HEAT TRANSFER DURING FLUIDIZED BED PUFFING of RICE GRAINS

A pneumatic rice puffing machine was developed for increasing the production capacity of puffed rice for which a knowledge of the heat transfer process during puffing was required. the physical properties of the rice grains and other fluidization parameters, necessary for this study was experimentally determined. the surface heat transfer coefficient in case of hot air fluidized bed puffing was found to be 155.39 W/m²K. the calculated grain surface temperature for puffing was about 170°C and this did not vary significantly for experimental puffing air temperatures ranging from 200°C to 270°C. the air temperature ranging from 240°C to 270°C with corresponding exposure time of 9.7 s to 7s was found to be optimum for higher expansion ratio (8.5 to 10) and better color of the product. the temperature differentials between surface and center temperatures and between surface and average temperatures of the grains at the time of puffing were found to vary linearly with various puffing air temperatures and their ratios remained almost constant at 2.056.