不同微流道形狀散熱器性能之數值研究

Numerical Study on the Heat Sink Performance of Microchannels with Different Channel Shapes

10.6840/cycu201700123

陳玉新

通道形狀 ； 通道長度 ； 散熱器 ； 多噴嘴式微通道散熱器 ； 熱阻抗 ； 溫度均勻性 ； Channel shapes ； channel length ； heat sink ； multi-nozzle microchannel heat sink ； thermal resistance ； temperature uniformity

中原大學機械工程學系學位論文

2017年

博士

張耀仁

英文

本研究的第一部分提出一種新型多噴嘴式微通道散熱器（MN-MCHS）， 詳細研究了微通道長度、長寬比、肋寬度，及幫浦功率和熱通量，發現其通道長度較短的MN-MCHS不僅明顯改善底部溫度的均勻性和熱動力性能指數(thermodynamic performance index)，也可以顯著的降低總熱阻抗。 隨著通道長度從10mm降低至1mm，溫度均勻性提高了約10倍，總熱阻提高了62％，壓降(pressure drop)降低了約12倍。在第一部分的所有情況顯示，MN-MCHS在最佳的結構下，可以消除高達1300W / cm 2的熱通量，並且使溫度保持在高於入口冷卻劑的溫度77.5℃之以下。此外，在相同的幫浦功率下，比單層MCHS與雙層MCHS分別改善總熱阻高達62％和47.3％。此MN-MCHS的結構是一種有潛能的MCHS結構，因為它可以透過優化其幾何尺寸來提高熱性能並降低壓降。 在第二部分中以可量測9.8mm×9.8mm×0.5mm的銅板作為SL-P-MCHS和MN-MCHS的襯底，使用水作為冷卻劑。 通道長度為0.2至5.6mm，以及五種不同的通道形狀，包括圓形，正方形，梯形，兩個凹形表面和兩個凸形表面，並且固定液壓直徑為200μm與雷諾數範圍700〜2200之間進行數據的研究。 利用新的網格劃分方式，找出一種最適合用於多噴嘴式微通道散熱系統的結構。其中以圓形的通道擁有最好的熱性能，可耗散高達1300W / cm 2的熱通量，並且在雷諾數為2200時最大溫度保持在低於75℃。此外，提出了一個新的方程式，透過通道長度與雷諾數，預測其入口與出口之間冷卻劑的溫度差異，以及根據雷諾數和熱通量，預測圓形通道底壁的最高溫度。 最後第三部分，以固定寬度100μm，長度2mm，高度500μm的模型進行分析。計算的模型包括通道和基板，水與矽作為冷卻劑和基板的材料，在模型的底壁上固定施加750W / cm 2的熱通量。為了研究通道深度對散熱器底壁溫度均勻性的影響，分析固定通道深度100μm至400μm，與沿著通道的長度增加100μm至400μm的通道深度。在本節實驗中發現，通道深度對散熱器底壁的溫度均勻性有非常重要的作用。與固定通道深度相比，沿著通道長度增加其通道深度可以將溫度均勻性提高到36.7％。

The present study was carried out by three different parts. In the first part: a novel multi-nozzle microchannel heat sink (MN-MCHS) was proposed. The channel length, channel aspect ratio, rib width, pumping power, and heat flux were numerically investigated in detail. It was found that the MN-MCHS with a shorter channel length not only could significantly improve the temperature uniformity on the bottom wall and thermodynamic performance index, but it also could significantly reduce the overall thermal resistance. With the decrease in the channel length from 10 mm to 1 mm, the temperature uniformity was enhanced by approximately 10 times, the overall thermal resistance improved 62% and the pressure drop was reduced approximately 12 times. For all cases in the first part, an optimal structure of the MN-MCHS could dissipate a heat flux up to 1300 W/cm2, and kept the temperature rising above the inlet coolant temperature under 77.5oC. In addition, at the same pumping power, it could improve the overall thermal resistance up to 62% and 47.3% compared to that of the single layer MCHS and the double layer MCHS, respectively. This structure of MN-MCHS is really a promising structure of MCHS because it can improve thermal performance and reduce the pressure drop by optimizing its geometric dimensions. In the second part: a copper plate measuring 9.8 mm × 9.8 mm × 0.5 mm was used as a fixed substrate for designs with single-layer-parallel microchannel heat sink (SL-P-MCHS) and MN-MCHS. Water was applied as the coolant. Channel lengths from 0.2 to 5.6 mm, and five different channel shapes, including a circle, square, trapezium, two concave surfaces, and two convex surfaces, were numerically investigated in detail at a constant hydraulic diameter of 200 µm and a Reynolds number in the range of 700 to 2200. A novel scheme for meshing is proposed. A structure for a multi-nozzle microchannel heat sink is presented. For all cases in this part, it was found that the best thermal performance was achieved with a circular channel shape which could dissipate a heat flux up to 1500 W/cm2, and the maximum temperature was kept at less than 75oC at a Reynolds number of 2200. Furthermore, novel equations were proposed to predict the temperature differences between inlet and outlet coolant temperatures depending on the channel length and Reynolds number, as well as to predict the maximum temperatures on the bottom walls of the circular channel shape depending on the Reynolds number and heat flux. In the third part: a unit cell, with a width of 100 µm, a length of 2 mm, and a height of 500 µm, was used as a fixed computational model for analysis. The computational model included a channel and substrate. Water and Silicon were utilized as the coolant and substrate’s material, respectively. A fixed heat flux of 750 W/cm2 was applied on the model’s bottom wall. To examine the effects of channel depth on the temperature uniformity of the heat sink’s bottom wall, different fixed channel depths of 100 µm to 400 µm, and increasing channel depths from 100 µm to 400 µm along the channel length were investigated in detail. For all cases in this part, it was found that channel depth plays a very important role in controlling temperature uniformity on the heat sink’s bottom wall. The increasing channel depth along the channel length could improve the temperature uniformity up to 36.7 % compared to that of a fixed channel depth.

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