Numerical And Experimental Study On Pool Boiling Heat Transfer Characteristics Of Slush Nitrogen

Slush nitrogen is the cryogenic two-phase fluid with small solid nitrogen particles suspended in liquid nitrogen.Slush nitrogen is a potential coolant for high temperature superconducting due to its high density and large heat capacity.However,the flow and heat transfer of slush nitrogen need to be further studied in order to promote its practical applications.The present work focuses on the pool boiling heat transfer characteristics of slush nitrogen by theoretical and experimental study as follows: 1.Based on Euler-Euler model,a numerical model for pool boiling heat transfer of slush nitrogen was established.The kinetic model of granular flow was used to describe the collision between particles and the interaction between particles and liquid phase.The RPI nucleate boiling model was used to describe the heat transfer mechanism at the boiling surface.The RPI boiling model and the boiling parameter models were verified to be capable of simulating the pool boiling of liquid nitrogen and slush nitrogen.The boiling processes of liquid nitrogen and slush nitrogen were studied by numerical simulation,and the characteristics of each phase as well as the flow characteristics in the pool were analyzed.2.An experimental platform for the pool boiling heat transfer of slush nitrogen was built.The freeze-thaw method was used to produce slush nitrogen and the capacitance-type density meter was adopted to determine the solid volume fraction of slush nitrogen.The steady-state boiling conditions were obtained by the heat flux control method.The characteristics of pool boiling heat transfer of slush nitrogen and the factors affecting heat transfer were observed experimentally.The experimental results show that the heat transfer characteristics of slush nitrogen matches with typical nucleate boiling heat transfer.The heat transfer of slush nitrogen is enhanced by increasing solid fraction.In addition,hysteresis phenomenon was also observed in the boiling of slush nitrogen.3.An experimental correlation for nucleate pool boiling heat transfer of slush nitrogen was established.The applicability of Rohsenow model to the nucleate pool boiling heat transfer of liquid nitrogen and slush nitrogen was analyzed,and then a heat transfer correlation for nucleate pool boiling heat transfer of liquid nitrogen and slush nitrogen,considering the effect of solid volume fraction,was summarized.