Numerical investigation on latent heat storage enhancement using a gradient-concentration nanoparticles phase change material

Latent heat storage (LHS) using phase change materials (PCMs) is a promising option for storing thermal energy. However, PCMs melting rate is low and non-uniform due to their low conductivity and local natural convection respectively, which limits the thermal energy storage efficiency. The combined full-fins and nanoparticles in gradient-concentration is proposed in this study to overcome this shortcoming. A vertical shell-tube LHS system is taken as the study objective. Two-dimensional transient numerical model considering natural convection was developed to analyze the performances of the storage system. The effects of half-fins, full-fins, and combination of both on the melting process were firstly studied. Results show that the design of full-fins inhibits the negative effect of natural convection at the last melting stage, which reduces the melting time by 5.4 and 4.1% compared to the case of half-fins at fins volume fraction (phi f) of 0.5 and 1.0 vol%, respectively. Then, the finned case of phi f = 1.0 vol% dispersed with 1.0 wt% multiple-walled carbon nanotubes (MWCNTs) was investigated and the effects of heat transfer fluid (HTF) inlet temperature and flow rate were explored. Results show that a 65.6% improvement on melting uniformity is obtained for combined full-fins and MWCNTs in the negative gradientconcentration compared to the combined half-fins and MWCNTs in uniform concentration. Besides, the complete melting time is reduced by 11.4%. The enhancement potential of combined full-fins and nanoparticles in the negative gradient-concentration first increases and then decreases with the increase of HTF inlet temperature, and it decreases with the increase of HTF flow rate.

Automated summary

The study proposed the combination of full-fins and nanoparticles in gradient-concentration to improve the performance of latent heat storage systems using phase change materials. Experimental results demonstrate that the design of full-fins reduces melting time during the melting process, and when combined with multi-walled carbon nanotubes, it enhances melting uniformity and further shortens the complete melting time.