Using Porous Fins for Heat Transfer Enhancement

2000 ◽  
Vol 123 (4) ◽  
pp. 790-795 ◽  
Author(s):  
S. Kiwan ◽  
M. A. Al-Nimr
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Performance ◽  
Thermal Conductivity Ratio ◽  
Operating Parameters ◽  
Conductivity Ratio ◽  
Transfer Enhancement ◽  
Porous Fin ◽  
Novel Method ◽  
Porous Fins

This work introduces a novel method that enhances the heat transfer from a given surface by using porous fins. The thermal performance of porous fins is estimated and compared with that of the conventional solid fins. It is found that using porous fin of porosity ε may enhance the performance of an equal size conventional solid fin and, as a result, save 100 ε percent of the fin material. The effect of different design and operating parameters on the porous fin thermal performance is investigated. Examples of these parameters are Ra number, Da number, and thermal conductivity ratio. It is found that more enhancement in the porous fin performance may be achieved as Ra increases especially at large Da numbers. Also, it is found that there is an optimum limit for the thermal conductivity ratio beyond which there is no further improvement in the fin performance.

Effects of a centered conducting body on natural convection of non-Newtonian fluid in a square enclosure with time-periodic temperature distribution

2020 ◽  
Author(s):  
Peixin Ye ◽  
Dinggen Li ◽  
Zihao Yu ◽  
Haifeng Zhang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Transient Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Transfer Ratio ◽  
Periodic Temperature ◽  
Power Law Index ◽  
Time Periodic

In this paper, a modified lattice Boltzmann model that incorporates the effect of heat capacity is adopted to study the effects of a centered conducting body on natural convection of non-Newtonian fluid in a square cavity with time-periodic temperature distribution. The effects of power-law index, Rayleigh number, heat capacity ratio, thermal conductivity ratio, body size, temperature pulsating period and the temperature pulsating amplitude on fluid flow and heat transfer are analyzed in detail. The results showed that the increase of Rayleigh number and thermal conductivity ratio as well as the decrease of power-law index can strengthen both transient and global heat transfer, while the increase of heat capacitance of fluid to the solid wall can only enhance the transient heat transfer, and has little effect on the overall heat transfer. Further, the increase of body size will reduce both the transient heat transfer ratio and the overall heat transfer ratio. In addition, the decrease of temperature pulsating period can enhance the transient heat transfer, but it will slightly weaken the overall heat transfer. Finally, the results show that both the transient and the overall heat transfer ratio are increased with the increase of temperature pulsating amplitude.

Upward and downward conjugate mixed convection heat transfer in a partially porous cavity

2016 ◽  
Vol 26 (1) ◽  
pp. 159-188 ◽  
Author(s):  
Abderrahim Bourouis ◽  
Abdeslam Omara ◽  
Said Abboudi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mixed Convection ◽  
Transfer Rate ◽  
Vertical Wall ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Content Type ◽  
Moving Wall ◽  
The Right

Purpose – The purpose of this paper is to provide a numerical study of conjugate heat transfer by mixed convection and conduction in a lid-driven enclosure with thick vertical porous layer. The effect of the relevant parameters: Richardson number (Ri=0.1, 1, 10) and thermal conductivity ratio (Rk=0.1, 1, 10, 100) are investigated. Design/methodology/approach – The studied system is a two dimensional lid-driven enclosure with thick vertical porous layer. The left vertical wall of the enclosure is allowed to move in its own plane at a constant velocity. The enclosure is heated from the right vertical wall isothermally. The left and the right vertical walls are isothermal but temperature of the outside of the right vertical wall is higher than that of the left vertical wall. Horizontal walls are insulated. The governing equations are solved by finite volume method and the SIMPLE algorithm. Findings – From the finding results, it is observed that: for the two studied cases, heat transfer rate along the hot wall is a decreasing function of thermal conductivity ratio irrespective of Richardson numbers contrary to the heat transfer rate along the fluid-porous layer interface which is an increasing function of thermal conductivity ratio. At forced convection dominant regime, the difference between heat transfer rate for upward and downward moving wall is insensitive to the thermal conductivity ratio. For downward moving wall, average Nusselt number is higher than that of upward moving wall. Practical implications – Some applications: building applications, furnace design, nuclear reactors, air solar collectors. Originality/value – From the bibliographic work and the authors’ knowledge, the conjugate mixed convection in lid-driven partially porous enclosures has not yet been investigated which motivates the present work that represent a continuation of the preceding investigations.

