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Computer Programs on Optimal Fin Configuration of Finned-Tube Heat Exchangers and the Adjoined Dryer
|Authors: ||Wu, Jia-sing|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
Fin-tube heat exchange;Drying chamber;Fin;Ventilation rate;Heating rate
|Issue Date: ||2017-05-24T08:23:22Z
|Abstract: ||本研究主要探討鰭管式熱交換器結構最佳化，並連結於乾燥室進行加熱能力分析，其主要工作流體為熱媒油與空氣。首先使用LMTD方法設計最佳化之鰭管式熱交換器，藉由程式計算，分析不同傳熱管長度、鰭片高度、鰭片密度、迴流數、管子排列方式等對於總熱傳係數之效應，並驗證主要構件符合CNS 12652、CNS 9789、TEMA RCB、機械圖表設計便覽等規範。由結構分析中發現在相同間距下，降低鰭片高度會提高鰭片效率，增加總熱傳係數，降低需求管數可節省熱交換器之成本。 將最佳化設計之鰭管式熱交換器連結乾燥室以ε-NTU法進行加熱能力計算，計算程式使用Microsoft Excel撰寫，程式內含相關物理性質並具查詢功能。首先輸入結構尺寸、操作溫度與流量等設計參數，計算出鰭管式熱交換器之雛型，再經由ε-NTU方法算出熱傳量及熱交換器空氣端出入口溫度，依次計算出下一時間階之結果，以求出乾燥室溫度到達穩態之時間，提供設計最佳化熱交換器並連結乾燥室，分析乾燥室內室體積、換氣率、乾燥物質量、熱交換器效率等參數，對於乾燥室溫升率與穩態溫度之影響。結果顯示影響乾燥室加熱能力最主要的是熱交換器效率，較佳的熱交換器效率乾燥室穩態溫度較高，加熱時間也較短。|
The objective of this study is to optimize the fin-tube heat exchangers which connected to a drying chamber. The working fluids are Dowtherm oil and air. During the thermal analysis, the LMTD method is applied. The heat transfer coefficients have been calculated in tube and shell sides respectively with some parameters such as length of tube, height and pitch of fins, number of passes, and layout, etc. The thicknesses of main elements in heat exchangers are verified by the contents in revenant CNS9789, CNS12652, and TEMA standards. It is observed that if reduction is made in fin height and pitch simultaneously results in improving the overall heat transfer coefficient. In other words, it diminishes the demand of heat transfer area as well as the number of tubes. A drying chamber is made to connect with the designed heat exchanger. Through the method of ε-NTU, the heating rate of the system can be assessed. The computer program was coded in Excel language which developed by Microsoft. First of all, input information includes the operating conditions and many sizes of the tube and fin array. Once the preliminary structure of fin-tube heat exchanger is suggested, through an ε-NTU calculation of the drying chamber, the temperature at the drying chamber and the inlet of heat exchanger can be estimated in each time step. Finally, when the steady state temperature is reached and the whole heating curve can be obtained. The effects of the size of drying chamber, ventilation rate, mass of desiccate, and heat loss are studied. All the above mentioned parameters influence the rate of temperature rise and the steady-state temperature of the drying chamber.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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