Flow In Rectangular Duct Research Articles

A Calculation Method for Developing Turbulent Flow in Rectangular Ducts of Arbitrary Aspect Ratio

This paper describes a full Reynolds stress transport equation model for predicting developing turbulent flow in rectangular ducts. The pressure-strain component of the model is based on a modified form of the Launder, Reece and Rodi pressure-strain model and the use of a linear wall damping function. Predictions based on this model are compared with predictions referred to high Reynolds number and low Reynolds number k–ε transport equation models and with experimental data taken in square and rectangular ducts. The results indicate that the proposed model yields improved predictions of primary flow development and Reynolds stress behavior in a square duct. The proposed model also yields Reynolds stress anisotropy and secondary flow levels that are compatible and agree well with experiment, without recourse to a quadratic damping function to model near-wall pressure-strain behavior.

Application of High-Frame-Rate Neutron Radiography with a Steady Thermal Neutron Beam to Two-Phase Flow Measurements in a Metallic Rectangular Duct

To apply the neutron radiography (NRG) technique to fluid research, high-frame-rate NRG with a steady thermal neutron beam was developed by gathering up-to-date technologies for neutron sources, scintillators, high-speed videos, and image intensifiers. This imaging system has many advantages such as a long recording time, high-frame-rate (up to 1,000 frame/s) imaging, and no need for a triggering signal. Visualization of air water two-phase flow in a metallic rectangular duct was achieved at the recording speeds of 250, 500, and 1,000 frame/s. The qualities of those consecutive images were good enough to observe the flow mechanism and to measure the flow characteristics. It was demonstrated that some characteristics of two-phase flow could be measured by using the current imaging system. To quantify geometric information from NRG images, measurements of flow regime, rising velocity of bubbles and wave height, interfacial length, and interfacial area in annular flow were performed by using the image processing technique. To quantify attenuation characteristics of neutrons in materials, measurements of average void fraction and void profile were conducted. It was confirmed that this new technique may have significant advantages in both visualizing and measuring high-speed fluid phenomena when the ordinary methods such as the optical method andmore » X-ray radiography cannot be applied.« less

Prediction of Turbulent Flow and Heat Transfer in a Ribbed Rectangular Duct With and Without Rotation

The present study deals with the numerical prediction of turbulent flow and heat transfer in a 2:1 aspect ratio rectangular duct with ribs on the two shorter sides. The ribs are of square cross section, staggered and aligned normal (90 deg) to the main flow direction. The ratio of rib height to duct hydraulic diameter equals 0.063, and the ratio of rib spacing to rib height equals 10. The duct may be stationary or rotating. The axis of rotation is normal to the axis of the duct and parallel to the ribbed walls (i.e., the ribbed walls form the leading and the trailing faces). The problem is three dimensional and fully elliptic; hence, for computational economy, the present analysis deals only with a periodically fully developed situation where the calculation domain is limited to the region between two adjacent ribs. Turbulence is modeled with the k–ε model in conjunction with wall functions. However, since the rib height is small, use of wall functions necessitates that the Reynolds number be kept high. (Attempts to use a two-layer model that permits integration to the wall did not yield satisfactory results and such modeling issues are discussed at length.) Computations are made here for Reynolds number in the range 30,000–100,000 and for Rotation number = 0 (stationary), 0.06, and 0.12. For the stationary case, the predicted heat transfer agrees well with the experimental correlations. Due to the Coriolis-induced secondary flow, rotation is found to enhance heat transfer from the trailing and the side walls, while decreasing heat transfer from the leading face. Relative to the corresponding stationary case, the effect of rotation is found to be less for a ribbed channel as compared to a smooth channel.

MHD flow in rectangular ducts with inclined non-uniform transverse magnetic field

Abstract This paper examines the three-dimensional liquid metal MHD flow in rectangular ducts with thin conducting walls and with an inclined non-uniform transverse magnetic field. The Hartmann number and interaction parameter are assumed to be large and the magnetic Reynolds number is assumed to be small. Under these assumptions, viscous and inertial effects are confined to thin boundary layers adjacent to the walls. Outside these layers, the governing equations are significantly simplified. For validation of the numerical solutions, exact analytical solutions are derived for the case of a rectangular duct of equal wall thickness and with a uniform magnetic field. Comparisons of the exact analytical and numerical solutions give excellent agreement. Variation of the fully developed flow pressure gradient with the wall conductance ratio, aspect ratio, and magnetic angle is discussed. Numerical solutions are presented for flow in the varying field region where the flow is perturbed due to three-dimensional effects. The three-dimensional pressure drop, i.e. in excess of the locally fully developed pressure, is presented and its implication to a fusion blanket is discussed. The velocity distributions are also presented.

