板式熱交換器內部之兩相分布模擬與流動分布不均勻性分析;Numerical Analysis of Two Phase Flow and Flow Maldistribution in Plate Heat Exchangers

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题名:	板式熱交換器內部之兩相分布模擬與流動分布不均勻性分析;Numerical Analysis of Two Phase Flow and Flow Maldistribution in Plate Heat Exchangers
作者:	朱彥丞;Zhu,Yan-Cheng
贡献者:	機械工程研究所
关键词:	計算流體力學;分布器;流動分布不均勻;山型紋;板式熱交換器;Flow maldistribution;Chevron corrugation;Distributor.;Computational fluid dynamics;Plate heat exchanger
日期:	2012-07-28
上传时间:	2012-09-11 18:18:21 (UTC+8)
出版者:	國立中央大學
摘要:	近年的板式熱交換器流動分布研究中，對於兩相流分布多以實驗方式分析，由於板式熱交換器內部流場不易觀察，學者均改用結構較簡單之平板管或者圓管代表真實板片。本研究使用計算流力軟體ANSYS FLUENT將業者開發的K050山型紋板式熱交換器真實板片組成之流場建模，探討兩相流與流動分布不均勻現象，分析分布器開口方向對流場影響及在多流道流場中分布器對氣液分布之影響。本研究分為兩部份，第一部份藉由實驗數據比對，以空氣與水為工作流體來研究不同分布器開口方向（12點鐘、3點鐘、4點鐘、5點鐘、6點鐘、9點鐘方向）對於單一流道兩相流現象。模擬結果顯示，3點鐘、4點鐘、6點鐘方向有較好的分布，在低雷諾數（Rel =500）時，分布器開口方向為3點鐘之案例的氣體分布較不均勻，而分布器開口方向為6點鐘有較佳的分布。在Rel =1500的案例中，3點鐘與6點鐘方向的案例均有較佳的流場分布，且標準差降低許多；整體來說增加雷諾數使流場轉變為紊流改善了流動不均勻情形。在Rel =3000的案例中，則是4點鐘方向的案例有最佳的流動分布，若考慮到壓降以及冷熱側流體流動路徑的影響，4點鐘方向是較佳的分布器入口設計。第二部份研究是針對10流道之K050板式熱交換器流場，研究分布器對於多流道之流動分布不均勻性的改善效果。模擬結果顯示，在未使用分布器的多流道板式熱交換器中，如果要有較均勻的汽液分布，必須使流場有較高的雷諾數，若是熱交換器在雷諾數小於1500的條件下，汽液分布會非常不平均。加入分布器後，汽態冷媒的分布不均勻現象可以獲得有效的改善，但是對於液態冷媒只有在低雷諾數時的效果較佳，當雷諾數升高時，分布器對於液態冷媒的分布不見得有效。In the recent years, most of investigations of two phase flow distribution in plate heat exchanger (PHE) were experimental study. Due to complexity of flow and thermal structure inside PHE, researchers used simpler flat/circular tubes to represent the real plate in PHE. This study used the Computational fluid dynamics software ANSYS FLUENT to model an industrial type of K050 chevron corrugation PHE and simulated the two phase flow distribution. Several eﬀects were studied, including two phase flow, flow maldistribution, the operating condition and the direction of the inflow distributor.This paper was divided into two parts. First, the air/water two phase flow was investigated for effect of various direction of air inflow distributor (12 clock, 3 clock, 4 clock, 5 clock, 6 clock and 9 clock) in the single channel PHE. Simulation results showed that the direction of 3, 4 and 6 clocks generated better flow distribution. At low Reynolds number (Rel =500), the case of 3 clock had the most uneven flow distribution, while better flow distribution was observed for the case of 6 clock. At medium Reynolds number (Rel =1500), all the three cases (3, 4, 6 clocks) improved their flow distribution with reduced standard deviation of flowrate. It can be concluded that the increase of the Reynolds number which transformed the flow into turbulent and improved the flow distribution across channels inside PHE. At the high Reynolds number (Rel =3000), the case of 4 clock had the best even flow distribution. Finally, consider the effects of the flow passages on the hot/cold sides and the pressure drop, air inflow at 4 clock of the distributor was recommended.The second part was investigation for the improvement of two phase flow distribution in a 10-channel PHE with an inflow distributor. Numerical results showed that at the multi-channels PHE without the distributor, the flow must operated at higher Reynolds number in order to have better flow distribution. If the PHE operated under Reynolds number lower than 1500, the vapor-liquid distribution can very uneven. With the inflow distributor added, the maldistribution of the vapor phase improved significantly. Yet the flow distribution of liquid phase only worked at low Reynolds number condition. As Reynolds number increased, the inflow distributor was not that effective for liquid flow distribution.
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