IMPROVING ENERGY EFFICIENCY IN COMBINED MICROWAVE-CONVECTIVE DRYING

Convective-microwave drying has been recognized as a convenient option for drying of valuable materials. However, the advantages of the meth od must be carefully evaluated in order to establish the limits for fu ll scale operating conditions because, as demonstrated in this work, t he reduction in the absolute drying time as a function of the applied microwave power is devalued by an increase in the unabsorbed microwave energy, decreasing the overall energy efficiency of the drying proces s. Experimental study of the energy efficiency of combined microwave-c onvective drying of agar gel and Gelidium seaweeds was carried out in a laboratory scale microwave-convective dryer by continuously followin g the absorption of microwave energy by the sample as well as the chan ge of the sample mass during the drying process, under different opera ting conditions. Several drying strategies based on the on-off applica tion of the microwave power were proposed and evaluated from the point of view of both drying kinetics and energy efficiency in order to pro gram and rationalize the use of microwave energy in the combined micro wave-convective drying process.