風扇流場中之旋轉式散熱機構

Abstract

本文主要目的為利用數值計算與實驗方法，研究在風扇所產生的流場中，發熱元件表面加裝旋轉運動機構對其流場與溫度場之影響，旋轉運動機構與發熱元件表面接近，並且在發熱元件表面上持續做旋轉運動，藉由旋轉運動破壞發熱元件表面的溫度邊界層，使低溫流體直接與發熱元件表熱面接觸，由於旋轉運動機構不停的旋轉運動，因此發熱元件表面上之溫度邊界層不斷的被破壞與重新生成，藉此種散熱機制可達到增加熱傳效率的目的。 在數值計算流場方面採用k-ε紊流模式，利用有限體積法求得風扇與旋轉運動機構之流場與溫度場分佈，在實驗方面利用熱線及熱電偶量測風速及溫度分佈，並以熱傳實驗方法驗證數值計算之結果，結果顯示發熱元件之熱傳性能，明顯受其相對於風扇位置之影響，在風扇中心軸下方之發熱元件其散熱性能欠佳，靠近風扇葉片外緣之發熱元件其散熱性能較優越，而在發熱元件表面裝設旋轉運動機構後，藉由旋轉運動機構的轉動，確實可明顯提升發熱元件之熱傳性能。

The main purpose of this article is to study the heat transfer enhancement by a rotating bar on the heated surface in the cooling fan flow. The characteristics of flow and thermal fields are analyzed with both numerical and experimental methods. When the rotating bar moves on the heated surface it can destroy the thermal boundary layer of the heated surface and makes cold flow to get contact with the heated surface. In this way the heat transfer performance of the heated surface can be more efficient. In the numerical analysis, the finite volume method is applied to solve the flow and thermal fields, and the k-ε turbulent model is adopted to solve the governing equations of the flow field. In experimental investigation, hot wire and thermal couple are used to measure the velocity of fluid and the temperature of heated surface. The numerical and experimental results show that the heat transfer performance of heated surface is affected by the location relative to the fan. The heated surface below the center of cooling fan has low heat transfer performance. On the contract, the heated surface below the outside blade of cooling fan has better heat transfer performance. After installing the rotating bar on the heated surface, the heat transfer of the heated surface is to be improved remarkably.