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Rationale, aims, and objectives: The true effect of laminar airflow (LAF) systems on postoperative infection is disputed, partly due to uncertainty regarding the validity of ventilation data in register studies. The aim of this study was to validate the information on operating room (OR) ventilation reported by the orthopaedic surgeons to the Norwegian Arthroplasty Register (NAR) after primary total hip arthroplasty (THA). Method: Forty of the 62 public orthopaedic units performing primary THA in Norway during the period 1987‐2015 were included. The hospitals' current and previous ventilation systems were evaluated in cooperation with the hospitals head engineer. We identified the type of ventilation system reported to the NAR and compared the information with the factual ventilation in the specific ORs at the time of primary THA. Results: A total of 108 067 primary THAs were eligible for assessment. None of the hospitals performed THA in true “greenhouse” (GH) ventilation. Fifty‐seven percent of the primary THAs were performed in ORs with LAF and 43% in ORs with conventional, turbulent ventilation (CV). Comparing the reported data with the validated data, LAF was reported with a sensitivity of 86%, specificity of 89%, and positive predictive value (PPV) of 92%, with an accuracy of 88%. CV was reported with a sensitivity of 89%, specificity of 87%, and PPV of 84%, with an accuracy of 88%. The total, mean misreporting rate was 12%. Conclusions: Surgeons were not fully aware of what kind of ventilation system they operated in. This study indicates that conclusions based on ventilation data reported on THA in the NAR should not be interpreted without considering the inaccuracy of the data. publishedVersion

Interest in understanding gas-to-particle phase transformation in several disciplines such as at-mospheric sciences, material synthesis, and combustion has led to the development of several distinct instruments that can measure the particle size distributions down to the sizes of large molecules and molecular clusters, at which the initial particle formation and growth takes place. These instruments, which include the condensation particle counter battery, a variety of electrical mobility spectrometers and the particle size magnifier, have been usually characterized in lab-oratory experiments using carefully prepared calibration aerosols. They are then applied, alone or in combination, to study the gas-to-particle transition in experiments that produce particles with a wide range of compositions and other properties. Only a few instrument intercomparisons in either laboratory or field conditions have been reported, raising the question: how accurately can the sub-10 nm particle number size distributions be measured with the currently available instrumentation? Here, we review previous studies in which sub-10 nm particle size distributions have been measured with at least two independent instruments. We present recent data from three sites that deploy the current state-of-the-art instrumentation: Hyytiala, Beijing, and the CLOUD chamber. After discussing the status of the sub-10 nm size distribution measurements, we present a comprehensive uncertainty analysis for these methods that suggests that our present understanding on the sources of uncertainties quite well captures the observed deviations be-tween different instruments in the size distribution measurements. Finally, based on present understanding of the characteristics of a number of systems in which gas-to-particle conversion takes place, and of the instrumental limitations, we suggest guidelines for selecting suitable in-struments for various applications.

We describe in this work a numerical simulation of chaotic heat transfer by laminar flow in a twisted pipe that consists of three bends. Observations on the secondary flow topology changed by the variation of Reynolds number and tube wall temperature as well as their coincidence with heat transfer enhancement are discussed. Both steady and pulsating flows with constant wall temperature are considered. Numerical simulations are performed for Reynolds numbers range 300 1) provide a more complex secondary flow and hence a better heat transfer. Pulsation energy consumption is higher than the energy needed for increasing Reynolds number of the steady flow to match the same heat transfer enhancement. However, a better heating uniformity is obtained in the pulsating flow, which is not the case in the steady flow.

Printed Circuit Heat Exchanger (PCHE) is a widely chosen plate type compact heat exchanger for high pressure applications. The present work mainly focuses on two high pressure applications; firstly, Helium Cooling System (HCS) of Test Blanket Module (TBM) in International Thermonuclear Experimental Reactor (ITER) and secondly, Intermediate Heat exchangers (IHX) in Very High Temperature Reactors (VHTR). In this work, a reduced numerical model for a single banked PCHE core working in He-He counter flow circuit has been numerically modelled and verified against the results available in the literature. The same model is then extended for studying the effect of three wavy channel configurations viz. triangular, sinusoidal and trapezoidal in a single banked PCHE core made of Alloy-617. The nature of local flow and heat transfer in the periodic channels has been studied by visualizing the vortex core using iso-normalized helicity surfaces. Thereafter, the thermo-hydraulic performances of these models are compared with straight channel PCHEs. Among the various models studied, the trapezoidal PCHE model is found to offer highest heat transfer with the largest pressure drop compared to sinusoidal, triangular and straight channel based PCHE models. A maximum of 41% increase in the heat transfer rate is predicted for the trapezoidal wavy channel compared to the straight channel PCHEs, for the tested operating conditions. For the sinusoidal and triangular wavy-channel PCHE configurations, the corresponding heat transfer advantages are predicted to be 33% and 28% respectively. The optimal thermo-hydraulic performance is also assessed, considering the thermal performance factor (TPF) obtained for all the three channels. The highest values of TPF are predicted for trapezoidal wavy channels (3.5) which is followed by sinusoidal (2.5) and triangular (1.5) wavy channels. (C) 2017 Elsevier Ltd. All rights reserved.

In this study, delta winglet-type vortex generators, widely used in conventional macro channels and proven to be effective, are used in microchannels to increase their heat transfer capacities. The effects of vortex generators on heat transfer and pressure loss characteristics are studied numerically for different angles of attack, vortex generator arrangement type, the transverse and longitudinal distance between vortex generators, vortex generator length and height, and different Reynolds numbers. The thermal and hydraulic characteristics are presented as the Nusselt number, the friction factor, and the performance evaluation criteria number (PEC) that takes into account the heat transfer enhancement and the corresponding increase in pressure loss. The variation of Nu/Nu0, f/f0, and PEC are found to be in the range of 1.03–1.87, 1.04–1.8, and 0.92–1.62, respectively. A multi-objective optimization study are performed with the response surface methodology analysis to see how different parameters affect heat transfer and pressure loss and to determine the most optimum design. Besides, local sensitivity analysis study is carried out through the RSM, and water inlet velocity for heat transfer enhancement is found to be the most effective parameter. Among the geometric parameters, vortex generator height is determined as the most effective factor. Finally, practical Nusselt number and friction factor correlations taking many parameters into account are proposed to be able to compare the results of other researchers, and for engineers designing microchannel cooling systems.

