- 期刊
奈米流體CuO／水在同心與偏心球間之熱傳對流研究
The study of heat transfer convection of CuO/water nanofluid between concentric and eccentric spheres
摘要
奈米流體CuO／水之暫態自然對流介於兩同心和偏心球間在等溫邊條件下之數值模擬研究。控制方程式為渦流方程式、流線函數方程式及溫度方程式分別以正交雙球座標系統表示之。正交網格可獲得較高精確的數值解。以萊利數，普朗多數，偏心率參數及奈米顆粒體積分率等效應分別驗證了奈米流體的流動和熱傳特性。對於普朗多數為7.0，奈米顆粒體積分率從0.0到0.04，偏心率變化從-0.625到+0.625及萊利數變化從10^3到5×10^5等變化可獲得在同心和垂直偏心球間之穩態和暫態熱傳結果。平均紐塞數幾乎是連續線性地隨著Ø和Ra增加而增加。臨界萊利數值為Ra=10^4，超越此值則平均紐塞數𝑁u對於偏心率e的分佈曲線由凹轉為凸的輪廓。
並列摘要
Transient natural convection of CuO/water nanofluid between two concentric and vertically eccentric spheres with isothermal boundary conditions is studied numerically. The governing equations, in terms of vorticity, stream function and temperature are expressed in the orthogonal bispherical coordinate system. The orthogonal meshes are obtained a highly accurate numerical solution of the problem. The effects of Rayleigh number, Prandtl number, eccentricity parameter and volume fraction of nanoparticle on the flow and heat transfer characteristics have been examined. Results were obtained for steady and transient heat-transfer in concentric and vertically eccentric spheres at a Prandtl number of 7.0 and a radius ratio of 2.0, with nanoparticles volume fraction from 0.0 to 0.04, eccentricity varying from -0.625 to +0.625 and the Rayleigh number ranging from 10^3 to 5×10^5. The average Nusselt number increases almost linearly and continuously with increasing Ø and increases with the increasing Ra. The critical Rayleigh number is Ra=10^4, beyond which the curves of the profile of average Nusselt number 𝑁u vs. eccentricity e begin to change inversely from concave to convex.