US3793993A

US3793993A - Vapor generator and control therefor

Info

Publication number: US3793993A
Application number: US00285629A
Authority: US
Inventors: W Teagan
Original assignee: Thermo Electron Corp
Current assignee: Thermo Fisher Scientific Inc
Priority date: 1972-09-01
Filing date: 1972-09-01
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26

Abstract

The vapor generator provides a uniform and controllable heat input for vaporizing organic working fluid in a vapor engine. A fluid-tight enclosure is partially filled with a heat transfer fluid for transferring heat from a heat source to organic working fluid conducted through the enclosure in a convoluted tube. A simplified pressure responsive temperature control apparatus provides safe and accurate operation.

Description

O United States Patent 1191 1111 3,793,993 Teagan 1 Feb. 26, 1974 [54] VAPOR GENERATOR AND CONTROL 1,880,533 10/1932 Thomas 122/367 THEREFOR [lgLrilakis mson et a Inventor: William g Acton, Mass- 2,363,118 11/1944 Chamberlain... 122/33 2,656,821 10/1953 Ray 122/33 [73] Asslgnee' w f xgz mgg 3,055,347 9/1962 Bailey et a1. 122 33 [22] Filed: Sept. 1, 1972 Primary Examiner-Kenneth W. Sprague [2]] pp NO: 285,629 Attorney, Agent, or Firm-James L. Neal [57] ABSTRACT [52] US. Cl. 122/33, 122/367 R 51 1 Int Cl F22) The vapor generator provides a uniform and controlla- 58 Field of Search...l22/32, 33, 367 R, 367 c, ble heat f f gamc l 122/367 A a vapor englne. A fluld-tlght enclosure 15 partially filled Wltl'l a heat transfer fluid for transferring heat from a heat source to organic working fluid conducted [56] References Cited through the enclosure in a convoluted tube. A simpli- UNITED STATES PATENTS fied pressure responsive temperature control appara- 3,603,l01 9/1971 Sul1livan 12/2/33 X tus provides safe and accurate operation. 3,138,199 6/1964 Be 1.... 122 321 X 2,868,178 1/1959 Peters 122/32 11 Clams, 3 Drawmg Flgures 2,791,204 5/1957 Andrus 122/33 PATENTED FEBZB I974 SHEET 1 BF 2 VAPOR GENERATOR AND CONTROL THEREFOR BACKGROUND OF THE INVENTION Vapor cycle engines, such as those operating according to the Rankine cycle, have experienced renewed interest. This is in large measure due to their nonpolluting characteristics, especially when compared with internal combustion and diesel engines. In developing vapor cycle engines suitable for modern uses, organic working fluids have emerged as highly desirable. However, one characteristic of organic fluids, when used as a working fluid in a vapor engine, which must be carefully dealt with is their thermal sensitivity. Many good organic working fluids are thermally stable at the normal working temperature of vapor cycle engines, but such fluids are often not stable sufficiently above such working temperatures to prevent decomposition from local overheating and hot spots occurring in ordinary vapor generators. Consequently, attention is directed to vapor generators capable of vaporizing organic working fluid but not overheating the fluid at any point. US. Pat. No. 3,477,412 of Sotiris Kitrilakis, assigned to the assignee of the present invention, discloses oneapproach to this problem.

It is an object of this invention to provide a highly simplified vapor generator suitable for use with organic working fluids.

It is another object of this invention to provide a vapor generator for organic working fluids which involves an uncomplicated, dependable and safe control system.

It is a further object of this invention to provide a vapor generator for organic working fluids characterized by a high degree of temperature uniformity in the heat transfer zone to thus avoid overheating of the organic working fluid.

SUMMARY OF THE INVENTION This invention pertains to a general purpose vapor generator particularly adaptable for use with a vapor cycle engine and other systems wherein the working temperature requires very accurate control. An essential feature of the invention resides in a fluid-tight enclosure partially filled with a suitable heat transfer fluid through which there extends a conduit for a second fluid ultimately to be heated which, in the case of a vapor cycle engine, is typically an organic working fluid. The conduit conducts fluid to be heated through the enclosure in heat exchange relationship with the heat exchange fluid. There is also provided a burner or other suitable heat source means for producing heat input to the heat transfer fluid. Heat input to the heat transfer fluid produces boiling and transfer fluid vapor fills the enclosure through which the conduit extends. The boiling liquid and the resulting vapor completely immerse the conduit in a fluid medium.

