A 3-D Heat Transfer and Fluid Flow Model for Cooling of a Single Egg under Forced Convection
Shell eggs are cooled under forced convection in commercial egg coolers. They are prone to contamination by pathogenic bacteria such as Salmonella spp., which can grow if the eggs are not properly chilled. Transmission of Salmonella Enteritidis in eggs has been reported, requiring proper chilling of the egg to minimize the risk of foodborne illness. Accurate estimation of egg temperature under various storage conditions would assist egg processing industries to evaluate the adequacy of the egg chilling unit operation to ensure food safety. In order to determine the center temperature of a shell egg under transient forced-air convection cooling, numerical simulations were carried out using a finite volume based computational fluid dynamics (CFD) model. Conduction heat transfer was solved inside the egg, and convective heat transfer was solved at the exterior surface of egg immersed in the fluid domain. Experimental tests were conducted to determine the center temperature of an egg placed inside the test chamber of a wind tunnel by varying the air velocity (0.3 to 1.2 m s-1) and air temperature (3.7°C to 11.4°C) at the inlet of the test chamber. The CFD model was validated by comparing the results with experimental observations. The root mean square error (RMSE) of the egg center temperature predicted by the CFD model varied from 0.2°C to 0.9°C at constant inlet air temperature. Further, the model was also validated for varying inlet air temperature with time. The simulated and experimental values of egg center temperature at various boundary conditions were found to be in good agreement, with RMSE ranging from 0.23°C to 0.37°C. The predicted egg temperatures from the heat transfer model can be provided as an input to a microbial growth model to estimate the potential growth of Salmonella spp. during egg cooling for assessing food safety.