蒸發式降溫水牆介質中濕空氣熱與質傳評估

Evaluation of Heat and Mass Transfer of Moist Air in Evaporative Cooling Pad Media

本研究中所採用之測試程序允許蒸發式降溫水牆性能可由降溫效率及靜壓差來描述。針對水牆效率所做之誤差分析指出，水牆效率數據可準確至±2.5%。長纖及短纖不織布之替代水牆材質在正常操作空氣速度範圍1.5~2.5m/s下，其計算出之靜壓差範圍在23~79Pa之間，而計算水牆效率則為50-86%。毛巾布水牆替代材質，靜壓差範圍在20~46Pa，而計算出之水牆效率由為60-71%。蒸發式降溫之替代水牆中長纖不織布，短纖不織布及毛巾布，依據熱力學及熱質傳理論合併相關試驗結果確實可以找出蒸發降溫程序中熱傳與質傳係數之相關性。針對短纖，長纖不織布及毛巾布其熱傳係數（h（下標 H））與其質傳係數（h（下標 m））關係分別可以數學式表示為（h（下標 H）/h（下標 m））（下標 s）=1.03ρC（下標 p）L（下標 e）（上標 2/3），（h（下標 H）/h（下標 m））（下標 L）=1.10ρC（下標 p）L（下標 e）（上標 2/3）及（h（下標 H）/h（下標 m））（下標 T）=1.05ρC（下標 p）L（下標 e）（上標 2/3）；其中ρ為空氣密度，C（下標 p）為空氣比熱，而L（下標 e）則為Lewis數。

A procedure for testing evaporative cooling pads is developed to relate efficiency, air velocity, and static pressure drop across the pads. Heat and mass transfer coefficients are also send-experimentally obtained for the evaporative cooling process through various evaporative cooling pad media. Three types of alternative pad materials are used: (1) short-cellulose, (2) long-cellulose, and (3) towel. Static pressure drops across the long-cellulose and short-cellulose media and their efficiencies varied from 23 to 79Pa and 50 to 86% respectively under operating air velocity of 1.5 to 2.5m/s, while 20 to 46Pa and 60 to 71% respectively for the towel material. Error analysis of efficiencies based on the accuracy of measured variables indicates that efficiency data are accurate to ±2.5%. Heat and mass transfer coefficients are nondimensionalized and curve fitted to yield a set of working equations. The results show that the relations between heat (h(subscript H)) and mass (h(subscript m)) trans coefficients for three alternative pad materials are: (1) short-cellulose:(h(subscript H)/h(subscript m))=1.03ρC(subscript p)L(subscript e)(superscript 2/3), (2) long-cellulose:(h(subscript H)/h(subscript m))=1.10ρC(subscript p)L(subscript e)(superscript 2/3), and (3) towel:(h(subscript H)/h(subscript m))=1.05ρC(subscript p)L(subscript e)(superscript 2/3) where p is air density, C(subscript ρ) is specific heat of air and L(subscript e) is Lewis number.