Modelling of the fin type heat exchanger for the HTS current leads of W7-X and JT-60SA

The Forschungszentrum Karlsruhe has taken over the responsibility for the design, construction and testing of the high temperature superconductor (HTS) current leads for two fusion experiments, i.e. the stellarator Wendelstein 7-X (W7-X) and the satellite tokamak JT-60SA. One important task for the design of the HTS current lead is the heat exchanger (HEX). In the current leads for W7-X and JT-60SA the HEX consists of the central conductor with meander flow fins to achieve a cross flow HEX. A design optimisation requires the knowledge of the heat transfer characteristics of the HEX. Therefore, 3D CFD simulations were performed to compute local Nusselt and Reynolds numbers. From the CFD results a 1D system code description and heat transfer correlations have been deduced. This paper describes the 3D-CFD and 1D system code as well as the results of the numerical calculations. The results were validated using experimental results of HEX mock-ups. The model was extended to the HEX covering the temperature range between 60 K and room temperature leading to a single Nusselt-Reynolds number correlation. Finally the parameters for optimised HTS current leads for W7-X and JT-60SA are presented.