Influence of inlet vapour quality perturbations on the transient response of flow-boiling heat transfer
Influence of inlet vapour quality perturbations on the transient response of flow-boiling heat transfer
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DOI：
10.1016/j.ijheatmasstransfer.2021.121017
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发表时间：
2021-05
影响因子：
5.2
通讯作者：
J. Dirker;W. van den Bergh;H. Moran;C. Markides;J. Meyer
中科院分区：
文献类型：
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作者：
J. Dirker;W. van den Bergh;H. Moran;C. Markides;J. Meyer
对于通常用于聚光太阳能有机朗肯循环系统的一些制冷剂，暂态热流密度对管内沸腾的影响尚未得到广泛研究。在本研究中，考虑了流动沸腾试验段入口蒸汽质量的突然阶跃变化（向上和向下）对换热系数的影响。实验采用R-245fa在饱和温度为35℃的800 mm水平光滑管内进行，内径为8.31 mm，测试截面热流密度为7.5 kW/m2。初始进口蒸汽质量在0.15和0.40的基值之间，质量通量为200和300 kg/m2s。确定了稳态条件下的基线传热系数，随后进行了一系列瞬态响应研究。为此，考虑了进口蒸汽质量的急剧上升和下降阶跃扰动。结果表明，当蒸汽质量阶跃大小为0.13时，实际换热系数与期望的准稳态换热系数存在差异。在下降阶段，传热系数比预期高8.7 ~ 11.7%，而在上升阶段，当质量通量为200 kg/m2s时，传热系数比预期低9.3 ~ 26.0%，具体取决于初始进口蒸汽质量。当质量通量为300 kg/m2s时，下台阶和上台阶的质量通量分别提高7.2%和16.7%，降低13.8%到17.8%。
The effect a transient heat flux has on in-tube boiling has not been studied extensively for some refrigerants commonly proposed for use in concentrated solar power organic Rankine cycle systems. In this study, the effect of abrupt step changes (upwards and downwards) in the inlet vapour quality to a flow-boiling test section on the heat transfer coefficient was considered. Tests were conducted with R-245fa at a saturation temperature of 35°C in an 800 mm horizontal smooth tube with an inner diameter of 8.31 mm and a constant test section heat flux of 7.5 kW/m2. Initial inlet vapour qualities ranged between base values of 0.15 and 0.40 with mass fluxes of 200 and 300 kg/m2s. Baseline heat transfer coefficients at steady-state conditions were determined, followed by a series of transient-state response investigations. For these, sharp upward and downward step perturbations of the inlet vapour quality were considered. It was found that for a step size magnitude of 0.13 in the vapour quality, the actual heat transfer coefficient differed from the expected quasi-steady-state heat transfer coefficients during the transient. During the downward step, it was 8.7 to 11.7% higher than the expected heat transfer coefficient, while during the upward step, it was 9.3 to 26.0% lower for a mass flux of 200 kg/m2s, depending on the initial inlet vapour quality. For a mass flux of 300 kg/m2s, it was 7.2% and 16.7% higher and 13.8 to 17.8% lower for the downward and upward step respectively.