US 3657877 A
A heat engine of modified Stirling cycle configuration utilizing condensable vapor as a working fluid in a variable liquid level regenerator. Condensation and evaporation of the working fluid take place in the variable liquid level regenerator continuously and in a controlled manner. In addition to the variable liquid level regenerator, which may be defined more aptly as a tidal regenerator, the basic components of the engine are a condenser, a vaporizer, a superheater, a power piston, a displacer piston and a control for the displacer piston.
Claims available in
Description (OCR text may contain errors)
United States Patent 15 3,657,877 Huffman 51 Apr. 25 M72  TIDAL REGENERATOR HEAT ENGINE Primary ExaminerMartin P Schwadron 2 N. ff [7 1 1m emor Fred Sudbury Mass Assistant Exammer--Allen M. Ostrager  Assignee: Thermo Electron Corporation, Waltham, Anorney-Kenway; .Ienney & Hildreth Mass.
221 Filed: Feb. 1, 1971 [571 ABSTRACT  AppL NO: 1,331 A heat engine of modified Stirling cycle: configuration utilizing condensable vapor as a working fluid in a variable liquid level regenerator. Condensation and evaporation of the working "60/5053, fluid take place in the Variable liquid level regeneramr Com '2 g tinuously and in a controlled manner. In addition to the varia- Fleld of Search i t i 24, 25, b e l e r ene o ay be d fine ore a U q l g h b f P y as a tida regenerator, t e asic components 0 the engine are  References Cited a condenser, a vaporizer, a superheater, a power piston, a dis- UNITED STATES PATENTS placer piston and a control for the displacer piston. 3,487,635 1/1970 Prast et al 60/24 8 Claims, 12 Drawing Figures PATENTEDAPR 25 m2 3, 657. 877
SHEET 1 LF 5 FIG. I
INVENTOR FRED N. IHUFFMAN ATTORNEYS PATENTEDAPR 25 I972 8, 657. 877 m1 2 CF 5 FIG. 2C FIG. 20
POWER STROKE END POWER STROKE INVENTOR FRED N. HUFFMAN ATTORNEYS PATENTEDAPR 25 I972 SHEET 3 [IF 5 FIG. 2F
RETURN STROKE FIG. 2E
BEGIN RETURN STROKE wmDkqmwaEwk ENTROPY FIG. 3
INVENTOR FRED N. HUFFMAN 740mg, J mey Q Hildzchi ATTORNEYS PATENTEDAPRZS m2 3. 657, 877
saw u m 5 FIG. 4 FIG. 5
INVENTOR FRED N. HUFFMAN fimwhy jenny Q HEX/16% ATTORNEYS PATENTED PR 25 I972 3, 657. 877
SHEET 5 BF 5 FIG. 7
QSUPERHEIIXT Q BOILER 89 QCONDENSER ELECTRONIC LOGIC MODULE TO HYDRAULIC OUTPUT INVENTOR FRED N.. HUFFMAN ATTORNEYS TIDAL REGENERATOR HEAT ENGINE BACKGROUND OF THE INVENTION Operation of a conventional Stirling cycle engine is basically dependent upon the contraction and compression of a given quantity of gas at low temperature and its expansion at high temperature. Generally, a displacer piston is used to transfer the working gas back and forth between a fixed high temperature zone and a fixed low temperature zone. The gas is heated in the hot zone and, as it expands and flows into the cold zone, it actuates a power piston. In its passage to the cold zone, the gas gives up a large quantity of heat to a regenerator. In the cold zone, the gas contracts and is compressed as the power piston reverses its stroke. The displacer piston then moves the gas back through the regenerator where it picks up heat stored from its previous passage. Because compression takes place at a lower temperature than expansion, a net surplus of work results.
Various modifications of the Stirling engine have been developed, but it has never achieved widespread use, chiefly because of the extremely high operating temperatures needed for reasonable power output.
SUMMARY OF THE INVENTION In the present invention, as noted above, a modified Stirling cycle configuration is utilized, and a condensable working fluid replaces the gas. The incorporation of a tidal regenerator in the engine permits efficient use of the condensable vapor. Thus, in a sense, the present invention may be considered a form of Rankine cycle engine modified to the extent that it has both vapor and liquid regeneration and neither mechanical valves nor feedpump. In a simple form of the present invention, one end of each of three parallel cylinders is connected to a common manifold. A power piston reciprocates in one of the cylinders; a displacer piston reciprocates in another of the cylinders; and a tidal regenerator containing working fluid is disposed in the third cylinder. A vaporizer to which heat is applied is disposed at the top of the regenerator, and a condenser from which heat is extracted is disposed at the bottom of the regenerator. Within the liquid regenerator thermal storage is provided for by means of a bed of heat retaining elements spaced far enough apart to prevent capillary action. The vapor regenerator is similar to the gas regenerator of a Stirling engine. The condenser is in communication with the so-called cold zone in the displacer piston cylinder below the displacer piston. The vaporizer is connected, preferably through a superheater, to the displacer cylinder hot zone above the displacer piston. The hot zone is actually formed in the manifold which connects the three cylinders and the manifold may incorporate a superheater.
