scholarly journals Natural Convection in Annulus Between Two Concentric Cylinders Partially Filled with Metal Foam Distributed with New Suggested Design

2022 ◽  
Vol 961 (1) ◽  
pp. 012032
Author(s):  
Israa H Alkinani ◽  
Luma Fadhil Ali
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Metal Foam ◽  
Current Model ◽  
Local Thermal Equilibrium ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Annular Space ◽  
Concentric Cylinders

Abstract The investigation of natural convection in an annular space between two concentric cylinders partially filled with metal foam is introduced numerically. The metal foam is inserted with a new suggested design that includes the distribution of metal foam in the annular space, not only in the redial direction, but also with the angular direction. Temperatures of inner and outer cylinders are maintained at constant value in which inner cylinder temperature is higher than the outer one. Naiver Stokes equation with Boussinesq approximation is used for fluid regime while Brinkman-Forchheimer Darcy model used for metal foam. In addition, the local thermal equilibrium condition in the energy equation of the porous media is presumed to be applicable for the present investigation. CFD ANSYS FLUENT software package (version 18.2) is used as a solver to this problem. Various parameters are examined; Rayleigh number, Darcy number, and thermal conductivity ratio to study the effect of them on fluid flow and heat transfer inside the annuli space in the suggested design of metal foam layer. current model is compared with the available published results and good agreement is noticed. Results showed that as Rayleigh number increases the dominated of convection mode increases and Nusselt increases. Also, Nusselt is larger at the higher Darcy and thermal conductivity ratio. It was found that at Rayleigh of 106 and thermal conductivity ratio of 104 Nusselt reach its higher value which is 6.69 for Darcy of 0.1 and 6.77 for Darcy of 0.001. A comparison between this design and the traditional design was established for Darcy 0.001 and thermal conductivity ratio 102, and its showed a good enhancement in Nusselt number and the greatest enhancement percentage was 44% at Rayleigh equal 5*104 while the lowest percentage is 6% for Rayleigh equal106.

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.

MHD natural convection flow in cavities filled with square solid blocks

2014 ◽  
Vol 24 (8) ◽  
pp. 1813-1830 ◽  
Author(s):  
Majid Ashouri ◽  
Mohammad Behshad Shafii ◽  
Hossein Rajabi Kokande
Keyword(s):  
Magnetic Field ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Code ◽  
Thermal Conductivity Ratio ◽  
Convection Flow ◽  
Conductivity Ratio ◽  
Natural Convection Flow ◽  
Content Type

Purpose – The purpose of this paper is to study the influence of magnetic field on natural convection inside the enclosures partially filled with conducting square solid obstacles. Also, the effect of thermal conductivity ratio between the solid and fluid materials is investigated for different number of solid blocks. Design/methodology/approach – The dimensionless governing equations are transformed into sets of algebraic equations using finite volume method and momentum equations are solved by the SIMPLE algorithm with the hybrid scheme. The validation of the numerical code was conducted by comparing the results of average Nusselt number with previously published works. Findings – The results indicate that both the magnetic field and solid blocks can significantly affect the flow and temperature fields. It is shown that for a given Rayleigh number, variation of Nusselt number might be increasing or decreasing with change in solid-to-fluid thermal conductivity ratio depending on magnetic field strength and number of solid blocks. Originality/value – No work has been reported previously on the effect of magnetic field on natural convection flow in a cavity partially filled with square solid blocks. The numerical analysis of conductivity ratio between the solid and fluid materials under the effect of magnetic field have been carried out for the first time.

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.

