US2282504A - Refrigeration - Google Patents

Description

y A. R. THOMAS ETAL 2,282,504

. REFRIGERATION Filed Aug. 3, 1940 2 Sheets-Shet 1v i/W 70km).

May12,1942. A. R. THQMAS m'L- 82,

REFRIGERKTION 4 Filed Aug. 3, 1940 2 Sheets-SheefZ Patented my 12, 1942 REFRIGERATION Albert R. Thomas and Philip P. Anderson, In, Evansville, Ind., assignors to Servel, Inc., New York, N. Y., a corporation of Delaware Application August 3, 1940, Serial No. 350,240

' 15 Claims. (01 62-5) Our invention relates to refrigeration, and more particularly to refrigeration systems of the kind operated by heat.

It is an object of this invention to supply steam to a jacket or chamber associated with a heat receiving part of refrigeration apparatus, such jacket having a vent to atmosphere, and controlling the supply of. steam so that at heat inputs less than a predetermined maximum a varying quantity of air can enter the interior of the jacket to form an air blanket about por tions of the heat receiving part. In the present embodiment the air blanket is arranged to be formed about the upper part of the jacketor chamber in which are disposed a plurality of riser tubes through which liquid is raised by gas or vapor-lift action, the vapor being formed and the liquid being lifted due to heating by the steam. By controlling the rate of flow of steam to the jacket, more or less of the riser tubes can be blanketed off with air and out of direct con tact with the steam, so that the effective tube surface area heated by the steam can be varied to effect regulation of the rate at which vapor is formed in the riser tubes and also :the rate at which liquid is lifted or raised therethrough.

The invention, together with the above and other objects and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawings forming a part of this specification, and

of which:

Fig. 1 is a view more or less diagrammatically illustrating a refrigeration system embodying the invention; and

Fig. 2 diagrammatically illustrates an air conditioning system with which the refrigeration system in Fig. 1 is associated.

Referring to Fig. l, the present invention is embodied in a two-pressure absorption refrig-' eration system like that described in our application Serial No. 239,762, filed November 10, 1938.

A system of this type operates at low pressures and includes a generator or expeller H], a condenser M, an evaporator l2, and an absorber l4 which are interconnected in such a manner that the pressure differential in the system is maintained by liquid columns.

I water vaporis expelled from solution.

The disclosure in our aforementioned application may be considered as being incorporated in this application, and, if desired, reference may be made thereto for a detailed description of the refrigeration system. In Fig. 1 the generator l0 includes an outer shell l5 within which are disposed a plurality of vertical riser tubes I6.

having the lower ends thereof communicating with a space I1 and the upper ends thereof extending into and above the bottom of a vessel l8. The space l9 within shell l5 and about the tubes l6 forms a steam chamber Is to which steam is supplied through a conduit 20 from a,

trol devices 25 to be described presently, and conduits 26 to the burners 23. Tubes 21 are connected to the conduits Hand terminate in the vicinity of burners 23 to provide a pilot flame for each burner when its associated control device 25 operates so that fuel will flow to the burner. As shown most clearly in Fig. 2, the heating tubes are arranged alongside each other and the burners are located at the front-of the steam boiler 2|. The upper end of each heating tube 22 joins a flue or riser 28 (Fig. 1) through which warm gases pass into the atmosphere from the boiler 2|. A suitable hand control valve 29 is provided in. conduit 23 so that, manual control of the steam flow to generator chamber I9 can be effected. A trap conduit 20a is connected to the lower end of shell IE to provide a drain for condensate formed in chamber I9.

The system operates at a partial vacuum and contains a water solution of refrigerant in absorption liquid, such as, for example, a water solution of 40% lithium chloride by weight. When steam is supplied through conduit 20 to chamber l9, heat is applied to tubes l6 whereby The absorption solution is raised by vapor-lift action with the expelled water vapor forming a central core within an upwardly rising annulus of the solution. The expelled water vapor rises I more rapidly than the solution and solution follows the inside walls of tubes It.

The water vapor flows upward through the tubes l6, vessel l8, conduit 30, vapor separating chamber 3|, and conduit 32 into condenser II in which it is liquefied. The condensate formed in condenser flows therefrom through a U-tube 33, flash chamber 34, and conduit 35 into evaporator I2.

