Device for thermal compression of a gaseous fluid

Abstract

A device for compressing a gaseous fluid includes a first chamber thermally coupled with a hot source, a second chamber thermally coupled with a cold source, a movable piston moved by a rod, and a regenerating exchanger establishing fluid communication between the first and second chambers. The rod is arranged in a cylindrical socket and guided in axial translation by a linear guiding system such as to guide the piston without contact relative to the sleeve. A sealing ring attached to the cylindrical socket surrounds the rod with a very low radial clearance, in order to limit the passage of the gaseous fluid along the mobile rod. Also disclosed is an integral cold casing having machined boreholes, a thermal screen in the hot casing, and a self-driving system with a resilient return means.

Claims

1. A compression device for compressing a gaseous fluid, comprising: an inlet for the gaseous fluid to be compressed and an outlet for the gaseous fluid in compressed form, a work enclosure containing the gaseous fluid, a first chamber, thermally coupled with a heat source adapted to provide heat to the gaseous fluid, a second chamber, thermally coupled with a cold source in order to transfer heat from the gaseous fluid to the cold source, a piston mounted so as to be movable along an axial direction within a cylindrical sleeve and separating the first chamber and second chamber, the piston being movable by a piston rod connected to the piston, in an axial reciprocating motion, a regenerative heat exchanger placing the first and second chambers in fluid communication, an auxiliary chamber, and a self-driving device acting on one end of the piston rod and comprising: a connecting rod coupled to the piston rod, a flywheel connected to the connecting rod, and a resilient double-acting return means coupled to the rod and having a neutral point corresponding to a position at or near a mid-stroke of the piston, wherein the connecting rod, flywheel, and resilient double-acting return means are positioned in the auxiliary chamber.

2. The compression device according to claim 1, wherein the double-acting resilient double-acting return means cyclically stores energy, in parallel with energy stored in the flywheel.

3. The compression device according to claim 1, wherein the resilient double-acting return means is a spring, working in traction and in compression.

4. The compression device according to claim 1, wherein the resilient double-acting return means comprises two springs working in opposition.

5. The compression device according to claim 1, wherein the self-driving device comprises a motor coupled to the flywheel.

6. The compression device according to claim 5, wherein the motor is an electric motor that is magnetically coupled to the flywheel.

7. The compression device according to claim 1, wherein the auxiliary chamber is fluidly coupled to the second chamber by a gap that enables the auxiliary chamber to have a mean pressure that is half of a sum of an inlet pressure at the inlet and an outlet pressure at the outlet during operation of the compression device.

8. The compression device according to claim 1, wherein the self-driving device comprises a first roller bearing that rotatably couples the connecting rod to the flywheel.

9. The compression device according to claim 8, wherein the connecting rod is connected to the piston rod by a second roller bearing.

10. A thermal system comprising a heat transfer circuit and at least one compression device according to claim 1.

11. The compression device according to claim 1, wherein the inlet and outlet are respective openings through the work enclosure and fluidly couple the second chamber to an external environment, the compression device further comprising: an inlet valve configured to open and close the inlet; and an outlet valve configured to open and close the outlet.

12. The compression device according to claim 11, wherein the inlet valve is configured to open when a pressure of the gaseous fluid in the second chamber is less than a first value and the outlet valve is configured to open when the pressure of the gaseous fluid in the second chamber is greater than a second value.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Other features, objects, and advantages of the invention will become apparent from the following description of some embodiments of the invention, given by way of non-limiting examples. The invention will also be better understood with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic axial sectional view of a device for compressing gaseous fluid according to the invention,

(3) FIG. 2 shows a partial detail view of the rod guidance,

(4) FIG. 3 shows a perspective view of a cold part comprised in the device of FIG. 1,

(5) FIG. 4 shows a perspective view of the hot portions comprised in the device of FIG. 1,

(6) FIG. 5 shows a perspective view of the cold part of FIG. 3, with cross-section and cutaway,

(7) FIG. 6 shows details concerning the sealing ring,

(8) FIG. 7 shows details of the piston-sleeve interface,

(9) FIG. 8 shows a diagram of the thermodynamic cycle implemented in the device, in particular for the self-driving device,

(10) FIG. 9 shows a second embodiment of the cold part,

(11) FIG. 10 shows a second embodiment concerning the self-driving device,

(12) FIG. 11 shows the piston assembly,

(13) FIG. 12 shows a partial view of the first housing, illustrating the portion having the lowest heat conductivity.

