Dr Paul Grassia joined Strathclyde in 2015 following an academic post at University of Manchester (1998--2015), postdoctoral research at Stanford University (1996--1998) and University of Chile (1994--1996), a PhD at University of Cambridge (1990--1994), and BSc (Hons) at University of Western Australia (1985--1989).
Working at the interface between chemical engineering, applied mathematics, physics and physical chemistry, Dr Grassia's research group studies foams, and does so, for two main reasons: first and foremost, because foams are interesting scientifically in their own right(!), and secondly because they are important in a multitude of engineering operations (e.g. froth flotation in minerals processing, foam fractionation in protein purification, polymer foam manufacture, foam improved oil recovery).
Just stop and think what truly amazing materials foams really are: if anyone told you they could make a substance that was 99% by volume air, and 0.999% by volume water, and yet that had flow properties total different from either air or water, would you believe them?
Dr Grassia's research on foams has focussed on two main areas treated at very different length scales: foam drainage and foam rheology. Work on drainage has primarily been at the continuum scale, whereas that on rheology has been at the bubble scale. One major research success in drainage has been modelling froth flotation systems, and demonstrating the role that thin capillary boundary layers play in flotation tank operation. Meanwhile a major success in rheology has been modelling bubble flows in confined systems (e.g. a microfluidic channel and/or a pore in an oil reservoir during foam improved oil recovery), demonstrating how viscous drag effects can lead foam structures to break up.
Dr Grassia's group also studies solid-liquid suspensions (in addition to gas-liquid foams). To a certain extent however these solid-liquid suspensions are merely `upside-down foams': solids in suspensions tend to fall, whereas bubbles in foam rise.
Dewatering of suspensions or sludges is in fact a particularly important engineering operation, that reduces the volume (and thereby facilitates the disposal of) solid-fluid wastes, whilst simultaneously providing a source of clean water. Robust design of equipment to dewater a given sludge relies on knowing the sludge's rheological properties, which in turn are sensitive to the local solid fraction and local microstructure. According to existing theories for a sludge under compression, two (phenomenological) material properties are sufficient to describe the dewatering behaviour: a compressive yield stress (describing the weight-bearing strength of the sludge) and a hindered settling function (describing its frictional resistance). The results of small scale laboratory tests (e.g. batch settling, centrifugation, pressure filtration) depend on the values of the phenomenological material properties. Research in the group has focussed on solving so called inverse problems to extract sludge material properties from laboratory test data, as well as using the material properties thus obtained to improve designs of sludge dewatering equipment.