This constitutes a highly efficient heat transfer system. The heat transfer fluid is in a condition of pool boiling which results in an exceedingly high heat transfer coefficient between the heat transfer fluid and any portion of the conduit extending into the boiling liquid. Further, portions of the conduit extending above the liquid level of the boiling heat transfer fluid are immersed in the fluid vapor. The fluid travelling through the conduit is at a lower temperature than the vaporized heat transfer fluid; the heat transfer fluid vapor thus condenses upon the conduit and gives up its latent heat of vaporization.

The fluid-tight enclosure may be substantially evacuated of non-condensables to create an equilibrium or near equilibrium condition in the enclosure. In this event, the enclosure pressure is solely a function of the enclosure temperature. Since the enclosure is filled with fluid vapor and boiling liquid in equilibrium, there is a substantially uniform pressure and temperature throughout the entire enclosure at any given time. A single pressure measurement therefore will provide all the needed temperature and pressure information for monitoring and control of the system. For example, a single pressure signal can be the only signal required to control heat output of the heat source as a function of working fluid temperature. Another advantage resulting from equilibrium conditions internal of the enclosure is that, at start-up, the heat transfer fluid begins to boil immediately upon being heated by the heat source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cut-away perspective view showing one preferred embodiment of the invention;

FIG. 2 is a cross-sectional view through another embodiment of this invention; and

FIG. 3 is a sectional view along lines 3-3 of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows a heat exchanger which will be described as a vapor generator for a vapor engine system, although it is suitable for general use. The vapor generator comprises a tube housing 102 and an evaporator housing 104, the two housings together constituting a single fluid-tight vessel, or enclosure, 105 having

openings

106 and 108 for purposes which will be subsequently described. Within the tube housing 102 there is installed a fluid-conducting tube 110 having an inlet port 112 and an outlet port 114. The tube conducts through the vapor generator tube housing 102 an organic working fluid for a vapor cycle engine. Con-,

densed working fluid from a vapor engine condenser, not shown, is admitted in the liquid state to the tube 110 through the inlet port 112. In the vapor generator 100, the working fluid is evaporated and passes from the tube 110 through the outlet port 114. It is then admitted to an expander, not shown, which forms a part of the vapor cycle engine in a manner well understood in the art.

In the evaporator housing 104, there is a heat source means consisting of a plurality of ducts 116 having heat transfer fins 118 therein. The ducts 116 conduct a heating fluid from an appropriate supply through the housing 104 and constitute the heat source means for the vapor generator. The evaporator housing 104 surrounding the ducts 116 contains a heat transfer fluid 120 approximately to the upper level of the ducts 116,

as indicated by the line 121. A plate 122 fastened to the end of the evaporator housing 104 is adapted to facilitate connection of the ducts 116 to a supply of heating fluid while maintaining a fluid-tight seal between the enclosure 105 and the environment. A similar plate, not shown, is located at the opposite end of the housing 104 for permitting discharge of the heating fluid from the ducts 116.

The inlet ends of the ducts 116 may be connected to the outlet of a burner, not shown, so that products of combustion from the burner will pass through the ducts to heat the transfer fluid 120. The outlet ends of the ducts 116 will then permit appropriate discharge of these products of combusion.

When products of combustion or other suitable hot fluids at a temperature level about the boiling point of the heat fluid 120 and the desired temperature level of the vapor engine working fluid pass through the ducts 116, pool boiling of the heat transfer fluid is produced and the vapor created thereby fills the tube housing 102. The relatively cool liquid working fluid entering the tube 1 at the inlet port 1 12 is heated through the wall of the tube 110 by condensation of transfer fluid vapor upon the outer surface thereof. The working fluid travels through the tube 1 10 with a sufficient residence time therein to vaporize and pass from the vapor generator through the outlet port 114 as a working fluid vapor. The residence time may be a function of the working fluid circulation rate produced in the vapor engine. The transfer fluid 120 which condenses on the tube 110 drops back to the liquid pool in housing 104. Thus, it will be appreciated that the tube wall, or the wall of any suitable conduit exposed to the interior of the enclosure 105, defines a condensing surface and serves to confine the ultimate fluid to be heated.

