US2437332A - Low-temperature test chamber - Google Patents

Description

March 9, 1948. A. a. NEWTGN I I Low TEMPERATURE TIEsT cnimgma 2 sheets-sheet I Filed Jan. 1, 1944 Swen tor flLw/N B. NEWTON Gttomeg Patented Mar. 9, 1948 sive.

UNITED STATES PATENT OFFICE- LOW-TEMPERATURE TEST CHAMBER Alwin B. Newton, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application January 1, 1944, Serial No. 516,611

12 Claims. (01. 62-2) The present invention relates to a low temperature refrigeration system for test chambers and the like.

Means have long been available for reaching very low temperatures. One of the simplest means of refrigerating to a very low temperature is to pack the objects to be cooled in solid carbon dioxide, the carbon dioxide vaporizing at about.

-109 F. More complicated means of obtaining low temperatures have comprised multiple stage refrigeration systems using compressors and other suitable equipment; systems of this sort being most commonly used for low temperature work. In addition, when properly controlled, the plural stage refrigeration system gives good results at various control points within a rather wide range of temperature. The multiple stage refrigeration system, has however, the disadvantage of complexity and cost. For small laboratories and for infrequent use, the cost of a plural stage refrigeration system is often too high to justify its use.

The present invention is directed towards providing a low temperature refrigeration system which is relatively simple in nature and inexpen- It must be granted that a system of the sort to be described is not particularly desirable for continuous operation nor is it as economical per unit of refrigeration as conventional systems. However, the present invention appears to provide a solution for those instances wherein infrequent operation is required, in which a refrigeration system is desired that is low in cost, will provide effective results, and wherein operating costs are reasonable.

It is therefore an object of this invention to provide a refrigeration system capable of attain-' It is an object to provide a refrigerating system wherein volatile material is used as a refrigerant and in which the capacity of the material may be increased by immersing same in a suitable liquid.

It is another object of this invention to provide a low temperature refrigeration system in which a. heat exchange means is cooled by a volatile refrigerant evaporating under controlled pressure conditions, the pressures being varied as desired over'a wide range.

It is another object of this invention to pro- Figure 2 is a schematic showing of a modified form of the invention, parts being in section and parts being broken away; and

Figure 3 is an elevational view, parts being in section and parts being broken away, of a modifled heat exchange means which may be used in the structure of Figure 2.

In Figure 1, pressure vessel I0 is fitted with lid H which is clamped in place by securing cally controlling the conditions under which said refrigerant may evaporate,

It is a further object to provide a refrigeration system in which solid carbon dioxide is a refrigerant and in which the capacity of the refrigerant for cooling may be increased by immersing same in alcohol.

means l2. Lid H includes a well l3 in the con tral portion of said lid and which'forms the cooling chamber in the present example. Well l3 may be fitted with lid I 4 having suitable openings therein to receive such instruments as thermometer I5 and temperature controller l6, to'be calibrated. To increase the heat conductivity from the walls of said well to the instruments contained within same, a heat conducting fluid such as alcohol may be contained in said well. Further, agitating means, not shown, may be used to keep said alcohol stirred and provided uniform temperatures within the well, and other agitating means, not shown,may be provided for bath 25, to be described.

A conduit l1 connects to the upper portion of said pressure vessel l0 and leads to a. modulating motor valve 20, said valve controlling fiow through pipe I! and connecting said pipe IT to pipe l9. Pipe l9 connects to vacuum pump I8 and bypass 63, said pump discharging through pipe said by-pass also connecting to pipe 65.- By-pass 63 includes check valve 64 which is arranged to permit flow only when the pressure'in pipe l9 exceeds that in pipe 65 and is used to permit 3 gases to flow around the pump when same is not being operated. Pipe |1 also connects with pipe 2| having therein pressure relief valve22, which protects the system from excessive pressure. Vacuum pump I8 is driven byelectric motor 23.

