In this paper numerical investigation of the phase transition of water at high hydrostatic pressure conditions occurring under a gravitational and a low-gravity environment are presented. The computational model consists of conservation equations of mass, momentum and energy. Phase transition phenomena are modelled with the enthalpy-porosity method. Numerical solutions are obtained for process stages dominated by free convection (cooling and heating) as well as by forced convection (compression and decompression). A high pressure assisted freezing/thawing is carried out in the pressure range from the ambient pressure up to 150 MPa. Differences in the thermofluiddynamics observed in the high pressure chamber operated under gravity and low-gravity conditions are discussed. The results reveal significant influence of gravity on the temperature and velocity distribution in the HP-chamber and consequently on the different ice growth characteristics. In comparison to gravity conditions, lower velocity and temperature heterogeneities under microgravity are noted. These phenomena can be explained with the absence of free convection during heating and cooling phases. Considering multiphase substances a damped convection mechanisms under microgravity can also contribute to lower transport activity of several elements or particles within a fluid matrix.