Статті в журналах: "Natural (free) convection"

1

De Angelis, Elisabetta. "Free energy budgets in viscoelastic natural convection." PAMM 12, no. 1 (December 2012): 507–8. http://dx.doi.org/10.1002/pamm.201210242.

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2

Lawrence, Jino, and Vanav Kumar Alagarsamy. "Fluid Flow and Heat Transfer Analysis of Quadratic Free Convection in a Nanofluid Filled Porous Cavity." International Journal of Heat and Technology 39, no. 3 (June 30, 2021): 876–84. http://dx.doi.org/10.18280/ijht.390322.

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The involvement of non-linear convection effects in a natural convective fluid flow and heat transfer along with the effects of magnetic field in a porous cavity is studied numerically. Cu-water filled cavity of higher temperature at the left wall and lower temperature at the right wall. The governing equations are organized to achieve the required flow by using two-dimensional equations of energy, continuity and momentum. Vorticity-stream function based dimensionless equations are solved using the finite difference techniques. The results are discussed for various dimensionless parameters such as the Darcy number, non-linear convection parameter, Hartmann number, Rayleigh number and solid volume fraction of the nanoparticles. An augment in streamline velocity and convection heat transfer are observed by increasing the Rayleigh number, non-linear convection parameter and Darcy number. The non-linear convection parameter has a lesser effect on the lower Rayleigh numbers. Diminished streamline intensity and reduction in convection heat transfer are noted for an increase in the strength of the applied magnetic field irrespective of the non-linear convection parameter.

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3

PADET, JACQUES, RENATO M. COTTA, EMILIA C. MLADIN, and COLETTE PADET. "Mixed thermal convection: fundamental issues and analysis of the planar case." Anais da Academia Brasileira de Ciências 87, no. 3 (August 25, 2015): 1865–85. http://dx.doi.org/10.1590/0001-3765201520140254.

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This paper aims to renew interest on mixed thermal convection research and to emphasize three issues that arise from the present analysis: (i) a clear definition of the reference temperature in the Boussinesq approximation; (ii) a practical delimitation of the three convective modes, which are the forced convection (FC), mixed convection (MC) and natural (or free) convection (NC); (iii) and, finally, a uniform description of the set FC/MC/NC in the similarity framework. The planar case, for which analytical solutions are available, allows a detailed illustration of the answers here advanced to the above issues.

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4

Jani, Jaronie Mohd, Sunan Huang, Martin Leary, and Aleksandar Subic. "Analysis of Convective Heat Transfer Coefficient on Shape Memory Alloy Actuatorunder Various Ambient Temperatures with Finite Difference Method." Applied Mechanics and Materials 736 (March 2015): 127–33. http://dx.doi.org/10.4028/www.scientific.net/amm.736.127.

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The demand for shape memory alloy (SMA) actuators for technical applications is steadily increasing; however SMA may have poor deactivation time due to relatively slow convective cooling. Convection heat transfer mechanism plays a critical role in the cooling process, where an increase of air circulation around the SMA actuator (i.e. forced convection) provides a significant improvement in deactivation time compared to the natural convection condition. The rate of convective heat transfer, either natural or forced, is measured by the convection heat transfer coefficient, which may be difficult to predict theoretically due to the numerous dependent variables. In this work, a study of free convective cooling of linear SMAactuators was conducted under various ambient temperatures to experimentally determine the convective heat transfer coefficient. A finite difference equation (FDE) was developed to simulate SMA response, and calibrated with the experimental data to obtain the unknown convectiveheat transfer coefficient, h. These coefficients are then compared with the available theoretical equations, and it was found that Eisakhaniet. almodel provides good agreement with the Experiment-FDE calibrated results. Therefore, FDE is reasonably useful to estimate the convective heat transfer coefficient of SMA actuator experiments under various conditions, with a few identified limitations (e.g. exclusion of other associative heat transfer factors).

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5

Prasad, V., F. A. Kulacki, and M. Keyhani. "Natural convection in porous media." Journal of Fluid Mechanics 150 (January 1985): 89–119. http://dx.doi.org/10.1017/s0022112085000040.

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Experimental results on free convection in a vertical annulus filled with a saturated porous medium are reported for height-to-gap ratios of 1.46, 1 and 0.545, and radius ratio of 5.338. In these experiments, the inner and outer walls are maintained at constant temperatures. The use of several fluid–solid combinations indicates a divergence in the Nusselt-number–Rayleigh-number relation, as also reported by previous investigators for horizontal layers and vertical cavities. The reason for this divergence is the use of the stagnant thermal conductivity of the fluid-filled solid matrix. A simple model is presented to obtain an effective thermal conductivity as a function of the convective state, and thereby eliminate the aforementioned divergence. A reasonable agreement between experimentally and theoretically determined Nusselt numbers is then achieved for the present and previous experimental results. It is thus concluded that a unique relationship exists between the Nusselt and Rayleigh numbers unless Darcy's law is inapplicable. The factors that influence the breakdown of Darcian behaviour are characterized and their effects on heat-transfer rates are explained. It is observed that, once the relation between the Nusselt and Rayleigh numbers branches out from that obtained via the mathematical formulation based on Darcy's law, its slope approaches that for a fluid-filled enclosure of the same geometry when the Rayleigh number is large enough. An iterative scheme is also presented for estimation of effective thermal conductivity of a saturated porous medium by using the existing results for overall heat transfer.

