Stirling engine with regenerator internal to the displacer piston and integral geometry for heat transfer and fluid flow

Abstract

A Stirling engine with internal regenerator and integral geometry for heat transfer and fluid flow has a displacer piston with a plurality of cavities traversing through the displacer piston and arranged in a specific cross sectional geometry. A heater head has heater fin protrusions that are arranged in the specific geometry, and a cooling bridge has cooler fin protrusions that are in the specific geometry. The displacer piston alternates between the heater head and the cooling bridge, with the cavities of the piston alternately enveloping the heater protrusions and the cooling protrusions, providing more efficient heat transfer to and from the working fluid. Each cavity in the displacer also contains a regenerator core, further improving heat transfer efficiency. The heater fin protrusions may also contain thermally conductive cores. A bellows assembly may also be used to seal the displacer piston from the heater head in order to reduce unswept volume.

Claims

1. A Stirling engine comprising: a cylindrical housing; a displacer piston; a heater head; a cooling bridge; a plurality of regenerator cores; coolant fluid; a bellows assembly; the cylindrical housing comprising a piston chamber; a working fluid being contained within the cylindrical housing; a central axis centrally traversing through the cylindrical housing; the displacer piston comprising a plurality of cavities; the heater head comprising a plurality of heater fin protrusions; the cooling bridge comprising a plurality of tubular cooler fin protrusions; the plurality of cavities being arranged in a specific cross sectional geometry; the plurality of heater fin protrusions being arranged to match the specific cross sectional geometry; the plurality of tubular cooler fin protrusions being arranged to match the specific cross sectional geometry; the plurality of regenerator cores being centrally positioned within the plurality of cavities; the cooling bridge being cooled by a circulatory fluid flow using the coolant fluid; the cylindrical housing comprising an annular coolant chamber and a working fluid chamber; the cooling bridge being positioned between the piston chamber and the working fluid chamber; the cooling bridge comprising a first circular plate and a second circular plate; the first circular plate and the second circular plate being concentrically positioned with the cylindrical housing; the first circular plate and the second circular plate being spaced apart from each other along the central axis; a cooling space being all empty space enclosed between the first circular plate and the second circular plate; the plurality of tubular cooling protrusions traversing through the first circular plate and the second circular plate; the working fluid chamber being in fluid communication with the piston chamber through the plurality of tubular cooling protrusions; the annular coolant chamber being concentrically positioned around the working fluid chamber; the annular coolant chamber comprising a coolant ingress and a coolant egress; the coolant ingress being in fluid communication with the coolant egress through the cooling space; a first end of the bellows assembly being annularly connected within the piston chamber adjacent to the heater head; a second end of the bellows assembly being annularly connected to the displacer piston; the displacer piston being sealed within the bellows assembly; each of the plurality of heater fin protrusions comprising an outer casing and a thermally conductive core; and the thermally conductive core being enclosed by the outer casing.

2. The Stirling engine as claimed in claim 1 comprising: the displacer piston, the cooling bridge and the heater head being concentrically positioned with the cylindrical housing; the displacer piston and the cooling bridge positioned within the cylindrical housing; the heater head traversing into the cylindrical housing along the central axis; the heater head and the cooling bridge being positioned opposite each other along the piston chamber; the displacer piston being positioned between the heater head and the cooling bridge; the displacer piston oscillating between the heater head and the cooling bridge; the displacer piston alternatingly displacing the working fluid between the heater head and the cooling bridge; and the plurality of cavities alternatingly enveloping the plurality of heater fin protrusions and the plurality of tubular cooler fin protrusions.

3. The Stirling engine as claimed in claim 1 comprising: the displacer piston being positioned within the piston chamber; and the heater head traversing into the piston chamber.

4. The Stirling engine as claimed in claim 1 comprising: each of the plurality of cavities being oriented parallel to the central axis; each of the plurality of heater fin protrusions being oriented parallel to the central axis; and each of the plurality of tubular cooler fin protrusions being oriented parallel to the central axis.

5. The Stirling engine as claimed in claim 1 comprising: the plurality of cavities traversing through the displacer piston; and one of the plurality of regenerator cores being positioned within each of the plurality of cavities.

