混合對流在平板漸縮管道內之流場分析

Abstract

摘要

本論文係利用數值方法，探討工作流體流經垂直漸縮等溫加熱的壁面管道時的所產生的流場及其熱傳特性。數值計算分為兩部分：第一部分為探討不同的傾斜角度時，在傾斜壁面中間部位及兩壁面角落稜線區熱傳性質之趨勢差異；第二部分為探討固定角度模型下，不同雷諾數(Re)對於流場內之熱傳性質變化之影響。

故本文所討論的操作參數為壁面傾斜角度(γ)以及雷諾數(Re)。其中操作雷諾數不同差異，是以間接方式調整出口流速進行。

數值研究結果顯示，調整漸縮壁面傾斜角度(γ)對於流場、溫度分佈、熱傳效率都有顯著的影響，隨著傾斜角度(γ)的增加熱傳效率不佳的稜線區逐漸縮小直到消失，其主要的原因在於壁面流體速度增加以及內部流場的變化；另外，提高雷諾數有助於提高流場散熱效率，不僅最大紐塞數因此增加，整體平均紐塞數也提高，在漸縮段入口區長度也有縮短的趨勢，但是，提高雷諾數對於稜線區的存在沒有顯著影響。

Abstract

The numerical study is carried out to investigate fluid flow and heat transfer characteristics in vertical channel with convergent wall at uniform temperature. The numerical results can be able to divide into two parts. As far as the first part was concerned, we changed the convergence angles, and observed the varying trend between two different zones in the flow field. As for the second part, we fixed the convergence angles, changed the Reynolds number and observed the varying trend in the flow field.

The parameters studied included the convergence angle and the Reynolds number.

The convergence angles and the Reynolds number were demonstrated significantly affected by the fluid flow, temperature distribution, and heat transfer rate. Increasing the convergence angles could be made the corner zone narrow down, and last disappeared. Increasing the Reynolds number leads to the fluid flow more heat transfer rate. Not only the maximum value of nusselt number, but the total average value of nusselt number was increased as well. The entrance length in the convergence section has been shortened. However, increasing of Reynolds number has no significant impact on corner zone.