熱輻射增益對自然對流熱沉影響研究

Abstract

本研究以實驗方法探討改變熱輻射效果是否會影響到自然對流為主軸，利用鰭片主面積相等，但改變灰體視因子之值，以求增強熱輻射效果，分別採用矩形、直角三角形、鈍角三角形(120。)，三種形狀來進行，排列形式有交錯和平行排列兩種；在粗度真空狀態下，可觀察熱沉之熱輻射能力，隨著壓力增加，熱輻射能力也隨之減弱，當壓力增加至約為100mm-Hg，自然對流效果會明顯出現。實驗結果發現，改善灰體視因子可以有效改善熱輻射效果；主面積為(2000mm2)時，在粗度真空狀態下量測熱輻射效果，相較於矩形鰭片，各樣式鰭片可使熱沉熱對流係數增加1.5%~11.89%，在自然對流(760mm-Hg)時，相對於矩形，效果可增加1.7%~12.69%；主面積為(3000mm2)時，效果增加3.5%~26.5%，自然對流時為 -0.6%~15%。根據本研究指出交錯排列形式之鳍片及鈍角三角形形狀可以改善自然對流之效果。

The present thesis is aimed to investigate natural convection heat sink performance by thermal radiation enhancement. The experiments use different kinds fin but same heat transfer area to change gray view factor. There are three different fin shapes including rectangular-fin, right-triangular-fin and obtuse-triangular-fin with two different arrangements, parallel and staggered. To measure thermal performance of heat sink, the chamber was kept in low vacuum state. As pressure increased, we can observe that natural convection gradually dominate heat transfer mechanisms. The experiment result shows that both radiation and natural convection thermal performance was improved by increasing gray view factor. Obtuse-triangular-fin can improve thermal efficiency effectively. Besides, staggered arrangement is better than parallel arrangement.