Entropy Generation Minimization (EGM) in High Temperature Superconducting (HTS) cables for optimization of thermohydraulic performance

Abstract

High Temperature Superconducting (HTS) cables have potential merits of large current carrying capacity and compactness with reduced transmission losses and Right-of-Way (RoW) compared to conventional transmission power cables. However, internal forced convective cooling is necessary to cool HTS cables using cryogenic coolant such as liquid nitrogen (LN2) to retain the superconductivity for efficient power transmission. Due to forced convective cooling, inevitable pressure drop occurs in these cables and result in development of temperature and velocity gradients. Further, the accounted temperature and velocity gradients in HTS cables lead to volumetric entropy generation which causes reduction in thermohydraulic performance.The present work focuses at investigating the volumetric entropy generation rate in HTS cable. Further, Entropy Generation Minimization (EGM) technique is used as an optimization tool to estimate the minimum volumetric entropy generation rate to optimize thermohydraulic performance in HTS cables. Furthermore, pumping power and cooling capacity at minimum entropy generation rate are calculated. Computational Fluid Dynamics (CFD) is used to analyze the pressure drop and heat transfer rate for different flow rates to estimate the friction factor, pumping power and cooling capacity with flow of LN2 in corrugated former in HTS cable. A 3D computational geometry is developed using commercial software ANSYS®. Relevant boundary conditions are imposed on the computational geometry to reflect the practical operating conditions of HTS cable. Finite Volume Method (FVM) of discretization is used to solve the governing equations in order to obtain pressure drop and heat transfer rate in HTS cables. The simulated results are validated with the results available in literature. From the analysis, it is identified that at a heat load of 2.1 W/m and at an inlet temperature of 77 K, optimum cooling capacity and pumping power with minimum entropy generation rate are possible at a flow rate of 14 L/min.