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首页> 外文期刊>International Journal of Heat and Mass Transfer >Heat transfer of developing and fully developed flow in smooth horizontal tubes in the transitional flow regime
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Heat transfer of developing and fully developed flow in smooth horizontal tubes in the transitional flow regime

机译：在过渡流态下，光滑水平管中已发展和已充分发展的流的热传递

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Limited experimental work has been done specifically focussing on how the heat transfer characteristics of developing flow in the transitional flow regime changes along the tube length, and how it compares with fully developed flow. The purpose of this study was therefore to experimentally investigate the heat transfer characteristics of developing and fully developed flow in smooth horizontal tubes in the transitional flow regime at a constant heat flux. An experimental set-up was designed, built and validated against literature. Two smooth circular test sections with inner diameters of 4 mm and 11.5 mm, respectively, were used and the maximum length-to-diameter ratios were 1373 and 872, respectively. Heat transfer measurements were taken at Reynolds numbers between 700 and 10 000 at different heat fluxes. The boundaries of the different flow regimes were defined mathematically, and terminology to define the transition characteristics were presented. It was found that the Reynolds number at which transition started was independent of axial position, and transition occurred at the same moment in time along the whole tube length. However, the end of transition was dependent on axial position and occurred earlier as the flow approached fully developed flow. Free convection effects affected both the start and end of the transitional flow regime, and caused the Reynolds number range of the transitional flow regime to decrease. Correlations were developed to determine the start and end of the transitional flow regime for developing and fully developed flow for mixed convection conditions. The transitional flow regime of developing flow was divided into three regions. In the first region, the width of the transitional flow regime decreased significantly with axial position and free convection effects were negligible. In region 2, the width of the transitional flow regime decreased with both axial position and free convection effects. In the fully developed region, the width of the transitional flow regime was independent of axial position, but free convection effects caused it to decrease and even to become negligible. It was concluded that the heat transfer characteristics of developing flow in the transitional flow regime changes as the flow develops and differ significantly from fully developed flow.
机译：已经进行了有限的实验工作，尤其着眼于在过渡流动状态下，发展中的流动的传热特性如何沿管长变化，以及如何与充分发展的流动进行比较。因此，本研究的目的是通过实验研究在恒定的热通量下，在过渡流动状态下，光滑水平管中正在发展和充分发展的流动的传热特性。设计了一个实验装置，并根据文献进行了验证。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。在不同的热通量下，在700至10000的雷诺数下进行传热测量。数学上定义了不同流态的边界，并提出了定义过渡特性的术语。发现转变开始的雷诺数与轴向位置无关，并且转变在整个管长的同一时刻发生。但是，过渡的结束取决于轴向位置，并且在流动接近完全展开的流动时发生得较早。自由对流影响过渡流态的开始和结束，并导致过渡流态的雷诺数范围减小。为了确定混合对流条件下流动的发展和充分发展，确定了相关性以确定过渡流动状态的开始和结束。发育流的过渡流态分为三个区域。在第一个区域，过渡流动形式的宽度随轴向位置而显着减小，并且自由对流效应可忽略不计。在区域2中，过渡流态的宽度随着轴向位置和自由对流效应而减小。在完全发达的区域，过渡流动形式的宽度与轴向位置无关，但是自由对流的影响导致过渡流体的宽度减小甚至可以忽略不计。结论是，在过渡流动状态下，发展中的流动的传热特性随着流动的发展而变化，并且与完全发展的流动有显着差异。

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