INVESTIGATION OF EROSION PROCESSES AS CLEANING MECHANISMS IN THE REMOVAL OF THIN DEPOSITED SOILS

The fouling of surfaces during the manufacture of liquid products is a serious problem for the foods industry. However, it also affects many other production processes such as paint manufacture and the production of detergents, the latter being of primary interest for this work. The use of cleaning chemicals to remove soil layers is considered highly undesirable. Not only does the disposal of the effluent produced cause environmental problems but also the costs involved make chemical cleaning economically unfavourable. By studying the damaging effects of purely physical erosion processes on thin deposited layers using water as the sole cleaning agent it is hoped that an understanding of the mechanisms governing erosive cleaning can be developed. If the efficiency of cleaning is maximised to such an extent that chemicals can be removed from the cleaning process then it should be possible to recycle cleaning water for use as process water. Potential erosion processes include liquid flow, impact by liquid jets and cavitation induced by ultrasound. Two rigs have been developed to study cleaning by liquid flow and jets while a commercial ultrasonic vibrator has been used to study the effects of cavitation. The aim throughout has been to compare the efficiencies, with respect to volume of cleaning water, of the different processes and to understand how individual parameters affect the efficiency of each process. The experimental techniques used in this study include high speed photography, flow visualization, and computational image analysis.