Reversible pneumatic drive expander

Abstract

A pneumatically driven cryogenic refrigerator operating primarily on the Gifford-McMahon (GM) cycle is switched from cooling to heating by a switch valve between a rotary valve and a drive piston that causes the displacer to reciprocate. The rotary valve has ports at two radii, one that cycles flow to the displacer and a second that cycles flow to the drive piston. Two ports cycle flow to the top of the drive piston, the “cooling” port optimizes the cooling cycle and the “heating” port provides a good heating cycle. A switch valve that changes the flow from one port to the other can be linearly or rotary actuated. The rotary valve does not reverse direction.

Claims

1. A cryogenic expander for receiving gas from a compressor at a first pressure and returning the gas at a second pressure, comprising: a displacer assembly pneumatically driven and reciprocating, comprising: a displacer in a displacer cylinder reciprocating between a warm end and a cold end of the displacer cylinder, creating a warm displaced volume and a cold displaced volume in the displacer cylinder, gas flowing between the warm and cold displaced volumes through a regenerator; a drive stem attached to a warm end of the displacer and extending through a stem sleeve; and a drive piston having a top and a bottom, the bottom of the drive piston attached to a top end of the drive stem, reciprocating in a drive piston cylinder, the drive piston having a larger diameter than the drive stem, the drive piston separating a top volume above the drive piston and a bottom volume below the drive piston; and a valve assembly capable of providing cooling and heating modes to respectively produce cooling and heating, comprising; a valve seat; a valve disc rotating on the valve seat, wherein the valve seat has ports at a first radius that connects to the displacer cylinder or valve actuators, ports at a second radius that connect to the drive piston cylinder, and a central port that connects to the compressor at the second pressure, the valve disc has slots that alternately connect the gas at the first pressure and second pressure to the ports at the first and second radii, and the ports at the second radius comprise a cooling port and a heating port, and wherein a direction of rotation of the valve disc remains constant; and a switch valve between the ports at the second radius and the top volume above the drive piston, wherein the switch valve is configured to connect either the cooling port or the heating port to the top volume above the drive piston to provide either the cooling or heating mode.

2. The cryogenic expander in accordance with claim 1 wherein the switch valve is configured to connect the heating port to the bottom volume below the drive piston when the expander is in the cooling mode, and to connect the cooling port to the bottom volume below the drive piston when the expander is in the heating mode.

3. The cryogenic expander in accordance with claim 2 wherein the switch valve is configured to connect the cooling port to the top volume above the drive piston when the expander is in the cooling mode, and to connect the heating port to the top volume above the drive piston when the expander is in the heating mode.

4. The cryogenic expander in accordance with claim 2 wherein the switch valve comprises a spool configured to rotationally switch the connections of the heating port and cooling port to the bottom volume below the drive piston.

5. The cryogenic expander in accordance with claim 1 wherein the switch valve is configured such that only the cooling port fluidly communicates with the top volume above the drive piston when the expander is in the cooling mode and only the heating port fluidly communicates with the top volume above the drive piston when the expander is in the heating mode.

6. The cryogenic expander in accordance with claim 5 wherein the switch valve comprises a spool configured to linearly switch the communications of the cooling port and heating port with the top volume above the drive piston.

7. The cryogenic expander in accordance with claim 5 wherein lines respectively connecting the cooling port and the heating port to the top volume above the drive piston have different flow impedances.

8. The cryogenic expander in accordance with claim 1 wherein the switch valve comprises: a spool to connect either the cooling port or the heating port to the top volume above the drive piston; and an actuator to activate the spool linearly or rotationally.

9. The cryogenic expander in accordance with claim 8 wherein the linearly activating actuator is configured to control pressure drop through the switch valve to control the speed at which the displacer moves up and down.

10. The cryogenic expander in accordance with claim 9 wherein the linearly activating actuator is configured to control a degree to which the switch valve is opened to control the pressure drop.

