Linear compressor has no crank mechanism compared with conventional reciprocating compressor. This allows higher efficiency, oil-free operation, lower cost and smaller size when linear compressors are used for vapour compression refrigeration (VCR) system. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency. This paper presents a review of linear compressors for refrigeration system. Different designs and modelling of linear compressors for both domestic refrigeration and electronics cooling (miniature VCR system) are discussed. Key characteristics of linear compressor are also described, including motor type, compressor loss, piston sensing and control, piston drift and resonance. The challenges associated with the linear compressors are also discussed to provide a comprehensive review of the technology for research and development in future.
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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