6. The Stirling engine as claimed in claim 1, wherein the displacer piston is a free piston design.

7. The Stirling engine as claimed in claim 6 comprising: a ferrous or magnetic material; an electrically conductive coil; the ferrous or magnetic material being integrated into the displacer piston; the electrically conductive coil being wrapped around the cylindrical housing; the electrically conductive coil being electrically connected to an electronic control system; and the electronic control system controlling electrical current flow through the electrically conductive coil in order to produce an electromagnetic field for moving the displacer piston.

8. The Stirling engine as claimed in claim 6 comprising: a spring; the spring being connected between the displacer piston and a spring annulus; the spring annulus being positioned opposite the heater head along the cylindrical housing; the cylindrical housing comprising a plurality of roller tracks; each of the plurality of roller tracks being oriented parallel to the central axis; the plurality of roller tracks being radially distributed around the central axis within the cylindrical housing; the displacer piston comprising a plurality of rollers; the plurality of rollers being radially distributed around the central axis on the displacer piston; the plurality of rollers being engaged to the plurality of roller tracks; and the plurality of rollers rolling within the plurality of roller tracks in a direction parallel to the central axis.

9. The Stirling engine as claimed in claim 6 comprising: a spring; and the spring being wound within the bellows assembly from the first end to the second end of the bellows assembly.

10. The Stirling engine as claimed in claim 6 comprising: an electrically conductive coil; and the electrically conductive coil being wound within the bellows assembly from the first end to the second end.

11. A Stirling engine comprising: a cylindrical housing; a displacer piston; a heater head; a cooling bridge; a plurality of regenerator cores; coolant fluid; a bellows assembly; the cylindrical housing comprising a piston chamber; a working fluid being contained within the cylindrical housing; a central axis centrally traversing through the cylindrical housing; the displacer piston comprising a plurality of cavities; the heater head comprising a plurality of heater fin protrusions; the cooling bridge comprising a plurality of tubular cooler fin protrusions; the plurality of cavities being arranged in a specific cross sectional geometry; the plurality of heater fin protrusions being arranged to match the specific cross sectional geometry; the plurality of tubular cooler fin protrusions being arranged to match the specific cross sectional geometry; the plurality of cavities traversing through the displacer piston; the plurality of regenerator cores being centrally positioned within the plurality of cavities; one of the plurality of regenerator cores being positioned within each of the plurality of cavities; the displacer piston, the cooling bridge and the heater head being concentrically positioned with the cylindrical housing; the displacer piston and the cooling bridge positioned within the cylindrical housing; the heater head traversing into the cylindrical housing along the central axis; the heater head and the cooling bridge being positioned opposite each other along the piston chamber; the displacer piston being positioned between the heater head and the cooling bridge, the displacer piston oscillating between the heater head and the cooling bridge; the displacer piston alternatingly displacing the working fluid between the heater head and the cooling bridge; the plurality of cavities alternatingly enveloping the plurality of heater fin protrusions and the plurality of tubular cooler fin protrusions; the cooling bridge being cooled by a circulatory fluid flow using the coolant fluid; the cylindrical housing comprising an annular coolant chamber, a piston chamber and a working fluid chamber; the cooling bridge being positioned between the piston chamber and the working fluid chamber; the cooling bridge comprising a first circular plate and a second circular plate; the first circular plate and the second circular plate being concentrically positioned with the cylindrical housing; the first circular plate and the second circular plate being spaced apart from each other along the central axis; a cooling space being all empty space enclosed between the first circular plate and the second circular plate; the plurality of tubular cooling protrusions traversing through the first circular plate and the second circular plate; the working fluid chamber being in fluid communication with the piston chamber through the plurality of tubular cooling protrusions; the annular coolant chamber being concentrically positioned around the working fluid chamber; the annular coolant chamber comprising a coolant ingress and a coolant egress; the coolant ingress being in fluid communication with the coolant egress through the cooling space; a first end of the bellows assembly being annularly connected within the piston chamber adjacent to the heater head; a second end of the bellows assembly being annularly connected to the displacer piston; the displacer piston being sealed within the bellows assembly; each of the plurality of heater fin protrusions comprising an outer casing and a thermally conductive core; and the thermally conductive core being enclosed by the outer casing.

12. The Stirling engine as claimed in claim 11 comprising: the displacer piston being positioned within the piston chamber; and the heater head traversing into the piston chamber.