MHD flow in rectangular ducts with inclined non-uniform transverse magnetic field

Abstract This paper examines the three-dimensional liquid metal MHD flow in rectangular ducts with thin conducting walls and with an inclined non-uniform transverse magnetic field. The Hartmann number and interaction parameter are assumed to be large and the magnetic Reynolds number is assumed to be small. Under these assumptions, viscous and inertial effects are confined to thin boundary layers adjacent to the walls. Outside these layers, the governing equations are significantly simplified. For validation of the numerical solutions, exact analytical solutions are derived for the case of a rectangular duct of equal wall thickness and with a uniform magnetic field. Comparisons of the exact analytical and numerical solutions give excellent agreement. Variation of the fully developed flow pressure gradient with the wall conductance ratio, aspect ratio, and magnetic angle is discussed. Numerical solutions are presented for flow in the varying field region where the flow is perturbed due to three-dimensional effects. The three-dimensional pressure drop, i.e. in excess of the locally fully developed pressure, is presented and its implication to a fusion blanket is discussed. The velocity distributions are also presented.

Magnetohydrodynamics and heat transfer benchmark problems for liquid-metal flow in rectangular ducts

Abstract This paper describes four benchmark problems to validate magnetohydrodynamic and heat transfer computer codes. The problems include rectangular duct geometry with uniform and non-uniform magnetic fields, with and without surface heat flux, and various rectangular cross-sections. Two of the problems are based on experiments. Participants in this benchmarking activity come from three countries: Russia, USA and Japan. The solution methods to the problems are described. Results from the different computer codes are presented and compared.

Simultaneously developing mixed convection in radially rotating rectangular ducts

The present work is concerned with a numerical study on laminar mixed convection flow and heat transfer in the entrance region of rotating isothermal rectangular ducts. The emphasis is placed on the rotational effects, including both the Coriolis force and centrifugal buoyancy, on non-isothermal flow and related heat transfer. The numerical results are presented for air flow in rectangular ducts over a wide range of the parameters. By examining the local field-solutions, the mechanisms for influences of Coriolis and centrifugal buoyancy forces can be addressed in detail. The results reveal that the variations of the local friction factor and heat transfer rate are closely related to the emergence, disappearance, growth, and decay of the rotation-induced secondary vortices. The friction factor and heat transfer rate can be enhanced by Coriolis effect. The predictions also demonstrate that the centrifugal buoyancy presents remarkable effects on the axial evolution of secondary vortices and, therefore, on the flow and heat transfer characteristics in a radially rotating duct. The buoyancy effects are different on the trailing, leading and side walls; and the rotational effects can be altered with the change in cross-sectional aspect-ratio.

Magnetohydrodynamics and heat transfer benchmark problems for liquid-metal flow in rectangular ducts

Magnetohydrodynamics and heat transfer benchmark problems for liquid-metal flow in rectangular ducts

Buoyancy Effect on the Flow Reversal of Three-Dimensional Developing Flow in a Vertical Rectangular Duct—A Parabolic Model Solution

Buoyancy Effect on the Flow Reversal of Three-Dimensional Developing Flow in a Vertical Rectangular Duct—A Parabolic Model Solution

Cooling panel optimization for the active cooling system of a hypersonic aircraft

Optimization of cooling panels for an active cooling system of a hypersonic aircraft is explored. The flow passages are of rectangular cross section with one wall heated. An analytical fin-type model for incompressible flow in smooth-wall rectangular ducts with coupled wall conduction is proposed. Based on this model, the a flow rate of coolant to each design minimum mass flow rate or coolant for a single cooling panel is obtained by satisfying hydrodynamic, thermal, and Mach number constraints. Also, the sensitivity of the optimal mass flow rate of coolant to each design variable is investigated. In addition, numerical solutions for constant property flow in rectangular ducts, with one side rib-roughened and coupled wall conduction, are obtained using a k-epsilon and wall function turbulence model, these results are compared with predictions of the analytical model.

