**Commenced**in January 2007

**Frequency:**Monthly

**Edition:**International

**Paper Count:**466

# Search results for: Natural convection

##### 466 Magnetohydrodynamic Damping of Natural Convection Flows in a Rectangular Enclosure

**Authors:**
M. Battira,
R. Bessaih

**Abstract:**

**Keywords:**
Natural convection,
Magnetic field,
Oscillatory,
Cavity,
Liquid metal.

##### 465 Investigation of Enhancement of Heat Transfer in Natural Convection Utilizing of Nanofluids

**Authors:**
S. Etaig,
R. Hasan,
N. Perera

**Abstract:**

**Keywords:**
Computational fluid Dynamics,
Natural convection,
Nanofluid and Thermal conductivity.

##### 464 Natural and Mixed Convection Heat Transfer Cooling of Discrete Heat Sources Placed Near the Bottom on a PCB

**Authors:**
Tapano Kumar Hotta,
S P Venkateshan

**Abstract:**

**Keywords:**
Discrete heat source,
mixed convection,
natural
convection,
vertical channel

##### 463 Natural Convection of Water-Based CuO Nanofluids in a Cylindrical Enclosure

**Authors:**
Baha Tulu Tanju,
Kamil Kahveci

**Abstract:**

**Keywords:**
CuO,
enclosure,
nanofluid,
natural convection

##### 462 Entropy Generation Analyze Due to the Steady Natural Convection of Newtonian Fluid in a Square Enclosure

**Authors:**
T. T. Naas,
Y. Lasbet,
C. Kezrane

**Abstract:**

The thermal control in many systems is widely accomplished applying mixed convection process due to its low cost, reliability and easy maintenance. Typical applications include the aircraft electronic equipment, rotating-disc heat exchangers, turbo machinery, and nuclear reactors, etc. Natural convection in an inclined square enclosure heated via wall heater has been studied numerically. Finite volume method is used for solving momentum and energy equations in the form of stream function–vorticity. The right and left walls are kept at a constant temperature, while the other parts are adiabatic. The range of the inclination angle covers a whole revolution. The method is validated for a vertical cavity. A general power law dependence of the Nusselt number with respect to the Rayleigh number with the coefficient and exponent as functions of the inclination angle is presented. For a fixed Rayleigh number, the inclination angle increases or decreases is found.

**Keywords:**
Inclined enclosure,
natural convection in enclosure,
Nusselt number.

##### 461 Numerical Investigation of Natural Convection of Pine, Olive, and Orange Leaves

**Authors:**
Ali Reza Tahavvor,
Saeed Hosseini,
Nazli Jowkar,
Behnam Amiri

**Abstract:**

**Keywords:**
Computational fluid dynamic,
heat flux,
heat
transfer,
natural convection.

##### 460 Effects of Roughness Elements on Heat Transfer during Natural Convection

**Abstract:**

**Keywords:**
Natural convection,
Rayleigh number,
surface
roughness,
Nusselt number,
Lattice Boltzmann Method.

##### 459 Numerical Modeling of Natural Convection on Various Configuration of Rectangular Fin Arrays on Vertical Base Plates

**Authors:**
H.R.Goshayeshi,
M.Fahim inia,
M.M.Naserian

**Abstract:**

In this research, the laminar heat transfer of natural convection on vertical surfaces has been investigated. Most of the studies on natural convection have been considered constantly whereas velocity and temperature domain, do not change with time, transient one are used a lot. Governing equations are solved using a finite volume approach. The convective terms are discretized using the power-law scheme, whereas for diffusive terms the central difference is employed. Coupling between the velocity and pressure is made with SIMPLE algorithm. The resultant system of discretized linear algebraic equations is solved with an alternating direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and heat transfer of natural convection on these surfaces without sliding is studied and finally optimization is done.

