The Experts below are selected from a list of 4695 Experts worldwide ranked by ideXlab platform

Stéphane Colin - One of the best experts on this subject based on the ideXlab platform.

  • shear work contribution to convective heat transfer of dilute gases in Slip Flow Regime
    European Journal of Mechanics B-fluids, 2017
    Co-Authors: Pamela Vocale, Gian Luca Morini, Marco Spiga, Stéphane Colin
    Abstract:

    Abstract In the literature some researchers highlighted that for a dilute gas in Slip Flow Regime and in presence of a non negligible viscous heating, the analysis of the gas micro-convection has to be tackled by modifying the thermal boundary conditions to account for the shear work due to the Slip at the wall. Although in the recent past a specific modified boundary condition has been proposed, theoretically justified and applied to investigate the effect of the shear work on the convective heat transfer in presence of dilute gases, in this paper is demonstrated that there is not a need of a modified boundary condition in order to take into account the effect of the shear work in the analysis of forced convection. In the present work by means of a comprehensive theoretical analysis is demonstrated that the modified boundary condition is useless for the analysis of the effect of shear work on the evaluation of the convective heat transfer coefficients in presence of a dilute gas with non-negligible viscous dissipation. Moreover, to evaluate the inaccuracy of the results obtained by using the modified boundary conditions the difference, in terms of Nusselt number, between the exact and the approximate solution has been numerically estimated for elliptical microchannels. The numerical outcomes point out that the adoption of the modified boundary condition leads to an underestimation or an overestimation of the Nusselt numbers depending on the values of Brinkman number and on the channel cross section geometry.

  • Numerical design of a Knudsen pump with curved channels operating in the Slip Flow Regime
    Heat and Mass Transfer, 2014
    Co-Authors: Vlasios Leontidis, Jie Chen, Lucien Baldas, Stéphane Colin
    Abstract:

    A numerical procedure has been developed for modeling 2D thermal creep Flows with Fluent^®. Complete first order velocity Slip, including thermal creep and walls curvature effects, as well as temperature jump, boundary conditions, are implemented via C routines. After validation on benchmark Flows, the technique is used for designing a Knudsen pump with curved microchannels and it is demonstrated that this micropump can be efficient in the Slip Flow Regime.

  • Numerical Simulation of Thermal Transpiration in the Slip Flow Regime With Curved Walls
    ASME 2012 10th International Conference on Nanochannels Microchannels and Minichannels, 2012
    Co-Authors: Vlasios Leontidis, Lucien Baldas, Stéphane Colin
    Abstract:

    Nowadays, modeling gas Flows in the Slip Flow Regime through microchannels can be achieved using commercial Computational Fluid Dynamics codes. In this Regime the Navier-Stokes equations with appropriate boundary conditions are still valid. A simulation procedure has been developed for the modeling of thermal creep Flow using ANSYS Fluent®. The implementation of the boundary conditions is achieved by developing User Defined Functions (UDFs) by means of C++ routines. The complete first order velocity Slip boundary condition, including the thermal creep effects due to an axial temperature gradient and the effect of the wall curvature, and the temperature jump boundary condition are applied. Motivation of the present work is the development of a simulation tool which will help in the pre-calculations and the preliminary design of a Knudsen micropump consisting of successively connected curved and straight channels and in a second step in the numerical optimization of the pump, in terms of geometrical parameters and operating conditions of the system.Copyright © 2012 by ASME

  • Gas MicroFlows in the Slip Flow Regime: A Critical Review on Convective Heat Transfer
    Journal of Heat Transfer, 2011
    Co-Authors: Stéphane Colin
    Abstract:

    Accurate modeling of gas microvection is crucial for a lot of MEMS applications (microheat exchangers, pressure gauges, fluidic microactuators for active control of aerodynamic Flows, mass Flow and temperature microsensors, micropumps, and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum, and dosing valves…). Gas Flows in microsystems are often in the Slip Flow Regime, characterized by a moderate rarefaction with a Knudsen number of the order of 10−2–10−1. In this Regime, velocity Slip and temperature jump at the walls play a major role in heat transfer. This paper presents a state of the art review on convective heat transfer in microchannels, focusing on rarefaction effects in the Slip Flow Regime. Analytical and numerical models are compared for various microchannel geometries and heat transfer conditions (constant heat flux or constant wall temperature). The validity of simplifying assumptions is detailed and the role played by the kind of velocity Slip and temperature jump boundary conditions is shown. The influence of specific effects, such as viscous dissipation, axial conduction and variable fluid properties is also discussed.

  • Gas Mass Flow Rate Measurement in T-Shaped Microchannels in Slip Flow Regime
    Volume 6: Fluids and Thermal Systems; Advances for Process Industries Parts A and B, 2011
    Co-Authors: Christine Barrot, Stéphane Colin, Lucien Baldas, Ju¨rgen J. Brandner, David Newport
    Abstract:

    A new setup was developed for gas mixing analysis in T-shaped microchannels. The principle of the Flow rate measurement was based on the Constant Volume (CV) method [1]. The mass Flow rate measurements of two gases N2 / CO2 mixing in a T mixer were carried out in the Slip Flow Regime and followed by a simulation work for comparison. The mass Flow rate has a magnitude of 10−8 or 10−7 kg/s and has good agreement with simulation for the lowest inlet over outlet pressures ratios and moderate agreement for the highest inlet over outlet pressures ratios.