DETAILED DESCRIPTION

(14) In the various figures, the same references designate identical or similar elements,

(15) FIG. 1 shows a device 1 for compression of a gaseous fluid, adapted for admitting a gaseous fluid (also called working fluid) through an inlet or intake 46 at a pressure P1, and supplying the compressed fluid at pressure P2 at an outlet denoted 47.

(16) As represented in FIGS. 1 to 12, the device is designed around an axial direction X, which is preferably oriented vertically, but this does not exclude another arrangement. A piston 7 is mounted so as to be movable along this axis at least within a cylindrical sleeve 50. Said piston hermetically separates two enclosed spaces, respectively referred to as the first chamber 21 and second chamber 22, these two chambers being contained within a work enclosure 2 that is hermetic (except for said inlets/outlets). The work enclosure 2 has an upper end 2h and a lower end 2b. The piston has a dome-shaped upper portion, for example hemispherical.

(17) The work enclosure 2 is defined by a first housing 11, arranged in the upper portion of the assembly and in thermal contact with the heat source at least in the upper area, and by a second housing 12, arranged in the lower portion and cooled by the cold source. Using known English terms, the first housing 11 can be called a heater and the second housing 12 can be called a cooler. The cylindrical sleeve 50 extends both into the second housing and inside the first housing, in contact with a part called the heat shield 35 which will be further discussed below.

(18) The first housing 11 is manufactured of stainless steel or of a metal alloy sufficiently resistant to withstand the temperatures of the hot portion. The second housing 12 is preferably made of a light metal alloy, as its operating temperature is lower.

(19) In the example shown, the first housing 11 and second housing 12 are directly assembled together without any intermediate part. However, they could be assembled together with one (or more) intermediate part(s).

(20) The first chamber 21, also called the hot chamber, is arranged above the piston and is thermally coupled to a heat source 6 adapted to provide heat to the gaseous fluid. The first chamber is rotationally symmetrical, with a cylindrical portion having a diameter corresponding to the diameter D1 of the piston and a hemispherical portion at the top.

(21) The heat source 6 entirely surrounds the hot chamber 21, and in particular is in contact with the first housing 11.

(22) The second chamber 22, also called the cold chamber, is arranged below the piston and is thermally coupled with a cold source 5 in order to transfer heat from the gaseous fluid to the cold source. The second chamber is generally cylindrical, having a diameter D1 corresponding to the diameter of the piston.

(23) Around the cylindrical sleeve 50 is arranged a regenerative heat exchanger 9, of the type conventionally used in Stirling-type thermodynamic engines. This exchanger 9 (also simply called a regenerator in the following) comprises fluid channels of small cross-section and elements for storing thermal energy and/or a dense network of metal wires. This regenerator 9 is arranged at an intermediate height between the upper end 2h and the lower end 2b of the work enclosure and has a hot side 9a towards the top and a cold side 9b towards the bottom. The hot side 9a is connected (in fluid communication) with the first chamber 21 by means of a heat communication channel 25 which includes manifolds 28, an annular passage 25, which connects to an opening 24 located at the top of the first chamber 21.

(24) The upper portion of the annular passage 25 allows fluid to lap against the upper portion of the first housing 11, where it is particularly hot as it is in contact with the heat source (very good thermal coupling).

(25) The heat communication channel 25 is formed by a thin radial gap (<4 mm, even <2 mm, even about 1 mm) formed between the first housing 11 and a part comprising a first heat shield. The first heat shield 35, formed by a thermally insulating annular cylindrical portion, is interposed between the piston 7 and the heat communication channel 25, and as a result the working fluid does not heat the side portions of the piston.

(26) The first heat shield 35 is made of ceramic or of a high temperature insulator. Its thickness is substantially constant in the example illustrated.

(27) The cylindrical portion may be extended at the top by a hemispherical portion of substantially constant thickness, this hemispherical portion being configured to match the shape of the outer surface of the piston when the latter is in its uppermost position; the top of the hemispherical portion is provided with an opening 24 to allow the passage of flows into and out of the first chamber 21.

(28) The cold side 9b of the regenerator 9 is connected (in fluid communication) with the second chamber 22, by means of a cold communication channel which comprises manifolds 27 and cold channels 26 in the form of boreholes in the second housing, their arrangement to be specified below.

(29) As is apparent from the figures, when the piston moves, the sum of the volumes of the first and second chambers 21,22 remains substantially constant, except that the volume occupied by the rod 8 is slightly greater when the piston is in its uppermost position. In addition, the volume of working fluid contained in the regenerator 9, the cold channels 26,27, and the heat communication channel 28,25 is constant, and therefore the total volume of gaseous fluid in the work enclosure 2 is more or less constant.