**Keywords:**
Natural convection,
vertical surfaces,
SIMPLE
algorithm,
Rectangular fins.

##### 458 Analyses of Natural Convection Heat Transfer from a Heated Cylinder Mounted in Vertical Duct

**Authors:**
H. Bhowmik,
A. Faisal,
Ahmed Al Yaarubi,
Nabil Al Alawi

**Abstract:**

Experiments are conducted to analyze the steady-state and the power-on transient natural convection heat transfer from a horizontal cylinder mounted in a vertical up flow circular duct. The heat flux ranges from 177 W/m^{2} to 2426 W/m^{2} and the Rayleigh number ranges from 1×10^{4} to 4.35×10^{4}. For natural air flow and constant heat flux condition, the effects of heat transfer around the cylinder under steady-state condition are investigated. The steady-state results compare favorably with that of the available data. The effects of transient heat transfer data on different angular position of the thermocouple (0^{o}, 90^{o}, 180^{o}) are also reported. It is observed that the transient heat transfer around the cylinder is strongly affected by the position of thermocouples. In the transient region, the rate of heat transfer obtained at 90^{o} and 180^{o} are higher than that of stagnation point (0^{o}). Finally, the dependence of the average Nusselt number on Rayleigh number for steady and transient natural convection heat transfer are analyzed, and a correlation equation is presented.

**Keywords:**
Steady-state,
transient,
natural convection,
Rayleigh number,
Nusselt number,
Fourier Number.

##### 457 Enhancement of Natural Convection Heat Transfer within Closed Enclosure Using Parallel Fins

**Authors:**
F. A. Gdhaidh,
K. Hussain,
H. S. Qi

**Abstract:**

A numerical study of natural convection heat transfer in water filled cavity has been examined in 3-Dfor single phase liquid cooling system by using an array of parallel plate fins mounted to one wall of a cavity. The heat generated by a heat source represents a computer CPU with dimensions of 37.5∗37.5mm mounted on substrate. A cold plate is used as a heat sink installed on the opposite vertical end of the enclosure. The air flow inside the computer case is created by an exhaust fan. A turbulent air flow is assumed and k-ε model is applied. The fins are installed on the substrate to enhance the heat transfer. The applied power energy range used is between 15 - 40W. In order to determine the thermal behaviour of the cooling system, the effect of the heat input and the number of the parallel plate fins are investigated. The results illustrate that as the fin number increases the maximum heat source temperature decreases. However, when the fin number increases to critical value the temperature start to increase due to the fins are too closely spaced and that cause the obstruction of water flow. The introduction of parallel plate fins reduces the maximum heat source temperature by 10% compared to the case without fins. The cooling system maintains the maximum chip temperature at 64.68°C when the heat input was at 40W that is much lower than the recommended computer chips limit temperature of no more than 85°C and hence the performance of the CPU is enhanced.

**Keywords:**
Chips limit temperature,
closed enclosure,
natural
convection,
parallel plate,
single phase liquid.

##### 456 Simulation of Natural Convection Flow in an Inclined open Cavity using Lattice Boltzmann Method

**Authors:**
H. Sajjadi,
M. Gorji,
GH.R. Kefayati,
D. D. Ganji,
M. Shayan nia

**Abstract:**

**Keywords:**
Lattice Boltzmann Method,
Inclination angle,
Opencavity,
Natural convection

##### 455 DQ Analysis of 3D Natural Convection in an Inclined Cavity Using an Velocity-Vorticity Formulation

**Abstract:**

In this paper, the differential quadrature method is applied to simulate natural convection in an inclined cubic cavity using velocity-vorticity formulation. The numerical capability of the present algorithm is demonstrated by application to natural convection in an inclined cubic cavity. The velocity Poisson equations, the vorticity transport equations and the energy equation are all solved as a coupled system of equations for the seven field variables consisting of three velocities, three vorticities and temperature. The coupled equations are simultaneously solved by imposing the vorticity definition at boundary without requiring the explicit specification of the vorticity boundary conditions. Test results obtained for an inclined cubic cavity with different angle of inclinations for Rayleigh number equal to 103, 104, 105 and 106 indicate that the present coupled solution algorithm could predict the benchmark results for temperature and flow fields. Thus, it is convinced that the present formulation is capable of solving coupled Navier-Stokes equations effectively and accurately.

