Plate-fin Heat-exchangers for a 10 kW Brayton Cryocooler and a 1 km HTS Cable

Abstract

Plate-fin heat exchangers (PFHX) are designed and fabricated for a cryogenic cooling system, serving for a 10 kW Brayton cryocooler and a 1 km HTS transmission cable under development in Korea. To achieve compactness and thermal efficiency at the same time, a recuperative HX for Brayton cycle and a sub-cooling HX of liquid nitrogen for HTS cable are designed as integrated parts. A key design feature is focused on the coldest part of sub-cooling HX, where the streams of liquid nitrogen and refrigerant (helium gas) are arranged as two-pass cross-flow so that the risk of freeze-out of liquid nitrogen can be reduced. Details of hardware PFHX design are presented and discussed towards its immediate application to the HTS cable system. A 10 kW Brayton cryocooler is under development in Korea as partial effort of the governmental project for hightemperature superconductor (HTS) power cable [1][2]. The goal of this project is to install and demonstrate the HTS cable and its cryogenic cooling system over 1 km length of transmission line (at 154 kV) in Jeju Island by 2016. The distributed thermal load is carried by a circulating flow of liquid nitrogen (LN) to the Brayton cooler [2]-[4] which is