Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : natural convection


Natural Convection Heat Transfer in Enclosure with Uniformly Heated Inner Elliptic Cylinder and Outer square Cylinder

Akeel Abdullah Mohammed

Engineering and Technology Journal, 2012, Volume 30, Issue 19, Pages 3435-3456

Experimental and numerical simulation study for natural convection heat
transfer formed by uniformly heated inclined elliptical cylinder concentrically
located in an enclosed square cylinder subjected to the ambient have been
investigated. Experiments have been carried out for Rayliegh number ranges from
0.9×106 to 3.3×106. The enclosure angles of inclination are f =0o (horizontal), 45o
(inclined), and 90o (vertical), and for axis ratio of elliptic cylinder
(minor/major=b/c) of 1:2, while the dimensions of outer square cylinder was
0.5×0.5×2 m. A numerical simulation was conducted by using commercial
Fluent CFD code to investigate the steady laminar natural convective heat
transfer for air between a heated elliptic cylinder and its square enclosure. It
covered a range of hydraulic radius ratios (HRR) of 1.97, 2.62, and 3.93 and
for orientation angles j = 0o (the major axis is vertical), 30o, 45o. Two
values of Rayligh number were taken: 0.9×106 and 3.3×106. The experimental
results showed that the heat transfer process improves as Rayliegh number
increases and is better in f =0o than other angles of inclination at the same
heat input. Theoretical results showed that the HRR, Rayligh number, and
angle of orientation have significant effect on the physical behavior of
stremlines and isotherms inside the equivalent annular gap.

An Investigation of Natural Convection Heat Transfer in a Square Enclosure Filled with Nanofluid

Ayad M. Salman

Engineering and Technology Journal, 2011, Volume 29, Issue 12, Pages 2346-2363

In this research, numerical solution of natural convection heat transfer of nanofluids in two-dimensional square enclosures is obtained for different values of Rayleigh numbers and volume fraction of nanofluids. Numerical simulation has then been undertaken for the mixture of Cu-water as nanofluid. The stream–vorticity form of the Navier–Stokes equations and energy equation are used in this study. The present model is utilized to obtain results in the range of Rayleigh number 103–105 and volume fractions of nanofluids (0.025-0.1). The enclosure which represent two-dimensional square enclosure with heated left side wall, while the right side was cold, the top and bottom walls were adiabatic. The governing equations are solved with finite-difference technique by central difference scheme. A computer program in (FORTRAN 90) was used to carry out the numerical solution. The results are a remarkable increase in the average Nusselt number with an increase in the volume fraction. An increase in the Rayleigh number results an increase in the average Nusselt number for a certain nanoparticle. In order to validate the numerical model, the results of two previous works for square enclosure filled by water based Al2O3 nano-particles as nanofluids. The first work was variation of average Nusselt number and volume fraction for Ra number Ra=103. There are excellent agreement in results and the maximum difference between these results reach 4.2%. A relation between average Nusselt number and Ra number also compared for other previous work. There are agreement in results and found the maximum difference between results reach to 6.5% approximately at Ra=105 which validate the present computational model.

An Investigation of Natural Convection Heat Transfer in a Square Enclosure Filled with Nanofluid

Ayad M. Salman

Engineering and Technology Journal, 2011, Volume 29, Issue 11, Pages 2216-2233

In this research, numerical solution of natural convection heat transfer of nanofluids in two-dimensional square enclosures is obtained for different values of Rayleigh numbers and volume fraction of nanofluids. Numerical simulation has then been undertaken for the mixture of Cu-water as nanofluid. The stream–vorticity form of
the Navier–Stokes equations and energy equation are used in this study. The present model is utilized to obtain results in the range of Rayleigh number 103–105 and volume fractions of nanofluids (0.025-0.1). The enclosure which represent twodimensional square enclosure with heated left side wall, while the right side was cold,
the top and bottom walls were adiabatic. The governing equations are solved with finite-difference technique by central difference scheme. A computer program in (FORTRAN 90) was used to carry out the numerical solution. The results are a remarkable increase in the average Nusselt number with an increase in the volume fraction. An increase in the Rayleigh number results an increase in the average Nusselt number for a certain nanoparticle. In order to validate the numerical model,
the results of two previous works for square enclosure filled by water based Al2O3 nano-particles as nanofluids. The first work was variation of average Nusselt number and volume fraction for Ra number Ra=103. There are excellent agreement in results and the maximum difference between theses results reach 4.2%. A relation between
average Nusselt number and Ra number also compared for other previous work. There are agreement in results and found the maximum difference between results reach to 6.5% approximately at Ra=105 which validate the present computational model.

