916 research outputs found
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Significance of the microfluidic concepts for the improvement of macroscopic models of transport phenomena
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.Complexity of transport phenomena - ranging from macroscopic motion of matter, heat transfer, over to the molecular motions determining the overall flow properties of fluids, or generally aggregation states of matter – inhibited development of a single mathematical model describing simultaneously
transport processes at all relevant scales. In classical engineering sciences at each scale level we have different equations, different fundamental variables and different methods of solution [4]. The established basis of the classical fluid dynamics - the Navier-Stokes equations [1, 3] - have apparently nothing in common with molecular physics. At the macroscopic scale of motion the molecular structure of matter
and the microscopic molecular motions are ignored (even though they determine the local macroscopic behaviour) [1, 3, 4]. To describe multiphase flows, still other methods must be used – increasing further the
number of equations, methods of solution etc. The serious disadvantage of this approach is, that equations describing macroscopic models (Navier-Stokes and there from derived equations), introduce multiple
theoretical problems: - higher order continuity requirements [3]; - numerous paradoxes in simple macroscopic flows (Bernoulli eq.); - different equations with different fundamental variables and different methods of solution, build a set of
disciplines devoted in principle to a single problem – dynamics of disperse systems
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Microfluidic droplet control by photothermal interfacial flow
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.Droplet-based microfluidics is an emerging field that can perform a variety of discrete operation of
tiny amount of reagent or individual cell. Noncontact manipulation of droplets in a microfluidic platform can
be achieved by using the Marangoni convection due to a local temperature gradient given by the irradiation
of heating light. This method provides noncontact, selective and flexible manipulation for droplets flowing in
microfluidic network. Although the potential of this selective operation method of droplets was confirmed,
the driving force exerted on droplets has not been quantitatively obtained. In this study, we have developed a
measurement system of the temperature field around droplets during the manipulation by light irradiation
and evaluated the manipulation force. In O/W emulsion system with oleic acid and buffer solution, oleic acid
for droplet and buffer solution for continuous phase, the temperature distribution around the droplets was
measured by laser-induced fluorescence. From the balance of drag force and photo-induced Marangoni force,
the driving force was determined. From the results, we confirmed the applicability of the noncontact droplet
manipulation using the photothermal Marangoni effect
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Microfluidic multiscale model of transport phenomena for engineering and interdisciplinary education applied to elements of a stirling engine
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 model based on elementary mathematical tools and basic corpuscular physics is applied to flow configurations simulating the Stirling engine. Universality and mathematical simplicity of the model is main objective of its development. This to facilitate its application not only in micro and standard macro, single- and multiphase flows in engineering but in biology, medicine and interdisciplinary sciences as well. As dynamics of disperse systems it promotes the common physical background of multiple, apparently unrelated phenomena. Main feature of the method - compared with standard methods - is departure from differential notation where possible to ensure suitability for analysis of discontinuous systems. Physical quantities are determined directly at required scale by choice of reference volumes/surfaces and use of the mean value theorem (MVT) of integral calculus where required. Thus the method is applicable to discrete particles and avoids higher order requirements of Navier-Stokes solutions. Besides saving one integration step it generally facilitates the analysis considerably. Newton’s second law is used explicitly as single equation of motion. Together with conservation laws it is applied to non-relativistic motion of particle systems in range from individual particles, atoms, molecules or even electrons, over to macroscopic particle sets in solid or flowing systems of traditional mechanics, up to celestial bodies of classical astro-physics. The basically microfluidic model was used to derive all definitions and equations of standard continuum fluid mechanics and multiphase flows. Compared with standard methods the here used model has the singular ability to describe consistently all phenomena related to one of most inspiring technical devices: to Stirling engine
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Continuous and Simultaneous Measurement of Micro Multiphase Flow Using confocal Micro-Particle Image Velocimetry (Micro-PIV)
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 objective of the paper is to present a “Multicolor Confocal Micro Particle Image Velocimetry
(Micro-PIV)” technique to visualize and measure dynamic behavior of each phase of micro multiphase flow
separately and simultaneously. The technique is applied to two types of micro two-phase flow. The first case
is to investigate a mechanism of micro droplet formation at a micro T-shaped junction. The measurement
data are compared to the numerical simulation using the CIP method. The second case is to investigate the
tank-tread motion of red blood cell induced by the surrounding plasma flow
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Numerical meshing issues for three-dimensional flow simulation in journal bearings
