This work aims to examine, via a complementary approach of experimental measurement and numerical simulation, transient transport processes associated with melting of a phase change material (PCM) placed inside a vertical rectangular enclosure with a free-moving ceiling. The core phase change material is n-octadecane with melting temperature about T-m = 28 degrees C. The vertical side walls of the enclosure were differentially heated isothermally while the remaining side walls were thermally insulated. Experiments have been undertaken for the air-saturated enclosure filled with MECPCM particles with the relevant parameters in the following ranges: the enclosure aspect ratio Asp = 24; the subcooling number Sc = 1.06-11.5; Stefan number Ste = 0.179-0.370; and the Rayleigh number Ra = 0.897-8.60 x 10(8). Meanwhile, numerical simulations have been performed based on a mathematical modeling mimicking the experimental configuration considered to further elucidate the transient transport processes of the free-moving ceiling of the enclosure. Finally, the formula of the dimensionless displacement of the top ceiling subjected to various thermal conditions are proposed and correlated with the related parameters, including the Stefan number Ste, the subcooling parameter Sc, Rayleigh number Ra and the Fourier number Fo. (C) 2015 Elsevier Ltd. All rights reserved.