Induced Buoyancy In Inclined Solar Chimney For Natural Ventilation

Zinah Jaber Khalaf; Jalal M. Jalil

Engineering and Technology Journal, 2011, Volume 29, Issue 2, Pages 183-194

A 2-D plane, steady, incompressible, turbulent flow field developed by natural
convection inside inclined solar chimney at different inclination angles ranging
from (30o to 90o), heat fluxes from (100 W/m² to 500 W/m²) and chimney
thickness(0.1, 0.2 m) chimney is investigated numerically. It is found that
maximum air temperature and maximum volume flow rate was 101.7oC, 306.3
m³/h respectively at heat flux,500 W/m2; inclination angle; 90o and chimney
thickness; 0.2m. Maximum outlet air velocity was 0.488 m/s at chimney
thickness; 0.1m, heat flux; 500 W/m2; and inclination angle; 90o. Increase in heat
flux, inclination angle and chimney thickness leads to increasing of volume flow
rate. Increase in chimney cross-sectional area leads to decrease in air velocity and
increase in volume flow rate

Numerical Study of Solidification in Cavity with the Presence of Natural Convection

Wahid S. Mohammad

Engineering and Technology Journal, 2010, Volume 28, Issue 6, Pages 1160-1168

A study of Laminar two dimensional transient solidification with time –
dependent natural convection in the melt is carried out. The mathematical model
for the numerical simulation is based on enthalpy porosity method. The governing
equations are descritized on a fixed grid by means of a finite volume technique.
The (SIMPLE) procedure was adopted to solve mass, momentum and energy
equations for pure phase change material (water) placed in a cooled rectangular
cavity. The cavity was cooled from top alone, right side wall alone, and right side
wall with top and bottom walls together. In the case of top cooling a parabolic
shaped pattern of ice water interface was formed. For the right side wall cooling
the effect of density changes has led to an abnormal flow circulation which has
moderately modified the heat balance of the freezing interface causing a colliding
of cool and warm fluid layers. A density variation was seen in the freezing
interface region in most of the cases. The results obtained show good agreement
with experimental and numerical results of other researchers for pure convection
with small discrepancies in the ice interface. These discrepancies may be
attributed to the physical modeling used for water freezing.

Investigation Of Heat Transfer Phenomena And Natural Flow Behavior Around A Heated Square Cylinder Placed In A Cooled Elliptical Enclosure

Sattar J. Habeeb

Engineering and Technology Journal, 2010, Volume 28, Issue 4, Pages 702-722

In this paper, a numerical study of the effect of a hot square cylinder placed on a
cooled elliptical enclosure of a laminar natural convection was carried out. This problem
is solved by using the partial differential equations, which are the stream vorticity
formulation for the flow and heat transfer in curvilinear coordinates. An elliptical
function is used, which makes the coordinate transformation from the physical domain
to the computational domain be set up by an analytical expression. About 48 tests are
performed for different ratios of the geometry such as, a /b =1.5,2.,3 , l /b = 0.25,0.5 ,
and Rayleigh number from 103 to 106, for two position of the major axis of the elliptical
enclosure, horizontal (HEE) and vertical (VEE). The results obtained in the form of
velocity vectors, streamlines, isotherms, and Nusselt number. The results show that, the
increase of the major axis of the enclosure ( a /b ratio) leads to increase the average
Nusselt number and decrease the flow strength for all Rayleigh numbers. Moreover, for
Ra≤104, there are a little difference in the results of ave Nu for all a / b and l / b ratios,
but if Ra increases, the change in the results is clear and large.