Kinematic model for a far infrared vacuum dryer

Energy analyses in drying of welsh onion from one source of far infrared radiation at an absolute pressure of 2.6 and 5 kPa were carried out to determine the energy input at which the highest level of efficiency would be attained. The experimental results were used not only to formulate an advanced mathematical model for the prediction of moisture content of onion as a function of drying time but also to study the dryer efficiencies. Less than half of energy input was utilized for evaporating water from the onion. Approximately 73-99% of operating efficiency, which was dependent on the dryer configuration, was converted into radiant energy. The highest radiant efficiency was obtained at 40W initial power supply, which was equivalent to the source temperature of about 100degreesC. An 80W initial electrical power supply at a 10 cm distance of heater from the onion surface showed the highest drying efficiencies. At 80W power, efficiency decreased with increasing distance from the heater source but at the expense of quality. For optimum drying efficiency without compromising quality, distance of heater from onion surface was proposed to be 10 cm.