The Experts below are selected from a list of 17577 Experts worldwide ranked by ideXlab platform

Chengchou Shieh - One of the best experts on this subject based on the ideXlab platform.

  • flow pattern of air water and two phase r 134a in small circular tubes
    International Journal of Multiphase Flow, 2001
    Co-Authors: Chienyuh Yang, Chengchou Shieh
    Abstract:

    Abstract Experimental investigation of two-phase flow patterns for refrigerant R-134a and air–water in horizontal tubes with inside diameter from 1.0 to 3.0 mm was performed. The air–water test results agree very well with previous work. However, R-134a flow leads to a shift in the slug to annular transition to lower value of gas velocity. The locations of bubble to plug and slug flow transition are also significantly affected by the working fluids properties. We concluded that, in addition to buoyant Force and turbulent fluctuations, Surface Tension Force is also an important parameter for flow pattern determination in small tubes. Surface Tension Force causes the system to act to minimize its interfacial area. It tends to keep bubbles retaining its circular shapes and also to keep the liquid holdup between the tube walls to retard the transition from slug to annular. Since the Surface Tension of air–water is much larger than that of R-134a, it makes the intermittent to bubble flow transition occurs earlier for air–water than for R-134a. And also leads to a shift in the slug to annular transition to lower value of gas velocity for R-134a.

  • Flow pattern of air–water and two-phase R-134a in small circular tubes
    International Journal of Multiphase Flow, 2001
    Co-Authors: Chienyuh Yang, Chengchou Shieh
    Abstract:

    Abstract Experimental investigation of two-phase flow patterns for refrigerant R-134a and air–water in horizontal tubes with inside diameter from 1.0 to 3.0 mm was performed. The air–water test results agree very well with previous work. However, R-134a flow leads to a shift in the slug to annular transition to lower value of gas velocity. The locations of bubble to plug and slug flow transition are also significantly affected by the working fluids properties. We concluded that, in addition to buoyant Force and turbulent fluctuations, Surface Tension Force is also an important parameter for flow pattern determination in small tubes. Surface Tension Force causes the system to act to minimize its interfacial area. It tends to keep bubbles retaining its circular shapes and also to keep the liquid holdup between the tube walls to retard the transition from slug to annular. Since the Surface Tension of air–water is much larger than that of R-134a, it makes the intermittent to bubble flow transition occurs earlier for air–water than for R-134a. And also leads to a shift in the slug to annular transition to lower value of gas velocity for R-134a.

Wen Yu Yeh - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical investigation into condensation heat transfer on horizontal elliptical tube in stationary saturated vapor with wall suction
    Applied Thermal Engineering, 2011
    Co-Authors: Tong Bou Chang, Wen Yu Yeh
    Abstract:

    Abstract An analytical investigation is performed into the problem of steady filmwise condensation flow over the outer Surface of a horizontal elliptical tube with wall suction effects within a stationary saturated vapor. In performing the analysis, the liquid film flow is governed by the combined effects of the gravitational Force and the Surface Tension Force. To facilitate the analysis, an effective suction function is introduced to represent the effect of the wall suction on the thickness of the liquid film such that the local condensate film thickness and local Nusselt number can be derived using a simple numerical shooting method. It is found that the tube ellipticity and the wall suction effect have a significant influence on the mean Nusselt number. Moreover, the Surface Tension Force has a significant effect on the local Nusselt number, but a negligible effect on the mean Nusselt number. An analytical solution is derived for the mean Nusselt number in the absence of wall suction effects. Finally, a closed-form correlation is presented for the mean Nusselt number when the effects of wall suction are taken into account. It is shown that the maximum difference between the numerical results and the closed-form correlation results is less than 5%.

  • Effects of uniform suction and Surface Tension on laminar filmwise condensation on a horizontal elliptical tube in a porous medium
    International Journal of Thermal Sciences, 2009
    Co-Authors: Tong Bou Chang, Wen Yu Yeh
    Abstract:

    This study performs a theoretical investigation into the problem of steady filmwise condensation flow over the external Surface of a horizontal elliptical tube embedded in a porous medium with suction at the tube Surface. The combined effects of the Surface Tension Force and the gravitational Force in driving the flow of the liquid film within the porous medium are modeled using Darcy's law. An effective suction function, f, is introduced to model the effect of the suction Force at the wall on the thickness of the condensate film. The theoretical results presented in this study show that the heat transfer performance can be enhanced by applying a suction effect at the wall. Furthermore, it is shown that the Surface Tension Force has a negligible effect on the mean Nusselt number.

Junseok Kim - One of the best experts on this subject based on the ideXlab platform.

  • a generalized continuous Surface Tension Force formulation for phase field models for multi component immiscible fluid flows
    Computer Methods in Applied Mechanics and Engineering, 2009
    Co-Authors: Junseok Kim
    Abstract:

    We present a new phase-field method for modeling Surface Tension effects on multi-component immiscible fluid flows. Interfaces between fluids having different properties are represented as transition regions of finite thickness across which the phase-field varies continuously. At each point in the transition region, we define a Force density which is proportional to the curvature of the interface times a smoothed Dirac delta function. We consider a vector valued phase-field, the velocity, and pressure fields which are governed by multi-component advective Cahn–Hilliard and modified Navier–Stokes equations. The new formulation makes it possible to model any combination of interfaces without any additional decision criteria. It is general, therefore it can be applied to any number of fluid components. We give computational results for the four component fluid flows to illustrate the properties of the method. The capabilities of the method are computationally demonstrated with phase separations via a spinodal decomposition in a four-component mixture, pressure field distribution for three stationary drops, and the dynamics of two droplets inside another drop embedded in the ambient liquid.