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6

Dávalos-Orozco, L. A., and E. Vázquez Luis. "Natural convection of a viscoelastic fluid with deformable free surface." Journal of Non-Newtonian Fluid Mechanics 85, no. 2-3 (September 1999): 257–71. http://dx.doi.org/10.1016/s0377-0257(98)00195-5.

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7

Ajayi, O. O. "Natural Convection in a Hemispherical Bowl With a Free Surface." Journal of Heat Transfer 108, no. 4 (November 1, 1986): 970–73. http://dx.doi.org/10.1115/1.3247043.

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8

Bower, S. M., and J. R. Saylor. "The effects of surfactant monolayers on free surface natural convection." International Journal of Heat and Mass Transfer 54, no. 25-26 (December 2011): 5348–58. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2011.08.008.

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9

SAID, Abdessadek AIT HAJ, Mahfoud ELFAGRICH, and Omar ABOUNACHIT. "Numerical investigation of free convection through a horizontal open-ended axisymmetric cavity." Indian Journal of Science and Technology 14, no. 13 (April 9, 2021): 1081–96. http://dx.doi.org/10.17485/ijst/v14i13.2259.

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Objectives: The purposes of this work are to investigate the free convective heat transfer in an axis-symmetric open-ended cavity heated from below and to propose useful correlations of Nusselt number. Methods: The governing equations that model the fluid flow and the temperature field are solved using a control volume-based finite differences method. Under steady state condition, the natural convective flow is considered to be laminar, incompressible and axisymmetric. The Boussinesq approximation with constant thermophysical properties is adopted. Numerical experimentations are performed to deduce the optimum sizes of the calculation domain and the mesh grid. Findings: the obtained results indicate that when Rayleigh number (Ra) and aspect ratio (A) are low the heat transfer is weak and mainly conductive. The increase of Ra and A enhances the convective heat transfer mode thereby the heat transfer is ameliorated. Unlike the Rayleigh Bénard convection, the transition from conduction to convection produces at critical value of Rayleigh number (Rac) that is variable dependent on A. Novelty: To the best of authors knowledge, the formula of (Rac) elaborated in this work for the studied cavity is the first attempt. As well, correlation of Nusselt numbers (Nu) for the cold upper plate in terms of Ra and A is performed. Comparisons between Nu at the lower plate given in previous work and Nusselt number at the upper plate is conducted. Keywords: free convection; circular plates; Nusselt number correlations; open ended cavity; critical Rayleigh number

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10

Cervantes de Gortari, Jaime G., Juan Cristóbal Torchia-Núñez, Juan Ángel Serrano-Gutiérrez, Enrique Guzmán-Vázquez, Federico Gutiérrez-Coria, Óscar Chávez-López, Israel Rosas-Yescas, and Eduardo Martínez-Gálvan. "Líneas de calor para convección natural en cavidades cerradas: Tres casos de estudio." Ingeniería, investigación y tecnología 11, no. 4 (October 1, 2010): 369–78. http://dx.doi.org/10.22201/fi.25940732e.2010.11n4.031.

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11

Robillard, L., T. H. Nguyen, and P. Vasseur. "Free Convection in a Two-Dimensional Porous Loop." Journal of Heat Transfer 108, no. 2 (May 1, 1986): 277–83. http://dx.doi.org/10.1115/1.3246916.

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A study is made of the natural convection in an annular porous layer having an isothermal inner boundary and its outer boundary subjected to a thermal stratification arbitrarily oriented with respect to gravity. For such conditions, no symmetry can be expected for the flow and temperature fields with respect to the vertical diameter and the whole circular region must be considered. Two-dimensional steady-state solutions are sought by perturbation and numerical approaches. Results obtained indicate that the circulating flow around the annulus attains its maximum strength when the stratification is horizontal (heating from the side). This circulating flow is responsible for an important heat exchange between the porous layer and its external surroundings. The flow field is also characterized by the presence of two convective cells near the inner boundary, giving rise to flow reversal on this surface. When the maximum temperature on the outer boundary is at the bottom of the cavity, the convective motion becomes potentially unstable; for a Rayleigh number below 80, there exists a steady-state solution symmetrical with respect to both vertical and horizontal axes; for a Rayleigh number above 80, an unsteady periodic situation develops with the circulating flow alternating its direction around the annulus.

