薄霧流之熱傳機制研究

Abstract

薄霧流為一種空氣混合微小液滴之兩相流，其散熱效果遠高於傳統空氣流冷卻。影響薄霧流之熱傳效果的因素相當多，像是液滴大小、流體速度、液滴濃度等。本研究以實驗的方式，對於垂直通道之薄霧流冷卻進行量測與分析。實驗使用水力直徑為40mm之方形垂直流道，於流道後端之壁面置入長為250mm之加熱區域，以紅外線熱像儀拍攝加熱面，量測整個加熱面的溫度，計算其熱傳效果。本實驗固定液滴流量0.5LPM，透過空氣流流量與輸入功率之調整，比較薄霧流與空氣流之散熱效果，以及分析加熱面之努賽爾數變化。實驗結果顯示，薄霧流冷卻能使加熱面溫度均勻且大量降低，其熱傳效果高於空氣流冷卻。薄霧流之熱傳效果會隨加熱片輸入功率而改變，輸入功率越高，加熱面溫度越高，熱傳效果越佳，最高可至空氣流冷卻的15倍。

Mist flow is a two-phase flow with water droplets and air flow. The heat transfer rate of mist cooling is higher than air cooling. The elements that affect the heat transfer rate of mist flow are the droplet size, flow velocity and droplet concentration. In this study, the heat transfer of mist cooling in vertical channel was experimentally measured and analyzed. The square channel with 40mm hydraulic diameter was used in this experiment. The heater with 250mm length was located on the wall of flow channel downstream. The infrared thermography was used to measure the temperature distribution of heated wall and the heat transfer rate was calculated. Through adjusting the flow rate and heat flux, the heat transfer rate of air cooling and mist cooling was compared. The surface temperature distribution of heated wall in mist cooling was lower and more uniform. The heat transfer rate of mist cooling was higher than air cooling and increased along streamwise direction. With higher heat flux, the heat transfer rate of mist cooling was higher and was fifteen times higher than air cooling.