Conjugate heat transfer in porous triangular enclosures with thick bottom wall

2009 ◽  
Vol 19 (5) ◽  
pp. 650-664 ◽  
Author(s):  
Yasin Varol ◽  
Hakan F. Oztop ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Conjugate Heat Transfer ◽  
Bottom Wall ◽  
Thick Wall ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Governing Equations ◽  
Content Type

PurposeThe purpose of this paper is to study the conjugate heat transfer via natural convection and conduction in a triangular enclosure filled with a porous medium.Design/methodology/approachDarcy flow model was used to write governing equations with Boussinesq approximation. The transformed governing equations are solved numerically using a finite difference technique. It is assumed that the enclosure consists of a conducting bottom wall of finite thickness, an adiabatic (insulated) vertical wall and a cooled inclined wall.FindingsFlow patterns, temperature and heat transfer were presented at different dimensionless thickness of the bottom wall, h, from 0.05 to 0.3, different thermal conductivity ratio between solid material and fluid, k, from 0.44 to 283 and Rayleigh numbers, Ra, from 100 to 1000. It is found that both thermal conductivity ratio and thickness of the bottom wall can be used as control parameters for heat transport and flow field.Originality/valueIt is believed that this is the first paper on conduction‐natural convection in porous media filled triangular enclosures with thick wall. In the last years, most of the researchers focused on regular geometries such as rectangular or square cavity bounded by thick wall.

Conjugate Nusselt Numbers for Simultaneously Developing Flow Through Rectangular Ducts

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Georgios Karamanis ◽  
Marc Hodes
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Extended Surface ◽  
Side Walls ◽  
Extended Surfaces ◽  
Prandtl Numbers

We consider conjugate forced-convection heat transfer in a rectangular duct. Heat is exchanged through the isothermal base of the duct, i.e., the area comprised of the wetted portion of its base and the roots of its two side walls, which are extended surfaces within which conduction is three-dimensional. The opposite side of the duct is covered by an adiabatic shroud, and the external faces of the side walls are adiabatic. The flow is steady, laminar, and simultaneously developing, and the fluid and extended surfaces have constant thermophysical properties. Prescribed are the width of the wetted portion of the base, the length of the duct, and the thickness of the extended surfaces, all three of them nondimensionalized by the hydraulic diameter of the duct, and, additionally, the Reynolds number of the flow, the Prandtl number of the fluid, and the fluid-to-extended surface thermal conductivity ratio. Our conjugate Nusselt number results provide the local one along the extended surfaces, the local transversely averaged one over the isothermal base of the duct, the average of the latter in the streamwise direction as a function of distance from the inlet of the domain, and the average one over the whole area of the isothermal base. The results show that for prescribed thermal conductivity ratio and Reynolds and Prandtl numbers, there exists an optimal combination of the dimensionless width of the wetted portion of the base, duct length, and extended surface thickness that maximize the heat transfer per unit area from the isothermal base.

scholarly journals Effect of Al2O3/water nanofluid on Conjugate Free Convection in a Baffle Attached Square Enclosure

Mechanika ◽  
2020 ◽  
Vol 26 (2) ◽  
pp. 126-133
Author(s):  
Thansekhar M.Rathinam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rayleigh Number ◽  
Free Convection ◽  
Conjugate Heat Transfer ◽  
Volume Fraction ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure

A numerical study of conjugate free convection heat transfer of Al2O3/water nanofluid inside a differentially heated square enclosure with a baffle attached to its hot wall has been carried out. A detailed parametric study has been carried out to analyze the effect of Rayleigh number (104 < Ra < 106), length, thickness and position of baffle, conductivity ratio and volume fraction of the nanoparticle (0<<0.2) on heat transfer. The thermal conductivity ratio of the baffle plays a major role on the conjugate heat transfer inside the enclosure. Higher the baffle length better is the effectiveness of the baffle. The average Nusselt number is found to be an increasing function of both thermal conductivity ratio and volume fraction of the nanofluid. The minimum enhancement of conjugate heat transfer is 30% when Al2O3/water nanofluid of 0.1 volume fraction is used for the entire range of Rayleigh number considered.

scholarly journals Numerical Simulation of Entropy Generation of Conjugate Heat Transfer in A Porous Cavity with Finite Walls and Localized Heat Source

2021 ◽  
Vol 84 (2) ◽  
pp. 116-151
Author(s):  
Ahmed Kadhim Hussein ◽  
Muhaiman Alawi Mahdi ◽  
Obai Younis
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Heat Source ◽  
Entropy Production ◽  
Conjugate Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Porous Cavity

