increased. As with water in a pipe under low-pressure, the liquified gas flows along one portion of the side of the conduit, concentrating the cooling to that portion until vaporization is substantially complete. As a result, icing occurs along the outside of the coil corresponding to the super-cooled side, and the convectional efficiency between coil and air if substantially reduced. The remaining portions of the conduit side are not efficiently utilized. It is desirable and would substantially increase the operating efficiency of the unit if the cold from the cryogenic gas could be applied uniformly to all portions of the interior of the coil.
The more significant and related problem of surging occurs in a system of the type described when vaporization inside the evaporative coil takes place at a rate which exceeds the rate at which the substantially vaporized gas can be discharged from the system, thus the internal pressure of the evaporative coil exceeds the discharge pressure and a backpressure results. The back-pressure forces vaporized gas back through the evaporative coil, the connecting conduits, and to the storage tank, where the tank pressure-regulator means allows gas to escape until the internal pressure of the evaporator is reduced sufficiently to allow the flow of liquid gas into the evaporator in the initial manner. As soon as the liquid gas begins to vaporize again, the internal pressure of the evaporator coil again begins to increase until the cycle is repeated. As gas in the system cycles in the manner described, the temperature of the evaporative coil and thus the air passing over the coil to be cooled oscillates or varies over a wide range, making it virtually impossible to obtain uniform cooling, and the warmer, vaporized gas flowing back on or through the liquid gas warms the previously cooled coil and accelerates vaporization in the tank and the conduits coupling to the evaporator such that a substantial decrease in efficiency is experienced, cryogenic gas is wasted, and temperature control is detrimentally affected. Attempts to overcome the effects of surging have not resulted in a satisfactory solution to the problem.
Thus, it is an object of this invention to provide improvements in cryogenic gas air-conditioning and refrigeration systems.
Another object is to provide a means for improving the efficiency of cryogenic gas refrigeration and air-conditioning systems.
Still another object is to provide means for accurately controlling the operation of cryogenic gas air-conditioning and refrigeration systems to provide improved temperature control of the space cooled by said systems.
A further object is to provide means for use in cryogenic gas air-conditioning and refrigeration systems for balancing the heat loading of the evaporative coil of the system to the pressure generated in the coil to provide a smooth and continuous flow of gas through the systems.
Other objects and advantages will be apparent from the specification and claims and from the accompanying drawing illustrative of the invention.
FIG. 1 is a diagrammatic view of an air-conditioning system embodying this invention.
FIG. 2 is a partially sectioned side view of the cryogenic gas conditioning device of this invention.
FIG. 3 is a partially sectioned front view of the conditioning device illustrated in FIG. 2.
FIG. 4 is a top view of a portion of the air-conditioning system of this invention and illustrating the connection of the gas-conditioning device to an evaporator assembly having two circuits.
Refer now to FIG. 1. A cooling system embodying the features of this invention is shown generally at 10. For purposes of illustration, the defined space to be cooled 23 can be taken as the passenger cabin of a small aircraft, and the line 36 can be taken as at least a portion of the body of the aircraft. The location of components between housing 36 and cabin 23 is not critical and several acceptable arrangements are possible, except, of course, the vents 34 must communicate with the space 23.
The system 10 includes a source of liquified, cryogenic gas 11, which in the embodiment described is a wellinsulated, low-pressure gas storage bottle. Liquid nitrogen is stored in this tank at a temperature of 320 F., thus the tank is insulated both to help retain the low temperature of the liquid gas stored therein and to prevent injury to personnel who might I come into contact with its exterior surface. Since low-pressure gas is used in the system described, the tank 1 1 may be shaped to fit any convenient space, and for aircraft applications can be shaped to fit under one or more seats in the passenger cabin.
Any one of several gases can be used in the system; however, liquid nitrogen is most often used and is chosen here for illustration purposes because it is easy to handle and is relatively inexpensive. Other liquid gases which might be used would include liquid argon, oxygen, helium and hydrogen. These gases are characterized by the fact that they boil and vaporize under standard atmospheric conditions at very low temperatures. For instance, liquid nitrogen boils and beings to vaporize at a temperature of approximately -319 F., at standard conditions.
