Role of distributed heating on enhancement of thermal mixing for liquid food processing with heat flow visualization method

Thermal treatment is an important step in food processing. The conventional methods of heating of an enclosure may result in inadequate thermal mixing and poor temperature distribution leading to energy wastage. In this work, an alternative, energy-efficient method of distributed heating of the cavity is studied and compared with the isothermal bottom wall heating case in enhancing the thermal mixing and improving the temperature distribution in the cavity. Steady laminar natural convection of liquid food materials with a representative Prandtl number, Pr = 3.14 is studied in the range of Rayleigh number, Ra = 10(3)-10(5) in differentially and discretely heated square cavities. Detailed analysis is carried out by visualizing the heat flow by heatlines. Further, the thermal mixing and the temperature uniformity are analyzed based on the cup-mixing temperature and root-mean square deviation. It is found that the thermal management policy of distributed heating significantly influences the thermal mixing and the temperature uniformity within liquid food. In a case with multiple discrete heat sources, a remarkable uniformity in temperature across the cavity is achieved with moderate thermal mixing. Based on heatlines, cup-mixing temperature and root-mean square deviation, optimal heating policy for food processing may be chosen. Industrial Relevance: Three types of discrete heating situation are considered. Numerical simulations were carried out to predict the temperature and flow characteristics. Numerical simulation results were benchmarked or validated with literature data. Thus, current numerical simulation results are useful to select the suitable heating strategy for efficient thermal processing of liquid food. The proposed methodology with the numerical data would be useful to practicing industries for efficient juice heating. (C) 2012 Elsevier Ltd. All rights reserved.