scholarly journals Energy and Entropy Production of Nanofluid within an Annulus Partly Saturated by a Porous Region

Entropy ◽  
2021 ◽  
Vol 23 (10) ◽  
pp. 1237
Author(s):  
Zehba A. S. Raizah ◽  
Ammar I. Alsabery ◽  
Abdelraheem M. Aly ◽  
Ishak Hashim
Keyword(s):  
Heat Transfer ◽  
Porous Layer ◽  
Volume Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Darcy Number ◽  
Bejan Number ◽  
Cold Temperatures ◽  
Volume Fractions ◽  
Porous Region

The flow and heat transfer fields from a nanofluid within a horizontal annulus partly saturated with a porous region are examined by the Galerkin weighted residual finite element technique scheme. The inner and the outer circular boundaries have hot and cold temperatures, respectively. Impacts of the wide ranges of the Darcy number, porosity, dimensionless length of the porous layer, and nanoparticle volume fractions on the streamlines, isotherms, and isentropic distributions are investigated. The primary outcomes revealed that the stream function value is powered by increasing the Darcy parameter and porosity and reduced by growing the porous region’s area. The Bejan number and the average temperature are reduced by the increase in Da, porosity ε, and nanoparticles volume fractions ϕ. The heat transfer through the nanofluid-porous layer was determined to be the best toward high rates of Darcy number, porosity, and volume fraction of nanofluid. Further, the local velocity and local temperature in the interface surface between nanofluid-porous layers obtain high values at the smallest area from the porous region (D=0.4), and in contrast, the local heat transfer takes the lower value.

Numerical Analysis of Fluid Flow and Heat Transfer in Entrance and Fully Developed Regions of a Channel With Porous Baffles

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Amin Davari ◽  
Mehdi Maerefat
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Simple Algorithm ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Darcy Number ◽  
Performance Ratio ◽  
Local Thermal Equilibrium ◽  
Thermal Conductivity Ratio ◽  
Flow And Heat Transfer

In the present study, analysis of fluid flow and heat transfer in the entrance and periodically fully developed regions of a channel with porous baffles is numerically studied. The Navier–Stokes and Brinkman–Forchheimer equations are used to model the fluid flow in the open and porous regions. The flow is assumed to be laminar. A finite-volume based method in conjunction with the SIMPLE algorithm is used to solve the equations. The local thermal equilibrium model is adopted in the energy equation to evaluate the solid and fluid temperatures. The effects of parameters such as baffle height, baffle spacing, Reynolds number, and thermal conductivity ratio between the porous baffles and the fluid on the flow field and local heat transfer rate are studied at relatively low and high values of Darcy number. Results show that local heat transfer coefficient significantly depends on the formation and variation of the recirculation caused by the porous baffles, such that, in the cases where use of porous baffles leads to recirculation zone, the local Nusselt number in the entrance region would be less than that of the fully developed region. It is also shown that heat transfer performance ratio is significantly improved for high Prandtl number fluids.

Unsteady natural convection in a partially porous cavity having a heat-generating source using local thermal non-equilibrium model

2019 ◽  
Vol 29 (6) ◽  
pp. 1902-1919 ◽  
Author(s):  
Marina S. Astanina ◽  
Mikhail Sheremet ◽  
C. Jawali Umavathi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Porous Layer ◽  
Equilibrium Model ◽  
Local Heat ◽  
Darcy Number ◽  
Content Type ◽  
Porous Cavity ◽  
Variation Parameter ◽  
Non Equilibrium

Purpose The purpose of this study is a numerical analysis of transient natural convection in a square partially porous cavity with a heat-generating and heat-conducting element using the local thermal non-equilibrium model under the effect of cooling from the vertical walls. It should be noted that this research deals with a development of passive cooling system for the electronic devices. Design/methodology/approach The domain of interest is a square cavity with a porous layer and a heat-generating element. The vertical walls of the cavity are kept at constant cooling temperature, while the horizontal walls are adiabatic. The heat-generating solid element is located on the bottom wall. A porous layer is placed under the clear fluid layer. The governing equations, formulated in dimensionless stream function, vorticity and temperature variables with corresponding initial and boundary conditions, are solved using implicit finite difference schemes of the second order accuracy. The governing parameters are the Darcy number, viscosity variation parameter, porous layer height and dimensionless time. The effects of varying these parameters on the average total Nusselt number along the heat source surface, the average temperature of the heater, the fluid flow rate inside the cavity and on the streamlines and isotherms are analyzed. Findings The results show that in the case of local thermal non-equilibrium the total average Nusselt number is an increasing function of the interphase heat transfer coefficient and the porous layer thickness, while the average heat source temperature decreases with the Darcy number and viscosity variation parameter. Originality/value An efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze unsteady natural convection within a partially porous cavity using the local thermal non-equilibrium model in the presence of a local heat-generating solid element. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer in enclosures with local heat-generating heaters and porous layers, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.

scholarly journals On the anomalous laminar heat transfer intensification in developing region of nanofluid flow in channels or tubes

2012 ◽  
Vol 468 (2144) ◽  
pp. 2383-2398 ◽  
Author(s):  
J. T. C. Liu
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Perturbation Scheme ◽  
Transfer Coefficients ◽  
Nanofluid Flow ◽  
Aluminium Oxide Nanoparticles ◽  
Similar Solutions

