An Experimental Study on Natural Convection Heat Transfer in an Inclined Square Enclosure Containing Internal Energy Sources

1988 ◽  
Vol 110 (2) ◽  
pp. 345-349 ◽  
Author(s):  
Jae-Heon Lee ◽  
R. J. Goldstein
Keyword(s):  
Natural Convection ◽  
Internal Energy ◽  
Extreme Values ◽  
Convection Heat Transfer ◽  
Energy Sources ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Inclination Angles ◽  
The Right ◽  
Rayleigh Numbers

An experiment was carried out to study two-dimensional laminar natural convection within an inclined square enclosure containing fluid with internal energy sources bounded by four rigid planes of constant equal temperature. Inclination angles, from the horizontal, of 0, 15, 30, and 45 deg for Rayleigh numbers from 1.0 × 104 to 1.5 × 105 were studied. At inclined angles of 0 and 15 deg, there are two extreme values of temperature and temperature gradient within the fluid, while there is only one at 30 and 45 deg. Local and average Nusselt numbers are obtained on all four walls. As the inclination angle increases, the average Nusselt number increases on the right (upper) and bottom walls, decreases on the left (lower) wall and stays almost constant on the top wall.

Three-Dimensional Laminar Natural Convection in an Inclined Air Slot With Hexagonal Honeycomb Core

1991 ◽  
Vol 113 (4) ◽  
pp. 906-911 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Z. Chen ◽  
M. Faghri
Keyword(s):  
Natural Convection ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Inclination Angles ◽  
Side Walls ◽  
Rayleigh Numbers

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in an inclined air slot with a hexagonal honeycomb core. The air slot is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the complex cross section onto a rectangle, coupled with a calculation procedure for fully elliptic three-dimensional flows. The calculations are performed for Rayleigh numbers in the range of 103 to 105, inclination angles in the range of −90 to 80 deg, Prandtl number of 0.7, and for five values of the aspect ratio. Three types of thermal boundary condition for the honeycomb side walls are considered. The average Nusselt number results are compared with those for a rectangular two-dimensional enclosure.

Natural Convection Heat Transfer From Horizontal Rectangular Ducts

2006 ◽  
Vol 129 (9) ◽  
pp. 1195-1202 ◽  
Author(s):  
Mohamed E. Ali
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rayleigh Numbers

Experimental investigations have been reported on steady state natural convection from the outer surface of horizontal ducts in air. Five ducts have been used with aspect ratios (Γ=duct height/duct width) of 2, 1, and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for transition regime using the axial distance as a characteristic length. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers, the aspect ratio, and area ratio for the laminar and transition regimes. The longitudinal or total averaged heat transfer coefficients are observed to decrease in the laminar region and to increase in the transition region. Laminar regimes are obtained only at very small heat fluxes, otherwise, transitions are observed.

Experimental Apparatus for the Determination of Nusselt and Rayleigh Numbers During Natural Convection From a Heated Horizontal Cylinder

2009 ◽  
Author(s):  
S¸evket O¨zgu¨r Atayılmaz ◽  
Ahmet Selim Dalkılıc¸ ◽  
Hakan Demir ◽  
Nuri Alpay Ku¨rekci
Keyword(s):  
Natural Convection ◽  
Convection Heat Transfer ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Nusselt Numbers ◽  
Surface Temperatures ◽  
Experimental Apparatus ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

Determination of Nusselt and Rayleigh numbers during natural convection heat transfer from horizontal cylinders are investigated experimentally and numerically. Experiments are done by means of the test cabin inside a conditioned room at different environmental and surface temperatures. The environmental and cylinder surface temperatures are ranging between 10–40 °C and 20–60 °C respectively. 1 m long horizontal copper cylinder is used and has outer diameters of 4.8 mm including centered silicone covered cylindrical resistant wires inside it. The experimental apparatus is designed to capable of changing the different operating parameters such as heat flux and environmental temperature. The existence of the gap on the closed surfaces in the test cabin which can cause a stack effect, affected temperature and velocity fields, disturbance of the natural convection condition is also checked. The detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure are reported and the study of experimental setups from the available literature survey with the existing one are compared in this paper. The uncertainty analysis method proposed by Kline and McClintock is used and explained elaborately. Detailed information and algorithm of numerical method are given to ease the understanding of the numerical part of study. Alteration of Nusselt numbers with Rayleigh numbers, the temperature distribution on the heated horizontal cylinder surface by means of Fluent CFD program are shown in the paper. In addition to this, Morgan’s correlation is used for the comparison of Nusselt number and is found in good agreement with the experimental results.

