Thermal performance difference of phase change energy storage units based on tubular macro-encapsulation

Abstract

Phase change energy storage (PCES) unit based on macro-encapsulation has the advantage of relatively low cost and potential for large-scale use in building energy conservation. Herein, the thermal performance of PCES unit based on tubular macro-encapsulation was compared and analyzed through numerical simulations using the enthalpy-porosity model with experimental validation. Different pipe materials (galvanized steel, PET, PERT, and PP) and tubular diameters (from 20 mm to 50 mm) were considered for comparison. The encapsulating impact factor (EIF), ratio between the phase change time using certain plastic encapsulation material and that using common galvanized steel, was raised up and used to evaluate the thermal characteristics of the PCES units based on plastic pipes. The calculated results indicate that steel encapsulation is better than plastic encapsulation in terms of thermal performance, but the difference is not obvious. When the water bath temperature changes from 45 ℃ to 55 ℃, the EIF decreases from 1.6 to 1.57, which means that the influence of water temperature on the EIF is small. Increasing thermal conductivity of phase change material (PCM) is a good choice in the present arrangement if the thermal storage process needs to be accelerated.