Investigations in mass transfer enhancement in textiles with ultrasound

A novel application of ultrasound is for the intensification of wet textile treatments, in which mass transfer in the inter- and intra-yam pores of the textile is the basic physical mechanism. This paper describes a simple methodology for the estimation of mass transfer enhancement in ultrasonic textile treatments. For this study, washing of EMPA 101 fabric, soiled with carbon soot and olive oil, is selected as a model process. In the absence of precise knowledge of the convection velocity resulting due to transient cavitation, a semi-empirical method is used to estimate mass transfer enhancement. The experimental soil removal rate during model process is determined by precise time-controlled ultrasonic treatment of the textile, with the source of cavitation nuclei located close to the textile surface. The mass transfer in the textile during the model process is found to occur in two distinct steps, characterized by two different convective diffusion coefficients. This effect is explained in terms of uneven soil distribution in the inter- and intra-yam region. The mass transfer enhancement factor, defined as ratio of convective diffusion coefficient to molecular diffusion coefficient of soil particles, is found to be in the range 1000-2000. In addition, it is found that the mass transfer enhancement increases with acoustic pressure amplitude during textile treatment. A qualitative estimate of the convection velocities generated in the vicinity of the bubble is provided using numerical simulations of bubble dynamics equation. (C) 2003 Elsevier Ltd. All rights reserved.