Heat transfer to laminar flow over a double backward-facing step

Heat transfer and laminar air flow over a double backward-facing step numerically studied in this paper. The simulations was performed by using ANSYS ICEM for meshing process and using ANSYS fluent 14 (CFD) for solving. The k-ɛ standard model adopted with Reynolds number varied between 98.5 to 512 and three step height at constant heat flux (q=2000 W/m2). The top of wall and bottom of upstream are insulated with bottom of downstream is heated. The results show increase in Nusselt number with increases of Reynolds number for all cases and the maximum of Nusselt number happens at the first step in compared to the second step. Due to increase of cross section area of downstream to generate sudden expansion then Nusselt number decrease but the profile of Nusselt number keep same trend for all cases where increase after the first and second steps. Recirculation region after the first and second steps are denoted by contour of streamline velocity. The higher augmentation of heat transfer rate observed for case 1 at Reynolds number of 512 and heat flux q=2000 W/m2

CFD Simulation of Heat Transfer and Turbulent Fluid Flow over a Double Forward-Facing Step

Heat transfer and turbulent water flow over a double forward-facing step were investigated numerically. The finite volume method was used to solve the corresponding continuity, momentum, and energy equations using the K-ε model. Three cases, corresponding to three different step heights, were investigated for Reynolds numbers ranging from 30,000 to 100,000 and temperatures ranging from 313 to 343 K. The bottom of the wall was heated, whereas the top was insulated. The results show that the Nusselt number increased with the Reynolds number and step height. The maximum Nusselt number was observed for case 3, with a Reynolds number of 100,000 and temperature of 343 K, occurring at the second step. The behavior of the Nusselt number was similar for all cases at a given Reynolds number and temperature. A recirculation zone was observed before and after the first and second steps in the contour maps of the velocity field. In addition, the results indicate that the coefficient pressure increased with increasing Reynolds number and step height. ANSYS FLUENT 14 (CFD) software was employed to run the simulations

A CFD study of turbulent heat transfer and fluid flow through the channel with semicircle rib

In the present paper turbulent heat transfer and fluid flow through the channel with semicircle ribs numerically studied. The SST k-ω turbulence Model with finite volume method was employed in simulation. The adopted boundary condition considered step heights of ribs varied from 2.5mm to 10mm with pitch ratio different from 2.5 to 40 and flow Reynolds number between 10000 to 25000 at constant surface temperature. The computational results showed recirculation region after each ribs which effect on performance of heat transfer rate. Increase of Reynolds number and number of ribs leads to increase in heat transfer coefficient. Step height and pitch ratio of ribs increase local heat transfer coefficient along the channel. This simulation has been done by ANSYS 14 FLUENT

Numerical study of turbulent heat transfer in separated flow: review

The numerical studies of turbulent heat transfer in separation flow presented in this paper. Enhancement of heat transfer rate in turbulent separation flow at sudden expansion in passage, over forward or backward facing-steps, blunt body, ribs channel, and swirl generators in channels were investigated numerically. Different models (CFD) used to study heat transfer characteristics and fluid flow in separation and reattachment region and compared results with previous experimental data. The effect of expansion ratio, Reynolds number, step height, (shape, number, and angle) of ribs and (length, twist angle, and gap width) twist the tape on improvement of heat transfer were referred. The numerical results indicated increases of heat transfer coefficients with increases in the above parameters. The numerical simulations derived from finite volume, element, and difference methods for evaluation of turbulent heat transfer in separated flow and employed several computational programs

MHD natural convection nanofluid flow in a heat exchanger: effects of brownian motion and thermophoresis for nanoparticles distribution

The free convection of Cu-water nanofluid is simulated and investigated inside a square heat exchanger chamber in the presence of MHD magnetic field. The Buongiorno model with the effects of Brownian and thermophoresis motion is considered to nanoparticles distribution inside the chamber. The geometry consists of a square chamber with two cylinders on the right and left sides as heater and cooler in order to create the buoyancy force, respectively. These cylinders represent hot and cold pipes, and the walls of the chamber are heat and mass insulation. the FVM with SIMPLE algorithm are used for velocity and pressure coupling. In current two-phase simulation, the effects of Rayleigh number, Hartmann number, inclination angle of chamber and volume fraction on streamline contours, isothermal lines, Lorentz force lines, nanoparticle distribution and Nusselt number are investigated. By modeling the motion of nanoparticles and evaluating it, a nanoparticle transport zone was observed. The diffusion effects of thermophoresis were significant in this zone. The nanoparticles were thrown from the hot cylinder to the cold cylinder. The application of a magnetic field enlarged the nanoparticle transport zone. However, increasing the Rayleigh number and decreasing the inclination angle of the enclosure caused the nanoparticles to disperse evenly

