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中国物理学会期刊

液态金属软表面池沸腾传热的实验研究

CSTR: 32037.14.aps.70.20202053

Enhanced pool boiling heat transfer on soft liquid metal surface

CSTR: 32037.14.aps.70.20202053
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  • 池沸腾是一种高效的传热方式, 目前主要通过刚性固体表面改性强化沸腾传热. 本文以乙醇为工质, 实验研究了光滑铜表面和液态金属软表面池沸腾传热. 发现液态金属软表面可有效降低沸腾起始点(ONB)壁面过热度, 饱和沸腾时, ONB壁面过热度从光滑铜表面的约18 ℃降低到软表面的约6 ℃, 沸腾传热系数最大提高了149%. 与光滑铜表面相比, 液态金属软表面增加了汽泡核化穴数量, 减小了汽泡尺寸, 提高了汽泡脱离频率. 观察到软表面弹性毛细波和汽泡射流现象. 弹性毛细波增强了壁面热边界层热质传递. 发现汽泡脱离过程中, 汽泡尾部在液态金属薄层内形成残余核化穴, 残余核化穴快速长大, 与上升的大汽泡聚合, 形成汽泡射流现象. 弹性毛细波及汽泡射流解释了液态金属软表面强化池沸腾传热的机理.

     

    Pool boiling is a high-efficient energy transfer method through the gas-liquid phase transition. It has the characteristics of small heat transfer temperature difference and high heat flux density. The current enhancement of boiling heat transfer is realized mainly through modifying the solid heating surface. So far, there has been no report on the study of pool boiling heat transfer on soft surfaces. Therefore, in this work the pool boiling heat transfer performances of ethanol on the copper surface and soft liquid metal surface are investigated experimentally. The experimental results indicate that soft surface can effectively reduce the wall superheat corresponding to the onset of boiling (ONB). In saturation boiling, the superheat of the wall surface at ONB is reduced by nearly 12 ℃, while the heat transfer coefficient is improved by 149%. It is found that soft surface enhances pool boiling heat transfer performance significantly by increasing nucleate site density, reducing the bubble departure diameter, and increasing bubble departure frequency. Unlike the copper surface, the soft surface deforms elastically under the action of the vertical component of surface tension γlvsinθ at the three-phase contact line of the vapor bubble. From the perspective of surface energy analysis, the difference in surface energy ΔELM between before and after bubble departure on soft liquid metal surface is smaller than in smooth surface ΔECS. The potential barrier of the soft surface is smaller than of the copper surface, and the buoyancy required for bubble separation is small, and the bubble is easy to separate. Elastocapillary wave and bubble jet phenomenon on the soft surface are observed particularly, which are generated on liquid metal under the action of elastic restoring force. The fluctuation of elastocapillary wave contributes to the enhancement of heat and mass transfer in thermal boundary layer and the generation of residual nucleation site. The residual bubble grows up rapidly and coalesces with the rising large bubble, forming bubble jet phenomenon. Elastocapillary wave and bubble jet contribute to the enhancement of pool boiling heat transfer on soft liquid metal surface.

     

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