HYBRID BRAYTON - GIFFORD-McMAHON EXPANDER

A method of producing refrigeration at cryogenic temperatures with a hybrid expander,

• the hybrid expander comprising
• a Brayton expansion engine comprising a reciprocating piston having a piston warm end and a piston cold end,
• a drive stem attached to the piston warm end, the drive stem having a stem warm end;
• a Gifford-McMahon expander comprising a displacer, the displacer being attached to the piston cold end;
• a controllable inlet valve and a controllable outlet valve, each controllable valve connected to a cold end volume directly adjacent to the piston cold end;
• the method comprising the steps of:
• (a) supplying gas at a first pressure from a source to the controllable inlet valve;
• (b) contemporaneously reciprocating the piston, the displacer, and the drive stem between a first position to a second position by
• (i) proximal to the first position,
• closing the controllable inlet valve,
• opening the controllable outlet valve to exhaust the gas at the second pressure into an exhaust line and to decrease a size of the cold end volume;
• (ii) proximal to the second position,
• closing the controllable outlet valve,
• opening the controllable inlet valve to admit the gas at the first pressure from an inlet line and to increase a size of the cold end volume.

A hybrid expander for producing refrigeration at cryogenic temperatures, the hybrid expander comprising

• a Brayton expansion engine comprising a reciprocating piston having a piston warm end and a piston cold end,
• a drive stem attached to the piston warm end, the drive stem having a stem warm end;
• a Gifford-McMahon expander comprising a displacer, the displacer being attached to the piston cold end;
• a controllable inlet valve and a controllable outlet valve, each controllable valve connected to a cold end volume directly adjacent to the piston cold end;
• a check inlet valve and a check outlet valve, each check valve connected to a warm end volume directly adjacent the piston warm end;
• wherein
• gas is supplied at a first pressure from a source to the controllable inlet valve and the check inlet valve;
• the piston, the displacer, and the drive stem are contemporaneously reciprocating between a first position to a second position by
• proximal to the first position,
• the controllable inlet valve is closed,
• the controllable outlet valve is opened to exhaust the gas at the second pressure into an exhaust line and to decrease a size of the cold end volume, and
• gas is drawn through the check inlet valve at the first pressure to increase a size of the warm end volume;
• (ii) proximal to the second position,
• the controllable outlet valve is closed,
• the controllable inlet valve is opened to admit gas at the first pressure to the cold end volume and to increase the size of the cold end volume,
• gas is exhausted through the check outlet valve at a third pressure;
• wherein the second pressure is lower than the first pressure;
• wherein the third pressure is higher than the first pressure.