水平矩形流道內高熱導圓柱對三維混合對流之影響

Influence of Highly Conductive Cylinders on Three-Dimensional Mixed Convection in a Horizontal Rectangular Channel

張財壽(Tsai-Shou Chang) ； 楓崑隆(Kuen-Lung Feng)

《燃燒季刊》 76期 (2012/02) Pp. 40-56

https://doi.org/10.30041/CQ.201202.0004

摘要

本文以數值模擬加熱面上高熱傳導性的圓柱對於三維穩態低速混合對流的影響，三維矩形流道之一垂直側面上為有限長加熱段，完全發展二維流體從水平矩形流道進口流入，工作流體為空氣，普蘭特數（Prandtlnumber, Pr），Pr為0.71，雷諾數（Reynolds number，Re）為100，葛拉秀夫數（Grashof number，Gr）為50,000保持不變。討論的參數為圓柱安裝位置、直徑（D）、高度（H）及個數。單一圓柱安裝位置因為靠近冷主流，平均紐塞數較高。圓柱可以增加熱傳，但也會在加熱面造成背風面，局部熱傳下降，所以整體而言，平均紐塞數雖有增加，但不大，例如當H=0.5，D=0.5的圓柱位於X=-1.5，Y=-1，平均紐塞數為4.9，約為1.26倍。反之，強制對流的平均紐塞數隨著直徑D大幅增加，可見熱浮力的重要性。多個圓柱組成管束，不論直排或橫排，平均紐塞數隨著排數而增加，5排5列時，強制對流及混合對流，平均紐塞數可以分別增加至3.18及2.56倍。

關鍵字

三維混合對流 ； 矩形流道 ； 圓柱

並列摘要

Numerical simulation was carried out to study the influence of the highly conductive cylinders installed on the heated surface on the low speed, three-dimensional mixed convection. A finite heated surface is located on one of the vertical walls of the rectangular channel. Cold air as being the working fluid flows into the rectangular channel with a two-dimensional, fully-developed velocity profile. Prandtle number (Pr) is 0.71. Reynolds number (Re) and Grashof number (Gr) are assigned to 100 and 50,000, respectively, remaining unchanged throughout this article.The investigated parameters are the position, diameter (D), height and number of the cylinders. The average Nusselt number is higher when a single cylinder is placed near the cold main stream. The additional surface of the cylinder can raise the heat transfer but the cylinder also produces a stagnation region behind the cylinder, locally reduces heat transfer there. Hence, overall heat transfer only can be insignificantly increased with the cylinder diameter. For example, with a H=0.5, D=0.5 cylinder located on X=-1.5 and Y=-1, average Nusselt number is 4.9 which is about 1.26 times of that without cylinder. On the contract, average Nusselt number is found to increase dramatically with the diameter D when the forced convection considered. A tube buddle is composed by multiple tubes average Nusselt number is increased with the row or column number of the buddle. With a 5×5 buddle, 3.18 and 2.56 times average Nusselt number can be obtained for forced and mixed convection, respectively.

並列關鍵字

Three-dimensional mixed convection ； rectangular channel ； cylinder