Our research is concentrated on several main areas:
Microstructured Process Systems
Our projects are to develop miniaturised chemical plant for:
- Biodiesel production
- Liquid fuels from biomass
- Methanol synthesis
- Ultra-clean combustion
Approaches and techniques are:
- Experimental measurements and detailed chemical modelling of gas-phase and catalytic reactions.
- Studies of flows and heat transfer in microchannels, using microvisualisation techniques and computational fluid dynamics (CFD).
- Process design of highly integrated process systems.
- Pilot plant development, operation and analysis
Computational Fluid Dynamics
Computational Fluid Dynamics (CFD) is the study of fluid flow, often combined with simultaneous heat or mass transfer, using computer modelling techniques. It provides a means of solving the Navier Stokes equations, together with conservation equations for energy, species etc. in complex geometries. By subdividing the region of interest into thousands or millions of small volumes (known as cells), the local pressure, velocity, temperature etc. are obtained for each cell. There is now commercial software available that is optimised to run on multi-core computers or clusters allowing simulation of complex phenomena. Our focus is on the extension of commercial software rather the development if new codes. Most of our modelling work uses the CFD solvers ANSYS CFX or ANSYS Fluent, and TranSAT for applications where we use the Level set method to determine gas-liquid interfaces.
Currently work is underway to collect more validation data across a number of flow regimes, and simulations of Taylor flow, annular flow and the influence of turbulence
Laminar Single Phase Flow
It is possible to obtain significant enhancement to heat transfer with a relatively low increase in the pressure drop by introducing bends in the channel that create Dean’s vortices. We have performed studies to investigate the effect of channel cross-section (circular, semi-circular, rectangular and triangular) and the channel path (serpentine, sinusoidal and trapezoidal) for a wide range of conditions in the laminar regime.
Turbulent Single Phase Flow
In laminar flow the conservation equations are known and can be solved in their native form. However, in turbulent flow it is necessary to introduce a turbulence model because it is impractical to use a computational mesh sufficiently fine to resolve all of the length-scales occurring in turbulent flow. Therefore empirical models are introduced to remove this problem at the cost of including further equations that need to be solved. A key task in the simulation of turbulent flow and heat transfer is ensuring that the turbulence model is suitable for the flow under study, especially when flow separation or heat transfer are important.
Two Phase Flow
In many important engineering applications the flow comprises two phases (a gas and a liquid) which can have very different flow regimes depending on the volume fractions of the gas. With increasing gas flow rate for fixed liquid flow rate the flow regime transitions from bubbly flow, to Taylor flow to annular flow. Each regime has different pressure drops and heat and mass transfer rates. As with turbulent flow, additional relations/assumptions are required to close the system of equations. In addition it is necessary to locate the interface between the gas and liquid phases. Many different methods to solve such flows have been developed.
Amongst the various flow regimes that occur Taylor flow is particularly important because of its properties (gas bubbles separated by liquid slugs with a film of liquid at the wall with little back mixing).
Thus far our work has considered the important numerical considerations in the modelling of such flows and the heat transfer enhancement they give.
Experimental Studies and Model Validation
A key component of the modelling work performed here is validation of the CFD results against experimental data. The length-scale of interest in our applications is channel diameters of the order of 0.1-2 mm, as these are used in micro-structured heat exchangers and reactors. The experimental facilities include a state-of-the-art microPIV system, which can be used to probe the conditions in the liquid film occurring in Taylor flow. In addition we can use the same high speed cameras to take high quality photographs which yield detailed information on bubble shapes. Instrumented flow rigs to determine pressure drop, heat transfer rates etc. across a wide range of flow regimes have been constructed and are used to collect data for the modeling of the results from CFD simulations.
Computational Chemical Engineering
Our research group uses a variety of techniques in computational chemistry to get detailed information at the molecular level of important industrial processes. The range of computational techniques includes periodic and non-periodic density functional methods, high level ab-initio methods, molecular dynamics and monte-carlo techniques. The current research areas are summarised below:
Surface Processes and Catalysis
Investigation of the structural, electronic and chemical properties of metallic and oxide surfaces. The effort is placed on evaluating energy reaction profiles of the adsorption of molecules on these surfaces and simulation of catalytic reactions at the surfaces and at inner sites. Three chemical processes that are under study are:
- Methanol oxydehydrogenation
- Phase stability of cobalt oxide surfaces
- Ammonia oxidation on platinum catalyst
Biomass Molecular Chemistry
Investigation of the effect of solvents on the degradation of sugars in aqueous phase. Two chemical aspects under study are:
- Degradation of biomass components under high pressure and high temperature water conditions
- High accurate prediction of thermodynamic properties of valuable biochemical species
Prediction of minimum energy profiles and ab-initio chemical kinetics of the reaction of gaseous oxidising agents with carbonaceous surfaces. Current topics of interest are:
- Functionalisation of zigzag and arm-chair graphene edges
- Stability and surface diffusion of oxygen atoms on a carbonaceous matrix
- Desorption mechanism of CO and CO2
Sulphur Chemistry in Combustion and Atmospheric Environments
High level ab initio calculations of reaction barriers and reaction rates for the reaction of sulfur species in the atmosphere. Current topics studied are:
- H2S oxidation kinetics under O2 atmosphere
- Stability, thermodynamic and spectroscopic properties of gaseous sulphur containing species
Experimental data are used to validate the predicted results obtained when it is possible. The experimental facilities include micro-reactor systems for liquid-liquid, gas-solid systems coupled with state-of-the-art analytical instrumentation such as GC, HPLC, MS, IR and UV-Raman. Experimental flow systems for reactions in the time range of a few seconds to minutes are available for the modelling of reaction pathways.