3D Numerical simulation of turbulent heat transfer and Fe

In this paper, 3D Simulation of turbulent Fe3O4/Nanofluid annular flow and heat transfer in sudden expansion are presented. k-ε turbulence standard model and FVM are applied with Reynolds number different from 20000 to 50000, enlargement ratio (ER) varied 1.25, 1.67, and 2, , and volume concentration of Fe3O4/Nanofluid ranging from 0 to 2% at constant heat flux of 4000 W/m2. The main significant effect on surface Nusselt number found by increases in volume concentration of Fe3O4/Nanofluid for all cases because of nanoparticles heat transport in normal fluid as produced increases in convection heat transfer. Also the results showed that suddenly increment in Nusselt number happened after the abrupt enlargement and reach to maximum value then reduction to the exit passage flow due to recirculation flow as created. Moreover the size of recirculation region enlarged with the rise in enlargement ratio and Reynolds number. Increase of volume Fe3O4/nanofluid enhances the Nusselt number due to nanoparticles heat transport in base fluid which raises the convection heat transfer. Increase of Reynolds number was observed with increased Nusselt number and maximum thermal performance was found with enlargement ratio of (ER=2) and 2% of volume concentration of Fe3O4/nanofluid. Further increases in Reynolds number and enlargement ratio found lead to reductions in static pressure

Experimental and numerical study of heat transfer to nanofluid flow in sudden enlargement of annular concentric pipe / Hussein Togun Abdullah

Turbulent heat transfer to separation nanofluid flow in annular concentric pipe has been studied numerically and experimentally. In numerical study, finite volume method with standard k-ε turbulence model in three dimensional domains is used. Three different types of water based (Al2O3, CuO, TiO2) nanofluids have been employed in this simulation. The adopted boundary conditions were expansion ratio (ER= 1.25, 1.67, and 2), Reynolds number ranging from 20000 to 50000, and Al2O3, CuO, TiO2 water based nanofluids with volume fractions varied between 0 to 2% at heat flux varied from 4000 W/m2 to 16000 W/m2. For experimental study, Al2O3 water based nanofluid was used to validate numerical results. The outer cylinder of downstream section was heated by uniform heat flux whereas the outer cylinder of upstream section and the overall length of the inner cylinder were unheated. The results show that the volume fraction of nanofluid and Reynolds number significantly affect the surface heat transfer coefficient; an increase in surface heat transfer coefficient was noted when both volume fraction of nanofluids and Reynolds number were increased for all the cases. The peak of the heat transfer coefficient had occurred after the sudden expansion moved far from the step height with the increase of sudden expansion dimensions due to separation flow in case of both pure water and nanofluid. It has been noted from the counter of streamline the size of recirculation zone increased with the increases of Reynolds number and expansion ratio. Increase of volume fraction of nanofluid enhances the heat transfer coefficient due to augmented heat transport by nanoparticles in base fluid which raises the convection heat transfer. The lowest pressure drop and maximum thermal performance are observed at Reynolds number 50000, 2% Al2O3 water based nanofluid at expansion ratio 2 in comparison to others. The improvement of heat transfer was about 36.6 % for pure water at expansion ratio 2 compared to heat transfer obtained in straight pipe. Augmentation of heat transfer could be achieved by using nanofluid at expansion ratio 2 where the total improvements were about 45.2% (TiO2), 47.3 %(CuO), and 49 %(Al2O3). Also the increment in the pressure drop was about 42% for pure water at expansion ratio 2 compared with straight pipe whereas by using nanofluid they were 62.6% (TiO2), 65.4% (CuO), and 57.6% (Al2O3). Good agreements were observed between numerical and experimental results all the way. Extension studies on thermal performances and pressure drop for separation flow over single or double and Forward or Backward-Facing steps have also been performed. Studies were conducted numerically with different models for flowing water and different types of nanofluids. Here heat transfer and pressure drop enhancements were observed following the similar trend obtained for sudden expansion configuration