The storage tank 11 is provided in a conventional manner with a pressure gauge 22 and a regulator of pop-off" valve 19, such that when the pressure in the tank exceeds a preselected value, the valve 19 opens momentarily to bleed gas out of the tank. In the embodiment described, the tank pressure is maintained at 22i3 psig, and the gas is vented to the atmosphere via conduit 36. In a refrigeration system or airconditioning system of the type described, it is often desirable to vent the vaporized gas into the space being cooled where it aids in the cooling process and will retard spoilage of vegetable produce or the like. Venting into the space to be cooled is not recommended where humans or animals are exposed to the vaporized gas.
The tank 1 I is provided with a second fitting which couples through conduits 27, 46, respectively, to a conditioning device shown generally at 25 and through a valve 20 to a quickdisconnect coupling 21. A second valve 37 is positioned in the conduit 27 between tank 11 and the conditioning device 25 and is also positioned between the conditioning device and the coupling between the tank 11 and the valve 20. This arrangement of valves 20 and 37 provides a means for charging the tank 11 with liquid gas.
Valves 20 and 37 are manually operated valves, and when it is desired to charge the tank 11 with liquid gas, valve 37 is closed, valve 20 is opened, and an external supply of liquid gas (not shown) is fed through the quick-disconnect coupling 21 to the tank 11 until the tank is filled to the desired level. Valve 20 is normally closed during operation of the system and valve 37 is normally open.
A conduit 26 couples the conditioning device 25 to an evaporator assembly 12, and particularly to the evaporator coil 39 of thatassembly. As will be fully described in the following disclosure, the conduit 26 is constructed of a relatively short piece of conduit, and in the embodiment illustrated will not exceed 6 inches in length.
A means, shown generally at 38, for providing quick cooling of the evaporator coil39 includes a conduit 45 coupled to the conduit 27, between valve 37 and device 25, and is coupled through a thermostatically controlled valve 29 to the conduit 26. When the valve 29 is open, liquid gas flowing past valve 37 will by-pass the conditioning device 25 and is communicated to the conduit 26, and thus directly into the evaporator coil The remaining or exit end of the evaporator coil 39 is coupled through a conduit 49 to a second thermostatically controlled valve 14 which is in turn coupled through a conduit 24 to the atmosphere or, when desired, to the defined space 23.
Thermostatically controlled valves 29 and 14 are electrically operated, respectively, by thermostats 35 and 16. Power is supplied to thermostats and valves by power supply 17, which in the embodiment illustrated, may be the standard aircraft or vehicle power supply. Each thermostat is provided, respectively, with temperature sensors 28, 15. The sensors 28, are preferably in physical contact with the coil 39 of evaporator 12.
A check-valve 51 is located in the conduit 27 which couples the tank 11 to the evaporator assembly 12 and is positioned between the valve 37 and the'conditioning device 25. The check-valve 51 may be located on either side of the junction between conduit 27 and the input side of by-pass circuit 38, but is preferably located between this junction and valve 37. The check-valve 51 is preferably a ball-type check valve, such as those which are commonlyknown for use with cryogenic systems and which will pass fluid freely as it flows from the tank 11 toward the evaporator 12, but will operate to prevent the flow of fluid in a reverse direction.
A second pressure-relief valve 50 is positioned in a conduit 52 which communicates with the conduit 49 at a point between the evaporator assembly 12 and the thermostatically controlled valve 14. The conduit 52 on the opposite side of the relief valve 50 from the evaporator assembly 12 either communicates with the exit conduit 24 or is itself vented to the atmosphere. The pressure relief valve 50 is similar to pressurerelief valve 18 and can be adjusted to provide the venting of pressures in the evaporator assembly 12 in excess of a given amount, for instance 26 psig, to the atmosphere. The pressure relief valve 50 and the check-valve 51 provide still another means for improving the efficiency of the air-conditioning system 10, as will hereinafter be described.
