Effect of Ordinary Frequency High Electric Fields on Evaporation and Drying

Abstract

Evaporation of water was enhanced by ordinary frequency (60 Hz) high electric fields (HEF), and the effect was directly proportional to the extent of treatment, i.e., increased with time and electric field, and decreased with separating head distance. Alternating current (AC) wire electric field was more effective in promoting evaporation of water than all direct currents (DC) and AC (plate) electric fields. As a result of the higher rate of evaporation, AC (wire) HEF caused a reduction of 1.0°C in the surface temperature in water and 4.5°C in ethanol. Both evaporation rate and surface temperature were resumed after the electric fields were discontinued. Furthermore, the evaporation rates of water and ethanol were equal to the respective controls after 60 min and 100 min of electric field cutoff, respectively. Similarly, HEF was very effective in promoting evaporation even at higher concentration of sugar or salt solutions. Cut discs (size: φ20 mm×10 mm, ca. 174 g, placed 10 mm apart on aluminum-foil) of apple flesh were dried under AC (wire) HEF under ambient conditions (25°C, 35%RH), and the higher the fields, the faster was the drying. After 10.0 h drying, the moisture contents of samples treated with 0.0, 5.7, 7.9 and 10.0 kV alternating electric fields (20 mm head distance) were 4.2, 3.6, 3.4 and 3.1 kg/kg dry solid, respectively.