Amit Agrawal - One of the best experts on this subject based on the ideXlab platform.

  • Heat transfer coefficient of gas Flowing in a circular tube under rarefied condition
    International Journal of Thermal Sciences, 2010
    Co-Authors: Anwar Demsis, Bhaskar Verma, S.v. Prabhu, Amit Agrawal
    Abstract:

    The purpose of this paper is to present heat transfer measurements of gas in a tube under rarefied condition The measurements are made in a circular tube of inner diameter 25 mm for approximately constant wall temperature boundary conditions, with nitrogen, oxygen, argon, and helium as the working fluids The range of Knudsen and Reynolds numbers covered in this study are 0.0022-0 032 and 0 13-14.7. respectively. Whereas the continuum values are correctly reproduced in our setup, the measured values for Nusselt numbers are very small in the Slip Regime. The measured values are two-five orders of magnitude smaller than the corresponding values in the continuum Regime, and suggest that the Nusselt number is a strong function of Reynolds, Knudsen and Brinkmann numbers in the Slip Flow Regime These are among the first heat transfer measurements in the Slip Flow Regime and the current theoretical and simulation models are inadequate to explain such low values of Nusselt number. (C) 2010 Elsevier Masson SAS.

  • Experimental determination of heat transfer coefficient in the Slip Regime and its anomalously low value.
    Physical Review E, 2009
    Co-Authors: Anwar Demsis, Bhaskar Verma, S.v. Prabhu, Amit Agrawal
    Abstract:

    In this paper, the measurement of the heat transfer coefficient in rarefied gases is presented; these are among the first heat transfer measurements in the Slip Flow Regime. The experimental setup is validated by comparing friction factor in the Slip Regime and heat transfer coefficient in the continuum Regime. Experimental results suggest that the Nusselt number is a function of Reynolds and Knudsen numbers in the Slip Flow Regime. The measured values for Nusselt numbers are smaller than that predicted by theoretical or simulation results, and can become a few orders of magnitude smaller than the theoretical values in the continuum Regime. The results are repeatable and expected to be useful for further experimentation and modeling of Flow in the Slip and transition Regimes.

D Chaudhary - One of the best experts on this subject based on the ideXlab platform.

  • oscillatory magnetopolar free convection Flow through a vertical porous plate embedded in a porous medium in Slip Flow Regime
    IOSR Journal of Mathematics, 2013
    Co-Authors: D Chaudhary
    Abstract:

    In this paper we study as Oscillatory two dimensional magnetopolar free convection Flow through a porous medium with combined heat and mass transfer and thermal radiation in Slip Flow Regime. The permeability and suction velocity are assumed to be time dependent. Using perturbation technique expressions for velocity (u), angular velocity (), temperature (), concentration (C), skin friction (C f) and Nusselt number (Nu) are obtained and a comparative study is made to analyze the effects of different parameters. We notice that as we increase permeability parameter (K) skin friction falls in the beginning but rises as we move away from the plate. Moreover, for both the basic fluids air (Pr = 0.71, Sc = 0.22) and water (Pr = 7, Sc = 0.61), velocity increases on decreasing the Slip at the boundary.

R C Chaudhary - One of the best experts on this subject based on the ideXlab platform.

  • free convective unsteady mhd Flow in Slip Flow Regime past a vertical plate with a convective surface boundary condition
    Journal of Informatics and Mathematical Sciences, 2018
    Co-Authors: Preeti Garg, G N Purohit, R C Chaudhary
    Abstract:

    This paper examines the unsteady free convective viscous incompressible MHD Flow past a vertical porous flat plate with convective surface boundary condition in Slip Flow Regime under the influence of uniform magnetic field acting perpendicular to the porous surface. Assuming time dependent variable suction velocity at the porous plate, analytical expressions for the Flow characteristics are obtained by using perturbation technique which converts the non-linear partial differential equations into ordinary differential equations. The effect of various parameters such as Prandtl number, Grashoff number, the Magnetic field parameter, Suction parameter and Convective heat change parameter on the transient velocity, transient temperature, skin friction coefficient and the rate of heat transfer are discussed with the help of graphs.

  • Effects of chemical reactions on MHD micropolar fluid Flow past a vertical plate in Slip-Flow Regime
    Applied Mathematics and Mechanics, 2008
    Co-Authors: R C Chaudhary, Abhay Kumar Jha
    Abstract:

    Heat and mass transfer effects on the unsteady Flow of a micropolar fluid through a porous medium bounded by a semi-infinite vertical plate in a Slip-Flow Regime are studied taking into account a homogeneous chemical reaction of the first order. A uniform magnetic field acts perpendicular to the porous surface absorb micropolar fluid with a suction velocity varying with time. The free stream velocity follows an exponentially increasing or decreasing small perturbation law. Using the approximate method, the expressions for the velocity microrotation, temperature, and concentration are obtained. Futher, the results of the skin friction coefficient, the couple stress coefficient, and the rate of heat and mass transfer at the wall are presented with various values of fluid properties and Flow conditions.

