- 學位論文
交叉流蜂巢狀蒸發冷卻器之研究
A Study of Cross-Flow Evaporative Cooler Using Honeycomb Paper Packing
摘要
本研究以內部填充蜂巢狀濕模板之交叉流直接蒸發冷卻器進行研究實驗，研究中以焓位勢理論為基礎，將 關係式運用於冷卻模板之上，計算出模板表面與空氣間之質傳係數。蒸發冷卻過程中當較高溫的空氣通過較低溫的水薄膜時，除了溫度下降的顯熱變化之外，並因模板表面與空氣間水蒸氣壓差產生質傳的潛熱變化。本實驗所用的紙板間流道之水力直徑( )約為8.777 mm，探討空氣及水流量、工作流體溫度、模板厚度及模板熱傳面積對質傳係數及熱傳量之影響，空氣雷諾數(Rea)介於220~1600之間、水側質量流率(Gw)約0.25~0.52kg/s-m2。 研究結果得知：當外氣條件越乾燥時，濕模板熱交換效率越好，空氣側入出口溫差越大；總熱傳量會隨供水溫度降低而上升。模板與空氣間的質傳係數會隨當供風量或水量增加而提升；濕模板有效度會隨供風量增加而提升，供水量增加而下降。在夏季中一般外氣條件下(外氣乾球約為30℃)，使用蜂巢狀濕模板蒸發冷卻器，可有效降低外氣溫度約7~11℃，並提昇約20~33%的相對溼度。經過因次分析及本實驗數據之回歸分析，提出本實驗濕模板表面質傳係數計算經驗公式，預測值與實驗值比對其中80%之數據誤差約為±10%以內，其餘20%之數據誤差約為±20%以內。
並列摘要
This study investigates the evaporation phenomena of a cross-flow evaporative cooler, in which the wet durable honeycomb paper, having 8.777 mm hydraulic diameter, constitutes as packing material. The evaporative cooling system is expected to act as both humidifier and cooler to create a comfortable indoor environment. Heat transfer rates and mass transfer coefficients are experimentally obtained for the evaporative cooling process at various packing thickness and frontal area, water and air flow rates. The air side Reynolds number varies between 220 and 1600, and the water mass velocity varies between 0.25 and 0.52 kg/sm2. The experimental results show that for the embient air dry ball temperature at about 30℃ the evaporative cooler reduces the air dry-ball temperature by about 7~11℃ and the relative humidity increases approximately 20~33%. The mass transfer coefficient increases as the air flow rate or water flow rate increases. The effectiveness of the evaporative cooler increases as increasing air flow rate, and it decreases as the water flow rate increases. These data are nondimensionalized and curve fitted to yield a correlation of the mass transfer coefficient, which fits the present data within +-20%.