Refrigeration is provided within pressure vessel III by a charge of immersed solid carbon dioxide 24, or other refrigerant, contained within a bath 25 of alcohol, or the like, said refrigeration being principally due to the evaporation or sublimation of said carbon dioxide. The evaporation of the carbon dioxide and the resulting refrigerating effect is controlled by a thermostatic device 26 comprising a temperature responsive bulb 21 connected by capillary tube 28 to bellows 29. Bellows 29 bears against pivoted lever 30 which operates arms 3| and 32, the action of bellows 29 on arm 30 being resisted by a tension spring 33. Adjustable screw means 34 is provided for adjusting the tension of said spring 33. Arm 32 carries mercury switch 35, which controls the operation of motor 23.. ,Arm 3| has a contact portion which sweeps over potentiometer coil 33 to control modulating motor valve 20. Adjusting screw 34, in addition to adjusting the tension of spring 33, also coacts with pivoted arm 31 which is maintained in contact with said adjusting means 34 by tension spring 33. Pivoted arm 31 has a bracket portion 39 which carries mercury switch 40. Mercury switch 40 contains terminals 4| and 42, in the control circuit of modulating valve 20; and terminals 43 and 44 in the control circuit of motor 23, the bridging of the pairs of terminals by the mercury of the switch permitting energizing of the respective circuits.

Obviously, the structural details shown of pressure vessel l0, well l3, and the objects contained within said well, |3, are to be considered illustrative only. Further, pressure relief valve 22 may be directly attached to pressure vessel ID or lid H, and vacuum pump |8-and valve 20 may be interchanged, if desired, or valve 20 may be on a'separate branch from conduit l1. .The insulation normally used for equipment of this sort is, oi course, contemplated, but it has been omitted from this figure and the others to slmplify the showings.

While solid carbon dioxide is the preferable refrigerant for this system, it is contemplated that other solid or liquid refrigerants may be used,

such as liquid ammonia, sulphur dioxide, halogenmay be operated throughout the operating range of the system, said valve serving to regulate the capacity of the vacuum pump when same is running. When using a pump of this sort, bypass 63 may not be needed.

The relation and function of the various parts above recited will be discussed in the following operation schedule.

Operation of Figure 1 To place the above described system in oper-:

ation, the control point of thermostatic device 25 should be adjusted to about -109 (with carbon dioxide refrigerant), lid removed from vessel N, and said vessel charged by placing solid,

carbon dioxide 24, or other refrigerant, in the bottom of same, said carbon dioxide being covered with alcohol, or other suitable liquid 25, to a suitable depth. Lid II is then replaced and securely clamped in sealed relation to said vessel |i|. Well I3 is filled to a suitable level'with alcohol, or the like, and thermometer l5 and the device to be tested or calibrated is inserted within said well and immersed in said alcohol, lid |'4 then being placed in position.

Thermostatic control means 26 is then adjusted to a suitable control point. As before-mentioned, vessel ID was charged at atmospheric pressure; hence the alcohol bath within said vessel would tend to reach about -109 F. Assuming that the control point is to be -150, the adjustment is made by loosening adjusting screw 34. Loosening adjusting screw 34 is accomplished by tuming said screw inwardly and releasing tension on spring 33. Turning adjusting screw 34 inwardly also coacts with pivoted arm 31 and bracket portion 39 to tip said bracket portion 39 downwardly and thus make contact between terminals 43 and 44 of mercury switch 40. Further, loosening adjusting screw 34 permits arm 32 to pivot counter-clockwise and thus complete a circuit within mercury switch 35.

With contacts made between terminals 43 and 44 and in mercury switch 35, motor 23 is started as follows: line 50, wire 5|, terminals 43 and 44, wire 52, mercury switch 35, wire 53, motor 23, wire 54, and line 55. Motor 23 is thus started, and vacuum pump I8, driven by same, reduces the pressure exerted on bath 25 and the immersed carbon dioxide 24 in pressure vessel l0, thus permitting said carbon dioxide to vaporize at a lower temperature. As carbon dioxide 24 vaporizes at the reduced pressure, and lowers the temperature of bath 25 and the immersed well l3, the pressure exerted by bellows 29 is lessened. When the predetermined control point is reached, and the pressure exerted bybellows 23 is overcome by spring 33, arm 32 is rotated clockwise and eontact is broken in switch 35, thus stopping motor 23 and vacuum pump I 8. Motor 23 will again be started when the rising temperature in bath 25 causes bellows 23 to expand and rotate arm 32 counter-clockwise, thus making contact with- .in mercury switch 35.

