Optimization of ground heat exchanger using microencapsulated phase change material slurry based on tree-shaped structure

Taking into account the potential of the tree-shaped ground heat exchanger to reduce pressure losses and microencapsulated phase change material slurry to enhance heat transfer performance, a new attempt combining microencapsulated phase change material slurry with tree-shaped structure is proposed in this paper. Firstly, to obtain the optimal structure of tree-shaped ground heat exchanger, influences of structure parameters on thermo-fluidic performance of ground heat exchanger are explored. Based on this optimal structure, numerical simulations adopting Eulerian-Eulerian approach are conducted to study hydraulic and heat transfer performance of microencapsulated phase change material slurry flowing through horizontal tree-shaped structure under constant flux. Comparison studies between different working fluid: water and microencapsulated phase change material slurry and different types of tube: horizontal straight tube and Y tube (tree-shaped tube) are studied. The results indicate that the numerical results accord well with experimental results. For tree-shaped ground heat exchanger with bifurcation level of 1, the optimal pipe diameter ratio meets D-0/D-1 = 2(3/7), D-1/D-2 = 1 and the optimal length ratio is L-0/L-1 = 1. Furthermore, the combination of microencapsulated phase change material slurry and tree-shaped structure can efficiently enhance thermal performance and reduce pressure losses. Considering comprehensive performance of microencapsulated phase change material slurry, the optimal volume fraction is 12% for Y tube, whose overall performance is 38.9% higher than that of pure water flowing through straight tube.