**Keywords:**
Natural convection,
velocity-vorticity formulation,
differential quadrature (DQ).

##### 454 Simulation of Natural Convection in Concentric Annuli between an Outer Inclined Square Enclosure and an Inner Horizontal Cylinder

**Authors:**
Sattar Al-Jabair,
Laith J. Habeeb

**Abstract:**

**Keywords:**
natural convection,
concentric annulus,
square
inclined enclosure

##### 453 Spectral Analysis of Radiation-Induced Natural Convection in Littoral Waters

**Authors:**
Yadan Mao,
Chengwang Lei,
John C. Patterson

**Abstract:**

The mixing of pollutions and sediments in near shore regions of natural water bodies depends heavily on the characteristics such as the strength and frequency of flow instability. In the present paper, the instability of natural convection induced by absorption of solar radiation in littoral regions is considered. Spectral analysis is conducted on the quasi-steady state flow to reveal the power and frequency modes of the instability at various positions. Results indicate that the power of instability, the number of frequency modes, the prominence of higher frequency modes, and the highest frequency mode increase with the offshore distance and/or Rayleigh number. Harmonic modes are present at relatively low Rayleigh numbers. For a given offshore distance, the position with the strongest power of instability is located adjacent to the sloping bottom while the frequency modes are the same over the local depth. As the Rayleigh number increases, the unstable region extends toward the shore.

**Keywords:**
Instability,
Littoral waters,
natural convection,
Spectral analysis

##### 452 Lattice Boltzmann Simulation of MHD Natural Convection in a Nanofluid-Filled Enclosure with Non-Uniform Heating on Both Side Walls

**Authors:**
Imen Mejri,
Ahmed Mahmoudi,
Mohamed A. Abbassi,
Ahmed Omri

**Abstract:**

This paper examines the natural convection in a square enclosure filled with a water-Al_{2}O_{3} nanofluid and is subjected to a magnetic field. The side walls of the cavity have spatially varying sinusoidal temperature distributions. The horizontal walls are adiabatic. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra=10^{3} to 10^{6}, Hartmann number varied from Ha=0 to 90, phase deviation (γ=0, π/4, π/2, 3π/4 and π) and the solid volume fraction of the nanoparticles between Ø = 0 and 6%. The results show that the heat transfer rate increases with an increase of the Rayleigh number but it decreases with an increase of the Hartmann number. For γ=π/2 and Ra=10^{5} the magnetic field augments the effect of nanoparticles. At Ha=0, the greatest effects of nanoparticles are obtained at γ = 0 and π/4 for Ra=10^{4} and 10^{5} respectively.

**Keywords:**
Lattice Boltzmann Method,
magnetic field,
Natural convection,
nanofluid,
Sinusoidal temperature distribution.

##### 451 Experimental Investigation of Heat Pipe with Annular Fins under Natural Convection at Different Inclinations

**Authors:**
Gangacharyulu Dasaroju,
Sumeet Sharma,
Sanjay Singh

**Abstract:**

Heat pipe is characterised as superconductor of heat because of its excellent heat removal ability. The operation of several engineering system results in generation of heat. This may cause several overheating problems and lead to failure of the systems. To overcome this problem and to achieve desired rate of heat dissipation, there is need to study the performance of heat pipe with annular fins under free convection at different inclinations. This study demonstrates the effect of different mass flow rate of hot fluid into evaporator section on the condenser side heat transfer coefficient with annular fins under natural convection at different inclinations. In this study annular fins are used for the experimental work having dimensions of length of fin, thickness of fin and spacing of fin as 10 mm, 1 mm and 6 mm, respectively. The main aim of present study is to discover at what inclination angles the maximum heat transfer coefficient shall be achieved. The heat transfer coefficient on the external surface of heat pipe condenser section is determined by experimental method and then predicted by empirical correlations. The results obtained from experimental and Churchill and Chu relation for laminar are in fair agreement with not more than 22% deviation. It is elucidated the maximum heat transfer coefficient of 31.2 W/(m^{2}-K) at 25˚ tilt angle and minimal condenser heat transfer coefficient of 26.4 W/(m^{2}-K) is seen at 45˚ tilt angle and 200 ml/min mass flow rate. Inclination angle also affects the thermal performance of heat pipe. Beyond 25^{o} inclination, heat transport rate starts to decrease.