Tetraheptylammonium bromide (THABr), tetrabutylammonium bromide (TBABr) and tetraethylammonium bromide (TEABr) dissolved in methanol or water methanol mixtures (similar to 1 mM) produce via positive electrospray atomization and high resolution classification electrical classification standard clean ions (monomer and dier) which are singly charged. THABr is hydrophobic and insoluble in water, TBABr and TEABr are hygroscopic and water soluble (0.6 and 2.8 kg/L respectively). These ions are used to study the effect of hygroscopicity on the activation of aerosol particles in the sub 2 nm range via the detection efficiency measurement of a boosted ultrafine TSI condensation particle counter (3025A). Water solubility of particles seems to play a role in the activation and growth with butanol vapor in the CPC (condensation particle counter) independently of the size.

This paper is concerned with the rather broad issue of the impact of abrupt changes (such as isolated roughness, gaps and local suctions) on boundary-layer transition. To fix the idea, we consider the influence of a two-dimensional localized hump (or indentation) on an oncoming Tollmien–Schlichting (T–S) wave. We show that when the length scale of the former is comparable with the characteristic wavelength of the latter, the key physical mechanism to affect transition is through scattering of T–S waves by the roughness-induced mean-flow distortion. An appropriate mathematical theory, consisting of the boundary-value problem governing the local scattering, is formulated based on triple deck formalism. The transmission coefficient, defined as the ratio of the amplitude of the T–S wave downstream of the roughness to that upstream, serves to characterize the impact on transition. The transmission coefficient appears as the eigenvalue of the discretized boundary-value problem. The latter is solved numerically, and the dependence of the eigenvalue on the height and width of the roughness and the frequency of the T–S wave is investigated. For a roughness element without causing separation, the transmission coefficient is found to be approximately 1.5 for typical frequencies, indicating a moderate but appreciable destabilizing effect. For a roughness causing incipient separation, the transmission coefficient can be as large as $O(10)$, suggesting that immediate transition may take place at the roughness site. A roughness element with a fixed height produces the strongest impact when its width is comparable with the T–S wavelength, in which case the traditional linear stability theory is invalid. The latter however holds approximately when the roughness width is sufficiently large. By studying the two hump case, a criterion when two roughness elements can be regarded as being isolated is suggested. The transmission coefficient can be converted to an equivalent $N$-factor increment, by making use of which the $\text{e}^{N}$-method can be extended to predict transition in the presence of multiple roughness elements.

The present investigation concerns the numerical solution of elliptic partial differential equations (PDEs) governing physical phenomena in heat transfer and fluid flow by the lattice Boltzmann method (LBM). A general form of dimensionless conservation equations and appropriate source terms to be included in the elliptic PDE are identified. Specific problems considered in this article include heat conduction in a composite domain characterised by a very high thermal conductivity ratio between components and the presence of a partially inclined interface between them. With respect to this problem, the influence of representing oblique interfaces by the simple staircase approximation is studied. On the other hand, hydrodynamically as well as thermally fully-developed laminar flow through rectangular duct and shrouded array of fins is also investigated, where the aspect ratio of the duct cross-section and the height of fins along with the ratio of thermal conductivities of the fin and the fluid are varied. Dimensionless quantities characterising considered problems are determined by LBM and compared with either analytical solutions (if available) or reference data obtained from the finite volume method (FVM). The two relaxation times (TRT) collision scheme with the specific eigenvalue combination fixed to a constant value within a typical range of validity is employed for solving the present problems. The appropriate implementation of boundary conditions and, if required, interface conditions is essential in order to maintain second order accuracy of LBM. It is observed that the accuracy of determination depends strongly on the employed specific eigenvalue combination and relatively weakly on the discrete velocity stencil. As a result, in most of the cases for a considered physical condition, an optimum (range of) specific eigenvalue combination(s) could be detected. Nevertheless, from the acquired results, the potential of LBM with the simple D2Q4 stencil for solving considered problems becomes evident. Therefore, the method proves to be promising for optimisation of duct cross-sections and fin shapes in channels with useful applications in the design of heat exchangers. (C) 2015 Elsevier Masson SAS. All rights reserved.

The objective of the present work is to study the influence of curvature and Reynolds number on local heat transfer coefficient in a helical coil with water as the working medium. The local wall temperature is measured not only in the axial direction (along the length of coil) but also in the circumferential direction using infrared thermal imaging technique. The test sections are made of thin walled stainless steel (SS 304) tubes having an inner diameter varying from 5.4 to 7.5 mm with a thickness of 0.2 and 0.25 mm. The coil diameter to the tube diameter ratio ranges from 13.1 to 67 and coil pitch is 50 mm. The experimental results of friction factor and overall averaged total Nusselt number are compared with the available correlations in the literature. Correlations are suggested for overall averaged and local circumferentially averaged Nusselt number for inner side, outer side and total surface (inner side and outer side) of a helical coil. (C) 2015 Elsevier Ltd. All rights reserved.

Condensation particle counter (CPC) technology has continued to evolve, with the introduction of several new instruments over the last several years. An important aspect in the characterization of these instruments is the measurement of their time response. Yet there is no standardly accepted approach for this measurement. Here we evaluate different classically used methods for determining CPC time response, and present the potential pitfalls associated with these approaches. Further, we introduce a new simple definition for the term response time, E, which is based on the first-order systems response, while providing a practical definition by corresponding to approximate to 95% change in concentration. We also present results for various commonly used CPCs, and for the Airmodus A11 nano Condensation Nucleus Counter (nCNC) system, the TSI 3777+3772 Nano Enhancer system, and Aerosol Dynamics Inc.'s (ADI) new versatile water condensation particle counter.Copyright (c) 2018 American Association for Aerosol Research

In this work, flow friction in microchannels decorated with micropillars was investigated experimentally, with an interest to understand the wetting transition through two simple means: Poiseuille number and scaling laws. Different wetting states were demarcated by qualitatively assessing the behaviour of Poiseuille number (Po = f.Re, where f is friction factor and Re is Reynolds number), which are further corroborated by confocal microscopy-based measurements and numerical simulations. The wetting transition ensued smoothly with an increase in Re, independent of the gas fraction (a ratio of area covered by the liquid-gas interface to the total projected area), for moderate gas fractions, whereas an early breakdown of the Cassie-Baxter state occurred irrespective of Re at high gas fractions. Additionally, the scaling laws were found to correlate well with the underlying state of the flow. Our observations revealed that the liquid-gas interface exhibits a partial slip, contrary to the common notion that it is shear free. It is inferred that an increase in effective flow area leads to a reduction in flow friction in textured microchannels. The present work underlines three important outcomes. The first is the identification of wetting states in flow conditions shown by tracking the Poiseuille number. The second is that the liquid-gas interface is deduced to behave like a partial slip boundary. The third is that a textured microchannel can be worse than an enlarged dimension microchannel.

