Studies of heat transport in cryogenic fluids toward superconducting applications

To meet the increasing global energy demand with minimal green house effect, electrical energy is a viable option. But, it requires an efficient electrical power system with optimal loss. Towards this, superconducting materials represent a promising way of improving the existing systems. However, the efficiency may be affected by a small temperature increase due to electromagnetic losses induced by time-varying magnetic fields. To minimize this, two approaches can be considered (i) reduce the losses and (ii) improve the heat exchange with the cooling environment. Although experimental and theoretical studies of the superconducting losses have been extensively pursued [1], few attempts have been made to combine the 'losses' and the 'cooling' aspects in the current scenario. Such studies require a detailed characterization of magneto-thermal interaction of the superconductors, as well as fundamental aspects of heat draining by the cryogenic fluid. Towards this, numerical studies on natural convection in an enclosed cavity, interacting with a constant heat source (heater) are carried out to understand the cooling efficiency of the cryogenic fluids (viz., liquid nitrogen, silicon oil and water). Natural convection heat transfer in an enclosure continues to be an active research area, due to its significance for both fundamental interests and engineering applications. Majority of the published studies can be classified into two groups: enclosure heated from below and cooled from above (Rayleigh–Bénard problem) and differentially heated enclosures [2]. Considerable attention has been given to natural convection from vertical/horizontal enclosures specified either with constant temperature or heat flux, while limited studies has been done with constant volumetric heat source [3]. The resulting characteristics of fluid flow and heat transfer are quite interesting and deserve a detailed investigation, which motivates for the present work. As a priori, three dimensional steady forms of incompressible Navier-Stokes equations are solved through finite volume approach [4]. Detailed flow features are presented in terms of velocity, temperature and path line profiles for different heater lengths. Comparative analyses are further reinforced in terms of average Nusselt number (Nu) for different fluids. It shows that, effective heat transfer enhancement occurs for liquid nitrogen with the shortest heater length, resulting in an efficient cooling. The profile of temperature and velocity magnitude distributions agrees well with the in-house experiment. Benchmark validation is found to be satisfactorily against the reported result [5]. Complete descriptions on geometrical details, governing equations, boundary conditions and solution methodology adopted for the numerical solution will be provided in full length paper. This study will be a gateway for further magneto-thermal analysis in an electromagnetic environment.