Interfacial transport phenomena

1. Interfacial transport phenomena PhD student Supervisor Research group Supported by Phone E-mail URL Research school + 31 53 489 3175 a.s.haase@utwente.nl www.utwente.nl/tnw/sfi JMBC/OSPT A. Sander Haase Rob G.H. Lammertink TNW/SFI ERC starting grant • Experimental: the bubble mattress • In this research project we aim at obtaining a more fundamental understanding of transport processes that take place at interfaces. We have investigated experimentally how a specific type of superhydrophobic surface – a bubble mattress – can be utilised to manipulate and control inter-facial momentum and mass transport(see Fig. 1). The measured effective slip lengths are in both qualitative and quantitative agreement with (previous) numerical and analytical results. The hydrodynamic friction drag can be reduced by more than 20% for a protrusion angle of 10°. • Numerical: interfacial mass transfer • Because of wall slip, a solute that dissolves from the slippery bubble surface is transported away by both diffusion and convection. Numerical analysis shows that for positive protrusion angles, and sufficiently large bubbles (Lg > 10 µm) and poro-sities (ε> 0.5), this convective transport enhan-ces interfacial mass transport, compared to a fully saturated and non-slippery wall (see Fig. 2). The enhancement vanishes for bubbles smaller than 10 µm, as the effective wall slip is proportional to the bubble size. This explains why for e.g. micro-porous membranes the assumption of a fully saturated and non-slippery wall holds so well. • Running and future research • Currently, experimental work is dedicated to liquid/liquid systems and high shear flows. Also Nusselt/Sherwood relations over superhydro-phobic surfaces are subject of research. Figure 1By establishing a bubble mattress in a chip (A), the effective slip length as function of protrusion angle could be determined experimentally (B). [E. Karatay et al.PNAS 110 (21): 8422-8426 (2013).] Figure 2 For bubble mattresses, the effect of the slippery interface on interfacial mass transport vanishes for very small bubbles. Enhancement is possible for bubbles larger than 10 µm. [A.S. Haase et al.Soft Matter 9 (37): 8949-8957 (2013).]