95/00697 Developing flow and heat transfer in a rectangular duct with a moving wall

95/00697 Developing flow and heat transfer in a rectangular duct with a moving wall

Friction Factor for Flow in Rectangular Ducts With One Side Rib-Roughened

Numerical simulations of incompressible turbulent flow through rectangular ducts with one side rib-roughened were performed to determine pressure drop. The “PHOENICS” software package was used for the computations, which required provision of a wall function for transverse rib-roughened surfaces. The present study was conducted in the range of 105≤ Reynolds number ≤ 107, 0.01 ≤ rib height to hydraulic diameter ratio ≤ 0.04, 10≤ pitch to rib height ratio ≤ 40. Using the numerical results, friction factor charts for various aspect ratios were generated. The numerical results agreed well with experimental data that was obtained for 105 < Reynolds number < 2 × 105. In addition, a scheme for predicting friction factor using existing correlations for smooth and rough walls was developed.

On the elimination of wall-topography parameters from second-moment closure

Current generation second-moment closures employ wall proximity/orientation parameters to ensure that the velocity fluctuations normal to the wall die out as the wall is approached faster than fluctuations parallel to the wall. The use of such devices renders the models unsuitable for application to surfaces of even moderately complex shape. It is argued that, for the case of flow parallel to the wall, no such parameters are needed if one adopts a model of the pressure–strain process that rigorously satisfies the two-component limit. The assertion is supported by computations of flow in square and rectangular ducts as well as for the low-Reynolds-number plane channel flow.

Numerical Analysis of Fully Developed Turbulent Flow in Rectangular Duct with Longitudinal Roughness Element.

A numerical analysis has been performed on developing turbulent flow in a rectangular duct of aspect ratio 2.25 : 1, two of whose long-side walls were roughened. Roughness elements with trapezoidal cross section were located along the strearmwise direction. In the calculation, an algebraic stress model was adopted in order to predict Reynolds stresses precisely, and a boundary-fitted coordinate system was introduced to briefly set the boundary conditions. Calculated results were compared with the experimental data available. As a result of this calculation, it was found that the present method could predict streamwise velocity and secondary flow well. The intensity of the secondary flow near the longitudinal roughness element was greater than that in the corner region. This phenomenon strongly suggests that a duct with a longitudinal roughness element is applicable for promoting heat and mass transfer without increasing pressure drop.

Correlation of Mass Transfer Coefficient in Stratified Gas‐Liquid Two‐Phase Flow in a Horizontal Rectangular Duct

AbstractLiquid‐side mass transfer coefficients were determined using a horizontal rectangular duct (3cm x 3cm and 4m length) with carbon dioxide desorbing from water and from aqueous solutions of malt syrup. Simultaneously, measurements were made of the parameters characterizing the liquid film flow such as the liquid film thickness and surface velocity. Experiments were mainly conducted within the range of stratified gas‐liquid two‐phase flow. Based on the analogy between mass and momentum transfer at the liquid film surface, the experimental data for the liquid‐side mass transfer coefficient were correlated with the liquid‐film flow velocity. In order to estimate the parameters of film flow, a correlation for the average film thickness was obtained, and the surface velocity was represented graphically as a function of the gas velocity, slip velocity and superficial liquid Reynolds number.

Characteristics of flow and heat transfer in air-mercury two-phase stratified flow under a vertical magnetic field

For cooling of the first wall and blanket in a magnetic confinement fusion reactor, the use of a helium-lithium annular-mist flow is proposed to mitigate the effects of a strong magnetic field on magnetohydrodynamic (MHD) pressure drop and the deterioration of heat transfer due to laminarization. In annular-mist flow, the magnetic field has mainly an effect on film flow of liquid lithium near the wall region. Instead of the helium-lithium annular-mist flow at high temperature, an air-mercury stratified flow in a horizontal rectangular duct in a vertical magnetic field was investigated to get more detailed information on the characteristics of interfacial waves, MHD pressure drop, and heat transfer. Below 0.4 tesla, when the magnetic flux density increases, the pressure drop decreases due to laminarization of mercury flow and damping of the interfacial waves. However, it increases above 0.5 T due to both the Hartmann flow effect and the increment in the mercury layer thickness. A new correlation was obtained for pressure drop multipliers in two-phase MHD flow. As the magnetic flux density increases, the heat transfer coefficient decreases monotonously and becomes about half of its initial value in the high magnetic flux density. however, when the gas Reynolds number is increased, the heat transfer deterioration is suppressed until the magnetic flux density becomes high enough. Criteria of Nusselt number deterioration under a magnetic field were obtained in various flow conditions. A computational analysis using the κ-ϵ turbulence model including magnetic effect terms was tried and compared with the experimental values of temperature profiles and heat transfer coefficients. The computational results agreed well with the experimental values in the condition with negligible interfacial waves.

