Development of heat dissipation system for electronic devices using flow boiling heat transfer

本研究的目的是了解如何利用流动沸腾换热来开发高热负荷电子器件的新型散热系统。本研究是在实际应用中遇到的工作流道窄、流量小的情况下进行的，采用水作为工质，以满足大功率和环境问题的要求。在这项研究中，对压力降、换热系数和最大热流密度这三个重要的设计因素进行了实验研究。一是根据本实验室已有的细长圆管内的实验数据，提出了压降与换热系数的关联式。另一种是窄缝矩形通道内的换热和压降的实验研究，分别为1 mm和1.5 mm缝隙、20 mm宽和80 mm长(加热长度为40 mm)。从第一个研究开始，压力滴头…细圆管内较大的p和沸腾换热系数可通过在常规管内建立的关联式来预测，同时考虑蒸汽流动的较大影响。在第二个实验中，测量了压力降、换热系数和质量流量为16~76 kg/m~2s时的最大热流密度。实验的主要发现如下。建议采用较小的间隙尺寸，最大压降可达500Pa.然后压降远低于圆管，建议采用小于1.0 mm的间隙。然而，压力降的波动比管内的要大得多。在热流密度与壁面过热度的关系上，管内换热系数与管内换热系数相似，但矩形通道内换热系数与局部质量的关系不同于圆管内的换热系数。针对圆管建立的关联式大大高估了最大热流密度，而利用矩形通道的数据建立的关联式给出了更好的预测。通道横截面上的液相分布对换热系数和最大热流密度有显著影响。较少

The purpose of this study is to obtain fundamental knowledge how to make use of flow boiling heat transfer to develop innovated heat dissipation system for high heat loaded electronic devices. This study was performed under conditions of narrow working flow path and low flow rate which are encountered in practical cases and used water as a working fluid to meet requirements of high source power and environmental issues. In the study pressure drop, heat transfer coefficient, and maximum heat flux which are important design factors are experimentally examined.Two types of studies were performed. One was to propose correlations for pressure drop and heat transfer coefficient in terms of experimental data in a fine circular tube previously obtained in our laboratory. The other was an experimental investigation about heat transfer and pressure drop in narrow rectangular channels, 1.0 and 1.5 mm gap and 20 mm width and 80 mm length (40 mm heated length).From the first study, the pressure dro … More p and boiling heat transfer coefficient in a fine circular tube could be predicted by correlations developed in a normal size tube by taking additional account of large effect of vapor flow. In the second study, experiments were performed to measure pressure drop, heat transfer coefficient, and maximum heat flux at mass flux of 16 to 76 kg/m^2s. The major findings of the experiments are as follows. Smaller gap size, than 1.0 mm was suggested since the maximum pressure drop as much as 500 Pa and then the pressure drop is much lower than the circular tube. However, the fluctuation of the pressure drop is much larger than that in the tube. The heat transfer coefficients are similar between the tube and the channel in the relationship between heat flux and wall superheat, but the relationship in the rectangular channel between the coefficient and local quality is different form that in the circular tube. The correlation developed for circular tubes highly overpredicted the maximum heat flux and the correlation developed by using data of rectangular channels give much better prediction. The liquid phase distribution in the cross section of the channel significantly affects the heat transfer coefficient and maximum heat flux. Less