The tidal regenerator is a key element of the engine and may consist of a bed of thermal storage elements retained in the cylinder through which the working fluid passes. In the bed, the level of working fluid in the liquid phase is controlled by the position of the displacer piston. Each level of the bed has a substantially constant characteristic temperature and, if the pressure in the system is higher than the saturation pressure of the fluid corresponding to the temperature at a given level, the working fluid will condense at the liquid surface until the system pressure matches the saturation pressure. If system pressure is lower than the saturation pressure at a given pressure-temperature level, liquid at that level will vaporize until the system pressure matches the saturation pressure. Thus, heat may be stored or supplied by the tidal regenerator, and net work output may be derived from the power piston as it is actuated by the large difference (relative to a gas cycle engine such as the Stirling) between vaporizer and condenser pressure.
The sequence of operations in the engine may be understood by considering the displacer piston to have been set in a position such that the level of liquid working fluid, or the tidal level, in the regenerator is adjacent the lower or condenser end of the regenerator, (the cold zone). The displacer piston at this time is at the top of its cylinder, and the power pistonis commencing its return stroke toward the top of its cylinder. Pressure within the system corresponds to the relatively low saturation temperature of the condenser. The power piston moves toward the top of its cylinder operating against only low pressure to terminate its return stroke. When the displacer piston moves to the bottom of its cylinder, the liquid level is raised through the tidal generator to the vaporizer at the top of the regenerator, (the hot zone). Pressure in the system is now the saturation pressure corresponding to the vaporizer temperature. The difference between the vaporizer pressure and condenser pressure is quite large, as compared to a gas cycle operating between the same source and sink temperatures. The power piston then commences its downward or power stroke. The expansion work of the power piston during its power stroke is much greater than its compression work.
Finally, after the power stroke, the displacer piston is moved to the top of its cylinder, and the liquid level drops from the vaporizer to the condenser. The system is then restored to the conditions prevailing at the beginning of the cycle.
The particular advantages of this vapor cycle engine are: (l) the ability to obtain a high pressure differential with a modest temperature difference, (2) elimination of mechanical valves, (3) eliminationof feedpump, (4-) silent operation, (5) ease of coupling to a hydraulic load, and (6) provision for both liquid and vapor regeneration and (7) adaptability to a variety of working fluids (including mixed working fluids). For a better understanding of the invention, reference should be made to the following description of preferred embodiments in which:
FIG. 1 is a semi-schematic outline of an engine in which key components are outlined;
FIGS. 2A through 2F are outline drawings of operational stages;
FIG. 3 is an idealized temperature-entropy diagram of the tidal regenerator heat engine;
FIGS. 4 through 6 are outlines of alternative engine structures; and
FIG. 7 is a practical tidal regenerator engine incorporating the present invention.
PREFERRED EMBODIMENT OF THE INVENTION In FIG. 1 there may be seen three parallel cylinders, a tidal regenerator cylinder 12, a displacement piston cylinder 14 and a power piston cylinder 16 whose upper ends are connected together by a manifold 18. Within the cylinder 12 a bed of thermal storage elements 20 consisting, for example, of metal balls held in position throughout the length of the cylinder 12, by means of support layers of open mesh or screening.
Within the cylinder 14, and arranged to reciprocate in response to externally applied force, is a displacement piston 22 having a piston rod 24 passing through the bottom wall of the cylinder 14. The displacement piston serves the dual functions of liquid displacement and thermally isolating the vapor and liquid regions of the engine. Suitable: seals would surround the shaft 24 in a practical structure to permit its reciprocating motion without leakage. Similar structure exists in the cylinder 16, a power piston 26 being arranged for reciprocation in that cylinder and having a piston rod 25 for power takeoff.
