本研究以數值模擬分析電子產品之外殼開孔情形影響內部水平鰭片熱沉之自然對流散熱效果。由於機殼遮蔽熱空氣上升的影響導致鰭片散熱不易，而將機殼適當地開孔有助於改善其散熱效果。針對CPU熱源假設為等溫且底面積為100 mm × 100 mm的固定熱沉的狀況，本研究模擬不同機殼開孔形式、開孔率以及機殼材料對於鰭片熱沉散熱的影響。先以單一通道找出增加散熱量之幾何變動趨勢後，再針對印刷電路板參與計算與否以及不同機殼材料模擬半個機殼之散熱情形。結果顯示由於受熱氣流趨向熱沉中心區域，開孔位於鰭片中央的上方機殼可使熱空氣較順暢地排出而具有較好的散熱效果。遠離鰭片上方之未開孔檔板具有引導環境空氣至熱源附近的作用，可以使空氣能夠被更有效地加熱。模擬半個機殼計算域時，印刷電路板是否參與計算對於鰭片總散熱量只有小幅影響，其差異低於熱沉與電路板在垂直擺放的狀況。使用塑膠做為機殼材料於水平擺放之機殼內鰭片散熱案例比使用鋁材料做為機殼的案例高出約20%的總散熱量。水平擺放下熱沉的熱傳量皆明顯低於垂直擺放下的熱傳量，當考慮印刷電路板參與熱傳下，塑膠機殼中其比值為0.73，但在鋁合金機殼中其比值降為0.61。

In this study, the effects of chassis perforation on the natural convection from a horizontal rectangular-fin heat sink have been studied numerically. The parameters include perforation pattern, local and overall opening ratio, and the thermal conductivity of the chassis material. In the first part, single-channel analysis is conducted for various perforation patterns. The results show that when the upper chassis wall is perforated over the middle region of the heat sink, with a single perforation or multiple dispersed perforations, the venting flow can be smooth and fast, yielding effective cooling of the heat sink. In the second part, the computation domain includes a half of the system. The effect of the heat transfer associated with the printed circuit board is found to slightly enhance the natural convection from the heat sink when the system is in the horizontal orientation. But stronger enhancement is displayed in the vertical orientation. When plastic is selected as the chassis material, the total heat flux of the heat sink within it is 20% higher than that of the aluminum alloy chassis in horizontal orientation. The total heat fluxes of the heat sink in a horizontal system are significantly lower than those in a vertical system. For example, the ratio of the total heat flux between two different orientations is 0.73 in a plastic chassis, but it decreases to 0.61 in an aluminum alloy chassis.

[1] 王品傑,精簡型電腦機殼開孔狀況對CPU鰭片熱沉自然對流的影響, 國立清華大學碩士論文, 2013.
[2] 葉家興, 機殼開孔對電腦CPU之熱沉鰭片的自然對流與熱輻射的影響, 國立清華大學碩士論文, 2013.
[3] F. Harahap, H.N. McManus Jr., Natural convection heat transfer from horizontal rectangular fin arrays, ASME J. Heat Transfer 89 (1967) 32-38.
[4] S.-C. Wong, G.-J. Huang, Parametric study on the dynamic behavior of natural convection from horizontal rectangular fin arrays, Int. J. Heat Mass Transfer 60(2013) 334-342.
[5]S. G. Taji, G. V. Parishwad, N. K. Sane, Experimental investigation of heat transfer and flow pattern from heated horizontal rectangular fin array under natural convection, Heat Mass Transfer 50(2014) 1005-1015.
[6] S. Inada, T. Taguchi, W.J. Yang, Effects of vertical fins on local heat transfer performance in a horizontal fluid layer, Int. J. Heat Mass Transfer 42 (1999) 2897–2903.
[7] E. Arquis, M. Rady, Study of natural convection heat transfer in a finned horizontal fluid layer, Int. J. Therm. Sci. 44 (2005) 43–52.
[8] S.A. Nada, Natural convection heat transfer in horizontal and vertical closed narrow enclosures with heated rectangular finned base plate, Int. J. Heat Mass Transfer 50 (2007) 667–679.

[9] J.C. Shyu , K. W. Hsu, K. S. Yang, C. C. Wang, Orientation effect on heat transfer of a shrouded LED backlight panel with a plate-fin array, Int. Comm. Heat Mass Transfer 42 (2013) 51–54.
[10] S. Naik, S. D. Probert, C. I. Wood, Natural-convection characteristics of a horizontally-based vertical rectangular fin-array in the presence of a shroud, Appl. Energ.28 (1987) 295-319.
[11] H.G. Yalcin, S. Baskaya, M. Sivrioglu, Numerical analysis of natural convection heat transfer from rectangular shrouded fin arrays on a horizontal surface, Int. Comm. Heat Mass Transfer 35 (2008) 299–311.
[12] Handbook of Fluent, ANSYS, Inc.
[13] S.V. Patankar, Numerical Heat Transfer and Fluid Flow, Hemisphere Publishing Corporation, 1980.
[14] F.P. Incropera , D. P. DeWitt, T. L. Bergman & A.S. Lavine, Fundamental of Heat and Mass Transfer, Wiley, 6th Ed.
[15] 林峻霈, 含均溫板之集中式高功率LED燈具之自然對流散熱鰭片設計, 國立清華大學碩士論文, 2011.
[16] Huang G.-J., Wong S.-C., Lin C.-P., Enhancement of natural convection heat transfer from horizontal rectangular fin arrays with perforations in fin base. Int. J. Therm. Sci. 84 (2014) 164-174.
[17] Y.S. Muzychka, J.R. Chlham, M.M. Yovanovich, Thermal spreading resistance of eccentric heat sources on rectangular flux channels, J. Electr. Packag. 125 (2003)178–185.
[18] G.J. Huang, S.C. Wong, Dynamic characteristics of natural convection from horizontal rectangular fin arrays, Appl. Therm. Eng. 42 (2012) 81–89.