Abstract:

Based on the flow heat transfer experimental data, the ability of different turbulence models to predict heat transfer on supercritical CO₂(S-CO₂) was evaluated and selected, and the SST k-ω turbulence model was confirmed as the optimal model. The effects of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the convective heat transfer characteristics of S-CO₂ were analyzed in a vertical heating tube with an inner diameter of 10mm.The results showed that Bu<10^-5, Bu*<5.6×10^-7 and K_v<3×10^-6 were not satisfied in some working conditions, indicating the effects of buoyance and flow acceleration could not explain the heat transfer characteristic at high mass flux. Based on the supercritical boiling theory, the S-CO₂ boiling heat transfer model in vertical heating tube was established, and the deterioration of S-CO₂ heat transfer was described. The detailed distribution of S-CO₂ thermophysical properties and turbulence in the radial direction showed that the supercritical heat transfer was greatly affected by the thickness of the pseudo-gas film, the thermal properties of the quasi-gas film and the turbulent kinetic energy in the near-wall region. The heat transfer mechanism of S-CO₂ at high mass flux was explained successfully. By introducing the supercritical boiling number, a heat transfer correlation formula for high quality flow rate was proposed.

Key words: supercritical CO₂, high mass flux, heat transfer, correction, numerical calculation

摘要：

利用已有的流动传热实验数据，对不同湍流模型预测超临界CO₂（S-CO₂）传热能力进行了评价及选取，确定了SST k-ω 湍流模型为最优模型。分析了入口温度、热流密度、质量流速、浮升力和流动加速效应对内径为10mm的垂直加热管内S-CO₂的对流传热特性的影响。结果表明：在一些工况条件下Bu<10^-5、Bu*<5.6×10^-7和K_v<3×10^-6并不满足，表明浮升力和流动加速度效应并不能解释高质量流速下的数值模拟结果。基于超临界类沸腾理论，建立了垂直加热管内S-CO₂类沸腾传热模型，并阐述了S-CO₂传热恶化现象，径向方向上S-CO₂热物性和湍流的详细分布表明超临界传热受类气膜的厚度、类气膜的热性质和近壁区湍流动能的影响很大，成功解释了S-CO₂在高质量流速下的传热机理。最后引入超临界沸腾数SBO，提出了适用高质量流速的传热关联式。

关键词: 超临界二氧化碳, 高质量流速, 传热, 关联式, 数值计算