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The flow structures were investigated around micro bubbles on extremely thin wires during subcooled nucleate boiling.Jet flows emanating from the bubbles were observed visually with the fluid field measurement using high-speed photography and a PIV system.The jet flows induced a strong pumping effect around a bubble.The multi-jet structure was further observed experimentally, indicating the evolution of flow structure around micro bubbles.Numerical simulations explore that the jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire.The bubble interface with multi-jet structure has abnormal temperature distribution such that the coolest parts were observed at two sides of a bubble extending into the subcooled bulk liquid rather than at the top.Evaporation and condensation on the bubble interface play important roles not only in controlling the intensity of the jet flow,but also in bringing out the multi-jet structure. 相似文献
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一、引言 理论和实验研究表明,高过冷度时膜沸腾传热将主要受流动参数和特性参数的支配,而与壁面温度的高低很少有关,存在着所谓的“自模化”。然而,实验观察和研究也显露出热负荷比较高时,膜沸腾会因微小的加热波动出现急剧的壁温上升,此时,“自模化”已不再存在,壁温将对传热有明显的影响。新的分析表明,极高过冷度液体的流动膜沸腾势必要求壁温急剧上升来维持很高的传热强度,并且这种壁温上升现象也不同于 相似文献
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