Intensification of mass transfer in wet textile processes by power ultrasound

In industrial textile pre-treatment and finishing processes, mass transfer and mass transport are often rate-limiting. As a result, these processes require a relatively long residence time, large amounts of water and chemicals, and are also energy-consuming. In most of these processes, diffusion and convection in the inter-yarn and intra-yarn pores of the fabric are the limiting mass transport mechanisms. Intensification of mass transport, preferentially in the intra yarn pores, is key to the improvement of the efficiency of wet textile processes. Power ultrasound is a promising technique for accelerating mass transport in textile materials. In this paper, the intensification of mass transfer in textiles under the influence of ultrasound on the basis of a total system approach is described. EMPA 101-test fabric was selected as a model for the cleaning process. This study focuses on two aspects, the mechanism of the ultrasound-assisted cleaning process and the effect of the presence of the cloth on the ultrasound wave field generated in a bath. It has been found that the dissolved gas content in the system plays a dominant role in the cleaning process. The cleaning effects observed are explained by two different mechanisms: small-amplitude acoustic bubble oscillations and micro-jets (resulting from the collapse of acoustic bubbles in the boundary layer between the fabric and the bulk fluid) that give rise to convective mass transfer in the intra-yarn pores. It has also been observed that the overall power consumption of the system varies with the position of the fabric in the acoustic field. This variation is explained on the basis of a model involving the specific flow resistance of the fabric and the physical properties of the standing waves.