GB1352153A - Thermodynamic reciprocating machine - Google Patents

Abstract

1352153 Refrigeration systems BRITISH OXYGEN CO Ltd 17 Nov 1971 [18 Nov 1970 24 March 1971] 54880/70 and 7746/71 Heading F4H A thermodynamic reciprocating machine consists of a displacer 2 reciprocable in a cylinder, a gas inlet 12 and a gas outlet 22 being provided in the cylinder wall, one or more valves 36 inside the cylinder being operable by movement of the displacer to open and close the inlet and outlet, gas entering through the inlet being conducted from space 26, via duct 32 and regenerator 34 to expansion chamber 6, the pressure serving to drive the displacer upwards until it is stopped by increasing pressure in driving chamber 8. The inlet 12 and outlet 22 both consist of a ring of small holes, and the cylinder is surrounded by a collar having two chambers 18, 20 connected respectively to the inlet pipe 14 and the outlet pipe 24. The inlet pipe 14 carries gas at 100 lbs/sq. in. and is also connected via a pressure reducing valve 48 and a one-way valve 50 to the chamber 8. Similarly chamber 8 is connected via a pressure relief valve 54 to the outlet pipe 24. The pressure reducing valve 48 maintains a certain minimum pressure in chamber 8, e.g. 40 lbs/sq. in. Oneway valve 50 protects valve 48 against pressure fluctuations caused by the reciprocation of the displacer. Relief valve 54 sets a maximum pressure in the chamber 8, e.g. 60 lbs/sq. in. The displacer has upper and lower sealing rings 38 and 40 and valve ring 36 is moved by surface 28 of the displacer to uncover the inlet 12 and cover the outlet 22 and it is returned to the position shown by surface 30. It is dimensioned so that it can just cover both the inlet and the outlet. When the ring 36 is in the position shown in Fig. 1 the inlet is closed and the outlet is open. Gas at 40 lbs fills chamber 8 and drives the displacer down, displaced gas being exhausted through the outlet 22. At the end of its stroke the displacer opens the inlet and closes the outlet so that gas at 100 lbs passes to the space 6 via bore 32 and regenerator 34. This pressure being higher than that in chamber 8 the displacer rises. Gas passing through the regenerator becomes chilled. As the displacer rises it causes ring 36 to close the inlet. The gas in chamber 8 continues to expand, becoming colder until the movement of the displacer is arrested by increasing pressure in chamber 8. This movement causes the ring 36 to open the outlet so that the gas in space 6 can expand to an outlet pressure of 51 lbs, thereby becoming still cooler. In passing through the regenerator 34 it cools this ready for the next opening of the inlet. The working surface 56 may be a copper plate and it may be attached to a cooling surface in a refrigerator system. A number of modifications are described: there may be separate rings for controlling the inlet and the outlet both operated by movement of the displacer (Fig. 2, not shown); a seal may be provided between the ring 36 and the surface 30 of the displacer operative at certain stages of the cycle (Fig. 4, not shown); the regenerator may be outside the cylinder (Fig. 5, not shown); the displacer and the cylinder may be extended to provide a two-stage expansion (Fig. 6, not shown); the driving chamber 8 may be divided in two by a plate with a one way valve and a small bleed between the two so that the displacer moves more quickly in one direction than the other (Figs. 9 and 12, not shown), valves 48 and 50 then being unnecessary; and the part of the cylinder having the inlet and outlet may be of smaller diameter than that containing the rest of the displacer (Fig. 13, not shown). The displacer may be made of a fibre-based phenolic resin or other resin and the valve ring or rings of reinforced PTFE.