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

本研究的目的是获得如何利用流动沸腾传热来开发高热负荷电子设备的创新散热系统的基础知识。本研究是在实际案例中遇到的窄工作流道和小流量条件下进行的，以水作为工作流体来满足高源功率的要求和环境问题。在研究中，对重要的设计因素压降、换热系数和最大热流密度进行了实验研究。进行了两种类型的研究。一是根据实验室先前获得的细圆管内的实验数据，提出了压降和传热系数的相关性。另一个是窄矩形通道的换热与压降实验研究，通道宽度分别为1.0和1.5 mm，通道宽度分别为20mm和80mm（加热长度为40mm）。从第一项研究来看，细圆管内的压降、p值和沸腾换热系数可以通过在正常尺寸管中建立的关系式来预测，并额外考虑了蒸汽流动的大影响。在第二项研究中，实验测量了在质量通量为16 ~ 76 kg/m^2s时的压降、换热系数和最大热流密度。实验的主要发现如下。由于最大压降可达500pa，因此比圆管的压降小得多，因此建议缝隙尺寸小于1.0 mm。然而，压降的波动要比管内的大得多。热流密度与壁面过热度的关系中，管内换热系数与管内换热系数相似，但矩形管内换热系数与壁面过热度的关系与圆形管内换热系数不同。用圆管建立的相关系数对最大热流密度的预测过高，而用矩形通道建立的相关系数对最大热流密度的预测较好。液相在通道截面上的分布对换热系数和最大热流密度有显著影响。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