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12

NARUSAWA, UICHIRO. "The second-law analysis of convective pattern change in a rectangular cavity." Journal of Fluid Mechanics 392 (August 10, 1999): 361–77. http://dx.doi.org/10.1017/s0022112099005595.

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Natural convection in a rectangular cavity is examined, utilizing the second law of thermodynamics. Through an application of the second law the rate of entropy generation associated with the convective pattern changes is evaluated for the onset of natural convection in a cavity with free boundaries, for which an exact solution is sought, as well as with rigid boundaries which is studied numerically. Entropy to be generated from the perturbed temperature and velocity fields is shown to depend on AR (aspect ratio of the cavity), Rac (the critical Rayleigh number) and a non-dimensional parameter, Ω, which is related to the ratio of entropy generation by viscous friction to that by thermal transport. The convective pattern change is related to a change in the spatial distributions of the rate of entropy generation due to heat transfer and due to dissipation, demonstrating that an application of the second law helps examine convective pattern changes quantitatively by dealing with temperature and velocity fields in a unified manner.

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13

Rostami, Sara, Saeed Aghakhani, Ahmad Hajatzadeh Pordanjani, Masoud Afrand, Goshtasp Cheraghian, Hakan F. Oztop, and Mostafa Safdari Shadloo. "A Review on the Control Parameters of Natural Convection in Different Shaped Cavities with and without Nanofluid." Processes 8, no. 9 (August 19, 2020): 1011. http://dx.doi.org/10.3390/pr8091011.

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Natural convection in cavities is an interesting subject for many researchers. Especially, in recent years, the number of articles written in this regard has grown enormously. This work provides a review of recent natural convection studies. At first, experimental studies were reviewed and, then, numerical studies were examined. Then, the articles were classified based on effective parameters. In each section, numerical studies were examined the parameters added to the cavity such as magnetic forces, fin, porous media and cavity angles. Moreover, studies on non-rectangular cavities were investigated. Free convection in enclosures depends more on the fluid velocity relative to the forced convection, leading to the opposite effect of some parameters that should essentially enhance rate of heat transfer. Nanoparticle addition, magnetic fields, fins, and porous media may increase forced convection. However, they can reduce free convection due to the reduction in fluid velocity. Thus, these parameters need more precision and sometimes need the optimization of effective parameters.

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14

El-Aziz, Mohamed Abd, and Aishah S. Yahya. "Unsteady Hydromagnetic Natural Convection Flow Past an Oscillating Vertical Surface with Hall Effect and Convective Boundary Condition." Journal of Computational and Theoretical Nanoscience 14, no. 1 (January 1, 2017): 718–27. http://dx.doi.org/10.1166/jctn.2017.6264.

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The aim of this paper is to analyze the effect of Hall current on unsteady MHD free convection flow of a viscous, incompressible and electrically conducting fluid past an oscillating vertical plate with convective boundary condition. The fluid flow is due to both the oscillation and the convective heating of the plate. The resulting governing equations are nondimensionalized and solved analytically using the Laplace transform technique. Numerical results for axial and transverse velocities and temperature as well as the skin-friction coefficient and Nusselt number are shown graphically for various values of pertinent flow parameters.

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15

Nguyen, Minh Tuan, Abdelraheem M. Aly, and Sang-Wook Lee. "A numerical study on unsteady natural/mixed convection in a cavity with fixed and moving rigid bodies using the ISPH method." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 3 (March 5, 2018): 684–703. http://dx.doi.org/10.1108/hff-02-2017-0058.

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Purpose This paper aims to conduct numerical simulations of unsteady natural/mixed convection in a cavity with fixed and moving rigid bodies and different boundary conditions using the incompressible smoothed particle hydrodynamics (ISPH) method. Design/methodology/approach In the ISPH method, the pressure evaluation is stabilized by including both of divergence of velocity and density invariance in solving pressure Poisson equation. The authors prevented the particles anisotropic distributions by using the shifting technique. Findings The proposed ISPH method exhibited good performance in natural/mixed convection in a cavity with fixed, moving and free-falling rigid body. In natural convection, the authors investigated the effects of an inner sloshing baffle as well as fixed and moving circular cylinders on the heat transfer and fluid flow. The heated baffle has higher effects on the heat transfer rate compared to a cooled baffle. In the mixed convection, a free-falling circular cylinder over a free surface cavity and heat transfer in the presence of a circular cylinder in a lid-driven cavity are simulated. Fixed or moving rigid body in a cavity results in considerable effects on the heat transfer rate and fluid flow. Originality/value The authors conducted numerical simulations of unsteady natural/mixed convection in a cavity with fixed and moving rigid bodies and different boundary conditions using the ISPH method.

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16

Gupta, A. D., Ashish Gupta, P. K. Mishra, Yashi Gupta, and R. K. Mehta. "Optimization of Inclination Angle of Cavity and Characteristics of Attached Fins on the Absorber for Performance Enhancement of Solar Collectors." International Journal of Bio-resource and Stress Management 12, no. 3 (June 30, 2021): 216–21. http://dx.doi.org/10.23910/1.2021.2223.