The water supplied to evaporator |2 vaporlzes therein to produce a refrigerating or cooling effect. The vapor formed in evaporator l2 passes through tubes 36 and 31 into a manifold 38 which is connected to absorber II. To prevent disturbances in evaporator I2, the fiash chamber U-tube 33. The flashed vapor formed in the initial cooling of the liquid flowing from the condenser passes through a conduit 39 to manifold 38 and mixes with the vapor formed in evaporator 12.

In absorber l4 refrigerant vapor is absorbed into concentrated absorption solution which enters through a conduit 40. The water vapor absorbed into solution dilutes the latter, and the diluted absorption solution fiows through a conduit 4|, a first passage in liquid heat exchanger 42, a conduit 43, vessel 44, and a conduit 45 into the lower space H of generator Ill. Water vapor is expelled out of solution in generator III by heating, and the solution is raised by vapor-lift action in vertical tubes l5, as explained above. Any liquid separated from vapor in separating chamber 3| fiows through a U-trap 45 back to vessel l8.

The absorption solution in vessel I8 is concentrated since water vapor has been expelled therefrom in generator I0. This concentrated solution flows through a conduit 41, a second passage in liquid heat exchanger 42, and conduits 48 and 40 into absorber l4. This circulation of absorption solution results from the raising of liquid by vapor-lift action in vertical riser tubes l5, whereby the solution can flow to the absorber I4 and return from the-latter to the generator III by force of gravity.

To provide a vent for conduit 48 the upper end thereof is connected by a conduit 49 to manifold 38. The upper end of vessel 44 is connected by a conduit 50 to vessel l8, whereby the pressure in the vessel 44 is equalized with the pressure in upper part of generator I 0 and condenser II. The lower parts of evaporator I2 are connected byconduits 5| and 5| to an upper part of vessel 44, so that unevaporated liquid may be drained from evaporator I2 into vessel 44.

The heat liberated with absorption of water vapor in absorber I4 is transferred to a suitable cooling medium, such as water, for example, which is supplied through a conduit 52 and flows upwardly through coils 53 and 54. The coils 53 and 54 are connected by a conduit 55 to condenser ll, so that the same cooling medium may be utilized to cool absorber l4 and condenser II. The cooling medium flows from condenser H through a conduit 55.

The system operates at low pressures with the generator Ill and condenser ll operating at one pressure and the -evaporator I 2 and absorber I 4 operating at a lower pressure, the pressure differential being maintainedby liquid colunms.

Thus, the liquid column formed in the tube 33 maintains the pressure differential between condenser .II and evaporator I2, The liquid column formed in conduit 4| maintains the pressure differential between the outlet of obsorber l4 and generator I 0, and the liquid column flow in conduit 48 and parts connected thereto including conduit 41 maintains the pressure differential between the inlet of absorber l4 and the upper part of generator I0. The liquid column formed in' conduit 5| -maintains the pressure difieren'tial between evaporator I 2 and vwsel 44 which is pressure-equalized through conduit 50 with the upper part of generator Hi. In operation, the liquid columns may form in conduits 4|, 4!, and down-leg of tube 33 to the levels 32, 1/, and z, for example. Conduit 33 is such that restrictionof gas flow is effected without appreciably restricting flow of liquid. The liquid column formed in vessel 44 and conduit 45 provides the liquid reaction head for raising liquid in the vertical tubes l5 by vapor-lift action.

The vessel 44 is of sufllcient volume to hold the liquid differential in the system and is of such cross-sectional area that the liquid level therein does not appreciably vary, so that a substantially constant reaction head is provided for lifting liquid in generator Ill. The vessel 44 is located below absorber l4 such a distance that, for the greatest pressure differential occurring between absorber l4 and the upper part, or vapor space, of generator I during operation of the system, the liquid column formed in conduit 4| is below the lower end of absorber l4.

The evaporator or cooling element I2 is arranged in a conduit 51 of an air conditioning system, as shown in Fig. 2. The duct-51 is connected to a suitable blower 58, whereby air is withdrawn from an enclosure 59 through a duct 50 and passes in thermal exchange relation with evaporator I2 in duct 51. The refrigerant supplied to evaporator l2 vaporizes therein to produce a cooling effect, as pointed out above, with consequent absorption of heat from the air passing over the exterior surfaces of the evaporator. The cooled air flows through the blower 58 into a duct 5| from which the cooled air is discharged into the enclosure 59.

