Two-phase flows occur frequently in nature and industrial applications, such as coastal engineering, land, air and marine propulsion, energy generation and in medical diagnostics and therapy. Many of these two-phase flows comprise essential interfacial transport mechanisms at microscale. Today, systems that comprise interfacial transport mechanisms and complex physicochemical phenomena at microscale are designed based predominantly on empirical observations, since a fundamental theoretical framework and associated predictive tools are not available. Direct numerical simulation (DNS) can provide a powerful and cost-efficient tool to study and predict the complex behaviour of two-phase flows and the associated interfacial transport mechanisms. However, despite extensive research efforts dedicated to two-phase flow modelling, substantial difficulties remain in simulating interfacial transport mechanisms at microscale. Having the means to accurately simulate interfacial transport mechanisms at microscale is an enabling technology for both industry and academia, which will aid the design of novel and improved processes as well as better consumer products, with direct economical and societal impact. The proposed research conducts an in-depth study of unprecedented detail of the complex physicochemical phenomena and transport mechanisms that govern microscopic two-phase flows. The proposed research includes the development of pioneering numerical techniques in the remit of continuum mechanics to predict the complex behaviour of two-phase flows at microscale as well as the study of interfacial transport mechanisms in two prototypical applications with immediate industrial relevance: a) two-phase microprocessor cooling and b) the dynamics of foams in lubricants. The novel numerical techniques will resolve key issues of available numerical methods and enable the DNS of interfacial transport mechanisms at microscale in a rational computational framework. The capability to directly simulate two-phase flows at microscale will not only increase our fundamental understanding of the complex physics governing interfacial transport mechanisms at microscale, but will also enable engineers to build better devices and systems that rely on such flows. Through the study of the prototypical applications, the proposed research will provide a detailed understanding of interfacial transport mechanisms at microscale, relevant to microfluidic two-phase flows in general and will directly contribute to the development of cooling systems that are capable of handling the heat generated by the next generation of microprocessors and the development of more reliable, efficient and economically friendly lubricants.

The smallest scale on which it is possible to design functional devices, including electronics, is the molecule scale (about 100,000 times smaller than the width of a human hair). This is the ultimate limit for miniaturisation and motivates research to manipulate and study the properties of individual molecules for applications in, e.g., information technologies and sensors. It is also the scale at which quantum phenomena dominate properties, so single-molecule structures offer a domain for investigations ranging from fundamental tests of quantum theory to developing components for future quantum technologies. To realise such experiments and technologies, it is necessary to incorporate individual molecules into electrical circuits. This is challenging because the typical size of a useful functional molecule is much smaller than the smallest wires that it is possible to fabricate, even with the most sophisticated lithography systems available today. Most researchers use one of two approaches. The first uses an electrical current or mechanical strain to make a tiny gap, a few nanometres across, in a thin wire, and then deposit the molecules of interest randomly, hoping that one and only one bridges the gap. This method relies on chance, and so it very rarely yields a working device: typically, only a very small proportion of devices fabricated show behaviour consistent with a single molecule in the gap and, because the shape of the gap and the orientation of the molecule are uncontrolled, it is rare for even such "working" devices to exhibit reproducible properties. The second method uses a scanning tunnelling microscope to locate and investigate molecules that are deposited on a conducting surface. This process is much more reliable and reproducible than the break junction method but it involves bulky experimental apparatus and it tightly limits the experimental geometry, ruling out the development of more complicated experiments or practical devices. These limitations in the existing methods have hamstrung the development of molecule-scale devices and technologies. Further progress in this field now requires the development of controlled and reliable methods that can be scaled to high volume production. This project will provide this methodology and demonstrate a range of prototype molecular devices. Our approach is based on DNA nanotechnology, which has, over the last decade, proved itself to be a powerful tool for controlled self-assembly of structures at the molecular scale. We will use these methods to direct the assembly of "packages" about 100 nanometres across. Constructed mainly from DNA with a precisely programmed structure, these packages will position gold nanoparticle contacts and the "target" molecular components, whose electrical transport properties we would like to exploit, with sub-nanometre accuracy. Our method produces trillions of packages at a time in a test-tube and ensures that each one has exactly the correct molecules incorporated in the correct positions and orientations between contacts. These gold nanoparticle contacts are large enough that we can connect them to laboratory equipment using standard nanolithography techniques. The technology has the potential for future development to connect multiple molecules in three-dimensional device architectures, and for the assembly of large-scale integrated molecular circuits. We propose to create several families of devices, designed to develop and prove this radically new molecular device fabrication methodology. These devices will give us an unprecedented experimental tool for probing electrical and magnetic properties of molecules, but they will also establish the potential for the industrial deployment of our technology. Central to the project are close interactions with industrial partners and knowledge transfer activities designed to accelerate commercial applications.

