往復運動薄板對管道內加熱壁面熱傳影響之研究

Abstract

本研究利用數值方法分析往復運動的薄板對管道內加熱壁面熱傳的影響；且近一步討論壁面熱傳的增益。數值計算方面，採用密度基底法解可壓縮流，並且在方程式中加入Preconditioning法，程式中所求解的是網格交界面的通量，方程式中的差分法皆為顯性差分。首先探討往復運動薄板提升管道內壁面熱傳效率的機制，進而比較不同薄板移動速度時，對壁面熱傳效率的影響。 由數值計算的結果得知，壁面上往復運動薄板推擠前方及上方流體而破壞其邊界層。同時牽引後方流體填補往復運動所產生的空間，因而生成新的邊界層，並且引導流體流向高溫壁面。邊界層的生成與低溫流體流向高溫壁面為提高熱傳效率的主要機制。此外隨著薄板移動度的增加，邊界層的破壞與生成較為頻繁，使的熱傳量大幅提升。

The study investigated the heat transfer enhancement by a reciprocated moving plate on the heat surface inside a duct. The characteristics of the flow and thermal fields are analyzed numerically. In the numerical analysis, taking density based method in to consideration, also adding preconditioning method in equations. All finite difference methods are explicit method. Observing the mechanisms of the heat transfer rate then discussing how the different plate moving speed effect the heat transfer rate. The numerical result shows that the motion of the plate destroys the boundary layer on the heat surface before the moving plate, and the boundary layer reforms behind the moving plate immediately. The boundary layer reformation and cold fluid induced by the moving plate flowing toward the heat surface are the major heat transfer enhancement mechanisms. Besides when the plate moves faster, the boundary layer reforms frequently. As a result, the heat transfer enhancement becomes huge.