Thermosolutal natural convection in a partly porous cavity with sinusoidal wall heating and cooling

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Abdeslam Omara ◽  
Mouna Touiker ◽  
Abderrahim Bourouis
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Clear Fluid ◽  
Content Type ◽  
Heating And Cooling ◽  
Fortran Code ◽  
Double Diffusive ◽  
Sinusoidal Wall

Purpose This paper aims to consider numerical analysis of laminar double-diffusive natural convection inside a non-homogeneous closed medium composed of a saturated porous matrix and a clear binary fluid under spatial sinusoidal heating/cooling on one side wall and uniform salting. Design/methodology/approach The domain of interest is a partially square porous enclosure with sinusoidal wall heating and cooling. The fluid flow, heat and mass transfer dimensionless governing equations associated with the corresponding boundary conditions are discretized using the finite volume method. The resulting algebraic equations are solved by an in-house FORTRAN code and the SIMPLE algorithm to handle the non-linear character of conservation equations. The validity of the in-house FORTRAN code is checked by comparing the current results with previously published experimental and numerical works. The effect of the porous layer thickness, the spatial frequency of heating and cooling, the Darcy number, the Rayleigh number and the porous to fluid thermal conductivity ratio is analyzed. Findings The results demonstrate that for high values of the spatial frequency of heating and cooling (f = 7), temperature contours show periodic variations with positive and negative values providing higher temperature gradient near the thermally active wall. In this case, the temperature variation is mainly in the porous layer, while the temperature of the clear fluid region is practically the same as that imposed on the left vertical wall. This aspect can have a beneficial impact on thermal insulation. Besides, the porous to fluid thermal conductivity ratio, Rk, has practically no effect on Shhot wall, contrary to Nuinterface where a strong increase is observed as Rk is increased from 0.1 to 100, and much heat transfer from the hot wall to the clear fluid via the porous media is obtained. Practical implications The findings are useful for devices working on double-diffusive natural convection inside non-homogenous cavities. Originality/value The authors believe that the presented results are original and have not been published elsewhere.

Study on Natural Convection in Horizontal Parallel Plate Channels Heated on Upper Wall and Partially Filled With Metal Foam

2020 ◽  
Author(s):  
Bernardo Buonomo ◽  
Vincenzo Fardella ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Salvatore Pragliola
Keyword(s):  
Porous Medium ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Metal Foam ◽  
Open Cavity ◽  
Temperature Fields ◽  
Local Thermal Equilibrium ◽  
Uniform Heat Flux

Abstract In this work, a numerical investigation on two-dimensional steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The lower plate is adiabatic. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the local thermal equilibrium (LTE) hypothesis is assumed. The structure of the porous medium is homogenous and isotropic, the thermophysical properties of the air and the porous medium are temperature independent and the fluid flow is laminar and incompressible. The aluminum foam has 10, 20 and 40 pore per inches (PPI) and its porosity ranges from 0.90 and 0.95. Rayleigh number values are examined, from 6.0 × 104 and 1.2 × 107. Results are presented in terms of velocity and temperature fields, temperature and velocity profiles at different significant sections are shown, to obtain a description of the natural convection inside the open-ended cavity. Finally, Average Nusselt number values are evaluated. The horizontal open cavity partially filled with metal foam presents improved heat transfer behavior for higher Rayleigh numbers. The enhancement depends on the porosity and pore density. The average Nusselt number for the partially filled open cavity is the double of the configuration without the foam, clear configuration, for the highest considered Rayleigh number.

A Numerical Study of Conjugate Heat Transfer by Natural Convection and Surface Radiation in a Square Enclosure With Thick Adiabatic Walls

2013 ◽  
Author(s):  
H. Hadim ◽  
K. Blecker
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Surface Radiation ◽  
Thick Wall ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure

A numerical solution of heat transfer by combined natural convection and surface radiation in a square enclosure with thick adiabatic top and bottom walls and isothermal vertical walls is presented. The present model was used to obtain new results with the addition of thermal conduction at the thick top and bottom walls for a thermal conductivity ratio, K = ksolid/kfluid, that ranges from 0 to 10, emissivity of the adiabatic walls that ranges from 0 to 1, and the Rayleigh Number that ranges from 103 to 106. The model was validated by comparing the results to a benchmark solution and other solutions found in the literature. The results showed that with an increase in thermal conductivity ratio, the flow circulation decreases while the average Nusselt Number increases indicating increased heat transfer across the thick walls and the fluid in the corners. The results indicate that while past studies have shown negligible impact of the emissivity of the adiabatic walls on characteristics of the flow and heat transfer within the cavity, when a wall with moderate heat capacity and conductivity is considered, the resulting flow velocity and temperature distribution within the cavity are found to be significantly influenced by the thick wall emissivity. As the conductivity ratio increases this discrepancy between thin and thick walls becomes greater, there is further need for a more complex and accurate model including the thick walls. The results also showed that an increase in the emissivity of the adiabatic walls results in a slight decrease in the average Nusselt Number.

Numerical Investigation of Laminar Natural Convection in a Square Cavity With Wavy Wall and Horizontal Fin Attached to the Hot Wall

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Ahmed Kadari ◽  
Nord-Eddine Sad Chemloul ◽  
Said Mekroussi
Keyword(s):  
Thermal Conductivity ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Thermal Conductivity Ratio ◽  
Wavy Wall ◽  
Square Cavity ◽  
Laminar Natural Convection ◽  
Fin Length

Laminar natural convection in differentially heated square cavity with right cold wavy wall and horizontal conducting fin attached to its left hot wall has been investigated numerically. The vertical walls are maintained at different isothermal temperatures, while the horizontal walls are insulated. The fluid that filled the cavity is air with Prandtl number of 0.71. The investigation has been performed for Rayleigh number in the range of 103–106, the thermal conductivity ratio was varied from 10 to 105, three fin lengths and positions have been examined (0.25, 0.5, and 0.75), and three numbers of undulation were tested (one, two, and three undulations). The wave amplitude and the fin thickness were kept constant at 0.05 and 0.04, respectively. The results obtained show that increasing the fin thermal conductivity or the Rayleigh number increases the average Nusselt number especially when the fin length increases. It was also found that the fin position enhances the heat transfer when the fin is placed opposite to the crest of the wavy wall. The trend of the local Nusselt number is wavy. The effect of undulations number appears when the fin length is greater than 0.5. The average Nusselt number enhanced when a conducting fin is added to the cavity with wavy wall and without fin by 51.23% and 56.85% for one and three undulations, respectively, when the Rayleigh number is 105 and the fin length is 0.75.

Conjugate Heat Transfer Using Liquid Metals and Alloys for Enclosures With Solid Conducting Blocks

2010 ◽  
Vol 2 (1) ◽  
Author(s):  
M. McGarry ◽  
C. Bonilla ◽  
I. Metzger
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Conjugate Heat Transfer ◽  
Liquid Metals ◽  
Thermal Conductivity Ratio ◽  
Temperature Sensitive ◽  
Conductivity Ratio ◽  
Prandtl Numbers

A validated computational model was created to simulate the heat transfer from a heated surface using liquid metals and alloys during conjugate heat transfer. This model explores the effect of the Rayleigh number, Prandtl number, thermal conductivity ratio, and aspect ratio on the Nusselt number along the hot surface. The data will show how to keep the temperature sensitive components along the hot wall cool by maximizing the amount of heat removed from the hot wall. The data show three distinct regions that occur as a function of the Rayleigh number for a fixed k∗ and d∗. The data also show that the thermal conductivity ratio between the fluid and the solid conducting block has little effect on the Nusselt number at a fixed Rayleigh number. However, when examining the effect of the aspect ratio on the Nusselt number, two distinct regions can be seen. The results demonstrate that in order to keep the temperature sensitive components cool along the hot wall, one would want to have large Rayleigh and Prandtl numbers. The easiest way to achieve large Rayleigh numbers is by increasing the height of the enclosure. Large Prandtl numbers can be achieved by choosing a fluid that is highly conductive. In addition, the choice of material for the center solid conducting block does not impact the amount of heat removed from the hot wall. However, increased cooling can be achieved by decreasing the spacing between the hot and the cold wall.

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