A conventional blower assembly 18 is provided to ventilate air across the evaporator assembly 12. In the embodiment described, the blower 18 circulates the air across the evaporator 12 at a rate of about 300 ft. per minute. The blower assembly 18 is powered by the power supply 17, and blower speed is controlled by means of an external speed controller such as 55. Ducting 32 provides a means for directing the air across the evaporator assembly 12 in the conventional manner. The ducting 32 is provided with an air inlet 33 and at least one outlet 34. The at least one outlet 34 is directed into the defined space 23 and in the embodiment illustrated, the inlet 33 communicates with atmosphere surrounding the vehicle 36.
It is possible to position the inlet 33 in the defined space 23 such that the air in the space 23 may be circulated, and with this arrangement, the blower 18 can either blow air across the evaporator 12 or can circulate the air in a reverse manner by drawing air from the defined space across the coil and then venting the air passing the evaporator back into the space. It is also possible to draw air through vent 33 from the exterior of the vehicle, i.e. the ambient air, and to blow this ambient air across the evaporator 12 and into the defined space 23.
The evaporator assembly 12 includes'coils 39 which are constructed in an elongated arrangement with five tubes or passes of the tubing per layer, in six layers. The stack of coils thus arranged are equipped with fins 48 in .a conventional manner to vastly improve the heat transfer or convection from the air to the fluid in the coil as compared to the transfer of heat from the air to the coil where there are no fins.
The conduits used in the preferred embodiment, including the coils of the evaporator 12, are all. standard copper tubing having substantially a-% in. outside diameter. Leakproof fluid connections are made with sealing clamps of the type hereinafter described.
Refer now to FIGS. 2 and 3. The conditioning device 25 includes a baffle 31 having an orifice 30 with a circular crosssection located substantially at the center thereof. The baffle 31 is constructed of a substantially flat, rigid material, preferably steel, which is preferably 0.030 in. thick; although, the exact thickness is not critical, except that the thickness of the baffle 31 should not exceed the diameter of the orifice 30 by any substantial amount. In the embodiment described, the orifice is 0.075 in. in diameter.
For ease of installation, the baffle 31 is cut in a circular shape, with an outside diameter substantially equal to the outside diameter of the standard inch copper tubing, and is then mounted in one end of an Gyro-Lock fluid coupling of the model and type described in the material that follows. Essentially, the Gyro-Lock coupling has a center portion 40 which is characterized by the fact that it has first and second ends which have a substantially circular cross-section and have standard screw-type threads on the exterior surface of each respective end. The coupling has a passageway communicating with the respective ends along a longitudinal axis of the coupling center portion 40. At approximately the center of the passageway is a passageway portion 44 having a reduced cross-section with respect to the remainder of the passageway, such that the portion of the passageway joining the reduced portion 44 with the larger passageway on either end of the center portion 40 forms shoulders. The larger portion of the passageway is sized to accommodate standard inch outside diameter copper tubing. From a predetermined point near each respective end, the passageway is machined progressively larger in diameter out to the respective end of the coupling to form a swage as hereinafter described. The baffle 31 is placed in a tight-fitting relationship in one of the larger portions of the passageway against the shoulder adjacent to ,the coupling center portion 40 and located in that side of the passageway. Copper tubing inserted in the passageway and secured in the manner described in the following material secures the baffle 31 in place. In this manner, the orifice 30 is fixedly positioned substantially in the center of the passageway, and all fluid passing through the coupling passageway must pass through the orifice.
The coupling is completed by first placing a retainer 41 on each piece of conduit to be joined. The retainer 41 has an interior threaded surface which is designed to mate with the exterior threaded surface on each end of the coupling center portion 40. The retainer 41 has a passageway interiorally of the threaded portion which accommodates the conduit, and at one end of the passageway, opposite the threaded portion, the passageway has a fiat surface, positioned substantially perpendicularly to the longitudinal axis of the passageway.
Also placed on the conduit is a circularly shaped metal seal 43, preferably brass or aluminum, having a shoulder around the periphery of a first end thereof for mating with the flat surface of the passageway of the retainer 41. Additionally, a cylindrically shaped swage or second seal portion 42 is placed on the conduit in front of the seal 43, such that beginning at the end of the conduit, in order, there is first the swage 42, then the seal 43 and then the retainer 41. The remaining end of the swage 42 is designed to accommodate the seal 43 and to operate in cooperation therewith and with the retainer 41 and the respective of center portion 40 to make a secure fluid-tight seal as the retainer threads are screwed tightly on the threads of the coupling center portion 40. Before the retainers 41 are finally tightened, the conduits, such as 26 and 27, are forced into the passageway and against the respective shoulder of passageway portion 44. Since the baffle 31 is normally placed adjacent to the conduit 27, on the up-stream side of the conditioning device 25.