**Keywords:**
Annular fins,
condenser heat transfer coefficient,
heat pipe,
natural convection,
tilt angle.

##### 450 Unsteady Natural Convection in a Square Cavity Partially Filled with Porous Media Using a Thermal Non-Equilibrium Model

**Authors:**
Ammar Alsabery,
Habibis Saleh,
Norazam Arbin,
Ishak Hashim

**Abstract:**

Unsteady natural convection and heat transfer in a square cavity partially filled with porous media using a thermal non-equilibrium model is studied in this paper. The left vertical wall is maintained at a constant hot temperature Th and the right vertical wall is maintained at a constant cold temperature Tc, while the horizontal walls are adiabatic. The governing equations are obtained by applying the Darcy model and Boussinesq approximation. COMSOL’s finite element method is used to solve the non-dimensional governing equations together with specified boundary conditions. The governing parameters of this study are the Rayleigh number (Ra = 10^5, and Ra = 10^6 ), Darcy namber (Da = 10^−2, and Da = 10^−3), the modified thermal conductivity ratio (10^−1 ≤ γ ≤ 10^4), the inter-phase heat transfer coefficien (10^−1 ≤ H ≤ 10^3) and the time dependent (0.001 ≤ τ ≤ 0.2). The results presented for values of the governing parameters in terms of streamlines in both fluid/porous-layer, isotherms of fluid in fluid/porous-layer, isotherms of solid in porous layer, and average Nusselt number.

**Keywords:**
Unsteady natural convection,
Thermal non-equilibrium model,
Darcy model.

##### 449 Natural Convection in Wavy-Wall Cavities Filled with Power-Law Fluid

**Authors:**
Cha’o-Kuang Chen,
Ching-Chang Cho

**Abstract:**

This paper investigates the natural convection heat transfer performance in a complex-wavy-wall cavity filled with power-law fluid. In performing the simulations, the continuity, Cauchy momentum and energy equations are solved subject to the Boussinesq approximation using a finite volume method. The simulations focus specifically on the effects of the flow behavior index in the power-law model and the Rayleigh number on the flow streamlines, isothermal contours and mean Nusselt number within the cavity. The results show that pseudoplastic fluids have a better heat transfer performance than Newtonian or dilatant fluids. Moreover, it is shown that for Rayleigh numbers greater than *Ra*=10^{3}, the mean Nusselt number has a significantly increase as the flow behavior index is decreased.

**Keywords:**
Non-Newtonian fluid,
Power-law fluid,
Natural convection,
Heat transfer enhancement,
Cavity,
Wavy wall.

##### 448 Natural Convection in a Porous Medium Cavity with an Applied Vertical Magnetic Field using Lattice Boltzmann Method

**Authors:**
H.A. Ashorynejad,
M. Farhadi,
K.Sedighi,
A.Hasanpour

**Abstract:**

**Keywords:**
Lattice Boltzmann method ,
Natural convection ,
Magnetohydrodynamic ,
Porous medium

##### 447 Numerical Study of Transient Laminar Natural Convection Cooling of high Prandtl Number Fluids in a Cubical Cavity: Influence of the Prandtl Number

**Authors:**
O. Younis,
J. Pallares,
F. X. Grau

**Abstract:**

This paper presents and discusses the numerical simulations of transient laminar natural convection cooling of high Prandtl number fluids in cubical cavities, in which the six walls of the cavity are subjected to a step change in temperature. The effect of the fluid Prandtl number on the heat transfer coefficient is studied for three different fluids (Golden Syrup, Glycerin and Glycerin-water solution 50%). The simulations are performed at two different Rayleigh numbers (5·106 and 5·107) and six different Prandtl numbers (3 · 105 ≥Pr≥ 50). Heat conduction through the cavity glass walls is also considered. The propsed correlations of the averaged heat transfer coefficient (N u) showed that it is dependant on the initial Ra and almost independent on P r. The instantaneous flow patterns, temperature contours and time evolution of volume averaged temperature and heat transfer coefficient are presented and analyzed.

