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### 第十一章

h 之求法（有相變化-冷凝）

• 純質蒸汽之冷凝

（A）一般為film type

冷凝形成film流下

（通常為層流）

（B）冷凝面經表面處理後可提昇為dropwis type

• 垂直管層流實驗值

• 垂直管擾流實驗值

• 管殼式熱換器的管方由直立BWG 16 號3/4 in銅管構成，苯在管內加熱，管長1.5m，溫度為70℃，水蒸汽在殼方冷凝，溫度157℃，若管壁熱傳阻力可忽略，Tw=139°C

• 求ho，

• hi=2000W/m2-℃ 求Uo

Uo=?

• 每支管可交換多少熱?冷凝多少水蒸氣?

• 水平

• 單管

• N支並列

• 管殼式熱換器的管方由水平BWG 16 號3/4 in銅管構成，苯在管內加熱，管長1.5m，溫度為70℃，水蒸汽在殼方冷凝，溫度157℃，Tw=143.6°C hi=2000W/m2-℃

• 若水平式管殼式熱換器，垂直方向每6支一列，求ho，Uo

• Uo=?

• 每支管可交換多少熱?冷凝多少水蒸氣?

• Nucleate boiling

• Film boiling

• Nucleate boiling 熱傳好，但不易控制。形成原因

• 1.表面有一點點粗糙or結一點點垢

• 2.      溶液中有不純物

• 3.      攪拌

• 4.      溶液性質

• 5.ΔTo,壓力因素