Study on performance of carbon nanotube composite phase change cold storage sphere with annular fins

Abstract

Aiming at the poor phase change material thermal conductivity, high shell layer thermal resistance and low cold storage efficiency in encapsulated cold storage sphere systems, we adopt computational fluid dynamics to numerically investigate the cold storage process after adding carbon nanotubes to phase change paraffin cold storage spheres. The heat transfer model of a new type of annular-finned cold storage sphere and cold storage device is established, and the effects of sphere diameter, shell material, fins and refrigerating medium flow rate on the cold storage process are investigated. The results show that the optimum fin length of the sphere is 11 mm and the optimum fin spacing is 8 mm at a sphere diameter of 50 mm. The completion time of the carbon nanotube-added annular finned sphere is 48 min shorter than that of the traditional pure paraffin sphere without fins, and the cooling efficiency increases by 61.7 %, which is better than those of adding either fins or carbon nanotubes; carbon nanotube additions are better than fin additions to the single-variable factors to enhance the cooling effect. The convective heat transfer coefficients at 4 m/s and 5 m/s refrigerating medium flow rates increase by 20.1 % and 42.3 %, respectively, compared with those at 3 m/s. We provide a theoretical basis and reference value for the optimal design of an accumulator sphere and its devices.