A key step in order to realise photo-electrochemical (PEC) water splitting to produce hydrogen sustainably, is reactor design. Good engineering will minimise energy losses (both optical and ohmic) due to reactor construction, whilst ensuring the H₂ and O₂ produced are separated, and this can subsequently relax the requirements on the photo-absorber material and/or electro-catalysts. In this paper we show that separation of the products through hydrodynamic flow alone would negate the need for the conventionally used membrane, which has an associated ohmic drop and cost. This is demonstrated to be possible using a ‘laminar flow between two parallel plates’ reactor design and AR/Pe and AR are found to be the two key dimensionless numbers that predict product cross-over (where AR, Pe are aspect ratio and Péclet number respectively). Supersaturation was used as an indicator of bubble formation, which disrupts the laminar flow required for separation and it is shown that by increasing the reactor pressure, higher current densities can be tolerated before supersaturation occurs. Removal of the dissolved hydrogen and oxygen from electrolyte is discussed. A multi-physics model, which employs an optical transfer matrix method, is used to validate the previous conclusions. Experimental data for hematite and Pt deposited on FTO was used as the anode and cathode respectively. Parasitic optical losses and efficiency improvement with stacking are shown for the example reactor configuration. Additionally, the concept of stacking this reactor design in order to absorb light in multiple passes is introduced. This approach relaxes a classical constraint on photo-absorber materials: large absorption length compared to small diffusion length of charge carriers in the semiconductor.

Dynamics and breakup of an axi-symmetric liquid jet injected upwards into another stationary or co-flowing immiscible liquid is investigated numerically. Simulations are done using an in-house code based on a novel DGLSM (dual grid level set method). Furthermore, a novel procedure – based upon physical interpretation of the various functions in Level Set Method – is demonstrated here as a powerful numerical tool to calculate certain parameters (diameter as well as frequency of drop formation and temporal variation of jet length at the axis), which characterize the unsteady interface-dynamics. Six different combination of the dispersed and continuous fluid are subjected to various injection velocity, resulting in a large variation in the non-dimensional governing parameters such as viscosity-ratio and Weber number. From the temporal variation of jet length and instantaneous interface, three drop formation regimes are proposed: Periodic Uniform Drop formation (P-UD), Quasi-Periodic Non-Uniform Drop formation (QP-NUD) and Chaotic Non-Uniform Drop formation (C-NUD); demarcated in a drop formation regime map for various Weber number and viscosity ratio. Their effect on the mean value of jet breakup length ( L d , m ), detached drop diameter ( D d , m ) and drop formation frequency ( St m ) is also studied. After a more detailed study on stationary continuous fluid, the effect of co-flowing continuous fluid is studied; and is found to stabilize the drop formation regime and increase the frequency of drop formation.

Tribology letters 65(3), 106 (2017). doi:10.1007/s11249-017-0888-7, Published by Springer International Publishing, Cham

In this study we characterized the performance of three new particle counters able to detect particles smaller than 3 nm during the Helsinki condensation particle counter (CPC) workshop in summer 2016: the Aerosol Dynamics Inc. (ADI; Berkeley, USA) versatile water condensation particle counter (vWCPC), TSI 3777 nano enhancer (TSI Inc., Shoreview, USA) and modified and boosted TSI 3010-type CPC from Université Blaise Pascal called a B3010. The performance of all CPCs was first measured with charged tungsten oxide test particles at temperature settings which resulted in supersaturation low enough to not detect any ions produced by a radioactive source. Due to similar measured detection efficiencies, additional comparison between the 3777 and vWCPC were conducted using electrically neutral tungsten oxide test particles and with positively charged tetradodecylammonium bromide. Furthermore, the detection efficiencies of the 3777 and vWCPC were measured with boosted temperature settings yielding supersaturation which was at the onset of homogeneous nucleation for the 3777 or confined within the range of liquid water for the ADI vWCPC. Finally, CPC-specific tests were conducted to probe the response of the 3777 to various inlet flow relative humidities, of the B3010 to various inlet flow rates and of the vWCPC to various particle concentrations. For the 3777 and vWCPC the measured 50 % detection diameters (d50s) were in the range of 1.3–2.4 nm for the tungsten oxide particles, depending on the particle charging state and CPC temperature settings, between 2.5 and 3.3 nm for the organic test aerosol, and in the range of 3.2–3.4 nm for tungsten oxide for the B3010.

The residence time distribution (RTD) of a whey protein (WP) suspension flowing through a heat treatment system was studied. The experimental system is the tubular heat exchanger and the helical holding section of a laboratory scale thermal process. RTD was measured in isothermal conditions at 60 degrees C, a temperature involving no WP aggregation, and at 87 degrees C, temperature at which WP aggregates. Two flow rates (20 L/h and 49 L/h) were tested with two different lengths of holding tube in order to maintain the same order of magnitude of the holding time. Methylene blue was used as tracer and spectrophotometer analysis were performed to determine the outlet concentration. These investigations yielded to great differences between the RTD in aggregation and no aggregation conditions. The minimum residence time is shorter when WP aggregation occurs due to the modification of the velocity field inside the tubular devices with the local enhancement of the viscosity. Fitting the experimental results with a new compartment model based on the generalized convection model give very good agreement contrary to the more classical RTD models. This RTD model could be used in combination with a population balance model in order to predict the WP aggregates size dispersion. (C) 2012 Elsevier Ltd. All rights reserved.

In the present work, an iterative numerical procedure to evaluate the fluid-solid interface condition in a conjugate heat transfer situation is proposed and implemented in a finite volume methodology using both structured and unstructured meshes. Two benchmark problems are solved, and the numerical solutions are found to be in good agreement with the analytical solutions. A parametric study is performed to analyze the physical behavior in the conjugate heat transfer problems, and correlations for the local Nusselt number are developed in one representative case. The conditions for which a conjugate analysis is required are determined.

