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S V Alekseenko - One of the best experts on this subject based on the ideXlab platform.

  • wave flow of the Condensate Film
    High Temperature, 2014
    Co-Authors: S P Aktershev, S V Alekseenko
    Abstract:

    Wave formation in a laminar Condensate Film flowing over an isothermal substrate has been studied by the numerical simulation method. An integral model modified taking into account the phase transformation has been applied for the description of nonlinear waves in a Condensate Film. It has been shown that natural waves, which strongly enhance heat transfer, develop on the surface of the Condensate Film due to the instability of the flow. The evolution of the two-dimensional forced waves and their effect on heat transfer have been studied.

  • nonlinear waves and heat transfer in a falling Film of Condensate
    Physics of Fluids, 2013
    Co-Authors: S P Aktershev, S V Alekseenko
    Abstract:

    Nonlinear wave formation and heat transfer in wavy Condensate Film flowing over the isothermal wall are studied numerically. The integral-boundary-layer model, modified with account of the phase transition has been used to describe the wave motion. The nonlinear evolution of both natural and forced two-dimensional waves was investigated, and wave effect on heat transfer in Condensate Film was determined. Heat transfer enhancement by waves due to the predominant contribution of the thin residual layer between the peaks was demonstrated. It is shown that by applying the superimposed periodic oscillations, one can intensify heat transfer within a certain range of frequencies as compared to the case of naturally occurring waves.

  • influence of condensation on the stability of a liquid Film moving under the effect of gravity and turbulent vapor flow
    International Journal of Heat and Mass Transfer, 2005
    Co-Authors: S P Aktershev, S V Alekseenko
    Abstract:

    Abstract The linear stability of Condensate Film flowing on an inclined isothermal plate under action of gravity and turbulent vapor flow was the subject of study. The cases of cocurrent and countercurrent flow of two phases were considered at an arbitrary inclination of the plane. The first part of this work deals with stationary Film flow. The impact of vapor flow on the Film is described by a given shear stress on the interface with account for the transverse mass flux due to phase transition. The integral method gives the analytical solution for distribution of Film thickness along the plane (with and without account for Film inertia) at different inclination angles. The second part of paper deals with linear stability of stationary Film flow. The fluctuation of shear stress on the surface was calculated using the quasilaminar model. The two-wave equation for Film thickness with phase transition and dispersion formulas were derived. The results of effect of condensation on Film stability are presented for a wide range of flow parameters.

  • the stability of a Condensate Film moving under the effect of gravity and turbulent flow of vapor
    High Temperature, 2003
    Co-Authors: S P Aktershev, S V Alekseenko
    Abstract:

    The linear stability of a Condensate Film moving along a vertical isothermal plate under the effect of gravity and turbulent vapor flow is investigated. The cases of both cocurrent and countercurrent motion of phases are treated with regard for phase transformation. An analytical solution for the distribution of Film thickness along the plate taking into account the Film inertia is obtained using the integral method. A two-wave equation is deduced for the Film thickness, and dispersion relations are derived. The effect of moving vapor on the Film stability in a wide range of flow parameters is shown.

Cha'o-kuang Chen - One of the best experts on this subject based on the ideXlab platform.

  • laminar Film condensation from a downward flowing steam air mixture onto a horizontal circular tube
    Applied Mathematical Modelling, 2009
    Co-Authors: Cha'o-kuang Chen, Yanting Lin
    Abstract:

