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Heat Transfer and Pressure Drop Characteristics of Smooth Horizontal Tubes in the Transitional Flow Regime

机译：过渡流动条件下光滑水平管的传热和压降特性

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摘要

The operating conditions of many heat exchangers are in, or close to, the transitional flow regime. However, in this regime, not a lot of design information is available and some design books even recommend to not design heat exchangers to operate in the transitional flow regime. Furthermore, it is known that the type of inlet of heat exchangers influences the transition characteristics. It was therefore the purpose of this study to measure heat transfer and pressure drop characteristics in smooth horizontal tubes using different types of inlets. The types of inlets were hydrodynamically fully developed, square-edged, re-entrant, and bellmouth. Experiments were conducted on a 14.48-mm inner diameter horizontal tube in which the water was cooled. Reynolds numbers ranged between 1000 and 20,000 and Grashof numbers were on the order of 10s. It was found that for adiabatic flow the square-edged inlet delayed transition to Reynolds numbers of around 2600, while the bellmouth inlet delayed it to about 7000. However, for diabatic flow, the transition was independent of the type of inlet. Laminar friction factors were much higher than their theoretically predicted values due to the secondary flows increasing the amount of mixing in the tube. Heat transfer measurements showed that transition with water was totally independent of the type of inlet used.
机译：许多热交换器的操作条件处于或接近过渡流动状态。但是，在这种情况下，没有很多设计信息可用，有些设计书甚至建议不要设计热交换器以在过渡流动状态下运行。此外，已知热交换器的入口的类型影响过渡特性。因此，本研究的目的是使用不同类型的入口来测量光滑水平管中的传热和压降特性。进水口的类型在流体动力学上得到了充分发展，为方形，折返式和喇叭形。在内径为14.48mm的水平管中进行了实验，在其中冷却了水。雷诺数在1000到20,000之间，而Grashof数在10s数量级。已发现，对于绝热流，方形入口将延迟转换为雷诺数约2600，而喇叭形入口将其延迟转换为约7000。但是，对于绝热流，转换与入口类型无关。层流摩擦系数远高于其理论预测值，这是由于二次流增加了管中的混合量。传热测量表明，与水的过渡完全独立于所使用的入口类型。

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  • 来源
    《Heat Transfer Engineering》 |2014年第15期|1246-1253|共8页
  • 作者

    JOSUA P. MEYER; JONATHAN A. OLIVIER;

  • 作者单位

    Department of Me-chanical and Aeronautical Engineering, University of Pretoria, Pretoria, 0002, South Africa;

    Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, South Africa;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
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