Computational study for natural convection effects on temperature during batch and continuous industrial scale radio frequency tempering/thawing processes

Abstract

Radio frequency (RF) processing have been used for tempering and thawing. There have been significant experimental and mathematical model based studies for this process especially in the last two decades. The modeling studies applied the convective boundary condition with effective heat transfer coefficient and constant medium temperature in through field flat plate RF systems. The objective of this study was first to develop a mathematical model for conjugate heat transfer (natural convection) in a staggered through field electrode RF system and to use this model for natural convection effects in industrial scale processes. For this purpose, the developed comprehensive mathematical model was experimentally validated using the data from frozen tuna samples. The air temperature variation was also used for validation. Then, the developed model was used in industrial scale process simulations with the presence of natural convection. The industrially preferred flat plate systems were used in this part to determine the temperature and electric field evolutions. The results demonstrated the significant effect of the natural convection on sample surface temperature distribution and temperature change of air within the cavity. The evolved natural convection resulted in the variation of the heat transfer coefficient along the sample surfaces with significant changes in temperature. Based on these results, it might be concluded that the effect of air temperature change within the cavity during an RF processes should also be controlled and considered for industrial system design and process optimization.