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Thermal-Boundary-Layer Response to Convected Far-Field Fluid Temperature Changes

机译:对流远场流体温度变化的热边界层响应

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摘要

Fluid flows of varying temperature occur in heat exchangers, nuclear reactors, nonsteady-flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method was developed with the capability to predict the transient laminar thermal-boundary-layer response for similar or nonsimilar flow and thermal behaviors. The method was tested for the step change in the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes in the magnitude and sign of the fluid-wall temperature difference were considered, including flow with no initial temperature difference and built-up thermal boundary layer. The equations for momentum and energy were solved based on the Keller-box finite-difference method. The accuracy of the method was verified by comparing with related transient solutions, the steady-state solution, and by grid independence tests. The existence of a similarity solution is shown for a step change in the far-field temperature and is verified by the computed general solution. Transient heat transfer correlations are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from predictions by quasisteady models commonly used. The deviation is greater and lasts longer for large Prandtl number fluids.
机译:温度变化的流体流发生在热交换器,核反应堆,非恒定流装置和内燃机中,其中传热过程会影响能量转换效率。开发了一种通用数值方法,能够预测相似或不相似的流动和热行为的瞬态层流热边界层响应。测试了该方法的二维半无限平板的远场流动温度的阶跃变化,该二维半无限平板具有稳定的流体动力边界层和恒定的壁温假设。考虑了流体壁温差的大小和符号的变化,包括没有初始温差的流动和积聚的热边界层。基于Keller-box有限差分法求解了动量和能量方程。通过与相关的瞬态解,稳态解进行比较,并通过网格独立性测试,验证了该方法的准确性。对于远场温度的阶跃变化,显示了相似性解决方案的存在,并通过计算得出的通用解进行了验证。给出了瞬态热传递相关性,这表明热传递的大小和方向都可能与通常使用的拟稳态模型的预测显着不同。对于大的普朗特数流体,该偏差更大,并且持续时间更长。

著录项

  • 作者

    Li Hongwei; Nalim M. Razi;

  • 作者单位
  • 年度 2008
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  • 原文格式 PDF
  • 正文语种 en_US
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