Influence of the microwave-accelerated process on the drying kinetics, mechanical properties and surface appearance of rubberwood (Heavea brasiliensis)

This paper investigated the impact of microwave-assisted drying on the energy consumption, drying rate, surface temperature, drying time, static bending properties, and quality of dried rubberwood (Heavea brasiliensis) using different scenarios of combined microwave and convective air drying. Combined microwave and convective drying experiments were performed at frequencies of 2.45 +/- 0.05 GHz and microwave power of 4.8 kW, air drying temperatures of 30, 50, and 70 degrees C, and air drying velocity of 5.0 m/s using a multifeed microwave-convection hot air and continuous belt system (CMCB). The test results showed that rubberwood drying in a microwave system with multiple wave feeding and convection heating together with a conveyor in a hybrid system reduced the moisture of rubberwood from 70% to an average of approximately 20%. In addition, the most suitable conditions for the experiment were drying at an air temperature of 30 degrees C for 30 min and then in a microwave at 30 degrees C, compared to 30 degrees C for 30 min and then turning on the microwave at temperatures of 50 and 70 degrees C. The minimum energy consumption for drying with this method was 16.3 kWh. The results also indicated that the end quality of rubberwood samples dried under microwave-assisted drying was similar to that of conventional drying but better than that of rubberwood samples dried under combined microwave and air drying.