(401h) Deposition of Solid Fabric Enhancers in the Domestic Clothes Dryer

Clothes drying is a common household process based on a simple principle; fabrics tumble in a drum through a flow of hot air, aiding the evaporation of water remaining after washing. Existing literature has routinely considered the dryer using black box thermodynamic models. This has led to recent improvements in dryer efficiency and the development of so called ‘high-efficiency’ appliances. However, consumer perception of drying performance considers more than just final fabric moisture content.

Surface feel, odour, wrinkling and static cling are important factors, difficult to control with changes to the drying process alone. These benefits may be delivered by addition of solid fabric enhancers (SFE) to the dryer using products such as dryer sheets. During drying, the SFE mixture is transferred to items of clothing in surface-surface interactions. These include direct contact between dryer sheets and fabrics, indirect transfer via the drum wall and secondary transfer between fabrics, as shown in Figure 1. Without full understanding of drying, development of these products has been limited to time and labour-intensive trial and error approaches. The behaviour of items within the dryer, including interactions between fabrics, SFE coated articles and the dryer drum, will be significant in both the drying process and delivery of fabric care benefits.

The dynamics of fabric and dryer sheet motion within the dryer have been examined to aid the development of new appliances, fabric enhancers and delivery articles. The objective is to further understanding of behaviour of these items throughout different regions of the dryer and along the length of the drying cycle (i.e. as moisture content decreases) for a range of consumer representative load conditions.

Positron Emission Particle Tracking (PEPT), developed at the University of Birmingham using a modified medical PET scanner, has been employed to track the location of a radioactively labelled tracer particle affixed to items within the dryer drum. Analysis of the timestamped Cartesian coordinates output by the PEPT machine learning tracking algorithm allows the tracer position, velocity and acceleration to be calculated. Individual tracer behaviour and time averaged Eulerian velocity profiles were used to understand motion during drying, as shown in Figure 2.

Six regions within the dryer drum were identified, demonstrating the range of movements experienced by items during tumbling. These showed clear correlation with existing flow regimes describing behaviour of granular media in rotating drums. Fabric motion was primarily cataracting to maximise the surface area of fabric available to interact with drying air in the falling region, with some conditions moving towards centrifuging or cascading flows. Movement in the axial direction was significantly slower than the primary radial flow. Dryer sheets were more prone to centrifuging than fabrics, with significant time spent in contact with the drum wall. Conversely, a wool dryer ball was more likely to cascade, spending time mixed into the top of a fabric bed which forms in the impact and lifting regions. Behaviour in this bed is primarily determined by frictional interactions with the drum wall, which subsequently affects behaviour in the 5 remaining regions. The most significant changes to this behaviour were observed when changing fabric moisture content and volumetric fill ratio, with wet fabrics and smaller load sizes both exhibiting faster falling speeds and spending more time in the fabric bed. The changes were most significant in the lifting, falling and detachment regions, with varying acceleration and shearing likely to influence both fabric wear and SFE delivery.

A deposition device is under development to simulate the range of interactions observed within the dryer at bench scale. This mimics the abrasive motion observed in PEPT experiments at a range of representative relative velocities and normal forces. The device is housed in a temperature and humidity controlled environment to ensure conditions are fully representative of those observed in the dryer. Following deposition an indicator will be used to identify SFE on the fabric surface and images analysed to quantify this across the range of conditions observed. This will enable the rapid testing of new SFE formulations and delivery articles without the need for full scale trials.

References

Ingram, A.; Seville, J. P. K.; Parker, D. J.; Fan, X.; Forster, R. G. Axial and Radial Dispersion in Rolling Mode Rotating Drums. Powder Technol., 2005, 158 (1–3), 76–91. https://doi.org/10.1016/j.powtec.2005.04.030.

Govender, I. Granular Flows in Rotating Drums: A Rheological Perspective. Miner. Eng., 2016, 92, 168–175. https://doi.org/10.1016/j.mineng.2016.03.021.

Windows-Yule, C. R. K.; Seville, J. P. K.; Ingram, A.; Parker, D. J. Positron Emission Particle Tracking of Granular Flows. 2020. https://doi.org/10.1146/annurev-chembioeng.

NicuÅŸan, A. L.; Windows-Yule, C. R. K. Positron Emission Particle Tracking Using Machine Learning. Rev. Sci. Instrum., 2020, 91 (1), 13329. https://doi.org/10.1063/1.5129251.