11. The cryogenic expander in accordance with claim 1 wherein the displacer stays at the warm end or the cold end of the displacer cylinder until the pressure has reached the first or second pressure before the displacer moves towards the other end when cooling and heating.

12. The cryogenic expander in accordance with claim 1 wherein the ports at the first radius are connected to the warm displaced volume of the displacer cylinder.

13. The cryogenic expander in accordance with claim 1 wherein the displacer assembly further comprises cold inlet and outlet valves connected to the cold displaced volume of the displacer cylinder, and wherein: the ports at the first radius are connected to the valve actuators; the valve actuators comprise a first valve actuator to open the inlet valve when the first valve actuator is connected to the first pressure of the compressor; and the valve actuators comprise a second valve actuator to open the outlet valve when the second valve actuator is connected to the first pressure of the compressor.

14. The cryogenic expander in accordance with claim 1 wherein the heating port is located closer to one of the ports at the first radius than the cooling port.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawing figures depict one or more implementations in accord with the present concepts, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements.

(2) FIG. 1 is a schematic of cryogenic refrigeration system 100 comprising a pneumatically actuated GM cycle expander having a single acting drive piston, a rotary valve, and a switch valve, supplied with gas from a compressor through interconnecting piping.

(3) FIG. 2 is a schematic of cryogenic refrigeration system 200 comprising a pneumatically actuated GM cycle expander having a double acting drive piston, a rotary valve, and a switch valve, supplied with gas from a compressor through interconnecting piping.

(4) FIG. 3 is a schematic of cryogenic refrigeration system 300 comprising a pneumatically actuated Brayton cycle expander having a single acting drive piston, a rotary valve, and a switch valve, supplied with gas from a compressor through interconnecting piping.

(5) FIG. 4 shows a cross section of the rotary valve, the switch valve, and the drive piston of system 100.

(6) FIG. 5 shows a cross section of the rotary valve, the switch valve, and the drive piston of system 200.

(7) FIG. 6a shows the pattern of slots in the valve disc, superimposed on the valve seat, when the displacer in system 100 is about to be vented to low pressure.

(8) FIG. 6b shows the sequence of the slots in the valve disc of system 100 passing over the ports in the valve seat as the valve disc rotates when the expander is producing cooling.

(9) FIG. 6c shows the P-V diagram for a cooling cycle with the points on the cycle numbered as shown in FIG. 6b.

(10) FIG. 7a shows the pattern of slots in the valve disc, superimposed on the valve seat, when the displacer in system 100 is about to be pressurized to high pressure.

(11) FIG. 7b shows the sequence of the slots in the valve disc of system 100 passing over the ports in the valve seat as the valve disc rotates when the expander is producing heating.

(12) FIG. 7c shows the P-V diagram for a heating cycle with the points on the cycle numbered as shown in FIG. 7b.

(13) FIGS. 8a-8d show FIGS. 1, 8(a), 8(c) and 9(c) of the '304 application, respectively.

DETAILED DESCRIPTIONS

(14) In this section, some embodiments of the invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments. Parts that are the same or similar in the drawings have the same numbers and descriptions are usually not repeated.

(15) Cryogenic expanders typically operate with the cold end down so the terminology up and down and top and bottom are in reference to this orientation. The same numbers are used for the same components in the drawings and subscripts are used to distinguish the equivalent part with a different configuration.

(16) With reference to FIG. 1, shown is a schematic of cryogenic refrigeration system 100 that shows in detail the central features of this invention, the valves and drive piston, in relation to the rest of the system, namely displacer 20a in cylinder 30, and compressor 15 which supplies gas at a first pressure, or high pressure Ph, to rotary valve 2 through line 16, and receives gas at a second pressure, or low pressure Pl, from rotary valve 2 through line 17. Rotary valve 2 has ports on a rotating disc that pass over ports on a stationary seat. Ports on the seat at a first radius 10a cycle gas to the warm end of displacer cylinder 30 through line 9, and ports at a second radius 11a cycle gas through switch valve 1 and line 18 to the top end of drive piston cylinder 6a. Line 18a starts at a first port on the second radius 11a of the valve seat, designated as the cooling port, and line 18b starts at a second port on the second radius 11a of the valve seat, designated as the heating port. The schematic drawing of switch valve 1 shows it is fixed in the position for cooling and is turned 90° counter-clockwise for heating. The schematic drawing of valve 2 shows gas in line 9 connected to cylinder 30 at high pressure, Ph, and gas in line 18 connected to cylinder 6a at low pressure, Pl, as displacer 20a is moving up.

