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首页> 外文期刊>International Journal of Heat and Mass Transfer >Single-phase mixed convection of developing and fully developed flow in smooth horizontal circular tubes in the laminar and transitional flow regimes
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Single-phase mixed convection of developing and fully developed flow in smooth horizontal circular tubes in the laminar and transitional flow regimes

机译：层流和过渡流态下光滑水平圆形管中展开和完全展开流动的单相混合对流

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摘要

Correlations to calculate the local and average heat transfer coefficients for single-phase laminar flow in horizontal circular tubes with a constant heat flux boundary condition are usually restricted to fully developed flow, high Prandtl numbers or constant fluid properties. What further complicates the heat transfer characteristics of developing flow, is the local transition from laminar to turbulent flow along the tube length, above the critical Reynolds number. The purpose of this study was to investigate the effects of free convection on the development of the local heat transfer characteristics in smooth horizontal circular tubes heated with a constant heat flux. An experimental set-up was designed, built, and results were validated against literature. Two smooth circular test sections with inner diameters of 4 mm and 11.5 mm were used, and the maximum length-to-diameter ratios were 1373 and 872, respectively. Heat transfer measurements were taken at Reynolds numbers between 500 and 10,000 at different heat fluxes. A total of 1046 mass flow rate measurements and 89,459 temperature measurements were taken. Water was used as the test fluid and the Prandtl number ranged between 3 and 7. Three different regions were identified for developing laminar flow and were qualitatively and quantitatively defined. Correlations were developed to determine the thermal entrance lengths, as well as local and average Nusselt numbers for developing and fully developed laminar flow in mixed convection conditions with a constant heat flux boundary condition. In the transitional flow regime, the laminar-turbulent transition along the tube length was divided into four regions, and it was found that the flow transitioned faster with increasing free convection effects and Reynolds number.
机译：计算具有恒定热通量边界条件的水平圆形管中单相层流的局部和平均传热系数的相关性通常仅限于充分发展的流量，高Prandtl数或恒定的流体特性。使显影流的传热特性进一步复杂化的是，沿着层管长度从层流到湍流的局部跃迁，高于雷诺临界值。这项研究的目的是研究自由对流对以恒定热通量加热的光滑水平圆形管中局部传热特性发展的影响。设计，建立了一个实验装置，并根据文献对结果进行了验证。使用两个内径分别为4 mm和11.5 mm的光滑圆形测试部分，最大长径比分别为1373和872。在不同热通量下，雷诺数在500和10,000之间进行传热测量。总共进行了1046次质量流量测量和89,459次温度测量。使用水作为测试流体，Prandtl数在3到7之间。确定了三个不同的区域来形成层流，并定性和定量地定义了区域。建立了相关性，以确定在恒定的热通量边界条件下混合对流条件下层流流动的发展和完全展开的层流的热入口长度以及局部和平均Nusselt数。在过渡流态中，沿管长的层流湍流过渡被划分为四个区域，并且发现随着自由对流效应和雷诺数的增加，流的过渡速度更快。

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