  • a continuous Surface Tension Force formulation for diffuse interface models
    Journal of Computational Physics, 2005
    Co-Authors: Junseok Kim
    Abstract:

    We present a new Surface Tension Force formulation for a diffuse-interface model, which is derived for incompressible, immiscible Navier-Stokes equations separated by free interfaces. The classical infinitely thin boundary of separation between the two immiscible fluids is replaced by a transition region of small but finite width, across which the composition of the one of two fluids changes continuously. Various versions of diffuse-interface methods have been used successfully for the numerical simulations of two phase fluid flows. These methods are robust, efficient, and capable of computing interface singularities such as merging and pinching off. But prior studies used modified Surface Tension Force formulations, therefore it is not straightforward to calculate pressure field because pressure includes the gradient terms resulting from the modified Surface Tension term. The new formulation allows us to calculate the pressure field directly from the governing equations. Computational results showing the accuracy and effectiveness of the method are given for a drop deformation and Rayleigh capillary instability.

Chienyuh Yang - One of the best experts on this subject based on the ideXlab platform.

  • flow pattern of air water and two phase r 134a in small circular tubes
    International Journal of Multiphase Flow, 2001
    Co-Authors: Chienyuh Yang, Chengchou Shieh
    Abstract:

    Abstract Experimental investigation of two-phase flow patterns for refrigerant R-134a and air–water in horizontal tubes with inside diameter from 1.0 to 3.0 mm was performed. The air–water test results agree very well with previous work. However, R-134a flow leads to a shift in the slug to annular transition to lower value of gas velocity. The locations of bubble to plug and slug flow transition are also significantly affected by the working fluids properties. We concluded that, in addition to buoyant Force and turbulent fluctuations, Surface Tension Force is also an important parameter for flow pattern determination in small tubes. Surface Tension Force causes the system to act to minimize its interfacial area. It tends to keep bubbles retaining its circular shapes and also to keep the liquid holdup between the tube walls to retard the transition from slug to annular. Since the Surface Tension of air–water is much larger than that of R-134a, it makes the intermittent to bubble flow transition occurs earlier for air–water than for R-134a. And also leads to a shift in the slug to annular transition to lower value of gas velocity for R-134a.

  • Flow pattern of air–water and two-phase R-134a in small circular tubes
    International Journal of Multiphase Flow, 2001
    Co-Authors: Chienyuh Yang, Chengchou Shieh
    Abstract:

    Abstract Experimental investigation of two-phase flow patterns for refrigerant R-134a and air–water in horizontal tubes with inside diameter from 1.0 to 3.0 mm was performed. The air–water test results agree very well with previous work. However, R-134a flow leads to a shift in the slug to annular transition to lower value of gas velocity. The locations of bubble to plug and slug flow transition are also significantly affected by the working fluids properties. We concluded that, in addition to buoyant Force and turbulent fluctuations, Surface Tension Force is also an important parameter for flow pattern determination in small tubes. Surface Tension Force causes the system to act to minimize its interfacial area. It tends to keep bubbles retaining its circular shapes and also to keep the liquid holdup between the tube walls to retard the transition from slug to annular. Since the Surface Tension of air–water is much larger than that of R-134a, it makes the intermittent to bubble flow transition occurs earlier for air–water than for R-134a. And also leads to a shift in the slug to annular transition to lower value of gas velocity for R-134a.

Tong Bou Chang - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical investigation into condensation heat transfer on horizontal elliptical tube in stationary saturated vapor with wall suction
    Applied Thermal Engineering, 2011
    Co-Authors: Tong Bou Chang, Wen Yu Yeh
    Abstract:

    Abstract An analytical investigation is performed into the problem of steady filmwise condensation flow over the outer Surface of a horizontal elliptical tube with wall suction effects within a stationary saturated vapor. In performing the analysis, the liquid film flow is governed by the combined effects of the gravitational Force and the Surface Tension Force. To facilitate the analysis, an effective suction function is introduced to represent the effect of the wall suction on the thickness of the liquid film such that the local condensate film thickness and local Nusselt number can be derived using a simple numerical shooting method. It is found that the tube ellipticity and the wall suction effect have a significant influence on the mean Nusselt number. Moreover, the Surface Tension Force has a significant effect on the local Nusselt number, but a negligible effect on the mean Nusselt number. An analytical solution is derived for the mean Nusselt number in the absence of wall suction effects. Finally, a closed-form correlation is presented for the mean Nusselt number when the effects of wall suction are taken into account. It is shown that the maximum difference between the numerical results and the closed-form correlation results is less than 5%.

  • Effects of uniform suction and Surface Tension on laminar filmwise condensation on a horizontal elliptical tube in a porous medium
    International Journal of Thermal Sciences, 2009
    Co-Authors: Tong Bou Chang, Wen Yu Yeh
    Abstract:

    This study performs a theoretical investigation into the problem of steady filmwise condensation flow over the external Surface of a horizontal elliptical tube embedded in a porous medium with suction at the tube Surface. The combined effects of the Surface Tension Force and the gravitational Force in driving the flow of the liquid film within the porous medium are modeled using Darcy's law. An effective suction function, f, is introduced to model the effect of the suction Force at the wall on the thickness of the condensate film. The theoretical results presented in this study show that the heat transfer performance can be enhanced by applying a suction effect at the wall. Furthermore, it is shown that the Surface Tension Force has a negligible effect on the mean Nusselt number.