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Numerical study of natural convection of heat exchangers immersed in a thermal storage vessel.

机译:浸入储热容器中的换热器自然对流的数值研究。

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摘要

The objective of this study is to gain physical insight into the transient velocity and temperature fields in a water filled thermal storage tank during discharge of the stored sensible heat via an immersed heat exchanger. The transient cooling process is first analyzed by an order of magnitude (scale) analysis of the governing conservation equations. This analysis yields a general semi-empirical correlation of the transient Nusselt number in terms of a single valued Rayleigh number. The Rayleigh number is determined at the initiation of discharge using known values of the initial water temperature and surface temperature of the heat exchanger. The approach is validated for two cases: a single horizontal tube and a 240 tube bundle, each immersed in a thin rectangular inclined tank representing an integral collector storage. The restriction on the practical use of the transient correlation is that the water filled tank is fully mixed throughout the discharge process.; Computational fluid dynamic models of discharge of the inclined rectangular tank and a vertical cylindrical tank provide details of the temperature distribution and flow field. The rectangular tank with a single tube heat exchanger is modeled in three dimensions with Fluent. Practical tube bundle heat exchangers are modeled by treating the heat exchanger as a porous medium within the fluid filled tank. The development of the numerical porous medium model is presented for local thermodynamic and non local thermodynamic cases. The model is validated using standard test cases without a heat exchanger and by comparison to temperature data for the rectangular tank. Results for the 240-tube bundle show conclusively that the buoyant flow in the tank results in a fully mixed tank in the region below the heat exchanger. Analysis of a coiled heat exchanger in a cylindrical storage tank provides additional evidence of mixing throughout the storage volume. The results also show that the mixed convection heat transfer to the heat exchanger is dominated by the forced convection component. An effort to improve the rate of discharge using baffles is moderately effective due to an increase in the water velocity across the heat exchanger.
机译:这项研究的目的是对通过浸没式热交换器排放的显热过程中充满水的储热罐中的瞬态速度和温度场进行物理分析。首先通过对控制守恒方程进行量级(比例)分析来分析瞬态冷却过程。通过单值瑞利数,该分析得出了瞬态Nusselt数的一般半经验相关性。瑞利数是在排放开始时使用热交换器的初始水温和表面温度的已知值确定的。该方法已针对两种情况进行了验证:单个水平管和240个管束,每个管束浸入代表整体收集器存储装置的矩形倾斜薄水箱中。暂态相关的实际使用的限制是在整个排放过程中,充满水的水箱必须充分混合。倾斜的矩形罐和垂直的圆柱形罐的排放的计算流体动力学模型提供了温度分布和流场的详细信息。带单管热交换器的矩形储罐使用Fluent进行了三维建模。实用的管束式换热器是通过将换热器视为充液罐内的多孔介质来建模的。针对局部热力学和非局部热力学情况,提出了数值多孔介质模型的发展。使用没有热交换器的标准测试案例并通过与矩形水箱的温度数据进行比较来验证该模型。 240管束的结果表明,罐中的浮力导致热交换器下方区域中的罐完全混合。对圆柱形储罐中的盘管热交换器的分析提供了在整个储藏空间中混合的其他证据。结果还表明,到换热器的混合对流传热受强制对流分量的支配。由于通过热交换器的水速度增加,使用挡板来提高排放速率的努力是适度有效的。

著录项

  • 作者

    Su, Yan.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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