Referring to FIG. 4, a portion of the air-conditioning system is shown. It is well known that the evaporator assembly 12 may have several circuits in order to improve the efficiency of the cooling to be obtained from the unit. For instance, where a large air volume is required, as for cooling a larger space, there will be several primary circuits in order to increase the effective frontal area of the evaporator which is subjected to the flow of air. In cryogenic gas cooling systems, the gas is introduced directly into the input of each of these separate circuits directly from the storage tank. In this invention, it is important that the cryogenic gas from the tank 11 be introduced to the evaporator assembly 12 in the proper manner. The apparatus shown in FIG. 4 is suitable for accomplishing this proper introduction when several circuits are necessary in the evaporator. As in F IG. 1, conduit 27 couples the tank 1 1, through valves 37 and 51, to the conditioning device 25. The conduit 26 now couples conditioning device 25 into a coupler 53. Coupler 53 also is adapted to connect, at an opposite end from conduit 26, to each of the three evaporator coils 39a, 39b, 39c, and provides a means for introducing the atomized gas out of conditioning device 25 into the evaporator coils without restrictions in the flow and in a continuous, substantially uninterrupted stream into the respective coils. The coupler 53 is a metal, preferably copper, device having a first end adapted to accept conduit 26 and is attached thereto, as by soldering. The second end of the coupler 53 is adapted to accept the three input portions of coils 39a, 39b, and 390, with these input portions arranged in a plane and the second end of the coupling flared accordingly, in that same plane. The ends of each input portion of coils 39a-39c are fitted into the coupler 53 and are spaced therein a short distance, for instance 1 inch, from the end of conduit 26, which is also secured to the coupler. The flared end of coupler 53 is crimped or otherwise secured to the respective ends of coils 39a-39c, and an appropriate sealant or soldering is used such that a fluid-tight coupling is made to the coil ends. The interior of the coupler 53 has a short passageway, and fluid is communicated from conduit 26, through the passageway, to the coils 3911-390. The path provided into each conduit 39a-39c is substantially smooth and has no substantial edges of sharp turns in the conduit to impede or disrupt the flow of fluid.
Examples of components utilized in the embodiment described are as follows:
1. Tank l1--Model VHT-25, manufactured by Minnesota Valley Engineering Co., of New Prague, Minnesota.
2. Valves and 37-Model 580, inch valve, manufactured by Walworth Co. of Raintree, Massachusetts.
3. Regulator valve 19 Model 559B3MP-22 manufactured by Circle Seal Co., of Anaheim, California.
4. Thermostatically controlled valves 29, l4-Model B651 manufactured by Sporlan, lnc., of St. Louis, Missouri.
5. Thermostats 16, 35 (including sensors 15, 28)Model A10 manufactured by Ranco, lnc., of Columbus, Ohio.
6. Evaporator assembly 12-5 X 6 coil in.) evaporator manufactured by The Dankard Company, Dallas, Texas.
7. Pressure Relief Valve 50-Model V06-l00-N6KA, manufactured by C. A. Norgren Co., Denver, Colorado.
8. Check Valve 51-Model 403 manufactured by Republic Valve Co., of Cleveland, Ohio.
In operation, super-cooled liquid nitrogen (LN is released from the storage tank 11, FIG. 1, into the evaporator 12 where it is vaporized and discharged through conduit 24, either into the atmosphere or, in the case where vegetable produce or the like will occupy the define space 23, into the space 23.
In a conventional manner, the blower l8 circulates air across the evaporator 12 and into or through the space 23, such that heat is absorbed by the liquid refrigerant in the evaporator, causing the refrigerant to vaporize. The heat in the air is conducted to the refrigerant by the fins 48 and the coils 39, and the air cooled in this manner is circulated through the defined space 23. The refrigerant, for instance the LN is stored at 320" F., and as it absorbs heat, it begins to vaporize and become a gaseous vapor as it passes through the coil 39.