It will be thus seen that control points below about -109 are attained by maintaining suitable reduced pressures over bath 25 and the immersed carbon dioxide 24, said reduced pressure .rbeing kept at proper levels by on and ofi control 55 of motor 23. When bracket portion 39 of pivoted arm 31 is tilted downwardly, and contact is made between terminals 43 and 44, contact is broken between terminals 4| and 42, thus biasing valve 20 Open as will be seen.

The motor of modulating valve 20 is operated by current supplied through the circuit: line 50, wire 56, motor valve 20, wire 51 and line 55. The motor is controlled by the circuit: arm member 3|, wire 58, motor valve 20, wire 59, coil 38, wire 6!], terminals 4| and 42, wire 6| and motor valve 20. It will thus be noted that with contacts broken between terminals 4| and 42, one control side of said modulating valve is opened and all of its control current must flow in the other branch of the control circuit thereby causing the valve to be biased toward an extreme position; in this case its open position.

To show the control of the system with control points above -109, assume the control point to be -20. Thermostatic device 26 is adjusted for a control point of by tightening adjusting screw 34, thereby increasing the tension of spring 33. Tightening adjusting screw 34 results 'in said screw being backed out of its support member, thereby allowing pivoted arm 31 and its related bracket 39 to rotate counter-clockwise,

due to action of spring 38. Counter-clockwise rotation of bracket 39 tends to tilt mercury switch 40 upwardly and contact is broken between terminals 43 and 44, thus preventing operation of motor 23. At the same time, however, contact is made between terminals 4| and 42, and modulating valve 20 is placed under control of arm 3| and potentiometer coil 33.

To attain a control point of 20 F., it isnecessary that the carbon dioxide be vaporized under pressures exceeding those of atmospheric, hence it is the function of modulating valve 20 to throttle the outlet of the vaporized gases from pressure vessel I0 in such manner that a suitable pressure may be built up in said vessel to thus control vaporization within same.

Assuming for the moment, that the temperatures within vessel I0 are below the control point, the pressure exerted by bellows 29 will be less than that required to successfully oppose the action of spring 33, and arm 3| will be rotated in a clockwise direction, thus moving it downwardly on potentiometer coil 36. In the downward position of arm 3| on coil 36, valve 20 is closed, thus prohibiting the escape of gases from pressure vessel I0 and permitting pressure to build up therein, As the pressure and temperature within said pressure vessel increases up to the desired. point, the pressure exerted by bellows 29 is increased. When the pressure exerted by bellows 29 is suiiicient to overcome, at least partially, the. pressures exerted by spring 33, arm 3| is rotated upwardly across coil 36 and valve 20 is partially opened. The opening of valve 20 will tend to reduce pressures in vessel I0 and thus reduce temperatures, said temperature reductionresulting in less pressure by bellows 29 and counter-clockwise movement of arm 3|, thereby again tending to close said valve 20. Valve 20 is thus throttled 'to maintain a predetermined pressure and temperature within the vessel. As previously mentioned, thermostat bulb 21 may be placed within well I3, if desired, thus making the control dependent upon the temperature within said well I3 rather than that of the bath in vessel I0.

When terminals 4 and 42 are not used and the modulating valve is operated. throughout the range of the system, thecontrol circuits are the same as shown with the exception that wires 6| and 60 are joined, The system functions the same as described at pressures above atmospheric; but at pressures below atmospheric, the throttling action of said valve may supplement or replace the on and oil control'exercised by mercury switch 35. Valve 20 exercises control over pump I9 by throttling its suction. Should the-positions of the valve and pump be reversed,

the discharge would be throttled.

Figures 2 and 3 I Figure 2 shows a modified form of the present invention. This figure shows a pressure vessel IOI containing therein an-alcohol bath I02 and lief valve I01. Immersed within bath I02 is coil I08 of heat exchang means I09, said heat exchange means I09 including coil IIO, contained within test chamber III, said coil IIO being connected in sealed relation with coil 108. Heat exchanger I09 is charged with a fill of a suitable refrigerant, such as one of the Freon group, in such manner that coil III! will normally contain some liquid refrigerant. Test chamber I II may comprise a suitable door H2 and a rack II3 to hold the devices to be tested. A radio I I4 is shown on rack I I3 as a device to be tested under low temperatures, but obviously this is only an illustration.

