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首页> 外文期刊>International Journal of Heat Exchangers >Specific Features of Heat Transfer and Hydraulic Resistance in Compact Heat Exchangers with Helical Tubes
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Specific Features of Heat Transfer and Hydraulic Resistance in Compact Heat Exchangers with Helical Tubes

机译：带螺旋管的紧凑型换热器的传热特性和水力阻力

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The bundles of helical tubes or rods are used in heat exchangers and in space nuclear propulsion power plant intended for piloted expedition to Mars and are characterized by high heat transfer areas per unit volume (above 1250m~2/m~3) and by enhancement of heat transfer by modifying the flow patterns near the surface. In this case one of the urgent problems is the determination of coefficients of heat transfer and hydraulic resistance in bundles of helical tubes and rods of small diameters to be manufactured from the reactor materials: carbides of refractory metals, graphite and stainless steel. The generalization results of new experimental investigations of hydraulic resistance and heat transfer are presented for a bundles of helical tubes of oval, three-blade and four-blade profiles in the form of the criteria equations at flow of different heat carriers: air, water and liquid oxygen. It is discovered, that in bundles with flow swirling of helical tubes or rods the boundary layer thickness is smaller in ten times as equivalent diameter of channel. Therefore, the rough of surface of helical rods is shown up on the lesser values of Reynolds number as compared with a circular tubes to be manufactured from those materials. Moreover, the transition of coefficients of hydraulic resistance and heat transfer from laminar to turbulent flow covers a considerable Reynolds number range (80-104) and is smooth. The loss of stability of laminar flow is conditioned by nonstability of boundary layer on the curved walls of helical tubes and by additional turbulization of flow. The discovered specific features of heat transfer and hydraulic resistance in helical tube bundles allowed to determine the mechanisms of enhancement of transport processes in this channels. The representation of experimental data on heat transfer and hydraulic resistance in helical rod bundles in the form of the proposed criterial relations extends the modeling potentialities of heat transfer and diminishes the number of experimental studies necessary to establish these relations.
机译：螺旋管束或棒束用于换热器和拟用于火星试飞的空间核推进动力装置，其特征是单位体积的传热面积高（1250m〜2 / m〜3以上），并且通过增加通过修改表面附近的流动模式进行热传递。在这种情况下，紧迫的问题之一是确定由反应堆材料制成的小直径螺旋管和棒束的传热系数和水力阻力，这些材料包括难熔金属的碳化物，石墨和不锈钢。以一束标准方程的形式，在不同的热载体（空气，水和空气）的流动下，以椭圆，三叶片和四叶片轮廓的螺旋管束的形式，给出了水力阻力和热传递的新实验研究的一般化结果。液态氧。已经发现，在具有螺旋管或棒的流动旋涡的束中，边界层厚度比通道的等效直径小十倍。因此，与由那些材料制造的圆形管相比，在较小的雷诺数值上显示出螺旋杆的表面粗糙。此外，从层流到湍流的水力阻力系数和传热系数的过渡范围涵盖了相当大的雷诺数范围（80-104），并且是平滑的。层流稳定性的损失取决于螺旋管弯曲壁上边界层的不稳定性和附加的湍流。螺旋管束中已发现的传热和水力阻力的特定特征决定了该通道中传输过程的增强机理。以建议的标准关系形式表示螺旋棒束中的传热和水力阻力的实验数据，扩展了传热的建模潜能，并减少了建立这些关系所必需的实验研究的数量。

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