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Optimal Design of Finned-Tube Heat Exchangers and Thermal Analysis by ANSYS
|Authors: ||SU, CHE-WEI|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
Fin-tube heat exchangers;Ansys;Height of fin;Pressure drop;number of passes;Excel
|Issue Date: ||2017-05-24T08:24:00Z
|Abstract: ||本研究主要探討鰭管式空氣加熱器之最佳化設計，加熱工作流體分別為熱水、水蒸氣與熱煤油。首先實驗量測單一鰭管鰭片溫度，計算不同高度鰭片的效率，與理論效率進行比較，接著根據實驗的流體溫度及流速，利用Ansys Fluent進行模擬，最後三種結果相互驗證。 設計採用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。程式以Microsoft Excel撰寫，內含流體物理性質查詢系統，尤其水蒸氣可以根據操作壓力，透過一套VB介面查詢；執行上，首先驗證能量平衡，接著粗估總熱括係數及殼管側流速，獲得設計雛形，最終藉由改變各個不同參數得到最佳化設計。 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，但總熱傳量與殼側壓降都會降低，最佳化的鰭片高度為8~10mm，增加迴流數可大幅增加管內流速，降低管側熱阻；排列方式上，增加水平排列及減少鰭管間距可增加總熱傳量，但壓力降也會跟著上升；管長增加可降低所需管數並提高管側流速。最後利用Ansys進行三維模擬可以補足理論公式，例如:流體進出口位置及迴流設計，均會造成溫度分佈及壓降數值之差異，但是理論上都沒考慮這些，因此利用程式及模擬，可以得到更準確的設計。|
The objective of this study is to optimize the design work of finned-tube air heaters. Water, steam and Dowtherm oil are chosen to be the hot working fluids. First, a single fin tube is investigated experimentally, and the measured temperatures and fin efficiency are verified by theoretical curves and Ansys software. During the thermal analysis, the LMTD method is applied. The pressure drop as well as heat transfer coefficients have been calculated in both the tube and shell sides. The length of tube, the height and pitch of fins, number of passes, and layout are varied parametrically. The computer program was coded in Microsoft Excel which includes fluid physical properties query systems, especially accompanied with a VB program to fit the required operating pressure. First, the energy balance was checked, and then the basic information includes sizes of the tube and fin array were served as input to the code. A preliminary design can be accessed once the fluid velocity inside the tube and the overall heat transfer coefficient are guessed,. Finally, the design is optimized by modifying the input parameters. Through structural analysis, it is found that in the same tube pace, reduction in the height of the fins can improve the fin efficiency, whereas the total heat transfer rate anf pressure drop decrease simultaneously. The optimum fin height is between 8 and10mm. The increase in number of passes in tube side can increase the velocity significantly which results in enhance the heat transfer rate. The effect of fin array allocation is also studied. Finally, the simulation results reveals that the locations of inlet and exit of the fluids appears the differences in temperature and pressure distributions, which can provide the reference of the design work.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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