An Experimental Study of the Phase Shift between Piston and Displacer in a Stirling Cryocooler

Abstract

Small cryocoolers are being widely applied to the areas of infrared detectors, superconductor filters, satellite communication, and cryopumps. Cryocoolers that utilize the Stirling cycle are characterized by small size, lightweight, low power consumption, and high reliability. For these reasons, FPFD (Free Piston Free Displacer) Stirling cryocoolers are widely used not only in tactical infrared imaging cameras, but also in medical diagnostic equipment. In this study, a Stirling cryocooler actuated by the electric force of a dual linear motor has been designed and manufactured. Next, to understand the operation of the cooler, the displacement of the piston has been measured by LVDTs (Linear Variable Differential Transformers), the displacement of the displacer has been measured via a laser optic method, and the phase shift between the piston and displacer has been analyzed. Finally, when the phase shift between displacement of the piston and displacer is 45°, the operating frequency is optimum and is decided by the resonant frequency of the expander, the mass and cross-sectional area of the displacer, and by friction and flow resistances.