Also in a conventional manner, a sensor 15 detects the temperature of the coils 39 of the evaporator 12 and provides an indication of the temperature detected to the thermostat 16. The thermostat 16 is set for a desired temperature of the coils 39, for instance 50 F. When the temperature detected by sensor 15 is less than the desired temperature by a predetermined amount, for instance, 2, the thermostat provides an electrical signal to solenoid valve 14 causing it to open. As the valve 14 opens, the LN again flows through the system, and the coil begins to cool down accordingly. As the temperature of the coils 39 lower and become cooler, the change is detected by sensor 15. When the temperature exceeds the desired temperature by 2 the thermostat l6 switches off, cutting off the current to valve 14, thereby causing the valve to close until the cycle is repeated. When the valve 14 closes, circulation of the gas in the evaporator 12 stops, after which time additional cooling of the air passing the evaporator 12 occurs only to the extent that the temperature of the metal and gas contained therein attempts to neutralize itself to a temperature corresponding to that of the surrounding air. Air passing the evaporator 12 is then directed into the space 23 to be cooled through vents 34 which provide, in cooperation with the blower 18, the circulation of the refrigerated air through the space, as desired.
The solenoid valve 29 and high-temperature by-pass circuit 38 provide a means to quickly cool the evaporator 12. The operation of this portion of the system 10 is more fully described in the material that follows, but for the purpose of the immediately following disclosure should be taken to be a closed circuit, i.e. the liquid gas cannot pass by this alternative path.
The device 25 provides a means for conditioning the cryogenic liquid gas to prevent surging in the evaporator 12 and to thereby enable the system 10 to be operated in an efficient manner. As previously explained, pressure in the evaporator coil 39 builds up rapidly as air is circulated across the coils 39 and fins 48. Since the exhaust outlet 14 is of a fixed size, the pressure at that point is easily exceeded by the pressure in the coil 39. In this condition, the gas cannot be completely exhausted through the outlet 24, and vaporized gas will flow to any point of lower pressure available to it, until the pressures in the system are equalized. It has been explained that it is important that the pressure in a cryogenic gas air-conditioning or refrigeration system should be kept at a low-pressure to make the system safe by reducing the possibility of explosion. in the system herein described, the cryogenic gas in the storage tank 11 is maintained at a pressure of 2&3 psig by means of the pressure regulator 19, thus the higher pressure gasses generated in the coil 12 as a result of vaporization of the cryogenic gas therein, flow back into the tank 11, and to the extent that the pressure exceeds 22:3 psig is vented to the atmosphere via vent conduit 36. While the gas flows in a reverse manner through the system 10, as described, the super-cooled liquid gas is cutoff from the coil 12, and the transfer of refrigerated air to the space 23 is momentarily cut off. Additionally, the warmed, vaporized gas returned to the storage tank 11 results in excessive vaporization of the liquified cryogenic gas in the tank 1 1, thereby causing a higher percentage of waste from the storage tank and resulting in a higher degree of inefiiciency.
The conditioning device 25 operates to prevent this waste and inefficiency by balancing the heat loading and transfer characteristics of the coil to the pressure in the coil to thereby produce a smooth and continuous flow of gas through the evaporator 12, without surging. The conditioning device 25 achieves this result in cooperation with the system 10, by atomizing the low-pressure, liquified, super-cooled gas and by creating a turbulent flow of the atomized gas into and at least partially through the evaporator 12.
Atomization of the gas is accomplished by sizing the orifice 30 (FIGS. 2 and 3) with respect to the pressure of the gas in the tank 11 and the ambient operating temperature of the system to obtain a controlled, very-slight amount of vaporization of the gas and atomization before it is introduced to the coil 12. For instance, for one set of conditions in the embodiment described, the temperature of the gas in the conduit 27 is 320 F., while in the conduit 26, the temperature of the gas is substantially 3l9.5 F.; thus, a slight, controlled amount of vaporization has occurred since a nominal pressure drop must accompany the temperature change. Additionally, the pressure on the orifice 30 causes the liquified gas to spray into conduit 26. The combination effect of the spray and partial vaporization results in the atomization of the gas which is desired. Heat transferred to the liquid, cryogenic gas as it passes through conduit 27 and heat generated by the passage of the liquid cryogenic gas through the orifice 30 reduces the temperature of the liquid gas as described, but does not reduce the temperature to the boiling point of the gas, thus the atomized gas having a turbulent flow exists in the conduit 26, and rapid vaporization of the liquid gas does not occur until the atomized gas reaches the evaporator coils 39.