13. The Stirling engine as claimed in claim 11 comprising: each of the plurality of cavities being oriented parallel to the central axis; each of the plurality of heater fin protrusions being oriented parallel to the central axis; and each of the plurality of tubular cooler fin protrusions being oriented parallel to the central axis.

14. The Stirling engine as claimed in claim 11, wherein the displacer piston is a free piston design.

15. The Stirling engine as claimed in claim 14 comprising: a ferrous or magnetic material; an electrically conductive coil; the ferrous or magnetic material being integrated into the displacer piston; the electrically conductive coil being wrapped around the cylindrical housing; the electrically conductive coil being electrically connected to an electronic control system; and the electronic control system controlling electrical current flow through the electrically conductive coil in order to produce an electromagnetic field for moving the displacer piston.

16. The Stirling engine as claimed in claim 14 comprising: a spring; the spring being connected between the displacer piston and a spring annulus, the spring annulus being positioned opposite the heater head along the cylindrical housing; the cylindrical housing comprising a plurality of roller tracks each of the plurality of roller tracks being oriented parallel to the central axis; the plurality of roller tracks being radially distributed around the central axis within the cylindrical housing; the displacer piston comprising a plurality of rollers; the plurality of rollers being radially distributed around the central axis on the displacer piston; the plurality of rollers being engaged to the plurality of roller tracks; and the plurality of rollers rolling within the plurality of roller tracks in a direction parallel to the central axis.

17. The Stirling engine as claimed in claim 14 comprising: a spring; and the spring being wound within the bellows assembly from the first end to the second end of the bellows assembly.

18. The Stirling engine as claimed in claim 14 comprising: an electrically conductive coil; and the electrically conductive coil being wound within the bellows assembly from the first end to the second end.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of the exterior of the present invention.

(2) FIG. 2 is a perspective exploded view of the present invention.

(3) FIG. 3 is a perspective exploded cross sectional view of the present invention.

(4) FIG. 4 is a head-on view of the cooling bridge inside the cylindrical housing.

(5) FIG. 5 is a perspective view of the cooling bridge and the cylindrical housing with a sectional cut along line A-A from FIG. 4.

(6) FIG. 6 is a side sectional view of the cooling bridge and the cylindrical housing.

(7) FIG. 7 is a side sectional view of the entire assembly of the present invention with the displacer piston at the heater head.

(8) FIG. 8 is a side sectional view of the entire assembly of the present invention with the displacer piston at the cooling bridge.

(9) FIG. 9 is an illustration of one method of controlling the position of the displacer piston with a ferrous material and an electrically conductive coil.

(10) FIG. 10 is a side sectional view of the heater head showing the internal thermally conductive cores of the heater fin protrusions.

(11) FIG. 11 is a side sectional view of the assembly of the present invention incorporating a bellows assembly as a seal between the displacer piston and the internal wall of the cylindrical housing.

DETAIL DESCRIPTIONS OF THE INVENTION

(12) All illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention.

(13) The present invention is a modification for a Stirling engine which incorporates an internal regenerator and integral geometry for improved heat transfer and fluid flow. Referring to FIGS. 1-3, in general, the present invention comprises a cylindrical housing 1, a displacer piston 2, a heater head 3, a cooling bridge 4, and a plurality of regenerator cores 5.

(14) The cylindrical housing 1 is the substantial physical structure that contains the majority of the present invention as is typical with Stirling engines. The cylindrical housing 1 comprises a piston chamber 11 and contains a working fluid 7. The working fluid 7 is preferably a gas, such as, but not limited to, hydrogen, helium, or air. A central axis 13 centrally traverses through the cylindrical housing 1, and defines a longitudinal direction. The displacer piston 2 is comprises a plurality of cavities 21, the heater head 3 comprises a plurality of heater fin protrusions 31, and the cooling bridge 4 comprises a plurality of tubular cooler fin protrusions 41.