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This research investigation was undertaken in ANDUAT, Kumarganj, Ayodhya, Uttar Pradesh, India to study the numerical optimization of natural convection heat suppression in a solar flat plate collector with straight fins. Optimal characteristics of an array of thin fins attached on the absorber plat were obtained by Particle Swarm Optimization algorithm (PSOA). Free convection considered dominant in the cavity. Governing equations contained continuity; momentum and energy are discretized by finite volume method. The medium is considered incompressible, whose free convection is dominant and Boussinesq approximation is applied. A simplified model of real systems is applied with free convection. Free convection problem is solved by SIMPLER algorithm. Two confined cavities with aspect ratios 30 and 60 are considered as flat plate solar collectors. The results indicate that significant reduction on the free convection heat loss can be obtained from solar flat plate collector by using plate fins, and an optimal plate fins configuration exit for minimal natural convection heat loss for a given range of Rayleigh number. Reduction of up to a maximum of 25% at 0 inclination angle was observed in aspect ratio 30. Results showed PSOA is able to obtain characteristics of attached adiabatic fins on the absorber plate also it can obtain optimal inclination angle of cavity to decrease heat losses from solar collectors. The results obtained provide a novel approach for improving design of flat plate solar collectors for optimal performance.

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17

Lin, S. C., K. P. Chang, and Y. H. Hung. "Natural convection within a vertical finite-length channel in free space." Journal of Thermophysics and Heat Transfer 8, no. 2 (April 1994): 366–68. http://dx.doi.org/10.2514/3.547.

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18

Dávalos-o, L. A., and P. G. López-m. "Natural convection in a rotating fluid layer with deformable free surface." Geophysical & Astrophysical Fluid Dynamics 80, no. 1-2 (September 1995): 75–102. http://dx.doi.org/10.1080/03091929508229764.

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19

Sundström, Lars-Göran, and Shigeo Kimura. "On laminar free convection in inclined rectangular enclosures." Journal of Fluid Mechanics 313 (April 25, 1996): 343–66. http://dx.doi.org/10.1017/s0022112096002236.

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A class of problems of natural convection in tilted boxes is studied by analytical and numerical methods. The convection is assumed to be driven by uniform fluxes of heat (or mass) at two opposing walls, the remaining walls being perfect insulators. Disregarding end-region effects, an exact analytical solution is derived for the state which occurs after initial transients have decayed. This state is steady except for a spatially uniform, linear growth in the temperature (or the species concentration) which occurs whenever the fluxes are not equal. It is characterized by a uni-directional flow, a linear stratification and wall-to-wall temperature profiles which, except for the difference in absolute values due to the stratification, are the same at each crosssection. The mathematical problem is in essence nonlinear and multiple solutions are found in some parameter regions. The Bénard limit of horizontal orientation and heating from below is found to give a first bifurcation for which the steady states both before and after the bifurcation are obtained analytically. For a tilted Bénard-type problem, a steady state with top-heavy stratification is found to exist and compete with a more natural solution. The analytical solution is verified using numerical simulations and a known approximate solution for a vertical enclosure at high Rayleigh numbers. The presented solution admits arbitrary Rayleigh numbers, inclination angles and heat fluxes. Some restrictions on its validity are discussed in the paper.

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20

Isah, B. Y., M. M. Altine, and S. K. Ahmad. "Thermal Radiation and Variable Pressure Effects on Natural Convective Heat and Mass Transfer Fluid Flow in Porous Medium." Nigerian Journal of Basic and Applied Sciences 27, no. 1 (May 26, 2020): 48–58. http://dx.doi.org/10.4314/njbas.v27i1.7.

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The study investigates the interaction of free convective flow with thermal radiation and variable pressure on natural convective heat and mass transfer fluid flow in porous medium. Solutions for time dependent energy, concentration and momentum equations were obtained by the perturbation series method after transforming into ordinary differential equations. The effect of various flow parameters such as: suction/injection ( δ) radiation (R ) magnetic field (M ) heat source (S ) chemical reaction ( Rc) on the skin friction, rate of heat transfer, velocity, temperature, and concentration profile influencing the physical situation were discussed with the aid of line graphs. Keywords: Thermal Radiation, Variable pressure, Perturbation, Natural Convection

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21

Bouhdjar, Amor, Hakim Semai, Amal Boukadoum, Sofiane Elmokretar, Azzedine Mazari, Mohamed Semiani, and Aissa Amari. "Improved Procedure for Natural Convection Garlic Drying." Acta Technologica Agriculturae 23, no. 2 (June 1, 2020): 92–98. http://dx.doi.org/10.2478/ata-2020-0015.