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.Hydrodynamic journal bearings are widely used in technical and industrial applications due to their favourable wearing quality and operating characteristics. In the recent years, various experimental and numerical analyses were carried out on the design layout, the load capacity and the durability of the bearing. For typical applications the two-dimensional Reynolds differential equation is solved numerically to calculate the pressure distribution in the oil film, which is essential to simulate the dynamic behavior of the bearing. This approach however, does not allow any detailed predictions of the local three-dimensional flow structures. To understand the mechanisms, which are driven by local flow phenomena, it is necessary to solve the full Navier-Stokes-Equations in 3D together with the conservation of mass. An accurate computation of a three-dimensional flow field requires a careful discretisation of the model. Moreover, only a deliberately chosen meshing based on the optimum number of cells across the gap achieves a sufficient numerical accuracy with acceptable computational effort. This work presents variations of the mesh generation of small gaps in journal bearing models and the computed flow fields, respectively. The threedimensional calculations are validated with measured experimental data done by Laser-Doppler-Velocimetry (LDV). In conclusion of this process the comparison of the velocity profiles of the flow field across the gap yield the necessary numerical discretisation limit applicable to the computation of the flow in journal bearings
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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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Numerical characterization of silicon DC electro-osmotic pumps: the role of the micro channel geometry
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 numerical analysis of silicon DC open channel EOPs is presented to show which parameters should be taken into account in the design of these devices. Particular attention is paid to the influence of the channel cross-section geometry on pump behavior, especially in relation to the electrical properties of the fluid. Rectangular and trapezoidal, micro and nano channels chemically etched on silicon wafers are considered and a broad range of operative conditions are analyzed. In order to make all the results available, two user-friendly correlations that predict the characteristic curves of the pumps are given as functions of the relevant parameters. The EOP model used to obtain the results is explained extensively, as well as the method used to solve it. A brief discussion on the domain in which it applies is also presented
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Microchannel fluid flow and heat transfer by lattice boltzmann method
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.Micro flow has become a popular field of interest due to the advent of micro electromechanical systems (MEMS). In this work, the lattice Boltzmann method, a particle-based approach, is applied to simulate the two-dimensional micro channel fluid flow.
We simulated fluid flow and heat transfer inside microchannel, the prototype application of this study is micro-heat exchangers. The main incentive to look at fluidic behaviour at micron scale is that micro devices tend to behave much differently from the objects we are used to handling in daily life. The choice of using LBM for micro flow simulation is a good one owing to the fact that it is based on the Boltzmann equation which is valid for the whole range of the Knudsen number. Slip velocity and temperature jump boundary conditions are used for the microchannel simulations with Knudsen number values covering the slip flow. The lattice Bhatnagar-Gross-Krook single relaxation time approximation was used. The results found are compared with the Navier-Stokes analytical and numerical results available in the literature and good matches are observed
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Poiseuille and Nusselt numbers for laminar flow in microchannels with rounded corners
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 work investigates the frictional and heat transfer behaviour of laminar, fully-developed flow in microchannels with trapezoidal and rectangular cross-section and rounded corners under H1 boundary
conditions. The equations of momentum and energy are solved numerically, and the results validated with analytical data, when available. The runs have been carried out for different aspect ratios and nondimensional radii of curvature Rc, with either all sides or three sides heated, one short side adiabatic for rectangular geometries and three sides heated, the longest one adiabatic for trapezoidal geometries. The Poiseuille and Nusselt numbers are reported and show, for the rectangular cross-section heated on all sides, a maximum increase for the highest value of the aspect ratio (β=1) with increments in the Poiseuille and Nusselt numbers of about 11% and 16% respectively for values of Rc * of 0.5, increasing as the geometry approaches the circular duct (12.5% and 21%). The increase is less pronounced as β decreases and also when only three sides are heated (maximum increase of Nu around 10%); in the case of the trapezoidal geometry
the effects of rounding the corners are almost negligible (a maximum increase in Nu of around 2%)
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Three dimensional flow structures in journal bearings
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.In general, the fluid flow in journal bearings can be described by the Navier-Stokes Equations and the conservation of mass. The application of the small gap criterion allows a simplification of these equations yielding the Reynolds Equation, which links the local gap size with the pressure gradient resulting in a powerful tool for the designing process of journal bearings. Typically, the Reynolds Equation is used in EHD-design software based on FE-methods, which is used to compute pressure distributions, forces, deformations and many more parameters needed for the selection of the right bearing geometry. However, there are regions in the journal bearing where the Reynolds Equation must fail, because either the small gap criterion or the Couette flow assumption is violated. There are pockets, grooves and holes, which are necessary to distribute the oil supply across the gap. Moreover, the oil feed represents a cross flow perpendicular to the circumferential main flow. In these regions three dimensional flow structures replace the
undisturbed Couette flow, which are strongly affected by vortices, but are non-turbulent due to the Re-scale. This work presents experimental data obtained from a cylinder apparatus with moderate gap sizes, which
features independently rotating cylinders and a cross flow through a hole in the sidewall. LDV-measurements of velocity profiles and visualization methods to animate the three dimensional nature of the
flow are presented. The experimental data are used to validate 3D-CFD calculations, which are expanded towards smaller gap sizes in the range of typical journal bearings in automotive applications
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