(17) Displacer 20a reciprocates in cylinder 30 between a warm end and a cold end creating warm displaced volume 25 and cold displaced volume 26. Gas flows between volumes 25 and 26 through ports 23 at the warm end, regenerator 22a, and ports 24 at the cold end in displacer body 21a. Seal 27 prevents gas from by-passing regenerator 22a. Displacer 20a is driven up and down by drive stem 7 which is connected at its bottom end to the top end of displacer 20a and at its top end to the bottom end of drive piston 5a. Drive piston 5a is driven up and down by the pressure difference between the cycling gas pressure in volume 12a above drive piston 5a and the pressure in buffer volume 13a below drive piston 5a acting on the area outside drive stem 7. Because drive piston 5a is only driven by the pressure changing from high pressure, Ph, to low pressure, Pl, on one side of the piston it is described as single acting. Seal 31 in the drive piston 5a keeps gas in volume 12a separate from the gas in volume 13a. Seal 28 in stem sleeve 8 keeps gas in volume 13a separate from the gas in volume 25.

(18) Typical operating pressures are around 2.2 MPa for the supply pressure, Ph, and 0.8 MPa for the return pressure, Pl, a pressure ratio of 2.8, so buffer volume 13a has to be more than about three times larger than displaced volume 12a in order for drive piston 5a to complete a full stroke. A much larger volume however is needed to reduce the pressure change in volume 12a to have nearly constant pressure difference across drive piston 5a during the full stroke. This large volume of buffer volume 13a, relative to volume 12a, is shown schematically as a separate volume from the displaced volume below drive piston 5a.

(19) With reference to FIG. 2, shown is a schematic of cryogenic refrigeration system 200 which differs from system 100 in having a double acting drive piston 5b. The pressure on the bottom of drive piston 5b is low pressure Pl when the pressure on top is high pressure Ph, and is high pressure Ph when the pressure on top is low pressure Pl. In system 100, line 18b from the heating port in rotary valve 2 is blocked at switch valve 1 during cooling, but in system 200 it is connected to volume 13b, below drive piston 5b, through switch valve 3 and line 19. Double acting drive piston 5b can have a smaller diameter than single acting drive piston 5a because the full pressure difference, Ph−Pl, acts on it, and volumes 12b and 13b above and below drive piston 5b can be as small as the volume displaced by drive piston 5b.

(20) Rotary valve 4 is similar to rotary valve 2 in having the port at a first radius on the valve seat to line 9 and second radius 10b, and in having the port at a second radius, 11b to lines 18a and 18b, and to line 18. Switch valve 3 is constructed such that gas from heating line 18b in rotary valve 4 connects to line 19 when gas from cooling line 18a connects to line 18, thus switching the pressures above and below drive piston 5b to opposite pressures as valve disc 4 rotates.

(21) Switch valve 3 is fixed in the position shown for cooling and is turned 90° counter-clockwise for heating. The schematic drawing of valve 4 shows gas in line 9 connected to cylinder 30 at high pressure, Ph, gas in line 18, connected to the top of cylinder 6b at low pressure, Pl, and gas in line 19, connected to the bottom of cylinder 6b at high pressure, Ph, as displacer 20a is moving up. While the mechanism for shifting a pneumatically driven cryogenic expander from cooling to heating is most applicable to a cryopump cooled by a GM cycle expander, it can also be applied to a pneumatically driven Brayton cycle expander as shown in FIG. 3.