We present an experimental and numerical study of three-dimensional pulsatile flow in a twisted pipe in order to show the effects of chaotic advection on mixing in this flow configuration. The numerical study is done by CFD code with a pulsatile velocity field imposed as an inlet condition. The experimental setup is composed principally of a "Scotch-yoke" pulsatile flow generator and a twisted duct. The twisted duct consists of six 90 degrees bends of circular cross-section; the plane of curvature of each bend is at 90 degrees to that of its neighbors. The secondary flow, generated by centrifugal force, the pulsating velocity field and also due to the change in curvature plane, leads to irregular fluid particle trajectories. Velocity measurements were made for a range of stationary Reynolds numbers (300

This work presents an experimental and numerical study of pulsated Dean flow, three-dimensional pulsatile flow in a curved pipe. The numerical study is performed by CFD code (Fluent 6) in which a pulsated velocity field is imposed as an inlet condition. The experimental setup involves principally a “Scotch-yoke” pulsatile generator and a 90° bend. Laser Doppler Velocimetry (LDV) measurements have shown that the Scotch-yoke generator produces pure sinusoidal instantaneous mean velocities with a mean deviation of 3%. Visualizations by laser-induced fluorescence (LIF) and velocity measurements, coupled with the numerical results, have permitted analysis of the evolution of the swirling secondary flow structures that develop along the bend during the pulsation phase. These measurements were made for a range of stationary Reynolds number ( 300 ⩽ Re st ⩽ 1200 ) , frequency parameter ( 1 ⩽ α = r 0 ( ω / ν ) 1 / 2 20 ) , and two velocity components ratios ( β = U max , osc / U st ) . We observe satisfactory agreement between the numerical and experimental results. For high β, the secondary flow structure is modified by a Lyne instability and a siphon effect during the deceleration phase. The intensity of the secondary flow decreases as the parameter α increases during the acceleration phase. During the deceleration phase, under the effect of reverse flow, the secondary flow intensity increases with the appearance of Lyne flow.

It has been well established that heat transfer in a helical coil is higher than that in a corresponding straight pipe However, the detailed characteristics of fluid flow and heat transfer inside helical coil is not available from the present literature This paper brings out clearly the variation of local Nusselt number along the length and circumference at the wall of a helical pipe. Movement of fluid particles in a helical pipe has been traced CFD simulations are carried out for vertically oriented helical coils by varying coil parameters such as (i) pitch circle diameter, (ii) tube pitch and (iii) pipe diameter and their influence on heat transfer has been studied. After establishing influence of these parameters, correlations for prediction of Nusselt number has been developed. A correlation to predict the local values of Nusselt number as a function of angular location of the point is also presented (C) 2009

Mixing by chaotic advection in a twisted-pipe flow is used here to investigate the efficiency of this flow in the liquid/liquid dispersion process. This study focuses on water/oil dispersions produced by continuous water injection into a main oil flow, for small Dean numbers. The drop sizes obtained with the chaoticadvection twisted-pipe flow are compared with those in a straight pipe and a helically coiled flow for the same conditions. It is found that the resulting dispersions are finer and more mono-dispersed in the chaotic advection flow. These results are compared with the theoretical maximum diameter d(max) determined by the Grace theory in which the viscous stress controls the breakup phenomena. For this purpose, the kinematic field is computed from the theoretical formulae for Dean flow. The strain rate fields in the pipe cross-section are then analytically computed and used to predict the maximum drop diameter. The theoretical values are identical for the three configurations (straight, helically coiled, and twisted pipe) up to a critical Dean number, where the secondary flow becomes significant. Beyond this value, the shear stress is enhanced in the twisted-pipe flow compared with the straight-pipe flow, and the predicted drop diameters are smaller. An interpretation of the higher dispersive performance of the chaotic flow is provided by the Lagrangian trajectories of the particles. (C) 2009 Elsevier Ltd. All rights reserved.

Dean instability for Newtonian fluids in laminar secondary flow in 180 degrees curved channels was studied experimentally and numerically. The numerical study used Fluent CFD code to solve the Navier-Stokes equations, focusing on flow development conditions and the parameters influencing Dean instability. An accurate criterion based on the radial gradient of the axial velocity was defined that allows detection of the instability threshold, and this criterion is used to optimize the grid geometry. The effects on Dean instability of the curvature ratio (from 5.5 to 20) and aspect ratio (from 0.5 to 12) are studied. In particular, we show that the critical value of the Dean number decreases with the increasing duct curvature ratio. The variation of the critical Dean number with duct aspect ratio is less regular. In the experimental study, flows were visualized in several tangential positions of a 180 degrees curved channel with aspect ratio 8 and curvature ratio 10. The flow is hydrodynamically developed at the entrance to the curved channel. The critical Dean number is detected and the development of secondary flow vortices by additional counter-rotating vortex pairs is observed. A diagram of different critical Dean numbers is established. (c) 2005 Elsevier SAS. All rights reserved.

Deposition of three marine bacterial strains with different cell surface hydrophobicities from artificial seawater to polyurethane coatings on glass with different surface tensions and elastic modulus was studied in situ in a parallel plate (PP) and stagnation point (SP) flow chamber. Different surface tensions of the coatings were established by changing the amount of fluorine, whereas using more or less branched polymers made different elastic moduli. Surface tensions of the coating, derived from measured contact angles with liquids, ranged from 11.9 to 44.9 mJ m(-2), while the elastic moduli, derived from force-distance curves as measured with an atomic force microscope were between 1.5 and 2.2 GPa. In both flow chambers, the most hydrophilic bacterium Halomonas pacifica adhered preferentially to the more hydrophilic, non-fluoridated coating, whereas the most hydrophobic bacterium Marinobacter hydrocarbonoclasticus showed a greater preference for the more hydrophobic coating. Bacterial adhesion in the PP flow chamber was not influenced by the elastic modulus of the coatings, but in the SP flow chamber bacteria adhered in higher numbers to hard surfaces than to coatings of lower elastic moduli. (C) 2003 Elsevier B.V. All rights reserved.