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AbstractVegetable drying is an energy consuming procedure despite the fact that it is the most efficient way to preserve agricultural products. This study investigates a new way to dry good quality garlic at lower cost. Thin garlic layer was submitted to free convection airflow at air drying temperature of 40 °C, 50 °C, and 60 °C. Using the slope method, effective diffusivity coefficient was determined at each drying temperature during the first and second falling drying rate periods. Considering the former, it increased with increasing temperature. In relation to latter, it decreased with the temperature increase. However, at low drying temperatures, process keeps on going to very low moisture content; and it develops to an asymptotic value at high temperatures, indicating that shrinking at high temperature prevents evaporation of some residual moisture. Considered separately, these temperatures do not reflect the conditions met in solar drying, since in solar systems, air temperature increases during the day with increasing solar radiation. Therefore, characterization of garlic drying by means of step temperature varying – the first hour of drying at 40 °C; the second hour of drying at 50 °C, and the remaining time of drying at 60 °C – might better correspond with conditions under solar drying and result in better understanding of the process.

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22

Jodat, A., and M. Moghiman. "An experimental assessment of the evaporation correlations for natural, forced and combined convection regimes." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, no. 1 (September 14, 2011): 145–53. http://dx.doi.org/10.1177/0954406211413961.

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In the present study, the applicability of widely used evaporation models (Dalton approach-based correlations) is experimentally investigated for natural, forced, and combined convection regimes. A series of experimental measurements are carried out over a wide range of water temperatures and air velocities for 0.01 ≤ Gr/Re2 ≤ 100 in a heated rectangular pool. The investigations show that the evaporation rate strongly depends on the convection regime's Gr/ Re2 value. The results show that the evaporation rate increases with the difference in vapour pressures over both forced convection (0.01 ≤ Gr/Re2 ≤ 0.1) and turbulent mixed convection regimes (0.15 ≤ Gr/Re2 ≤ 25). However, the escalation rate of evaporation decreases with Gr/ Re2 in the forced convection regime whereas in the turbulent mixed convection it increases. In addition, over the range of the free convection regime ( Gr/Re2 ≥ 25), the evaporation rate is affected not only by the vapour pressure difference but also by the density variation. A dimensionless correlation using the experimental data of all convection regimes (0.01 ≤ Gr/Re2 ≤ 100) is proposed to cover different water surface geometries and airflow conditions.

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23

Moore, G. A., and K. G. T. Hollands. "Natural Convection Heat Transfer From a Plate in a Semicircular Enclosure." Journal of Heat Transfer 114, no. 1 (February 1, 1992): 121–26. http://dx.doi.org/10.1115/1.2911236.

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In the subject geometry, a long thin plate at uniform temperature is contained coaxially and symmetrically in a long semicircular trough closed at the top and having a uniform but different temperature. Heat flows across the air-filled region between the two by both natural convection and gaseous conduction. The problem of characterizing the free convective component of this heat transfer—that is, the component caused by bulk fluid motion—is treated experimentally by using a heat balance technique, with the measurements being repeated at different pressures, in order to cover a wide Rayleigh number range, from Ra ≈ 10 to Ra ≈ 108. Nusselt number versus Rayleigh number plots are presented for each of several combinations of plate-to-trough spacing and tilt angle, and the plots are correlated by equations. The problem of characterizing the conductive component is treated by numerically solving the steady diffusion equation in the air-filled region, and the results are correlated as a function of the spacing and the plate thickness.

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24

Chew, T. C., A. O. Tay, and N. E. Wijeysundera. "A Numerical Study of the Natural Convection in CPC Solar Collector Cavities with Tubular Absorbers." Journal of Solar Energy Engineering 111, no. 1 (February 1, 1989): 16–23. http://dx.doi.org/10.1115/1.3268281.

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The laminar free convection in a compound parabolic concentrator (CPC) solar collector cavity is numerically simulated using the finite element method. Results are presented for representative CPC collectors with tubular absorbers of concentration ratio 2. The effect of Grashof number, truncation and tilt angle were investigated. Generally, higher rates of heat transfer between the tubular absorber and the flat cover plate of the cavity are associated with larger Grashof numbers and shallower cavities. The maximum heat transfer rates occur when the tilt angle is about 60 deg. Contour plots are obtained for the field variables and these provide an insight into the spatial characteristics of the convective mechanisms within the cavity.

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25

Gregor, Kosec, and Božidar Šarler. "Meshless Approach to Solving Freezing with Natural Convection." Materials Science Forum 649 (May 2010): 205–10. http://dx.doi.org/10.4028/www.scientific.net/msf.649.205.

