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Optimisation of crust freezing in meat processing via Computational Fluid Dynamics

In this work a numerical model for two-dimensional axisymmetric continuous freezing by impingement of processed meat or similar products in food industry moving along a conveyor belt is presented. The model represents a more computationally efficient alternative to solve conjugate heat transfer between a fluid and a solid, accompanied by phase change in some constituents of the solid phase. In the model presented here it is assumed that the solid can be represented as an homogeneous medium, with its thermophysical properties depending on the temperature. The impingement freezing model is conceived to be valid for highly processed vegetarians products or meat such as sausages, mince or ham freezing. Furthermore, this approach is much simpler in terms of computational cost whilst it still captures the complexity of continuous freezing under industrial setting. The methodology is implemented as a new solver in the widely used open-source Computational Fluid Dynamics (CFD) library OpenFOAM. Overall, highly non-linear freezing behaviour was found due to the phase change inside the solid and the associated heat of fusion. We studied the effect of high fluid Reynolds numbers as well as investigating the optimal distance between the jet and the solid surface for different speeds of the conveyor. We found that the maximum freezing is obtained positioning the jet at a distance H = 7.2D (where D is the diameter of the impinging jet) and setting the speed of the conveyor such that the Péclet number of the solid is $\text{Pe}_{\text{s}}=8244$. The methodology developed allows to obtain detailed insight on the freezing process for various impingement configurations at a minimum computational cost using a freely available open-source tool.