In this research, the entropy production of the conjugate heat transfer in a tilted porous cavity in respect to heat source and solid walls locations has been studied numerically. Three different cases of the cavity with finite walls thickness and heat source locations are considered in the present study. For both cases one and two, the cavity considered has a vertical finite walls thickness, while the cavity with the horizontal finite walls thickness is considered for case three. For cases one and two, the left sidewall of the cavity is exposed to heat source, whereas the rest of this wall as well as the right sidewall are adiabatic. The upper and lower cavity walls are adiabatic. For case three, the lower wall is exposed to a localized heat source, while the rest of it is assumed adiabatic. The upper wall is cold, whereas the left and right sidewalls are adiabatic. The flow and thermal fields properties along with the entropy production are computed for the modified Rayleigh number (150 ? Ram ? 1000), thermal conductivity ratio (1 ? Kr ? 10), heat source length (0.2 ? B ? 0.6), aspect ratio (0.5 ? AR ? 2) and walls thickness (0.1 ? D1 ? 0.2 and 0.1 ? D2 ? 0.2) respectively. The results show that, the maximum values of the entropy generated from fluid friction develop close to the cavity wall-fluid interfacial, while the maximum values of the entropy generated from heat transfer develop nearby the heat source region. The average Bejan number (Beav) is higher than (0.5) for cases one and two. While for case three, it was found to be less than (0.5). Also, the results show that as the modified Rayleigh number, thermal conductivity ratio, heat source length and aspect ratio increased, the fluid flow intensity in the cavity increased. While, it decreased when the walls thickness increased. From the results, it is concluded that case three gives a higher heat transfer enhancement. The obtained results are compared against another published results and a good agreement is found between them.

scholarly journals Conjugate Heat Transfer in Rayleigh-Bénard Convection in a Square Enclosure

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Habibis Saleh ◽  
Ishak Hashim
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rayleigh Number ◽  
Wall Thickness ◽  
Staggered Grid ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure ◽  
Conjugate Natural Convection ◽  
Rayleigh Benard

Conjugate natural convection-conduction heat transfer in a square enclosure with a finite wall thickness is studied numerically in the present paper. The governing parameters considered are the Rayleigh number5×103≤Ra≤106, the wall-to-fluid thermal conductivity ratio0.5≤Kr≤10, and the ratio of wall thickness to its height0.2≤D≤0.4. The staggered grid arrangement together with MAC method was employed to solve the governing equations. It is found that the fluid flow and the heat transfer can be controlled by the thickness of the bottom wall, the thermal conductivity ratio, and the Rayleigh number.

Numerical Analysis of Conjugated Convection-Conduction Heat Transfer in a Microtube Gas Flow

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
K. M. Ramadan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Viscous Dissipation ◽  
Wall Thickness ◽  
Gas Flow ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Axial Conduction ◽  
Transfer Parameters

Abstract Numerical solutions for conjugate heat transfer of a hydro-dynamically fully developed, thermally developing, steady, incompressible laminar gas flow in a microtube with uniform wall heat flux boundary condition are presented. The mathematical model takes into account effects of rarefaction, viscous dissipation, flow work, shear work, and axial conduction in both the wall and the fluid. The effect of the tube wall thickness, the wall-to-fluid thermal conductivity ratio, as well as other factors on heat transfer parameters is investigated, and comparisons with the case of zero wall thickness are presented as appropriate. The results illustrate the significance of heat conduction in the tube wall on convective heat transfer and disclose the significant deviation from those with no conjugated effects. Increasing the wall thickness lowers the local Nusselt number. Increasing the wall-to-fluid thermal conductivity ratio also results in lower Nusselt number. In relatively long and thick microtubes with high wall-to-fluid thermal conductivity ratio, the local Nusselt number exhibits minimum values in the entrance regions and at the end sections due to axial conduction effects. The analysis presented also demonstrate the significance of rarefaction, shear work, axial conduction, as well as the combined viscous dissipation and flow work effects on heat transfer parameters in a microtube gas flow. The combined flow work and viscous dissipation effects on heat transfer parameters are significant and result in a reduction in the Nusselt number. The shear work lowers the Nusselt number when heat is added to the fluid.

Unsteady Conjugate Natural Convective Heat Transfer and Entropy Generation in a Porous Semicircular Cavity

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Ali J. Chamkha ◽  
Igor V. Miroshnichenko ◽  
Mikhail A. Sheremet
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Stream Function ◽  
Entropy Generation ◽  
Solid Wall ◽  
Thermal Conductivity Ratio ◽  
Bejan Number ◽  
Heat Conducting ◽  
Dimensionless Time ◽  
Conductivity Ratio

The problem of unsteady conjugate natural convection and entropy generation within a semicircular porous cavity bounded by solid wall of finite thickness and conductivity has been investigated numerically. The governing partial differential equations with the corresponding initial and boundary conditions have been solved by the finite difference method using the dimensionless stream function, vorticity, and temperature formulation. Numerical results for the isolines of the stream function, temperature, and the local entropy generation due to heat transfer and fluid friction as well as the average Nusselt and Bejan numbers, and the average total entropy generation and fluid flow rate have been analyzed for different values of the Rayleigh number, Darcy number, thermal conductivity ratio, and the dimensionless time. It has been found that low values of the temperature difference reflect the entropy generation, mainly in the upper corners of the cavity, while for high Rayleigh numbers, the entropy generation occurs also along the internal solid–porous interface. A growth of the thermal conductivity ratio leads to an increase in the average Bejan number and the average entropy generation due to a reduction of the heat loss inside the heat-conducting solid wall.

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