Effect on Natural Convection of the Distance Between an Inclined Discretely Heated Plate and a Parallel Shroud Below

2002 ◽  
Vol 124 (3) ◽  
pp. 441-451 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Vincenzo Naso
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Heated Plate ◽  
Heat Sources ◽  
Channel Spacing ◽  
Nusselt Numbers ◽  
Test Conditions ◽  
Inclination Angles ◽  
Rayleigh Numbers ◽  
Opposite Tendency

An experimental study on air natural convection on an inclined discretely heated plate with a parallel shroud below was carried out. Three heated strips were located in different positions on the upper wall. The distance between the walls, b, was changed in the range 7.0–40.0 mm and two values of the heat flux dissipated by the heaters were taken into account. Several inclination angles between the vertical and the horizontal were tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources are presented. The analysis shows that, for angles not greater than 85 deg, increasing the distance between walls does not reduce the wall temperatures, whereas at greater tilting angles (>85 deg) there is an opposite tendency. This is confirmed by flow visualization at angles equal to 85 deg and 90 deg and b=20.0 and 32.3 mm. Dimensionless maximum wall temperatures are correlated to the process parameters in the ranges 1.2s˙104⩽Ral cos θ⩽8.6s˙105; 0 deg⩽θ⩽88 deg; 0.48⩽l/b⩽1.6 and 10⩽L/b⩽32.6 with 1.0⩽d/l⩽3.0; the agreement with experimental data is good. The spacing which yields the best thermal performance of the channel is given. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles in the ranges 20⩽Rax′⩽8.0s˙105 and 0 deg⩽θ⩽88 deg. The exponent of monomial correlations between local Nusselt and Rayleigh numbers are in the 0.23–0.26 range. Comparisons with data from the literature, in terms of Nusselt number, exhibited minor discrepancies, mainly because of some difference in test conditions and of heat conduction in the channel walls.

Experimental and Numerical Studies of Natural Convection in Trapezoidal Cavities

1989 ◽  
Vol 111 (2) ◽  
pp. 372-377 ◽  
Author(s):  
S. W. Lam ◽  
R. Gani ◽  
J. G. Symons
Keyword(s):  
Natural Convection ◽  
Energy Transport ◽  
Convection Heat Transfer ◽  
Experimental Results ◽  
Heat Flow Rate ◽  
Nusselt Numbers ◽  
Numerical Studies ◽  
Surface Inclination ◽  
Experimental Values ◽  
Rayleigh Numbers

Natural convection heat transfer has been studied experimentally and numerically for horizontal prismatic cavities of trapezoidal section having a hot horizontal base, a cool inclined top, and insulated vertical walls. Experimental results are presented for a cavity with width-to-mean height ratio of 4, Rayleigh numbers (based on the mean cavity height) from 103 to 107, and top surface inclinations from 0 to 25 deg to the horizontal. For a given top surface inclination, the Nusselt–Rayleigh relationship follows the usual trend, but with an interesting anomaly, in which higher Nusselt numbers than expected are obtained in the range 8 × 103 < Ra < 2 × 105 for inclinations of 0 and 5 deg. Overall, as the inclination of the top surface is increased, the Nusselt number decreases, an effect that becomes greater at higher angles. The proportions of convective heat flow rate into the high side and low side of the cavity were measured and show distinct maxima at particular Rayleigh numbers (which are independent of the top surface inclination angle). The equation Nu = 0.168 [Ra (1 + cos θ)/2]0.278 [(1 − cos θmax)/(cos θ − cos θmax)]−0.199 correlates the experimental results to within 6.9 percent for the ranges 4 × 103 < Ra < 107 and 0 deg ≤ θ ≤ 25 deg, apart from the anomalous region previously indicated. It is suggested that this correlation applies for A ≥ 4. The numerical model uses a false transient ADI finite difference scheme to solve the governing two-dimensional vorticity and energy transport equations. Nusselt numbers computed by the model are in good agreement with the experimental values. The convective flow patterns generated by the model exhibit changes in number and in size of cells for different Rayleigh numbers and different top surface inclinations.

scholarly journals Numerical Investigation of Laminar Natural Convection in Inclined Square Enclosure with the Influence of Discrete Heat Source

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Chithra Devaraj ◽  
Eswaramurthi Muthuswamy ◽  
Sundararaj Kandasamy
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Source ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Correlation Coefficients ◽  
Computational Procedure ◽  
Square Enclosure ◽  
Rayleigh Numbers

Natural convection heat transfer in a two-dimensional square enclosure at various angles of inclination is investigated numerically using a finite volume based computational procedure. The heat transfer is from a constant temperature heat source of finite length centred at one of the walls to the cold wall on the opposite side while the remaining walls are insulated. The effect of area ratio of the heat sourceAfrom 0.2 to 1.0, Rayleigh number Ra from 103to 107, and angle of inclination of the enclosureθvarying from 0° to 360° on the flow field and heat transfer characteristics are investigated. Streamline and isothermal line patterns are found to be similar at low Rayleigh numbers whereas at high Rayleigh numbers the differences are significant due to the influence of the parameters considered. Average Nusselt number decreases drastically as the position of the heat source is moved above the horizontal centre line of the enclosure. Correlation of the average Nusselt number which depends on the parameters of interest is obtained in the general formCRamAn. The correlation coefficients are determined by multiple regression analysis for the entire range of Rayleigh numbers analysed and the values found by correlation equations are in good agreement with the numerical results.