As shown' in Figs. 1 and 2, each of the con- 1 trol devices 25 includes a solenoid coil 52 formed to receive a plunger 53 to which is fixed a valve 54. When a solenoid coil 52 is electrically energized, the plunger 63 and valve 54 are raised against the force of gravity, whereby the valve noid coil 52 is deenergized.

Any suitable control may .be provided for controlling the control devices 25 and hence the fiow of fuel to burners 23. Although we do not wish to be limited thereto, we have illustrateda control arrangement like that described in application Serial No. 350,237, of A. R. Thomas, filed August 3, 1940. In this type of control the burners 23 are controlled sequentially responsive.

to a temperature'condition affected by the refrigeration apparatus.

- As shown in Fig. 2, the solenoid coils 62 are connected to conductors 55 and 51 which are' connected to a suitable source of electrical supply. One terminal of each coil 52 is connected by a conductor 58 to the conductor 55, and the other terminal of each coil is connected by a conductor 59, a switch 10, and a conductor H to the conductor 51. The switches I0 are of the snap-action type and include toggle arms 12 and 13 pivotally connected at their inner ends at 14 to a support, and a coil spring I5 connected to the outer ends of the arms.

Stops '15 are provided to limit movement of lower toggle arms 13 in one direction. When moved in the opposite direction the contacts TI at the ends of toggle arms 13 cooperate with fixed contacts 18 to complete the circuits for the solenoid coils 52.

through and is movable in suitable supports 8|.

The right hand end of slide bar 88 is formed with a recess 82 to receive the upper end of a lever 83 which is pivoted intermediate its ends at 84 to a frame 85. The lower end of lever 83 is pivotally connected to a rod 86 which is secured to an expansible and contractible bellows 81 having one end thereof fixed and secured to the frame 85. A spring 88 is interposed between the bellows 81 and the left hand end of frame 85.

The bellows 81 is connected by a capillary tube 89 to a thermal bulb 98 which is located in the enclosure 59. The bellows 81, tube 89, and bulb 98 constitute an expansible fluid thermostat containing a suitable volatile fluid which increases and decreases in volume with corresponding changes in temperature. The bellows 81 expands and contracts with increase and decrease in volume of the volatile fluid, and these movements of the bellows 81 are, utilized to control the switches 18. In Fig. 2 both of the switches 18 are open and the solenoid coils 62 are deenergized, so that the valves 64 are in their closed positions and the supply of fuel toburners 23 is shut ofi. In the open positions of the switches 18 the contacts 11 and 18 are separated and the toggle arms 13 bear against the stops 16.

The control just described is effective to sequentially control the devices 25, and hence con-.- trol the flow of fuel to burners 23, so that the evaporator or cooling element l2 will be capable of maintaining the air in enclosure 59 at a desired low temperature. When the air inenclosure 59, and hence the evaporator l2, tends to rise above the desired low temperature, the volatile-fluid of the expansible fluid thermostat increases in volume and causes the bellows. 81 to expand against the tension of coil spring 88. With expansion of bellows 8'! clockwise movement is imparted to lever 83 about pivot 84 whereby slide bar 88 is moved toward the right.

As the slide bar 88 is moved toward the right, the upper toggle arms 12 move clockwise about the pivots l4, and, when the coil springs 15 are moved past the straight line positions of the toggle arms 12 and 13, the lower toggle arms 13 move with a snap-action toward the right to close contacts TI and E8. The closin of contacts 1'1 and I8 completes the electrical circuits for the solenoid coils 62 of the control devices 25, whereby the valves 68 are moved to their open positions to permit flow of fuel to the burners'23. By providing the pilot flame tubes 21, the burners 23 are immediately ignited with opening of the valves 64, so that hot gases will pass through the heating tubes 22 to heat the water in boiler 2| to produce steam.

It will be noted in Fig. 2 that the upper toggle arms I2 of the switches 18 are at different angles with respect to the vertical. As slide bar 88 is moved toward. the right, in the manner described air tends to rise above the low temperature atwhich it is desired to maintain the enclosure 59,

'conduit 28 to generator steam chamber due to expansion of bellows 81 will first cause one ofthe burners 23 to become effective to heat boiler 2|. slide bar 88 toward the right, the toggle arms 12 and 13- of the right hand switch will reach a straight line position, and, when the coil spring 15 of this switch moves past the straight line position of the toggle arms, the lower toggle arm I3 will snap to the right to completethe electrical circuit for the right hand control device 25. By first closing one switch 18 and then the other switch 18 in the manner described above, the

burners are controlled sequentially responsive to a temperature condition which is affected by the temperature of evaporator i2.

