HEAT TRANSFER IN COMMERCIAL IMPINGEMENT OVENS

A point of concern when using air impingement ovens is the wide variation of heat transfer coefficient on the surface of a product. Practically two sources of non-uniformity exist: local variation of heat transfer coefficient of jets and non-uniform air velocity of finger duct nozzles. Local variation of heat transfer coefficient was investigated by numerical simulation using v2 f turbulence model and non-uniform air velocity of nozzles was investigated by numerical simulation of air flowing through tapered duct. Results showed that Jet temperature variation did not affect the Nu distribution. The Numax was more than twice of Nuave. Also, for the desired jet velocity (10 m/s), the average jet velocity of nozzles increased along with finger duct of Oven from 8.8 m/s to its maximum value (13.9 m/s). The difference between maximum and minimum jet velocities was 58%. The horizontal components of velocity increased along with duct that result in higher flow divergence from nozzles exit and consequently lower heat transfer on a product surface.