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This paper for the first time explores the application of the meshless approach, structured on the Local Radial Basis Function Collocation Method (LRBFCM), for solving the freezing process with convection in the liquid phase for a metals-like material in a closed rectangular cavity. The enthalpy one-domain formulation is used to avoid inclusion of additional boundary conditions at the fluid-solid interface. To avoid numerical instabilities, the freezing of a pure substance is modeled by a narrow phase change interval. The fluid flow is solved by a local pressure-velocity coupling, based on the mass continuity violation [1-3], and the explicit time stepping is used to drive the system to the free boundary solution. The results are presented through temperature and streamfunction contours and the liquid-solid interface position at the steady state, as well as the time development of the average Nusselt number and the time development of the cavity average liquid fraction. Results are validated with already benchmarked melting example [3]. The paper represents first steps in solution of the Hebdich and Hunt experiment by an alternative numerical technique, different from the classical finite volume or finite element methods [4].

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26

Ahmmed, S. F., and M. S. A. Sarker. "MHD Natural Convection Flow of Fluid From a Vertical Flat Plate Considering Temperature Dependent Viscosity." Journal of Scientific Research 2, no. 3 (August 23, 2010): 453. http://dx.doi.org/10.3329/jsr.v2i3.4776.

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A two-dimensional natural convection flow of a viscous incompressible and electrically conducting fluid past a vertical impermeable flat plate is considered in presence of a uniform transverse magnetic field. Here the viscosity is taken as dependent on temperature whereas the thermal conductivity is assumed constant. We also investigate the effect of magnetic field on the natural convection flow of a viscous incompressible and electrically conducting fluid. The effect of variable viscosity and magnetic field on local skin friction, the rate of heat transfer and the profiles for velocity as well as viscosity in the entire free convection regime are presented and discussed. Keywords: Natural convection; Magnethydrodynamics (MHD); Viscosity; Prandtl number. © 2010 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v2i3.4776 J. Sci. Res. 2 (3), 453-463 (2010)

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27

Sheremet, Mikhail A., Ioan Pop, and Alin V. Rosca. "The influence of thermal radiation on unsteady free convection in inclined enclosures filled by a nanofluid with sinusoidal boundary conditions." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 8 (August 6, 2018): 1738–53. http://dx.doi.org/10.1108/hff-09-2017-0375.

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Purpose The purpose of this study is a numerical analysis of transient natural convection in an inclined square cavity filled with an alumina-water nanofluid under the effects of sinusoidal wall temperature and thermal radiation by using a single-phase nanofluid model with empirical correlations for effective viscosity and thermal conductivity. Design/methodology/approach The domain of interest includes the nanofluid-filled cavity with a sinusoidal temperature distribution along the left vertical wall. Horizontal walls are supposed to be adiabatic, while right vertical wall is kept at constant low temperature. Temperature of left wall varies sinusoidally along y-coordinate. It is assumed in the analysis that the thermophysical properties of the fluid are independent of temperature and the flow is laminar. The governing equations have been discretized using the finite difference method with the uniform grid. Simulations have been carried out for different values of the Rayleigh number, cavity inclination angle, nanoparticles volume fraction and radiation parameter. Findings It has been found that a growth of radiation parameter leads to the heat transfer enhancement and convective flow intensification. At the same time, an inclusion of nanoparticles illustrates a reduction in the average Nusselt number and fluid flow rate. Originality/value The originality of this work is to analyze unsteady natural convection in a square cavity filled with a water-based nanofluid in the presence of a sinusoidal temperature distribution along one wall. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

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28

KUMAR R, AJITH, and Kunjunni M. "Effect of Linearly Varying Heating Inside a Square Cavity under Natural Convection." Journal of Applied Research and Technology 19, no. 4 (August 24, 2021): 336–44. http://dx.doi.org/10.22201/icat.24486736e.2021.19.4.1573.

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Telecommunication devices such as ADSL Modems or Wi-Fi routers are being widely used around the globe. Thermal management of such equipments are of critical importance as the increased power consumptions caused by technological upgrades results in increased heat generation within these systems. The heat transfer process inside such sealed and passively cooled equipments can be simplified as natural convection inside enclosures. Studying actual conditions inside electronic enclosure are necessary for their effective thermal management. This study aims at investigating the effect of non-isothermal heating inside such enclosures with linearly varying temperature distribution on free convection inside square enclosure. The issue of free convection of air interior of a square chamber with linearly varying temperature distributions on the left partition is studied numerically. The effect of change of Rayleigh number, temperature distributions, on flow and temperature field and rate of transfer of heat are analysed. Rayleigh number is chosen to vary in between 103 and 106. Four different cases of linearly varying temperature distributions are considered. The outcomes are presented as stream line plot, isotherm contour and average Nusselt number. The outcomes depicted that case of linearly increasing temperature along the height gives higher Nusselt number than other cases.

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29

Afrand, Masoud, Nima Sina, Hamid Teimouri, Ali Mazaheri, Mohammad Reza Safaei, Mohammad Hemmat Esfe, Jamal Kamali, and Davood Toghraie. "Effect of Magnetic Field on Free Convection in Inclined Cylindrical Annulus Containing Molten Potassium." International Journal of Applied Mechanics 07, no. 04 (August 2015): 1550052. http://dx.doi.org/10.1142/s1758825115500520.

