Particle self-diffusiophoresis near solid walls and interfaces

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The purpose of this paper is to explore, from a theoretical viewpoint, the mechanisms whereby locomotion of low-Reynolds-number organisms and particles is affected by the presence of nearby no-slip surfaces and free capillary surfaces. First, we explore some simple models of the unsteady dynamics of low- Reynolds-number swimmers near a no-slip wall and driven by an arbitrarily imposed tangential surface slip. Next, the self-diffusiophoresis of a class of two-faced Janus particles propelled by the production of gradients in the concentration of a solute diffusing into a surrounding fluid at zero Reynolds and P´eclet numbers is studied, both in free space and near a no-slip wall. The added difficulty now is that the tangential slip is not arbitrarily chosen but is given by the solution of a separate boundary value problem for the solute concentration. Finally, an analysis of a model system is used to identify a mechanism whereby a non-self-propelling swimmer can harness the effects of surface tension and deformability of a nearby free surface to propel itself along it. The challenge here is that it is a free boundary problem requiring determination of the surface shape as part of the solution

On emerging micro- and nanoscale thermofluidic technologies

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.This paper highlights examples of my current research in heat transfer and fluidics at the interface of energy applications and micro- and nanoscale technologies. It is not the scope of this paper to present an exhaustive account of all current and past activities related to its title. It is rather an account of current research in my laboratory in this area, containing both the underlying scientific challenges as well as the hoped final outcome in terms of applications. To this end, examples from the areas of energy conversion, as well as energy transport will be discussed. In the area of energy conversion an original, deformable, direct methanol microfuel cell will be presented made of lightweight, flexible, polymer-based materials. A basic understanding and control of two-phase flows (in this case methanol and carbon dioxide) in microchannels as well as novel materials processing and microfabrication methods are directly related to the performance of such energy conversion devices. In the area of energy conservation and reuse, examples from the information technology are employed. Specifically, new concepts of liquid (water) cooling of chips reaching heat removal rates in excess of 700 W/cm2 in domains with restricted heights of the order of one mm will be presented. One additional advantage of using water to cool high density electronics is energy reuse, due to the potentially much higher exergy content of the coolant compared to air cooled technologies. The last part of the paper focuses on the employment of functional nanostructures such as carbon nanotubes and nanowires of conductive and semiconductive materials for the efficient transport of electricity and heat and the need for the development of novel technologies for the manufacturing, characterization as well as handling of such nanostructures

Microfluidics for Energy Applications

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Microfluidic methods developed primarily for medical applications have much to offer energy applications. This short paper will provide the motivation and outline my group’s recent work in two such areas: (1) microfluidics and optics for bioenergy and (2) microfluidics for carbon management. Full details will be provided in talk. Within the bioenergy theme, we are developing photobioreactor architectures that leverage micro-optics and microfluidics to cater both light and fluids to maximize productivity of microalgae. Within the carbon management theme we are developing a suite of methods to study porescale transport and reactivity in carbon sequestration and enhanced oil recovery. Results indicate potential for order of magnitude gains in photobioreactor technology and a 100-fold improvement over current subsurface fluid transport analysis methods

Rotating magnetic field actuation of a multicilia configuration

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The current paper continues the analysis of a completely novel method of fluid manipulation technology in micro-fluidics systems, inspired by nature, namely by the mechanisms found in ciliates. More information on this subject can be found at http://www.hitech-projects.com/euprojects/artic/. In order to simulate the drag forces acting on an array of artificial cilia, we have developed a computer code that is based on fundamental solutions of Stokes flow in a semi-infinite domain. The actuation mechanism consists of a bi-directional rotating excitation magnetic field. The magnetization induced by the magnetic field was calculated in a separate routine based on the Integral Nonlinear Equations Approach with 1D discretization of wire (cilium). Time averaged x-coordinate mass flow rates are computed for several cilium configurations resulting. The outcome and originality of this paper consist on assessing magnetic actuation as a practical tool for obtaining a consistent one-directional fluid flow.This work has been supported through grant ARTIC FP6-2004-NMP-TI4

