560 research outputs found
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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
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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 PΒ΄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
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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 groupβs 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
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Cilia-mediated signalling in the embryonic nodes: A computational fluid-structure-protein interaction (FSPI) model
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 breaking of left-right symmetry in the mammalian embryo is believed to occur in a transient embryonic structure, the node, when cilia create a leftward flow of liquid. It has been widely confirmed that this nodal flow is the first sign of left-right differentiation; however, the mechanism through which embryonic cilia produce their movement and how the leftward flow confers laterality are still requiring investigation. The ciliary motility in the embryonic node involves complex dynein activations and the handed information is transmitted to the cells by the flow produced by cilia, either mechanically and/or by advection of a chemical species. In this paper, we present a computational model of ciliary ultrastructure (protein-structure model) and discuss the scenarios that incorporate this internal microtubule-dynein system with the external fluidic environment (fluid-structure-protein interaction model, FSPI). By employing
computational fluid dynamics, deformable mesh computational techniques and fluid-structure interaction analysis, and solving the three-dimensional unsteady transport equations, the protein-triggered mechanism of
nodal ciliary motility has been studied, which is a primary component for the FSPI model. Future work regarding the integrative model is discussed, that will provide more accurate quantitative information on the
flow rate, ciliary motion, and molecule/ particle transport in the embryonic node and support the plausibility of hypotheses regarding left-right information transmission
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Comparison of heat transfer characteristics in surface cooling with boiling microjets of water, ethanol and HFE7100
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 basis of microjet technology is to produce laminar jets which when impinging the surface have a very high kinetic energy at the stagnation point. Boundary layer is not formed in those conditions, while the area of film cooling has a very high turbulence resulting from a very high heat transfer coefficient. Applied technology of jet production can result with the size of jets ranging from 20 to 500ΞΌm in breadth and 20 to 100ΞΌm in width. Presented data are used in order to validate authors own semi-empirical model of surface cooling by evaporating microjet impingement in the stagnation point. Main objective of this paper was to investigate the physical phenomena occurring on solid surfaces upon impingement of the single microjet in case of three fluids. Intense heat transfer in the impact zone of microjet has been examined and described with precise measurements of thermal and flow conditions of microjets. Reported tests were conducted under steady state conditions for surface cooling by single microjet producing an evaporating film. Obtained database of experimental data with analytical solutions and numerical computer simulation allows the rational design and calculation of microjet modules and optimum performance of these modules for various industrial applications
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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
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Design of gas micro distribution systems consisting of long tubes
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.A novel algorithm is developed for the design of gaseous micro distribution systems consisting of long tubes based on linear kinetic theory. Provided that the geometry of the pipe network is fixed the algorithm is capable of estimating the mass flow rates through the pipes as well as the pressure heads at the nodes of the network. The pressure distribution along each pipe element may also be provided. The analysis is valid and the results are accurate in the whole range of the Knudsen number, while the involved computational effort is very small. This is achieved by successfully integrating the well known kinetic results for single tubes into a typical solver for designing gas pipe networks.The European Communities under the contract of Association EURATOM / Hellenic Republic
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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
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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
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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
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