Fluid flow and heat transfer in air jet impingement in food processing

Air impingement technology is gaining popularity in food-processing operations such as baking, freezing, drying, and toasting. In this article, physical characteristics of impinging jets, such as turbulent mixing in the free jet region, stagnation, boundary-layer formation, recirculation, and their interactions with food products in terms of heat and mass transfer have been reviewed. The discussion includes experimental methods used for measurement of heat and mass transfer for single and multiple slot and circular jets. Procedures used for measurement of heat-transfer coefficient such as lumped sensor method, micro-calorimetric approach, and use of flux sensors are presented. Typical qualitative and quantitative flow-field studies using planar visualization and laser Doppler anemometry have been reviewed. Numerical modeling of air impingement systems is discussed with special consideration of problems arising in food-processing systems.