高效能熱水器之冷凝熱交換器研究

Study of Condensing Heat Exchanger apply on High Efficiency Water Heater

張鈞捷(Chang, Chun Chien)

指導教授 ： 廖英皓 ； 王啟川

國立交通大學/工學院/機械工程系所/碩士(2018年)

摘要

本文探討高效率熱水器的冷凝式熱交換器，熱交換過程牽涉顯熱及水蒸氣潛熱，煙氣中水蒸氣冷凝釋放出的潛熱可大幅提升熱交換器效率。實驗使用熱水器提供煙氣，對不銹鋼四分管、三分管裸管熱交換器進行測試。在水蒸氣體積百分濃度為9%時，三分管平均熱傳係數比乾空氣熱傳高3倍，四分管熱傳係數比乾空氣熱傳高2倍，三分管熱傳量增幅高於四分管，小管徑裸管可降低尾流影響，使流體均勻接觸後方管陣，兩不銹鋼熱交換器皆可增加16升熱水器效能4%。研究探討塑膠疏水材質對冷凝熱傳的影響，做PE三分管全塑膠熱交換器，但因管壁溫度過高無法發生冷凝，僅發生顯熱熱傳。為改善此缺點，在煙氣溫度高的熱交換器前半部使用不銹鋼管，在後半部分使用薄壁PTFE管，PTFE管壁面為滴狀凝結，總熱傳量相較不銹鋼仍降低24%。

關鍵字

冷凝熱交換器 ； 塑膠材質 ； 疏水性

並列摘要

This study experimentally studied the condensing coils of water heater. The experiment is conducted with flue gas from typical gas fired water heater, and two stainless steel bare tube bundles contain diameter are 4/8″ and 3/8″ are respectively tested. It is shown that the average heat transfer coefficient of 3/8″ tube bundle is three times higher than that of the dry operation when the water vapor volume concentration is 9%. Similarly, and 4/8″ tube bundle shows two-fold improvement as compared to dry operation. he increase in heat transfer rate of 3/8″ heat exchanger is higher than those of 4/8″. In addition, to investigate the applicability of hydrophobic plastic material upon condensation performance. PE with 3/8″ bare tube bundle is made and tested. However, no appreciable condensation occurs due to the comparatively high wall thickness and extremely low thermal conductivity of plastic material, indicating a very poor condensing performance. This situation can be slightly improved by replacing the top part of the tube bundle by stainless steel tubes. Through this design, dropwise condensation is observed on PTFE surface, but the total heat transfer rate is still 24% lower than the fully stainless tube bundle.

並列關鍵字

condensing heat exchanger ； plastic material ； hydrophobic

參考文獻

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