  • combined heat and mass transfer in magneto micropolar fluid Flow from radiate surface with variable permeability in Slip Flow Regime
    Zamm-zeitschrift Fur Angewandte Mathematik Und Mechanik, 2007
    Co-Authors: R C Chaudhary, Preeti Jain
    Abstract:

    An analysis is presented to study the effects of radiation on the hydromagnetic free convection Flow (set up due to temperature as well as species concentration) of an electrically conducting micropolar fluid past a vertical porous plate through porous medium in Slip-Flow Regime. A uniform magnetic field acts perpendiculary to the porous surface which absorbs the micropolar fluid with variable suction velocity. The Rosseland approximation is used to describe the radiative heat flux in energy equation. The numerical results of velocity distribution of micropolar fluids are compared with the corresponding Flow problems for a Newtonian fluid. Assuming variable permeability of the medium, numerical results are presented graphically in the form of velocity, micro rotation, and temperature profiles for different material parameters entering into the analysis. Also, the results of the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall are discussed with the help of figures.

  • effect of variable suction on transient free convective viscous incompressible Flow past a vertical plate with periodic temperature variations in Slip Flow Regime
    2003
    Co-Authors: Pawan Kumar Sharma, R C Chaudhary
    Abstract:

    The unsteady free convective viscous incompressible Flow past a vertical porous flat plate with periodic temperature in Slip-Flow Regime has been discussed. Assuming variable suction at the porous plate, analytical expressions for Flow characteristic are obtained. The effects of various parameters on the transient velocity, transient temperature, the skin-friction and rate of heat transfer are discussed with the help of graphs.

Debasish Dey - One of the best experts on this subject based on the ideXlab platform.

  • Gravity Modulation Effects of Hydromagnetic Elastico-Viscous Fluid Flow past a Porous Plate in Slip Flow Regime
    ISRN Applied Mathematics, 2014
    Co-Authors: Debasish Dey
    Abstract:

    The two-dimensional hydromagnetic free convective Flow of elastico-viscous fluid (Walters liquid Model B′) with simultaneous heat and mass transfer past an infinite vertical porous plate under the influence of gravity modulation effects has been analysed. Generalized Navier’s boundary condition has been used to study the characteristics of Slip Flow Regime. Fluctuating characteristics of temperature and concentration are considered in the neighbourhood of the surface having periodic suction. The governing equations of fluid motion are solved analytically by using perturbation technique. Various fluid Flow characteristics (velocity profile, viscous drag, etc.) are analyzed graphically for various values of Flow parameters involved in the solution. A special emphasis is given on the gravity modulation effects on both Newtonian and non-Newtonian fluids.

  • free convective visco elastic boundary layer Flow past an inclined permeable plate in Slip Flow Regime
    International Journal of Mathematical Archive, 2012
    Co-Authors: Rita Choudhury, Hillol Kanti Bhattacharjee, Debasish Dey
    Abstract:

    A n analytical study of two dimensional free convective boundary layer Flow of an electrically conducting visco-elastic fluid past an inclined porous plate in Slip Flow Regime has been investigated. The visco-elastic fluid Flow is characterized by Walters liquid (Model B / ). The suction of the plate is assumed to be constant. A magnetic field of strength B 0 is applied normal to the plate. Let x-axis be taken along the inclined plate and y-axis be taken perpendicular to the plate. Navier’s generalized boundary conditions for Slip Flow Regime have been used. The perturbation scheme has been used to solve the governing equations of the fluid motion. The approximate solutions for velocity and temperature fields have been derived. Results are discussed for the Flow past a heated plate ( 0). The velocity profiles have been shown graphically and the shearing stress at the plate is given in tabular form for various values of the visco-elastic parameter with the combination of other Flow parameters involved in the solution.

  • free convective elastico viscous fluid Flow with heat and mass transfer past an inclined porous plate in Slip Flow Regime
    Latin American Applied Research, 2012
    Co-Authors: Rita Choudhury, Debasish Dey
    Abstract:

    The unsteady free convective elastico- viscous fluid Flow past a porous inclined plate in Slip Flow Regime in presence of periodic temperature and concentration has been analyzed. The suction at the plate is assumed to be fluctuating with time. The governing equations of the problem have been solved by using perturbation scheme. The approximate so- lutions have been derived for the velocity, tempera- ture field, concentration field, skin friction, rate of heat transfer and rate of mass transfer. The values of the skin friction co-efficient are calculated numeri- cally and presented in tabular form for various val- ues of the Flow parameters. The influence of visco- elastic parameter with the combination of other Flow parameters on the velocity field have been obtained and illustrated graphically.