求解非絕熱雙套管熱交換器考慮熱輻射效應可靠總熱傳特性之程式研發

忽略熱輻射的對數平均溫差(LMTD)法已經被人們習慣運用在各種型式熱交換器的總熱傳率的計算。我們發現以LMTD法只能應用於絕熱的雙套管熱交換器，且內外管間流體必須具有很高的熱對流係數，才能得可靠解。對於非絕熱雙套管熱交換器，應用LMTD法並不正確。在本研究中，延伸本團隊對單圓管熱交換器考慮熱輻射影響之對數平均熱傳率(LMHTR)法的可得較可靠解的概念，進一步來研究非絕熱雙套管熱交換器，在考慮熱輻射效應影響對數平均熱傳率(LMHTR)法的總熱傳特性。當忽略熱輻射時，運用LMHTR法求得內管流體的總熱傳率和LMTD法都是相同的；但當內外管間流體為低對流係數的空氣或氣體時，則熱輻射必須被考慮，運用LMTD法求得的內管或內外管間的流體熱傳率與LMHTR法比較，其差值遠超過工程所能接受的差值範圍。應用LMTD法所設定內管和內外管間的流體的熱傳率是相等的假設，且對於非絕熱雙套管熱交換器也不正確。所以，對非絕熱雙套管熱交換器，必須應用LMHTR法才能求得實際且完整的結果。

關鍵字

非絕熱；雙套管熱交換器；熱輻射；對數平均熱傳率(LMHTR)法；對數平均溫差(LMTD)法

並列摘要

The log mean temperature difference (LMTD) method neglecting heat radiation is conventionally used to calculate the total heat transfer rate for all types of heat exchangers. We discover that LMTD method can only obtained reliable solution in situations of insulated double pipe heat exchanger with high heat convection coefficient fluid located between inner and outer pipes. Thus, applying LMTD method to a non-insulated double pipe heat exchanger cannot obtain reliable solution. In this investigation, the log mean heat transfer rate (LMHTR) method considering heat radiation extended from the same concept in former study of single-pipe heat exchanger, is developed to calculate the total heat transfer characteristics of a non-insulated double-pipe heat exchanger. It is found that in this study that the total heat transfer rate of inner fluid obtained by LMHTR method is the same as that obtained by LMTD method while heat radiation effect is neglected but not for that of fluid between the inner and outer pipes. While air (or gas) with low convection coefficient is flowing between the inner and outer pipes, hence the heat radiation must be considered; it is found that the total heat transfer rate of fluid inside inner pipe and fluid between inner and outer pipes obtained by LMTD method are big different from that obtained by LMHTR method. LMTD assumed that the total heat transfer rate of fluid located in inner pipe is the same as that of fluid between inner and outer pipes; it is inaccurate for the non-insulated double pipe heat exchanger. Thus, the practical and complete results can only be obtained by LMHTR method, developed by this study, in any situations of a non-insulated double-pipe heat exchanger.

並列關鍵字

non-insulated ； double-pipe heat exchanger ； heat radiation ； log mean heat transfer rate (LMHTR) method ； LMTD method

參考文獻

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求解非絕熱雙套管熱交換器考慮熱輻射效應可靠總熱傳特性之程式研發

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