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

泥浆流体，如泥浆氢和泥浆氮，是两相（固-液）单组分低温流体，在液体中含有固体颗粒。本研究的目的是研究管道中泥态氮流动的强制对流换热特性和热流体不稳定性，并开发评估管道中泥态氮流动热流体现象的数值计算程序。在固相分数为0 ~ 40 wt%，平均流速为1 ~ 6m/s的条件下，进行了泥态氮在水平铜管中流动的强制对流换热系数和摩擦压降的实验测试。通过与过冷液氮实验结果的对比，发现并消除了压降降低导致的泥态氮换热系数变差现象。这对于将熔渣液作为制冷剂应用于超导设备具有重要意义。基于双流体模型，建立了包括重力效应在内的三维数值模拟方法，阐明了低温两相泥浆在直管流动中的特性。计算结果与新型PIV （Particle Image velocity metry）方法测量的固体颗粒速度分布吻合较好。因此，所开发的数值程序已被验证能够以足够的精度计算泥浆流动特性。

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.