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Computational Modeling of Convective Heat Transfer in Compact and Enhanced Heat Exchangers.

机译：紧凑型和增强型换热器中对流换热的计算模型。

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摘要

Compact heat exchangers are employed in many different applications because of their high surface area density. Plate-fin heat exchangers in particular are well suited for gas-to-gas and air-to-air recuperators and heat recovery units, among many other applications. In this thesis, constant property, fully or periodically developed laminar flows of air (Pr = 0.72) inside a variety of different inter-fin channels of plate-fin heat exchangers are studied computationally, with the goal of achieving better understanding of plate-fin heat exchangers and providing new designs with superior performance to the existing ones.;Majority of plate-fin channels have rectangular, trapezoidal or triangular cross-sectional shapes. Their convective behavior for air flows is investigated and solutions and polynomial equations to predict the Nusselt number are provided. Besides the limiting cases of a perfectly conducting and insulated fin, the actual conduction in the fin is also considered by applying a conjugate conduction-convection boundary condition at the fin surface between partition plates. For the latter, new sets of solutions and charts to determine the heat transfer coefficient based on the fin materials, channel aspect ratio, and fin density are presented.;Furthermore, while large fin density increases the heat transfer surface area, the convection coefficient can be increased by geometrical modification of the fins. To this end, two different novel plate-fin configurations are proposed and their convective behavior investigated in this thesis. These include (1) slotted plate-fins with trapezoidal converging-diverging corrugations, and (2) offset-strip fins with in-phase sinusoidal corrugations.;The enhanced heat transfer performance of the plate-fin compact core with perforated fin-walls of symmetric, trapezoidally profiled, converging-diverging corrugations is modeled computationally. Air flow rates in the range 10 ≤ Re ≤ 1000 are considered in a two dimensional duct geometry described by the trapezoid inclination angle, the convergent-divergent amplitude ratio, the dimensionless corrugation pitch, and a surface porosity beta of 10%. The fin-wall flow transpiration is seen to promote enhanced heat transfer by inducing cross stream mixing, and periodic disruption and restarting of boundary layers. With uniform heat flux [H1] at the fin walls, an unusual performance is obtained where higher Nusselt number is accompanied with reduction in the corresponding friction factor, relative to a non-slotted geometry of the same dimensions.;In the case of sinusoidal wavy offset-strip channels, the performance enhancement is evaluated for air flows in the range of 10 ≤ Re ≤ 1000, with fins at constant wall temperature [T], the effect of the wavy-fin amplitude, inter-fin spacing, and fin offset position on the thermal-hydraulic performance is reported. It is generally seen that S-shaped offset channels perform better than C-shaped ones. An average of 400% reduction in volume of a plate-fin heat exchanger can be achieved with S-shaped offset fins when compared to that with plain parallel fins.
机译：紧凑型热交换器由于其高的表面积密度而被用于许多不同的应用中。特别是板翅式换热器非常适合用于气体对气体和空气对空气的换热器以及热回收装置以及许多其他应用。本文通过计算研究板翅式换热器各种不同翅片间通道内的恒定特性，完全或周期性形成的层流空气（Pr = 0.72），以期更好地理解板翅式换热器，并提供比现有换热器性能更高的新设计。;大多数板翅式通道的横截面形状为矩形，梯形或三角形。研究了它们在气流中的对流行为，并提供了预测Nusselt数的解和多项式方程。除了极好的导电和绝缘鳍片的极限情况外，还通过在隔板之间的鳍片表面施加共轭传导-对流边界条件来考虑鳍片中的实际传导。对于后者，提出了基于翅片材料，通道纵横比和翅片密度来确定传热系数的新的解决方案和图表集；此外，尽管翅片密度较大，但对流系数却可以通过翅片的几何修改增加。为此，本文提出了两种不同的新型板翅结构，并研究了其对流行为。其中包括（1）具有梯形收敛-发散波纹的开槽板翅片，以及（2）具有同相正弦波状波纹的偏置条翅片;具有开孔翅片壁的板翅紧凑型芯增强的传热性能通过计算对对称，梯形轮廓，收敛-发散的波纹进行建模。在由梯形倾斜角，会聚-发散振幅比，无因次波纹节距和10％的表面孔隙度β所描述的二维管道几何形状中，考虑了10≤Re≤1000范围内的空气流速。翅片壁的流汗被认为通过引起横流混合以及边界层的周期性破坏和重新开始而促进了增强的热传递。在翅片壁上具有均匀的热通量[H1]时，相对于相同尺寸的非开槽几何形状，在较高的努塞尔特数和相应的摩擦系数降低的情况下，可获得非同寻常的性能。偏置条通道，对于在10≤Re≤1000范围内的气流，在恒定壁温[T]的情况下评估了性能增强，波纹状波幅的幅度，翅片间距和翅片偏移的影响报告了热工液压性能的位置。通常可以看到，S形偏移通道的性能优于C形偏移通道。与普通平行散热片相比，S形偏置散热片平均可减少板翅式热交换器的体积400％。

著录项

  • 作者

    Huzayyin, Omar Ahmed Soliman.;

  • 作者单位

    University of Cincinnati.;

  • 授予单位 University of Cincinnati.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 193 p.
  • 总页数 193
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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