Direct numerical modelling of interfacial transport mechanisms at microscale

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 proposed research establishes core technologies for the growing number of microfluidic applications by developing theoretical models and numerical techniques for microfluidic two-phase flows and by resolving critical shortcomings of available numerical models. The new insights into transport mechanisms at microscopic interfaces will make a sizeable contribution to the understanding of two-phase flows. These insights have a widespread scientific, engineering and technological applicability and will provide engineers with tools to design and optimise processes concerning energy conversion, lubrication, heat and mass transfer, flood and coastal defences as well as medical devices. Developing the complex knowledge-base in two-phase flow modelling and interface physics, particularly for microfluidic applications, and the associated simulation tools at a leading UK university will ensure the competitiveness of UK businesses in this increasingly important field of engineering. As previously demonstrated in various branches of engineering, e.g. Aeronautics and Bioengineering, powerful simulation tools lead to better engineering, better products and more efficient processes.

Two-phase cooling systems, as studied as part of this proposal, will play a key role in sustainably increasing the performance of computer systems. Given the forecasted 1 trillion semiconductor units shipped annually by 2016, the potential economic and societal impact is evident. Two-phase cooling systems that use evaporation as their main heat sink can significantly increase the cooling and energy efficiency of microprocessor cooling systems. For operators of large data centres and supercomputing facilities, two-phase cooling systems will significantly reduce energy costs and decrease their carbon footprint. Many large computer clusters for physical computing and data analysis are operated by universities and research institutions, which face tightening budgets and for which the increased energy efficiency provided by two-phase cooling systems is particularly interesting. For companies working on microelectronics, being at the forefront of this development is critical for success in the highly-competitive semiconductor market.

The proposed research on the dynamics of foams will lead to improved, more efficient and economically-friendly lubricants. Having a reliable and accurate theoretical and numerical framework to study and predict the formation of foams is of substantial value for petrochemical companies that develop and produce lubricants, in order to stay competitive in this continuously growing market. For operators of large machinery as well as end-users such lubricants will enable a decrease in operating costs and an increase in reliability. The new insights into the physics of foams will also positively impact other applications that feature foams, such as wastewater treatment, the decontamination of nuclear reactors or the oil and gas recovery by means of hydraulic fracturing (fracking).

Through close collaboration with my industrial partners, the timescale for the proposed research to make a tangible impact for the practical applications studied in this fellowship can be kept relatively short and is expected to be three to five years after inception of the first results. The marketing of two-phase cooling systems for microelectronics is imminent, due to the continuous increase in heat generation by microprocessors. Having a reliable predictive tool to optimise the composition of lubricants will cut the time to market of new lubricants considerably. With respect to other applications, not explicitly considered as part of this research, the timescale for practical impact is more difficult to estimate. However, a noticeable impact on the development of medical inhalers and fuel combustion (evaporation), processes for surface coating (film flows and evaporation) and hydraulic fracturing (foams) is expected within a seven year time frame.