Dynamics of textile motion in a front-loading domestic washing machine

Positron Emission Particle Tracking (PEPT), a technique which enables high-speed detection of a radioactively labeled particle in three-dimensional opaque systems, has been used to track a single tracer particle attached to a textile as it is rotated and tumbled amongst other textiles in a commercially available domestic washing machine, with the aim of understanding the mechanisms by which mechanical action is imparted onto wet textiles during washing. These mechanisms were first identified by comparing the wash process to other well-researched chemical engineering processes, such as the mixing of solids in rotating drums, the impact of grinding media in comminution mills and the flow through bi-porous textile media observed in resin transfer molding processes. The results show that the textiles experience the greatest mechanical action upon impact after having been projected into the air by the motion of the rotating drum, and as textile loading increases, the free-fall velocity and deceleration upon impact of the textiles decreases, leading to less mechanical action in the impact region of the drum. Shear rates of the textile were also estimated based on an Eulerian approach, yielding highest measured shear rates in the impact region. The motion of the textile is also shown to be two-dimensional, with little movement along the depth of the drum over time and a dead zone region was identified near the axis of rotation of the drum, where textiles experience less mechanical action than textiles located nearer to the rotating drum wall. (c) 2012 Elsevier Ltd. All rights reserved.