CtFD-based correlations for the thermal-hydraulics of an HTS current lead meander-flow heat exchanger in turbulent flow.

The Karlsruhe Institute of Technology is responsible for the design, construction and testing of the high temperature superconductor (HTS) current leads for the Wendelstein 7-X stellarator and for the JT-60SA tokamak. These HTS current leads mount a heat exchanger of the meander-flow type, in which the helium flows between the fins and is forced to cross flow with respect to the central Cu bar, which actually carries the current. Since an important issue in the operation of the HTS current lead is the optimization of the cooling power consumption, the helium thermal-hydraulics in such complex geometry becomes rather important. In this paper we extend a computational thermal fluid dynamics (CtFD) technique, previously introduced by the same authors and validated on short samples of meander flow heat exchanger and on the W7-X HTS current lead prototype, to a systematic analysis of the helium thermal-fluid dynamics inside different meander flow geometries. The first aim is to clarify under what operative conditions the flow regime can be considered turbulent and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and the heat transfer in the meander flow geometry have also been derived, which are applicable with good accuracy for the design of HXs over a broad range of geometries.