A pressure tap 126 to the interior of the tube housing 104 provides a reading of the pressure therein by means of a pressure gauge 128. Since the pressure in the tube housing 102 is a function of the housing temperature, the pressure signal may also yield a temperature reading.

In order to maximize the efficiency of a vapor cycle engine, it is necessary to operate the engine at as high a working fluid temperature as possible. This implies that the temperature will be close to those temperatures at which unacceptable organic working fluid decomposition takes place. Organic working fluids can be obtained which are thermally stable at the maximum working temperature of the vapor cycle engine. However, most have thermal stability not sufficiently above the maximum working temperature of the engine to avoid thermal breakdown if local heating within certain zones of the vapor generator exceeds substantially the maximum anticipated working temperature of the engine. That is to say, most vapor generators are characterized by hot spots in which the temperature is substantially above the overall vapor generator temperature; with organic working fluids, these hot spots have been found to produce a wholly unacceptable amount of thermal decomposition. Therefore, for maximum efficiency, the vapor generator must maintain the working fluid temperature very near that temperature level at which thermal breakdown will occur while simultaneously avoiding tube wall temperature above that level at any point.

In the vapor generator described above, the temperature in the enclosure 105 is substantially uniform, being the temperature of the boiling heat transfer fluid 120 and its vapor. The temperature of the heat transfer fluid does not change substantially with momentary fluctuations in the temperature of the hot gases passing through the ducts 116. Therefore, the temperature of the enclosure 105, and thereby of the condensing surface formed by the tube 110, can be safely and accurately maintained at a predetermined level by governing the temperature or volume of hot gases flowing through the ducts 116. This temperature control may be a function of the temperature and pressure in the enclosure 105. It may be accomplished by connecting the pressure tap 126 to a conventional pressure responsive burner control system substantially in the manner fully explained in connection with the apparatus of FIG. 2. As a fail-safe measure, a frangible plug 130 in the wall of the enclosure is provided as a safety release in the event the pressure and temperature in the tube housing approaches dangerously high levels.

Temperature uniformity of the system and controllability of the system are enhanced if the fluid-tight enclosure' 105 is at least partially evacuated of noncondensables until the pressure therein is not substantially above the vapor pressure of theheat transfer fluid 120. The enclosure 105 with the heat transfer fluid therein may be evacuated by a vacuum pump and then sealed. Evacuation also removes potentially corrosive water vapor and permits construction from ordinary and inexpensive materials such as steel or cast iron. Further, under evacuated conditions, temperature and pressure throughout the enclosure will always be essentially uniform and the pressure in the enclosure will be a function only of the temperature in the enclosure. The liquid and vapor temperature is easily measured at any single point. It may be measured directly by a single thermocouple or thermal switch mounted anywhere in the evacuated enclosures. Alternately, the vapor pressure in the enclosure, which provides a direct measure of temperature, may be measured and used toprovide a system control, in the manner referred to above and described in greater detail in connection with the apparatus of FIG. 2.

Since the temperature is uniform througout the evacuated enclosure, there is no possibility of localized hot spots damaging the vapor engine working fluid in the tube 110. The temperature of the working fluid can not exceed that of the heat transfer fluid 120. Therefore, absolute control of the maximum temperature of the working fluid and positive prevention of its degradation is achieved. Control of the transfer fluid temperature and residence time of the working fluid in the enclosure 105 permits a preselected working fluid temperature to be attained. Further, when the enclosure is evacuated, the evaporator housing 104 may be configured so that it holds only a small amount of heat transfer fluid 120. In this event, the heat transfer fluid heats very rapidly, thus reducing to a minimum the start-up time for the vapor generator and therefore of the vapor engine. For example, one experimental vapor generator will provide start-up time of approximately 60 seconds.

The vapor generator 10 of FIG. 2 comprises basic as semblies forming a burner 12, combustion chamber 14, an enclosure 16 in which heat transfer takes place, and an exhaust passage 18.

