Impact of overall and particle surface heat transfer coefficients on thermal process optimization in rotary retorts

This study attempts to examine the significance of recent research that has focused on efforts to estimate values for global and surface heat transfer coefficients under forced convection heating induced by end-over-end rotation in retorting of canned peas in brine. The study confirms the accuracy of regression analysis used to predict values for heat transfer coefficients as a function of rotating speed and headspace, and uses them to predict values over a range of process conditions, which make up the search domain for process optimization. These coefficients were used in a convective heat transfer model to establish a range of lethality-equivalent retort temperature-time processes for various conditions of retort temperature, rotating speed, and headspace. Then, they were coupled with quality factor kinetics to predict the final volume average and surface quality retention resulting from each process and to find the optimal thermal process conditions for canned fresh green peas. Results showed that maximum quality retention (surface and volume average retention) was achieved with the shortest possible process time (made possible with highest retort temperature), and reached the similar level in all cases with small difference between surface and volume average quality retention. The highest heat transfer coefficients (associated with maximum rotating speed and headspace) showed a 10% reduction in process time over that required with minimum rotating speed and headspace. The study concludes with a discussion of the significance of these findings and degree to which they were expected.