Forced convective heat transfer of slush nitrogen in a horizontal pipe

In the present study, the flow and heat transfer characteristics of slush nitrogen in a horizontal pipe of 10.0 mm in diameter were investigated experimentally and theoretically. The flow velocity was in the range of 0.9-3.4 m/s, and the solid volume fraction was up to 30.0%, and the slush Reynolds number ranged from 1.89 × 104 to 1.01 × 105. The Eulerian-Eulerian multiphase model incorporated with the kinetic theory of granular flow was employed to investigate the forced convective heat transfer of slush nitrogen by taking into account of the heat and mass transfer between the solid and liquid phases. It was found that the pressure drop of slush nitrogen was higher than that of subcooled liquid nitrogen and increased with the solid volume fraction due to the existence of solid particles, and it showed different dependences on the flow velocity in the heterogeneous and pseudo-homogenous flows. Due to the latent heat involved in the solid-liquid phase change, the local heat transfer coefficients of slush nitrogen were higher than that of subcooled liquid nitrogen. The heat transfer between solid and liquid phases was enhanced as the solid volume fraction increased, leading to higher local heat transfer coefficient and lower and more stable fluid temperature of slush nitrogen. Although the dependences of the local heat transfer coefficient on the velocity and solid volume fraction were similar in both the homogeneous and heterogeneous flows, the distribution of the fluid temperature on the cross-section was found to vary with the flow patterns because of the non-uniform distribution of solid particles. The heat transfer correlation was proposed based on the experimental results for predicting the heat transfer performance of the heterogeneous and pseudo-homogenous slush nitrogen flows with various solid volume fractions.