The Role of Processing Parameters on Energy Efficiency during Microwave Convective Drying of Porous Materials

Abstract

A small-scale microwave convective dryer was built to study the effects of microwave power level, air temperature, and air velocity on drying kinetics, temperature development, and specific energy consumption (MJ/kg evaporated water) using statistical designs. Increased microwave power had a large significant effect on moisture loss and temperature development and it reduced specific energy consumption. Increased air temperature and air velocity increased specific energy consumption, as their effect on drying kinetics was smaller in the system used. Low air temperature slowed the drying process, without affecting the relationship between average sample temperature and average moisture content during drying.

Influence of dielectric and sorption properties on drying behaviour and energy efficiency during microwave convective drying of selected food and non-food inorganic materials

“…7, together with their breakdowns. The breakdowns illustrate in which form energy is supplied to the material, however, with the experimental set-up used it is mainly the microwave energy supplied that contributes to the evaporation of water in the material (Holtz et al, 2009). All materials, except the lightweight concrete with lower initial moisture content, showed specific energy consumption between 15 and 18 MJ/kg evaporated water, despite the differences in initial and final moisture contents and different lengths of drying time.…”

“…In a previous study (Holtz et al, 2009), the effect of processing parameters on kinetics and energy efficiency was investigated for lightweight concrete under the same drying system. Microwave power, air temperature, and to some extent air velocity had an effect on drying kinetics and on the energy consumption during drying.…”

“…The drying equipment used has been described in detail in previous work (Holtz et al, 2009). It comprised a straight aluminium waveguide (86 Â 43 mm) fitted with an air-cooled magnetron (2.45 GHz, 2M244-M16, Panasonic).…”

“…In terms of high energy efficiency, the optimal choice of processing parameters during microwave convective drying is strongly related to their effect on drying time and drying kinetics (Holtz et al, 2009;Sharma and Prasad, 2006;Tulasidas et al, 1995). However, very few studies have looked into the effect of material properties on energy efficiency.…”

Microwave‐Assisted Drying of Foods – Equipment, Process and Product Quality

“…Table 9.2 presents the SEC and drying efficiency values for different microwaveassisted drying processes of food materials, as determined by various research groups. The minimal theoretical value of SEC for a dryer is 2.3 MJ per kg of evaporated water, based on the maximal theoretical specific moisture extraction ratio (SMER) of 1.55 kg per kWh and the latent heat of water evaporation at 100 C (Holtz et al, 2009). These results are expected to depend heavily on the scale and design of dryers, as well as on the method used to measure energy consumption (Durance and Wang, 2002).…”