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Effects of surfactants on subcooled pool boiling characteristics: An experimental study
International Journal of Heat and Mass Transfer ( IF 5.2 ) Pub Date : 2022-09-19 , DOI: 10.1016/j.ijheatmasstransfer.2022.123419
Zhen Yang, Yuanpeng Yao, Huiying Wu

Surfactants are often used as additives to stabilize the dispersed phase of the water-based multicomponent fluids (such as non-azeotropic emulsion) for enhancing the boiling process, but their effects on the boiling heat transfer of water are still not clear. In this paper, a pool boiling experiment is designed to investigate the specific effects of surfactants (Tween20 (Polysorbate 20), Span20 (Arlasel 20), and Tween20-Span20 mixture) on the subcooled boiling heat transfer characteristics of pure water. The experimental results are analyzed by considering the influences of addition type and concentration of surfactant as well as the applied heat loads. It is found that: (1) Tween20 can achieve excellent boiling enhancing performance (decreasing the wall superheat by up to 10.4 °C and raising the boiling heat transfer coefficient by up to 13.4%) by increasing the number of nucleation sites. And the enhancement is improved with the increase of concentration when the heat flux is below a certain level, while it is weakened at high heat flux for Tween20 with a high concentration (1 mL L-1). The reason is that high concentration Tween20 results in an excessive increase of nucleation sites which prevents the return of working fluid and weakens the enhancement of heat transfer. (2) Span20 shows a boiling enhancement only when its concentration is 0.05 mL L-1 (lower than the CMC) among the test ones. Further increment in Span20 concentration (exceeding the CMC) leads to a large increase of wall superheat because it increases the viscosity of working fluid and deteriorates the heat transfer performance. (3) Tween20-Span20 mixture significantly aggravates the aforementioned boiling deterioration effect of Span20 (due to the reduced CMC for the mixture of Tween20 and Span20, weakening the heat transfer), and thus is not suitable for preparing boiling-heat-transfer-enhancing fluids. These results can provide a better understanding of surfactants and guide the practical preparation of multicomponent fluids for boiling heat transfer enhancement.



中文翻译:

表面活性剂对过冷池沸腾特性的影响:一项实验研究

表面活性剂常作为添加剂用于稳定水基多组分流体(如非共沸乳液)的分散相以增强沸腾过程,但其对水沸腾传热的影响尚不清楚。在本文中,设计了一个池沸腾实验来研究表面活性剂(Tween20 (Polysorbate 20)、Span20 (Arlasel 20) 和 Tween20-Span20 混合物)对纯水过冷沸腾传热特性的具体影响。通过考虑添加类型和表面活性剂浓度以及施加的热负荷的影响来分析实验结果。研究发现:(1) Tween20 可以实现优异的沸腾增强性能(使壁面过热度降低高达 10.4 ℃,沸腾传热系数提高高达 13。4%)通过增加成核位点的数量。并且当热通量低于一定水平时,这种增强随着浓度的增加而提高,而对于高浓度的 Tween20(1 mL L-1 )。原因是高浓度Tween20导致成核位点过多增加,阻碍了工质回流,削弱了传热增强作用。(2) Span20 仅在其浓度为 0.05 mL L -1时才显示出沸腾增强(低于 CMC)在测试中。Span20 浓度的进一步增加(超过 CMC)导致壁面过热度大幅增加,因为它增加了工作流体的粘度并恶化了传热性能。(3) Tween20-Span20 混合物显着加剧了 Span20 的上述沸腾劣化效应(由于 Tween20 和 Span20 混合物的 CMC 降低,传热减弱),因此不适合制备沸腾传热增强剂流体。这些结果可以更好地理解表面活性剂,并指导多组分流体的实际制备以增强沸腾传热。

更新日期:2022-09-19
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