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首页> 外文期刊>International Journal of Heat Exchangers >Heat Transfer from an Array of Cylinders in Oscillatory Flow
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Heat Transfer from an Array of Cylinders in Oscillatory Flow

机译：从振荡流中的一系列气缸传热

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摘要

Flow and heat transfer from a single cylinder that forms a part of an in-line array has been numerically analyzed under oscillatory flow conditions. The cylinder is a phospher-bronze wire, while the fluid is air. The flow and the thermal fields depend on the extent of blockage, parameterized by the porosity. Calculations have been reported in the present study mainly for a porosity of 0.71. Reynolds numbers of up to 20 based on the cylinder diameter have been employed in the calculations. Navier-Stokes equations are utilized for the gaseous phase, while the thermal problem involves conjugate heat transfer between the fluid and the solid. The flow field is determined using a harmonic analysis formulation, while the temperature field is obtained by marching in time. Numerical results of the present study show that the variation of friction factor with Reynolds number for oscillatory flow has a trend similar to that of steady flow. In this respect, frequency has a secondary role in determining friction factor. The first wire of the array has a higher friction factor compared to the developed section of the array. Inertial effects appear first in the third harmonic of the flow field. When the metallic wire is subjected to heating alone, the steady flow Nusselt number increases with Reynolds number. The Nusselt number also increases with the forcing frequency. The influence of flow development on heat transfer is found to be small. The local variation of dimensionless heat flux over the wire surface is qualitatively similar to that for steady flow, once the flow-direction is taken into account. Simulation with hot and cold fluid alternately moving past the wire reveals the following: The reciprocal of the twice the time constant of the gas-wire system is a characteristic frequency that determines the extent of energy exchange between the wire and the gas. When the frequency of the pulsating flow is matched with this value, the separation of the maximum and minimum tem- peratures attained by the wire is seen to be the greatest. As the forcing frequency increases, the duration of the transients increase and steady state is delayed. The effectiveness of energy transfer between the wire and the fluid decreases at higher Reynolds numbers.
机译：在振荡流动条件下，已经对来自形成串联阵列一部分的单个气缸的流动和传热进行了数值分析。圆柱体是磷青铜线，而流体是空气。流动和热场取决于由孔隙率参数化的阻塞程度。据报道，本研究主要针对孔隙率为0.71进行了计算。在计算中采用了基于圆柱直径的高达20的雷诺数。 Navier-Stokes方程用于气相，而热问题涉及流体和固体之间的共轭传热。流场是使用谐波分析公式确定的，而温度场是通过随时间推移获得的。本研究的数值结果表明，振荡流的摩擦系数随雷诺数的变化趋势与稳定流相似。在这方面，频率在确定摩擦因数方面具有次要作用。与阵列的展开部分相比，阵列的第一根导线具有更高的摩擦系数。惯性效应首先出现在流场的三次谐波中。当单独对金属线进行加热时，稳定流努塞尔数随雷诺数而增加。努塞尔数也随着强迫频率而增加。发现流动发展对热传递的影响很小。一旦考虑了流动方向，导线表面上无因次热通量的局部变化在质量上类似于稳定流动的局部变化。热流体和冷流体交替流过金属丝的模拟显示以下内容：气体金属丝系统时间常数的两倍的倒数是决定金属丝与气体之间能量交换程度的特征频率。当脉动流的频率与此值相匹配时，导线所达到的最大和最小温度之差被认为是最大的。随着强迫频率的增加，瞬变的持续时间增加并且稳态被延迟。在较高的雷诺数下，导线与流体之间的能量转移效率降低。

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