Natural Convection in a Rocking Square Enclosure: Experimental Results

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
R. Chávez ◽  
F. J. Solorio ◽  
J. G. Cervantes
Keyword(s):  
Natural Convection ◽  
Strong Dependence ◽  
Oscillation Amplitude ◽  
Central Line ◽  
Experimental Results ◽  
Working Fluid ◽  
Closed Cavity ◽  
Square Enclosure ◽  
Image Velocimetry ◽  
Horizontal Symmetry

Experimental results for the natural convection in a rocking enclosure are presented. A square closed cavity heated from below and cooled from above periodically turns around of its horizontal symmetry central line. The oscillation amplitude was from −15 deg to 15 deg, and four time periods were employed (30 min, 60 min, 90 min, and 120 min) for three established Rayleigh numbers (3×104, 6×104, and 1×105). High purity glycerin was used as the working fluid, and particle image velocimetry (PIV) was employed to obtain the velocity fields. The obtained flow patterns have a strong dependence on the Rayleigh number.

Numerical computation of natural convection inside a curved-shape nanofluid-filled enclosure with nonuniform heating of the bottom wall

2019 ◽  
Vol 30 (01) ◽  
pp. 1950006 ◽  
Author(s):  
Abdellaziz Yahiaoui ◽  
Mahfoud Djezzar ◽  
Hassane Naji
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Pure Water ◽  
Bottom Wall ◽  
Working Fluid ◽  
Nonuniform Heating ◽  
Square Enclosure ◽  
Nusselt Numbers

This paper performs a numerical analysis of the natural convection within two-dimensional enclosures (square enclosure and enclosures with curved walls) full of a H2O-Cu nanofluid. While their vertical walls are isothermal with a cold temperature [Formula: see text], the horizontal top wall is adiabatic and the bottom wall is kept at a sinusoidal hot temperature. The working fluid is assumed to be Newtonian and incompressible. Three values of the Rayleigh number were considered, viz., 103, 104, 105, the Prandtl number is fixed at 6.2, and the volume fraction [Formula: see text] is taken equal to 0% (pure water), 10% and 20%. The numerical simulation is achieved using a 2D-in-house CFD code based on the governing equations formulated in bipolar coordinates and translated algebraically via the finite volume method. Numerical results are presented in terms of streamlines, isotherms and local and average Nusselt numbers. These show that the heat transfer rate increases with both the volume fraction and the Rayleigh number, and that the average number of Nusselt characterizing the heat transfer raises with the nanoparticles volume fraction.

Computational and PIV Analysis of the Fluid Flow in a Channel With an Oscillating Finned Surface

2008 ◽  
Author(s):  
Bolaji O. Olayiwola ◽  
Gerhard Schaldach ◽  
Peter Walzel
Keyword(s):  
Reynolds Number ◽  
Cooling System ◽  
Oscillation Amplitude ◽  
Working Fluid ◽  
Experimental Conditions ◽  
Performance Predictions ◽  
Image Velocimetry ◽  
Flow Reynolds Number ◽  
Finned Surface ◽  
Piv Analysis

Experimental and CFD studies were performed to investigate the kinematics of flow resulting from oscillation of a finned surface in a duct. The experiments were performed with working fluid with a kinematic viscosity of 1.8×10−6 m2/s. A steady flow Reynolds number in the laminar range of 0 < Re < 400 was studied. The oscillation Reynolds number Reosc was between the range of 50 and 1000. Oscillation amplitude range of 0.2 mm < A < 1.0 mm together with oscillation frequency in the range of 5 Hz < f < 90 Hz were employed. The acquired images were analysed using the particle image velocimetry (PIV) software. Three experimental conditions were studied, i.e. oscillating finned surface in a fluid at rest, steady finned flow and oscillating finned flow. CFD simulations were performed using the software suit CFX11 from ANSYS GmbH, Germany. The simulation results were compared with the PIV measurements using the time averaged velocity. The results of the visualization reveal periodic recirculation eddies around the fins which enhances the fluid mixing. The flow patterns and the crossflow effects depend on the geometries of the fins and the oscillation parameters. CFD results allow for performance predictions of different geometries and flow conditions. Enhanced heat transfer was obtained at moderate flow rates when applied in cooling system. Triangular finned geometry gives better performance.

Intrinsic permeability of materials ranging from sand to rock-fill using natural air convection tests

2011 ◽  
Vol 48 (5) ◽  
pp. 679-690 ◽  
Author(s):  
Jean Côté ◽  
Marie-Hélène Fillion ◽  
Jean-Marie Konrad
Keyword(s):  
Natural Convection ◽  
Experimental Results ◽  
Heat Extraction ◽  
Test Results ◽  
Intrinsic Permeability ◽  
Square Enclosure ◽  
Rock Fill ◽  
Air Convection ◽  
Effective Particle ◽  
Winter Time

Air convection within coarse rock-fills enhances winter-time heat extraction from underlying soils. Modeling this phenomenon requires the knowledge of intrinsic permeability. This study focuses on the measurement of intrinsic permeability using natural air convection within a 1 m3 test cell. Upward heat flow conditions are applied to various specimens. Test results are analyzed using a theoretical solution of natural convection in a square enclosure. Four materials were studied, with effective particle sizes (d10) ranging from 90 to 150 mm and porosities ranging from 0.37 to 0.41. The results showed that intrinsic permeability increases with increasing d10. The experimental results were adequately predicted by the Kozeny–Carman and Chapuis equations. Only slight deviations were observed, which is considered acceptable given that these equations were developed for materials with much smaller values of d10. The experimental results of this study confirm the value of intrinsic permeability recently used in a study of natural convection within a rock-fill dam in northern Quebec, Canada.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

Numerical Simulation of Heat Transfer in Laminar Natural Convection of Mixed Newtonian-Non-Newtonian and Pure Non-Newtonian Nanofluids in a Square Enclosure

2021 ◽  
pp. 1-44
Author(s):  
Ajay Vallabh ◽  
P.S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Base Fluid ◽  
Volume Fraction ◽  
Numerical Study ◽  
Transfer Model ◽  
Nanoparticle Concentration ◽  
Left Wall ◽  
Square Enclosure ◽  
First Case

Abstract This paper presents a steady-state heat transfer model for the natural convection of mixed Newtonian-Non-Newtonian (Alumina-Water) and pure Non-Newtonian (Alumina-0.5 wt% Carboxymethyl Cellulose (CMC)/Water) nanofluids in a square enclosure with adiabatic horizontal walls and isothermal vertical walls, the left wall being hot and the right wall cold. In the first case the nanofluid changes its Newtonian character to Non-Newtonian past 2.78% volume fraction of the nanoparticles. In the second case the base fluid itself is Non-Newtonian and the nanofluid behaves as a pure Non-Newtonian fluid. The power-law viscosity model has been adopted for the non-Newtonian nanofluids. A finite-difference based numerical study with the Stream function-Vorticity-Temperature formulation has been carried out. The homogeneous flow model has been used for modelling the nanofluids. The present results have been extensively validated with earlier works. In Case I the results indicate that Alumina-Water nanofluid shows 4% enhancement in heat transfer at 2.78% nanoparticle concentration. Following that there is a sharp decline in heat transfer with respect to that in base fluid for nanoparticle volume fractions equal to and greater than 3%. In Case II Alumina-CMC/Water nanofluid shows 17% deterioration in heat transfer with respect to that in base fluid at 1.5% nanoparticle concentration. An enhancement in heat transfer is observed for increase in hot wall temperature at a fixed volume fraction of nanoparticles, for both types of nanofluid.

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