High pressure technology offers a lot of possibilities for save food processing. With pressures up to 10000 bar it is possible to inactivate enzymes and microorganisms or to support phase changes. Because of some benefits of phase transition at high pressure, e.g. small crystals that in comparison to conventional procedures do not damage tissues of bio-materials and with increasing pressure significantly decreasing latent heat, the investigation of freezing and thawing become more and more important. In the current paper, investigations of heat and momentum transfer during phase change of water both at ambient pressure and under high hydrostatic pressure conditions are carried out. Theoretical modelling of phase change processes bases on the conservation equations of mass, momentum and energy. Additionally, according to the enthalpy-porosity method the phase transition characteristic source terms in these equations are implemented. In order to solve the equation system, the commercial framework CFX-4.4 is applied. The standard software is arranged for high pressure applications with a help of additional subroutines. The velocity, temperature and phase distribution at high and normal pressure differ from each other. Anomaly of water density at normal pressure and its decay at high pressure significantly affect the flow behaviour of water in the chamber. This phenomenon is responsible for different ice kinetics and its forms. It can be generally stated that the fluid mechanical load on liquid bio-substance at high pressure is about 30-50 % greater than at ambient pressure.