**Keywords:**
Transient natural convection,
High Prandtl number,
variable viscosity.

##### 446 Study of Natural Convection in a Triangular Cavity Filled with Water: Application of the Lattice Boltzmann Method

**Authors:**
Imen Mejri,
Ahmed Mahmoudi,
Mohamed A. Abbassi,
Ahmed Omri

**Abstract:**

The Lattice Boltzmann Method (LBM) with double populations is applied to solve the steady-state laminar natural convective heat transfer in a triangular cavity filled with water. The bottom wall is heated, the vertical wall is cooled, and the inclined wall is kept adiabatic. The buoyancy effect was modeled by applying the Boussinesq approximation to the momentum equation. The fluid velocity is determined by D2Q9 LBM and the energy equation is discritized by D2Q4 LBM to compute the temperature field. Comparisons with previously published work are performed and found to be in excellent agreement. Numerical results are obtained for a wide range of parameters: the Rayleigh number from to and the inclination angle from 0° to 360°. Flow and thermal fields were exhibited by means of streamlines and isotherms. It is observed that inclination angle can be used as a relevant parameter to control heat transfer in right-angled triangular enclosures.

**Keywords:**
Heat transfer,
inclination angle,
Lattice Boltzmann Method,
Nusselt number,
Natural convection,
Rayleigh number.

##### 445 Natural Convection Heat Transfer from Inclined Cylinders: A Unified Correlation

**Authors:**
Neetu Rani,
Hema Setia,
Marut Dutt. R.K. Wanchoo

**Abstract:**

An empirical correlation for predicting the heat transfer coefficient for a cylinder under free convection, inclined at any arbitrary angle with the horizontal has been developed in terms of Nusselt number, Prandtl number and Grashof number. Available experimental data was used to determine the parameters for the proposed correlation. The proposed correlation predicts the available data well within ±10%, for Prandtl number in the range 0.68-0.72 and Grashof number in the range 1.4×10^{4}–1.2×10^{10}.

**Keywords:**
Heat transfer,
inclined cylinders,
natural convection,
Nusselt number,
Prandtl number,
Grashof number.

##### 444 Effect of Eccentricity on Conjugate Natural Convection in Vertical Eccentric Annuli

**Authors:**
A. Jamal,
M. A. I. El-Shaarawi,
E. M. A. Mokheimer

**Abstract:**

**Keywords:**
Conjugate natural convection,
eccentricity,
heat transfer,
vertical eccentric annuli.

##### 443 Investigation of Heat Transfer by Natural Convection in an Open Channel

**Authors:**
Mahmoud S. Ahmed,
Hany A. Mohamed,
Mohamed A. Omara,
Mohamed F. Abdeen

**Abstract:**

Experimental study of natural convection heat transfer inside smooth and rough surfaces of vertical and inclined equilateral triangular channels of different inclination angles with a uniformly heated surface are performed. The inclination angle is changed from 15º to 90º. Smooth and rough surface of average roughness (0.02mm) are used and their effect on the heat transfer characteristics are studied. The local and average heat transfer coefficients and Nusselt number are obtained for smooth and rough channels at different heat flux values, different inclination angles and different Rayleigh numbers (Ra) 6.48 × 105 ≤ Ra ≤ 4.78 × 106. The results show that the local Nusselt number decreases with increase of axial distance from the lower end of the triangular channel to a point near the upper end of channel, and then, it slightly increases. Higher values of local Nusselt number for rough channel along the axial distance compared with the smooth channel. The average Nusselt number of rough channel is higher than that of smooth channel by about 8.1% for inclined case at θ = 45o and 10% for vertical case. The results obtained are correlated using dimensionless groups for both rough and smooth surfaces of the inclined and vertical triangular channels.

