Steady-state transverse heat transfer in a single channel CICC

Abstract

Current mathematical models and numerical codes used for thermal–hydraulic analyses of forced-flow superconducting cables used in the fusion technology, such as, e.g. Cable-in-Conduit Conductors (CICCs), are typically 1D. They demand reliable constitutive expressions for the transverse momentum, energy and optionally also mass transport processes occurring between different parallel conductor components, in order to reliably simulate the behavior of any superconducting magnet design either at normal operating conditions or during a quench evolution. Energy transport processes can effectively be expressed using heat transfer coefficient (HTC) and the considered wetted perimeter/surface. Only few HTC correlations for flow in a CICC bundle have been proposed in the literature, but none of them is widely accepted for predictive use. As a result, in thermal-hydraulic studies of conductors designed for the EU-DEMO coils standard heat transfer correlations for flows in smooth tubes are utilized, although they do not seem very appropriate for CICCs. Systematic measurements of heat transfer coefficients in a CICC bundle should be conducted to provide an experimental database for further trials to develop a reliable predictive heat transfer correlation. In the present work we report the results of measurements of the steady-state HTC between a jacket wall and demineralised water flowing (i) in a smooth tube and (ii) in a CICC bundle of the reference sample (JT60-SA TF conductor). The measurements were carried out at the THETIS installation. We used four values of water inlet temperature, in the range 30–68 °C, and various mass flow rates, in the range 0.15 – 0.40 kg/s, to obtain the results in possibly wide range of Pr and Re numbers. The experimental values of HTC for CICC slightly increased with the mass flow rate from about 7500 to 9400 W/(m2∙K) in the considered Re range (890–3490) and were almost independent on temperature. The performed experiment was also simulated with the THEA code for additional validation of the obtained HTC values.