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Title: Numerical Investigation on Characteristics of Supercritical CO2 Heat Transfer in Vertical Circular Tubes with Circumferentially Half-Side Heating
题目：半周加热垂直圆管内超临界CO2传热特性研究
Authors: ZHANG Yan, ZHANG Xinyi, YAN Chenshuai, WU Wenhua, GAO Erman
作者：张炎，张鑫奕，闫晨帅，武文华，高尔蔓
单位：东北电力大学能源与动力工程学院
Journal of Thermal Science, 2024, 33(5): 1744-1756.
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摘要
Abstract: The design of heat exchangers in the advanced supercritical power conversion system cannot be separated from the study of heat transfer issues. Half-side heating mode is often encountered for solar receiver and supercritical boiler. Here, the characteristics of supercritical CO2 (sCO2) convection heat transfer in vertical tubes with circumferentially half-side heating was numerically investigated through the SST k-ω turbulent model which matches well with the experimental data. Then, heat transfer between sCO2 upflow and downflow was compared. Similar to film boiling heat transfer at subcritical pressure, numerical results were processed according to the supercritical pseudo-phase transition hypothesis, with liquid-like phase in the tube core region and vapor-like film in the region near the heated tube wall. The structure of two layers was demarcated by pseudo-critical temperature Tpc. Therefore, sCO2 heat transfer was assessed according to double thermal resistances caused by vapor-like film near the wall and core liquid-like phase. The findings suggest that wall temperature for upflow is higher than that for downflow, which is attributed to larger thermal resistance in the fluid domain for upflow than that for downflow. The difference guarantees the excellent heat transfer performance for downflow than upflow. It is also further concluded that the formation of vapor-like film near the wall due to pseudo-phase transition plays a key role in dominating wall temperature and inducing heat transfer deterioration in half-side heating tubes. The present contribution is significant to the design of supercritical heat exchanger under half-side heating mode.
摘要：换热器热设计是超临界CO2布雷顿循环发电系统涉及的关键问题之一。太阳能集热器和超临界CO2锅炉冷却壁通常会存在半周加热圆管的传热模式。然而，半周加热垂直圆管内超临界CO2换热特性（特别是传热恶化机理）尚不清晰，严重制约了超临界换热器的开发设计。本文对半周加热垂直圆管内超临界CO2对流换热特性进行数值研究，分析了不同运行参数下流动方向对超临界CO2换热的影响。类比于亚临界膜态沸腾，基于类相变假设对超临界CO2换热计算结果进行处理，即类临界温度Tpc将管内超临界CO2划分为核心类液相区和近管壁类气膜。进一步地，采用近壁类气膜和核心类液相的双重热阻评估超临界CO2换热能力。计算结果表明，对比向下流动，超临界CO2向上流动的传热阻力更大，合理解释了向上流动壁温高于向下流动的原因。而且，近壁类气膜的形成是控制壁温变化、诱导传热恶化发生的关键因素。研究结果对半周加热模式下超临界换热器设计具有重要的理论指导价值。
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引用格式
ZHANG Yan, ZHANG Xinyi, YAN Chenshuai, WU Wenhua, GAO Erman, Numerical Investigation on Characteristics of Supercritical CO2 Heat Transfer in Vertical Circular Tubes with Circumferentially Half-Side Heating, Journal of Thermal Science, 2024, 33(5): 1744-1756.
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