The embodiment described is designed to operate in an ambient operating temperature range of between 80 and 120 F. For standard in. copper then, theorifice 30 which will accomplish the most effective result in this range and at these conditions is 0.075 in. in diameter. The orifice 30 will, of course, be sized differently-if the operating ambient temperature range varies somewhat from that indicated above. in any case, the orifice 30 is sized to provide an atomized condition downstream of the orifice, with only a nominal loss in the temperature of the gas. The amount of vaporization which occurs will be proportional to the temperature change, thus a substantial physical-change in the gas, i.e., substantially complete vaporization does not occur until the atomized gas reaches the evaporator 12. The liquified gas, conditioned as described, cools the sides of the coils 39 in the evaporator 12 uniformly, since the turbulence of the gas introduced by the action of the orifice 30 causes the atomized gas to be uniformly applied to all portions of the inside wall of the coils, thus the maximum degree of cooling per unit of gas flowing through the unit is achieved. Further, surging is substantially eliminated over the operating range of the system 10, since the coil 39 is not charged fully in one rush of super-cooled liquid. Having properly selected the size of the orifice 30 with respect to the pressure of the storage tanks and the operating ambient temperature of the system, the gas is fed through the conditioning device at a rate and in a form which can be vaporized in the coil 39 at a constant and continuous rate, thus the orifice 31 also serves to meter the gas to the coil at a rate which provides the maximum amount of cooling to the coil in a form in which the gas can be vaporized in the most efficient manner. With the gas pressurized at 22 psig, as described, the internal pressure of the evaporator coil 39 normally rises to a point where the pressure in the coil either equals or only slightly exceeds the pressure of vaporized gas at the outlet 14. The physical presence of the baffle 31 reduces the amount of back-pressure due to excess pressure in the coil 39 that reaches the storage tank 11, and since any pressure differential between the pressure in the coil and the outlet 24 will be slight, the pressure differential is easily absorbed by the conditioned gas without creating an excessive safety hazard or affecting the efficiency of the operation of the system 10. This performance is further improved, however, through the use of the check-valve 51 and the pressure regulator 50, as hereinafter described.
during a cooling cycle will It has previously been stated that the thickness of the baffle 31 should not exceed the diameter of the orifice 30 by any substantial amount. This is necessary in order to assure that the effective size of the orifice 30 is not reduced by boundary layer effect, and to assure that the proper spraying effect is obtained at the outlet of the orifice to create the turbulence and atomization required.
If the atomized gas is sprayed into a conduit, and the distance it must travel is too great, the droplets of the atomized, liquified gas will re-combine into one fluid stream, therefore, it is necessary 'to assure that the conduit 26 is kept short enough in length such that the atomized gas reaches the evaporator 12 in the atomized state. In the embodiment described, the conduit 26 is kept less than 6 inches in length and the desired result is achieved.
One additional result is obtained by using the techniques described above. When surging" is present in a particular cryogenic gas air-conditioning or refrigeration system or the system is otherwise operated inefliciently, it is virtually impossible to precisely control the temperature of the vaporized gas emitted from the discharge conduit 24; however, utilizing the invention described herein, the discharge temperature can be controlled to within :3 of a desired mean, thus another important result is achieved. In a typical aircraft cryogenic cooling system utilizing this invention, the tank 11 holds about 400 of the cryogenic gas LN Where the discharge temperature is erratic, as in a surging system, the outlet temperature vary about :15 percent with respect to the temperature of the air being discharged out of outlet 34 into space 23. At an outlet or discharge temperature of 70 F the LN when vaporized, absorbs about 186 BTU/1b., thus, the maximum system cooling capability is 40X186 or about 7,440 BTU. When'the dischargetemperature can be accurately controlled in accordance with this invention, a more complete vaporization of the liquified gas can be achieved, thus adding even more to the efficiency of the system. For instance, by increasing the volume of air passed across the evaporator 12, the discharge temperature at conduit 24 of the system described herein and embodying this invention, can be accurately controlled to within 12 of the temperature of the air passing through vents 34 into space 23. Where the discharge temperature is controlled in this manner, more cooling can be had from the same gas such that the outlet temperature of the discharge gas is reduced to approximately F. At this temperature, 211 BTU of cooling are available from each pound of LN therefore the system capacity is increased to 40x21 1 or 8,440 BTU, or an increase of 13-14 percent. This is an important feature in all cryogenic gas cooling systems in that it reduces the cost of operation, but is of special importance in applications such as'aircraft where weight is an important feature, since more cooling is available from each pound of the expendable refrigerant. The discharge temperature of the system described will not vary more than 2-3 in normal operation.
