A Standard Method to Determine Loss Coefficients of Conduit Components Based on the Second Law of Thermodynamics
A Standard Method to Determine Loss Coefficients of Conduit Components Based on the Second Law of Thermodynamics
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基于热力学第二定律确定管道部件损耗系数的标准方法
DOI：
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发表时间：
2012
期刊：
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通讯作者：
H. Herwig
中科院分区：
文献类型：
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作者：
B. Schmandt;H. Herwig
管道系统导管部件中的损失可以通过使用部件特定损失系数K来计算。特别是在小型和微型系统中，这些损失系数（层流中的损失系数强烈依赖于雷诺数）的准确知识是重要的。与直通道的贡献相比，有限的空间通常将导致单个部件的高损耗贡献。基于第二定律分析（SLA）的数值模拟确定单个组分的K值已被证明是一种非常有吸引力的方法。流场模拟显示了损失分布以及上游和下游冲击长度（Lu，Ld），否则充分发展的流会受到部件的影响。数值SLA方法作为一种标准方法介绍，说明和验证与90度弯曲与正方形横截面的高精度测量。计算了基于流场数值模拟的局部熵产生率，并对其进行了仔细的解释。K、Lu和Ld的部件特定值被收集在表格中，并通过沿着弯曲的中心线沿着的熵产生速率分布的曲线图来说明。通过专门为此目的建造的测试设施的实验结果进行了验证：90度弯曲中的层流是由受控齿轮泵诱导的，该齿轮泵使用不同粘度的聚二甲基硅氧烷作为工作流体。
Losses in conduit components of a pipe system can be accounted for by using component specific loss coefficients K. Especially in mini- and micro-systems an exact knowledge of these loss coefficients (which in laminar flow strongly depend on the Reynolds number) is important. Limited space will generally lead to a high loss-contribution of single components compared to the contribution of the straight channels. The determination of K-values of single components based on a numerical simulation using the Second Law Analysis (SLA) has turned out to be a very attractive method. The simulation of the flow field shows the distribution of losses and upstream and downstream lengths of impact (Lu, Ld) where the otherwise fully developed flow is affected by the component. The numerical SLA-Method is introduced as a standard method, illustrated and validated with highly accurate measurements in a 90 deg bend with a square cross section. The local entropy generation rates based on the numerical simulation of the flow field are computed and carefully interpreted. Component specific values of K, Lu are Ld are collected in a table and illustrated by plots of the entropy generation rate distribution along the bend’s centerline. Validation is achieved with experimental results from a test facility exclusively built for this purpose: Laminar flow in a 90 deg bend is induced by a controlled gear pump with polydimethylsiloxanes of different viscosities as working fluids.Copyright © 2012 by ASME