The rate of vaporization of carbon dioxide I03 .and the resulting refrigerating effect of same, is determined by the pressure imposed on bath I02 and refrigerant I03. sel IOI are influenced by a modulating valve H6 and a vacuum pump II5, said valve being connected to vessel IOI by conduit H1 and discharging through conduit IIII into vacuum pump H5 and by-pass I90, said by-pass and pump discharging to exhaust pipe I9I. By-pass I90 includes check valve I92 which permits flow around pump II5 only when the pressure in pipe H8 is higher than that in pipe I9I. As in the previous example, the use of a pump permitting free passage of gases when said pump is not being run would make the by-pass unnecessary.

The circulation of heat exchange fluid between coils I00 and I I0 is controlled by solenoid valve H9, and the cooled medium of test chamber III is circulated over coil IIO by a fan means I20.

The operations of vacuum pump II5, modulating valve II6, solenoid valve H9, and fan I20 are all controlled by a thermostatic device I2I. Thermostatic device I2| comprises a volatile fluid filled bulb I22 located within test chamber I I I, and connected by a capillary tube I23 to bellows I24. Bellows I24 coact with arm member I25 to cause pivotal movement thereof, said arm I25 having associated therewith arms I26 and I21. The action of bellows I24 on arm I25 is I resisted by tension spring I28 attached at one end to said arm I25 and at the other end to one arm of bell-crank lever I29. Arm I26 coacts with J one end terminals I34 and I35, and having at the other end thereof, terminals I36 and I31. Switch support I32 is connected by link I33 to bell-crank I39. Said device I2I also includes pivoted switch support I40 having thereon mercury switch I4I, said switch support I 40 being connected by link I42 to one arm of bell-crank I43. Modulating motor I44, which adjusts device I2I, includes a pivotal operatin lever I45, said pivotal operating lever being connected by link orconnecting rod means I46 to bell-cranks I29, I39 and I43. Modulating motor I44, as well as the motor of modulating valve II 6, is similar to that described in Patent 2,028.110, issued to D. G. Taylor. The position of arm I45 of modulating motor I44 is determined by timer I41 which comprises a immersed carbon dioxide I03, it being,nol2ed-that-eschedulingcam I48 coactlng with a pivoted arm these materials are ven as'exaniples only, other materials b ng contemplated, as in the preceding example. The alcohol and carbon dioxide are charged into the vessel through removable closure I04, said closure being held in place by fas- I49. said arm I49 sweeping over coil I50'to thereby control saidmotor I 44. As in the previous example, modulating valve II6 may be operated in conjunction with vacuum pump Hi to supplement or replace the Pressures within vespotentiometer a rheostat control of said pump. Valve H6 may be made operative throughout the range of the system by connecting wires I15 and I16.

In Figure 3, modified means are shown for transferring heat from test chamber III to bath I02 comprising heat exchange'coil I55, located within chamber III and connected at one end to pump I56 and perforated inlet pipe I51, and connected at its other end to perforated outlet pipe I58. Inlet pipe I51 and outlet pipe I58, as shown, are located within vessel IM and immersed in bath I02. The fluid of bath I02 enters pipe I51 and is caused to circulate by pump I56, through said coil I55 and out through perforated pipe I58, said material I02 flowin across refrigerating material I03 as it leaves pipe I58 and flows towards pipe I51. Pump I56 is preferably driven by electric motor means and is controlled by the same circuit as solenoid valve II9 of Figure 2. Obviously, the direction of circulation may be reversed, if desired.

