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Fundamental Studies of Crossflow Heat Exchangers for Laminar and Turbulent Flows

机译：层流和湍流错流换热器的基础研究

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摘要

The focus of this thesis research is heat transfer and fluid flow in heat exchangers where a fluid flows across heated cylindrical elements. Three unique devices are considered, and highly detailed and accurate solutions are obtained for each by making use of advanced numerical simulation techniques. As prerequisite to the implementation of these solutions, validation of the numerical procedure was obtained by comparing highly accurate and complete experimental data to the numerical predictions for a relevant test case.;The first considered situation is a two-dimensional, in-line tube bank where the number of rows and the Reynolds number serve as parameters. New methods were devised to determine the prevailing flow regime in the tube bank, one based on the calculation of the turbulent viscosity and the other utilizing a comparison of heat transfer coefficients respectively determined from laminar and turbulent models. Array-based average heat transfer coefficients showed that shorter arrays gave rise to higher values of the transfer coefficient, in contrast to certain literature predictions.;The second studied case is the simultaneous treatment of heat transfer in a pin-fin array and the fluid flow created by a conventional rotating fan which is delivered to the inlet of the array. The basic issue is the nature of the delivered flow. Even when a blower curve is used, it is assumed that the delivered flow is uniformly distributed across the heat exchanger. In reality, when blade rotation of the fluid mover are taken into account, the uniformity disappears. In fact, the delivered flow includes a swirl component superimposed on the main axial flow. The velocity of the delivered flow may be larger adjacent to the walls than it is in the core of the flow. In many cases, backflow occurs, driven by the rotation of the hub of the fan. The outcome of the work is that correct results require simultaneous treatment of the fluid mover and the heat exchanger. The final dealt-with case is the cylinder in crossflow and provides the most complete set of transient heat transfer results ever.
机译：本文研究的重点是热交换器中的传热和流体流动，其中流体流经加热的圆柱体。考虑了三个独特的设备，并通过使用先进的数值模拟技术为每个设备提供了高度详细和准确的解决方案。作为实施这些解决方案的先决条件，通过将高精度和完整的实验数据与相关测试案例的数值预测进行比较，来获得数值程序的验证。;首先考虑的情况是二维，直列式管束行数和雷诺数用作参数。设计了新的方法来确定管束中的主流流动方式，一种基于湍流粘度的计算，另一种利用比较分别从层流模型和湍流模型确定的传热系数的方法。基于阵列的平均传热系数表明，与某些文献预测相反，较短的阵列会导致较高的传热系数值。第二个研究案例是同时处理针翅阵列中的传热和流体流动由传统的旋转风扇产生，该风扇被传送到阵列的入口。基本问题是交付流程的性质。即使在使用鼓风机曲线时，也可以假设输送的流量在整个热交换器中均匀分布。实际上，当考虑流体推动器的叶片旋转时，均匀性消失。实际上，所输送的流包括叠加在主流上的涡流分量。靠近壁的输送流的速度可能比流芯处的速度大。在许多情况下，由于风扇轮毂的旋转而产生回流。工作的结果是，正确的结果需要同时处理流体推动器和热交换器。最终处理的情况是气缸处于错流状态，并提供了有史以来最完整的瞬态传热结果。

著录项

  • 作者

    Ahn, Jungwon.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 150 p.
  • 总页数 150
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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