分離與附著柱鰭陣列窄管計算流場熱傳研究

Numerical Heat Transfer and Flow in Narrow Channel with Attached and Detached Pin Fin

This numerical study comparatively examines the flow and heat transfer characteristics hi two rectangular channels with attached and detached pin-fin arrays at Reynolds numbers (Re) of 10000. 15000, 20000, 25000 and 30000 using the commercial code Star CD. Clearances (C) between pin-tips and endwall for the present detached pin-tin array are fixed at 1/4 pin-diameter (d). The presence of pin-to-endwall clearances modifies the endwall flow structures by way of generating the accelerating flows over the pin-tips and results in the large-scale three dimensional vortical flows along two side walls of the detached pin-tin channel that leads to regional heat transfer enhancements. The lack of vortices and flow separations tripped by the attached pin-fins considerably reduces the inlet-to-exit pressure drops hi the detached pm-fin channel. But the absence of horseshoe vortices and the downstream wakes as well as the shear-layer separations over the endwall in the detached pin-fin channel moderates the gradients at endwall Nusselt number (No) distributions and reduces the area averaged endwall Nu (average)(Nu). As the endwall Nit with detached pin-tins is somewhat less than that with attached pin-fins but the channel pressure drop is much lower than that of the later, the thermal performance factors for the detached pin-fin channel ire improved from those of the attached pin-fin channel. 本數值研究使用STAR CD軟體，分析比較矩型窄道設置傳統柱鰭（attached pin-fin）與分離柱鰭（detached pin-fin）陣列於雷諾數＝10000，15000，20000，25000，30000時之熱傳及壓損特性。分離柱鰭陣列與管道壁面之間隙（C）固定為四分之一柱鰭直徑（d）。由於分離柱鰭與管道壁而間出現加速流場，遂改變其近壁流域之流場結構，並於分離柱鰭管道兩側導引出三維之渦流結構、治管道兩側緣形成熱傳強化區。由於出現於傳統柱鰭管道近壁流域之渦流及流體分離現象於分離柱鰭處消失，因次大幅降低分離柱鰭管道之進出口壓損。但是傳統柱鰭壁面與柱鰭連處之馬蹄形渦流以及其下游之分離剪力層亦於分離柱鰭處消失，致使分離柱鰭壁面之Nu數分佈趨勢較為緩和；但其熱傳係數略低於傳統柱鰭之壁面熱傳係數。雖然分離柱鰭管道之熱傳性能略遜於傳統柱鰭管道者，但是基於分離柱鰭管道之較低壓損係數，使得設置C=1/4d之分離柱鰭管道呈現高於傳統柱鰭管道之熱性能係數。