**Keywords:**
Natural heat transfer convection,
constant heat flux,
open channels,
heat transfer.

##### 442 Numerical Analysis of Turbulent Natural Convection in a Square Cavity using Large- Eddy Simulation in Lattice Boltzmann Method

**Authors:**
H. Sajjadi,
M. Gorji,
GH.R. Kefayati,
D. D. Ganji,
M. Shayan Nia

**Abstract:**

**Keywords:**
Turbulent natural convection,
Large Eddy
Simulation,
Lattice Boltzmann Method

##### 441 Lattice Boltzmann Simulation of Natural Convection Heat Transfer in an Inclined Open Ended Cavity

**Authors:**
M.Jafari,
A.Naysari,
K.Bodaghi

**Abstract:**

In the present study, the lattice Boltzmann Method (LBM) is applied for simulating of Natural Convection in an inclined open ended cavity. The cavity horizontal walls are insulated while the west wall is maintained at a uniform temperature higher than the ambient. Prandtl number is fixed to 0.71 (air) while Rayligh numbers, aspect ratio of the cavity are changed in the range of 103 to 104 and of 1-4, respectively. The numerical code is validated for the previously results for open ended cavities, and then the results of an inclined open ended cavity for various angles of rotating open ended cavity are presented. Result shows by increasing of aspect ratio, the average Nusselt number on hot wall decreases for all rotation angles. When gravity acceleration direction is opposite of standard gravity direction the convection heat transfer has a manner same as conduction.

**Keywords:**
Lattice Boltzmann Method,
Open Ended Cavity,
Natural Convection,
Inclined Cavity.

##### 440 Effect of Prandtl Number on Natural Convection Heat Transfer from a Heated Semi-Circular Cylinder

**Authors:**
Avinash Chandra,
R. P. Chhabra

**Abstract:**

**Keywords:**
Constant heat flux,
Constant surface temperature,
Grashof number,
natural convection,
Prandtl number,
Semi-circular
cylinder

##### 439 Numerical Solution of Transient Natural Convection in Vertical Heated Rectangular Channel between Two Vertical Parallel MTR-Type Fuel Plates

**Authors:**
Djalal Hamed

**Abstract:**

The aim of this paper is to perform, by mean of the finite volume method, a numerical solution of the transient natural convection in a narrow rectangular channel between two vertical parallel Material Testing Reactor (MTR)-type fuel plates, imposed under a heat flux with a cosine shape to determine the margin of the nuclear core power at which the natural convection cooling mode can ensure a safe core cooling, where the cladding temperature should not reach a specific safety limits (90 °C). For this purpose, a computer program is developed to determine the principal parameters related to the nuclear core safety, such as the temperature distribution in the fuel plate and in the coolant (light water) as a function of the reactor core power. Throughout the obtained results, we noticed that the core power should not reach 400 kW, to ensure a safe passive residual heat removing from the nuclear core by the upward natural convection cooling mode.

**Keywords:**
Buoyancy force,
friction force,
friction factor,
finite volume method,
transient natural convection,
thermal hydraulic analysis,
vertical heated rectangular channel.

##### 438 Steady State Natural Convection in Vertical Heated Rectangular Channel between Two Vertical Parallel MTR-Type Fuel Plates

**Authors:**
Djalal Hamed

**Abstract:**

**Keywords:**
Buoyancy force,
friction force,
friction factor,
MTR-type fuel,
natural convection,
vertical heated rectangular channel.

##### 437 Free Convection in a Darcy Thermally Stratified Porous Medium That Embeds a Vertical Wall of Constant Heat Flux and Concentration

**Authors:**
Maria Neagu

**Abstract:**

This paper presents the heat and mass driven natural convection succession in a Darcy thermally stratified porous medium that embeds a vertical semi-infinite impermeable wall of constant heat flux and concentration. The scale analysis of the system determines the two possible maps of the heat and mass driven natural convection sequence along the wall as a function of the process parameters. These results are verified using the finite differences method applied to the conservation equations.

**Keywords:**
Finite difference method,
natural convection,
porous
medium,
scale analysis,
thermal stratification.