STIRLING ENGINE WITH A MEMBRANE CONNECTING THE PISTON TO THE CYLINDER OF THE STIRLING ENGINE AND A METHOD OF USING THIS STIRLING ENGINE

Abstract

The present invention relates to a low temperature, low frequency Stirling engine. Its special geometry allows for large heat exchanger surfaces and great regenerators in order to reach good Carnoization efficiency factors. Displacer and power piston may be connected with circular polymer based membrane sealings to the cylinder walls. The cold space of the Stirling Engine may cylindrically Surround the outer periphery of the working cylinder, making thermal isolation obsolete. The engine is for instance suited to operate as base power prime mover using thermal solar collectors and may be coupled with hot oil or pressurized water heat storages. In the reverse mode, the Engine works as effective Heat-Pump/Cooling Engine

Claims

1. A method of using at least two Stirling engines, wherein the at least two engines are coupled such that at least one engine functions as a thermal prime mover and drives the second engine, operating inversely as a cooling engine or heat pump.

2. The method according to claim 1, wherein the reversibly operating Stirling engine is driven by external energy.

3. The method according to claim 1 or 2, wherein the external energy source is a photovoltaic panel and the Stirling engine cooler produces ice for storage.

4. The method according to claim 1, wherein the prime mover acts as tri-generation system for electricity, heating and cooling in combination with solar thermal collectors and adequate heat storages.

5. The method according to claim 1, wherein the low speed, high torque output of the flywheel is directly mechanically connected to different subsystems selected from compressor, mills, saws, conveyor belts and mixtures thereof.

Description

OVERVIEW OF THE FIGURES

[0230] FIGS. 1-1a are a representation of a low temperture Stirling engine according to one aspect of the present invention. Individually, FIG. 1 represents a schematic cross section of the low temperature Stirling engine according to the invention. FIG. 1a is an additional view of a low temperature Stirling engine according to one aspect of the present invention.

[0231] FIG. 2 is a graphical represenation of a low temperature Stirling engine as around the clock operating solar water pump according to one aspect of the present invention.

[0232] FIG. 3 is a graphical representation of flywheel with adjustable excentric pm according to one aspect of the present invention.

[0233] FIG. 4 is a graphical representation of flywheel with power regulation according to one aspect of the present invention.

[0234] FIG. 5 is a graphical representation of a Stirling engine with a domelike cylindrical cover according to one aspect of the present invention.

[0235] FIG. 6 (centrally presented on the FIG. 2 page) schematically represents the power output in different pressure environments.

[0236] FIG. 7 is a representation of efficiencies in function of the delta temperature between hot gas and cold gas.

[0237] FIG. 8 is a Volume-Pressure representation the phases of a typical Stirling engine.

DETAILED DESCRIPTION OF THE FIGURES

[0238] FIG. 1 represents a schematic cross section of the low temperature Stirling engine according to the invention. Cylindrical housing (1) containing the hermetically enclosed working medium (2), symbolized by (XXX). (3) is the circular displacer piston, attached to the cylindrical hot side heat exchanger by a double sheet, flexible polymer membrane (4). The displacer piston (3) is thermally insulating; as well as the membrane (4) which is filled between the two layers with flexible insulation material (foam, fibers).

[0239] The displacer piston oscillates vertically in the space of the working medium (preferably a gas), driven by a rod (5) connected to the displacer excenter (5a). The displacer piston (3) separates hermetically the working medium room (2) into the hot expansion room (2a) and the cold compression room (2b).

[0240] The displacer piston (3) shifts periodically the working medium through the cylindrical heater respectively heat exchanger (12), regenerator (11), cooler respectively heat sink (13) assembly and vice versa. By this way, the working medium is periodically heated and cooled and consequently creates a sinusoidal pressure fluctuation, as represented in (15) and moving through four steps as represented in volume-pressure diagram (14). These pressure fluctuations act on the power piston (6) which closes the cylindrical Stirling housing (1) toward the top. The power piston (6) is connected hermetically toward the housing (1) by an air inflated, flexible double membrane (7). This double membrane can be either completely air tight or, connected to a flexible tube with one way valve (7a) ending in the cold working medium room (2b). The pressure fluctuation (15) in this room fills periodically the double membrane (7) with the peak pressure of the cycle, thus compensating for eventual leakages of the double membrane.

