New analytical method for single-phase convective heat transfer and unified mechanism analyses on buoyancy-induced supercritical convective heat transfer deterioration

Single-phase convective heat transfer process can be regarded as a combination of two simultaneous processes, inner heat flux diffusion and absorption/release by equivalent inner heat sources, based on the analogy of convective heat transfer to conductive heat transfer. Inspired by this idea, a new analytical method for sing-phase convective heat transfer was developed from the perspective of synergy between equivalent inner heat source efficiency field (h' field) and effective thermal conductivity field (lambda(eff) field). This new method employs h(c) and w' to quantize the effects of h' field and lambda(eff) field on convective heat transfer, making a quantitative and comprehensive analysis for most single-phase convective heat transfer phenomena possible. Subsequently, the buoyancy-induced convective heat transfer deterioration (HTD) of supercritical water under heating boundary conditions were analyzed using this new method. It was found that the supercritical HTD for upward flow is caused by the decline of both the lambda(eff) and h' fields, especially in the near-wall regions. While, the supercritical HTD at the top part of the wall for horizontal flow is due to the fact that the high-value part of the h' field is moved downward by a pair of vortices induced by buoyancy. Thus, the inner heat fluxes released from the top part of the wall have to be diffused through a much longer distance, leading to the HTD. (C) 2019 Elsevier Ltd. All rights reserved.