Design charts for linear motor of miniature stirling cryocoolers

摘要

Small capacity Stirling cryocoolers generally use linear electromagnetic drive (also called linear motor) for long life, maintenance free operation and high reliability. Such motors are normally of moving coil type. Earlier, in free piston, free displacer (FPFD) Stirling cryocoolers, the displacer was driven by the pressure pulses from the compressor. However, in the split configuration the displacer is also driven by a linear motor. This provides better control over its mean position, stroke and phase lend over the compressor piston. The design of such a moving coil linear motor consists of two parts: magnetic circuit design and coil design. Computer programs have been developed for magnetic circuit design and coil design. Based on this, design charts have been developed to assist preliminary design of linear motor. These charts enable the designer to get outer diameter of the magnet, flux density in the gap, flux leakage factor and length of wire for a given output power and stroke. The design charts are applicable for the output power range of 10-100 Watts at motor efficiency of 75% with amplitude of the piston equal to ±5, ±6 and ±7 mm.