Operation of Figures 2 and 3 To operate the structure as outlined in Figure 2, the control point should be adjusted to about -109. The manner in which the control point may be adjusted and the operation of the control will be brought out presently. With the control point adjusted to about 1 09, valve H6 is open and vacuum pump I I is not operating. Closure I04 is removed from vessel IOI and a charge of solid carbon dioxide I03, or other refrigerant used, is placed within said vessel. After charging the vessel with carbon dioxide, the carbon dioxide and coil I08 are covered by alcohol, or other lqiuid, closure I04 then being replaced and tightly secured by fastening means I05. The system is now ready for operation and the control point may be adjusted as desired. In the system as disclosed, the control point may be established, or may be varied in a predetermined manner by timer means I41 which includes schedule cam I48, adjusted by suitable means and operable by the mechanism of I41, and pivoted arm I49, it being the purpose of the timing and scheduling mechanism to operate the refrigeration system in a manner duplicating predetermined conditions. For instance, if it be desired to duplicate the conditions of temperature of an aircraft flying in the sub-stratosphere, the mechanism may be so adjusted as to change the temperature in the test chamber in the same sequence as the temperature is changed by said aircraft in flight. Obviously, the mechanism may be adjusted to maintain the temperature at any control point within its range,

For the purpose of illustration, assume that it is desired to test the characteristics of radio II 4 from 120 to -10 within a period of thirty minutes. Cam I48 will be so adjusted relative to pivoted arm I49 that said arm will be in a position to establish a control point of -120. The cam is made of such contour and rotated when started at sufficient speed to rotate arm I49 counter-clockwise across coil I 50 sufiiciently to raise the control point to 10 within the time period of thirty minutes. Modulating motor I44 is so related to the timing mechanism and its potent-iometer coil I50, that arm I45 is at the extreme left position when arm I49 is at the clockwise extreme of coil I50, and arm I45 is at the extreme right position when arm I49 is at the extreme counter-clockwise end of coil I50.

Assuming that the position of arm I49 on coil I50 is such as to maintain a. control point of 8 F., arm I45 is in the left portion of its travel, and bell cranks I29, I39 and I43 have been rotated in a clockwise direction. The rotation of bell crank I29 has served to loosen the adjustment of spring I28 thereby permitting arm 'I25 to rotate counter-clockwise, thus moving arms I26 and I21 counter-clockwise. Rotation of bell crank I39 has caused the tilting of mercury switch I33 in such manner that contact is made between terminals I34 and I35 and contact is broken between terminals I36 and I31. The rotation of bell crank I43 has tilted mercury switch MI in such manner as to make contact between its terminals; therefore valve H6 is open, vacum pump H5 is operating, valve H9 is open, and fan I20 is operating, as shown, by the following circuits: The circuit placing vacuum pump H5 in operation is as follows: line I60, wire I6I, wire I6Ia, wire I62, terminal I34, terminal I35, wire I63, arm I21, resistance I3l, wire i64, motor I65, wire I66, wire I61, and line I68.

As determined by the following circuits, valve H6 is open: The motor of valve H6 is supplied with current by line I68, wire I61, wire I69, mercury switch I4I, wire I10, wire I1I, modulating motor valve II6, wire 12, wire I6I, and line I60; thus operating current is supplied to modulating motor valve H6. The control circuit for motor valve H6 is as follows: arm I26, wire I13, motor valve H6, wire I14, coil I30, wire I15, terminal I31, terminal I36, wire I16 and motor valve II8. However, as no contact is made between terminals I36 and I31, no current flows through one side of the control circuit of said valve, hence all the current flows through the other branch of the control circuit and the valve is modulated to an extreme position, in this case, wide open.

Valve H9 is open and fan I20 is operating by the following circuit: line I68, wire I61, wire I69, mercury switch I4I, wire I10, wire I11, wire I18, wire I98, fan I20, wire I19, wire I80, wire I8I, wire I6Ia, wire I6I, and line I68. Valve H9 is connected in parallel with fan I20, by wires I82 and I83 and is opened upon being energized.

The operating current for modulating motor I44 is furnished by the circuit: line I68, wire I61, wire I69, mercury switch I4I, wire I10, wire I11, wire I84, modulating motor I44, wire I85, wire I8I, wire I6Ia, wire I6I, and line I60. Modulating motor I44 is controlled by the circuit: arm I49, wire I95, motor I44, wire I96, potentiometer coil I50, wire I91 and motor I44. As previously mentioned, clockwise movement of arm I49 drives arm I45 of motor I44 in a counter-clockwise direction.

