Numerical evaluation on the flow and heat transfer characteristics of microencapsulated phase change slurry flowing in a circular tube

In order to alleviate the peak-valley difference of the energy supply load, thermal energy storage techniques have become the promising way. Microencapsulated phase change material slurry (MPCS) is a newly-developed tool to achieve high energy storage efficiency and charge/discharge efficiency due to its large thermal energy density and good heat transfer performance. In the present work, it was numerically investigated that the flow and heat transfer characteristics of MPCS in a horizontal circular pipe under constant heat flux on the pipe wall. It was found that the higher inlet velocity, smaller piping size, higher latent heat capacity, lower fluid viscosity and larger heat flux resulted in higher heat transfer coefficient. For the case under the conditions of vinlet = 0.5 m/s, cm = 10 wt%, q = 200 kW/m2, Tinlet = 300 K, D = 10 mm and d = 20 μm, the local heat transfer coefficient of the heat collecting pipe reached 25.2 kW/m2 K in the flow inlet region, remained within the range of 21.7-22.4 kW/m2 K in the melted region and dropped to 20.15 kW/m2 K in the outlet region. Finally, temperature field of MPCS was presented to analyze its superiority on heat transfer performance, indicating the reduction of the temperature difference between the wall and the fluid during heat transfer process was about 39% smaller than that of water.