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首页> 外文期刊>International Journal of Heat and Mass Transfer >Experimental and numerical study of fluid flow and heat transfer in a twisted square duct
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Experimental and numerical study of fluid flow and heat transfer in a twisted square duct

机译：方管中流体流动与传热的实验与数值研究

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摘要

Heat transfer and friction factor characteristics of air flow inside twisted square duct are studied experimentally and through three-dimensional numerical simulations. Experiments were conducted for air with uniform wall temperature boundary condition, twist ratio of 11.5 and 16.5, and Reynolds number 600-70,000. Laminar to turbulent flow transition point was identified. The results show considerable enhancement in heat transfer and pressure drop in both laminar and also in turbulent flow regimes till Reynolds number of 9500. Twist ratio of 11.5 shows relatively higher heat transfer and pressure drop compared to straight square duct. Three-dimensional analysis of steady fully-developed laminar flow inside twisted duct of square cross section flow area is carried out for Reynolds number range of 100-100,000 using commercially available software. The numerical study is conducted for a uniform wall temperature case, twist ratio of 2.5, 5,10 and 20, for Prandtl number range of 0.7 to 20. The maximum value for product of friction factor and Reynolds number is observed for a twist ratio of 2.5 and a Reynolds number of 3000. The maximum Nusselt number is observed for the same values for Prandtl number of 20. Correlations for friction factor and Nusselt number are developed involving swirl parameter in the laminar flow regime. Correlations are also provided for the entire range of turbulent regime. Local distribution of friction factor ratio and Nusselt number across a cross-section is presented. Based on constant pumping power criteria, enhancement factor is defined to compare twisted ducts with straight ducts. Selections of twisted square duct are presented in terms of enhancement factor. It is found that twisted duct performs well in laminar and also to some extent in turbulent flow regime due to strong presence of secondary flow. It is recommended to use twisted square duct in laminar flow regime for entire range of Prandtl number studied. Maximum enhancements factor of 10.5 is obtained with twist ratio of 2.5, Prandtl number of 20 and Reynolds number of 3000. Guidelines are provided for selection of twisted square duct in terms of Reynolds number and Prandtl number. Comparison with twisted elliptic tube and twisted tape are discussed. These results would help in the design and development of compact heat exchanger.
机译：通过三维数值模拟实验研究了方管内部气流的传热和摩擦系数特性。对具有均匀壁温边界条件，扭曲比为11.5和16.5，雷诺数为600-70,000的空气进行了实验。确定了层流到湍流的过渡点。结果表明，在层流和湍流状态下，传热和压降都得到了显着提高，直到雷诺数为9500。捻度比为11.5时，与直角方管相比，传热和压降相对较高。使用市售软件，对100-100,000的雷诺数范围进行了方形横截面流通面积的扭曲导管内稳定充分发展的层流的三维分析。在壁温均匀的情况下进行了数值研究，扭曲比为2.5、5,10和20，普朗特数范围为0.7到20。摩擦比和雷诺数乘积的最大值在2.5和雷诺数3000。对于普朗特数20的相同值，观察到最大努塞尔数。在层流状态下，涉及涡旋参数的摩擦系数和努塞尔数相关性得到发展。还提供了整个湍流范围的相关性。给出了横截面的摩擦系数比和Nusselt数的局部分布。基于恒定的抽气功率标准，定义了增强因子，以比较扭曲的风道和直的风道。扭曲方管的选择根据增强因子进行介绍。结果发现，由于次级流的强烈存在，扭曲的导管在层流中表现良好，在湍流状态中也有一定程度的表现。对于整个研究的普朗特数，建议在层流状态下使用扭曲方管。在扭曲比为2.5，普朗特数为20，雷诺数为3000的情况下，可获得最大增强因子10.5。为选择扭曲方管提供了有关雷诺数和普朗特数的准则。讨论了与扭曲椭圆管和扭曲带的比较。这些结果将有助于紧凑型热交换器的设计和开发。

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