The burner 12 is mounted above the combustion chamber 14 and includes a nozzle 20 for directing fuel into the combustion chamber and a blower 22 for providing a supply of air. The fuel and air constitute the combustible mixture which burns in the combustion chamber. Swirler blades 24 surround the nozzle, 20 to provide turbulence within the combustion chamber.

The combustion chamber 14, enclosure 16 and exhaust passage 18 are all formed integrally as described below. An outer cylindrical wall 26 defines one wall of the enclosure 16 and the exhaust passage 18 while an inner cylindrical wall 28 forms a second wall of the enclosure and exhaust passage. The upper part of the enclosure 16 is formed by an annular wall 30 and the lower portion thereof by a similar annular wall 32. The annular wall 32 divides the enclosure 16 from the exhaust passage 18, the exhaust passage being below and coextensive with the enclosure. Inside the inner cylindrical wall 28 is the combustion chamber 14 in which fuel and air are directed from the burner 12. The enclosure 16 is partially filled with a heat transfer fluid 34 and, as with the apparatus of FIG. 1, preferably evacuated of non-condensables, such as air, until the pressure in the enclosure is at least substantially down to or below the vapor pressure of the heat transfer fluid.

Between the combustion chamber 14 and the exhaust passage 18, there is provided a port 36 for permitting products of combustion to pass from the combustion chamber 14 to the exhaust passage 18. Referring to FIG. 3, it can be seen that the combustion products divide and pass along both sides of the annular exhaust passage and are discharged through a port 38 in the outer wall 26. There are extending down into the exhaust passage 18 from the lower wall 32a plurality of heat transfer fins 40. The heat transfer fins are in a generally plate-like configuration and shaped to guide the flow path of the combustion products through the exhause passage 18.

FIG. 3 illustrates a fin configuration which directs the combustion products flow in a generally semi-circular fashion around both sides of the annular combustion chamber, conforming essentially to the flow path which the combustion products would naturally pursue. It should be understood, however, that other flow paths may be produced by the fins 40.

Heat transfer fins 42 extend upwardly from the bottom annular end wall 32 into the heat transfer fluid 34. The

heat transfer fins

40 and 42 provide, respectively, enhanced heat transfer between the products of combustion and the bottom end wall 32 and between the bottom end wall and the heat transfer fluid 34.

A convoluted tube 44 is wound in spiral fashion through the enclosure 16 for conducting vapor engine working fluid therethrough. At ambient temperature, the spiral tube is partly immersed in condensed heat transfer fluid and partly above the level of the liquid heat transfer fluid. Working fluid may enter the tube 44 in the liquid form at an inlet 46 and pass from the vapor generator to vapor state at an outlet 48. The tube 44 may have associated therewith external heat transfer fins 50 and internal heat transfer fins 52 for enhancing its heat transfer characteristics.

The walls of the vapor generator are insulated to retain heat and increase its efficiency of operation. Preferably,-all wall surfaces of the enclosure 16 not exposed to combustion products from the combustion chamber 14 are insulated, as well as certain wall surfaces of the exhaust passage 18. Cylindrical insulating sheets 54 cover the outer cylindrical wall 26 and insulating sheet 56 extends across the bottom portion of the combustion chamber 14 and the exhaust passage 18. The insulating sheet 56 may be supported by an end wall 58. The upper portion of the inner cylindrical wall 28, above the liquid level of the heat transfer fluid 34,

- is also insulated by a cylindrical insulating member 60.

It is desirable to insulate the portion of the wall 28 of the evacuated chamber 16 exposed to the combustion chamber 14 which is not immediately adjacent heat transfer fluid in the liquid state to prevent overheating of that portion of the wall. By way of further explanation, the portion of the inner cylindrical wall 28 immediately adjacent heat transfer fluid 34 in the liquid state is in good heat transfer relationship to the heat transfer fluid and heat energy is easily transferred through the wall 28 to the fluid 34. However, the portion of the wall 28 above the liquid level of the heat transfer fluid 34 is contacted interior of the enclosure 16 only by the zone filled with a certain amount of heat transfer fluid vapor, this vapor not constituting a good medium for transferring heat from the wall 28.

