Cryogenic Heat Exchanger With Photo-Etched Mini-Perforated Plates Allowing Flow-Bypass

Abstract

A perforated plate heat exchanger can be made very compact by the reduced perforation size. Hence, it fits to the field where high effectiveness but small size is demanded, i.e., cryogenic applications. The compactness of a perforated plate heat exchanger can even reach that of a cryogenic regenerator. We are developing a compact perforated plate heat exchanger for replacing a low-temperature regenerator. In the compact perforated plate heat exchanger, small perforations (diameter: ∼ 150 μm) were patterned by photo-etching on thin copper plate (75 μm thick). Spacers were made of Kapton film (25 μm thick) or stainless steel plate (30 μm thick). Kapton film spacer is for an experimental heat exchanger which requires convenient disassembly, and stainless steel spacer is for the final product which will be diffusion-bonded. In this type of heat exchanger, stream-to-channel convection heat transfer coefficient is so large that conduction along the plate can rather restrict overall heat transfer rate between cold and hot streams. In order to avoid such conduction-restricted overall heat transfer, 14 strip-shaped channels were formed spirally to reduce effective conduction length and enhance lateral conduction. Transverse bypass among cold or hot stream channels were also adopted to relieve flow mal-distribution. Thermal performance of the heat exchanger was both analyzed and experimented between liquid nitrogen temperature and room temperature. The result shows quite good agreement.