Abstract:

As an efficient heat dissipation device, microchannel heat sinks have been widely used to solve the problem of high heat flux dissipation in micro-electronic devices, photoelectricity, automotive, aerospace industries and energy field and so on. To solve the problems of small heat transfer area, low heat transfer performance and boiling hysteresis of traditional smooth microchannels, a porous wall microchannel structure was proposed in this paper, and laser direct writing method was used to prepare efficient and stable porous wall microchannels. The porous wall microchannel significantly increases the heat transfer area, promotes the disturbance of the fluid, and provides many stable boiling cores, thereby enhancing single-phase and two-phase heat transfer. By building a microchannel heat transfer performance test system, the single-phase and two-phase heat transfer performance of porous wall microchannels and smooth microchannels were tested and compared. Experimental results indicated that the Nu number of porous wall microchannel was increased by 21%—31% compared with the untreated rectangular microchannel. In two-phase boiling heat transfer, porous structure promoted the nucleation of boiling bubbles and reduced the onset temperature of nucleate boiling (ONB), which was 35% lower than that of the untreated rectangular microchannel. At the same time, porous structure could ensure continuous liquid supply during the boiling process, thereby greatly improving the boiling heat transfer performance and avoiding the occurrence of drying out in advance. The two-phase boiling heat transfer coefficient h_tp was up to 83% higher than that of the untreated rectangular microchannel. The two-phase heat transfer coefficient h_tp of porous wall microchannel structure at the mass flux of G=500kg/(m²·s) was increased by 30% compared with that at the mass flux of G=200kg/(m²·s).

Key words: microchannel, heat transfer, two-phase flow, laser direct writing, porous structure

摘要：

微通道散热器作为一种高效散热器件，广泛应用于微电子、光电、汽车、航天国防、能源等领域。针对传统光滑微通道传热面积小、换热性能偏低、沸腾迟滞等问题，本文提出一种多孔壁面微通道结构，并采用激光直写方法实现微通道多孔壁面的高效、稳定生成。该多孔壁面微通道显著增大了换热面积、促进流体的扰动、提供大量稳定沸腾核心，从而强化单相与两相沸腾传热。通过搭建微通道换热性能测试系统，测试对比了多孔壁面微通道与光滑微通道的单相对流、两相沸腾传热性能。发现多孔壁面微通道的Nu数相对于光滑微通道提升了21%~31%。在两相沸腾换热过程中，其粗糙多孔结构促进了沸腾气泡成核，其核态沸腾起始温度相比于光滑微通道降低了35%。同时粗糙多孔结构可以保证沸腾过程中的液体持续供给，从而大幅提升了沸腾换热能力，避免了干涸现象的提前发生，其两相沸腾换热系数相对于未处理的光滑微通道最大提升了83%。此外，还开展了不同流量下多孔壁面微通道的沸腾传热性能测试，发现在质量流率为G=500kg/(m²·s)下的沸腾换热系数相对于G=200kg/(m²·s)情况下最大提升了30%。

关键词: 微通道, 传热, 两相流, 激光直写, 多孔结构