[0241] The power piston (6) extracts the cycle energy produced thermodynamically by the working medium (2) into mechanical energy. Its oscillating movement is transmitted by the power piston rod (8) to the power piston excenter (8a). This excenter is transforming the lateral oscillation of the power piston (6) into the rotational movement of the axes (9) connected to the flywheel (10).

[0242] The crank mechanism represented by (8), (8a), (5) and (5a) coordinates the movement of the displacer piston (3) versus the power piston (6) in function of the time. This way, the thermodynamical Stirling cycle (two isothermal and two isochoric process steps), as more detailed described above is realized.

[0243] The present invention for instance exemplified in FIG. 1 and the additional view of the Stirling engine in FIG. 1a represents the simplest realization of the Stirling enginean engine working with air at ambient pressure.

[0244] The large dimensions allow, as mentioned for large surfaces of the heater-regenerator-cooler (12, 11, 13) unit, with the explained positive effects for the engines efficiency.

[0245] The slightly conical design of the cylinder (I) makes also possible another feature of the present invention: as the cooler (13) forms the outer cylinder of the unit (12, 11, 13), the Stirling engine must not be thermally insulated from the ambient. This topology advantage against classical Stirling engines represents a significant simplification and a gain of economy.

[0246] The large heat exchanger surfaces in combination with the low frequencies allow to use atmospheric air as working medium. This is another important advantage against high temperature engines needing hydrogen or helium.

[0247] In FIG. 2a typical application of the present invention is represented. It shows the low temperature Stirling engine as around the clock operating solar water pump. (26) represents the mentioned solar collector field, producing thermal heat of 150 C. with 50% efficiency and storing it for night time operation within the storage tank (25). The hot fluid of the tank flows through the hot-side heat exchanger (12) of the low temperature Stirling engine. A smaller part of the water pumped out of the borehole flows through the cooler (13) and from there via pipe (13a) to the customer (24a). The flywheel with high torque and moderate rotational speed actions a first water hydraulic cylinder (16) mounted to an excentric pin (16a) and a rotating fix point (17).

[0248] The periodically pressurized water in the first water hydraulic cylinder is transported via a thin steel tube (18) into a second, submersed water hydraulic working cylinder (19) at the ground of the borehole. This second water hydraulic cylinder oscillates in coherence with the working frequency of the engine connected working cylinder (16). The second water hydraulic cylinder (19) acts toward a valves and spring cylinder (20a) containing to one way valves (20, 22) and a spring (21). At its movement toward the inner dead point, cylinder (19) opens valve (20) and valves and spring cylinder (20a) fills with water. When moving upward, the second water hydraulic cylinder (19) closes valve (20) and opens valve (22); consequently the water is pushed through the riser tube (23), to the surface.

[0249] Before flowing in the customer reservoir (24a), the pumped water is pushed into a water/air reservoir (24).

[0250] (24) changes the pulsating water flow into a regular one. Spring (21) brings back the hydraulic pump to its initial stage after each working pulse.

[0251] FIG. 2 further represents a water/depth delivery graph which shows the excellent pumping capacity of an atmospherically working low temperature Stirling engine with 400 W mechanical power output and showing the flow rate as a function of pumping depth at 400 W hydraulic power with the head (in meters) on the X-axis and the flow rate (in lieters/minute) on the Y-axis.

[0252] In FIG. 3 it is schematically represented, how the excentric pin (16a) on which the hydraulic cylinder (16) is mounted, can be moved by a sliding mechanism (16b) in any position between the center of rotation of the flywheel (16c) and the outer diameter of the flywheel (16d). This means, that according to the water/depth delivery graph in FIG. 2 the related piston stroke related to a given borehole depth can be adjusted, so that the low temperature Stirling engine pump always works at its best operational point.

