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Vladimir Titarev - One of the best experts on this subject based on the ideXlab platform.

  • Comparative study for rarefied gas flow into vacuum through a short Circular Pipe
    Vacuum, 2014
    Co-Authors: V. V. Aristov, Vladimir Titarev, E. M. Shakhov, S. A. Zabelok
    Abstract:

    Abstract The problem of rarefied gas flow into vacuum through a short Circular Pipe is studied numerically by solving the Boltzmann kinetic equation. Comparison of the results obtained with the exact and S-model collision integrals is presented across a large range of Knudsen numbers. Computed values of mass flow rate are also compared against the DSMC results and experimental data from existing literature.

  • Rarefied gas flow in a Circular Pipe of finite length
    Vacuum, 2013
    Co-Authors: Vladimir Titarev
    Abstract:

    Abstract The paper is devoted to the study of a rarefied gas flow through a Circular Pipe caused by small pressure differences between the reservoirs attached to the ends of the Pipe. The analysis is based on of the direct numerical solution of the Boltzmann kinetic equation with the linearized model collision integral of Shakhov. The solution of the problem is computed for a wide range of the rarefaction parameter values and is compared with the kinetic and continuum solutions for an infinitely long Circular Pipe as well as with the flow into vacuum.

  • Rarefied gas flow through a long Circular Pipe into vacuum
    2012
    Co-Authors: Vladimir Titarev, E. M. Shakhov
    Abstract:

    Rarefied gas flow through a Circular Pipe into vacuum is studied on the basis of the direct numerical solution of the kinetic equation. The main emphasis of the study is on the end effects. The problem is solved in the completed geometrical setup with the Pipe and reservoirs as well as incomplete setup in which the reservoirs are replaced by emission/no emission boundary conditions. The results for the flow rate and density distribution along the Pipe are compared with the approximate solution based on the use of the locally one-dimensional assumption.

  • Computational study of a rarefied gas flow through a long Circular Pipe into vacuum
    Vacuum, 2012
    Co-Authors: Vladimir Titarev, E. M. Shakhov
    Abstract:

    Abstract The paper presents an analysis of the non-linear rarefied gas flow through a Circular Pipe into vacuum. The main attention is given to the case of the large length to radius ratio. The problem is studied on the basis of the numerical solution of the S-model kinetic equation. Results are compared with the available DSMC data for short tubes as well as with the asymptotic solution corresponding to the infinitely long Pipe.

E. M. Shakhov - One of the best experts on this subject based on the ideXlab platform.

  • Comparative study for rarefied gas flow into vacuum through a short Circular Pipe
    Vacuum, 2014
    Co-Authors: V. V. Aristov, Vladimir Titarev, E. M. Shakhov, S. A. Zabelok
    Abstract:

    Abstract The problem of rarefied gas flow into vacuum through a short Circular Pipe is studied numerically by solving the Boltzmann kinetic equation. Comparison of the results obtained with the exact and S-model collision integrals is presented across a large range of Knudsen numbers. Computed values of mass flow rate are also compared against the DSMC results and experimental data from existing literature.

  • Rarefied gas flow through a long Circular Pipe into vacuum
    2012
    Co-Authors: Vladimir Titarev, E. M. Shakhov
    Abstract:

    Rarefied gas flow through a Circular Pipe into vacuum is studied on the basis of the direct numerical solution of the kinetic equation. The main emphasis of the study is on the end effects. The problem is solved in the completed geometrical setup with the Pipe and reservoirs as well as incomplete setup in which the reservoirs are replaced by emission/no emission boundary conditions. The results for the flow rate and density distribution along the Pipe are compared with the approximate solution based on the use of the locally one-dimensional assumption.

  • Computational study of a rarefied gas flow through a long Circular Pipe into vacuum
    Vacuum, 2012
    Co-Authors: Vladimir Titarev, E. M. Shakhov
    Abstract:

    Abstract The paper presents an analysis of the non-linear rarefied gas flow through a Circular Pipe into vacuum. The main attention is given to the case of the large length to radius ratio. The problem is studied on the basis of the numerical solution of the S-model kinetic equation. Results are compared with the available DSMC data for short tubes as well as with the asymptotic solution corresponding to the infinitely long Pipe.

Erkan Kizilirmak - One of the best experts on this subject based on the ideXlab platform.

  • EFFECTS OF REYNOLDS NUMBER, BAFFLE ANGLE, AND BAFFLE DISTANCE ON 3-D TURBULENT FLOW AND HEAT TRANSFER IN A Circular Pipe
    2015
    Co-Authors: Oğuz Turgut, Erkan Kizilirmak
    Abstract:

    In this study, steady-state 3-D turbulent forced convection flow and heat transfer characteristics in a Circular Pipe with baffles attached inside Pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number of 3000-50,000, Prandtl number of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle α of 30°-150°. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that Circular Pipe having baffles has a higher Nusselt number and friction factor compared to the smooth Circular Pipe without baffles. Periodically fully developed conditions are obtained after a certain module. Maximum thermal performance factor is obtained for the baffle angle of 150°. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. All the numerical results are correlated within accuracy of ±10% and ±15% for average Nusselt number and Darcy friction factor, respectively.