(15) The displacer piston 2 is cylindrical and is concentrically positioned within the piston chamber 11 of the cylindrical housing 1 between the heater head 3 and the cooling bridge 4. Each of the plurality of cavities 21 is oriented parallel to the central axis 13 and fully traverses through the displacer piston 2. As seen in FIGS. 2-3, the plurality of cavities 21 are arranged in a specific cross sectional geometry 6. The specific cross sectional geometry 6 may be any desired cross sectional geometry, and is defined in order to make certain that cross sectional geometries for the plurality of cavities 21, the plurality of heater fin protrusions 31 and the plurality of tubular cooler fin protrusions 41 are the same. In one embodiment of the present invention, in the specific cross sectional geometry 6, the plurality of cavities 21 are equally distributed across a cross section of the displacer piston 2 so that a large portion of the cross section is empty space, with numerous holes separated by relatively thin portions of material. The primary goal of having numerous distributed geometrical elements of negative space is to maximize surface area within the displacer piston, improving heat transfer and fluid flow. As cavities within the displacer piston 2 and corresponding mating protrusions on the heater head 3 and the cooling bridge 4 increase in number, overall surface area for heat transfer is increased, resulting in quicker and more efficient heat transfer and improved overall thermal efficiency.

(16) As seen in FIGS. 3, 7 and 8, each of the plurality of regenerator cores 5 is a portion of material which is able to receive and transfer heat energy quickly. The plurality of regenerator cores 5 is centrally positioned within the plurality of cavities 21, such that one of the plurality of regenerator cores 5 is positioned within each of the plurality of cavities 21. In one embodiment, each of the plurality of regenerator cores 5 is positioned centrally within the displacer piston 2, such that the displacer piston 2 is symmetric about the plurality of regenerator cores 5. In alternate embodiments, however, the plurality of regenerator cores 5 may be longitudinally offset within the plurality of cavities 21. The plurality of regenerator cores 5 traverse substantially less longitudinal distance than the plurality of cavities 21 so that the plurality of cavities 21 may receive the plurality of heater fin protrusions 31 and the plurality of tubular cooler fin protrusions 41 on opposing longitudinal sides of the displacer piston 2.

(17) In one embodiment of the present invention, each of the plurality of regenerator cores 5 is made of thin, highly convoluted, compressed metal wire, similar to steel wool. This allows the plurality of regenerator cores 5 to maximize surface area available to receive and store heat energy while remaining porous. In one embodiment of the present invention, the displacer piston 2 is made with the plurality of regenerator cores 5 being positioned within the plurality of cavities 21 during manufacture. In an alternate embodiment of the present invention, the plurality of regenerator cores 5 is positioned within the plurality of cavities 21 by pressing an amount of regenerator core material into each of the plurality of cavities 21 from one opening of the fin cavity. In another alternate embodiment, two halves of the displacer piston 2 are brought together to sandwich a disc of regenerator core material between the two halves.

(18) The heater head 3 is concentrically positioned with the cylindrical housing 1 and traverses into the piston chamber 11 along the central axis 13. In one embodiment of the present invention, the heater head 3 itself is a physically separate component which is affixed to the cylindrical housing 1 by a cylindrical flange interface 19 between the heater head 3 and the cylindrical housing 1. A bolt pattern is radially spaced out around the cylindrical axis on the cylindrical flange interface 19, through which a plurality of bolts may be affixed in order to attach the heater head 3 to the cylindrical housing 1.

(19) As can be seen in FIGS. 1, 2, 3, 7 and 8, each of the plurality of heater fin protrusions 31 is oriented parallel to the central axis 13. The plurality of heater fin protrusions 31 is arranged to match the specific cross sectional geometry 6 such that the plurality of heater fin protrusions 31, having a positive geometry, may interface with the plurality of cavities 21, which have negative geometry, so that the plurality of heater fin protrusions 31 may be enveloped by the plurality of cavities 21 by moving the displacer piston 2 along the central axis 13. The plurality of heater fin protrusions 31 is heated by a heat source from outside the cylindrical housing 1, such as, but not limited to, a natural gas flame, a burner section, a diesel oil burner, or another heat source.

(20) It is desirable for the plurality of heater fin protrusions to be highly thermally conductive to facilitate efficient transfer of heat from the heat source outside of the cylindrical housing to the working fluid inside the cylindrical housing. Therefore, in one embodiment shown in FIG. 10, each of the plurality of heater fin protrusions comprises an outer casing 32 and a thermally conductive core 33. The outer casing 32 acts as a casing enclosing the thermally conductive core 33. Preferably, the thermally conductive core 33 traverses the majority of the length of the heater fin protrusions. The coefficient of thermal expansion of the outer casing 32 and the coefficient of thermal expansion of the thermally conductive core 33 should be approximately equivalent to avoid stresses caused by different rates of expansion or contraction between the outer casing 32 and the thermally conductive core 33. The material of the outer casing 32 of each of the heater fin protrusions should be a high temperature alloy, such as, but not limited to, copper. In one embodiment, the thermally conductive cores 33 are similar in material and arrangement to the plurality of regenerator cores within the displacer piston, being thin, highly convoluted, compressed metal wire. In one embodiment, the thermally conductive cores 33 are made from a solid material.

