Numerical simulation of fluid-structure coupled heat transfer characteristics of supercritical CO₂ pool heat transfer

Abstract

The heat transfer of supercritical pseudo-boiling has been preliminarily studied, but the definition of gas-liquid interface is still not uniform. The fluid-structure coupling numerical simulation of heat transfer characteristics in supercritical CO<sub>2</sub> pool was carried out using laminar flow model, Platinum wire is the heating element, <i>d</i>=70 μm, the <i>q</i><sub>w</sub> range is 0~2000 kW/m<sup>2</sup>, the <i>P</i> range is 8~10 MPa, multi-scale mesh is used to model the heating wire, simulated values agree well with the experimental data. The results show that the natural convection zone is characterized by an increase in <i>h</i> with <i>q</i><sub>w</sub> due to an increase in the circumferential average Rayleigh number <i>Ra</i><sub>ave</sub> of the heating filament with <i>q</i><sub>w</sub>. The temperatures of the four characteristic working conditions in the evaporation-like zone of the class show a decreasing trend along the <i>r</i> direction. Analogy with subcritical heat transfer, by calculating the thermal conductivity ratio <i>Q</i><sub>con</sub>/<i>Q</i><sub>t</sub>, the supercritical is divided into three regions, <i>T</i><<i>T</i><sub>L</sub> is liquid-like region (LL), <i>T</i><sub>L</sub><<i>T</i><<i>T</i><sub>M</sub> is two-phase-like region (TPL), <i>T</i>><i>T</i><sub>M</sub> is vapor-like region (VL), the rule is the same as that of <i>x</i> partition with supercritical pseudo-boiling dryness; According to the curves of average thermal conductivity <i>λ</i><sub>ave</sub> and thermal resistance <i>R</i><sub>G</sub> with heat flux <i>q</i><sub>w</sub> determined by calculating thermal conductivity ratio, the variation law of heat transfer coefficient <i>h</i> with <i>q</i><sub>w</sub> in evaporation-like region can be well explained, as <i>q</i><sub>w</sub> increases, the thermal conductivity thermal resistance <i>R</i><sub>G</sub> increases, and the heat from the heating filament is difficult to be transferred to the fluid outside the vapor-like membrane, leading to a decrease in the heat transfer coefficient <i>h</i> when <i>q</i><sub>A</sub><<i>q</i><sub>w</sub><<i>q</i><sub>C</sub>, and a significant increase in <i>λ</i><sub>ave</sub> when <i>q</i><sub>w</sub>><i>q</i><sub>C</sub>, and the recovery of heat transfer when <i>h</i> rises again.In this paper, a new method for determining the gas-liquid interface of supercritical pool heat transfer is proposed, which explains the heat transfer mechanism of evaporation-like zone well, and provides a theoretical basis for the development of supercritical pool heat transfer in the future.