The choice of substrate material in a chip that combines ultrasound with microfluidics for handling biological and synthetic microparticles can have a profound effect on the performance of the device. This is due to the high surface-to-volume ratio that exists within such small structures and acquires particular relevance in polymer-based resonators with 3D standing waves. This paper presents three chips developed to perform particle flow-through separation by ultrasound based on a polymeric SU-8 layer containing channelization over three different substrates: Polymethyl methacrylate (PMMA); Pyrex; and a cracked PMMA composite-like structure. Through direct observations of polystyrene microbeads inside the channel, the three checked chips exhibit their potential as disposable continuous concentration devices with different spatial pressure patterns at frequencies of resonance close to 1 Mhz. Chips with Pyrex and cracked PMMA substrates show restrictions on the number of pressure nodes established in the channel associated with the inhibition of 3D modes in the solid structure. The glass-substrate chip presents some advantages associated with lower energy requirements to collect particles. According to the results, the use of polymer-based chips with rigid substrates can be advantageous for applications that require short treatment times (clinical tests handling human samples) and low-cost fabrication. © 2015 by the authors; licensee MDPI, Basel, Switzerland., The study has been performed in the framework of two Spanish National Research Project BIO2011-30535-C04-01,02,03, “Development of a high throughput for isolation of tumor cells circulating in peripheral blood”., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

This paper presents experimental and three-dimensional numerical study of early onset of separation with rarefied gas flow through a tube with single sharp 90 bend. Experiments are conducted for nitrogen gas flowing at low pressures in three conventional size tubes. The flow is dynamically similar to gas flow in a microchannel as the Knudsen number range (0.0003 < Kn < 0.0385) covers part of the continuum and the slip flow regime while maintaining the Reynolds number between 0.27 and 418.5. The static pressures along the inner, outer and top walls are measured for different mass flow rates and analyzed to understand the flow behavior. The static pressure measurement indicates adverse pressure gradient near the bend along the inner and outer walls of the tube at much lower value of Reynolds number as compared to conventional flow. The numerical solution of the Navier-Stokes equations with the Maxwell's slip boundary condition shows good agreement with experimental data and helps bring out the complex flow behavior near the bend. The adverse pressure gradient, velocity profile, flow streamlines and velocity vectors in the bend plane clearly indicates secondary flows near the bend at as low a Reynolds number as unity. The flow acceleration and the presence of secondary flows near the bend causes a larger pressure drop as compared with a straight tube. Empirical correlations for Poiseuille number and additional pressure drop coefficient are proposed as part of this work. It is noted that limited experimental data exists in the literature for such flows; these results should therefore help enhance the fundamental understanding of gas flow in microchannels with bend. (C) 2015 Elsevier Inc. All rights reserved.

Heat transfer and pressure drop characteristics of water based CuO nanofluid inside a horizontal tube were investigated experimentally. The upper limitation of the particle volume fraction with respect to heat transfer performance was also found. CuO-water nanofluids with volume fractions of 0.5%, 1%, 2%, and 4% were prepared by dispersing the CuO nanoparticles with an average diameter of 33 nm into deionised water. Experiments were carried out under the steady-state, constant heat flux, and turbulent flow regime conditions. The variations of the average Nusselt number and the friction factor with the Reynolds number were presented. For all given particle volume concentrations, heat transfer enhancements were calculated. It was concluded that the particle volume concentrations higher than 1% vol. were not appropriate with respect to the heat transfer performance of the CuO-water nanofluid. No heat transfer enhancement was observed at Re - 4.000. The highest heat transfer enhancement was achieved at Re = 16.000 and phi = 0.005. Turkish Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [105M292]; Ataturk University Research Project FoundationAtaturk University [BAP-2007/50] This study was supported by The Turkish Scientific and Technological Research Council of Turkey (TUBITAK Project no. 105M292) and Ataturk University Research Project Foundation (Project no. BAP-2007/50). The authors wish to thank TUBITAK and Ataturk University. WOS:000363628800001

In this work, experimental and three-dimensional numerical study is performed on single phase liquid flow in two scenarios: heated diverging and heated converging microchannel. Microchannel with 8 angle of divergence and 156 mu m of hydraulic diameter is employed for experiments in both diverging and converging modes. The objectives are to obtain the Nusselt number and to understand the conjugate effect in varying cross-section microchannels with the viewpoint of using such geometries in the design of heat sinks for electronics cooling. The experiments are performed for mass flux and heat flux range of 113-1200 kg/m(2)-s (Re = 30-274) and 0.3-9.5 W/cm(2), respectively, with de-ionized water as the working fluid. The surface and bulk mean temperatures are measured, and used to calculate the heat transfer coefficient. Numerical results show that the conjugate effect results in different nature of heat flux distribution in diverging vs. converging microchannel. This leads to a nearly constant heat flux condition and 35% higher heat transfer in converging microchannel compared with diverging microchannel. It is further observed that less pumping work is required in diverging and converging microchannels as compared with uniform cross-section microchannel. The thermo-hydraulic performance of diverging and converging microchannels is of significance in the development of compact heat sinks. (C) 2014 Elsevier Ltd. All rights reserved.

Magnetic resonance imaging (MRI) can be used in vivo in combination with computational fluid dynamics (CFD) to derive velocity profiles in space and time and accordingly, pressure drop and wall shear stress distribution in natural or artificial vessel segments. These hemodynamic data are difficult or impossible to acquire directly in vivo. Therefore, research has been performed combining MRI and CFD for flow simulations in flow phantoms, such as bends or anastomoses, and even in human vessels such as the aorta, the carotid, and the abdominal bifurcation. There is, however, no unanimity concerning the use of MRI velocity measurements as input for the inflow boundary condition of a CFD simulation. In this study, different input possibilities for the inflow boundary conditions are compared. MRI measurements of steady and pulsatile flow were performed on a U bend phantom, representing the aorta geometry. PAMFLOW (ESI Software, Krimpen aan den Ussel, The Netherlands), an industrial CFD software package, was used to solve the Navier-Stokes equations for incompressible flow. Three main parameters were found to influence the choice of an inflow boundary condition type. First, the flow rate through a vessel should be exact, since it proves to be a determining factor for the accuracy of the velocity profile. The other decisive parameters are the physiology of the flow profile and the required computer processing unit time. Our comparative study indicates that the best way to handle an inflow boundary condition is to use the velocities measured by MRI at the inflow plane as being fixed velocities. However, before using these MRI velocity data, they first should be corrected for the partial volume effect by filtering and second scaled in order to obtain the correct flow rate. This implies that a reliable flow rate measurement absolutely is needed for CFD calculations based on MRI velocity measurements.

