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首页> 外文期刊>Heat Transfer Engineering >1st and 2nd Law Characteristics in a Micropipe: Integrated Effects of Surface Roughness, Heat Flux and Reynolds Number
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1st and 2nd Law Characteristics in a Micropipe: Integrated Effects of Surface Roughness, Heat Flux and Reynolds Number

机译：微管的第一定律和第二定律特性：表面粗糙度，热通量和雷诺数的综合影响

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摘要

A computational study of the integrated effects of surface roughness, heat flux, and Reynolds number on the 1st and 2nd law characteristics of laminar-transitional flow in a micropipe is presented. Analyses are carried by solving the variable fluid property continuity, Navier-Stokes, and energy equations for the surface roughness, heat flux, and Reynolds number ranges of 1-50 μm, 5-100 W/m~2, and 1-2000, respectively. Computations put forward that surface roughness not only accelerates transition to lower Reynolds number but also augments heat transfer rates, such that the transitional Reynolds numbers and intermittency values are evaluated as ～1650, ～575, and ～450 and 0.132, 0.117, and 0.136 for the surface roughness cases of 1, 20, and 50 μm, respectively. Thermocritical Reynolds numbers are identified by determining the viscous dissipation rates, which characterize the heating/cooling behavior and the related Reynolds number range. Surface roughness comes out to have no role on entropy generation at low Reynolds numbers; moreover, entropy generation is found to be inversely proportional with mean temperature variation, where the trends become almost asymptotic at the lower limit of the investigated Reynolds number range. Being independent of surface roughness, heat flux, and Reynolds number, radial irreversibility distribution ratio is determined to be negligible at the pipe centerline, indicating that the frictional entropy is minor and the major portion of the total entropy generation is thermal based.
机译：提出了表面粗糙度，热通量和雷诺数对微管层流过渡流动的第一和第二定律特征的综合影响的计算研究。通过求解可变的流体性质连续性，Navier-Stokes和能量方程，进行表面粗糙度，热通量和雷诺数范围为1-50μm，5-100 W / m〜2和1-2000的分析，从而进行分析，分别。计算结果表明，表面粗糙度不仅可以加速过渡到较低的雷诺数，而且可以提高传热速率，因此过渡雷诺数和间歇性值分别被估计为〜1650，〜575和〜450，而对于表面粗糙度分别为1、20和50μm。通过确定粘性耗散率来确定热临界雷诺数，该粘性耗散率表征了加热/冷却行为以及相关的雷诺数范围。结果表明，在低雷诺数下，表面粗糙度对熵的产生没有影响。此外，发现熵的产生与平均温度变化成反比，平均温度变化在所研究的雷诺数范围的下限处趋于渐近。不受表面粗糙度，热通量和雷诺数的影响，在管道中心线处确定的径向不可逆分布比率可忽略不计，这表明摩擦熵很小，总熵产生的主要部分是基于热的。

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