scholarly journals Natural convection of Newtonian fluids between two concentric cylinders of a special cross-sectional form

2020 ◽  
pp. 190-190
Author(s):  
Houssem Laidoudi ◽  
Mustapha Helmaoui ◽  
Mohamed Bouzit ◽  
Abdellah Ghenaim
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Inclination Angle ◽  
Average Nusselt Number ◽  
Outer Cylinder ◽  
Cross Sectional ◽  
The Mean

In this paper, we performed a numerical simulation of natural convection of Newtonian fluids between two cylinders of different cross-sectional form. The inner cylinder is supposed to be hot and the outer cylinder is assumed to be cold. The diameter of inner cylinder to the diameter of outer cylinder defines the radii ratio (RR= 2.5). The governing equations describing the physical behavior of fluid flow and heat transfer are solved using finite volume method. The effects of Prandtl number (Pr = 0.71 to 100), Rayleigh number (Ra = 103 to 105) and inclination angle of inner cylinder (? = 0? to 80?) on streamlines, isotherms and dimensionless velocity are presented and discussed. Also, the mean average Nusselt number of inner cylinder is plotted versus the governing parameters. All present simulations are considered in two-dimensions for steady laminar flow regime. The obtained results showed that the flow between cylinders is more stable for the inclination angle ? = 0?. Increase in Rayleigh number increases the heat transfer rate for all values of inclination angle. Furthermore, the effect of Prandtl number on the mean average Nusselt number becomes negligible when Pr is over the value 7.01. For example at Pr = 0.71 and Ra =105, increase in inclination from 0? to 40?decreases the average Nusselt number by 5.4%. A new correlation is also provided to describe the average Nusselt number as function of Pr and Ra at ? = 0?.

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.

Convective Flow in Annuli of Stationary and Rotating Horizontal Cylinders

1997 ◽  
Author(s):  
T. S. Lee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Cooling System ◽  
Cylindrical Annulus ◽  
Receiver System ◽  
The Mean ◽  
Effects Of Rotation

Heat transfer and fluid flow processes in enclosed spaces have been extensively studied due to their importance in energy conversion, storage and transmission systems. Concentric and eccentric annular geometries are most commonly encountered in solar collector-receiver system, cooling system in nuclear reactors etc. For mixed flow in the annulus between concentric or eccentric cylinders in a rotating system, most work were performed for the cases of vertical cylindrical annulus. More recently, the effects of recirculation on the natural convection between the annular region in horizontal rotating cylinders have become a topic of interest to researchers. The applications of these studies include food processing and the interest in seeking improved methods for crystallographic perfection in industrial processes, above studies are for air with Pr≅1.0. However, other effects of rotation on heat transfer characteristics for low Prandtl number fluids are encountered in high power electric machines with heated shafts, such as a mercury slip ring assembly. For the present study, natural convection is driven by vertical temperature gradient and vertical gravity force. The interaction with the effect of rotation of the inner cylinder is expected to lead to complicated flows. Studies show that the mean Nusselt number increases with Rayleigh number. At a Prandtl number of order 1.0 with a fixed Rayleigh number, when the inner cylinder is made to rotate, the mean Nusselt number decreases through out the flow. At lower Prandtl number of the order 0.1 to 0.01, the mean Nusselt number remained fairly constant with respect to the rotational Reynolds number.

scholarly journals CONJUGATE NATURAL CONVECTION IN A POROUS ENCLOSURE SANDWICHED BY FINITE WALLS AND SUBJECTED TO CONVECTION COOLING CONDITION

2021 ◽  
Vol 25 (01) ◽  
pp. 131-142
Author(s):  
Hassan H. Hatem ◽  
◽  
Luma F. Ali ◽  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Wall Thickness ◽  
Inclination Angle ◽  
Average Nusselt Number ◽  
Saturated Porous Medium ◽  
Bottom Wall ◽  
Conjugate Natural Convection

Steady conjugate natural convection heat transfer in a two-dimensional enclosure filled with fluid saturated porous medium is studied numerically. The two vertical boundaries of the enclosure are kept isothermally at same temperature, the horizontal upper wall is adiabatic, and the horizontal lower wall is partially heated. The Darcy extended Brinkman Forcheimer model is used as the momentum equation and Ansys Fluent software is utilized to solve the governing equations. Rayleigh number (1.38 ≤ Ra ≤ 2.32), Darcy number (3.9 * 10-8), the ratio of conjugate wall thickness to its height (0.025 ≤ W ≤ 0.1) , heater length to the bottom wall ratio (1/4 ≤  ≤ 3/4) and inclination angle (0°, 30° and 60°) are the main considered parameters. The presented results show the effect of these parameters on the heat transfer and fluid flow characteristics. These results include streamlines, isotherm patterns, and local and average Nusselt number for different values of the governing parameters. It is found that either increasing the Rayleigh number and the ratio of conjugate wall thickness to its height (d/H) or decreasing the ratio of heat source width to bottom wall (l/L ), the average Nusselt number is increased. Also, it was observed that the average Nusselt number does not change substantially with inclination angle.

