scholarly journals Numerical investigation into natural convection heat transfer enhancement of copper-water nanofluid in a wavy wall enclosure

2012 ◽  
Vol 16 (5) ◽  
pp. 1309-1316 ◽  
Author(s):  
Ching-Chang Cho ◽  
Her-Terng Yau ◽  
Cha’o-Kuang Chen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Wavy Wall ◽  
Convection Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Numerical investigations are performed into the natural convection heat transfer characteristics within a wavy-wall enclosure filled with Cu-water nanofluid. In the paper, the bottom wall of the enclosure has a wavy geometry and is maintained at a constant high temperature, while the top wall is straight and is maintained at a constant low temperature. The left and right walls of the enclosure are both straight and insulated. In performing the simulation, the Boussinesq approximation is used to model the governing equations. The study examines the effect of the nanoparticle volume fraction, the Rayleigh number, the wave amplitude, and the wavelength on the heat transfer characteristics. It is shown that the heat transfer performance can be enhanced as the volume fraction of nanoparticles increases. It is also shown that for a given Rayleigh number, the heat transfer effect can be optimized via an appropriate changing of the geometry conditions.

Influence of Cu-Water and CNT-Water Nanofluid on Natural Convection Heat Transfer in a Triangular Solar Collector

2020 ◽  
Author(s):  
Didarul Ahasan Redwan ◽  
Md. Habibur Rahman ◽  
Hasib Ahmed Prince ◽  
Emdadul Haque Chowdhury ◽  
M. Ruhul Amin
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Solar Collector ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Abstract A numerical study on natural convection heat transfer in a right triangular solar collector filled with CNT-water and Cuwater nanofluids has been conducted. The inclined wall and the bottom wall of the cavity are maintained at a relatively lower temperature (Tc), and higher temperature (Th), respectively, whereas the vertical wall, is kept adiabatic. The governing non-dimensional partial differential equations are solved by using the Galerkin weighted residual finite element method. The Rayleigh number (Ra) and the solid volume-fraction of nanoparticles (ϕ) are varied in the range of 103 ≤ Ra ≤ 106, and 0 ≤ ϕ ≤ 0.1, respectively, to carry out the parametric simulations within the laminar region. Corresponding thermal and flow fields are presented via isotherms and streamlines. Variations of average Nusselt number as a function of Rayleigh number have been examined for different solid volume-fraction of nanoparticles. It has been found that the natural convection heat transfer becomes stronger with the increment of solid volume fraction and Rayleigh number, but the strength of circulation reduces with increasing nanoparticles’ concentration at low Ra. Conduction mode dominates for lower Ra up to a certain limit of 104. It is also observed that when the solid volume fraction is increased from 0 to 0.1 for a particular Rayleigh number, the average Nusselt number is increased to a great extent, but surprisingly, the rate of increment is more pronounced at lower Ra. Moreover, it is seen that Cu-water nanofluid offers slightly better performance compared to CNT-water but the difference is very little, especially at lower Ra.

Natural Convection Heat Transfer Phenomena in Packed Bed Systems

2014 ◽  
Author(s):  
Olugbenga O. Noah ◽  
Johan F. Slabber ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Energy ◽  
Unit Volume ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Heat Transfer Characteristics ◽  
Coated Particles ◽  
Transfer Characteristics

Natural convection heat transfer in fluid-saturated porous media has in recent years gained considerable attention especially in High Temperature Reactors (HTR). It is lately proposed that Light Water Reactors (LWT) can be made safer by re-designing the fuel in the fuel assembly. In the proposed design, porous medium containing fuel in the form of loose coated particles in a Helium environment is introduced inside the cladding tubes of the fuel elements. These coated particles are treated as a bed from where heat is transferred to the cladding tube and the gas movement is due to natural convection. This proposal will require an understanding of the heat transfer characteristics from heated particles fuel to the gas atmosphere within the cladding tubes. In this present study, the natural convection heat transfer characteristics in packed beds from fluid-to-particle and bed particles to helium gas (thermal energy storage system) was experimentally investigated. Medium condition in this study was homogenous, isotropic, negligible radiant heat transfer and at local thermal non-equilibrium (LTNE). Theoretical formulation of microscopic thermal energy balance in the medium was employed in the analysis of experimental data. This formulation accounts for the convective heat transfer coefficient, the net rate of heat conduction into a unit volume of the solid and the heat production per unit volume of the particle. Dimensionless parameters like the Nusselt, Grashof, Prandtl, Rayleigh and Biot numbers defining heat transfer effect in the medium were equally determined and results validated with the KTA correlation.

scholarly journals Prediction of Natural Convection Heat Transfer Phenomena of Nanofluids in Corrugated Annulus

2020 ◽  
Author(s):  
Sattar Aljobair ◽  
Akeel Abdullah Mohammed ◽  
Israa Alesbe
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Outer Cylinder ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Abstract The natural convection heat transfer and fluid flow characteristic of water based Al2O3 nano-fluids in a symmetrical and unsymmetrical corrugated annulus enclosure has been studied numerically using CFD. The inner cylinder is heated isothermally while the outer cylinder is kept constant cold temperature. The study includes eight models of corrugated annulus enclosure with constant aspect ratio of 1.5. The governing equations of fluid motion and heat transfer are solved using stream-vorticity formulation in curvilinear coordinates. The range of solid volume fractions of nanoparticles extends from PHI=0 to 0.25, and Rayleigh number varies from 104 to 107. Streamlines, isotherms, local and average Nusselt number of inner and outer cylinder has been investigated in this study. Sixty-four correlations have been deduced for the average Nusselt number for the inner and outer cylinders as a function of Rayleigh number have been deduced for eight models and five values of volume fraction of nano particles with an accuracy range 6-12 %. The results show that, the average heat transfer rate increases significantly as particle volume fraction and Rayleigh number increase. Also, increase the number of undulations in unsymmetrical annuli reduces the heat transfer rates which remain higher than that in symmetrical annuli. There is no remarkable change in isotherms contour with increase of volume fraction of nanofluid.

scholarly journals Enhancement of natural convection heat transfer in a U-shaped cavity filled with Al2O3-water nanofluid

2012 ◽  
Vol 16 (5) ◽  
pp. 1317-1323 ◽  
Author(s):  
Ching-Chang Cho ◽  
Her-Terng Yau ◽  
Cha’o-Kuang Chen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Heated Wall ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
The Mean

This paper investigates the natural convection heat transfer enhancement of Al2O3-water nanofluid in a U-shaped cavity. In performing the analysis, the governing equations are modeled using the Boussinesq approximation and are solved numerically using the finite-volume numerical method. The study examines the effects of the nanoparticle volume fraction, the Rayleigh number and the geometry parameters on the mean Nusselt number. The results show that for all values of the Rayleigh number, the mean Nusselt number increases as the volume fraction of nanoparticles increases. In addition, it is shown that for a given length of the heated wall, extending the length of the cooled wall can improve the heat transfer performance.

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