In a typical application, the system described herein has been used to air condition a 150 cu. ft. aircraft cabin, and, in this case, operating in an ambient temperature of 90 F., the temperature of the cabin has been maintained at 72:2 for in excess of 3 hours with a 40 pound tank of liquid nitrogen gas. This system exceeds by a substantial factor the cooling time available from a 40 pound tank of liquid nitrogen used with previously known systems, and in these earlier systems the temperature of the equivalent space has been known to vary as much as 15 and has never equaled the 4 of control available with the system described herein. While cryogenic gas cooling systems of the type described herein have not been extensively used for the reasons previously mentioned, data available indicates that 15-20 percent more cooling time is available from the same quantity of cryogenic gas from a cooling system embodying the invention described herein than has previously been available from the surging systems.
When the space 23 to be cooled is at a very high initial temperature, for instance, in excess of the structure of the evaporator 12 is normally warmed to a correspondingly high temperature. In this case, it is desirable to quickly cool the evaporator 12 to increase the rate at which the space 23 can been cooled by the air-conditioning system; therefore, an automatic, quick-cooling circuit 38 is provided which by-passes the conditioning device 25 and allows a large quantity of the cryogenic gas to be transferred to the evaporator 12 at a faster rate than can be provided through the conditioning device 25. This apparatus provides a means for quickly filling the evaporator 12 with the liquid gas, thus rapidly cooling the coil 39 to operating temperature.
The thermostat 35 and sensor 28 control the operation of the circuit 38. The thermostat 35 is set for a temperature in coils 39 of 90 F., such that when the temperature of the coils 39 sensed by sensor 28 exceeds this level, the solenoid valve 29 is opened in response to electrical signal from the thermostat 35. When the temperature of coils 39 is reduced below the predetermined level, i.e. 90 F., the electrical signal is removed and the valve 29 returns to its normally closed position, and the system operation returns to that described above before oscillations in the system caused by surging" have time to occur.
The check-valve 51 operates to assure that any high-pressures created in the coils 39 are not transmitted back into the storage tank 11. When any back-pressure from the coil 39 reaches the check-valve 51, the valve closes in a manner well known in the art, and the gas cannot, therefore, reach the tank, where it would result in heating, vaporization and waste of the stored cryogenic gas. In the system described, backpressure may occur when the valve is closed, since at that time the gas in the coils 39 continues to vaporize and expand as air continues to flow across the evaporator 12. As previously stated, the coil 39 can withstand some back-pressure; however, as a safety measure and to assure, in cooperation with check-valve 51 that no reverse-flow gas reaches the storage tank 11, the pressure-relief valve is set to open at a pressure of 26 psig, such that whenever the pressure in the coil 39 reaches that value, it will be discharged to the atmosphere rather than flowing back into the tank 11. This then results in even greater efficiency in the utilization of the cooling available from each pound of stored refrigerant.