Depositions of negatively charged polystyrene particles in a parallel plate flow chamber to negatively and positively charged collector surfaces are compared at different shear rates and ionic strengths. The observation of adhering particles was done in situ during the deposition process with the aid of an image analyzer and the adsorption and desorption of each particle was monitored individually using a special tracking algorithm. Initial deposition rates j(0)(EXP) were higher to positively charged glass than to negatively charged glass collector surfaces, depending on shear rates and ionic strength. All observed experimental deposition rates were, however, smaller than the Smoluchowski-Levich (SL) approximate solution of the convective-diffusion (CD)equation. Initial deposition rates were also calculated using an exact numerical solution of the CD equation; they were two times higher than the experimentally observed deposition rates for positively charged glass and about equal or lower for negatively charged glass. The desorption rates j(des)(t) Of polystyrene particles on positively charged glass were nearly zero under all conditions, whereas the desorption rates from the negatively charged glass were considerable and finally balanced the adsorption rates j(ads)(t). From the residence time dependent desorption probability beta(t - tau), it could be determined that polystyrene particles on negatively charged collector surfaces have the highest probability of desorption within the first 5-10 min after deposition. Experimental results were subsequently compared with those from a proposed adsorption-desorption model for deposition kinetics, using the parameters derived as an input, and with a Monte Carlo simulation of the deposition process. A high degree of similarity between experimental results, the adsorption-desorption model and the Monte Carlo simulation results was observed, which indicates; the consistency of the applied experimental methods and theoretical models.

The hydrophobic and electrostatic characteristics of bacterial cell surfaces were compared with attachment proclivity and biomass accumulation over time between wildtype Pseudomonas aeruginosa serotype O6 (possesses A and B band LPS), and three LPS-deficient mutants, vi;. A28 (A(+)B(-)), R5 (A(+)B(-)), and Gt700 (A(-)B(-)). The hydrophobic character of each serotype was determined by hydrophobic interaction chromatography and salt-aggregation, and strains were ranked similarly by each method, viz. R5 greater than or equal to A28 > Gt700 > O6. The anionic characteristics of cell-surfaces were determined by electrostatic interaction chromatography and by zeta-potential measurements, and ranked R5 > A28 greater than or equal to Gt700 > O6. Adhesion and biofilm accumulation on stainless steel were significantly different between strains, following the order R5 > A28 much greater than O6 > Gt700. Biofilm rankings were similar on glass, a second hydrophilic substratum. The mutant strains with a strongly hydrophobic character (R5 and A28) demonstrated a significantly greater capacity to form biofilms. These adherent mutants also appeared to have a more anionic cell surface, which may have played a role in biofilm formation on the hydrophilic substrata.

Analysis is presented for conjugate heat transfer in a parallel-plate microchannel. Axial conduction in the fluid and in the adjacent wall is included. The fluid is a constant property gas with a slip-flow velocity distribution. The microchannel is heated by a small region on the channel wall. The analytic solution is given in the form of integrals by the method of Green's functions. Quadrature is used to obtain numerical results for the temperature and heat transfer coefficient on the heated region for various Peclet number, Knudsen number, and wall materials. A region downstream of the heater is also explored. These results have application in the optimal design of small-scale heat transfer devices for biomedical applications, electronic cooling, and advanced fuel cells. © 2014 by the American Institute of Aeronautics and Astronautics, Inc.

The objective of this study is to characterize a new heating process in fluids, chaotic advection. The main mechanism generating this Row is the production of spatially chaotic trajectories in an alternating Dean flow. The present work examines the effects of chaotic advection on heat transfer at low Reynolds numbers. in order to assess the enhancement of heat transfer by chaotic advection, a helical heat exchanger and a chaotic heat exchanger (both of shell-and-tube type) of the same heat-transfer surface area and the same tube length were tested. The coils were assembled from 90 degrees bends, and the chaotic coil was produced merely by turning each bend at a +/-90 degrees angle with respect to the previous one. Experiments were performed for Reynolds numbers ranging from 60 to 200. Temperature profiles measured in the cross-section of the coils show that chaotic advection substantially homogenizes and enhances heating. Moreover, it is shown that the homogeneity of heating in chaotic flow is almost independent of the Reynolds number. Parallel to the temperature profiles measurements, axial velocity profiles were measured by laser Doppler velocimetry at the exit from the coils and used to characterize the flow in the isothermal regime and compare the temperature profiles to the velocity profiles. Global heat-transfer measurements show that the chaotic heat exchanger is more efficient than the helical one, with an efficiency enhancement between 13 and 27%. (C) 1997 Elsevier Science Ltd.

This study compares residence time distributions in a helically coiled tube and a spatially chaotic system. The chaotic system consists of an array of bends, the plane of curvature of each one makes a 90 degrees angle with that of its neighbors. Chaotic trajectories are obtained by the switch in the symmetry plane of the Dean vortices which appear in the bends. Mixing in the two configurations is compared by modeling the residence time distributions, experimentally determined by means of a two-measurement-point technique, using the axial dispersion plug-flow model. For Reynolds numbers greater than 2500, axial dispersion in the chaotic system is more than 20% less than in a helically coiled tube having the same number of bends. The decrease in axial dispersion is due to the generation of chaotic trajectories, which also contribute to an increase in transverse dispersion. Thus, the chaotic curved pipes system appears very promising in producing good mixing, especially in a laminar flow regime.

Isothermal and nonisothermal friction factors and mean Nusselt numbers for uniform wall temperature (UWT) heating and cooling of Servotherm oil (Pr = 195-375) were experimentally determined for their flow in a circular tube (Re-a = 70-4000) with twisted tape inserts (y = 2.41-4.84). Isothermal friction factors were found to be 3.13-9.71 times the plain tube values. The Nusselt numbers were found to be 2.28-5.35 and 1.21-3.70 limes the plain tube forced convection values based on constant flow rate and constant pumping power, respectively, for the minimum twist ratio tape. Correlations were developed for the prediction of isothermal friction factors and the Nusselt numbers. A correlation representing the effect of heat transfer on Friction Factors is also proposed. Copyright (C) 1996 .

In this paper, we measured the local initial deposition rates of streptococci to adhering actinomyces, acting as protruding local sinks on a glass collector, as a function of the actinomyces density in a parallel plate flow chamber. The local initial deposition rates, i.e., deposition in the vicinity of actinomyces, j(0,1) compared well with values predicted by a model based on convective diffusion perpendicular to the collector surface and convection parallel to the collector surface when the seeding density of adhering actinomyces was below 0.5 x 10(6) cm(-2) (0.03% surface coverage). However, at higher sink densities the model breaks down due to particle depletion of the suspension downstream of a protruding sink.