The burner 12 is controlled by a burner control means 13 which communicates through a pressure line 15 to the evacuated enclosure 16. The burner control means 13 is responsive to pressure in the enclosure through the line 15 so that the firing rate of the burner 12 is directly a function of the pressure and temperature levels in the enclosure 16. The burner control means may be any suitable device capable of varying the output of the blower 22 and the nozzle 20 in accordance with the pressure signal received through line 15. There is provided a pressure gauge 17 for giving visual or audible signals corresponding to the pressure level in the evacuated enclosure 16.

Operation of the vapor generator 10 will now be described. As in the apparatus of FIG. 1, working fluid is exhausted as a liquid from a vapor engine condenser (not shown) and subsequently vaporized and fed as a vapor to a vapor engine expander (not shown). The working fluid is transported through the vapor generator 10 by the tube 44, liquid working fluid from the condenser being received by the inlet port 46 and leaving as vapor through the outlet port 48.

As the working fluid travels through the tube 44 it is vaporized by products of combustion from the combustion chamber 14. The blower 22 directs air from the atmosphere or another suitable supply through swirler blades 24 into the combustion chamber. Simultaneously, the nozzle 20 injects a supply of fuel. The fuel and air constitute a combustible mixture which, when ignited in a suitable manner, burns to produce hot gases which pass through the port 36 and travel along the exhaust passage 18 to the exhaust port 38. As the combustion products pass through the exhaust passage 18, they encounter heat transfer fins 40 and the bottom annular end wall 32 of the enclosure 16. Combustion products also engage insulating sheet 56 and the outer cylindrical wall 26 which is insulated by insulating cylinder 64. The insulating

members

54 and 56 minimize heat loss and a maximum amount of heat is transferred through the annular end wall 32. The heat is transferred both directly from the end wall 32 to the heat transfer fluid 34 and also from heat transfer fins 32 to the heat transfer fluid. The heat transfer fluid 34 is heated to boiling and the enclosure 16 is filled with the vapor of the fluid 34.

The working fluid and the tube 52 are at a lower temperature than the temperature of the heat transfer fluid. Accordingly, heat is transferred to the working fluid through the walls of the tube 44. Depending upon the location of the tube 52 within the enclosure 16 and the level of the surface of the fluid 34, heat is transferred by either or both of two operations. Heat may be transferred directly through the walls of the tube 52 by the boiling working fluid when the tube or a portion thereof is immersed in the pool of boiling working fluid.

When the tube or portion of it is located above the liquid level of the pool of heat transfer fluid, it is heated by condensation thereon of the relatively hot heat transfer fluid vapor to which it is exposed. When the heat transfer fluid condenses on the surface of the tube 52, it gives up its latent heat by vaporization, which is then transferred through the tube walls to the working fluid. Both methods of heat transfer are highly efficient. However, efficiency may be increased by providing more area over which heat transfer may occur. To achieve the increased area, the embodiment of FIG. 2 shows heat transfer fins 50 extending outwardly from the tube 44 into the enclosure 16 and heat transfer fir 52 extending from the inner surface of the tube 44. Heat transfer to the working fluid vaporizes the work ing fluid during its travel through the tube 52 so that a hot vapor is discharged through the outlet 48. Residence time of the working fluid in the vapor generator 10 is preferably sufficient to allow the working fluid vapor to substantially reach the heat transfer fluid temperature.

The burner control means 13 can be set by a selector means 19 to maintain a predetermined working fluid vapor temperature, for example 700 F. Thereafter, if the working fluid begins to rise above this temperature, there will be a corresponding rise in pressure interior of the enclosure 16. The pressure in the evacuated enclosure 16 is directly proportional to the temperature therein. In response to the pressure increase, and the corresponding temperature increase, the burner control means 13 will reduce the heat output of the burner 12. For example, the pressure increase may trip a pressure switch which will deenergize a solenoid to reduce or terminate fuel flow while simultaneously adding a resistance in the fan circuit to slow down or stop the fan and thereby reduce or terminate air flow. On the other hand, if working fluid vapor temperature begins to drop, a corresponding drop in enclosure 16 pressure will produce a reversal of the aforesaid events and result in an increased heat output of the burner 12. By use of the pressure signal, response delay is eliminated. That is, a signal which is a function of temperature, is given immediately with temperature change. As stated earlier, devices which measure temperature directly may be used, but they often do not provide immediate response to temperature change. The pressure control also constitutes an effective safety device for the vapor generator in that it will always reduce or cut off the heat input as the pressure internal ofthe enclosure increases above a predetermined level, thus avoiding a dangerous pressure build-up. As a fail-safe device, a