(21) The cooling bridge 4 is concentrically positioned within the cylindrical housing 1 opposite the heater head 3 along the piston chamber 11. Similarly to the plurality of heater fin protrusions 31, each of the plurality of tubular cooler fin protrusions 41 is oriented parallel to the central axis 13. The plurality of tubular cooler fin protrusions 41 is arranged to match the specific cross sectional geometry 6 such that the plurality of tubular cooler fin protrusions 41, having a positive geometry, may interface with the plurality of cavities 21, which have negative geometry, so that the plurality of tubular cooler fin protrusions 41 may be enveloped by the plurality of cavities 21 by moving the displacer piston 2 along the central axis 13. In one embodiment of the present invention, each of the plurality of tubular cooler fin protrusions 41 is hollow to allow working fluid 7 to pass through.

(22) The displacer piston 2 and the cylindrical housing 1 are dimensioned such that there is only a small gap between the displacer piston 2 and the cylindrical housing 1. The displacer piston 2 oscillates between the heater head 3 and the cooling bridge 4 and alternatingly displaces the working fluid 7 between the heater head 3 and the cooling bridge 4. The plurality of cavities 21 alternatingly envelops the plurality of heater fin protrusions 31 and the plurality of tubular cooler fin protrusions 41 as the displacer piston 2 moves between the heater head 3 and the cooling bridge 4. When the fin cavities of the displacer piston 2 are enveloping the plurality of heater fin protrusions 31 of the heater head 3, the majority of the working fluid 7 is displaced away from the heater head 3, towards the cooling bridge 4, and the cooling bridge 4 cools the working fluid 7, causing the pressure of the working fluid 7 to drop. When the plurality of cavities 21 of the displacer piston 2 are enveloping the plurality of tubular cooler fin protrusions 41 of the cooling bridge 4, the working fluid 7 is displaced towards the heater head 3, where the working fluid 7 is heated by the heater head 3, causing the pressure of the working fluid 7 to rise.

(23) In one embodiment of the present invention, the displacer piston 2 is connected to a crank mechanism according to a beta type Stirling engine design. In one embodiment of the present invention, however, the displacer piston 2 is a free piston design. The following is a description of the preferred free piston embodiment.

(24) In one embodiment, the present invention further comprises a ferrous or magnetic material 8, an electrically conductive coil 9, and a spring 16. The ferrous or magnetic material 8 is integrated into the displacer piston 2, preferably close to the circumference of the displacer piston 2. The electrically conductive coil 9 is wrapped around the cylindrical housing 1. The electrically conductive coil 9 is electrically connected to an electronic control system 10. The electronic control system 10 controls electronic current flow through the electrically conductive coil 9 in order to produce an electromagnetic field, creating a force in the ferrous or magnetic material 8 and thus moving the displacer piston 2. This arrangement is similar to the function of a solenoid. FIG. 9 shows a conceptualization of the use of the ferrous or magnetic material 8, the electrically conductive coil 9 and the electronic control system 10.

(25) The spring 16 is connected between the displacer piston 2 and a spring annulus 17. The spring annulus 17 is positioned concentrically within the cylindrical housing 1, opposite the heater head 3 along the cylindrical housing 1. In one embodiment, the cooling bridge 4 is positioned between the displacer piston 2 and the spring annulus 17 and there is a concentric gap between the cooling bridge 4 and the cylindrical housing 1, so that the spring 16 encircles the cooling bridge 4.

(26) The displacer piston 2 requires physical support to hold the displacer piston 2 in the correct concentric position within the cylindrical housing 1. To this end, the cylindrical housing 1 further comprises a plurality of roller tracks 14, wherein each of the plurality of roller tracks 14 is oriented parallel to the central axis 13. The plurality of roller tracks 14 is radially distributed around the central axis 13 within the cylindrical housing 1. The displacer piston 2 further comprises a plurality of rollers 22. The plurality of rollers 22 is similarly radially distributed around the central axis 13 on the displacer piston 2, so that the plurality of rollers 22 are engaged to the plurality of roller tracks 14, wherein the plurality of rollers 22 roll within the plurality of roller tracks 14 in a direction parallel to the central axis 13. As the displacer piston 2 moves longitudinally within the cylindrical housing 1, the plurality of rollers 22 and the plurality of roller tracks 14 ensure that the displacer piston 2 stays concentric with the cylindrical housing 1 and does not rotate.