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).

This research will develop a new way of rapidly making high-quality metal parts by Additive Manufacturing, often referred to as 3D printing. This work, if successful, will lead to faster, cheaper and more environmentally-friendly production of functional parts to be used in the UK's leading industries. It will help maintain the competitive advantage of manufacturing industries in the UK and result in enhanced industrial output and lead to improved exports. The UK academic community will gain by opening up new research opportunities to chemists, materials scientists and engineers in universities. The public will gain through the manufacture of new products and job-creation in key industrial sectors in the UK.

BONSAI is an ambitious 3-year research project aimed at investigating the fundamental heat and mass transfer features of boiling flows in miniaturised channels. It combines cutting-edge experiments based on space/time-resolved diagnostics, with high-fidelity interface-resolving numerical simulations, to ultimately provide validated thermal-design tools for high-performance compact evaporators. The proposed project assembles multidisciplinary expertise of investigators at Imperial College London, Brunel University London, and the University of Nottingham, with support from 3 world-leading research institutes: Alan Turing Institute, CERN (Switzerland) and VIR2AL; and 11 industry partners: Aavid Boyd Thermacore, Alfa Laval, CALGAVIN, HEXAG&PIN, HiETA, Hubbard/Daikin, IBM, Oxford nanoSystems, Ricardo, TMD and TTP. The recent trend towards device miniaturisation driven by the microelectronics industry has placed an increasing demand on removing higher thermal loads, of order of MW/m2, from areas of order cm2. In some applications (e.g. refrigeration) new 'green' refrigerants are needed, but in small volumes due to flammability or cost, while in others (e.g. batteries for EV and other applications) non-uniform or unsteady heat dissipation is highly detrimental to performance and lifetime. Flow boiling in multi-microchannel evaporators promises to meet such challenging requirements with low fluid volumes, also allowing better temperature uniformity and smaller pumping power, in systems that go well beyond the current state-of-the-art. Due to significant industrial (heat exchange) and environmental (efficient energy use) interest, the understanding of boiling heat transfer has improved in recent years, with focus on flow pattern transitions and characteristics, pressure drop, and heat transfer performance. However, our current understanding is simply insufficient to facilitate the wider use of these micro-heat-exchangers in industry, which remains unexploited. BONSAI has been tailored specifically to address the fundamental phenomena underlying boiling in miniaturised devices and their relevance to industrial design. The challenges to be addressed include the impact of channel shape and surface characteristics on flow instabilities, heat transfer and pressure drop, and the relationship between the time-dependent evolution of the liquid-vapour interface, thin liquid-film dynamics, flow field, appearance of dry vapour patches, hot spots, and local heat transfer characteristics. The extensive experimental/numerical database generated will be exploited via theoretical and novel machine-learning methods to develop physics-based design tools for predicting the effects of industrially-relevant thermohydraulic parameters on system performance. The collaboration with our partners will ensure alignment with industrial needs and accelerate technology transfer to industry. In addition, HiETA will provide Metal Additive Manufacturing heat sinks that will be assessed against embossing technologies as ways of mass-producing microchannel heat exchangers, Oxford nanoSystems will provide nano-structured surface coatings, and IBM will support visits to their Research Labs focussed on efficient parallelisation of the numerical solver and scale-out studies. The proposed research will not only enable a wider adoption of two-phase thermal solutions and hence the meeting of current and future needs across industrial sectors, but also will lead to more efficient thermal management of data-centres with associated reduction in energy consumption and carbon footprint, and the recovery and reuse of waste heat that is currently being rejected. This will constitute an important step towards meeting the UK's emission targets by 2050. Additionally, BONSAI will integrate with EPSRC Prosperity Outcomes of Delivery Plan 2016-20 and enable technological advances in relation to the Manufacturing the Future theme, contributing to a Productive and Resilient Nation.