LES simulations and Nusselt number decomposition of turbulent mixed convection of liquid metals flowing in a vertical pipe

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

Download Full-text

MIXED-CONVECTION HEAT TRANSFER TO SODIUM IN A VERTICAL PIPE

Experimental Heat Transfer ◽

10.1080/08916159408946473 ◽

1994 ◽

Vol 7 (1) ◽

pp. 71-90 ◽

Cited By ~ 16

Author(s):

J. D. Jackson ◽

B. P. Axcell ◽

A. Walton

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Convection Heat Transfer ◽

Convection Heat ◽

Vertical Pipe ◽

Mixed Convection Heat Transfer

Download Full-text

95/00721 Numerical study of transient conjugated mixed convection in a vertical pipe

Fuel and Energy Abstracts ◽

10.1016/0140-6701(95)95976-9 ◽

1995 ◽

Vol 36 (1) ◽

pp. 42

Keyword(s):

Mixed Convection ◽

Numerical Study ◽

Vertical Pipe

Download Full-text

Mixed Convection Adjacent to 3-D Backward-Facing Step

10.1115/imece2000-1408 ◽

2000 ◽

Author(s):

A. Li ◽

B. F. Armaly

Keyword(s):

Heat Flux ◽

Nusselt Number ◽

Mixed Convection ◽

Buoyancy Force ◽

Three Dimensional ◽

The Other ◽

Convection Flow ◽

Backward Facing Step ◽

Grashof Number ◽

Recirculating Flow

Abstract Results from three-dimensional numerical simulation of laminar, buoyancy assisting, mixed convection airflow adjacent to a backward-facing step in a vertical rectangular duct are presented. The Reynolds number, and duct geometry were kept constant at Re = 200, AR = 8, ER = 2, and S = 1 cm. Heat flux at the wall downstream from the step was kept uniform, but its magnitude was varied to cover a Grashof number (Gr) range between 0.0 to 4000. All the other walls in the duct were kept at adiabatic condition. The flow, upstream of the step, is treated as fully developed and isothermal. The relatively small aspect ratio of the channel is selected specifically to focus on the developments of the three-dimensional mixed convection flow in the separated and reattached flow regions downstream from the step. The presented results focus on the effects of increasing the buoyancy force, by increasing the uniform wall heat flux, on the three-dimensional flow and heat transfer characteristics. The flow and thermal fields are symmetric about the duct’s centerline. Vortex generated near the sidewall, is the major contributor to the three dimensional behavior in the flow domain, and that feature increases as the Grashof number increases. Increasing the Grashof number results in an increase in the Nusselt number, the size of the secondary recirculating flow region, the size of the sidewall vortex, and the spanwise flow from the sidewall toward the center of the channel. On the other hand, the size of the primary reattachment region decreases with increasing the Grashof number. That region lifts away and partially detaches from the downstream wall at high Grashof number flow. The maximum Nusselt number occurs near the sidewalls and not at the center of the channel. The effects of the buoyancy force on the distributions of the three-velocity components, temperature, reattachment region, friction coefficient, and Nusselt number are presented, and compared with 2-D results.

Download Full-text

Mixed convection of functionalized DWCNT-water nanofluid in baffled lid-driven cavities

Thermal Science ◽

10.2298/tsci160225216e ◽

2018 ◽

Vol 22 (6 Part A) ◽

pp. 2503-2514 ◽

Cited By ~ 1

Author(s):

Esfe Hemmat ◽

Arani Abbasian ◽

Wei-Mon Yan ◽

Alireza Aghaie ◽

Masoud Afrand ◽

...

Keyword(s):

Nusselt Number ◽

Mixed Convection ◽

Richardson Number ◽

Average Nusselt Number ◽

Volume Fraction ◽

Minimum Length ◽

Convection Flow ◽

Flow And Heat Transfer ◽

Inclination Angles ◽

Nanoparticles Volume Fraction

The present study aims to evaluate the mixed convection flow and heat transfer of functionalized DWCNT/water nanofluids with variable properties in a cavity having hot baffles. The investigation is performed at different nanoparticles volume fraction including 0, 0.0002, 0.001, 0.002, and 0.004, Richardson numbers ranging from 0.01 to 100, inclination angles ranging from 0 to 60? and at constant Grashof number of 104. The results presented as streamlines and isotherms plot and Nusselt number diagrams. According to the finding with increasing nanoparticles volume fraction and distance between the left hot baffles of nanoparticles average Nusselt number enhances for all considered Richardson numbers and cavity inclination angles. Also with increasing Richardson number, the rate of changes of average Nusselt number increase with increasing distance between the left hot baffles. For example, at Richardson number of 0.01, by increasing L1 from 0.4 to 0.6, the average Nusselt number increases 7%; while for similar situation at Richardson number of 0.1, 1.0, and 10, the average Nusselt number increases, respectively, 17%, 24%, and 26%. At all Richardson numbers, the maximum value of average Nusselt number is achieved for a minimum length of left baffles. This article has been corrected. Link to the correction <a href="http://dx.doi.org/10.2298/TSCI190203032E">10.2298/TSCI190203032E</a>

