Laundry process intensification by ultrasound

Abstract

In domestic textile laundering processes, mass transfer and mass transport are often rate limiting. Therefore, these processes require a long processing time, large amounts of water and chemicals, and they are energy consuming. In most of these processes, diffusion and convection in the inter-yarn and intra-yarn pores of the fabric are limiting mass transport mechanisms. Intensification of mass transport, preferentially in the intra-yarn pores, is the key in the improvement of the efficiency of wet textile processes. Conventional methods of intensification of mass transport (e.g. operation at elevated temperatures) are not always feasible due to the undesired side effects such as fabric damage. Increasing the flow rate does not deliver the desired effect due to the multi-porous complex structure of textile materials. Van der Donck et al. [Tenside Surf. Det. 35 (1998) 119; 36 (1999) 222] reported that the deformation of yarns by placing a fabric in a pulsating flow or repeated mechanical elongation of the yarns improved mass transport. However, the additional mass transport caused by deformation is limited in practice. Power ultrasound is a promising technique to accelerate mass transport in textile materials. Several papers appeared in this field, which report an improvement in energy efficiency and processing time of the wet textile processes in the presence of ultrasound. In this paper, the different time and length scales are discussed in the intensification of the mass transport in laundry processes in the presence of ultrasound and compared with more conventional processes. It has been concluded that the characteristic mass transport rates in textiles can be increased by a factor of 6 applying ultrasound.