With the parts in the position shown, vacuum pump H5 is operating at a fairly high speed due to the comparatively small amount of resistance in its control circuit, valve H6, is fully open, as before noted, valve H9 is open, and fan I20 is operating. The operation of vacuum pump II5 lowers the pressure imposed on bath I02 and carbon dioxide I03, thus permitting said carbon dioxide to vaporize readily and at low temperatures. The low temperatures attained by the bath I02 are imposed on coil I08 and thereby reduce the temperature and pressure of the heat exchange refrigerants therein correspondingly. Liquid forming in coil I08 by condensation runs into coil III) by gravity, wherein, due to the heat supplied from chamber III to said coil, said refrigerant is vaporized and rises into said coil I88 to be again liquified by the chilled bath. The temperature of coil IIO will tend to closely approximate that of bath I02, for its temperature is due to the pressure of the refrigerant within it. The pressure of the refrigerant within coil IIO will be determined by the condensing effect of coil I08 brought about by the low temperature of the surrounding bath I02.

Fan I20 is not a necessary part of the present system but is useful in circulating cooled medium within chamber III and thereby increases the effectiveness of cooling coil IIO. It is the purpose of valve II9 to trap as much liquid refrigerant incoil I08 as is possiblewhen there is no demand for refrigeration and the system is turned off. During all operating conditions, however, said valve H9 is open .as previously described.

Should the action of vacuum pump H reduce 'the temperature more than is desired, the effect ture as desired, the resulting higher temperature increases the pressure on bellows I24 and causes counter-clockwise rotation of arm I25 and arm I21, the counter-clockwise rotation of arm I21 diminishing the resistance of coil I3I and thereby speeding the action of motor I65.

As the scheduling cam I48 is rotated and the control point is raised by moving arm I49 counter-clockwise, arm I45 is moved to the right and bell cranks I29, I39 and I43 are rotated arm T28 tending to close the valveto again reestablish the necessary pressure, it being noted that a control point of.70 F., requires a pressure above atmospheric when carbon dioxide is wires I15 and-I16 are joined, and if the rheostat counter-clockwise. The counter-clockwise movement of the bell crank I 29 increases the tension on spring I and tends to cause clockwise move--' ment of arm I25. 'lhecounter-clockwise move ment of bell crank I30 changes the'slant of mercuryswitch I33 so that contact isbroken between terminals I34 and I35 at a control point of about --109F. and operation of motor I is stopped. At the same time, contact is made hethe system is not being operated.

To show the controlling circuits in effect at control points above about l09 F., assume-a control point of '70 F., with a control point of '70, motor I65 is not operated due to breaking of the contact between terminals I34 and I35 of mercury switch I33 as previously described, With contact made between terminals I36 and I31, modulating valve III; is now operative by the circuit previously described. The circuit is so arranged that clockwise movement of arm I26 tends to. close valve H6 and counter-clockwise movement of said arm tends to open said valve. By throttling valve II 8, a pressure may be maintained over bath I02 and refrigerant I03 which controls the evaporating temperature of the refrigerant in the mannerdesired. If the pressure is lowered unduly by too wide a valve opening, the evaporation is increased, thus resulting in lower temperatures, and causing a relaxing of the pressure of bellows I24 and a movement of tween terminals I36 and I3! and modulating the refrigerant. too high a pressure in the vessel will cause excessively high temperatures to be maintained, and will cause an expansion of bellows I24, 9. counter-clockwise movement of arm I26, and an opening of said valve to'relieve said pressure.

When valve H5 is operated throughout the range of the system, it controls pressures above atmospheric in the manner described. At pressures below atmospheric, it may be used to controlthe capacity of pump suction. 'This throttling control may,-as before noted, either supplement or replace the rheostat control described. Touse valve II6 continuously,

control is to be replaced, Wires I63 and I64 are joined, permitting the elimination of arm I21 and resistance I 3I. The control circuits areotherwise as shown and the function of the system as a whole remains unchanged.

Likewise, the maintenance of 5- by throttling its As inthe previous example, conduit I08 and pressure relief valve I01 are provided toprevent the accumulation of dangerous pressures within vessel ml and other parts.