heat fusible plug 55, or the like, is provided to avoid excessive pressure build-up in the enclosure 16. A control system similar to that shown in FIG. 2 may be associated with the apparatus of FIG. 1 to control either the output of heat source or the flow rate of the hot gases through ducts 116.

Any heat transfer fluids which have thermodynamic properties suitable to the specific application to which the particular vapor generator is put may be used in vapor generators of this invention. A primary requirement is that the heat transfer fluid be thermally stable at the maximum anticipated operating temperature of the vapor generator. Other properties which are desirable are the possession of a high condensing heat transfer eoefficient and a vapor pressure low enough that containment of it is not excessively expensive or potentially dangerous at the highest anticipated working temperature. On the other hand, it is not required that the heat transfer fluid be thermally stable at a temperature level substantially above the maximum anticipated operating temperature of the vapor generator because of the extreme ease with which the temperature and pressure conditions in the enclosure 16 are monitored and controlled.

One heat transfer fluid which has proved highly successful in operation of the vapor generator for a vapor cycle engine is Dowtherm A (biphenyland biphenyl I oxide), manufactured by Dow Chemical Company, lo-

cated atMidland, Michigan 48640. Dowtherm A has a good condensing heat transfer coefficient. Fo r exarn ple, under a typical condition working fluid enters the vapor generator at 380 F and exists at 550 F while the Dowtherm A is maintained at a temperature of 600 F. The heat transfer coefficient is then 280 Btu/hr-ft F at entrance and 200 Btu/hr-ft F at exit when a 7% inch OD tube is used. Another advantage of Dowtherm A is that it contracts when it freezes and thereby does not damage the vapor generating equipment. It is also thermally stable above the maximum working temperature for most vapor cycle engines, for example, above 700 F. At 700 F, Dowtherm A has a relatively low vapor pressure of approximately 107 psia. At F, taken as typical ambient temperature, its vapor pressure is less than 0.01 psia; at 550 F, a typical operating temperature, the vapor pressure is 27.59 psia. At 496 F, the vapor pressure is 14.7 psia; at 600 F it is 45.55 psia. Accordingly, it will be seen that a vapor generator utilizing Dowtherm A can operate over most of its range with a subatmospheric pressure, and in any event, with very low pressure internal of the enclosure 16. Further, it is reportedly thermally stable at temperature of around 800 F so there is no problem with thermal decomposition in the vapor generators described above. However, whether used as a working fluid or heat transfer fluid, its thermal stability is not high enough to tolerate hot spots without also encountering local thermal decomposition at these hot spots.

Other suitable organic heat transfer fluids are Dowtherm E (ortho-dichlorohenzene), also manufactured by Dow Chemical Company; flurocarbons FC-75 and FC-4 manufactured by Minnesota Mining and Manufacturing Co. of St. Paul, Minnesota; blem sh- 5mm naphthalene) from Soken Chemical Engineering Co., Ltd. of Japan; KSK oil from Kureka Chemical Co., Ltd. of Tokyo, Japan and Gardena, California; Anisole (phenyl methyl ether); and para-methyl isopropyl benzene. Further information concerning the above fluids may be found in Handbook of Heat Transfer Media, Paul L. Geiringer; Reinhold Publishing Corp., N.Y. (1962). Toluene, hexafluorobenzene and trifluoroethanol may also be used as heat transfer fluids.

In addition to the organics, certain inorganics such as stenic tetrachloride, tetrametlyltin and tetramethylgermane may be used.

