Complex interfacial flows with heat transfer: Analysis, direct numerical simulations and experiments

Multiphase flows often play a central role in engineering and have numerous practical applications. The proposed research focuses on free-surface thin-film flows over heated substrates. Such flows are part of the general class of interfacial flows which involve such diverse effects as dispersion and nonlinearity,
dissipation and energy accumulation, two- and three-dimensional phenomena and hence they are of great fundamental significance. Film dynamics and stability are governed by the effects of gravity, inertia, capillarity, thermocapillarity, viscosity, as well as surface topology and conditions. The thermocapillary forces give rise to an important surface phenomenon known as the Marangoni effect, in which variations in surface tension due to temperature result in liquid flow. The Marangoni effect leads to film deformation, driving it to rise locally and thus to generate instabilities that lead eventually to the formation of wave structures. In low-Reynolds (Re)-numbers heated falling films the thermocapillary forces are in competition with those of gravity and viscosity. In shear-driven horizontal flows, gravity is absent and the driving force is that of viscous shear at the gas-liquid interface. At higher Re inertia begins to play an increasingly dominant role.

Film flows show great promise in terms of their heat exchange capabilities. We aspire to harness and extend this promise, which will allow step improvements to the performance and efficiency of a host of technologies and industrial applications that rely crucially on film flows. This proposal seeks funding for a comprehensive three-year research programme into a three-pronged novel experimental, theoretical and numerical investigation aimed at rationally understanding and systematically predicting the hydrodynamic characteristics of liquid films flowing over heated surfaces, and furthermore, how these characteristics control the heat transfer potential of the corresponding flows. The proposal aims to answer these questions, with the goal of being able to accurately and efficiently predict complex physical behaviour in
heated film flows. We focus specifically on two paradigm flows: gravity-driven falling films and gas-driven horizontal films. The analytical work will be complemented by detailed numerical simulations that will act to verify the efficacy of the developed flow models while both analysis and computations will be contrasted with advanced experiments. The work will be undertaken by a team from the Chemical and Mechanical Engineering Departments at Imperial College London with complementary skills and strengths: Kalliadasis (Analysis--Theory), Markides (Experimental Fluid Mechanics) and van Wachem (Multiphase Flow Modelling--Computations).

In addition to the academic impact described earlier, the following types of impact are envisaged:

Society--economy: Providing physical insight in thin-film flows with heat transfer and the appropriate modelling/predictive tools for such systems would allow researchers and engineers, whose technological processes involve at some stage such flows, to tackle classes of problems that have been inaccessible to them so far. There is also a wide spectrum of applications from traditional industries, such as chemical plants and nuclear industry to rapidly growing areas such as microfluidics and MEMS. The computational tools will be of benefit to the control and optimisation of technological processes that exploit thin-film flows as they would allow their rapid design or the designer surfaces for targetted heat transfer applications.

Industrial links--interaction with industry: We participate in a number of industrial, economic and decision-making networks and groupings, all of which could serve as vehicles to facilitate the wider impact of the research and to ensure that it is channeled towards the appropriate applications. Furthermore, we place great emphasis on the interactions between the project and the industrial collaborations. Direct knowledge exchange between the academic and industrial partners is planned while the research outputs will be used directly to allow successful development of new technological concepts and ideas.

Human resources: The project will offer an excellent training opportunity of the PDRAs it will employ. Indeed, training will take place in a highly cross-disciplinary context at the cross-road between applied mathematics, fluid dynamics and computational engineering/physics. This in turn will increase the specialist knowledge of the UK at the interface of these areas.