    Abstract This investigation develops a numerical model of laminar Film condensation from a downward-flowing steam-air mixture onto a horizontal circular tube. The significant non-similarity of the coupled two-phase flow laminar Film condensation is such that the boundary layer governing conservations of momentum, species and energy in the mixture and liquid phases are solved by finite-volume methods. Numerical analysis of both the local Condensate Film thickness and heat transfer characteristics elucidated the simultaneous effects of inlet-to-wall temperature difference and inlet air concentration, the Reynolds number of the mixture, and the dimensionless parameter, F , by adopting a unified Condensate parameter. The local Nusselt number and liquid Film thickness increase as both the non-condensable air mass fraction and the tube temperature decreases. The numerical results on local heat transfer and Film thickness for low/no non-condensable gas (air) agree closely with the theoretical results of Yang [Sheng-An Yang, Superheated laminar Film condensation on a nonisothermal horizontal tube, J. Thermophys. Heat Transfer 11(4) (1997) 526–532], Fuji [T. Fujii, H. Uehare, C. Kurata, Laminar Filmwise condensation of flowing vapor on a horizontal tube, Int. J. Heat Mass Transfer 15 (1972) 235–246] and Homescu and Panday [D. Homescu, P.K. Panday, Forced convection condensation on a horizontal tube: Influence of turbulence in the vapor and liquid phases, J. Heat Transfer Trans. ASME 121(4) (1999) 874–885]. Meanwhile, the comparison of average heat transfer coefficient with the experimental data from Rose and Lee [W.C. Lee, J.W. Rose, Forced convection Film condensation on a horizontal tube with and without non-condensing gases, Int. J. Heat Mass Transfer 27(4) (1984) 519–528] demonstrates reasonably good agreement with the parameter F ( = gdh fg μ L / ⌊ k L U 0 2 ( T 0 - T W ) ⌋ , the ratio of gravity to mixture velocity) and G (= ( T 0 - T W ) ( k L / h fg μ L ) ( ρ L μ L / ρ m μ m ) , the suction effect).

  • nonlinear stability analysis of thin Condensate falling Film inside a rotating vertical cylinder
    International Journal of Heat and Mass Transfer, 2006
    Co-Authors: Chuni Chen, Cha'o-kuang Chen, Yuetzu Yang
    Abstract:

    Abstract This paper investigates the stability of thin Condensate Film flowing down on the inner surface of a rotating vertical cylinder by means of long wave perturbation method in a two-step procedure. In the first step, the normal mode method is used to characterize the linear behavior. In the second step, an elaborated nonlinear Film flow model is solved by using the method of multiple scales to characterize flow behavior at various states of sub-critical stability, sub-critical instability, supercritical stability, and supercritical explosion. The procedure follows the previous research [C.I. Chen, C.K. Chen, Y.T. Yang, Int. J. Heat Mass Transfer 47 (2004) 1937–1951] which concerns with the thin Condensate falling Film on the outer surface of a rotating vertical cylinder. The modeling results indicate that by increasing the rotation speed, Ω, and the radius of cylinder, R, the Condensate Film becomes more stable, which is totally opposite to the previous study.

  • simplified approach of turbulent Film condensation on an inclined elliptical tube
    International Journal of Heat and Mass Transfer, 2006
    Co-Authors: Cha'o-kuang Chen
    Abstract:

    Abstract The present theoretical study investigates turbulent Film condensation on an inclined elliptical tube. Adopting the assumption of an isothermal wall surface, the energy equation, forced balance equations and thermal balance equations are derived to describe the phenomena of the Condensate Film. Results are obtained for the heat transfer coefficient over a wide range of vapor velocities, i.e. low condensation parameter to high condensation parameter. The optimal inclination angle of the tube in different length–radius ratios and eccentricity can be obtained in the present results. This study also discusses the influence of the degree of eccentricity of the elliptical tube on the heat transfer coefficient. Finally, a comparison is provided between the results of the present study and those reported in a previous theoretical study. It is found that a good agreement exists between the two sets of results.

  • perturbation analysis to the nonlinear stability characterization of thin Condensate falling Film on the outer surface of a rotating vertical cylinder
    International Journal of Heat and Mass Transfer, 2004
    Co-Authors: Chuni Chen, Cha'o-kuang Chen, Yuetzu Yang
    Abstract:

    Abstract The linear and nonlinear stability theories for characterization of Condensate Film flow down on the outer surface of a rotating infinite vertical cylinder is investigated analytically. A generalized nonlinear kinematic model is derived to represent the physical system and is solved by the long-wave perturbation method in a two-step procedure. In the first step, the normal mode method is used to characterize the linear behaviors. The amplitude growth rates and the threshold conditions are characterized subsequently and summarized as the by-products of the linear solutions. In the second step, an elaborated nonlinear Film flow model is solved by using the method of multiple scales to characterize flow behaviors at various states of sub-critical stability, sub-critical instability, supercritical stability and supercritical explosion. The modeling results indicate that by increasing the rotation speed, Ω , and decreasing the radius of cylinder, R, the Film flow becomes less stable, generally.

