冷卻流體方向效應對多孔性介質槽道熱流特徵之分析

Analysis of Coolant Fluid Orientation on Thermo-Fluidic Characteristics of the Porous Channel

鄭澤明(Tzer-Ming Jeng) ； 曾憲中(Sheng-Chung Tzeng) ； 羅婷尹(Ting-Yin Luo)

《建國科大理工期刊》 33卷2期 (2014/04) Pp. 77-90

摘要

本研究以實驗方法探討90度轉彎流與低槽寬－粒徑比的堆疊銅粒密實床槽道其熱流特性，銅粒之粒徑（d）有三種：2 mm、4 mm 與6 mm，槽道為固定尺寸，槽寬－粒徑比例（D_h/d）分別為7.5、3.75、2.5三種，變動參數包括加熱面與雷諾數（Re），結果發現粒徑越小者其摩擦係數（C_f）愈大，而在d=2 mm時，直流之C_f略高90度轉彎流，其它粒徑下此兩種流方之C_f則大致相同；而在低D_h/d與大Re時，直流與90度轉彎流系統之紐塞數（Nu）都會先沿槽道軸向遞增，然後才開始遞減至出口；此外，基本上平均紐塞數Nu是以粒徑d=6 mm (D_h/d=2.5)為最大，其次是粒徑d=2 mm (D_h/d=7.5)，粒徑d=4 mm (D_h/d=3.75)其Nu值最小，直流系統之Nu會略大於90度轉彎流，尤其是當分析之流道長度縮減時，至於不同加熱面對局部與平均紐塞數的影響並不顯著。

關鍵字

堆疊銅粒密實床 ； 90度轉彎流 ； 槽寬－粒徑比例 ； 熱傳遞

並列摘要

This study experimentally investigated the fluid flow and heat transfer in the brass-beads-packed-bed channel with the 90-deg turned flow and the small ratio of channel width to bead diameter. The diameters (d) of brass beads were 2 mm, 4 mm and 6 mm. The corresponding ratios (D_h/d) of channel width to bead diameter were 7.5, 3.75 and 2.5. The other parameters included the heated surface and Reynolds number. The results indicate that the friction factor (C_f) increased with decreasing the bead diameter. Besides, the C_f values of the straight-flow system were slightly higher than those of the 90-deg-turned-flow system at the cases of d=2 mm, they were similar for the cases of d=4 mm and 6 mm. When the D_h/d was small and the Re was large, the local Nusselt number (Nu) firstly increased along the streamwise direction and then decreased until the exit. Furthermore, the average Nusselt number (Nu) of d=6 mm (D_h/d=2.5) was maximum, and that of d=4 mm (D_h/d=3.75) was minimum. The Nu of d=2 mm was generally medium. The Nu for the straight-flow system was generally higher than that for the 90-deg-turned-flow system, especially for the shorter length of the channel being analyzed. However, the effect of the heated surface on the heat transfer was insignificant.

並列關鍵字

brass-beads packed bed ； 90-deg turned flow ； ratio of channel width to bead diameter ； heat transfer