Unconstrained melting of phase change material in cylindrical containers inside hot water tanks: Numerical investigation and effect of aspect ratios

•A method for dynamically determining mushy zone constants was established.•An unconstrained melting model with variable mushy zone constants was developed.•Correlation of phase change material's melting time and aspect ratios was calculated.•Flatter containers are superior to slenderer containers in practical designs.•Increasing bottom to total surface area ratios raises heat transfer coefficients.