Development of small 2K cryocooler (II)-high efficient and low pressure drop heat exchanger-

This paper describes a design and experimental results of a recuperative heat exchanger used in a small 2K cryocooler. High and low pressures for this heat exchanger are about 1.0 MPa and 1.6 kPa respectively. The technical point of this heat exchanger is a low pressure drop in low pressure path. To keep a high heat transfer and a low pressure drop, small copper spheres, 3 mm in diameter, are filled in the low pressure path. Copper spheres are stuck each other and also stuck with a copper tube for a high pressure path. To reduce the heat conduction loss through the copper spheres, stainless steel screen meshes separate the spheres into small segments. The heat exchanger diameter and length are optimized from a viewpoint of an efficiency and a pressure drop. Details of the design and experimental results of the heat exchangers are presented.