Thermal performance of water-based suspensions of phase change nanocapsules in a natural circulation loop

Experiments were conducted to investigate the heat transfer characteristics of water-based suspensions of phase change nanocapsules in a natural circulation loop with mini-channel heat sinks and heat sources. A total of 23 and 34 rectangular mini-channels, each with width 0.8 mm, depth 1.2 mm, length 50 mm and hydraulic diameter 0.96 mm, were evenly placed on the copper blocks as the heat source and heat sink, respectively. The adiabatic sections of the circulation loop were constructed using PMMA tubes with an outer diameter of 6 mm and an inner diameter of 4 mm, which were fabricated and assembled to construct a rectangular loop with a height of 630 mm and a width of 220 mm. Using a core material of n-eicosane and a shell of urea-formaldehyde resin, the phase change material nanocapsules of mean particle size 150 nm were fabricated successfully and then dispersed in pure water as the working fluid to form the water-based suspensions with mass fractions of the nanocapsules in the range 0.1-1 wt.%. The results clearly indicate that water-based suspensions of phase change nanocapsules can markedly enhance the heat transfer performance of the natural circulation loop considered.