Numerical Study on Conjugate Conduction–Convection in a Cubic Enclosure Submitted to Time-Periodic Sidewall Temperature

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Wei Zhang ◽  
Zhu Huang ◽  
Chuhua Zhang ◽  
Guang Xi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Wall Thickness ◽  
Numerical Study ◽  
Finite Thickness ◽  
Pseudospectral Method ◽  
Thermal Conductivity Ratio ◽  
Conjugate Conduction ◽  
Time Periodic ◽  
Diffusivity Ratio

The laminar conjugate conduction-natural convection heat transfer in a cubic enclosure of finite thickness conductive walls and central cavity filled with fluid is comprehensively studied by using recently developed high accuracy temporal-spatial multidomain pseudospectral method. The enclosure is assumed to have one sidewall submitted to time-periodic pulsating temperature and the opposing sidewall constant temperature, and the top, bottom and two lateral sidewalls are adiabatic. The present study is devoted to explore the fluid mechanics and heat transfer mechanisms of the time-periodic conjugate conduction-natural convection in the enclosure, with particular highlights on the heat transfer resonance and back heat transfer phenomena, the perturbation propagation patterns and the three-dimensional characteristics. The computations are performed for wide ranges of controlling parameters of engineering significance, i.e., the dimensionless wall thickness 0 ≤ s ≤ 0.10, the solid–fluid thermal conductivity ratio 10 ≤ k ≤ 50 and diffusivity ratio 0.001 ≤ a ≤ 0.1, and the sidewall temperature pulsating period 1 ≤ P ≤ 103. Numerical results reveal that the time-periodic fluid flow and conjugate heat transfer performances of the enclosure system are greatly affected by the conductive walls and complexly dependent on the controlling parameters. The thickness and thermophysical properties of the conductive walls, together with the pulsating period of the sidewall temperature, govern the sidewall temperature disturbance propagation patterns (amplitude, phase position and speed) within the enclosure. The heat transfer resonance only appears in cases of large diffusivity ratio, but the variation of period-averaged heat transfer rate with respect to the pulsating period is quite different from that of the zero wall thickness enclosure. The back heat transfer exists in region close to the corners formed by either the top or bottom walls and the enclosure hot sidewall, and the former is more remarkable in both scale and duration and is gradually disappearing as the pulsating period increases.

Conjugate Natural Convection in a Square Porous Cavity Filled with a Nanofluid in the Presence of Two Isothermal Cylindrical Sources

2021 ◽  
Vol 80 (1) ◽  
pp. 147-164
Author(s):  
Islam Bouafia ◽  
Razli Mehdaoui ◽  
Syham Kadri ◽  
Mohammed Elmir
Keyword(s):  
Natural Convection ◽  
Wall Thickness ◽  
Numerical Study ◽  
Solid Wall ◽  
Finite Thickness ◽  
Convection Heat Transfer ◽  
Thick Wall ◽  
Thermal Conductivity Ratio ◽  
Porous Cavity ◽  
Conjugate Natural Convection

In this work, a numerical study has been performed for the problem of steady-state natural convection in a square porous cavity having a solid wall of finite thickness and conductivity filled by a nanofluid in the presence of two isothermal cylindrical sources. The external walls of the cavity are considered adiabatic and the circular sources are maintained at a hot and cold uniform temperatures. The internal thick wall has been a conducting solid. The governing dimensionless equations are solved using Galerkin finite element method and Darcy-Brinkman model assumed to be adopted. The results are presented as isotherms, streamlines, stream function values, average and local Nusselt number for various combinations of Rayleigh and Darcy numbers, concentration of nanoparticles, Thermal conductivity ratio, and dimensionless wall thickness of the solid portion. The convection heat transfer can be enhanced by increasing of these parameters except for the wall thickness.

NATURAL CONVECTION HEAT TRANSFER FROM A DISCRETE HEAT SOURCE COUPLED WITH CONDUCTION DOMINATED PHASE CHANGE

1998 ◽  
Vol 22 (3) ◽  
pp. 269-289
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Heat Source ◽  
Phase Change ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Discrete Heat Source

A numerical study has been conducted for the heat transfer from a discrete heat source by natural convection in air above coupled with conduction dominated melting of a phase change material (PCM) below via a wall of finite thermal diffusivity. Results indicate that the presence of a PCM layer underneath the wall significantly delays the temperature rise of the heat source. The time delay increases as the thermal diffusivity of the wail material decreases and as the thickness of the PCM layer increases. For high thermal conductivity wall materials [Formula: see text] the steady state heat source temperatures are similar and independent of the PCM layer. On the other hand, for [Formula: see text], the steady state temperatures are higher and dependent on the thickness of the PCM layer. A correlation is proposed in terms of the thickness of the PCM layer and the thermal conductivity ratio of the wall.