With the structure of Fig, 2 modified as suggested'by Fig.3, the control action ispreciseiy as before with the exception that the current flowing throughwires I82 and I83, instead of opening valve II9, serves to energize electrically driven pump-I56 and thereby circulate chilled alcohol bath means I02 through pipe I51, pump I56, coil I55, and pipe I58.

A single charge of refrigerant is usually sumcient for most test purposes but it is also contemplated that suitable charging means may be used to introduce charges of refrigerant into the chamber while the system is bein operated, and thus prolong the operating period.

Solid carbon dioxide has been given as the preferred refrigerant in theabove examples of the present invention because it is easily handled and is cheap and readily available, However, as previously noted, other solid or liquid refrigerants may be used, most of the common refrigerants being readily available in liquid form. As some of the more common refrigerants, such as ammonia, have irritating fumes, they should preferably be introduced into the chamber by piping, not shown.

Obviously, disposal of the discharged gases from the present system offers much less of a problem when carbon dioxide is used. Carbon dioxide has further merit in increasing the safety of the system. When volatile and inflammable "-ibaths, such as alcohol. petroleum fractions, etc., .are used. a portion of these materials may. be evaporated and discharged with the refrigerant.

However, the carbon dioxide, being in much trollable low temperature refrigeration system,

ideally suited for those installations wherein relativolylow cost of equipment and moderate cost of operation are important and wherein infrequent operation of the equipment does not justify the added costs of more elaborate systems.

The examples above described of the present invention are considered to be and are not intended to limit the structure or the illustrative only 11 system to the details described, It is obvious, that upon an inspection of the present disclosure, many modifications of the present invention will become apparent to one skilled in the art. It is the intent, therefore, that the scope of the present invention be determined by the appended claims.

I claim as my invention:

1. In a refrigerating system capable of operating over a range of temperature for utilizing a refrigerant having a vapor pressure above atmospheric pressure at the upper end of said temperature range and below atmospheric pressure at the lower end of said range, means for controlling the vapor pressure of said refrigerant including throttling valve means and pumping means, adjustable condition responsive means, and means for connecting said condition responsive means in controlling relation to said valve means for maintaining a refrigerant temperature in said upper range or in controlling relation to said pumping means for maintaining a refrigerant temperature in said lower range.

2. In a refrigerating system, a pressure vessel for containing a charge of volatile refrigerant of a sort wherein the vapor pressure of said refrigerant is above atmospheric pressure at higher refrigerating temperatures and below atmospheric pressure at lower refrigerating temperatures, means for regulating the pressure within said vessel comprising valve means and fluid pumping means, temperature responsive means, means for adjusting the control point of said temperature responsive means, adjustable energy control means permitting operation of either said valve means or said pumping means, and means simultaneously adjusting said control point and said energy control means in such manner as to permit operation of said valve for said higher refrigerating temperatures and to permit operation of said pump for said lower refrigerating temperatures.

3. In a low temperature refrigerating system, comprising an enclosed pressure vessel for containing a liquid having a low freezing point and a refrigerant having a boiling point above said freezing, point disposed within said liquid,a coil of a closed circuit circulating fluid heat exchange means within said vessel and arranged to be in heat exchange relation with said liquid, another coil of said heat exchange means being within a space to be refrigerated, control means, said control means comprising a throttling valve, a fluid translating device, and means having an adjustable control point responsive to the temperature of the space to be refrigerated, said temperature responsive means controlling said throttling valve when control point temperature is above a predetermined level and controlling said fluid translating device when the control point temperature is below said predetermined level.

4. Control means for an expendable refrigerant refrigerating system comprising, in combination, modulating means arranged to control the operation of a throttle valve, control means capable of controlling a fluid translating device, additional controlling means including means supplementing said modulating control means for said valve and means supplementing said control means for said translating device, condition re"- sponsivemeans operable to actuate said modulating means and said control means in a manner to maintain said condition. at a predetermined control point, and adjusting means, said adjusting means simultaneously adjusting said condition responsive means to a given control point and adjusting said additional controlling means to selectively permit operation of said throttle valve or said translating means.

