入出口相對位置對矩形容器內熱傳性能之影響

The Effect of Relative Position between Inlet and Outlet Ports on the Heat Transfer Performance in a Rectangular Cavity

卓韋男(Wei-Nan Jhou)

指導教授 ： 施陽正

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2010年)

https://doi.org/10.6841/NTUT.2010.00297

摘要

在許多工程結構中常常可看見與容器有關的結構物，包括了混合腔體、電子產品冷卻、建築通風、太陽能集熱器及儲熱設備…等之設計，其內部複雜的流場及熱傳特性一直為工業界及學者所探討。本文利用計算流體力學軟體FLUENT針對二維混合流之容器入出口相對位置(固定入口於左壁面頂端，出口則由上壁面中間沿容器壁作順時鐘改變，共有10種入出口相對位置)、幾何外型(包括正方形與長方形)及流體狀態(雷諾數、普朗特數、格拉斯霍夫數)上的差異對容器內流場及溫度場的影響。根據模擬結果顯示，在相同容器及雷諾數的情況下，隨著普朗特數越大，由於容器內熱擴散現象逐漸小於熱對流現象，使得容器壁之熱傳性能越來越好；隨著容器邊長寬比越大，穿越流受到容器壁及周圍渦流擠壓程度亦越大，容器內流場越複雜，發現出口位置在下壁面中間之前，容器壁之熱傳性能隨著長寬比越大而越好，其後，受到穿越流短循環越來越嚴重的影響，容器壁之熱傳性能漸漸變小，當雷諾數越大，其現象越明顯，各形狀之熱傳性能差異亦越大；在相同容器、雷諾數及普朗特數的情況下，當格拉斯霍夫數等於104時，容器內流場才有明顯的改變，穿越流受到周圍渦流擠壓而扭曲，其壓降及容器壁之熱傳性能因而較大。

關鍵字

計算流體力學 ； 浮力效應 ； 雷諾數 ； 紐賽數 ； 普朗特數 ； 格拉斯霍夫數

並列摘要

In many engineering applications, there are a lot of equipments composed of the cavity, including mixing chamber, electronic cooling products, ventilation of buildings, collection of solar energy and heat storage system, etc. The complex flow field and heat transfer characteristics within the cavity are always attractive to the industry and researchers. In this study, the CFD software-FLUENT was adopted to the effects of different 2-D mixing flow inlet-outlet relative positions(fixed inlet on top of left wall, outlets change clockwise start from middle of top wall, 10 different relative positions in total), geometrical shapes(include square and rectangular), and fluid states (Reynold Number, Prandtl Number, Grashof Number) on flow field and thermal field within the container.
According to the simulation results, we found that under the same condition of container and Reynold Number, the greater the Prandtl Number, the better the heat transfer performance while heat diffusion become less than heat convection progressively; The greater the aspect ratio of the container, the greater the degree of compression for throughflow by wall of containers and surrounding vortex, also it increases the complexity of flow field in the container.
We found that the best outlet position is before the middle of bottom wall, the heat transfer performance increases as the aspect ratio of container increases, then decreased due to increased effect of throughflow short cycle. This effect has become more obvious as the Reynold Number increases, the differences of heat transfer performance of different shapes is increased too. Within the same container, same Reynold and Prandtl Number, the field flow has changed dramatically when Grashof Number equals 104 , the throughflow is twisted due to compression of surrounding vortex, making its Pressure drop and heat transfer performance greater.

並列關鍵字

Computational Fluid Dynamics (CFD) ； Boussinesq ； Reynold Number ； Nusselt Number ； Prandtl Number ； Grashof Number

參考文獻

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