Experimental investigation on heat transfer characteristics during melting of a phase change material with dispersed TiO2 nanoparticles in a rectangular enclosure

•Melting process of n-octadecane containing TiO2 is experimentally investigated.•Melted volume fractions and Nusselt number reveals heat transfer mechanisms.•Correlations based on dimensionless numbers are proposed to predict melting quality.•Dispersing nanoparticles affects heat transfer characteristics during melting. This paper presents an experimental investigation on the melting process of n-octadecane as a phase change material (PCM) with dispersed titanium oxide (TiO2) nanoparticles. Experiments were performed in a rectangular enclosure heated at constant rates from one vertical side corresponding to Rayleigh numbers in the range 0.57×108–43.2×108 and Stefan number in the range 5.7–23.8. The rheological behavior of liquid PCM/TiO2 at the mass fractions of 2 and 4% tended to Bingham fluids, thus the melting experiment was conducted for Bingham numbers in the range 0–31.1. Heat transfer during melting was characterized by visualizing the solid-liquid interface as well as recording the temperature distribution in the enclosure. Experimental results showed that at the initial stage of melting, heat transferred by conduction, and at later times, natural convection dominated heat transfer. Dispersing TiO2 nanoparticles led to increase in Bingham number and consequently the natural convection and melting rate deteriorated. Two correlations were proposed to predict the Nusselt number and melted volume fraction as a function of Fourier number, Rayleigh number, Stefan number, Bingham number and mass fraction of nanoparticles.