Unsteady behavior and mass transfer performance of the combined convective flow in a horizontal rectangular duct heated from below

This paper reports a research for the mixed-convective flow and its mass transfer performance controlled by a preset side-wall temperature profile in a horizontal rectangular duct heated from below, which simulates a horizontal thermal Chemical Vapor Deposition (CVD) reactor. The experiment is carried out in a fully developed region at a Rayleigh number of about 3.4 × 10 5 to reveal various flow patterns depending on Reynolds number and the temperature profile on the side walls. Various unsteady flows are shown to be chaotic by calculating a set of Liapunov exponents from the observed time series of fluid temperature. In the case of an unsteady flow with time-averaged uniform temperature, the time-averaged mass transfer rate on the bottom wall of the duct becomes almost uniform in both the spanwise and the streamwise direction.

Characteristics of flow and heat transfer in air-mercury two-phase stratified flow under a vertical magnetic field

Abstract For cooling of the first wall and blanket in a magnetic confinement fusion reactor, the use of a helium-lithium annular-mist flow is proposed to mitigate the effects of a strong magnetic field on magnetohydrodynamic (MHD) pressure drop and the deterioration of heat transfer due to laminarization. In annular-mist flow, the magnetic field has mainly an effect on film flow of liquid lithium near the wall region. Instead of the helium-lithium annular-mist flow at high temperature, an air-mercury stratified flow in a horizontal rectangular duct in a vertical magnetic field was investigated to get more detailed information on the characteristics of interfacial waves, MHD pressure drop, and heat transfer. Below 0.4 tesla, when the magnetic flux density increases, the pressure drop decreases due to laminarization of mercury flow and damping of the interfacial waves. However, it increases above 0.5 T due to both the Hartmann flow effect and the increment in the mercury layer thickness. A new correlation was obtained for pressure drop multipliers in two-phase MHD flow. As the magnetic flux density increases, the heat transfer coefficient decreases monotonously and becomes about half of its initial value in the high magnetic flux density. however, when the gas Reynolds number is increased, the heat transfer deterioration is suppressed until the magnetic flux density becomes high enough. Criteria of Nusselt number deterioration under a magnetic field were obtained in various flow conditions. A computational analysis using the κ-ϵ turbulence model including magnetic effect terms was tried and compared with the experimental values of temperature profiles and heat transfer coefficients. The computational results agreed well with the experimental values in the condition with negligible interfacial waves.

Heat and fluid flow in rectangular solar air heater ducts having transverse rib roughness on absorber plates

An experimental investigation has been carried out to determine the effect of transverse wire roughness on heat and fluid flow characteristics in transitionally rough flow region (5 < e+ < 70) for rectangular solar air heater ducts with an absorbec plate having transverse wire roughness on its underside. The investigation covered a Reynolds number range of 3000–18000 for a duct aspect ratio of 6.8–11.5, relative roughness height of 0.018–0.052 at a relative roughness pitch of 10 encompassing a range of roughness Reynolds number between 5–70. Simple correlations for a Nusselt number and friction factor have been developed in terms of geometrical parameters of roughness, duct cross section, and the flow Reynolds number.

Some characteristics of gas-liquid flow in narrow rectangular ducts

Flow regime, void fraction, slug bubble velocity and pressure loss were measured for rectangular ducts with a narrow gap and a large aspect ratio. The neutron radiography technique was used to visualize the flow and the void fraction was obtained by image processing. The void fraction was well-correlated by the drift flux model with the existing correlation for the distribution parameter, which was about 1.35. Similar results were obtained for the slug bubble velocity, however the distribution parameter was in the range 1.0–1.2. The frictional pressure loss was well-correlated by the Chisholm-Laird correlation. In collaboration with previously obtained data, it was found that the Chisholm's parameter C, however, changed from 21 to 0 as the gap decreased.