(30) According to the advantageous constructive architecture chosen, the volume of hot gases which includes the first chamber 21 and the hot channels 25 all the way to the regenerator, when the piston is at its uppermost position, is less than 15% of the volume swept by the piston between the lowest point and the highest point, or even less than 10%.

(31) Similarly, the volume of cold gases when the piston is at the lowest point, which includes the residual volume of the second chamber 22 and the cold communication channels 26, is less than 15% of the total volume swept by the piston, or even less than 10%.

(32) From the point of view of its structural architecture, the device comprises: the second housing 12 which defines the second chamber 22 by means of the abovementioned sleeve together with the lower portion of the piston; this part is relatively solid, and further includes the inlet 46 and outlet 47 for the fluid, the first housing 11, which defines the first chamber 21 by means of the inner surface of the heat shield 35 together with the top of the piston 7h, and which comprises an insulating sleeve area formed by a portion of lower thermal conduction 37 that faces part of the regenerator (see FIG. 12), the heat shield 35 forming the cylindrical sleeve 50 on its inner surface and defining on its outer surface the radially inner surface of the heat communication channel 25, an auxiliary heat shield 36 interposed between the heat communication channel 25 and the portion 37 of lower conduction of the first housing, a mobile assembly 78 comprising said piston 7 and a rod 8 integral to the piston; said rod 8 has a round cross-section of diameter D2 and provides a centering and attachment system 87 on the axis of the piston; the aforementioned regenerator 9, arranged inside the upper structural part 11 and around the sleeve 50.

(33) Below the rod 8 is arranged a system for controlling the movement of the piston, which is contained within an auxiliary housing 13 that defines a third chamber 23 or auxiliary chamber 23. The auxiliary housing 13 is fixed to a flange 10 that is part of the first housing 11, by means of screws threaded through holes 160.

(34) Optionally, the device may also comprise a specific self-driving device 4 as its control system, which will be discussed further below.

(35) In addition, the second housing 12 comprises an axial bore 12a which receives a snugly fitted cylindrical socket 17 having an inner cylindrical surface that is machined with precision. The socket is force-fitted into the bore 12a of the lower structural part 12.

(36) This socket 17 receives a linear guiding system 3 which accurately guides the rod 8 in order to accurately guide the piston 7, preferably with no contact with the sleeve as will be explained further below.

(37) In the illustrated example, the linear guiding system 3 is a cylindrical roller bearing, preferably a cylindrical sheath 30 with balls or rollers 31. The rollers 31 roll on the socket and the sheath 30 moves at half the speed of the rod 8.

(38) In an alternative (not shown), the linear guiding system 3 may comprise plain bearings made of PTFE (Polytetrafluoroethylene).

(39) For fluidtightness with respect to the movable rod, a cylindrical sealing ring 18 is fixed within the cylindrical socket 17 and is separate from the guiding system; this sealing ring 18 surrounds the rod with a radial clearance el of between 2 and 20 m, greatly limiting the passage of gaseous fluid along the movable rod 8 (see FIG. 6). Preferably, the radial clearance el is preferably between 10 and 15 m.

(40) Due to the precision guidance of the rod, precision guidance of the piston is accordingly obtained due to the rigid attachment of the piston to the rod. More precisely, the piston 7 has an outer edge 73,74 arranged adjacent to the sleeve 50 and the outer edge of the piston is guided within the sleeve without friction with a functional clearance e2 between the outer joining edge and the sleeve of between 5 m and 30 m, preferably about 10 m (see FIG. 7). The outer edge is preferably integrally obtained from the lower portion 71 of the piston, but any other solution is possible.

(41) Due to this precise geometry, satisfactory fluidtightness is obtained in dynamic mode during the reciprocating movements of the piston, the frequency of the alternating movements being between a few Hertz and a few tens of Hertz to a few hundred Hertz.

(42) In addition, this arrangement prevents any wear due to friction or contact; one can thus do without any liquid lubrication, such that the device is devoid of liquid lubrication.

(43) Unlike a positive displacement compressor, in this thermal compressor it is the heat exchanges which move the piston and not the rod and connecting rod. Therefore there is very little radial force on the rod and piston in this thermal compressor, which allows accurate guidance and no friction as mentioned above. We thus obtain a service life of tens of thousands of hours without maintenance.

(44) The fluid selected as the working fluid may be any suitable fluid, in particular any light gas; it may be ammonia, but CO2 may be chosen for environmental reasons.

(45) According to an example implementation of the invention, the temperature of the cold portion is in the vicinity of 50 C., while the temperature of the hot portion is in the vicinity of 650 C.