The present work theoretically addresses the experimental observations of nanofluid flow exhibiting highly intensified laminar heat transfer rates at the leading edge of channels or tubes. The basis for this study is the continuum conservation equations for nanofluids. The Rayleigh–Stokes approximation is applied to the nonlinear advective effects and a perturbation scheme, in ascending powers of the nanoparticle volume fraction, is applied. The disparate thicknesses of momentum, heat and volume fraction is exploited to advantage in securing analytical, similar solutions. The volume fraction layer is ‘infinitely’ thin in that its effect on the momentum and thermal transport is essentially its bulk value far from the wall. The composite resulting zeroth- and first-order perturbations show that an increasing modification in the velocity and temperature profiles occur with increasing volume fraction and that this is caused, and quantitatively assessed, by inertial effects of advection and enhanced nanofluid transport properties. Some satisfactory explanations of experiments are made for aluminium oxide nanoparticles in water, in terms of the ratio of nanofluid to base fluid heat transfer coefficients, local heat transfer coefficient and the Nusselt number.

scholarly journals Characterization of Local Nano-Heat Transfer Fluids for Solar Thermal Collection

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Kawira Millien
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Copper Nanoparticles ◽  
Energy Demand ◽  
Volume Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Solar Thermal ◽  
Heat Transfer Fluids

Performance of organic oils in solar thermal collection is limited due to their low thermal conductivity when they are compared to molten salt solutions. Extraction of organic oils from plants can be locally achieved. The purpose of this study was to investigate the effect of use of copper nanoparticles in some base local heat transfer fluids (HTFs). Addition of volume fraction of 1.2% of the copper nanoparticles to oil-based heat transfer fluids improved their thermal conductivity as deduced from the thermal heat they conducted from solar radiation. The oil-based copper nanofluids were obtained by preparation of a colloidal solution of the nanoparticles. Impurities were added to increase the boiling point of the nano-heat transfer fluids. Stabilizers were used to keep the particles suspended in the oil-based fluids. The power output of the oil-based copper nano-heat transfer fluids was in the range of 475.4 W to 1130 W. The heat capacity of the steam in the heat exchanger was 93.7% dry and had a thermal capacity of 5.71 × 103 kJ. The heat rate of flow of the oil-based copper nano-heat transfer fluids was an average of 72.7 Js−1·kg−1 to 89.1 Js−1·kg−1. The thermal efficiency for the oil-based copper nano-heat transfer fluids ranged from 0.85 to 0.91. The average solar thermal solar intensity was in the range 700 Wm−2 to 1180 Wm−2. The heat exchanger used in this study was operating at 4.15 × 103 kJ and a temperature of 500.0°C. The heat transfer fluids entered the exchanger at an average temperature of 381°C and exited at 96.3°C and their heat coefficient ranged between 290.1 Wm−2°C and 254.1 Wm−2°C. The average temperatures of operation ranged between 394.1°C and 219.7°C with respective temperature efficiencies ranging between 93.4% and 64.4%. It was established that utilization of copper nanoparticles to enhance heat transfer in oil-based local heat transfer fluids can mitigate energy demand for meeting the world’s increasing energy uses, especially for areas inaccessible due to poor land terrain.

MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material

2019 ◽  
Vol 29 (10) ◽  
pp. 3559-3583 ◽  
Author(s):  
Ali J. Chamkha ◽  
Fatih Selimefendigil
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Thermal Conductivity ◽  
Volume Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Thermal Conductivity Ratio ◽  
Content Type ◽  
Hot Surface ◽  
Change Material

Purpose The purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters. Design/methodology/approach Finite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied. Findings It was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10. Originality/value Such configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects.

Study on fluid flow and heat transfer in fluid channel filled with KKL model-based nanofluid during natural convection using FVM

2019 ◽  
Vol 29 (8) ◽  
pp. 2622-2641
Author(s):  
Yongsheng Rao ◽  
Zehui Shao ◽  
Alireza Rahimi ◽  
Abbas Kasaeipoor ◽  
Emad Hasani Malekshah
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Natural Convection ◽  
Entropy Generation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Bejan Number ◽  
Content Type ◽  
Flow And Heat Transfer

PurposeA comprehensive study on the fluid flow and heat transfer in a nanofluid channel is carried out. The configuration of the channel is as like as quarter channel. The channel is filled with CuO–water nanofluid.Design/methodology/approachThe Koo–Kleinstreuer–Li model is used to estimate the dynamic viscosity and consider the Brownian motion. On the other hand, the influence of nanoparticles’ shapes on the heat transfer rate is considered in the simulations. The channel is included with the injection pipes which are modeled as active bodies with constant temperature in the 2D simulations.FindingsThe Rayleigh number, nanoparticle concentration and the thermal arrangements of internal pipes are the governing parameters. The hydrothermal aspects of natural convection are investigation using different approaches such as average Nusselt number, total entropy generation, Bejan number, streamlines, temperature fields, local heat transfer irreversibility, local fluid friction irreversibility and heatlines.Originality/valueThe originality of this work is investigation of fluid flow, heat transfer, entropy generation and heatline visualization within a nanofluid-filled channel using a finite volume method.

Local Heat Transfer Downstream of a Turbulent Separation of Any Intensity

2002 ◽  
Vol 33 (1-2) ◽  
pp. 8
Author(s):  
Eleonora Ya. Epik
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Separation
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