The work aims to address the effects of mushy zone constant (1 x 10(4 )<= C <= 1 x 10(8) kg m(-3) s(-1)) and gravitational acceleration (1.635 <= g <= 9.810 m s(-2)) on the thermal storage release behaviors of paraffin wax (phase change material, PCM), by performing numerical investigations in a rectangular cavity with partially thermal active walls. The enthalpy-porosity method is employed to simulate the solid-liquid phase-change process and flow evolution at the PCM interface. The numerical model is validated by the published literature data. It is confirmed that the thermal storage behaviors are significantly influenced by the mushy zone constant and gravitational acceleration. PCM liquid fraction is essentially increased as decreased in mushy zone constant and increased in gravitational acceleration, with maximum discrepancies are reached 88%. However, very limited impacts are conducted on the thermal release process with maximum PCM liquid fraction discrepancy only 2%. Furthermore, the proposed equations regarding how to calculate the value of mushy zone constant are also outlined and commented. Therefore, proper examination and verification for mushy zone constant is very important and necessary before solid-liquid phase-change thermal storage process is accurately simulated by enthalpy-porosity model. (C) 2018 Elsevier Ltd. All rights reserved.