When the air in the enclosure 59 tends to rise above the desired low temperature, the bellows 81 may expand enough to-cause one or both of the burners to become operative to effect heating of boiler 2|. The steam produced by the boiler 2| due to heating by the burners 23 flowsthrough whereby an increased refrigerating or cooling effect is produced by the evaporator l2 which is transmitted to air flowing through the duct 51 to the enclosure 59.

Conversely, when the air in the enclosure 59, and hence the evaporator l2, tends to fall below the desired low temperature, the volatile fluid of the expansible fluid thermostat decreases in vol ume and causes the bellows 8! to contract. Contraction of bellows 8| imparts counter-clockwise movement to lever 83 whereby slide bar 88 moves toward the left. Under these conditions the upper toggle arms 12 move counter-clockwise about the pivots l4, and, when the coil springs 15 have moved past the straight line positions of the toggle arms in the opposite direction from that described above, the lower toggle arms 13 move with a snap-action toward the'left withsuch movement being limited by the stops 15. This movement of the lower toggle arms 13 causes separation of contacts l1 and 18 to open the switches 18, so that the electrical circuits of the solenoid coils 62 are opened. This causes deenergization. of the solenoid coils 62 and the valves 64 move to their closed positions to shut off flow of fuel to the burners 23. When this occurs, the heating of boiler 2| is decreased and the production of steam is reduced, so that the refrigerating or cooling effect produced by the evaporator I2 is also reduced.

Assuming'that both of the switches 18 are closed, and that the slide bar 88 is movingtoward the left due to contraction of bellows 81, the right hand switch '18 will open first to cause deenergization of the right hand control devict 25. With continued movement of slide-gbar 88 toward the left, the other switchwlflwill be opened, whereby both of the control-devices 25 will be deenergized and flow of fuel shut off to both of the burners 23. However, the air in the enclosure 59 may fall below the desired low temperature such an amount as to cause only one of the switches I8 to open, so that one of the burners 23 will continue to effect heating of the boiler 2|.

In accordance with this invention, the steam boiler system operates substantially at atmospheric pressure, so that self regulation, is effected of the rate at which vapor forms in the generator riser tubes l6 and the rate at which absorption liquid is raised in the tubes by vapor'v lift action. This is accomplished by providing a the movement of slide bar 88 toward the right With continued movement of trap conduit a.

steam vent 9| at the upper part of generator chamber l9 which permits air to enter the upper 7 full length heating of the riser tubes I6 is effected by the steam with practically no steam passing through the vent 8| into the atmosphere. The condensate formed in chamber l9 collects in the bottom part thereof and is drained through With all of the surfaces of tubes l6 heated by steam and effective to' expel refrigerant from absorption solution, maximum capacity is obtained from generator III with vapor being formed in the tubes i6 and liquid being raised by the vapor at a maximum rate.

When the control described above has operated so that only one of the burners 23 is supplying heat to the steam boiler 2|, the-supply of steam to the generator chamber I9 is reduced. With the steam heating system operating substantially at atmospheric pressure due to the provision of the vent ill, the generator chamber l9 at heat inputs less than maximum will only be partly filled with steam. The steam supply at low load a is such that only the bottom part of chamber l9 contains steam and the upper part thereof contains air which enters into the chamber from the atmosphere through vent 9|. With the upper part of chamber is containing air, all of the surfaces of the tubes it are not heated by steam.

Thus, the air blankets oiT the upper parts of the riser tubes l6 from direct contact with the steam so that full length heating of the tubes is not effected and the eifective tube heating surface is reduced. With less heating of the tubes i8 along their lengths, less vapor is formed and less absorption solution is raised or pumped upward through the tubes I6 by vapor-lift action, and this is what is referred to herein as self regulation.