The vapor generator is sufficiently versatile that a wide range of other fluids may be used. For example, it will accommodate use of water as a heat transfer fluid. However, there are disadvantages. For example, water is corrosive relative to the organics and has a vapor pressure of approximately 1,100 psia at 550 F. A working fluid exit temperature of 700 F is associated with a water vapor pressure of over 3,200 psi. Containment of water vapor at this temperature requires a relatively heavy construction and is a potential safety hazard. If relatively high operating temperatures are always required, certain metals may be used as heat transfer fluids, for example, mercury and tin. It should be pointed out that a fluid having a very low pressure might not be desirable. For example, if the vapor pressure at 550 F should be in the vicinity of l or 2 psi, the heat transfer properties of the fluid might be reduced below levels generally considered acceptable.

The present invention has been described in reference to preferred embodiments. It should be understood that modifications may be made by those skilled in the art without departing from the scope of the invention.

I claim:

1. A vapor generator for a vapor engine using organic working fluid, said vapor generator comprising:

a. means forming a sealed, fluid-tight enclosure of annular configuration forming a combustion chamber in the center of the annulus;

b. heat transfer fluid non-decomposable at the anticipated maximum working temperature of said vapor generator partially filling said enclosure in the liquid state, said enclosure being at least partially evacuated of non-condensables to establish a pressure level therein not substantially above the vapor pressure of said heat transfer fluid;

c. conduit means for conducting organic working fluid into heat exchange relationship with the interior of said enclosure; and

d. heat source means for directing a combustible mixture into said annulus and pool boiling said heat transfer fluid at a temperature level equivalent to or above the boiling point of said organic working fluid whereby heat energy is transferred through the wall of said conduit means to said organic working fluid.

2. A vapor generator according to claim 1 wherein said annular enclosure comprises concentric side walls and top and bottom annular'end walls, further comprismg:

a. an annular exhaust passage substantially coextensive with said annular enclosure and extending downwardly from said bottom end wall;

b. means forming at least one entrance opening between said combustion chamber and said exhaust passage to admit combustion products to said exhaust passage; and

0. means in said exhaust passage forming at least one exit opening remote from said entrance opening for discharging exhaust gases, whereby exhaust gases travel from said combustion chamber, along a path adjacent the bottom end wall of said enclosure, before being discharged.

3. A vapor generatr according to claim 2 wherein said exit opening is situated 180" from said entrance opening.

4. A vapor generator according to claim 2 further comprising:

a. heat transfer fins extending upward from said bottom end wall into said heat transfer fluid; and

b. heat transfer fins extending downward from said bottom end wall into said exhaust passage.

5. A vapor generator according to claim 4 wherein said downwardly extending heat transfer fins comprise elongated plate-like members for directing the flow path in said exhaust pgssage.

6. A vapor generator according to claim 2 further comprising thermal insulation along the common wall between said enclosure and said annular space restricted substantially to the portion of said common wall above the level of liquid in said enclosure.

7. A vapor generator according to claim 1 further comprising means responsive to the pressure in said enclosure for controlling the heat input to said heat transfer fluid, to thereby maintain a predetermined operating temperature level in said vapor generator.

8. A vapor generator according to claim 1 further comprising:

a. pressure actuated means for controlling the heat input to said heat transfer fluid;

b. means for applying a signal proportional to the pressure internal of said enclosure to said pressure actuated means, said signal providing the total information required for enabling said pressure actuated means to variably control said heat input and maintain working fluid vapor discharged from said vapor generator at a predetermined temperature level.

9. A vapor generator for closed cycle vapor engine utilizing a thermally sensitive organic working fluid, said vapor generator comprising:

a. means forming a substantially rigid, sealed, fluidtight enclosure of substantially constant volume, substantially devoid of fluids which are noncondensable over the working temperature range of said vapor generator, partially filled throughout said range with a heat transfer fluid in the liquid state, said heat transfer fluid being nondecomposable throughout said range;

b. heat source means for vaporizing a portion of said heat transfer fluid;

c. conduit means extending through said enclosure with at least a portion thereof out of contact with said heat transfer fluid in the liquid state and forming a condensing surface upon which vaporized heat transfer fluid condenses to transfer thereto its latent heat of vaporization, said conduit means having an inlet for admitting working fluid into heat exchange relationship with the interior of said enclosure and an outlet for discharging working fluid from said heat exchange relationship; and

d. pressure responsive control means, responsive only to the vapor pressure within said enclosure, coupled to said heat source means for controlling the output thereof to maintain the heat transfer fluid vapor, and thereby the entire condensing surface, at a temperature level not lower than the boiling point of said working fluid and below the temperature at which an unacceptable amount of thermal degradation of said working fluid occurs, whereby said vapor generator is enabled to heat working fluid at said outlet to vaporization without producing thermal decomposition thereof.

