Development of a new forced convection heat transfer correlation for CO2 in both heating and cooling modes at supercritical pressures
Development of a new forced convection heat transfer correlation for CO2 in both heating and cooling modes at supercritical pressures
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DOI：
10.1016/j.ijthermalsci.2011.07.004
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发表时间：
2011-12
影响因子：
4.5
通讯作者：
Hongzhi Li;A. Kruizenga;M. Anderson;M. Corradini;Yu-shan Luo;Haijun Wang;Huixiong Li
中科院分区：
文献类型：
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作者：
Hongzhi Li;A. Kruizenga;M. Anderson;M. Corradini;Yu-shan Luo;Haijun Wang;Huixiong Li
本研究对原型印刷电路热交换器在冷却和加热条件下超临界压力下二氧化碳的强制对流换热进行了实验和数值研究。实验测试段有9个半圆形通道，水力直径为1.16 mm，长度为0.5 m。主要运行参数包括入口压力 7.5–10 MPa、质量通量 326 kg/m2s 和 762 kg/m2s、入口温度 10 °C 至 90 °C、平均热通量 30 kW/m2。除了重现常规实验案例外，数值模型还实现了 60 kW/m2 和 90 kW/m2 的更高热通量，以研究热通量的影响。实验与使用 SST k-w 模型的 FLUENT 模拟之间发现了良好的一致性，近壁区域已完全解析。系统地分析了超临界压力下加热和冷却模式之间对流传热的独特行为。开发了一种物理上更合理的属性平均技术，即基于概率密度函数 (PDF) 的时间平均属性，以解释属性对瞬时局部温度的非线性依赖性的影响。此外，将实验和计算数据与 Dittus-Boelter 和 Jackson 相关性的经验预测进行了比较。结果表明，Dittus-Boelter相关法对于预测传热系数平均值有较好的精度，但不能考虑热流密度的影响。相比之下，杰克逊相关性通过属性比率校正项来解释属性在径向方向上的分布，可以预测加热和冷却条件下传热特性的区别。然而，它高估了整个实验条件范围内传热系数的平均值。最后，开发了一种新的相关性，通过基于 PDF 的时间平均特性来评估超临界压力下加热和冷却模式下 CO2 的强制对流换热。将实验和计算数据与新开发的关联式的预测结果进行比较表明，它的效果相当好；即，在各种热通量的加热或冷却模式下，超过 90% 的数据预测精度在 ±25% 之内。
Experimental and numerical investigations on forced convection heat transfer of carbon dioxide at supercritical pressures in a prototypic printed circuit heat exchanger under both cooling and heating conditions have been performed in this present study. The experiment test section has nine semi-circular channels with a hydraulic diameter of 1.16 mm and a length of 0.5 m. Primary operational parameters include inlet pressure of 7.5–10 MPa, mass fluxes of 326 kg/m2s and 762 kg/m2s, inlet temperatures from 10 °C to 90 °C and the average heat flux was 30 kW/m2. Beyond reproducing the regular experimental cases, numerical modeling also implemented higher heat fluxes of 60 kW/m2and 90 kW/m2in order to investigate the effect of heat flux. Good agreement was found between the experiments and FLUENT simulations using an SST k–w model with the near-wall region being completely resolved. The distinctive behavior of convection heat transfer at supercritical pressures between heating and cooling modes was systematically analyzed. A more physically reasonable property-averaging technique, Probability Density Function (PDF)-based time-averaged property, was developed to account for the effect of nonlinear dependency of properties on instantaneous local temperature. Furthermore, experimental and computational data were compared to empirical predictions by the Dittus–Boelter and Jackson correlations. The results showed that Dittus–Boelter correlation has better precision for the average value of the predicted heat transfer coefficient but cannot take account of the effect of heat flux. In contrast, the Jackson correlation, with property ratio correction terms to account for the distribution of the properties in the radial direction, could predict the distinction of heat transfer characteristics under heating and cooling conditions. However, it overestimates the average value of heat transfer coefficient in the whole range of the experiment conditions. Finally, a new correlation evaluated by PDF-based time-averaged properties for forced convection heat transfer of CO2in both heating and cooling mode at supercritical pressures was developed. Comparison of experimental and computational data with the prediction results by the new developed correlation reveals that it works quite well; i.e., more than 90% data in either heating or cooling mode with various heat fluxes are predicted within an accuracy of ±25%.