Parameter analysis and fast prediction of the optimum eccentricity for a latent heat thermal energy storage unit with phase change material enhanced by porous medium

Abstract

Abstract The melting performance of porous-medium-enhanced phase change material (PCM) in a horizontal shell-and-tube latent-heat thermal energy storage unit (LHTESU) with eccentric structure is studied through a fixed-grid numerical method. The effects of ratio of outer and inner diameter, thermal conductivity of porous medium, porosity and heating temperature on the recommended eccentricity of LHTESU are discussed. Correlations for fast prediction of the optimum eccentricity are built. Results show that the mixed use of porous medium and eccentric structure can save as much as 43.1% of the total melting time compared with the pure use of porous medium. There exists an optimum eccentricity to get the shortest total melting time. The optimum eccentricity increases with the increase of ratio of outer and inner diameter, porosity and heating temperature, and decreases with the increase of thermal conductivity. For fast prediction of the optimum eccentricity and saved melting time, a modified Rayleigh number is proposed to reflect the effect of porous medium on natural convection, especially the flow resistance caused by porous medium. The effects of the four parameters on the optimum eccentricity can be integrated by the relationship between the optimum eccentricity and the modified Rayleigh number. Correlations of The optimum eccentricity and saved melting time are obtained respectively for convenient calculation and evaluation of the feasibility of eccentricity.