(22) With reference to FIG. 3, shown is a schematic of cryogenic refrigeration system 300 comprising a pneumatically actuated Brayton cycle expander having a single acting drive piston. The Brayton cycle expander of system 300 has the main inlet and outlet valves, 9a and 9b, at the cold end of cylinder 30b. Gas flows from compressor 15 to inlet valve 9a from high pressure line 16 through counter-flow heat exchanger 50, and returns from outlet valve 9b through heat exchanger 50 and low pressure line 17. Displacer 21b has a regenerator, 22b, which cycles gas from cold end volume 26 to warm end volume 25 to keep the pressures above and below displacer 21b nearly the same and allow the valve mechanism and drive piston mechanism of system 100 or system 200 to be used to produce cooling or heating. The ports on rotary valve 2′ at the first radius 10c are relatively small since they only cycle a small amount of gas to pneumatic actuators 29a and 29b that open and close cold inlet and outlet valves 9a and 9b. Pneumatic actuator 29a opens valve 9a when it is connected to high pressure Ph and is closed when connected to low pressure Pl. The same is true for actuator 29b and valve 9b.

(23) With reference to FIG. 4, shown is a cross section of switch valve 1, rotary valve 2, and drive piston 5a of system 100. Rotating disc 2a is turned by valve motor 40, motor shaft 41, and pin 42 that engages slot 44 in the top of disc 2a. Valve discs shown for this invention have two cycles per revolution and thus have two symmetrical high and low pressure slots. The valve seats have two symmetrical ports for flow to the displacer but may have only one pair of ports for flow to the drive piston. The bottom of valve disc 2a is in contact with valve seat 2b and is shown with slot 17a that connects low pressure return port 17 with line 18a to drive piston volume 12a through spool 1b. This is the cooling mode. System 100 switches to a heating mode when linear actuator 1a pulls spool 1b to the right such that line 18b connects to drive piston volume 12a. Lines 18a and 18b may have different flow impedances so that the speeds at which drive piston 12a moves up and down in the heating and cooling modes may be different. The different flow impedances may be established by the degree to which the switch valve is opened or by fixed port sizes. Controlling the degree to which the switch valve is opened may be used to control the piston speed.

(24) The switch valve 1 may be configured such that only the cooling port 18a fluidly communicates with the top volume 12a above the drive piston 5a when the expander is in the cooling mode and only the heating port 18b fluidly communicates with the top volume 12a above the drive piston 5a when the expander is in the heating mode. The linearly activating actuator 1a may be configured to control the pressure drop through the switch valve 1 to control the speed at which the displacer 20a moves up and down.

(25) With reference to FIG. 5, shown is a cross section of switch valve 3, rotary valve 4, and drive piston 5b of system 200. The bottom of valve disc 4a is in contact with valve seat 4b and is shown with slot 16a, which connects high pressure supply port 16 with line 18b to drive piston volume 12b through spool 3b and line 18, and slot 17a which connects low pressure return port 17 with line 18a to drive piston volume 13b through spool 3b and line 19. This is the heating mode. System 200 switches to a cooling mode when rotary actuator 3a turns spool 3b 90° such that line 18a connects to drive piston volume 12b and line 18b connects to piston volume 13b.

(26) FIGS. 6a and 7a exemplarily show rotary valves of systems 100-300 in two positions. FIG. 6b for cooling and FIG. 7b for heating, show the timing of the high and low pressure slots in the valve disc passing over the ports in the valve seat, which is the equivalent of opening and closing valves. FIGS. 6c and 7c then show the opening and closing of the valves on P-V diagrams for cooling and heating. FIGS. 6a and 7a show slots 16a and 17a in the face of valve disc 2a looking at it from the valve motor and turning counter-clockwise against valve seat 2b. Port 9 in valve seat 2b at a first radius 46 connects to displacer cylinder 30 and opens as valve V1 (see FIG. 6b) when high pressure slot 16a passes over it and as low pressure valve V2 when low pressure slot 17a passes over it. Lines 18a and 18b in valve seat 2b at a second radius 45 connect to the top of drive piston cylinder 6a and open as valves V3a and V3b when high pressure slot 16a passes over them and as low pressure valves V4a and V4b when low pressure slot 17a passes over them. Switch valve 1 blocks the flow from line 18b when the expander is cooling and blocks the flow from line 18a when the expander is heating.