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Three-dimensional (3D) numerical simulation of natural convection of an electrically conducting fluid under the influence of a magnetic field in an inclined cylindrical annulus has been performed. The inner and outer cylinders are maintained at uniform temperatures and other walls are thermally insulated. The governing equations of this fluid system are solved by a finite volume (FV) code based on SIMPLER solution scheme. Detailed numerical results of heat transfer rate, Lorentz force, temperature and electric fields have been presented for a wide range of Hartmann number (0 ≤ Ha ≤ 60) and inclination angle (0 ≤ γ ≤ 90). The results indicate that a magnetic field can control the magnetic convection of an electrically conducting fluid. Depending on the direction and strength of the magnetic field, the suppression of convective motion was observed. For vertical cylindrical annulus, increasing the strength of the magnetic field causes the loss symmetry, and as the consequence, isotherms lose their circular shape. With increasing the Hartmann number the average Nusselt number approaches a constant value. For vertical annulus, the effect of Hartmann number on the average Nusselt number is not prominent compared to the case of horizontal annulus.

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30

Sarr, J., C. Mbow, H. Chehouani, B. Zeghmati, S. Benet, and M. Daguenet. "Study of Natural Convection in an Enclosure Bounded by Two Concentric Cylinders and Two Diametric Planes." Journal of Heat Transfer 117, no. 1 (February 1, 1995): 130–37. http://dx.doi.org/10.1115/1.2822292.

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The two-dimensional heat transfer induced by free laminar convection in an enclosure is numerically investigated in this work. A constant wall heat flux is applied on the inner cylinder while the outer is maintained at an uniform temperature, the others walls being adiabatic. The influence of the modified Grashof number (102 ≤ Gr ≤ 106) and an aspect Fr on convective motion and heat transfer is examined. A comparison of the heat transfer between different fluids such as air, ammonia–liquid, and carbon dioxide–liquid is also displayed. Holographic interferometry is used to visualize the temperature field within the enclosure and to confirm the two-dimensional behavior of the convective flow. The results show that maximum heat transfer is found for Fr = 1, when the Grashof number is up to 103, and the conduction regime is reached for a modified Grashof number less than 103. On the other hand, the average Nusselt number increases with the Prandtl number, Fr = 1.

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31

TORII, Shuichi, Toshiaki YANO, and Fumihiro TSUCHINO. "Effect of Gravity on Unsteady Natural Convection in Square Cavity in Free Fall." Journal of the Visualization Society of Japan 17, Supplement2 (1997): 149–52. http://dx.doi.org/10.3154/jvs.17.supplement2_149.

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32

Xie, Yihui Han and Xiaoping. "Robust Globally Divergence-Free Weak Galerkin Finite Element Methods for Natural Convection Problems." Communications in Computational Physics 26, no. 4 (June 2019): 1039–70. http://dx.doi.org/10.4208/cicp.oa-2018-0107.

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33

Lakkis, Issam. "Grid-Free Vortex Methods for Natural Convection; Handling Source Terms and Nonlinear Diffusion." Numerical Heat Transfer, Part B: Fundamentals 62, no. 5 (November 2012): 370–98. http://dx.doi.org/10.1080/10407790.2012.707013.

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34

Yaroslavtseva, N. A., and N. G. Ivanov. "Numerical simulation of natural convection in wedge-shaped domain with isothermal free surface." Journal of Physics: Conference Series 929 (November 2017): 012097. http://dx.doi.org/10.1088/1742-6596/929/1/012097.

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35

Rajkumar, M. R., G. Venugopal, and S. Anil Lal. "Natural convection from free standing tandem planar heat sources in a vertical channel." Applied Thermal Engineering 50, no. 1 (January 2013): 1386–95. http://dx.doi.org/10.1016/j.applthermaleng.2012.05.041.

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36

Mil'kov, S. N., G. S. Sukhov, and L. P. Yarin. "Combustion of a liquid with a free surface under conditions of natural convection." Combustion, Explosion, and Shock Waves 23, no. 4 (1988): 385–92. http://dx.doi.org/10.1007/bf00749296.

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37

Ben Hamida, Mohamed Bechir. "Fluid-Structure Interaction Analysis in Natural Convection Heat Transfer Inside a T-Shaped Cavity with a Flexible Baffle." Journal of Nanofluids 11, no. 2 (April 1, 2022): 169–91. http://dx.doi.org/10.1166/jon.2022.1838.