10. A heat transfer device according to claim 9 wherein said heat transfer fluid comprises biphenyl and biphenyl oxide.

11. A heat transfer device according to claim 9 wherein said pressure responsive means comprises a variable control for selecting the operating temperature of said condensing surface.

Claims

1. A vapor generator for a vapor engine using organic working fluid, said vapor generator comprising: a. means forming a sealed, fluid-tight enclosure of annular configuration forming a combustion chamber in the center of the annulus; b. heat transfer fluid non-decomposable at the anticipated maximum working temperature of said vapor generator partially filling said enclosure in the liquid state, said enclosure being at least partially evacuated of non-condensables to establish a pressure level therein not substantially above the vapor pressure of said heat transfer fluid; c. conduit means for conducting organic working fluid into heat exchange relationship with the interior of said enclosure; and d. heat source means for directing a combustible mixture into said annulus and pool boiling said heat transfer fluid at a temperature level equivalent to or above the boiling point of said organic working fluid whereby heat energy is transferred through the wall of said conduit means to said organic working fluid.

2. A vapor generator according to claim 1 wherein said annular enclosure comprises concentric side walls and top and bottom annular end walls, further comprising: a. an annular exhaust passage substantially coextensive with said annular enclosure and extending downwardly from said bottom end wall; b. means forming at least one entrance opening between said combustion chamber and said exhaust passage to admit combustion products to said exhaust passage; and c. means in said exhaust passage forming at least one exit opening remote from said entrance opening for discharging exhaust gases, whereby exhaust gases travel from said combustion chamber, along a path adjacent the bottom end wall of said enclosure, before being discharged.

3. A vapor generatr according to claim 2 wherein said exit opening is situated 180* from said entrance opening.

4. A vapor generator according to claim 2 further comprising: a. heat transfer fins extending upward from said bottom end wall into said heat transfer fluid; and b. heat transfer fins extending doWnward from said bottom end wall into said exhaust passage.

5. A vapor generator according to claim 4 wherein said downwardly extending heat transfer fins comprise elongated plate-like members for directing the flow path in said exhaust passage.

8. A vapor generator according to claim 1 further comprising: a. pressure actuated means for controlling the heat input to said heat transfer fluid; b. means for applying a signal proportional to the pressure internal of said enclosure to said pressure actuated means, said signal providing the total information required for enabling said pressure actuated means to variably control said heat input and maintain working fluid vapor discharged from said vapor generator at a predetermined temperature level.

9. A vapor generator for closed cycle vapor engine utilizing a thermally sensitive organic working fluid, said vapor generator comprising: a. means forming a substantially rigid, sealed, fluid-tight enclosure of substantially constant volume, substantially devoid of fluids which are non-condensable over the working temperature range of said vapor generator, partially filled throughout said range with a heat transfer fluid in the liquid state, said heat transfer fluid being non-decomposable throughout said range; b. heat source means for vaporizing a portion of said heat transfer fluid; c. conduit means extending through said enclosure with at least a portion thereof out of contact with said heat transfer fluid in the liquid state and forming a condensing surface upon which vaporized heat transfer fluid condenses to transfer thereto its latent heat of vaporization, said conduit means having an inlet for admitting working fluid into heat exchange relationship with the interior of said enclosure and an outlet for discharging working fluid from said heat exchange relationship; and d. pressure responsive control means, responsive only to the vapor pressure within said enclosure, coupled to said heat source means for controlling the output thereof to maintain the heat transfer fluid vapor, and thereby the entire condensing surface, at a temperature level not lower than the boiling point of said working fluid and below the temperature at which an unacceptable amount of thermal degradation of said working fluid occurs, whereby said vapor generator is enabled to heat working fluid at said outlet to vaporization without producing thermal decomposition thereof.