REVEALING AND STUDYING OF THE MECHANISM OF MOISTURE REMOVAL FROM MATERIALS ON EXPOSURE TO ULTRASONIC NONCONTACT EFFECT

The article is devoted to the study of the process of removing moisture from capillary-porous materials by its dispersion during the collapse of cylindrically-shaped cavitation bubbles formed in the capillaries of the material under ultrasonic exposure. A model has been proposed and developed that made it possible to explain the mechanism of dispersion during realization of the life cycle of a bubble in a capillary — slow growth, rapid expansion with deformation, and subsequent collapse. The range of sound pressure levels at which dispersion begins (from 150 dB) to the level at which bubbles reach the size of the capillary and the increase in the drying effi ciency stops (170 dB) has been determined theoretically. It was also shown that for maximum effi ciency in moisture removal, the size of the dehydrated sample must correspond to the ultrasonic wavelength in air. The mechanism of ultrasonic dispersion of liquid during drying has been confi rmed experimentally and it has been established that to reduce the drying time by more than 40%, exposure with a level in the range of 165–170 dB is necessary, and the dried materials must be placed in the form of particles or layers having dimensions or thicknesses corresponding to the ultrasonic wave length. The practical implementation of ultrasonic drying using the example of food products (red beets) confi rmed the eff ectiveness of the proposed mechanism and ensured a reduction in drying time by 1.9 times on reducing energy demand by 1.6 times.
The article is devoted to the study of the process of removing moisture from capillary-porous materials by its dispersion during the collapse of cylindrically-shaped cavitation bubbles formed in the capillaries of the material under ultrasonic exposure. A model has been proposed and developed that made it possible to explain the mechanism of dispersion during realization of the life cycle of a bubble in a capillary — slow growth, rapid expansion with deformation, and subsequent collapse. The range of sound pressure levels at which dispersion begins (from 150 dB) to the level at which bubbles reach the size of the capillary and the increase in the drying effi ciency stops (170 dB) has been determined theoretically. It was also shown that for maximum effi ciency in moisture removal, the size of the dehydrated sample must correspond to the ultrasonic wavelength in air. The mechanism of ultrasonic dispersion of liquid during drying has been confi rmed experimentally and it has been established that to reduce the drying time by more than 40%, exposure with a level in the range of 165–170 dB is necessary, and the dried materials must be placed in the form of particles or layers having dimensions or thicknesses corresponding to the ultrasonic wave length. The practical implementation of ultrasonic drying using the example of food products (red beets) confi rmed the eff ectiveness of the proposed mechanism and ensured a reduction in drying time by 1.9 times on reducing energy demand by 1.6 times.
Author:  V. N. Khmelev, A. V. Shalunov, S. A. Terent′ev, R. N. Golykh, and V. A. Nesterov
Keywords:  drying, energy effi ciency, ultrasonic vibrations, dehydration, intensifi cation, dispersion
Page:  925 - 937