Download Full-text

Augmentation of Pure Mixed Convection Heat Transfer in a Non-newtonian Power-law Fluid Filled Lid-driven Trapezoidal Cavity with Double Rotating Cylinders

Journal of Heat Transfer ◽

10.1115/1.4051127 ◽

2021 ◽

Author(s):

Hasib Ahmed Prince ◽

Didarul Ahasan Redwan ◽

Enamul Hasan Rozin ◽

Sudipta Saha ◽

Mohammad Arif Hasan Mamun

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Mixed Convection ◽

Numerical Investigation ◽

Power Law ◽

Convection Heat Transfer ◽

Cavity Surface ◽

Rotating Cylinders ◽

Power Law Fluid ◽

Driven Cavity

Abstract In this study, a numerical investigation on mixed convection inside a trapezoidal cavity with a pair of rotating cylinders has been conducted. Three different power-law fluid indexes (n = 1.4, 1.0, and 0.6) have been considered to model different sets of non-Newtonian fluids. Four separate cases are considered dependent on the rotation orientation of the cylinders within the cavity. In the first two cases, the cylinders rotate in the same direction, i.e., both counter-clockwise (CCW), and both clockwise (CW), whereas, in the other two cases, cylinders rotate in opposite directions (CW-CCW and CCW-CW). Simulations have been carried out over a broad range of Reynolds number (from 0.5 to 500) and angular speeds (a dimensionless value from 0 to 10). The average Nusselt number values at the isothermal hot inclined cavity surface are determined to evaluate heat transfer performance in various circumstances. Streamlines and isotherm contours are also plotted for better understandings of the effects of different cases for various parameters on thermal and fluid flow fields. It is found that the Nusselt number varies non-linearly with different angular speeds of the cylinders. The combined effect of the mixing induced by cylinder rotation and viscosity characteristics of the fluid dictates the heat transfer in the system. Predictions from the numerical investigation provide insights onto the sets of key parametric configuration that have dominant influence on the thermal performance of lid driven cavity with double rotating cylinders.

Download Full-text

Mixed Convection and Entropy Generation of an Ag-Water Nanofluid in an Inclined L-Shaped Channel

Energies ◽

10.3390/en12061150 ◽

2019 ◽

Vol 12 (6) ◽

pp. 1150 ◽

Cited By ~ 5

Author(s):

Taher Armaghani ◽

Muneer Ismael ◽

Ali Chamkha ◽

Ioan Pop

Keyword(s):

Nusselt Number ◽

Mixed Convection ◽

Entropy Generation ◽

Richardson Number ◽

Volume Fraction ◽

Governing Equations ◽

Nanoparticles Volume Fraction ◽

The Mean ◽

The Right ◽

Volume Method

This paper investigates the mixed convection and entropy generation of an Ag-water nanofluid in an L-shaped channel fixed at an inclination angle of 30° to the horizontal axis. An isothermal heat source was positioned in the middle of the right inclined wall of the channel while the other walls were kept adiabatic. The finite volume method was used for solving the problem’s governing equations. The numerical results were obtained for a range of pertinent parameters: Reynolds number, Richardson number, aspect ratio, and the nanoparticles volume fraction. These results were Re = 50–200; Ri = 0.1, 1, 10; AR = 0.5–0.8; and φ = 0.0–0.06, respectively. The results showed that both the Reynolds and the Richardson numbers enhanced the mean Nusselt number and minimized the rate of entropy generation. It was also found that when AR. increased, the mean Nusselt number was enhanced, and the rate of entropy generation decreased. The nanoparticles volume fraction was predicted to contribute to increasing both the mean Nusselt number and the rate of entropy generation.

Download Full-text

Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field

Nanomaterials ◽

10.3390/nano10030449 ◽

2020 ◽

Vol 10 (3) ◽

pp. 449 ◽

Cited By ~ 6

Author(s):

Ali J. Chamkha ◽

Fatih Selimefendigil ◽

Hakan F. Oztop

Keyword(s):

Magnetic Field ◽

Heat Transfer ◽

Nusselt Number ◽

Aspect Ratio ◽

Mixed Convection ◽

Average Nusselt Number ◽

Volume Fraction ◽

Rotational Velocity ◽

Rotating Cone ◽

The Impact

Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between −300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10 − 4 and 5 × 10 − 2 ), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.

Download Full-text