Modeling heat transfer during hot water sanitization of a commercial mushroom slicer

A heat transfer model within a three-lane mushroom slicer was solved using the Finite Element Method (FEM) to obtain a conservative estimate of the temperature at the cold spot within the slicer during hot water sanitization under natural convection. Computational fluid dynamics (CFD) modeling of the heating of a single spacer by hot water under natural convection showed that the bottom surface of the spacer heated slower compared to the top surface. This was due to buoyancy forces and density gradients during natural convection leading to the formation of a wake of cold water at the bottom of the spacer. The FEM model predicted the location of the cold spot during hot water sanitization under natural convection to be at the bottom inside surface of a spacer at the center of the upper shaft and this agreed with the experimentally determined time-temperature data. The experimentally determined time for the cold spot to reach the target temperature during sanitization at 65 degrees C was 5.2 min, whereas that predicted by the FEM model was 6.1 min. It is recommended that the higher value of the time to reach the target temperature at the cold spot as predicted by the FEM model be used as a come-up time to establish the minimum treatment times for sanitization at 65 degrees C. Practical Applications Many of the mushroom processing facilities use a three-lane mushroom slicer manufactured by DutchTecSource (Netherlands). A practice used currently in the mushroom industry for routine sanitization of mushroom slicers is heating the slicer head in boiling water for an hour. Studies at Penn State have shown that Listeria monocytogenes can be eliminated from food contact surfaces using hot water sanitization. In order to validate sanitization treatments in a mushroom slicer, it is imperative to determine cold spots and the come-up times to reach the target temperature therein. Since the geometry of this commercial three-lane mushroom slicer is highly irregular, a FEM-based approach was used to model heat transfer. The data obtained from this study can be used by mushroom processors to establish the minimum treatment times for hot water sanitization of commercial mushroom slicers.