Fundamental Study of Heat Transfer Characteristics of Flowing Slush Nitrogen

Abstract

Slush nitrogen is a mixture of liquid and solid nitrogen. Fine solid particles are dispersed in liquid phase. It enables us to utilize latent heat and increase the quantity of refrigerant supplied. Therefore, it can be expected to be useful as a high-performance refrigerant for high-temperature superconductive devices. This study discusses the heat transfer characteristics of slush nitrogen when flowing in pipes. The relationship between the heat transfer coefficient and velocity is investigated experimentally. The flow velocity, temperature (sub-cooled liquid nitrogen) and mass solid fraction are controlled parameters. The results revealed that, under the condition when the Reynolds number is less than 100,000, the heat transfer coefficient of slush nitrogen is larger than that of sub-cooled liquid nitrogen. Furthermore, the heat transfer characteristic of sub-cooled liquid nitrogen is almost equal to the prediction by Colburn's equation (i.e., empirical equation on heat transfer in pipes during turbulent flow).