scholarly journals Effect of Various Tilted Positions of a Thin Fin on Natural Convection of Laminar Viscous Flow in a Square Cavity

2021 ◽  
Vol 39 (5) ◽  
pp. 1634-1642
Author(s):  
Syed Fazuruddin ◽  
Seelam Sreekanth ◽  
G Sankara Sekhar Raju
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Finite Difference ◽  
Average Nusselt Number ◽  
Vertical Position ◽  
Inclination Angles ◽  
Rayleigh Numbers

An exhaustive numerical investigation is carried out to analyze the role of an isothermal heated thin fin on fluid flow and temperature distribution visualization in an enclosure. Natural convection within square enclosures finds remarkable pragmatic applications. In the present study, a finite difference approach is performed on two-dimensional laminar flow inside an enclosure with cold side walls and adiabatic horizontal walls. The fluid flow equations are reconstructed into vorticity - stream function formulation and these equations are employed utilizing the finite-difference strategy with incremental time steps. The parametric study includes a wide scope of Rayleigh number, Ra, and inclination angle ϴ of the thin fin. The effect of different Rayleigh numbers ranging Ra = 104-106 with Pr=0.71 for all the inclination angles from 0°-360° with uniform rotational length of angle 450 of an inclined heated fin on fluid flow and heat transfer have been investigated. The heat transfer rate within the enclosure is measured by means of local and average Nusselt numbers. Regardless of inclination angles of the thin fin, a slight enhancement in the average Nusselt number is observed when Rayleigh number increased for both the cases of the horizontal and vertical position of the thin fin. When the fin has inclined no change in average Nusselt number is noticed for distinct Rayleigh numbers.

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.

Lattice Boltzmann Method for Combined Natural Convection Surface Radiation in Open Cavity

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
Ayoub Msaddak ◽  
Mohieddine Ben Salah ◽  
Ezeddine Sediki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Lattice Boltzmann Method ◽  
Inclination Angle ◽  
Lattice Boltzmann ◽  
Surface Radiation ◽  
Surface Emissivity ◽  
Boltzmann Method

Lattice Boltzmann method (LBM) is performed to study numerically combined natural convection and surface radiation inside an inclined two-dimensional open square cavity. The cavity is heated by a constant temperature at the wall facing the opening. The walls normal to the heated surface are assumed to be adiabatic, diffuse, gray, and opaque while the open boundary is assumed to be black at ambient temperature. A Bathnagar, Gross and Krook (BGK) collision model with double distribution function (D2Q9-D2Q4) is adopted. Effects of surface radiation, inclination angle, and Rayleigh number on the heat transfer are analyzed and discussed. Results are presented in terms of isotherms, streamlines, and Nusselt number. It was found that the presence of surface radiation enhances the heat transfer. The convective Nusselt number decreases with increasing surface emissivity as well as with Rayleigh number, while the total Nusselt number increases with increasing surface emissivity and Rayleigh number. The inclination angle has also a significant effect on flow and heat transfer inside the cavity. However, the magnitude of total heat transfer decreases considerably when open cavity is tilted downward.

Finite Element Simulation on Natural Convection Flow in a Triangular Enclosure Due to Uniform and Nonuniform Bottom Heating

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
S. Roy ◽  
Tanmay Basak ◽  
Ch. Thirumalesha ◽  
Ch. Murali Krishna
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Nusselt Number ◽  
Natural Convection ◽  
Prandtl Number ◽  
Average Nusselt Number ◽  
Bottom Wall ◽  
Nonuniform Heating ◽  
Triangular Enclosure ◽  
Prandtl Numbers

A penalty finite element analysis with biquadratic elements has been carried out to investigate natural convection flows within an isosceles triangular enclosure with an aspect ratio of 0.5. Two cases of thermal boundary conditions are considered with uniform and nonuniform heating of bottom wall. The numerical solution of the problem is illustrated for Rayleigh numbers (Ra), 103⩽Ra⩽105 and Prandtl numbers (Pr), 0.026⩽Pr⩽1000. In general, the intensity of circulation is found to be larger for nonuniform heating at a specific Pr and Ra. Multiple circulation cells are found to occur at the central and corner regimes of the bottom wall for a small Prandtl number regime (Pr=0.026−0.07). As a result, the oscillatory distribution of the local Nusselt number or heat transfer rate is seen. In contrast, the intensity of primary circulation is found to be stronger, and secondary circulation is completely absent for a high Prandtl number regime (Pr=0.7–1000). Based on overall heat transfer rates, it is found that the average Nusselt number for the bottom wall is 2 times that of the inclined wall, which is well, matched in two cases, verifying the thermal equilibrium of the system. The correlations are proposed for the average Nusselt number in terms of the Rayleigh number for a convection dominant region with higher Prandtl numbers (Pr=0.7 and 10).