Gas flow through a micro-orifice due to small pressure difference

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Rarefied gas flow through a micro-orifice connecting two reservoirs at small pressure differences is considered in the whole range of rarefaction by the linearized BGK kinetic model equation. The problem is computationally challenging due to the five dimensional nature of the distribution function and techniques such as parallelization and numerical schemes of low memory requirements have been applied. Results include the distributions of density, velocity, temperature, as well as flow rates. The independence of flow rate in terms of the wall surface accommodation properties is confirmed.The European Community under the contract of Association EURATOM/Hellenic Republic

Cylindrical couette flow in the transition regime by the method of moments

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The moment method is employed to study the characteristics of cylindrical Couette gas flow under rarefied conditions. Computed velocity profiles from the linearised R13 and R26 moment equations are compared with direct simulation Monte Carlo data. It is found that the moment method can extend the macroscopic equations into the early transition regime, but the surface curvature narrows the validity range of the macroscopic models. The slip velocity on the inner and outer cylinder is not equal due to curvature effects and the torque acting on the cylinder wall decreases as the rarefaction becomes stronger

Multiscale simulation strategies and mesoscale modelling of gas and liquid flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.This paper presents a review of multiscale simulation strategies for the modelling of micro- and nanoscale flows. These have been developed in the last two decades in an attempt to bridge the application gap between molecular and continuum simulation methods preventing the simulation of many micro- and nanofluidic devices. The paper is focused on hybrid molecular-continuum methods and reviews different coupling strategies, including geometrical decomposition in conjunction with state- and flux coupling, pointwise coupling, the heterogeneous multiscale method and the equation free approach. The different applications of these methods are briefly discussed

Gas separation through carbon nanotubes

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Layering phenomena of carbon dioxide and methane transported through carbon nanotubes are being examined through molecular dynamics. The layering formation is investigated for carbon nanotubes ranging from (6,6) to (20,20) subjected to pressures spanning between 5-20 bar at 300 K. Well defined layers are developed both in the internal and external surface of the nanotubes for all the examined cases. It is also shown that the number of layers along with their absolute strength varies as a function of the nanotube's diameter, carbon dioxide and methane's density and gas-structure interactions. Finally, the diffusion inside the interior of the nanotubes has been examined showing a Fickian diffusion mode

Absolute and convective instabilities in non-local active-dissipative equations arising in the modelling of thin liquid films

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Absolute and convective instabilities in a non-local model that arises in the analysis of thin-film flows over flat or corrugated walls in the presence of an applied electric field are discussed. Electrified liquid films arise, for example, in coating processes where liquid films are deposited onto a target surfaces with a view to producing an evenly coating layer. In practice, the target surface, or substrate, may be irregular in shape and feature corrugations or indentations. This may lead to non-uniformities in the thickness of the coating layer. Attempts to mitigate film-surface irregularities can be made using, for example, electric fields. We analyse the stability of such thin-film flows and show that if the amplitude of the wall corrugations and/or the strength of the applied electric field is increased the convectively unstable flow undergoes a transition to an absolutely unstable flow

Influence of metallic porous microlayer on pressure drop and heat transfer of stainless steel plate heat exchanger

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The experimental analysis of passive heat transfer intensification in the case of plate heat exchanger has been carried out. On the heat transfer surface of heat exchanger the metallic porous layer was created. The experiment was accomplished in two stages. In the first stage the commercial stainless steel gasketed plate heat exchanger was investigated, while in the second one – the identical heat exchanger but with the modified heat transfer surface. The direct comparison of thermal and flow characteristics between both devices was possible due to the assurance of equivalent conditions during the experiment. Equivalent conditions mean the same volumetric flow rates and the same media temperatures at the inlet of heat exchangers in the corresponding measurement series. Experimental data were collected for the single-phase convective heat transfer in the water-ethanol configuration. The heat transfer coefficients were determined using the Wilson method