  • weakly nonlinear stability analysis of Condensate Film flow down a vertical cylinder
    International Journal of Heat and Mass Transfer, 1996
    Co-Authors: Cheni Hung, Cha'o-kuang Chen, Jungshun Tsai
    Abstract:

    Weakly nonlinear stability theory is used to study the stability characteristics of Condensate Film flowing down the outer surface of a vertical cylinder. The surface tension and the mass transfer due to phase change are taken into account at the liquid-vapor interface. A method of perturbation is applied for the solution and the results show that supercritical stability in the linearly unstable region and subcritical instability in the linearly stable region exist. The lateral curvature of the cylinder has a destabilizing effect on the flow stability. The curvature of the cylinder will intensify the instability of the Film flow in comparison with that of the planar flow. A possible application of the present results to some aspects of the qualitative design of a coating process is given.

Ping Cheng - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann simulation of forced condensation flow on a horizontal cold surface in the presence of a non condensable gas
    International Journal of Heat and Mass Transfer, 2017
    Co-Authors: Chaoyang Zhang, Ping Cheng, W J Minkowycz
    Abstract:

    Abstract A multi-component/multi-phase (MCMP) lattice Boltzmann method (LBM) with vapor/liquid phase change is proposed in this paper. Two equations of state (EOS) including Peng-Robinson (PR) EOS for water and ideal gas EOS for the non-condensable gas (NCG) are applied in the thermal equation. Based on this newly developed MCMP phase-change LB model, the problem of forced condensing flow on a horizontal cold plate at constant wall temperature in the presence of NCG is simulated. Effects of the NCG inlet fraction and plate subcooled temperature on forced Film condensation under the same inlet velocity are simulated. Condensate Film thickness, distributions of velocity/temperature/NCG fraction in the entire flow field, as well as condensation heat transfer on the cold plate are obtained numerically. The effect of an interfacial parameter (containing inlet NCG fraction and wall temperature) on Film thickness is shown in good agreement with an existing analytical model, which validates the correctness and accuracy of this newly developed MCMP phase-change LB model. Since this novel model does not involve any approximations/assumptions nor the use of empirical correlations for interfacial mass transfer, the results can be considered as the first attempt in the direct numerical simulation of laminar forced condensation heat transfer on a horizontal cold plate in the presence of a NCG.

  • lattice boltzmann simulation of steady laminar Film condensation on a vertical hydrophilic subcooled flat plate
    International Journal of Heat and Mass Transfer, 2013
    Co-Authors: Ping Cheng
    Abstract:

    Abstract Based on the newly developed phase-change Lattice Boltzmann method (LBM), the problem of steady laminar Film condensation on a hydrophilic vertical flat plate at a subcooled temperature is simulated in this paper. The effects of inertia force, interface shear stress and convection terms are fully taken into consideration in the LBM simulation. The Condensate Film thickness, velocity and temperature distributions, and heat transfer characteristics at steady state conditions are obtained numerically. The simulation results are found in good agreement with the classical analytical solutions. The deviations between the classical solutions and those of LBM simulation become somewhat larger at high Jakob numbers and low Prandtl numbers. The contact angle of the fluid with the surface is found to have very little effects on Film condensation. It is shown that the LBM can be applied to condensation problems successfully and accurately for the first time.

  • transition from annular flow to plug slug flow in condensation of steam in microchannels
    International Journal of Heat and Mass Transfer, 2008
    Co-Authors: Xiaojun Quan, Ping Cheng, Huiying Wu
    Abstract:

    Abstract A visualization study has been conducted to investigate the transition from annular flow to plug/slug flow in the condensation of steam in two different sets of parallel microchannels, having hydraulic diameters of 90 μm and 136 μm, respectively. The steam in the parallel microchannels was cooled on the bottom by forced convection of water and by natural convection of air from the top. It is found that the location, where the transition from annular flow to plug/slug flow takes place, depends on mass flux and cooling rate of steam. The effects of mass flux and cooling rate on the occurrence frequency of the injection flow in a single microchannel, having a hydraulic diameter of 120 μm and 128 μm, respectively, are investigated. It is found that two different shapes of injection flow occur in the smooth annular flow in microchannels: injection flow with unsteady vapor ligament occurring at low mass flux (or high cooling rate) and injection flow with steady vapor ligament occurring at high mass flux (or low cooling rate). It is also found that increase of steam mass flux, decrease of cooling rate, or decrease of the microchannel diameter tends to enhance instability of the Condensate Film on the wall, resulting in occurrence of the injection flow further toward the outlet with an increase in occurrence frequency.