At the base of the tidal regenerator cylinder 12, is a con denser 30, and at the top of the cylinder 12 is a vaporizer 32. As indicated by the Qnf and Om symbols, heat is applied to the vaporizer 32 and extracted from the condenser 30. Accordingly, a temperature gradient is established along the length of the cylinder 12. A working fluid which may be simply water, or preferably a fluid mix such as water-ammonia or water-trichloroethanol, is present in the cylinder 12 and its tidal or liquid level is as shown at 34. Above that level, the fluid is in the vapor phase, as is explained in greater detail below.
Above the vaporizer 32, there may be disposed in the manifold 18 vapor regenerating elements 36 which may be loosely packed or wound metal wire of small diameter or other material having high surface area-low axial conduction characteristics. These elements may be restrained from migration by small bore sleeves comprising the superheater 38 in the manifold 18 and may also be kept from the vaporizer 32 by any suitable barrier which does not interfere with vapor passage.
Reference has previously been made to the temperature gradient in the tidal regenerator cylinder 12 and to the fact that each level in the cylinder 12 has a substantially constant characteristic temperature. Displacement of the piston 22, downwardly, for example, raises the tidal level 34 through the regenerator cylinder 12 and its storage bed to a higher temperature level, as in the vaporizer 32, in the limiting case. Thesystem balanced pressure is now the saturation pressure corresponding to the vaporizer temperature. At the other extreme, when the piston 22 is displaced upwardly, the level 34 falls through the regenerator cylinder and its storage bed to the low temperature level of the condenser 30.
Simultaneously with the rise of the displacement piston 22, the power piston 26 rises to the top of its cylinder doing little compression work because system pressure is low and vapor swept out of the power piston cylinder 16 and manifold 18 passes through the regenerator cylinder 12 to be condensed in large measure in the condenser 30. Of course, when the tidal level 34 is in the condenser 30, the low system pressure corresponds to the saturation temperature of the condenser.
The operating sequence may perhaps be more clearly understood by referring to FIGS. 2A through 215. The thermodynamic path of the tidal regenerator engine on a temperature-entropy diagram is correlated with the piston configurations in FIG. 3. The somewhat modified engine configuration shown in FIG. 2 is thermodynamically equivalent to that shown in FIG. 1. For mechanical convenience, the combined displacement and vapor-liquid segregation functions of the displacement piston in FIG. 1 are divided between the displacer piston and interface piston in FIG. 2.
FIG. 2A shows the positions of the displacer piston 22, interface piston 94 and power piston 26 at the end of the return stroke. The displacer piston 22 is at the bottom of its stroke and the power piston 26 is at the top of its stroke. Note that in all cases the motion of the interface piston 94 is hydraulically coupled to that of the power piston 26. The tidal level is in the condenser 30, and the low system pressure corresponds to the saturation temperature of the condenser 30. These conditions correspond to state point A in FIG. 3.
FIG. 2B illustrates the beginning of the power stroke initiated by the transition of the displacer piston 22 to the top of its stroke. The transition moves the tidal level from the condenser 30 to the boiler (or vaporizer) 32. Now, the system pressure throughout the entire engine is the saturation pressure corresponding to the temperature of the boiler 32. These conditions are represented by state point B in FIG. 3.
Because sat vapor The difference between maximum pressure (corresponding to the boiler temperature) and minimum pressure (corresponding to the condenser temperature) is great relative to The piston configuration at the beginning of the return stroke is shown in FIG. 2E. The corresponding state point, E, is given in FIG. 3. This step is initiated by moving the displacer piston and, consequently, the tidal level to their lowest position. The system pressure then returns to its minimum value. The thermodynamic path D E is followed during the constant volume depressurization.
FIG. 2F illustrates the return or compression stroke of the power piston 26, as it sweeps the vapor from the interface cylinder, doing very little work against low system pressure. This condensation process, indicated by the line F in F IG. 3, is terminated in FIG. 2A thus recommencing the cycle.
In FIGS. 4 through 6, various configurations of the tidal regenerator engine are shown. These may be broadly classified into two groups: (I) doubly loaded piston machines and (2) displacement piston machines. FIG. 4 illustrates a doubly loaded piston machine in which the top of the vaporizer 32 is connected only to a power piston cylinder 16, and the condenser 30 is connected to another power piston cylinder 16a. Between the vaporizer and the condenser is the tidal regenerator 12. Both power pistons are connected to a common crankshaft in the manner of a Stirling engine alpha configuration, as defined by Rider.
In FIG. 5, a displacement piston machine is illustrated. In this instance, both the displacer piston 22 and the power piston 26 operate in the same cylinder, the vaporizer 32 communicating with the cylinder 16 above the displacer piston 22, and the condenser 30 communicating with the same cylinder below the displacement piston but above the power piston 26. The power output and timing of the pistons are completely analgous to those of the beta configuration of the Stirling engine.
