Parametric Study of Turbulent Separated Convection Flow Over a Backward-Facing Step in a Duct

2007 ◽  
Author(s):  
Jianhu Nie ◽  
Yitung Chen ◽  
Robert F. Boehm ◽  
Hsuan-Tsung Hsieh
Keyword(s):  
Heat Transfer ◽  
Friction Coefficient ◽  
Prandtl Number ◽  
Inclination Angle ◽  
Stanton Number ◽  
Step Height ◽  
Recirculation Region ◽  
Convection Flow ◽  
Backward Facing Step ◽  
Simulation Code

Simulations of turbulent convection flow adjacent to a two dimensional backward-facing step are presented to explore the effects of step height, step inclination angle, a mounted rib and Prandtl number on velocity field and heat transfer. Reynolds number and duct’s height downstream from the step are kept constant at Re0 = 28000 and H = 0.19m, respectively. Uniform and constant heat flux of qw = 270W/m2 is specified at the stepped wall downstream from the step, while other walls are treated as adiabatic. The selection of the values for these parameters is motivated by the fact that measurements are available for this geometry and they can be used to validate the flow and heat transfer simulation code. The simulated results compare very well the measurements. The primary and secondary recirculation regions increase in size as the step height increases. The friction coefficient becomes smaller in magnitude with the increase of the step height. The peak Stanton number becomes smaller as the step height increases. The reattachment location becomes longer as the step inclination angle increases. With increase of the step inclination angle, the secondary recirculation region disappears. The peak friction coefficient inside the primary recirculation region becomes smaller as the step inclination angle decreases. Installation of a baffle on the upper wall causes the primary recirculation region to become smaller. The Stanton number decreases as the Prandtl number increases.

Heat Transfer Enhancement of Separated Convection Flow Adjacent to Backward-Facing Step With Baffle

2006 ◽  
Author(s):  
Jianhu Nie ◽  
Yitung Chen ◽  
Lijian Sun ◽  
Hsuan-Tsung Hsieh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Three Dimensional ◽  
Constant Heat Flux ◽  
Convection Flow ◽  
Spanwise Direction ◽  
Streamwise Direction ◽  
Backward Facing Step ◽  
Laminar Forced Convection

Simulations of three-dimensional laminar forced convection adjacent to inclined backward-facing step in rectangular duct are presented to examine effects of the baffle on flow and heat transfer distributions. The step height is maintained as constant. A baffle is mounted onto the upper wall and its distance from the backward-facing step is varied. The inlet flow is hydrodynamically steady and fully developed with uniform temperature. The bottom wall is heated with constant heat flux, while other walls are maintained as being thermally adiabatic. Velocity, temperature, Nusselt number, and friction coefficient distributions are presented. A baffle mounted onto the upper wall increases the magnitude of maximum Nuselt number at the stepped wall. One segment of the xu-line developing close to the backward-facing step becomes shorter with the decrease of the distance of the baffle from the backward-facing step. It becomes more relatively uniform in the spanwise direction as the distance decreases. The other segment developing adjacent to the sidewall moves further downstream as the baffle moves in the streamwise direction. The maximum Nusselt number does not appear at the center of the duct, as one may expect. It develops near the sidewall, and it moves further downstream as the location of the baffle moves in the streamwise direction. The friction coefficient at the stepped wall decreases as the distance of the baffle from the inlet increases.

scholarly journals Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhanwei Liu ◽  
Xinyu Li ◽  
Tenglong Cong ◽  
Rui Zhang ◽  
Lingyun Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Liquid Sodium ◽  
Heat Transfer Characteristics ◽  
Backward Facing Step ◽  
Heating Wall ◽  
Transfer Characteristics ◽  
Cfd Models ◽  
Flow And Heat Transfer

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

Lattice Boltzmann Computations of Natural Convection Heat Transfer of Nanofluid in a Square Cavity Heated by Protruding Heat Source

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Mustapha Faraji ◽  
El Mehdi Berra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Inclination Angle ◽  
Lattice Boltzmann ◽  
Base Fluid ◽  
Numerical Code ◽  
Convection Flow ◽  
Square Enclosure ◽  
Rayleigh Numbers

Abstract This paper reported the mathematical modeling and numerical simulation of natural convection flow of Cu/water nanofluid in a square enclosure using the lattice Boltzmann method (LBM). The cavity is heated from below by heat source and cooled by the top wall. The vertical walls are adiabatic. After validating the numerical code against the numerical and experimental data, simulations were performed for different Rayleigh numbers (104–0.5 × 107), nanoparticles volume fractions (0–8%), and cavity inclination angle (0 deg–90 deg). The effects of the studied parameters on the streamlines, on isotherms distributions within the enclosure, and on the local and average Nusselt numbers are investigated. It was found that heat transfer and fluid flow structure depend closely on the nanoparticle concentration. Results show differences in stream separation between a base fluid and the nanofluid. Also, adding small nanoparticles fractions, less than 6%, to the base fluid enhances the heat transfer for higher Rayleigh numbers and cavity inclination angle less than 30 deg. It is concluded that the optimal dilute suspension of copper nanoparticles can be applied as a passive way to enhance heat transfer in natural convection engineering applications.