  • instability of Condensate Film and capillary blocking in small diameter thermosyphon condensers
    International Journal of Heat and Mass Transfer, 1999
    Co-Authors: Ho Teng, Ping Cheng, Tianshou Zhao
    Abstract:

    Abstract Instability of the Condensate Film in a small-diameter-tube condenser was investigated by using an integro-differential approach. The disturbance wave parameters were predicted based on the characteristic equation derived in this study, and the results were in good agreement with the available experimental data reported in the literature. Capillary blocking taking place in a small-diameter-thermosyphon condenser was also examined. The proposed mechanism for capillary blocking reasonably explains the observed two-phase-flow phenomena during formation of capillary blocking.

Roger R Riehl - One of the best experts on this subject based on the ideXlab platform.

  • mathematical model of a loop heat pipe with cylindrical evaporator and integrated reservoir
    Applied Thermal Engineering, 2008
    Co-Authors: Valeri V Vlassov, Roger R Riehl
    Abstract:

    Abstract This paper presents a mathematical model of a loop heat pipe (LHP), which has been validated with experimental results. The LHP behavior was then predicted as a thermal control component of a satellite under different scenarios of orbital heat fluxes impression on the condenser–radiator. The mathematical model features the monitoring of the vapor–liquid front in the condenser, as well as the rate of flooding in the compensation chamber. The features of eventual entering of vapor phase in the liquid line and partial condensing of vapor in the vapor line is also embedded in the model. In the LHP condenser, the Condensate Film thickness in the tube is determined by the solution of the conjugate equations of energy, momentum and mass balance in the control volume, considering shear stress at the interface. Evaporator and compensation chamber are both described by a few transient nodes with generalized thermal and mass links, where the key parameters were adjusted by experimental test results. The evaporator, integrated with compensation chamber, consists of cylindrical stainless steel case with inserted an ultra-high molecular weight (UHMW) polyethylene primary wick and the secondary wick is made with stainless steel mesh. The condenser is a coiled tube thermally connected to an aluminum plate, having a radiator function; acetone was used as the working fluid. The tests conditions have been reproduced in the mathematical model and its parameters were adjusted in order to improve the model capacity to represent the real LHP operation.

  • mathematical model of a loop heat pipe with cylindrical evaporator and integrated reservoir
    Applied Thermal Engineering, 2008
    Co-Authors: Valeri V Vlassov, Roger R Riehl
    Abstract:

    Abstract This paper presents a mathematical model of a loop heat pipe (LHP), which has been validated with experimental results. The LHP behavior was then predicted as a thermal control component of a satellite under different scenarios of orbital heat fluxes impression on the condenser–radiator. The mathematical model features the monitoring of the vapor–liquid front in the condenser, as well as the rate of flooding in the compensation chamber. The features of eventual entering of vapor phase in the liquid line and partial condensing of vapor in the vapor line is also embedded in the model. In the LHP condenser, the Condensate Film thickness in the tube is determined by the solution of the conjugate equations of energy, momentum and mass balance in the control volume, considering shear stress at the interface. Evaporator and compensation chamber are both described by a few transient nodes with generalized thermal and mass links, where the key parameters were adjusted by experimental test results. The evaporator, integrated with compensation chamber, consists of cylindrical stainless steel case with inserted an ultra-high molecular weight (UHMW) polyethylene primary wick and the secondary wick is made with stainless steel mesh. The condenser is a coiled tube thermally connected to an aluminum plate, having a radiator function; acetone was used as the working fluid. The tests conditions have been reproduced in the mathematical model and its parameters were adjusted in order to improve the model capacity to represent the real LHP operation.

John R. Thome - One of the best experts on this subject based on the ideXlab platform.