Effects of Nonuniform Heating and Wall Conduction on Natural Convection in a Square Porous Cavity Using LTNE Model

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
A. I. Alsabery ◽  
A. J. Chamkha ◽  
I. Hashim ◽  
P. G. Siddheshwar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Wall Thickness ◽  
Solid Wall ◽  
Finite Thickness ◽  
Weighted Average ◽  
Nonuniform Heating ◽  
Conductivity Ratio ◽  
Cold Temperatures ◽  
Porous Cavity

The effects of nonuniform heating and a finite wall thickness on natural convection in a square porous cavity based on the local thermal nonequilibrium (LTNE) model are studied numerically using the finite difference method (FDM). The finite-thickness horizontal wall of the cavity is heated either uniformly or nonuniformly, and the vertical walls are maintained at constant cold temperatures. The top horizontal insulated wall allows no heat transfer to the surrounding. The Darcy law is used along with the Boussinesq approximation for the flow. The results of this study are obtained for various parametric values of the Rayleigh number, thermal conductivity ratio, ratio of the wall thickness to its height, and the modified conductivity ratio. Comparisons with previously published work verify good agreement with the proposed method. The effects of the various parameters on the streamlines, isotherms, and the weighted-average heat transfer are shown graphically. It is shown that a thicker bottom solid wall clearly inhibits the temperature gradient which then leads to the thermal equilibrium case. Further, the overall heat transfer is highly affected by the presence of the solid wall. The results have possible applications in the heat-storage fluid-saturated porous systems and the applications of the high power heat transfer.

scholarly journals Natural Convection in a Differentially Heated Square Enclosure with a Solid Polygon

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
R. Roslan ◽  
H. Saleh ◽  
I. Hashim
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Critical Size ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Left Wall ◽  
Square Enclosure

The aim of the present numerical study is to analyze the conjugate natural convection heat transfer in a differentially heated square enclosure containing a conductive polygon object. The left wall is heated and the right wall is cooled, while the horizontal walls are kept adiabatic. The COMSOL Multiphysics software is applied to solve the dimensionless governing equations. The governing parameters considered are the polygon type,3≤N≤∞, the horizontal position,0.25≤X0≤0.75, the polygon size,0≤A≤π/16, the thermal conductivity ratio,0.1≤Kr≤10.0, and the Rayleigh number,103≤Ra≤106. The critical size of the solid polygon was found exists at low conductivities. The heat transfer rate increases with the increase of the size of the solid polygon, until it reaches its maximum value. Here, the size of the solid polygon is reaches its critical value. Further, beyond this critical size of the solid polygon, will decrease the heat transfer rate.

Natural Convection Heat Transfer in a Vertical Air Layer Partitioned Into Cubical Enclosures of Finite Wall Thermal Conductivity and Thickness

1999 ◽  
Author(s):  
Y. Yamaguchi ◽  
Y. Asako
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Wall Thickness ◽  
Finite Thickness ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Wide Range

Abstract Three-dimensional natural convection heat transfer characteristics in a vertical air layer partitioned into cubical enclosures of finite wall thermal conductivity and finite thickness were obtained numerically. The outer surfaces of the enclosure are prescribed at different temperatures. These walls are often encountered in applications such as door panels and thermal insulation boards. The analyses were performed for finite wall thickness and conductivity, for Ra = 104 and 105 and for a wide range of wall thickness and thermal. The results were presented in form of temperature distributions and contour plots of Num and Qwall/Qtotal. From comparison of the results with ideal boundary conditions, a correlation for heat transfer for partitioned walls was developed. It was shown from the results that the ratio of heat transfer into the partition walls to the total heat transfer from the hot wall is a function of the product of wall thermal conductivity and thickness.

An Investigation of the Effect of interrupted fin arrangements on the Thermal Performance of a Heat Sink under a Free Convection Condition

2019 ◽  
Vol 7 (1) ◽  
pp. 43-53
Author(s):  
Abbas Jassem Jubear ◽  
Ali Hameed Abd
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Performance ◽  
Heat Sink ◽  
Numerical Study ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The heat sink with vertically rectangular interrupted fins was investigated numerically in a natural convection field, with steady-state heat transfer. A numerical study has been conducted using ANSYS Fluent software (R16.1) in order to develop a 3-D numerical model.  The dimensions of the fins are (305 mm length, 100 mm width, 17 mm height, and 9.5 mm space between fins. The number of fins used on the surface is eight. In this study, the heat input was used as follows: 20, 40, 60, 80, 100, and 120 watts. This study focused on interrupted rectangular fins with a different arrangement and angle of the fins. Results show that the addition of interruption in fins in various arrangements will improve the thermal performance of the heat sink, and through the results, a better interruption rate as an equation can be obtained.

scholarly journals Effects of the Wall Properties on the Cooling Efficiency in a Thermosyphon Containing PCM Suspensions

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 572
Author(s):  
Ching-Jenq Ho ◽  
Shih-Ming Lin ◽  
Chi-Ming Lai
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Wall Thickness ◽  
Thermal Conductivity Ratio ◽  
Heat Transfer Efficiency ◽  
Wall Properties ◽  
Heating Section ◽  
Cooling Section ◽  
Optimum Heat ◽  
Parameter Ranges

This study explores the effects of pipe wall properties (thermal conductivity k and wall thickness tw) on the heat transfer performance of a rectangular thermosyphon with a phase change material (PCM) suspension and a geometric configuration (aspect ratio = 1; dimensionless heating section length = 0.8; dimensionless relative elevation between the cooling and the heating sections = 2) that ensures the optimum heat transfer efficiency in the cooling section. The following parameter ranges are studied: the dimensionless loop wall thickness (0 to 0.5), wall-to-fluid thermal conductivity ratio (0.1 to 100), modified Rayleigh number (1010 to 1011), and volumetric fraction of PCM particles (0 to 10%). The results show that appropriate selection of k and tw can lead to improved heat transfer effectiveness in the cooling section of the PCM suspension-containing rectangular thermosyphon.

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