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

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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.