In FIG. 6, separate cylinders are used for the displacement piston 22 and the power piston 26, and the vaporizer 32 communicates only with the displacer piston cylinder. Here, power output and timing are in accordance with gamma" configuration of the Stirling engine, as defined by Robertson. Note that in both FIGS. 4 and 5 the displacement piston 22 must follow the power piston 26 during the stroke so that the liquid level in the tidal regenerator (and, hence, system pressure) be maintained.
FIG. 7 illustrates a practical embodiment of the present invention which combines mechanical simplicity and efficiency of operation. A tidal regenerator assembly is provided, and it includes liquid regenerator 72 which is made of relatively small-bore, thin-wall, low-thermal conductivity tubing, interposed between a boiler or vaporizer 74 and a condenser 76. It is desirable that the liquid regenerator 72 have such characteristics and be of the design mentioned in order that heat losses may be limited.
Within the liquid regenerator tube 72, a quantity of material such as metal wool is packed to enhance cooling and heating of the working fluid which passes through the regenerator as is explained in greater detail below. Within the boiler 74, there may be disposed a quantity of brazed balls to enlarge hot surface area from which better vaporization of the working fluid may be had. The condenser 76 may contain a similar quantity of brazed balls 82 which similarly enhance condensation of the vapor.
Connected to the top of the boiler is a U-shaped vapor regenerator 84 containing a quantity of high surface-area, low axial-conduction material such as loosely wound, smalldiameter wire 86. The purpose of the wire is to economize on overall thermal input by conserving a portion of the vapor superheat from previous cycles for use in a given cycle, as will also be explained in greater detail. At the right hand extremity of the vapor regenerator 84, is a superheater 88 which may also contain brazed balls for improving cycle efficiency by superheating the vapor.
A generally dumb-bell shaped interface piston assembly is connected to the superheater. At the top of the assembly is a cylinder 89 of relatively large bore to the interior upper surface of which a vapor bellows 90 is sealed. The superheater 88 is in communication with the interior of the vapor bellows 90,
but the remainder of the interior of the large bore cylinder is sealed from the superheater 88 by the bellows 90. The large bore cylinder 89 is connected to a concentric cylinder 92 of smaller bore within which a thermal isthmus piston 94 reciprocates. Hydraulic coupling of displacement of the end of the bellows 90 to the thermal isthmus piston 94 is effected by an interface fluid 95 of low vapor pressure and good thermal stability which fills the cylinder 89 and the upper portion of the cylinder 92. The same fluid 95 pressure-balances the bellows 90, thereby adding to its life and reliability.
Another large bore cylinder 96 is connected to the lower end of the smaller cylinder 92. Within the cylinder 96 a fluid bellows 98 is sealed, and another interface liquid 99 is provided between the piston 94 and the bellows 98, serving a function similar to that of the fluid 95. Usually fluids 9S and 99 will be of the same composition.
Beneath the fluid bellows 98 a pressure balance line 100 connects the lower portion of the cylinder 96 with a cylinder 102 within which there is sealed a displacer diaphragm 104. A binary solenoid 106 is mechanically connected directly to the center of the displacer diaphragm 104 by means of a shaft 108. Action of the binary solenoid 106 may be controlled electrically by an electronic logic module 112. Working fluid in the regenerator section is visible above the diaphragm 104. The use of bellows and diaphragm instead of sliding piston seals eliminates leakage losses. Scale factors are such that leakage losses are particularly severe in small engines.
A hydraulic line 114 is connected at the base of the cylinder 98 to exemplify one of the mechanisms by which power takeoff may be effected. The line may be coupled to any suitable utilization or other hydraulically actuatable element. Other power take-offs are feasible, but the illustrated system has features such as sealed coupling to the engine which make it attractive.
The electronic logic module 112 may be a conventional solid state circuit to provide current pulses to the solenoid 106. The solenoid 106 in turn operates upon the displacer diaphragm 104 to move the level of liquid working fluid back and forth between the condenser 76 and the boiler 74. The pressure balance line 100 provides gross pressure balance within the system except for the relatively small pressure differentials which result from the small fluid flow forces. The presence of the pressure balance line 100 is particularly advantageous in that it allows the tidal level to be shifted with a minimum expenditure of energy by the binary solenoid. The binary solenoid may be of the latching type or equipped with a permanent magnet to hold it in either of the positions which it assumes without power expenditure. Most heat engines rely upon a flywheel and some rotary mechanism for piston return and phasing, and such structures can be used with the tidal regenerator engine of this invention, but electronic control is preferred and is possible mainly because only a small volume of fluid must be displaced in the pressure-balanced system. With electronic control, the engine oscillation rate may be easily varied.
