Study Of The Effect Of Pressurised Freezing On The Growth Characteristics Of Pork Ice Crystals

As the demand for pork gradually increases,researchers have been studying and analysing various methods of freezing frozen pork as an aid to freezing.Pressure freezing technology has been experimentally analysed and compared for a wide range of food products,while at a micro level the effect of pressure on food quality lies in the intracellular ice crystals.The size,shape and growth rate of intracellular ice crystals during the freezing process can cause irreversible damage to the microstructure of the cells.Pressurised freezing is therefore an important area of research to mitigate the extent of damage to pork during freezing and chilling.In this paper,the effect of pressure changes on ice crystal growth is investigated by numerical simulations of dendrite growth in pure water and binary solution crystallisation using the phase field method.The effect of pressure changes on dendrite growth is investigated in depth,laying a good foundation for the eventual implementation of food-assisted freezing technology.A special point of the curve based on the classical crystal nucleation theory where the free energy of the bulk term and the free energy of the surface term are equal,is used to derive and analyse the effect of the size of the critical nucleus on the change in subcooling under pressure when the crystal is nucleated as a sphere;and a noise perturbation term is added to optimise the numerical simulation of the two phase field control equations so that the results are closer to the actual ice crystal morphology.The effects of noise perturbations,initial nucleus size,dimensionless temperature and number of nuclei on ice crystal growth are discussed in the Kobayashi phase field control model.The introduction of the noise perturbation term transformed the ice crystal morphology into non-perfect hexagonal ice crystals;the greater the intensity of the noise perturbation,the more rugged the ice crystal growth direction and the more irregular the final growth morphology;The size of the initial nucleus decreases with increasing pressure,and as the initial nucleus becomes progressively larger,the growth rate becomes faster and the final shape more complex and sharp;as the value of the dimensionless equilibrium temperature increases after pressurisation,the rate of dimensionless growth of a single dendrite hexagonal tip becomes larger;as the pressure changes based on the small size of the initial nucleus and the high dimensionless temperature,the number of nuclei increases and the growth of more dendrite tips is inhibited,and the dendrites grow competitively and inhibit each other,in line with the theoretical research reasoning.In adopting the Wheeler phase field control model for the simulation of ice crystal growth under pressure,the control equation for the solute field is introduced more than that of the Kobayashi model,so the effect of the solute diffusion coefficient on the dendrites is added to the discussion of the effects of noise perturbation intensity,subcooling,and the number of nuclei on the phase field,temperature field,and solute field.Change in noise term as above;As the pressure increases the subcooling degree increases,the side branches of dendritic growth become more developed,the growth competition is more intense and the tip growth rate is faster;when the solute diffusion coefficient decreases with increasing pressure,the solute concentration in the solid phase gradually approximates to the initial concentration,the solute concentration at the bottom of the nucleus also gradually decreases and the solute segregation ratio becomes smaller;As the number of nuclei increases with pressure,the growth rate of individual ice crystals increases,but the large number of nuclei makes the resulting ice crystals finer and smaller.In the freezing experiments on pork,the ice crystal morphology under microscope was compared at atmospheric pressure,0.13 MPa and 0.16 MPa,with increasing pressure the ice crystals were finer and the microstructure of the pork was more regular.The simulation of two phase field equations demonstrates that the combined effect of the parameters due to the change in pressurisation can lead to a more desirable fine and numerous initial nuclei and thus to the growth of a dendritic system that is beneficial for freezing,which to some extent can provide a theoretical basis for the development of pressurised freezing technology.