二維封閉空間內流體受傾斜角度、長寬比與萊利數影響之自然對流熱傳研究

Free Convection Heat Transfer in a Two-dimensional Enclosure with Inclined Alignment, Aspect Ratio and Rayleigh Number Effects

邱偉勝(Wei-Sheng Chiu)

指導教授 ： 周榮源

國立虎尾科技大學/工程學院/機械與機電工程研究所/碩士(2010年)

https://doi.org/10.6827/NFU.2010.00063

摘要

中文摘要
本文目的是針對二維封閉矩形空間中，研究不同流體受不同長寬比之幾何形狀、不同擺放角度及不同莱利數Ra影響下之自然對流熱傳現象。本文以數值模擬方法來分析矩形空間中之二維穩態流場現象，並與實驗結果做一比較。數值分析所使用之理論模型為左、右壁分別為高溫壁及低溫壁，其餘之壁面皆設為絕熱壁，且理論模型中，分別將空氣、純水、混合流體(水及乙二醇)作為工作流體，來探討受到長寬比、傾斜角度及萊利數Ra等效應影響時溫度場及流場變化及自然對流熱傳Nu值變化。數值模擬所考慮之參數範圍為：萊利數Ra=103~106；普朗特數Pr=0.71, 5.83, 62.1(分別為空氣、純水、混合流體)；長寬比Ar=2, 4, 8；傾斜角度0°~360°。實驗量測方面則考慮有限溫差下，改變旋轉角度(0°, 10°)和不同的長寬比(Ar=2, 4)，以及不同流體(純水、混合流體)時之自然對流現象，並以雷射觀察流體之流場分佈。由研究結果顯示，不同流體之平均紐賽數均隨著萊利數的增加而上升；而在相同萊利數的情況下，隨著長寬比的增加平均紐賽數降低。

關鍵字

封閉矩形 ； 自然對流 ； 長寬比 ； 傾斜角

並列摘要

Abstract
The problem of two-dimensional steady state natural convection heat transfer in a rectangular enclosure filled with different fluids, different aspect ratio, inclined alignment and Rayleigh number has been investigated numerically and experimentally. Use fortran set up to two-dimensional flow field analyse. It’s about putting the air, water, mixture fluids(water/EG) in a rectangular enclosure container which has two sides. One of it is cooling surface, another is heating surface, and others are adiabatic surfaces. In the numerical formulation, the effects of variable heat transfer of the fluids associated with temperature and gravity. he numerical simulations have been undertaken for the pertinent dimensionless parameters in the following ranges: the Rayleigh number Ra=103~106; the Prandtl number, Pr=0.71, 5.83, 62.1, It is air, water, mixture fluids(water/EG); aspect ratio, Ar=2, 4, 8; degree(0°~360°); experimental consideration limited temperature difference along with angle of tilt (0° and 10°) and different aspect ratio (Ar=2, 4) of natural convection phenomenon to water, mixture fluids. The experimental result is by laser watching stream function. In result, the average Nusselt number increases with improve the Rayleigh number of different fluids. And on the same Rayleigh number, the average Nusselt number decreases with extend the aspect ratio.

並列關鍵字

aspect ratio ； natural convection heat transfer ； inclined alignment

參考文獻

參考文獻

[1] G. DE Vahl Davis, “Natural convection of air in a square cavity : a bench mark numerical solution,” International Journal for Numerical Methods in Fluids, Vol.3, pp.249-264, 1983.

[2] Claudio Cianfrini, Massimo Corcione and Pier Paolo Dell’Omo, “Natural convection in tilted square cavities with differentially heated opposite walls,” International Journal of Thermal Sciences,Vol.44, pp.441-451, 2005.

[3] Wei Tong, “Flow structure and temperature measurements in a 3-D vertical free convective enclosure at high Rayleigh numbers,” International Journal of Heat and Fluid Flow, Vol.20, pp.624-633, 1999.

[4] S. S. Hsieh and S. S. Yang, “Aspect ratio effect on natural convection in water near its density maximum temperature,” International Journal of Heat and Mass Transfer. Vol.40, pp.1467-1480, 1997.