Linear compressors with clearance seals and flexure bearings have been used for many years for space applications, and this article describes the development of linear compressors at Oxford. A new design of moving magnet motor is introduced and the use of flexure springs, linear motors, valves and their integration are all discussed. A ring down test indicates that the ‘viscous’ damping in the linear compressor is acceptable (in terms of the decay ratio against the number of periods). The measured motor characteristics compared well with the vector fields electromagnetic finite element model. With a revised structural design it is predicted that the motor efficiency would be ∼86% for the rated power (200 W shaft power at 50 Hz) enabling the linear compressor to have a high overall efficiency. The companion paper covers the experimental evaluation of the linear compressor.

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A new type of oil-free moving magnet linear compressor with clearance seals and flexure springs has been designed for incorporation into a vapour compression refrigeration system with compact heat exchangers for applications such as electronics cooling. A linear compressor prototype was built with a maximum stroke of 14 mm and a piston diameter of 19 mm. An experimental apparatus was built to measure the compressor efficiencies and coefficient of performance (COP) of a refrigeration system with the linear compressor, using R134a. The resonant frequency for each operating condition was predicted using the discharge pressure, suction pressure and stroke. Refrigeration measurements were conducted for different strokes under each pressure ratio with a fixed condenser outlet temperature of 50 °C and evaporator temperature ranging from 6 °C to 27 °C. The results show that the COPs are around 3.0 for tests with a pressure ratio of 2.5 (evaporator temperature of 20 °C).

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