Microminiature stirling cycle cryocoolers and engines

A method for constructing a Stirling cycle thermomechanical transducer comprising:

• (a) forming a cooperating diaphragm, back space, expansion space and heat exchanger for each of a plurality of spaced apart, heat-accepting, fluid-expansion ends of a plurality of Stirling transducer pressure vessels by etching away selected portions of silicon wafers and then aligning and joining the wafers together in the plane as an integral, expansion end plate;
• (b) forming a cooperating diaphragm, back space, compression space and heat exchanger for each of a plurality of spaced apart, heat ejecting, fluid compression ends of a plurality of Stirling transducer pressure vessels by etching away selected portions of silicon wafers and then aligning and joining the wafers together in the plane as an integral compression end plate;
• (c) forming a plurality of heat regenerators joined together as an integral regenerator plate, each regenerator having fluid openings on opposite sides of the regenerator plate, the openings being spaced apart for registration with said end plates;
• and
• (d) interposing, aligning and joining the regenerator plate between the expansion end plate and the compression end plate to form a unitary structure comprising a plurality of Stirling transducers.

An improved Stirling cycle thermomechanical transducer having:

• (A) a pressure vessel defining an enclosed work space including fluid passages and containing a compressible and expansible fluid, the pressure vessel comprising:
• (a) a heat-accepting, fluid expansion region having
• (i) an expansion region
• (ii) a flexible expansion diaphragm forming a wall of the expansion space;
• and
• (iii) a heat-accepting, heat exchanger bounding the expansion space;
• and
• (b) a heat-ejecting, fluid compression region having:
• (i) a compression space;
• (ii) a flexible compression diaphragm forming a wall of the compression space;
• and
• (iii) a heat-ejecting, heat exchanger bounding the compression space;
• and
• (c) a heat regenerator interposed between said regions and including a perforate matrix in fluid communication with the expansion space and the compression space;
• and
• (B) a control circuit apparatus linked to the diaphragms for controlling the mode, amplitude, phase and frequency of the deflections of the diaphragms which alternately strain to provide periodic variations of the expansion space and compression space volumes and for maintaining a nominal 90.degree. phase lead of the expansion space volume ahead of the compression space volume;
• wherein the improvement comprises the combination of:
• the control circuit apparatus being adapted to operate the transducer above 500 Hz;
• and the passages in the work space being sufficiently narrow to provide a Wolmersley number, which is characteristic of the irreversibilities generated by the oscillating flow of the working fluid in the work space, being below substantially 5 and the amplitude of diaphragm vibrations are sufficiently small to provide the working fluid a maximum Mach number below substantially 0.1 at an operating frequency above 500 Hz.