Effect of eccentricity-ratio and rotation on a Poiseuille flow across a stationary/rotating cylinder is studied numerically for various Reynolds number ( Re =50–150) at a blockage ratio of β = 20 % . Several interesting flow-patterns and flow-transition, for various eccentricity-ratio ( − 75 % ≤ γ ≤ + 75 % ) and rotational-velocity ( 0 ≤ α ≤ 2 ) at Re =100 are noted. The flow patterns are understood with the help of streamlines and vorticity contours. The ensuing flow is analyzed with the help of separation point on the surface of the cylinder, strength and trajectory of the shed-vortices and flow distribution above and below the cylinder. Flow-transition from unsteady to steady flow is reported as a flow-regime map, at various values of α and γ . Stabilization effect is more at positive as compared to negative eccentricity, for counter clockwise (CCW) rotating cylinder. It is established that the mechanism of flow-stabilization is different for positive and negative eccentricity, for rotating cylinder. For stationary cylinder, increase in eccentricity causes a reduction in the drag-coefficient and Strouhal-number; and a change in the direction of lift force at higher eccentricity ratio. Under the influence of rotation, a reduction (enhancement) in the drag-force is obtained at a constant positive (negative) eccentricity. Stabilization effect of rotation and eccentricity can be used for flow control.

The deposition efficiencies and reversibilities of bacterial adhesion (Staphylococcus epidermidis HBH2 169, Acinetobacter calcoaceticus RAG-1, and Streptococcus thermophilus B) on different substratum surfaces under flow were determined using real-time in situ image analysis. For each combination of strain and substratum, the Lifshitz-Van der Waals, electrostatic, and acid-base Gibbs energies of interaction were calculated from measured zeta potentials and contact angles on the basis of a DLVO approach sensu stricto and an extended DLVO approach. In order to compare the adhesion of microorganisms with that of inert spherical particles, monodisperse polystyrene latex particles were also included in this study. The depth of the secondary interaction minimum in the distance dependence of the total Gibbs energy of interaction fully governed the deposition efficiency and the desorption of both inert particles as well as of the microorganisms. Deposition efficiencies increased with increasing depth of the secondary interaction minimum, while desorption decreased with increasing depth. Initial desorption was always higher than final desorption, but nevertheless particle and bacterial adhesion remained reversible. The reversibility observed partly represented the real thermodynamic reversibility of the process. However, collisions between flowing and adhering particles and bacteria also contributed to the reversibility observed. The DLVO approach sensu stricto did not adequately explain the phenomena observed on hydrophobic fluoroethylenepropylene substrata, because in the sensu stricto approach long-range hydrophobic attraction due to acid-base interactions is not included. For hydrophobic interacting surfaces, including bacterial cell surfaces, long-range hydrophobic attraction has to be accounted for, yielding relatively high deposition efficiencies and low desorption rates. Summarizing, it can be concluded that initial bacterial adhesion can be explained in terms of overall physicochemical surface properties and that it is mediated by reversible, secondary minimum DLVO interactions. (C) 1995 Academic Press,Inc.

The deposition efficiencies and reversibilities of bacterial adhesion (Staphylococcus epidermidis HBH2 169, Acinetobacter calcoaceticus RAG-1, and Streptococcus thermophilus B) on different substratum surfaces under flow were determined using real-time in situ image analysis. For each combination of strain and substratum, the Lifshitz-Van der Waals, electrostatic, and acid-base Gibbs energies of interaction were calculated from measured zeta potentials and contact angles on the basis of a DLVO approach sensu stricto and an extended DLVO approach. In order to compare the adhesion of microorganisms with that of inert spherical particles, monodisperse polystyrene latex particles were also included in this study. The depth of the secondary interaction minimum in the distance dependence of the total Gibbs energy of interaction fully governed the deposition efficiency and the desorption of both inert particles as well as of the microorganisms. Deposition efficiencies increased with increasing depth of the secondary interaction minimum, while desorption decreased with increasing depth. Initial desorption was always higher than final desorption, but nevertheless particle and bacterial adhesion remained reversible. The reversibility observed partly represented the real thermodynamic reversibility of the process. However, collisions between flowing and adhering particles and bacteria also contributed to the reversibility observed. The DLVO approach sensu stricto did not adequately explain the phenomena observed on hydrophobic fluoroethylenepropylene substrata, because in the sensu stricto approach long-range hydrophobic attraction due to acid-base interactions is not included. For hydrophobic interacting surfaces, including bacterial cell surfaces, long-range hydrophobic attraction has to be accounted for, yielding relatively high deposition efficiencies and low desorption rates. Summarizing, it can be concluded that initial bacterial adhesion can be explained in terms of overall physicochemical surface properties and that it is mediated by reversible, secondary minimum DLVO interactions. (C) 1995 Academic Press,Inc.

Flow visualization experiments and numerical simulations were performed on a narrow three-dimensional backward-facing step (BFS) flow with the main objective of characterizing the secondary bubble appearing at the top wall. The BFS has been widely studied because of its geometrical simplicity as well as its ability to reproduce most of the flow features appearing in many applications in which separation occurs. A BFS test rig with an expansion ratio of 2 and two aspect ratios (AR = 4 and AR = 8) was developed. Tests were performed at range of Reynolds numbers ranging from 50 to 1000; visualization experiments provided a qualitative description of secondary bubble and wall-jet flows. Large eddy simulations were carried out with two different codes for validation. Numerical solutions, once validated with experimental data from the literature, were used to acquire a deeper understanding of the experimental visualizations, to characterize the secondary bubble as a function of the flow variables (Reynolds and AR) and to analyze the effect of the secondary bubble on primary reattachment length. Finally, to decouple the sidewall effects due to the non-slip condition and the intrinsic flow three-dimensionality, numerical experiments with free-slip conditions over the sidewalls were computed. The main differences were as follows: When the non-slip condition is used, the secondary bubble appears at a Reynolds number of approximately 200, increases with the Reynolds number, and is limited to a small part of the span. This recirculation zone interacts with the wall-jets and causes the maximum and minimum lengths in the reattachment line of the primary recirculation. Under free slip conditions, the recirculation bubble appears at a higher Reynolds number and covers the entire channel span. Published by AIP Publishing.