Convection Heat Transfer of Power-Law Fluids Along the Inclined Nonuniformly Heated Plate With Suction or Injection

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Jize Sui ◽  
Liancun Zheng ◽  
Xinxin Zhang
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Skin Friction ◽  
Power Law ◽  
Inclination Angle ◽  
Convection Heat Transfer ◽  
Heated Plate ◽  
Convection Heat ◽  
Power Law Fluids ◽  
Suction Or Injection

A comprehensive analysis to convection heat transfer of power-law fluids along the inclined nonuniformly heated plate with suction or injection is presented. The effects of power-law viscosity on temperature field are taken into account in highly coupled velocity and temperature fields. Analytical solutions are established by homotopy analysis method (HAM), and the effects of pertinent parameters (velocity power-law exponent, temperature power index, suction/injection parameter, and inclination angle) are analyzed. Some new interesting phenomena are found, for example, unlike classical boundary layer problem in which the skin friction monotonically increases (decreases) with suction increases (injection increases), but there exists a special region where the skin friction is not monotonic, which is strongly bound up with Prandtl number, which have never been reported before. The nonmonotony occurs in suction region for Prandtl number Npr < 1 and injection region for Npr > 1. Results also illustrate that the velocity profile decreases but the heat convection is enhanced obviously with increasing in temperature power exponent m (generalized Prandtl number Npr has similar effects), the decreases in inclination angle lead to the reduction in convection and heat transfer efficiency.

Natural Convection Between Two Horizontal Cylinders in an Adiabatic Circular Enclosure

1993 ◽  
Vol 115 (1) ◽  
pp. 158-165 ◽  
Author(s):  
C. J. Ho ◽  
W. S. Chang ◽  
C. C. Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Inclination Angle ◽  
Numerical Study ◽  
Convection Flow ◽  
Vertical Orientation ◽  
Recirculating Flow ◽  
Visualization Experiments ◽  
Horizontal Cylinders ◽  
Gap Width

A numerical study of natural convection flow structure and heat transfer has been undertaken for air around two horizontal, differentially heated cylinders confined to an adiabatic circular enclosure. Parametric simulations were performed to assess the effects of gap width between cylinders as well as the inclination angle of the enclosure with respect to gravity. Results clearly indicate that the fluid flow complexity and heat transfer characteristics of air amid the cylinders and enclosure wall are strongly affected by the Rayleigh number, the inclination angle, and the gap width between the cylinders. With the exception of the vertical orientation, heat exchange between the differentially heated cylinders is predominantly controlled by a counterclockwise recirculating flow enclosing them. In addition, flow visualization experiments were conducted for the physical configuration under consideration, and a generally good agreement for the flow pattern was observed between the predictions and the experiments, further validating the present numerical simulation.

scholarly journals Effect of Temperature-Dependent Variable Viscosity on Magnetohydrodynamic Natural Convection Flow along a Vertical Wavy Surface

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Nazma Parveen ◽  
Md. Abdul Alim
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Variable Viscosity ◽  
Skin Friction Coefficient ◽  
Effect Of Temperature ◽  
Convection Flow ◽  
Temperature Dependent ◽  
Natural Convection Flow

The effect of temperature dependent variable viscosity on magnetohydrodynamic (MHD) natural convection flow of viscous incompressible fluid along a uniformly heated vertical wavy surface has been investigated. The governing boundary layer equations are first transformed into a nondimensional form using suitable set of dimensionless variables. The resulting nonlinear system of partial differential equations are mapped into the domain of a vertical flat plate and then solved numerically employing the implicit finite difference method, known as Keller-box scheme. The numerical results of the surface shear stress in terms of skin friction coefficient and the rate of heat transfer in terms of local Nusselt number, the stream lines and the isotherms are shown graphically for a selection of parameters set consisting of viscosity parameter (), magnetic parameter (), and Prandtl number (Pr). Numerical results of the local skin friction coefficient and the rate of heat transfer for different values are also presented in tabular form.

Radiation effect on heat transfer over a stretching surface

2000 ◽  
Vol 78 (12) ◽  
pp. 1107-1112 ◽  
Author(s):  
E MA Elbashbeshy
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Radiation Effect ◽  
Convection Flow ◽  
Radiation Parameter ◽  
Stretching Surface ◽  
Boundary Layer Equations ◽  
Temperature Parameter ◽  
Forced Convection Flow

We determine the effect of radiation on the forced convection flow of an optically dense incompressible fluid along a heated horizontal stretching surface. The boundary-layer equations are transformed to ordinary differential equations containing a radiation parameter R*, velocity exponent parameter M, Prandtl number P r, and surface temperature parameter θ ω. The effect of these parameters are studied. Graphical results for the velocity and temperature are presented and discussed. PACS Nos.: 44.40+a, 47.27-i

scholarly journals The Influence of the Recirculation Region: A Comparison of the Convective Heat Transfer Downstream of a Backward-Facing Step and Behind a Jet in a Cross Flow

1989 ◽  
Author(s):  
V. Scherer ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cross Flow ◽  
Separated Flows ◽  
Numerical Code ◽  
Recirculation Region ◽  
Backward Facing Step ◽  
Nusselt Numbers ◽  
Wide Range

Convective heat transfer is examined in two typical examples of separated flows, namely: the flow over a backward-facing step and a two-dimensional jet entering a cross flow. Local Nusselt numbers were determined in and behind the recirculation region. The main parameters influencing the heat transfer, the Reynolds number and the momentum flux ratio of the jet and the cross flow, have been varied in a wide range. In addition to heat transfer measurements, the flow field has been documented using a LDA-system and oil film techniques. The static pressure distribution at the wall within the separated flow is also given. The measurements are compared with the results of a numerical code, based on a finite volume method, where the well known k-ε-model is employed. The differences in Nusselt numbers predicted with a one- and a two-layer model are shown to demonstrate the influence of wall functions on heat transfer. The numerical and experimental results are compared with available data, and the differences and similarities in the heat transfer behaviour of separated flows are discussed.

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