非絕熱和絕熱圓管考慮與忽略熱輻射效應之熱傳特性差異性的探討

The study of the heat-transfer characteristics difference between considering and neglecting the heat radiation effect on a non-insulated and insulated circular duct

林淑聯(Lin, Shu-Lian)

指導教授 ： 黃景良

共同指導教授 ： 吳澤松(Tser-Son Wu)

崑山科技大學/工程學院/機械工程研究所/碩士(2009年)

https://doi.org/10.6828/KSU.2009.00037

摘要

有包覆與無包覆絕熱材料的管路被大量用於現代的工業界與建築物中，由於熱輻射方程式包含了溫度四次方的計算，造成在數學上的分析非常複雜。所以，大部分的專家和學者認為，基於以往的經驗，若絕熱表面與外界環境之間的溫差非常小，則之間的熱輻射因素可被忽略，以簡化分析。因此，許多熱傳遞學或冷凍空調理論等教科書裡的絕熱例題或是實際的商業封裝絕熱設計，常常忽略了熱輻射效應。然而，本文將證明在某些條件下熱輻射效應不可被忽略。本文發展了一個專用的LabVIEW程式來計算考慮熱輻射之有包覆與無包覆絕熱材料的管路，結果顯示，在低空氣對流熱傳係數與高表面放射率的薄絕緣層條件底下，若忽略了熱輻射效應將導致不正確的絕熱設計；此外，本文也說明了較小的表面放射率可有很大程度地提升絕熱效果。

關鍵字

熱傳特性 ； 圓管 ； 隔熱材厚度 ； 圖控程式

並列摘要

Non-insulated and insulated ducts are commonly used in many industries and various buildings. Since the equation of heat radiation contains the 4th order exponential of temperature, it becomes very complicate to solve such equation. Most heat transfer researchers argue that from their own experiences, the heat radiation effect can be ignored due to the small temperature difference between insulated and non-insulated surfaces and surrounding. This thesis focuses in detail on the impact of heat radiation effect on the accuracy of heat transfer characteristics of non-insulated and insulated ducts by comparing the results obtained by considering and neglecting heat radiation effect. A LabVIEW programming is developed in this thesis to calculate the heat transfer characteristics of non-insulated and one to three insulated layers insulated circular ducts with heat radiation effect taken into account. It is found that neglecting heat radiation effect is likely to produce large errors of non-insulated and thin-insulated ducts in cases of ambient air with low external convection heat coefficients and with larger surface emissivity, especially when the ambient air temperature is different from that of surroundings under conditions of large internal fluid convection coefficients. Another important finding in this thesis is that using ducts with greater surface emissivity can greatly improve the heat exchanger effect, and ducts with smaller insulated surface emissivity result in better insulation.

並列關鍵字

heat-transfer characteristics ； circular duct ； insulation thickness ； LabVIEW programming

參考文獻

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