加熱區在上方之垂直往復式冷卻渠道混合對流實驗

Abstract

本研究主要目的在以實驗方法去探討混合對流在一振動ㄇ型渠道內對壁面熱傳效率之影響情形，並搭配數值模擬來提高實驗之可信度。實驗設備大致上可以分為三部份︰冷卻渠道、往復運動機構、溫度控制系統，工作流體為空氣。另外使用放煙線法進行流場可視化的拍攝，以實際流場變化情形與數值模擬之流線圖互相驗證，兩者結果非常吻合。 實驗針對不同的進口流體雷諾數和渠道無因次往復振動頻率及不同溫差下來進行討論，由結果得知熱傳效率會因為渠道振動而提高，熱傳增益受到自然對流的效應影響較進口流體雷諾數增加影響較大，相較之下渠道低無因次振動頻率增加及進口流體雷諾數增加影響較不明顯，所得到最大熱傳增益在51%以內。且溫度增加會使得自然對流效應增強，使部分加熱區熱傳效率增加，且流體進口與重力相反的情況下受自然對流的影響較重力同向明顯。整體看來混合對流其熱傳效率較強制對流來的好。

In order to investigate the heat transfer phenomena in a U-shaped channel with reciprocating motion, an experimental work is conducted and validated by an auxiliary computational procedure simultaneously. The experimental apparatus consist of three parts, a cooling channel, reciprocating mechanism and heating control. The working fluid is air and the parameters of Reynolds number , temperature and oscillating frequency are varied. In addition, a flow visualization using the Smoke-wire method is adopted to indicate the flow field and compared with the streamline of the numerical results. The comparisons between experimental and numerical results are consistent well. The results show that the heat transfer rate is mainly dominated by nature convection effect, and less affected by increasing the low oscillating frequency and Reynolds number. The enhancement of the heat transfer is confirmed and within 51% in this study. In general , the aid of mixed convection is to remove more heat than force convection.