Heat and Mass Transfer and Energy Aspects in Combined Infrared-Convective Drying of Bee-Pollen

Abstract

A hybrid drying process based on the application of infrared (IR) radiation combined to non-heated air flow was proposed for bee-pollen drying. The IR source was located at a distance of 32 cm from the samples. Experiments in the hybrid dryer were conducted with pollen grains arranged in a single layer and exposed to three radiation intensity levels (150, 300 and 450 W/m2) and three air velocity levels (1.0, 2.0 and 3.0 m/s) at 25°C. The surface temperature of the material was measured during drying through an optical pyrometer. The effects of the process parameters on the drying kinetics and specific energy consumption were evaluated. Experimental results showed that for any particular air velocity increasing IR heat flux led to an intensification of mass transfer rate, decreasing drying time and thus reducing energy consumption. Minimum energy consumption in hybrid frying of pollen was associated with the application of the highest radiation intensity and lowest air velocity. It was also found that cooling effect increased with air velocity, which resulted in a decreased driving force for mass transfer and increased drying time and energy consumption.