Operation of the engine of FIG. 6 is similar to what has previously been described with reference to somewhat simpler structures. The electronic module 112 supplies programmed pulses to energize the solenoid 106 which moves the diaphragm 104 upwardly or downwardly. The diaphragm 104 is made preferably of sheet metal or an elastomer, and its size and length of throw in the relatively large cylinder 102 is sufficient to move the tidal level from one end of the relatively small tidal regenerator cylinder 72 to the other end, or, from the boiler or vaporizer 74 to the condenser 76 and vice versa. Heat is, of course, applied to the vaporizer 74 and to the superheater 88 and extracted from the condenser 76. Thus, the working fluid is cycled to create minimum and maximum pressure alternately with resultant flexing of the bellows 90 and reciprocation of the isthmus piston 94. That reciprocation is connected into useful work output through the bellows 98 to the hydraulic line 114.
Variations of the tidal regeneratorv other than those described are possible. Also, the working fluid may be any one of numerous materials or mixtures of materials. For example, a mix of 61 percent ammonia and 39' percent water can be used with greater efficiency than water alone. Various liquid metals and organics are also suitable. In some instances, working fluid may be utilized in the supercritical region for improved efiiciency.
Although direct mechanical coupling to the power piston may be useful, use of hydraulic coupling is attractive for many applications of the tidal regenerator engine. For example, the tidal regenerator engine would be especially suitable for: (l) circulating heated water through a divers suit, (2) underwater propulsion (either propeller or jet), (3) underwater hydraulic tool power supply, (4) power generators, (5) implantable circulatory support systems and (6) remote pumping and terrestrial propulsion. I
ll. A heat engine comprising a closed system, a condensable vapor serving as a working fluid in said closed system, a tidal regenerator, forming a part of said closed system, means for establishing a temperature gradient across said regenerator, means for alternately establishing the level of said working fluid in its liquid phase at points of high temperature and at points of low temperature in said tidal regenerator, pressure in said closed system being relatively high when said level is at said points of high temperature and relatively low when said level is at said points of low temperature, and means responsive to changes of said pressure communicating with said system for converting said changes to mechanical energy.
2. A heat engine as defined in claim 1 wherein said closed system includes a vaporizer to which heat is applied and a condenser from which heat is extracted disposed at opposite ends of said tidal regenerator, whereby said temperature gradient is established, said system further comprising a control system for actuating said means for alternately establishing the level of said working fluid in its liquid phase, whereby said level is alternately substantially in said vaporizer and substantially in said condenser, pressure in said closed system being relatively high when said level is in said vaporizer and relatively low when said level is in said condenser.
3. A heat engine as defined in claim 1 wherein pressure within said engine varies with said level of said working fluid in its liquid phase.
4. A heat engine as defined in claim 1 wherein said means for alternately establishing the level of said working fluid in its liquid phase at points of high temperature and at points of low temperature comprises a displacement cylinder for said work ing fluid, a displacement piston reciprocable in said displacement cylinder, and means for actuating said displacement piston to move said working fluid through said engine.
5. A heat engine as defined in claim 4 wherein said means for actuating said displacement piston comprises means for generating electrical pulses and an electromechanical converter responsive to said pulse generating means connected to and driving said piston.
6. A heat engine as defined in claim 1 wherein said means responsive to changes of said pressure communicating with said system for converting said changes to mechanical energy comprises a power cylinder and a power piston reciprocable therein, said power piston being driven in one direction by said relatively high pressure in said system and returning in the other direction against said relatively low pressure in said system.
7. A heat engine as defined in claim 1 wherein said working fluid consists of a mixture of different fluids.
8. A heat engine as defined in claim 1 wherein said means for alternately establishing the level of said working fluid in its liquid phase at points of high temperature and at points of low temperature includes an interface cylinder and an interface piston reciprocable in said interface cylinder, a displacement cylinder and a displacement piston reciprocable in said displacement cylinder, and said means responsive to changes of original positions in their respective cylinders generating output power from said power piston, means for actuating said displacement piston in the opposite directions to move said level of working fluid to a point of low temperature and low pressure, whereby said interface piston and said power piston move in the other direction against low pressure in their respective cylinder to resume their original positions.