Numerical and experimental investigation of the flow and heat transfer characteristics for cold storage heat exchanger

Decreasing the freezing time of the cold storage heat exchanger was an effective way to reduce the risk of cold chain breakage and the fluctuation of cold chain temperature. A validated unsteady mathematical model of the cold storage heat exchanger was established to analyze the transient evolution of temperature, velocity, ice distribution, and heat transfer coefficient for different diameters of heat transfer tubes and coolant temperatures. The results showed that there were four stages of temperature in the cold storage heat exchanger, namely the primary cooling stage, the freezing stage, the secondary cooling stage, and the constant temperature stage. The ice fraction distribution and the heat transfer coefficient were inextricably linked to the water's natural convection. The average heat transfer coefficient decreased with decreasing coolant temperature and increasing heat transfer tube diameters. The freezing time decreased with the coolant temperature and the diameter of the heat transfer tubes decreasing. The tendency of the inhomogeneity of ice distribution first increased with the ice fraction up to 0.75 and then decreased with the ice fraction over 0.75. The inhomogeneity the decrease in the coolant temperature when the diameter of the heat transfer tubes was greater than 2 mm.