In this paper we measured the influence of interparticle interactions between flowing and adhering particles on initial deposition rates, blocked areas, and residence time dependent desorption during deposition of polystyrene latex particles to glass. The initial deposition rates increased linearly with particle concentrations in suspensions as expected from theoretical mass transport calculations. Deposition efficiencies of 0.78 and 0.62 were obtained for wall shear rates, G, of 15 and 50 s(-1), respectively. Blocked areas, A(1) expressed as the number of particle cross sections, gamma, decreased from initially high to low values (A(1,G=15) = 10 and A(1,G=50) = 18, at infinite particle concentration) as a function of the particle concentration. This decrease in blocked area with particle concentration was explained as a consequence of the increased backscattering of flowing particles colliding with adhering particles. Backscattering due to collisions between flowing particles is obviously more frequent at higher Concentrations. Blocked areas, calculated using pair distribution functions, corresponded well with those obtained from deposition kinetics. Initial desorption rate coefficients, beta(0) ranging from 0.3 x 10(-3) to 2.0 x 10(-3) s(-1), increased linearly with particle concentration in suspension due to an increase in the number of collisions between adhering and flowing particles per unit time. The final desorption rate coefficients, beta(infinity,) ranging from 0.002 x 10(-3) to 0.01 x 10(-3) s(-1), and the relaxation time, 1/delta, of the desorption rate coefficient, ranging from 50 to 1000 s, decreased as a function of the particle concentration because, as the effective interaction potential minimum is not the same for each adhering particle, weakly adhering particles will be removed first. The effective interaction potential minimum decreases as a function of shear rate due to increased hydrodynamic drag and lift forces resulting in higher desorption rate coefficients at higher shear rates.

Heat-transfer analysis in microfluidic devices is of great importance in applications such as micro-heat exchangers and microreactors. This work reports on improvements in temperature measurement techniques, which can be the source of large errors due to their intrusiveness and the unreliability of conventional thermal sensors. Gold thin films were deposited on a borosilicate substrate to realize a 2D heat flux sensor for heat-transfer measurement along the main flow within microchannels. Two applications are shown, one related to micro-heat exchangers and the other to microreactors. For the micro-heat exchanger, the effect of length scale on heat transfer in a straight microchannel was investigated and the validity of macroscale correlations for convective heat transfer was checked for deionized water flowing in microchannels of heights 12 to 52 μm. For the microreactor, the reaction enthalpy of an acid–base reaction measured using the new heat-flux sensor had only a 5% discrepancy from the standard value, showing the efficiency of the new thin-film device.Copyright © 2012 by ASME

We here report on the separation of yeast cells, with micro-engineered membranes having pores that are typically five times larger than the cells. The separation is due to neither shear-induced diffusion, nor initial lift, but to an effect similar to fluid skimming. The separation performance is linked to the ratio between cross-flow and transmembrane flux, and could be captured with a dimensionless number relating those. On the basis of this dimensionless number, flux and transmission of the cells could be predicted. The mechanism rests on having a sufficiently high cross-flow velocity, such that particles are not dragged too deep in the pore, but are dragged with the cross-flow back into the feed stream. The separation factor can simply be changed by changing the ratio between crossflow velocity and transmembrane flux. Since the membranes have very large pores, fouling does not play a role. Constant high transmembrane flux values of 200–2200 L/m 2 h were reached for transmembrane pressures ranging from 0.02 to 0.4 bar (typical industrial fluxes are 150 L/m 2 h bar with a maximum of 2000 L/m 2 h bar for short periods of time, comparable to 50–400 L/m 2 h [1,2] ). Although the effect is strongest with monodispersed pores, it will be possible to exploit the mechanism with conventional membranes. As such, it may open up a new route towards non-fouling crossflow microfiltration.

International audience; Spatial variations of cake thickness along flat-sheet membranes were previously evidenced from filtration experiments [J. Mendret, C. Guigui, P. Schmitz, C. Cabassud and P. Duru, An optical method for in situ characterization of fouling during filtration, AlChE Journal, 53 (2007) 2265-2274.]. Neither gravity effects nor pressure drop in channel could explain these unexpected variations. Therefore a theoretical model was developed to investigate growth of a cake on a non-uniform permeability membrane. The model considers two dimensional flow of a particle suspension in a rectangular channel with one porous wall under suction. Cake growth is assumed to be proportional to local filtration velocity. Its macroscopic properties are prescribed from empirical power laws obtained from the aforementioned experiments. A finite element method using mesh deformation was adopted to solve the governing equations of the problem, i.e., the coupled Navier-Stokes and Darcy Brinkman equations, to simulate a complete filtration run. Comparisons between simulations and experiments are in good agreement. Then a careful analysis of the numerical results reveals a non-uniform initial filtration velocity along the porous wall which rapidly becomes uniform. On the contrary, a non-uniform cake thickness still remains after a long time of filtration which profile is similar to the initial membrane permeability profile. Moreover increase of the transmembrane pressure significantly reduces the time necessary to recover a uniform behaviour of the filter. (C) 2010 Elsevier B.V. All rights reserved.

This contribution is based on the Lanchester Lecture of the Royal Aeronautical Society held in Manchester, UK, in October 2009. The lecture reflected on further possible perspectives for aeronautical research, in particular with respect to aerodynamics. The air transport system of today has matured to very high performance and safety standards. However, due to the ongoing global developments of economy and ecology, new challenges have to be faced. Thus, the relevance of all engineering aeronautical disciplines contributing to the final aircraft configuration is now closely scrutinised, and especially aerodynamics is challenged whether any investment in further research is still justified. In this contribution, it is argued that, when carefully exploited, aerodynamics still offers a substantial technological perspective, well beyond the concepts for the next generation of aircraft as currently being pursued. As an example, the aerodynamics of a forward swept-wing are discussed and it is outlined that, when combining the transonic characteristics of a forward swept-wing with the advantages of natural laminar-flow, considerable improvements in efficiency may be gained. However, this potential may only be leveraged through a strategic, long-term orientation of fundamental and applied research.

International audience; The drill-string dynamics is difficult to predict due to the non-linearities and uncertainties involved in the problem. In this paper a stochastic computational model is proposed to model uncertainties in the bit-rock interaction model. To do so, a new strategy that uses the non-parametric probabilistic approach is developed to take into account model uncertainties in the bit-rock non-linear interaction model. The mean model considers the main forces applied to the column such as the bit-rock interaction, the fluid-structure interaction and the impact forces. The non-linear Timoshenko beam theory is used and the non-linear dynamical equations are discretized by means of the finite element method. (C) 2009 Elsevier Ltd. All rights reserved.

Bends are frequently encountered in microdevices and therefore a fundamental understanding of How through them is important. In this paper, we have used the lattice Boltzmann method to study flow of a gas through a microchannel with a single 90 degrees bend. The computations are two-dimensional, isothermal, and for the Reynolds and Knudsen numbers typically observed. We rind that the pressure drop in segments of equal lengths before and after the bend is different, and a recirculatory motion is seen near the bend even when the flow Reynolds number is less than unity. The velocity and pressure distribution between the bend and straight microchannels is almost identical at large Knudsen numbers, indicating that the flow does not feel the presence of the bend in such cases. This is attributed to rarefaction of the gas which hinders transfer of information across the now. (C) 2009