Skip to content
Research Fellows Directory

John Gray

Professor John Gray

Research Fellow


University of Manchester

Research summary

My research is focussed on granular flows, which are one of the most commonly processed materials in industry. Applications range from mining and construction to the manufacture of bulk chemicals, pharmaceuticals and foods. We are all familiar with handling granular materials, even if it is pouring ones cereal into a bowl at breakfast or putting sugar in our tea! However, actually being able to predict these flows is still a major theoretical challenge. This is because they sometimes behave like a solid, a liquid or a gas. In most flows, all three granular phases will be active and the picture is complicated further, by the fact that there is usually a mixture of particles with different sizes, densities, shapes and surface roughnesses. This polydispersity can lead to unexpected segregation, which can cause severe handling difficulties and usually degrades the quality of the final product. In the worst cases complete batches have to be discarded at significant cost. My work uses a combination of small scale experiments, theory and numerical computation to improve our ability to predict the flow and segregation of these granular flows, which has significant potential to improve the way in which grains are processed. Bizarrely my work is also of direct relevance to large scale natural hazards, such as snow avalanches, debris flows and pyroclastic flows. This is because they are also granular flows that are composed of a huge number of individual particles that are able segregate. In some flows, larger more resistive grains accumulate at flow fronts and are pushed aside to spontaneously form levees that channelize the flow and enhance run-out. I find the subject fascinating and I am often amazed by the beautifully structured patterns than can be formed by the combination of flow and segregation.

Grants awarded

Particle-segregation and rheology of granular flows

Scheme: Wolfson Research Merit Awards

Dates: Jan 2016 - Dec 2020

Value: £25,000