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研究生:賴振田
論文名稱:圓鰭管熱交換器含共軛熱傳效應之三維熱液動性分析
論文名稱(外文):Three-dimensional thermal-hydraulic performance analysis of circular finned-tube heat exchanger with conjugate problem
指導教授:張錦裕張錦裕引用關係
學位類別:碩士
校院名稱:國立成功大學
系所名稱:機械工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:1997
畢業學年度:85
語文別:中文
論文頁數:150
中文關鍵詞:圓鰭管熱液動性
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本文分別以數值及實驗方法探討三種不同鰭管式熱交換器之熱液動性能。其中兩種為不同鰭片高度、不同管間距的圓鰭管式熱交換器(test A及Test B)及一種橢圓鰭管式熱交換器(test C),而橢圓鰭管(test C)是由圓鰭管(test B)相同的圓管壓製而成,具有相同周長。在數值方面,假設三維穩態及層流流場,探討鰭片和管壁面為定溫(無限熱導度)時,在不同正向風速下(1∼ m/s),三維熱流場通道內溫度、壓力及鰭片表面紐賽數、壓降係數的變化;同時更進一步討論考慮共軛熱傳效應(有限熱導度)時,三維熱流場的熱傳性能及鰭片表面的溫度變化,進而和等溫鰭片比較,並計算出鰭片效率及其整體效率。最後並比較三個測試本體間的性能差異。在實驗方面,利用吸入型開放式風洞測試系統,配合一套環境控制設備,針對前述的三個測試本體,藉由管內側走高溫水(79℃),鰭片側走低溫空氣的方式(27℃),進行乾盤管的性能測試。在不同正向風速下(2∼6 /) ,比較數值模擬和實驗結果的熱傳係數及壓降大小。
由數值分析的結果,圓鰭管(test B)有較大的壓降,整體壓降約為橢圓鰭管(testC)的3.74倍;而熱傳係數方面,圓鰭管test B的熱傳係數約為橢圓鰭管的1.36倍,但是單位壓降的熱傳係數橢圓鰭管反而高於圓鰭管test B約2.5倍;考慮共軛熱傳效應時,熱傳係數圓鰭管test B約會下降5.0%∼14.7%,而橢圓鰭管下降幅度最小為6.0%∼10.7%。在鰭片效率方面,schmidt一維法與數值解的鰭片效率約有2∼5%的誤差。由實驗和數值分析的結果的比較,在壓降方面兩者相當吻合,在熱傳係數方面,數值解大致上會高估於實驗值80∼100%。


The thermal-hydraulic characteristics of three different kind of finned-tube heat exchangers (test A, B and C) are studied numerically and experimentally. Tests A and B are circular finned-tubes, while test C is an elliptic finned-tube, which has the same perimeter as that of test B. The flow is assumed to be steady, three-dimensional and laminar. The numerical results for the streamline, isotherm, Nusselt number and fin efficiency are first presented at various frontal velocities (1∼5 m/s) for the case of isothermal fin assumption (i.e., the fin conductivity is infinite). The conjugate convective heat transfer in the flow field and heat conduction in the circular fins are also considered. Experiments were conducted in a steady-state induced draft wind tunnel.
 The numerical result indicated that the pressure drop of circular finned-tube heat exchanger (test B) is 3.74 times of elliptic finned-tube heat exchanger (test C), while the heat transfer coefficient of circular finned-tube (test B) is 1.36 times of elliptic finned-tube (test C). The heat transfer coefficient per unit of pressure drop for test C is (elliptic finned-tube) is 2.5 times test B (circular finned-tube). The conjugate effect reduces the heat transfer conefficient about 6.0%∼10.7% for test B and 5.0%∼14.7% for test C. The one dimensional approximation (Schmidt method) overestimates the fin efficiency by about 2∼5%. The numerical results for the pressure drop are in excellent agreement with the experimental data; although both the calculated and experimental results of the average heat transfer coefficients are in the same order of magnitude, the numerical results overestimate the heat transfer coefficient by 80-100%.

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