(46) The insulating sleeve 37 is obtained by a plurality of recesses 38 separated by radial walls 39 as shown in FIG. 12, this alternation of recesses and radial walls being repeated around the entire circumference of the first housing of the upper portion of the regenerator 9.

(47) Around the thermally insulating sleeve area is arranged a collar 15 which is intended to reinforce the mechanical strength of the first housing in the area of lowest heat conductivity. The end of the radial walls 39 is forced radially inward by the presence of this collar 15, which can be mounted with slight prestressing and therefore providing satisfactory mechanical strength of this intermediate portion of the first housing 11.

(48) In addition, the first housing 11 comprises a first reinforcing flange 11 a arranged between the upper domed portion and the insulating sleeve area, and a second reinforcing flange 11b serving as a mounting flange for attachment to the second housing 12.

(49) The first housing 11 is assembled to the second housing 12 at the interface plane P by means of a plurality of screws inserted through holes 110 at the bottom of the hot part (flange 11b of the first housing 11) and holes 112 at the top of the cold part, which may be threaded holes.

(50) Operation of the compressor is ensured by the reciprocating motion of the piston 7, as well as by the action of an inlet valve 46a on the inlet 46, and a check valve 47a for discharging through the outlet 47.

(51) The various steps A, B, C, D, described below are shown in FIGS. 1 and 8.

(52) Step A.

(53) The piston, initially at the top, moves downward and the volume of the first chamber 21 increases while the volume of second chamber 22 decreases. This pushes the fluid through the regenerator 9 from bottom to top and heats it in the process. The pressure Pw increases concomitantly.

(54) Step B.

(55) When the pressure Pw exceeds a certain value, the outlet valve 47a opens and the pressure Pw settles at the compressed fluid discharge pressure P2, and fluid is expelled at the outlet (the inlet valve 46a of course remains closed during this time). This continues until the piston reaches the bottom stopping point.

(56) Step C.

(57) The piston is now moving from the bottom upwards and the volume of the second chamber increases while the volume of the first chamber decreases. This pushes the fluid through the regenerator 9 from top to bottom, and cools it in the process. The pressure Pw decreases concomitantly. The outlet valve 47a closes when the upward movement begins.

(58) Step D.

(59) When the pressure Pw drops below a certain value, the inlet valve 46a opens and the pressure Pw settles at the fluid intake pressure P1, and fluid is drawn through the inlet 46 (the outlet valve 47a of course remains closed during this time). This continues until the piston reaches the top stopping point. The inlet valve 46a will close when the piston begins its descent.

(60) The movements of the rod 8 can be controlled by any suitable driving device arranged in the auxiliary chamber 23. In the illustrated example, there is a self-driving device 4 acting on one end of the rod. This self-driving device 4 comprises a flywheel 42, and a connecting rod 41 connected to said flywheel by a pivoting connection, for example a roller bearing 43. The connecting rod 41 is connected to the rod by another pivoting connection, for example a roller bearing 44.

(61) In the example illustrated, the self-driving device 4 is housed in an auxiliary chamber 23 filled with the gaseous working fluid at a pressure denoted Pa. The sealing ring 18 is interposed between the second chamber 22 and the auxiliary chamber 23. When the device is in operation, the pressure Pa in the auxiliary chamber 23 converges to an average pressure substantially equal to half the sum of the min P1 and max P2 pressures. When the device is shut down for some time, the pressure in the auxiliary chamber Pa becomes equal to the pressure in the second chamber 22. In fact, due to the functional clearance of between 2 and 20 m between the ring 18 and the rod 8, the very slight leak does not allow maintaining a pressure differential over the long term, but in dynamic mode this very slight leak does not affect operation and remains negligible.

(62) When the flywheel rotates one turn, the piston sweeps a volume corresponding to the distance between the uppermost point and the lowermost point, multiplied by the diameter D1.

(63) The diameter of the rod D2 is greater than one-fourth the diameter D1 of the piston, such that the pressure exerted on the piston is (PwPa)D2.

(64) The thermodynamic cycle, as represented in FIG. 8, provides positive work to the self-driving device.

(65) As illustrated in FIG. 8, the forces exerted on the piston provide energy to the flywheel during steps A,B while in step C, D it is the flywheel which supplies power to the piston train, knowing that the piston must at all times overcome the minimal residual friction or rolling resistance. The work provided by the complete cycle has a positive balance; as a result, the reciprocating motion of the piston 7 can be self-maintained by said driving system 4.