  • Effects of Reynolds number, baffle angle, and baffle distance on three-dimensional turbulent flow and heat transfer in a Circular Pipe
    Thermal Science, 2015
    Co-Authors: Oğuz Turgut, Erkan Kizilirmak
    Abstract:

    In this study, steady-state three-dimensional turbulent forced convection flow and heat transfer characteristics in a Circular Pipe with baffles attached inside Pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number Re of 3000-50,000, Prandtl number Pr of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle a of 30o-150o. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that Circular Pipe having baffles has a higher Nusselt number and friction factor compared to the smooth Circular Pipe without baffles. Maximum Nusselt number and friction factor are obtained for the baffle angle of 90o. Nusselt number increases while baffle distance increases in the range of studied; however, friction factor decreases. Periodically fully developed conditions are obtained after a certain module. Thermal performance factor increases with increasing baffle distance in the rage of studied but decreases with increasing Reynolds number; maximum thermal performance factor is obtained for the baffle angle of 150o. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. The accuracy of the results obtained in this study is verified by comparing the results with those available in the literature for smooth Circular Pipes. All the numerical results are correlated within accuracy of ±10 and ±15% for average Nusselt number and Darcy friction factor, respectively.

Teoman Ayhan - One of the best experts on this subject based on the ideXlab platform.

  • Experimental investigation of propeller type swirl generator for a Circular Pipe flow
    International Communications in Heat and Mass Transfer, 1999
    Co-Authors: Tulin Bali, Teoman Ayhan
    Abstract:

    Abstract The objective of this paper is to introduce the subject of heat transfer augmentation by inserting a propeller type swirl generator in a Circular Pipe. The propeller type swirl generator creates a flow pattern which is like a decaying swirl flow. This flow pattern is observed for laminar flow. The main advantage of this type of swirl generator is that it is easy to install the device into a Circular Pipe. Average and local Nusselt numbers were calculated by the method explained in detail in the main text. Comparison of the local Nusselt numbers for swirl flow considered in this study and local Nusselt numbers for flow in a smooth Pipe revealed that the local Nusselt number increases substantially when the swirl generator is used. The swirl related heat transfer enhancement becomes stronger as Reynolds number increases.

Duhan Jung - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic stability of a semi-Circular Pipe conveying harmonically oscillating fluid
    Journal of Sound and Vibration, 2008
    Co-Authors: Duhan Jung, Jintai Chung, Andre P. Mazzoleni
    Abstract:

    The dynamic stability of a semi-Circular Pipe conveying harmonically oscillating fluid is investigated in this study. For analysis, harmonically oscillating flow is regarded as a parametrically excited system with time-varying coefficients. Considering the extensibility and nonlinearity of the semi-Circular Pipe, the equations of motion and the associated boundary conditions are obtained by using the extended Hamilton principle. Applying Floquet theory to the derived equations, the stability of the Pipe is analyzed for variations of the amplitude and oscillating frequency of the fluid velocity. The effects of the mean value for the fluid velocity on the stability are also analyzed. It is found that the semi-Circular Pipe may become unstable when the fluctuation frequency approaches some multiples or sum of the out-of-plane natural frequencies. Furthermore, it is observed that the instability regions increase with the mean value of the velocity. The results obtained via the stability analysis are verified by time responses computed by using a direct time integration method.

  • In-plane and out-of-plane motions of an extensible semi-Circular Pipe conveying fluid
    Journal of Sound and Vibration, 2007
    Co-Authors: Duhan Jung, Jintai Chung
    Abstract:

    Abstract In-plane and out-of-plane motions of a semi-Circular Pipe conveying fluid are analyzed in this paper. Assuming that the centerline of the semi-Circular Pipe is extensible, nonlinear equations of in-plane and out-of-plane motions are derived according to the extended Hamilton principle. The Lagrange nonlinear strain theory and the Euler–Bernoulli beam theory are used to derive the equations. The derived equations of motion are discretized by applying the Galerkin method. Linearized equations around the equilibrium position are obtained from the discretized equations, and then the dynamic characteristics of the Pipe are investigated. In addition, some modelling issues, which are related to the nonlinearity of the circumferential strain and stress, are discussed. This study finds that a semi-Circular Pipe conveying fluid does not lose stability even at a high fluid velocity. Although a model using the Lagrange nonlinear strain and the corresponding nonlinear stress yields the most accurate computational results of the natural frequencies, a model using the Lagrange strain and a linearized stress is recommended to compute the natural frequencies efficiently while still maintaining accuracy.

  • New fluid velocity expression in an extensible semi-Circular Pipe conveying fluid
    Journal of Sound and Vibration, 2007
    Co-Authors: Duhan Jung, Jintai Chung, Hong Hee Yoo
    Abstract:

    A new expression for fluid velocity is presented for a fluid-conveying semi-Circular Pipe with an extensible centreline. The proposed fluid velocity expression is obtained from the material derivative, while the previous velocity expressions are from Love's kinematical relations. In order to show that the new fluid velocity expression is more reasonable than the previous velocity expressions, the equations of in-plane motion derived with the new expression are compared to the equations derived with the previous expressions. Furthermore, the equilibrium positions, natural frequencies and mode shapes obtained with both the new and previous expressions are analysed and discussed.