Numerical simulation of fluid-structure coupled heat transfer characteristics of supercritical CO<sub>2</sub> pool heat transfer
Authors: Yu Bo-Wen , He Xiao-Tian , Xu Jin-Liang ,   Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy Utilization, North China Electric Power University, Beijing 102206, China,   Key Laboratory of Power Station Energy Transfer Conversion and System, Ministry of Education, North China Electric Power University, Beijing 102206, China
Published: April 2024

The heat transfer of supercritical pseudo-boiling has been preliminarily studied, but the definition of gas-liquid interface is still not unified. The fluid-structure coupling numerical simulation of heat transfer characteristics in supercritical CO<sub>2</sub> pool is carried out by using laminar flow model. Platinum wire is the heating element, with diameter <i>d</i> = 70 μm. The heat flux density <i>q</i><sub>w</sub> is in a range of 0–2000 kW/m<sup>2</sup>, and the pressure <i>P</i> is in a range of 8–10 MPa. Multi-scale mesh is used to model the heating wire, and simulation values accord well with the experimental data. The results show that due to the increase of the circumferential average Rayleigh number <i>Ra</i><sub>ave</sub> of the heating filament with <i>q</i><sub>w</sub>, the characteristic of the natural convection zone is that <i>h</i> increases with <i>q</i><sub>w</sub>. The temperatures of the four characteristic working conditions in the evaporation-like zone show a downward trend along the <i>r</i> direction. Through analogy with subcritical heat transfer and 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 according to 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> versus 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 transfer to the fluid outside the vapor-like membrane, leading the heat transfer coefficient <i>h</i> to decrease 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 of determining the gas-liquid interface of supercritical pool heat transfer is proposed. This method can effectively explain the heat transfer mechanism in the evaporation-like zone, and provide a theoretical basis for developing supercritical pool heat transfer in the future.