5. A low temperature refrigeration system comprising an enclosed pressure vessel for containing a liquid having a low freezing point and a refrigerant having a boiling point above said freezing point disposed within said liquid; heat exchange means disposed in a space to be cooled, said heat exchange means having inlet and outlet connections within said vessel disposed for circulation of said liquid; means for circulating said liquid through said heat exchange means; control means, said control means comprising a throttling valve, a fluid translating device, and means responsive to the temperature of the space being refrigerated, said temperature responsive means having an adjustable control point, said temperature responsive means controlling said throttling valve when control point temperature is above a predetermined level and controlling said fluid translating device when the control point temperature is below said predetermined level, said control means causing circulation of said liquid throughout the operating range of said system.

6. In a refrigerating system, an enclosed pressure vessel for containing a liquid having a low freezing point and a volatile refrigerant having a low boiling point immersed within said liquid, a cooling chest having means arranged to be in heat exchangelrelation with said liquid, means for regulating the evaporation of said volatile refrigerant comprising fluid translating means, throttling valve means, means responsive to the temperature within said chest, said temperature responsive means controlling the action of the fluid translating device and said modulating valve and having an adjustable control point, and, means for varying the control point of the tem-' perature responsive means in a predetermined manner.

'7. In a low temperature refrigerating system,

an enclosed pressure vessel for containing a liquid vice, and a means having an adjustable control point responsive tothe temperature of the space to be refrigerated, said temperature responsive means controlling said throttling valve when the control point temperature is above a predetermined value and controlling said throttling valve and fluid translating device when the control point temperature is below said predetermined value,

8. In a refrigerating system, an enclosed pressure vessel for containing a volatile refrigerant means, temperature responsive means, said temperature responsive means having an adjustable control point, modulating motor means for adjusting said control point, means for controlling said modulating motor, and means for varying the pressure :uithin said vessel, said pressure varying means being operated in response to said temperature responsive means.

9. A' low temperature refrigeration system 13 comprising an enclosed pressure vessel for containing a liquid having a low freezing point and a refrigerant having a boiling point above said freezing point disposed within said liquid, means arranged to be in heat exchange relation with said liquid, means for varying the pressure in said vessel, control means, said control means comprising temperature responsive means forcontrolling the action of saidpressure varying means, and timing means, said timing means varying the control point of said temperature responsive means in a predetermined manner.

10. Control means for an expendable refrigerant refrigerating system comprising, in combination, modulating means arranged to control the operation of a throttle -valve,'control means capable of 'Controlling a fluid translating device, additional controlling 'means including .means supplementing said modulating control means for said valve and means supplementing said control means for said translating device, means responsive to a condition indicative of a need for operation of the refrigerating system operable to actuate said modulating means and said control means in a manner to maintain said condition at a predetermined control point, and adjusting means, said adjusting means simultaneously adjusting said condition responsive means to a givencontrol point and adjusting saidadditional controlling means to selectively permit operation of said throttle valve or said translating means.

11. Control means for an expendable refrigerant refrigerating system having throttle valve means and fluid translating means for controlling the flow of I exhaust refrigerant comprising in combination, modulating means arranged to control the operation of said throttle valve means, control means capable of controlling said fluid translating device, additional controlling means including means supplementing said modulating control means for said valve and means supplementing said control means for said translating device. means responsive to a conditionindicative of a need for operation of said refrigerating system operable to actuate saidmodulating means and said control means in a manner to maintain said condition at a predeter- "mined control point, and adjusting means, said adjusting means simultaneously adjusting said condition responsive means to a given control point and adjusting said additional controlling means to selectively permit operation of said throttle valve or said translating means.

12. In control means for a refrigerating sys- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 1 Date 1,943,971 Hulse Jan. 18, 1934 2,083,611 Marshall June 15, 1937 2,097,685 Bolton Nov. 2, 1937 2,176,001 Jennings Oct. 10, 1939 2,215,327, Karsten Sept. 17, 1940 2,269,172 Birdsall Jan. 6, 1942 2,282,385 Shawhan May 13, 1942 2,333,899 Stickel Nov. 9, 1943

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