[0253] Another important feature of the present invention is schematically shown in FIG. 4. It deals with the power regulation of the low temperature Stirling engine. It is executed in a similar way as already described for the regulation of the hydraulic water pump. In this case, the excenter pin (5a), moving backward and forward the displacer rod (5), can be continuously moved from the center of the rotation to the outer perimeter along the diameter of the rotating crank disk; consequently the displacer amplitude, which is in direct correlation with the delivered engine power, can be continuously changed from zero stroke (power) to maximum stroke (power). This can be either controlled manually by fixing the pin in a given position, or by moving the pin continuously and during the engine operation by an hydraulically or electrically operated linear actuator.

[0254] FIG. 5 presents a domelike cylindrical cover (27) with a rotational bearing around the axis (9). Such set up allows, without loosing the design guidelines of relative low frequencies and large heat exchange and regenerator surfaces, to fill the atmospheric low temperature Stirling engine with slightly compressed air, typically up to 5 bars.

[0255] The power output of pressurized engines is augmenting practically linearly with the absolute pressure, as long as the relation between power output and heat exchanger surface stays favorable. We found that this is the case up to 5 bars pressure.

[0256] The higher power output results from the larger pressure fluctuations of the working medium, as schematically shown in FIG. 6 (under (12) on the page of FIG. 2).

[0257] Therefore, slightly pressurized low temperature Stirling engines bear the possibility to reduce the necessary volume and therefore amount of necessary material in a well defined range.

[0258] The same holds true for a slight enhancement of the working frequency, up to 4 Hz.

[0259] FIG. 1 shows a cross section of a realized atmospheric low temperature Stirling engine. With a diameter of 1 m, a height of 0.4 m and a frequency of 1.5 Hz it delivers 0.5 kW shaft power.

[0260] If, as for instance principically described for FIG. 6, as an example this engine is pressurized to 4 bars, it will deliver approximatively 2 kW. By further enhancing the working frequency to 3 Hz, it will deliver approx. 4 kW.

[0261] FIG. 7 shows the efficiencies in function of the delta Temperature between the hot gas and the cold gas with the delta Temperature (in Kelvin) on the X-axis and the Carnot efficiency (nn %) on the Y-axis.

[0262] The solid line represents the low temperature Stirling engine. Camoization factor >>50%. The dotted line represents the ideal Stirling engine. The solid line with triangle represents the high temperature Stirling engine with Camoization factor of 50%.

[0263] FIG. 8 represents the ideal Sirling cycle (Volume versus Pressure) with 4 steps wherein QI=Q2=oscilating, reversible heat exchange with the regenerator.

LIST OF REFERENCE NUMERALS USED

[0264] 1 cylinder respectively cylindrcal housing respectively cylindrcal stirling housing

[0265] 2 working medium respectively working medium room

[0266] 2A expansion chamber

[0267] 2B compression chamber

[0268] 3 displacement piston

[0269] 4 displacer piston membrane

[0270] 5 rod respectively displacer rod

[0271] 5A displacer excenter

[0272] 6 power piston

[0273] 7 power piston membrane

[0274] 7A one way valve

[0275] 8 power piston rod

[0276] SA power piston excenter

[0277] 9 axes

[0278] 10 flywheel

[0279] 11 regenerator

[0280] 12 heat exchanger respectively cylindrical heater

[0281] 13 heat sink respectively cooler

[0282] 13A pipe

[0283] 14 volume-pressure diagramm

[0284] 15 pressure-fluctuation diagramm

[0285] 16 first water hydraulic cylinder

[0286] 16A excentric pin

[0287] 16B sliding mechanismen

[0288] 16C flywheel

[0289] 16D flywheel

[0290] 17 rotation fix point

[0291] 18 thin steel tube

[0292] 19 second, submersed water hydraulic working cylinder

[0293] 20 one way vilave

[0294] 20A spring cylinder

[0295] 21 spring

[0296] 22 one way valve

[0297] 23 riser tube

[0298] 24 water/air reservoir

[0299] 24A customer reservoir

[0300] 25 storage tank

[0301] 26 solar collector field

[0302] 27 cylindrical cover respectively airtight cover