James Sprittles is an EPSRC funded Research Fellow in Applied Mathematics at the University of Birmingham.
He graduated from the University of Birmingham (2005) and received his Ph.D. (2010) from the same institution for a thesis entitled ‘Dynamic Wetting/Dewetting Processes in Complex Liquid–Solid Systems’; which was undertaken in close collaboration with Kodak European Research.
J.E. Sprittles’ research is concerned with the application of complex mathematical models to a cluster of industrially relevant capillary flows. He has developed a specially designed numerical platform to simulate this class of flows.
Dynamic Wetting, Flow Over Chemically Patterned Surfaces, Computation of Viscous Flow Near A Corner, Propagation Of Wetting Fronts Through Porous Media
A major obstacle to the design of ink-jet printing devices for targeted deposition of microdrops is that the interaction of a microdrop with a solid substrate cannot be inferred from experiments with larger drops, whose behaviour is relatively easy to observe. Consequently, it is necessary to have a theory based on first-principles which, once verified against large-drop experiments, can take one down to the dimensions inaccessible to experiments.
In this research, the behaviour of spreading microdrops is examined, over a wide range of parameter space, and results obtained using different theories for the dynamic wetting process are compared. This is achieved by developing a numerical code which incorporates, besides the conventional `slip models' for the moving contact line, the more mathematically complex theory of interface formation.
The study allowed us to indicate clear, experimentally verifiable, qualitative differences between the models' predictions. In particular, the transition between different flow regimes, such as deposition or rebound of the microdrop, is seen to be strongly dependent on the treatment of the dynamic contact angle.
Flow Over Chemically Patterned Surfaces
The classical fluid dynamics boundary condition of no slip suggests that variation in the wettability of a solid should not affect the flow of an adjacent liquid. However, experiments and molecular dynamics simulations indicate that this is not the case.
In this work, we have shown how flow over a solid substrate with variations of wettability can be described in a continuum framework using the interface formation theory developed earlier. Results demonstrate that a shear flow over a perfectly flat solid surface is disturbed by a change in its wettability, i.e., by a change in the chemistry of the solid substrate.
Computation of Viscous Flow Near a Corner
We have shown that an attempt to compute numerically a viscous flow in a domain with a piece-wise smooth boundary by straightforwardly applying well-tested numerical algorithms (and numerical codes based on their use, such as COMSOL Multiphysics) can lead to spurious multivaluedness and nonintegrable singularities in the distribution of the fluid's pressure.
The origin of this difficulty is that, near a corner formed by smooth parts of the piece-wise smooth boundary, in addition to the solution of the inhomogeneous problem, there is also an eigensolution. For obtuse corner angles this eigensolution (a) becomes dominant and (b) has a singular radial derivative of velocity at the corner. A method is developed that uses the knowledge about the eigensolution to remove multivaluedness and nonintegrability of the pressure.
Propagation Of Wetting Fronts Through Porous Media
This research is concerned with the flow of liquid through solids which are permeated by a network of holes; such materials are known as porous media. Understanding how a liquid will flow through a porous structure is the key element to a range of industrial phenomena.
Often a full scale experiment of such a flow is unpractical, expensive and/or dangerous. Consequently theoretical modelling becomes a tool which can be used to probe the dynamics of such flows to ensure safety, insight and optimisation of the appropriate process.
We intend to use our previous expertise in Dynamic Wetting to develop more advanced models for this process, beginning with the simplest case in which a liquid invades an initially dry porous medium.
Sprittles, J.E. and Shikhmurzaev, Y.D. (2011), Viscous flow in domains with corners: Numerical artifacts, their origin and removal. Computer Methods in Applied Mechanics and Engineering, 200:1087-1099.
Sprittles, J.E. and Shikhmurzaev, Y.D. (2011), Viscous flow in corner regions: Singularities and hidden eigensolutions. International Journal for Numerical Methods in Fluids, 65: 372–382.
Sprittles, J.E. and Shikhmurzaev, Y.D. (2009), A continuum model for the flow of thin liquid films over intermittentlty chemically patterned surfaces. The European Physical Journal Special Topics, 166:159-163.
Sprittles, J.E. and Shikhmurzaev, Y.D. (2007),
Viscous flow over a chemically patterned surface. Physical Review E., 76:021602.