113 research outputs found
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Microstructure devices for process intensification: Influence of manufacturing tolerances and measurement uncertainties
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.Process intensification by miniaturization is a common task for several fields of technology. Starting from manufacturing of electronic devices, miniaturization with the accompanying opportunities and problems gained also interest in chemistry and chemical process engineering. While the integration of enhanced functions, e.g. integrated sensors and actuators, is still under consideration, miniaturization itself has been realized in all material classes, namely metals, ceramics and polymers. First devices have been manufactured by scaling down macro-scale devices. However, manufacturing tolerances, material properties and design show much larger influence to the process than in macro scale. Many of the devices generated alike the macro ones work properly, but possibly could be optimized to a certain extend by adjusting the design and manufacturing tolerances to the special demands of miniaturization. Thus, some considerations on the design and production of devices for micro process engineering should be made to provide devices which show reproducible and controllable process behavior. This following publication gives some examples
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Multiscale modeling of physical and biological systems
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
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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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Regulation of endothelial cell activity and vascular inflammation by shear stress
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.Atherosclerosis, a chronic inflammatory disease of arteries, develops predominantly at branches, bends, and bifurcations in the arterial tree that are exposed to low or disturbed blood flow. The endothelium is in direct contact with flowing blood and hence is exposed to shear stress, a mechanical force that varies with time, magnitude, and direction, according to vascular pulsatility and anatomy. Bends and bifurcations of
arteries that are susceptible to lesion formation are exposed to low/oscillatory shear stress, a mechanical environment that influences vascular physiology by enhancing inflammatory activation and promoting
endothelial cell (EC) apoptosis. In contrast, relatively straight, unbranched regions of the arterial tree that are
exposed to high shear stress are protected from inflammation, EC death and lesion development. Thus low shear stress may predispose arteries for lesion formation whereas high shear stress may prevent
atherosclerosis by enhancing endothelial protection. In this paper, I will summarize some of the molecular mechanisms behind the spatial localization of vascular inflammation and atherosclerosis, emphasizing
studies by my research group of two key proinflammatory signaling pathways, the mitogen-activated protein kinase (MAPK) pathway and the nuclear factor-kappa-B (NF-κB) pathway.This study is funded by the British Heart Foundation
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Reliability of large-eddy simulation
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
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A second-order slip model for arbitrary accomodation at the wall
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.We present a kinetic-theory derivation of second-order slip boundary conditions for a
plane isothermal pressure driven gas owing through a microchannel. In the proposed approach, the distribution function is expanded in terms of orthogonal polynomials and the system of moment equations in the expansion coefficients is analytically solved. The velocity slip coefficients, as well as their Knudsen layer corrections, are obtained by evaluating the solution in the near continuum limit. In comparison with other methods, the present approach is accurate and easy to implement. The results are presented for the Bhatnagar-Gross-Krook-Welander (BGKW) kinetic model equation and Maxwell's boundary conditions, but can be extended to more general collision integral and different scattering kernels.Fondazione Cariplo within the framework of the project Surface interactions in micro/nano device
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Coherent microscopy and optical coherence tomography for biomedical applications
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.In recent years many new methods of 3D optical imaging have been introduced that are applicable to the study of micro- and nano-scale flows. Coherent microscopy and optical coherence tomography join more established methods such as coherence scanning interferometry and confocal microscopy. These methods are very closely related and, using linear systems theory, can be compared in terms of their point spread and transfer functions. This paper introduces linear theory, demonstrates the main differences between the methods and discusses their use in micro- and nano-scale flow measurement. It is shown that coherent microscopy is currently the only method capable of single shot recording and consequently simultaneous whole-field flow measurement. Its use is limited to sparsely seeded flows however, such that individual particles can be identified. The other techniques provide increased 3D discrimination. Using a large numerical aperture, confocal microscopy and coherence scanning interferometry provide the most detailed 3D images making use the additional information available when the object is illuminated with plane waves propagating at different angles. In contrast optical coherence tomography uses the information that is available when the object is illuminated with different wavelengths. It is shown that the fundamental difference between these approaches is that the lateral and axial resolutions are decoupled in OCT making the technique easily scalable. This and the development of modern tunable laser sources, make OCT the method of choice for many biomedical applications
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The hybrid grid implemented DSMC method used in 2D triangular micro cavity flows
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.In this study a new hybrid grid is implemented in a 2D DSMC solver to be used in 2D triangular micro cavity flows. Currently DSMC is the prominent method to analyze micro scale gas flows which are rarefied. Because of the computational cost, DSMC solvers are generally used in rarefied gas conditions in which continuum based solvers are useless. If the efficiency of DSMC solvers is improved, the application range of these solvers can be increased further where the continuum based solvers dominate. Indexing the particles according to their cells is one of the main steps in the DSMC method. Either the particles are traced cell-by-cell along their trajectories or coordinate transformation techniques are used in this step. The first option requires complex trigonometric operations and search algorithms which are computationally expensive. But it can be used in both structured and unstructured grids. Although the second option is computationally more efficient, it demands specially tailored structured grids which are more geometry dependent compared to the unstructured grids. Here it is shown that a novel hybrid grid structure can be used successfully in 2D DSMC solver to analyze triangular shaped lid-driven micro cavity flows. Hybrid grids used in this study are much less dependent of the geometry like unstructured grids. Additionally, hybrid grids like structured grids facilitate coordinate transformation techniques in order to increase the efficiency of the particle indexing step in the DSMC method
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Thrust effectiveness of micronozzle
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.Thrust of the divergent part of axially symmetric micronozzle is under the study. It’s input to total thrust is considered by means of analysis of relative thrust determined as divergent part’s thrust related to nozzle’s thrust without divergent part when gas issuing into vacuum. An inviscid one-dimensional flow is used as start condition of analysis. For this case, it is shown from conservation laws that divergent part of infinite length has finite relative thrust depending only on sort of issuing gas. Analysis of the influence of shear stress on thrust of divergent part with the use of theory of laminar boundary layer shows that optimal nozzle wall angle at the exit increases and optimal length decreases with decreasing of nozzle’s dimension in comparison with initial inviscid case. This conclusion is approved by results of numerical simulation of flow inside nozzles with throat diameter 10 micrometers and various form of divergent part based on Navier – Stokes equations with both no-slip and slip wall conditions. Detailed analysis of flow shows advantage of micronozzles with wall form far from traditionally used in “large” thrusters.This study is partially supported by the Russian Foundation for Basic Research (Project 11-08-00422-а)
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Uncertainty quantification (UQ)
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.Uncertainty Quantification (UQ) is an emerging field in computational engineering that can provide certificates of fidelity in a simulation beyond the standard numerical error, and it includes uncertainty in boundary conditions, constitutive laws, materials properties and geometries. UQ is particularly impornat at microscales where geometric roughness and material properties cannot be readily quantified experimentally.
Here we present a general framework for UQ based on the generalized polynomial chaos approach and various extensions that do not require modification of existing codes and are particularly effective in Microsystems with many uncertain parameters (e.g. high dimensionality)
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