(27) FIGS. 6a, 6b, and 6c show the cooling cycle starting at the end of the expansion stage with cold displaced volume 26 at a maximum, displacer 20a at the top, and the pressure greater than the low pressure, Pl. The numerals 1-8 in FIGS. 6b and 6c show valve timing and the corresponding P-V cycles which are summarized as follow.

(28) 1: Valve V2 opens so that pressure in the displacer drops to low pressure Pl.

(29) 2: After the pressure has dropped to Pl, V3a opens and the pressure difference across the drive piston pushes the displacer towards the bottom.

(30) 3: Before the displacer reaches the bottom, V2 closes so that the pressure increases as cold gas is transferred to the warm end while the displacer moves the rest of the way to the bottom.

(31) 4: V1 opens so that the pressure increases to high pressure Ph.

(32) 5: V3 closes.

(33) 6: V4 opens and the pressure difference across the drive piston pushes the displacer towards the top.

(34) 7: Before the displacer reaches the top, V1 closes so that the pressure decreases as warm gas is transferred to the cold end while the displacer moves the rest of the way to the top.

(35) 8: V4 closes.

(36) There are two principles in this cycle, first is that the pressures in the drive piston are switched after the pressures in the displacer are switched, and second, valves V1 and V2 close before the displacer reaches the end of the stroke, top and bottom.

(37) FIGS. 7a, 7b, and 7c show the heating cycle starting at the beginning of the low pressure stage with displaced volume 26 at a minimum, displacer 20a at the bottom, and the pressure greater than the low pressure, Pl. The numerals 1-8 in FIGS. 7b and 7c show valve timing and the corresponding P-V cycles which are summarized as follow.

(38) 1: Valve V2 opens so that pressure in the displacer drops to Pl. Note that valve V3b is still open keeping high pressure gas on drive piston 5a to hold it down.

(39) 6: After the pressure has dropped to Pl, V4b opens so that the pressure difference across the drive piston pulls the displacer towards the top.

(40) 3: Before the displacer reaches the top, V2 closes so that the pressure increases as warm gas is transferred to the bottom end while the displacer moves the rest of the way to the top.

(41) 4: V1 opens so the pressure increases to high pressure, Ph. Note that V4b is still open causing the drive piston to hold the displacer at the top.

(42) 7: V1 closes followed by the pressure dropping as the displacer moves to the bottom and gas is transferred from the cold end to the warm end.

(43) There are three principles in this cycle. The first is that the pressure above the drive piston holds the displacer at the top or bottom when valves V1 and V2 switch pressure. The second is that the pressure above the drive piston is switched after high or low pressure is reached, and the third is that valves V1 and V2 are closed before the displacer reaches top or bottom. It is important to note that optimizing the cooling cycle by having V2 open longer than V1 and having V1 open more than 90° after V2 does not penalize the heating cycle because heating line 18b can be located more than 90° from cooling line 18a.

(44) The valve timing for system 300 can be the same as for system 100. Representations of the valve and valve timing for system 200 would show more symmetry because the pressures above and below drive piston 5b have to switch at the same time. Compromises are thus needed to balance a good cooling cycle with a good heating cycle.

(45) The following claims are not limited to the specific components that are cited. For example switch valve 1 which is shown as being linearly actuated can be replaced with a rotary activated valve. The heating port on the second radius can alternately be on a third radius. It is also within the scope of these claims to include operating limits that are less than optimum to simplify the mechanical design. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention and the embodiments described herein.