Mathematical modeling of cryogenic food freezing.

摘要

Liquid nitrogen (LN;First, freeze-cracking susceptibility of foods during cryogenic freezing was evaluated. Results demonstrated that fruits and vegetables, meat and dairy products were generally more susceptible to freeze-cracking than bakery products. Several properties including moisture content, density, porosity, modulus of elasticity (E), Poisson's ratio (;The second manuscript describes the design and construction of an environmental chamber. The chamber can be attached to an Instron Universal Testing Machine for determination of E, ;Transient heat transfer analysis was then conducted using finite element method (FEM) for a 2-dimensional axisymmetric domain of Tylose gel during cryogenic freezing. Predicted temperature distribution was close to experimental result except the predicted surface temperature decreased slower than experimental value. This may be due to surface cracking during cryogenic freezing as confirmed by visual observations.;In the fourth manuscript, nonlinear static analysis with FEM was conducted on the same domain as in the heat transfer. Calculated stresses showed initial development at the sample surface and gradually moved toward the center. Local stresses were developed at the freezing boundary. Displacement results were verified by overall strain of the cylinder using an approximated value of thermal expansion coefficient. Based on the model developed in this study, internal stress during freezing can be predicted. Freezing rate can then be adjusted to the level not allowing the internal stress exceeding the material strength.;A freeze-cracking mechanism was postulated based on the information collected from the heat transfer, stress and displacement analyses. Internal stress development was caused by volume expansion during water-ice phase transition and temperature-dependent mechanical properties.