scholarly journals Experimental investigation of natural convection in an enclosure with partial partitions at different angles

2014 ◽  
Vol 18 (4) ◽  
pp. 1133-1144 ◽  
Author(s):  
Osameh Ghazian ◽  
Hossein Rezvantalab ◽  
Mehdi Ashjaee
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Wood Fiber ◽  
Convection Heat Transfer ◽  
Heated Wall ◽  
Isolated Cells ◽  
Nusselt Numbers ◽  
Vertical Walls ◽  
Rayleigh Numbers ◽  
Partial Partitions

Natural convection heat transfer in a partially partitioned enclosure has been investigated experimentally using Mach-Zehnder Interferometry technique. The top and bottom of the enclosure are insulated while one of the vertical walls is heated isothermally. The partitions are made of wood fiber and are attached to the heated wall with angles changing from 30? to 150? in different experiments. The length of each partition is equal to the width of the enclosure, therefore dividing the enclosure to isolated cells only at 90?. At other angles the cells are interconnected near the cold wall. Rayleigh number based on the enclosure width is changed from 3500 to 32000. Results for the local and the average Nusselt numbers at the heated wall of the enclosure are presented and discussed for various partition angles and Rayleigh numbers. It is found that, at each Rayleigh number, there exists an optimum inclination angle which minimizes the average Nusselt number.

ANALYSIS OF NATURAL CONVECTION HEAT TRANSFER BETWEEN TWO HORIZONTAL CYLINDERS AND THEIR ENCLOSURE

1992 ◽  
Vol 16 (1) ◽  
pp. 17-32 ◽  
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Nusselt Numbers ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

A numerical study has been conducted for natural convection heat transfer for air around two horizontal heated cylinders placed inside a rectangular enclosure cooled from the side. Three cylinder spacings were investigated. The local and overall Nusselt numbers were determined over the range of Rayleigh numbers from 104 to 106. It is found that the thermal performance of the unit is strongly influenced by the Rayleigh number and, to a lesser extent, by the cylinder spacing. A correlation is suggested for the overall Nusselt number.

Unsteady Darcian Natural Convection within Porous Media of Square Enclosure at Various Rayleigh Numbers

2013 ◽  
Vol 390 ◽  
pp. 18-22
Author(s):  
Ali Hooshyar Faghiri ◽  
Hikmet Şeli Aybar ◽  
Mehrdad Khamooshi
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Constant Temperature ◽  
Transient State ◽  
Left Wall ◽  
Square Enclosure ◽  
Transient Period ◽  
The Right ◽  
Rayleigh Numbers

Transient natural convection within a 2D square cavity filled with a porous medium is numerically investigated. The left wall is suddenly heated to a constant temperature Th, while the right wall is suddenly cooled to a constant temperature Tc. Both the horizontal walls are insulated. The Finite Volume numerical method is used to solve the dimensionless governing equations. The results are obtained for the initial transient state assuaging to the steady state, and for Rayleigh number values of 102–104. It is indicated that the average Nusselt number showing an undershoot during the transient period and that the time needed to reach the steady state is longer for low Rayleigh number and shorter for high Rayleigh number.

scholarly journals Natural Convection in an Inclined Square Enclosure Containing Internal Energy Sources

1970 ◽  
Vol 37 ◽  
pp. 24-32
Author(s):  
Md. Tofiqul Islam ◽  
Sumon Saha ◽  
Md. Arif Hasan Mamun ◽  
Goutam Saha
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Internal Energy ◽  
Removal Rate ◽  
Heat Removal ◽  
Square Enclosure ◽  
Inclination Angles ◽  
Element Method

Natural convection in an inclined differentially heated square enclosure containing internally heated fluid has been investigated numerically using the Galerkin finite element method. The horizontal walls are adiabatic, while the side walls are isothermal but kept at different temperatures. Flow and heat transfer characteristics through isotherms, streamlines and average Nusselt numbers have been presented for the external Rayleigh number 103 to 106, internal Rayleigh number 105 to 108 and inclination angles 0° to 30°. The obtained computational results indicate that the strength of the convective currents depends on the internal energy. Heat removal rate is optimized at zero inclination angle for relatively weak external heating mode for all values of internal energy.Keywords: Natural convection, finite element method, square enclosure, Rayleigh number.doi:10.3329/jme.v37i0.816Journal of Mechanical Engineering Vol.37 June 2007, pp.24-32

Sign in / Sign up

Export Citation Format

Share Document