It has been found that restrictions efiecting the flow of the atomized gas out of the conditioning device 25 will cause the atomized gas to re-form into a liquid and that with such restrictions downstream of the conditioning device 25, the advantageous results obtained from the conditioned gas are lost. By restrictions are meant sharp turns in the conduits where the interim of the conduit has edges or T-connections or the like where obstructions or partial obstructions are placed in the path of the atomized gas. Such restrictions cause boundarylayer and eddy-current effects in the fluid which restrict the effective cross-sectioned area of fluid stream and cause points of increased pressure in the conduit which will break down the atomized condition of the gas and will cause the atomized gas to return to its original liquid state. This is particularly a problem where the atomized gas is to be introduced into a plurality of coils in the evaporator 12. The fluid flow into the evaporator coils 39 from the conditioning device 25 must be kept continuous and smooth. 90 or even 180 turns can be made if the flow is kept smooth and continuous by omitting restrictions from the path of the fluid stream. For a single coil evaporator, this does not present much of a problem, because restrictions are easily avoided. FIG. 4 illustrates a suitable means for providing a smooth and continuous flow of atomized fluid into the plurality of evaporator coils 39a-39c. The atomized gas out of conditioning device 25 flows smoothly and continuously into each respective input portion of coils 39a-39c, since the flow path does not include any restrictions. Additionally, the input portions of the coils 390-39 are formed without restrictions and the coils themselves do not normally include restrictions of the type described.
It will be evident, too, that various further modifications are possible in the manner of practicing the invention and in the arrangement and construction of the invention herein described. Accordingly, it should 'be understood that the forms of the present invention described above and shown in the accompanying drawing are illustrative only and not intended to limit the scope of the invention.
What is claimed is: I
1. Apparatus for cooling a defined space, comprising:
a supply of super-cooled liquid gas;
evaporator means for substantially vaporizing said liquid gas;
conditioning means coupled to the supply and to the evaporator means for atomizing the liquid gas and for creating turbulence in said atomized gas prior to the introduction of the gas into said evaporator means;
discharge means for disposing of the vaporized gas; and
control means for regulating the flow of the vaporized gas to provide a temperature control of the space to be cooled.
2. The apparatus claimed in claim 1 wherein the conditioning means includes second means for providing a smooth and continuous flow of atomized gas to the evaporator means.
3. The apparatus claimed in claim 2 wherein the evaporator means includes a plurality of evaporator coil circuits, and the second means includes means for providing a smooth and continuous flow of atomized gas to each of the plurality of evaporator coil circuits.
4. Apparatus for air-conditioning a defined space by vaporizing a liquid gas at a controlled rate, comprising:
a source of liquid gas;
evaporator means for substantially vaporizing the liquid gas;
first controlling means for regulating the flow of the vaporized gas to provide a temperature control of the space to be refrigerated;
a system of conduits coupling the source of liquid gas to the evaporator means, the evaporator means to the controlling means, and for disposing of the substantially vaporized gas; and
second controlling means for balancing the heat loading of the evaporator means to the pressure in the evaporator means to increase the cooling efficiency of the apparatus.
5. Apparatus for cooling a defined space, comprising:
a supply of super-cooled liquid gas;
evaporator means for substantially vaporizing said liquid gas;
a conduit coupling the supply to the evaporator means;
a baffle fixedly positioned in the conduit perpendicularly of the longitudinal axis thereof, and having an orifice located in said bafile substantially at the center thereof;
discharge means for disposing of the vaporized gas; and
control means for regulating the flow of the vaporized gas to provide a temperature control of the space to be cooled.
6. The apparatus claimed in claim 5 wherein the conduit is in. conduit, the baffle is a metal plate 0.030 in. thick, and the orifice is 0.075 in. in diameter.
7. The apparatus claimed in claim 6 wherein the baffle is positioned less than 6 inches from the evaporator means.
8. The method for improving the efliciency of cooling a defined space with a predetermined amount of super-cooled liquid gas to be substantially vaporized in an evaporator to provide cooling for said space, the method comprising:
flowing super-cooled liquid gas to said evaporator;
atomizing said liquid gas to a predetermined degree before it reaches said evaporator; and
creating a controlled amount of turbulence in said gas before it reaches said evaporator.
9. The method claimed in claim 8 including the step of providing a smooth, continuous and unobstructed flow of atomized and turbulent gas into the evaporator.
10. The method claimed in claim 8 wherein when the temperature of the evaporator exceeds a predetermined amount, as the super-cooled liquid gas initially flows toward the evaporator, the method includes the intermediate step of flowing the super-cooled liquid gas directly into the evaporator until the evaporator cools to a second predetermined tembulence are resumed.