Abstract:

In order to meet the environmental protection requirements and enhance the flow boiling heat transfer capacity of microchannel heat sinks, a new environmentally friendly low surface tension working fluid, SF-33, was selected for flow boiling heat transfer research. Large-sized microchannel heat sink with an open gap between the top of channels and the bottom of the cover plate was designed and fabricated. A flow boiling heat transfer experimental platform was established. The characteristics of subcooled flow boiling heat transfer and pressure drop of the low surface tension coolant SF-33 at different inlet temperatures and mass fluxes were investigated. The influence of flow pattern transitions on heat transfer was analyzed based on visualization results. The results revealed the presence of four flow patterns, including bubbly flow, slug flow, slug-localized churn flow, and slug-localized stratified flow. The open structure and large flow space affected the flow pattern distribution inside the microchannel heat sink. With the increase in heat flux and outlet vapor quality, both the heat transfer coefficient and pressure drop of the microchannel flow boiling increased gradually. Lowering the coolant's inlet temperature could delay the occurrence of CHF and reduce the inlet and outlet pressure drops. Additionally, it was observed that under different mass flux conditions, there were significant differences in the trend of inlet and outlet pressure drop changes with increasing heat flux.

Key words: open microchannel, low surface tension coolant, SF-33, flow boiling, heat transfer

摘要：

为满足环保要求并提高微通道热沉的流动沸腾换热能力，本文选用一种新型的环境友好型低表面张力工质SF-33进行流动沸腾换热研究，设计并制备了在通道顶部与盖板底部间具有开放间隙的大尺寸微通道热沉，搭建了流动沸腾换热实验平台，探究SF-33在不同入口温度、质量流速下的过冷沸腾换热特性及压降特性，并基于可视化结果分析流型转变对换热的影响。结果发现，在本文工况范围内出现了4种流型，包括泡状流、弹状流、气弹-局部搅混流及气弹-局部分层流，开放结构以及较大的流通空间影响了微通道热沉内的流型布局。随着热流密度及出口干度的增加，微通道的换热系数及压降均随热流密度的增加而逐渐增大。降低工质入口温度，能够延缓临界热流密度（CHF）的发生，同时减小进出口压降。并且发现在不同质量流速条件下，随着热流密度增加，进出口压降的变化趋势存在显著差异。

关键词: 开放型微通道, 低表面张力工质, SF-33, 流动沸腾, 换热