It should be understood that more than two burners 23 and control devices 25 can be employed so that a more sensitive control of the heat input to the boiler and of the steam supply to chamber I9 is effected. By providing more than two burners 23 to supply heat to steam boiler 2|, therefore, the rate at'which steam is supplied to the generator chamber l9 can be controlled between even narrower limits than with the two burners illustrated. In any event, it will be understood that the rate at which vapor is formed in riser tubes i6 and absorption liquid is raised in the tubes is proportional to the heat input, the extent to which the air blankets oil the riser tubes l6 increasing and decreasing with variations in the heat input to the boiler 2 I.

At low loads on the refrigeration system when the rate at which refrigerant'is expelled from absorption solution is reduced, the heat input is decreased and the absorption solution is more dilute than atheavier loads. Dilute absorption solution liquidtends to beraised more rapidly by vapor-lift action. However, by providing the vent 9| and permitting air to enter chamber is so that a part of the heating surface of the tubes I6 is blanketed oil by the air, the circulation of regulation of vapor formation and lifting of liquid by vapor-lift action is effected, by operating the steam boiler system associated with a generator or vapor expeller of a heat operated refrigeration system substantially at atmospheric pressure by the provision of a vent in the gen-' erator steam chamber.

While a single embodiment of the invention has been shown and described, it will be apparentto those skilled in the art that various modifications and changes may be made without departing from the spiritandscope of the invention, as pointed out in the following claims.

What is claimed is:

1. In a refrigeration system operated by heat and having a cooling element and a heat receiving part provided with a chamber, a boiler, a heater for heating said boiler to produce steam in the latter, said chamber being connected to receive steam from said boiler and having a permanent opening to atmosphere, and means to control said heater responsive to a temperature condition affected by said cooling element whereby air can pass through said opening from the atmosphere into said chamber with changes in heat input to said boiler by said heater.

2. Ina refrigeration system operated by heat and having a heat receiving part provided with a chamber, a boiler having a heating tube, a fuel burner adapted to project its flame into said tube whereby hot gases pass through the latter to produce steam in said boiler, an electrical control deviceior controlling flow-of fuel to said burner, said chamber having a permanent open-. ingto atmosphere and being connected to receive steam from said boiler, and means responsive to a temperature condition affected by said refrigeration system for controlling operation of said device. 4

3. In a refrigeration system operated by heat and having a vapor expeller provided with a chamber and a riser tube extending vertically in the latter, means to supply steam to said chamber from a suitable source of supply to cause heating of absorption solution in said riser tube and effect expulsion of vapor from solution therein and raise liquid therethrough by vapor-lift action,,said chamber having a permanent opening to atmosphere whereby air can pass into'said chamber and partly fill said chamber to blanket all a portion of the heating surface of said tube from the steam when the supply of steam to the chamber is reduced, and a device for controlling the supply of steam to said chamber from the source of supply. 4. In a refrigeration system operated by heat and having a cooling element and a heat receiving part provided with a' chamber, a boiler, a heater for heating said boiler to produce steam in the latter, said chamber being connected to receive steam from said boiler and having a permanent opening to atmosphere, and a device to control said heater. 5. In refrigeration apparatus for cooling an enclosure to which is connected a duct through which air is caused to flow to theenclosure, said refrigeration apparatus being operated by heat and having a cooling element in the duct and a heat receiving part provided with a chamber, a boiler, a heater for heating saidboiler to produce steam in the latter, said chamber having a perand having a heat receiving part provided with a chamber, a boiler, a heater for heating said boiler to produce steam in the latter, said chamber having a vent permanently open to the atmosphere and being connected to receive steam from said boiler, the aforementioned parts being so constructed and arranged that at a definite rate of heat input to said boiler by said heater and a predetermined load-on the refrigeration system the steam supplied to said chamber fills the latter substantially completely with the steam condensing in said chamber and substantially no flow of steam occurring through said vent, and means to control said heater to reduce the heat input to said boiler below said definite rate and hence reduce the supply of steam to said chamber, so that air can enter the interior of said chamber through said vent and blanket off of steam to the jacket is below a predetermined amount.

10. In a multiple pressure refrigeration system having a generator and a condenser adapted to operate at one pressure and an evaporator and an absorber adapted to operate at a lower pressure, and conduits connecting the aforepart of said chamber from the steam to reduce the quantity of heat received ing part.

7. A refrigeration system as set forth in claim 6 in which said means to control said heater operates responsive to a temperature condition affected by a part of the refrigeration system.

