Impingement Heat Transfer Effects on Baking of Flat Bread

An impingement oven designed for flat breads baking was instrumented to monitor the processing conditions and record variables responsible for changes in dough characteristics. Image processing was used to monitor the volume and surface color changes during baking. Fluctuations of oven temperature and jet velocity were minimized using electronic controllers, leading to better repeatability and accuracy. Impingement heat transfer distribution effects on flat bread baking was investigated by numerical simulation and related to the bread color. Considerable effect of local variations in impingement heat transfer and nonuniform nozzle exit velocity distribution on the color of baked bread was observed. At H/D > 4, jet temperatures < 200°C, and jet velocity of 10 m/s, local heat transfer distribution and surface darkening was negligible and a uniform surface color was obtained. Notably, velocity variations of ±20% inherent in the finger nozzles used in the oven design did not result in significant color change, which depends more on the local temperature attained by the bread surface.