  • numerical modeling of laminar annular Film condensation for different channel shapes
    International Journal of Heat and Mass Transfer, 2010
    Co-Authors: Stefano Nebuloni, John R. Thome
    Abstract:

    This paper presents a theoretical and numerical model to predict Film condensation heat transfer in mini and micro-channels of different internal shapes. The model is based on a finite volume formulation of the Navier-Stokes and energy equations and it includes the contributions of the unsteady terms, surface tension, axial shear stresses, gravitational forces and wall conduction. Notably, interphase mass transfer and near-to-wall effects (disjoining pressure) are also included. Dimensional analysis and characteristic numbers of the process are proposed and simulation results are shown both in dimensionless and dimensional representations. Isothermal, iso-heat flux and variable heat flux external wall boundary conditions have been implemented and their effects on the distribution of the heat flux are shown and compared. The instantaneous local and perimeter-averaged heat transfer coefficients, the liquid Condensate Film thickness distribution, the cross sectional void fraction and the mean vapor quality can be obtained for different channel shapes. Results obtained for steady state conditions are presented for circular, elliptical (with different eccentricities), flattened (with different aspect ratios) and flower shape cross sections for R-134a and ammonia, for hydraulic diameters between 10 pm and 3 mm. A time dependent simulation with variable heat flux is presented for a copper channel having a length of 4 cm and a rectangular cross section with a hydraulic diameter of 133 mu m and an aspect ratio of 2, showing the importance of axial conduction at this length scale. The model has been validated versus various benchmark cases and versus experimental data available in literature. (C) 2010 Elsevier Ltd. All rights reserved.

  • conjugate heat transfer in annular laminar Film condensation in microchannels comparison of numerical model to experimental results
    2010 14th International Heat Transfer Conference Volume 2, 2010
    Co-Authors: Stefano Nebuloni, John R. Thome
    Abstract:

    A comparison of the recently proposed numerical model for annular laminar Film condensation heat transfer in microchannels of different internal shapes (circular, square, rectangular, etc.), including the effects of conjugate heat conduction in the channel walls, is made versus recent independent experimental results experiencing this effect. Notably, the thinning of the Condensate Film induced by surface tension due to gravity forces and shape of the surface, also known as the ‘Grigorig’ effect, has a strong consequence on the local heat transfer coefficient in condensation. The model, which is based on a finite volume formulation of the Navier-Stokes and energy equations for the liquid phase only, accounts for the contributions of the surface tension, axial shear stresses and gravitational forces and for the conjugate effects of axial and peripheral wall conduction and nonuniform heat flux. The model was previously validated versus experimental data available in the literature without accounting for conjugate effects, predicting microchannel heat transfer data to within 20% or better. Specifically, the updated version of the model includes the coupling between the thin Film fluid dynamics, the heat transfer in the condensing fluid and the heat conduction in the channel wall. Since it is imperative to demonstrate that numerical heat transfer models are accurate and reliable, the present paper focuses on validating this new conjugate model versus recent actual experimental data for various small channels and test fluids experiencing this effect. The results are very encouraging and are presented here.Copyright © 2010 by ASME

  • conjugate heat transfer in annular laminar Film condensation in microchannels comparison of numerical model to experimental results
    2010 14th International Heat Transfer Conference Volume 2, 2010
    Co-Authors: Stefano Nebuloni, John R. Thome, Davide Del Col
    Abstract:

    A comparison of the recently proposed numerical model for annular laminar Film condensation heat transfer in microchannels of different internal shapes (circular, square, rectangular, etc.), including the effects of conjugate heat conduction in the channel walls, is made versus recent independent experimental results experiencing this effect. Notably, the thinning of the Condensate Film induced by surface tension due to gravity forces and shape of the surface, also known as the ‘Grigorig’ effect, has a strong consequence on the local heat transfer coefficient in condensation. The model, which is based on a finite volume formulation of the Navier-Stokes and energy equations for the liquid phase only, accounts for the contributions of the surface tension, axial shear stresses and gravitational forces and for the conjugate effects of axial and peripheral wall conduction and nonuniform heat flux. The model was previously validated versus experimental data available in the literature without accounting for conjugate effects, predicting microchannel heat transfer data to within 20% or better. Specifically, the updated version of the model includes the coupling between the thin Film fluid dynamics, the heat transfer in the condensing fluid and the heat conduction in the channel wall. Since it is imperative to demonstrate that numerical heat transfer models are accurate and reliable, the present paper focuses on validating this new conjugate model versus recent actual experimental data for various small channels and test fluids experiencing this effect. The results are very encouraging and are presented here.Copyright © 2010 by ASME