Prototype continuous microwave foam-mat dryer: design and fabrication

A prototype microwave foam mat dryer with continuous operation was fabricated for tomato and guava. Results of preliminary studies on microwave foam mat drying of tomato and guava were used to design the prototype. The continuous foaming operation was achieved with the help of a submersible pump controlled by a time switch which ensured the delivery of pulp into foaming container and streamlined the delivery of foam on the drying surface (belt). The drying section presented a combination of hot air and microwaves, which resulted in accelerated heating and subsequently drying of the foam. Dried flakes were collected at the exit with the scrapper blade, which ensured appreciable recovery. The quality evaluation of guava pulp and tomato pulp dried at different microwave powers and inlet air temperatures revealed that the products dried at 1000 W microwave power and 50 °C exhibited excellent physicochemical properties in both the cases. Performance evaluation study depicted that the capacity of the dryer for guava drying was 4.84 l/h, the final moisture retention in the dried powder was 0.059 g H₂O/g d.m, recovery was 98.34% and energy consumption was 1.32 kWh/l. Similarly, for tomato drying the capacity, final moisture content, recovery and energy consumption were 4.03 l/h, 0.062 g H₂O/g d.m, 91.29% and 1.49 kWh/l respectively.