Transport phenomenon in jet impingement baking:

In food industry, hot air jet impingement ovens are used to bake pizza shells, crackers, cookies, and to toast ready-to-eat cereals. Despite its significant applications and advantages (faster processing and better quality products) in food processing industry, there is a very limited understanding of detailed transport processes (heat and mass transport) involved in jet impingement baking. To develop quantitative understanding of transport processes during jet impingement baking, we have modeled the flow field and its associated thermal transport phenomenon for a cookie shaped and a hot dog geometry using numerical simulation and have validated it using experimental data. To predict temperature and moisture distribution during baking, we have developed four different baking models based on coupled heat and mass transfer. These models differ based on coupling of heat and mass transport terms, vapor transport, thermodiffusion and stages of a baking process. Results of flow field and its associated thermal transport studies demonstrated that numerical simulation approach can be used to predict both flow field and thermal transport during jet impingement baking. The results highlight that local and average surface heat transfer coefficient values are a function of nozzle to plate spacing, jet inlet velocity and geometry of target product. Comparison of temperature and moisture profiles among the models show significant differences in temperature and moisture profile. Based on comparison of these models, we established that vapor transport process is important for modeling of a baking process, while thermo-diffusion process does not make a significant contribution to moisture transport. The results also demonstrate that introduction of stages in baking based on empirical approaches can introduce artificial steps in temperature-time profile. Comparison of numerically predicted center point temperature with experimental measurements in a potato disk shows that modified model II (with vapor transport and a single stage baking process) provides the best match with the experimentally measured data. In summary, we have modeled the complete transport process during jet impingement baking, which can predict the baking time, crust thickness, temperature and moisture distributions within the food for a given jet velocity and air temperature.Ph.D.Includes bibliographical references (p. 241-246)by Mark E. Nag