(66) The self-driving work is proportional to the cross-section of the rod, and therefore the cross-section of the rod will be selected to generate sufficient work. For example, a diameter D2 that is at least one-fourth the diameter D1 of the piston will be chosen.

(67) An electric motor (not shown) is coupled, in the present example by magnetic means, with the flywheel. This motor will give an initial push to start the cycle. The motor also serves to regulate the cycling speed when in steady state. The magnetic coupling between motor and flywheel eliminates any rotating joint issues and the associated potential leaks.

(68) In addition, advantageously according to an optional aspect illustrated in FIG. 10, there is an additional double-acting resilient return means 45, which operates in parallel with the abovementioned rod-flywheel assembly. For example, this may be formed by a spring alternately pulled and compressed and having a length at rest that is chosen so as not to exert any force at the cycle midpoint.

(69) The elastic return means cyclically stores and restores energy.

(70) Alternatively, there may be two springs which work antagonistically and exert forces that are balanced at the cycle midrange.

(71) Advantageously, the forces on the rod-flywheel assembly are reduced because a portion of the forces is supported by the resilient return system.

(72) One can thus more accurately dimension the bearings 43,44, which contributes to optimization of the driving mechanism and to the lack of need for maintenance.

(73) To minimize heat transfer by conduction, the piston is constructed in two parts, as shown in particular in FIG. 11: a base 71 with very precise geometric characteristics as described above (in particular the edge 73) and a head 72 which is made of a material offering little heat conductivity or made as several tiers separated by thermal insulation.

(74) In addition, the rod 8 is cooled by a baffle device 14 that deflects the flow of cooled gaseous fluid; this device guides the fluid so that the cooled gaseous fluid laps against the rod 8 and cools it.

(75) The baffle 14 is in the form of a disc of outer diameter D1 with a central hole of a slightly larger diameter than that D2 of the rod (see FIG. 2), thereby defining a passage 14a, which causes the cold working fluid to lap against the rod 8 and cool it.

(76) The channels are created as boreholes machined in the lower structural part 11, in other words the first housing or cooler. Preferably, the first housing is a solid single part as shown in FIGS. 3 and 5.

(77) The cold channels 26 of gaseous working fluid are formed at this location by boreholes 16 running parallel to the axial direction X and arranged circumferentially adjacent to one another around the second chamber. Said boreholes 16 comprise boreholes of small diameter 67 and boreholes of larger diameter 66 in the diametrical areas of connection to the inlet 46 and outlet 47.

(78) In addition, first auxiliary cold channels 51 conveying the coupling fluid from the cold source run parallel to the axial direction and are arranged in a square facing the holes 160 of the flange 10; in addition, other second auxiliary cold channels 52 extend along Y1 perpendicularly to the axial direction and serve as the manifold for the first auxiliary cold channels 51 by connecting to them (see FIG. 5); in addition, other second auxiliary cold channels 53 extend along Y2 perpendicularly to X and to Y1.

(79) The first auxiliary cold channels 51 and the second auxiliary cold channels 52 are also created by boreholes through the solid part formed by the first housing 11.

(80) In addition, the cold chamber comprises a lower groove 55 of a diameter greater than the diameter D of the piston, which serves as a manifold for the cold channels 26 (boreholes 16) to place said cold channels 26 in communication with the bottom 65 of the second chamber 22 (see FIGS. 2 and 3).

(81) In addition, according to an alternative solution represented in FIG. 9, all the first auxiliary cold channels 57,58 are obtained by boreholes perpendicular to the axial direction. A first series 57 of boreholes are arranged along Y2, one above the other and passing through the circle on which are arranged boreholes 16; a second series 58 of boreholes are also arranged one above the other along Y1, intersecting the boreholes 57 of the first series at right angles and in fluid communication therewith, and also passing through the circle on which are arranged boreholes 16. This variant offers certain advantages in the industrial production of such a solid part and in its machining.

(82) It should be noted that the check valves 46a, 47a may be of any type commonly used in compressors and are not necessarily placed close to the inlet and outlet 46,47.

(83) It should be noted that the arrangement of the device could be reversed, namely with the cold portion at the top and the hot portion at the bottom, but it is understood that the vertical arrangement eliminates the effects of gravity with respect to the radial direction of the device and in particular with respect to guiding the rod and guiding the piston and eliminating friction.

(84) It should be noted that to increase the level of compression, it is possible to arrange several compression devices as described above in series.

(85) It should be noted that the boundary between the first housing and the second housing may be located at a different position.

(86) The insulating sleeve 37 may be formed by a specific part interposed between the first and second housings.