Enhancement of Heat Transfer Rate and Minimization of Process Time by ResonantAcousticRTM Mixing During In-Container Sterilization of Foods

ResonantAcousticRTM Mixing (RAM) is a novel in-container mixing technology that has found many applications in industries where it is desired to mix highly viscous materials in sealed containers. The food industry might also be able to benefit from RAM during thermal processing of foods in containers. Inducing mixing in food containers during thermal processing has been applied successfully in the last two centuries to provide high quality food products to the consumer. RAM is believed to have the potential to extend the viscosity range of products that can be properly mixed in containers during thermal processing. Therefore, one objective of this study was to quantify the mixing achieved in a lab scale RAM unit (LabRAM) for products of different apparent viscosities. To do so, fluid to particle heat transfer coefficients (hfp) were measured between a copper ball and banana puree samples at different viscosities. Results showed that the hfp values ranged between 337 and 5554 W/m2 K. In general, these values are much higher than those reported in literature for other mixing technologies.;Another objective of the current study was to use planar laser induced fluorescence (PLIF) to observe the progression of mixing in a LabRAM and quantify the mixing time to attain a well mixed state when two miscible liquid streams were placed in a container and mixed at different mixing intensities. Uniformity of mixing increased with increasing mixing intensity. The results showed that the time to attain a well mixed product ranged from 3.0 s to 35.6 s throughout the product and process parameters studied.;Another objective of this study was to compare the thermal process times for three different processing technologies, namely still retort, Shaka RTM process, and RAM integrated thermal process. Samples of different apparent viscosities were used to cover a wide spectrum of viscosities that are encountered in the food industry. Based on the results obtained, while the effectiveness of the ShakaRTM process varied (thermal process times were reduced by 16% to 91% with respect to the still retort process) within the viscosity range studied, RAM integrated thermal process was capable of shortening the thermal process times significantly (ranged between 83% and 94%) for all tested samples.;These results suggest that RAM integrated thermal processing could be pursued further from a commercial point of view, to minimize thermal process times and improve the quality of products for existing products, and to design new products of higher apparent viscosities which were not possible to retort successfully previously due to prohibitively long thermal process times.