Forced Convection Heat Transfer Characteristics of Slush Nitrogen in Turbulent Pipe Flows

半融化流体，例如半融化氢和半融化氮，是在液体中含有固体颗粒的两相（固-液）单组分低温流体。本文旨在研究氮浆在管内流动的强制对流换热特性和热-流不稳定性，在固体含量为0 ~ 40wt%，平均流速为1 ~ 6 m/s的范围内，对氮泥浆进行了实验研究，并对氮泥浆的热流体现象进行了数值模拟。得到了水平铜管内的强制对流换热系数和摩擦压降。通过与过冷液氮实验结果的对比，发现并消除了由于压降降低而引起的液氮传热系数恶化现象。这一结果对低温两相流在超导设备中的应用具有重要的指导意义。为了研究低温两相流在直管中的流动特性，建立了基于双流体模型的考虑重力影响的三维数值模拟方法。计算结果与PIV（Particle Image Velocimetry）方法测量的固体颗粒速度分布吻合较好。因此，开发的数值代码已被验证能够计算泥浆流特性具有足够的精度。

Slush Fluids, such as slush hydrogen and slush nitrogen, are two-phase (solid-liquid) single-component cryogenic fluids containing solid particles in a liquid. The objectives of the present study are to investigate the forced convection heat transfer characteristic and thermo-fluid instability of slush nitrogen flowing in a pipe, and to develop the numerical code to evaluate the thermo-fluid phenomenon of the slush fluid flowing in a pipe.Experimental tests were performed with the slush nitrogen in the ranges of solid fraction from 0 to 40 wt% and mean velocity from 1 to 6m/s to obtain both the forced convection heat transfer coefficient and the frictional pressure drop flowing in a horizontal copper pipe. Compared with the experimental results of subcooled liquid nitrogen, the deterioration phenomena of heat transfer coefficients for slush nitrogen caused by the pressure drop reduction were found and cleared in the present study. This is the important and useful result for applying the slush fluid as a refrigerant to superconducting equipments.Three-dimensional numerical simulation method including the gravity effect based on the two-fluid model has been developed to clarify the characteristics of the cryogenic two-phase slush fluid in a straight pipe flow. It was found that the calculated results were in good agreement with the velocity distributions of solid particles measured by the new PIV (Particle Image Velocimetry) method. In consequence, the developed numerical code has been verified to be able to calculate the slush flow characteristics with sufficient accuracy.