MHD heat transfer and entropy generation in inclined trapezoidal cavity filled with nanofluid

2017 ◽  
Vol 27 (10) ◽  
pp. 2174-2202 ◽  
Author(s):  
Kamel Milani Shirvan ◽  
Soroush Mirzakhanlari ◽  
Hakan F. Öztop ◽  
Mojtaba Mamourian ◽  
Khaled Al-Salem
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Sensitivity Analysis ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Entropy Generation ◽  
Inclination Angle ◽  
Effective Parameters ◽  
Content Type ◽  
The Mean

Purpose The main purpose of this paper is to define 2D numerical study and a sensitivity analysis of natural convection heat transfer and entropy generation of Al2O3-water nanofluid in a trapezoidal cavity, with considering of the presence of a constant axial magnetic field. Design/methodology/approach The effects of the three effective parameters, the Rayleigh number, Hartmann number (Ha) and also inclination angle on the heat transfer performance and entropy generation, are investigated using a finite volume approach. The sensitivity analysis of the effective parameters is done utilizing the response surface methodology. Findings The results obtained showed that the mean Nusselt number and total entropy generation increase with the Rayleigh number. Also, increasing the inclination angle reduces the mean Nusselt number (regardless of the magnetic field). In addition, it is found that the mean Nusselt number increases until Ha = 10 and then decreases by increasing of Ha number, regardless of the inclination angle. The sensitivity of the mean Nusselt number to the Ha number and inclination angle α is negative. It is concluded that to maximize the mean Nusselt number and minimize the entropy generation, simultaneously, the Ha and inclination angle must be 50° and 0°, respectively. Originality/value There is no published research in the literature about sensitivity analysis of magneto-hydrodynamic heat transfer and entropy generation in inclined trapezoidal cavity filled with nanofluid.

A Numerical Study of the Simultaneous Natural Convective Heat Transfer From the Upper and Lower Surfaces of a Thin Isothermal Horizontal Circular Plate

2016 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Abdulrahim Kalendar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
The Mean ◽  
Adiabatic Section

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.

scholarly journals Numerical Investigation of the Effect of Baffle Inclination Angle on Nanofluid Natural Convection Heat Transfer in A Square Enclosure

2019 ◽  
Vol 12 (2) ◽  
pp. 61-71 ◽  
Author(s):  
Barik AL-Muhjaa ◽  
Khaled Al-Farhany
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Solid Wall ◽  
Convection Heat Transfer ◽  
Convection Heat

The characteristics of the conjugate natural convection of (Al2O3-water) nanofluid inside differentially heated enclosure is numerically analyzed using COMSOL Multiphysics (5.3a). The enclosure consists of two vertical walls, the left wall has a thickness and maintain at a uniform hot temperature, while the opposite wall at cold temperature and the horizontal walls are isolated. A high thermal conductivity thin baffle has been added on the insulated bottom wall at a different inclination angles. The effect of the volume fractions of nanoparticles (f), Rayleigh number (Ra), solid wall thermal conductivity ratio (Kr), baffle incline angles (Ø) and the thickness of solid wall (D) on the isothermal lines, fluid flow patterns and the average Nusselt number (Nu)  has been investigated. At low Rayleigh number (Ra=103 to 104) the Isothermal lines are parallel with the vertical wall which is characteristic of conduction heat transfer. on the other hand, when Rayleigh number increase to (Ra=106),  the isotherms lines distribution in the inner fluid become parallel curves with the adiabatic horizontal walls of the enclosure and smooth in this case convection heat transfer becomes dominant. As the Rayleigh number further increases, the average Nusselt number enhance because of buoyancy force become stronger. In addition, the fluid flow within the space is affected by the presence of a fin attached to the lower wall that causes blockage and obstruction of flow near the hot wall, hence the recirculation cores become weak and effect on the buoyant force. The maximum value of the stream function can be noticed in case of nanofluid at (Ø=60), whereas they decrease when (Ø > 60), where the baffle obstruction causing decreases in flow movement. So that the left region temperature increases which cause reduction of the convective heat transfer by the inner fluid temperatures. This is an indication of enhancing of insulation. When the inclination angle increases (Ø >90), the baffle obstruction on flow and fluid resistance becomes smaller and the buoyancy strength increase, as a result, the heat transfer is increasing in this case. As a result of increasing the thermal conductivity from 1 to 10, an increase in the amount of heat transferred through the solid wall to the internal fluid have been noticed. This change can be seen in the isothermal lines, also, there was growth and an increase in the temperature gradient. The increasing of wall thickness from (D=0.1 to 0.4) leads to reduce the intensive heating through the solid wall as well as small heat transferred to the inner fluid. Therefore, it can be noticed that when the wall thickness increases the stream function decrease.

Sign in / Sign up

Export Citation Format

Share Document