8. In refrigeration apparatus having an enclosure to which is connected a duct through which air is caused to flow to the enclosure, said refrigeration apparatus having a cooling element in the duct and a heat receiving part provided with a chamber, a boiler, a heater for heating said boiler to produce steam in the latter said chamber having a vent permanently open to atmosphere and being connected to receive steam from said boiler, the aforementioned parts being so constructed and arranged that, for a definite heat input to said boiler by said heater and a predetermined load on said cooling element, the steam supply to said chamber fills the latter substantially completely with the steam condensing in said chamber and substantialy no flow of steam occurring through said vent, and means responsive to fall of a temperature condition affected by said cooling element to reduce the heat input to said boiler below the definite rate and hence reduce the supply of steam to said chamber, so that atmospheric air can enter through said vent to partly fill the space of said chamber and by said heat receivblanket off a portion thereof from the steam to reduce the quantity of heat received by said heat receiving part.

9. In an absorption refrigeration system having an absorber and a generator provided with a liquid upfiow conduit, a jacket disposed about said upfiow conduit, a pipe connected to said jacket for supplying steam to the latter from a source of supply, the steam being effective to heat said upfiow conduit to cause expulsion of vapor from absorption liquid therein and effect lifting of liquid therethrough by vapor lift acand blanket off a part of said upfiow conduit from the steam to reduce the effective heating surface of said upfiow conduit when the supply mentioned parts to provide circuits for circulation of refrigerant and absorption liquid, said generator having a chamber within which is disposed a vertically extending member connected at its lower end to receive absorption liquid from the absorber, a conduit-connected to a lower part of ,said chamber for supplying steam thereto from a source of supply, said chamber having a permanently open atmospheric vent in the upper part thereof, the steam supplied to said chamber being effective to cause expulsion of vapor from absorption solution in said member and lifting of liquid therethrough by vapor lift action, said vent permitting air to enter the interior of said chamber from the atmosphere when the supply of steam to said chamber is below a predetermined maximum, and a device for controlling the supply of steam from the source of supply to said chamber through said conduit whereby the quantity of air within said chamber and the portion of said member blanketed by air from the steam is inversely proportional to the rate of flow of steam to said chamber.

11. A refrigeration system operated by application of heat and including a part having a heat transfer surface to which operating heat is applied for transfer to the system, a chamber having a wall formed by said heat transfer surface, and an inlet for admitting steam to said chamber, said chamber having a permanent opening to atmosphere at a point remote from said inlet so that air may flow in either direction through said opening and steam flowing from said inlet towards said opening comes in heating contact with said surface over an extent of said surface de-'- pendent upon the relative proportions of steam and air in said chamber.

12. A refrigeration system operated by application of heat and including a part having a heat transfer surface to which operation heat is applied for transfer to the system, a chamber having a wall formed by said heat transfer surface, said chamber being connected to receive steam at one point; and a substantially constant pressure fluid at'a second'point remote from said first point so that steam admitted at said first point flows toward said second point in heating contact with said surface, the heating contact being over an extent of said surface dependent upon the quantity of steam in said chamber with respect to the qauntity of constant pressure fluid therein, said constant pressure fluid being displaced from said chamber upon increase in quantity of steam therein, and said constant pressure fluid entering said chamber upon decrease in quantity of steam therein, the pressure in said chamber at all times being that of said constant pressure fluid.

13. A refrigeration system operated by application of heat and including a part having a heat transfer surface to which operating heat is applied for transfer to the system, a chamber hav-' ing a wall formed by said heat transfer surface, and an inlet for admitting heating vapor to said chamber, said chamber having provisions for permanent breathing remote from said inlet so which heating vapor is supplied to said chamber,

said chamber also. having provision for permanent breathing so that a non-heating medium at substantially constant pressure may at all times flow into and out of said chamber, and apparatus to control said supply of heating vapor to said 15 chamber. 1

15. A refrigeration system operated by heat and having a cooling element and a heat receiv ing part provided with a chamber, said chamber having an inlet through which heating vapor is supplied to the chamber, said chamberalso hav-'-- ing provisionfor permanent breathing so that a non-heating medium at substantially constant pressure may at all times flow into and out of said chamber, and apparatus to control said supply of heating vapor to said chamber responsive to a temperature condition affected by said cooling element.

ALBERT R. THOMAS.

PHILIP P. ANDERSON, JR.

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