(27) As seen in FIGS. 6-8, in one embodiment of the present invention, the cooling bridge 4 is cooled by a circulatory fluid flow using a coolant fluid 18. The following is a description of an example of a cooling arrangement according to one embodiment. In alternate embodiments, other means may be used for cooling the cooling bridge 4.

(28) The cylindrical housing 1 further comprises an annular coolant chamber 15 and a working fluid chamber 12. The cooling bridge 4 is positioned between the piston chamber 11 and the working fluid chamber 12. The cooling bridge 4 further comprises a first circular plate 42 and a second circular plate 43. The first circular plate 42 and the second circular plate 43 are concentrically positioned within the cylindrical housing 1.

(29) The first circular plate 42 and the second circular plate 43 are spaced apart from each other along the central axis 13. A cooling space 44 is defined by all empty space between the first circular plate 42 and the second circular plate 43. The plurality of tubular cooler fin protrusions 41 traverses through the first circular plate 42 and the second circular plate 43. As a result, the working fluid 7 may pass through the plurality of tubular cooler fin protrusions 41 so that the working fluid chamber 12 is in fluid communication with the piston chamber 11 through the plurality of tubular cooler fin protrusions 41. The annular coolant chamber 15 is concentrically positioned around the working fluid chamber 12 and is separated from the working fluid chamber 12 so that the coolant fluid 18 and the working fluid 7 are not allowed to mix. The annular coolant chamber 15 comprises a coolant ingress 151 and a coolant egress 152. The coolant ingress 151 is in fluid communication with the coolant egress 152 through the cooling space 44. Coolant flows into the coolant ingress 151 and through the cooling space 44, and heat transfer occurs between the working fluid 7 within the plurality of tubular cooler fin protrusions 41. The coolant fluid 18 should always be at a lower temperature than the working fluid 7, so that the cooling bridge 4 is constantly cooling the working fluid 7 similarly to how the heater head 3 is constantly heating the working fluid 7.

(30) Referring to FIG. 11, one embodiment of the present invention further comprises a bellows assembly 200. In one embodiment, the bellows assembly 200 is an edge welded bellows. In one embodiment, the bellows assembly 200 is a formed bellows. The bellows assembly 200 is an elastic vessel that can be compressed and extended under varying pressure or vacuum conditions. The bellows assembly 200 serves as a seal between the heater head and the displacer piston. The integration of the bellows assembly 200 reduces unswept volume within the piston chamber in order to increase the overall efficiency of the system, since a smaller volume of working fluid experiences less overall energy exchange during the heating and cooling cycles to achieve the same effect. The bellows assembly 200 comprises a first end 210 and a second end 220 which are positioned opposite each other along the bellows assembly 200, being the longitudinal extremities of the bellows assembly 200. The first end 210 of the bellows assembly 200 is annularly connected within the piston chamber adjacent to the heater head. The second end 220 of the bellows assembly 200 is annularly connected to the end of the displacer piston that is closer to the cooling bridge, thus sealing the displacer piston within the bellows assembly 200. The first end 210 of the bellows assembly 200 stays stationary, being connected to the inside of the cylindrical housing, while the second end 220 of the bellows assembly 200 reciprocates back and forth with the movement of the displacer piston.

(31) In one embodiment, the spring 16 is integrated into the bellows assembly 200, with the spring being wound within the bellows assembly 200 from the first end 210 to the second end 220 of the bellows assembly 200. Similarly, in one embodiment, the electrically conductive coil is wound within the bellows assembly 200 from the first end 210 to the second end 220. In various embodiments, the spring, the electrically conductive coil, or both, may be integrated into or within the bellows assembly 200 in any conceivable manner, or embodied as separate components that are attached, connected, placed adjacent to or otherwise arranged together with, within, or around the bellows assembly 200, or in any other means, in order to facilitate adequate movement of the displacer piston within the cylindrical housing. Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.