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The purpose of this paper is to investigate the free convection flow through a flexible baffle in a T-shaped enclosure. This study is established in two-dimensional space. The 2D numerical analysis is performed with Comsol Multiphysics on the basis of the finite element method. The effect of all parameters influencing the convection heat transfer and the deformation baffle are rigorously studied. Results obtained show that the convection heat transfer and the warp baffle deformation are improved by increasing the Rayleigh and Prandtl numbers. By cons, the convection heat transfer is reduced by increasing the elasticity modulus of the flexible baffle and increasing the length of baffle. However, the stress over the baffle is improved. The variation of baffle position is not an important factor that affects the convection heat transfer inside the cavity; by contrast, the stress over the baffle is more important with a higher baffle position.

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38

Sukhotskii, A. B., and G. S. Sidorik. "EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR." ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations 60, no. 4 (July 7, 2017): 352–66. http://dx.doi.org/10.21122/1029-7448-2017-60-4-352-366.

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The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

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39

Pullepu, B., E. Ekambavanan, and A. J. Chamkha. "Unsteady Laminar Natural Convection from a Non-Isothermal Vertical Cone." Nonlinear Analysis: Modelling and Control 12, no. 4 (October 25, 2007): 525–40. http://dx.doi.org/10.15388/na.2007.12.4.14684.

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Natural convection effects of the numerical solution for unsteady, laminar, free convection flow over an incompressible viscous fluid past a non-isothermal vertical cone with surface temperature T′w(x) = T′∞ + axn varying as power function of distance from the apex (x = 0) is presented here. The dimensionless governing equations of the flow that are unsteady, coupled and non-linear partial differential equations are solved by an efficient, accurate and unconditionally stable finite difference scheme of Crank-Nicolson type. The velocity and temperature fields have been studied for various parameters Prandtl number, semi vertical angle 0◦ < φ < 90◦ and n. The local as well as average skin-friction and Nusselt number are also presented and analyzed graphically. The present results are compared with available results in literature and are found to be in good agreement.

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40

Keram, Aytura, and Pengzhan Huang. "A Uzawa-Type Iterative Algorithm for the Stationary Natural Convection Model." Entropy 24, no. 4 (April 13, 2022): 543. http://dx.doi.org/10.3390/e24040543.

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In this study, a Uzawa-type iterative algorithm is introduced and analyzed for solving the stationary natural convection model, where physical variables are discretized by utilizing a mixed finite element method. Compared with the common Uzawa iterative algorithm, the main finding is that the proposed algorithm produces weakly divergence-free velocity approximation. In addition, the convergence results of the proposed algorithm are provided, and numerical tests supporting the theory are presented.

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41

Massarotti, Nicola, Michela Ciccolella, Gino Cortellessa, and Alessandro Mauro. "New benchmark solutions for transient natural convection in partially porous annuli." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 3/4 (May 3, 2016): 1187–225. http://dx.doi.org/10.1108/hff-11-2015-0464.

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Purpose – The purpose of this paper is to focus on the numerical analysis of transient free convection heat transfer in partially porous cylindrical domains. The authors analyze the dependence of velocity and temperature fields on the geometry, by analyzing transient flow behavior for different values of cavity aspect ratio and radii ratio; both inner and outer radius are assumed variable in order to not change the difference ro-ri. Moreover, several Darcy numbers have been considered. Design/methodology/approach – A dual time-stepping procedure based on the transient artificial compressibility version of the characteristic-based split algorithm has been adopted in order to solve the transient equations of the generalized model for heat and fluid flow through porous media. The present model has been validated against experimental data available in the scientific literature for two different problems, steady-state free convection in a porous annulus and transient natural convection in a porous cylinder, showing an excellent agreement. Findings – For vertically divided half porous cavities, with Rayleigh numbers equal to 3.4×106 for the 4:1 cavity and 3.4×105 for the 8:1 cavity, the numerical results show that transient oscillations tend to disappear in presence of cylindrical geometry, differently from what happens for rectangular one. The magnitude of this phenomenon increases with radii ratio; the porous layer also affects the stability of velocity and temperature fields, as oscillations tend to decrease in presence of a porous matrix with lower value of the Darcy number. Research limitations/implications – A proper analysis of partially porous annular cavities is fundamental for the correct estimation of Nusselt numbers, as the formulas provided for rectangular domains are not able to describe these problems. Practical implications – The proposed model represents a useful tool for the study of transient natural convection problems in porous and partially porous cylindrical and annular cavities, typical of many engineering applications. Moreover, a fully explicit scheme reduces the computational costs and ensures flexibility. Originality/value – This is the first time that a fully explicit finite element scheme is employed for the solution of transient natural convection in partially porous tall annular cavities.

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42

Kuhn, Shine-Zen (Joseph), Hwan Kook Kang, and Per F. Peterson. "Study of Mixing and Augmentation of Natural Convection Heat Transfer by a Forced Jet in a Large Enclosure." Journal of Heat Transfer 124, no. 4 (July 16, 2002): 660–66. http://dx.doi.org/10.1115/1.1482081.

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This paper presents an experimental study of gas mixing processes and heat transfer augmentation by a forced jet in a large cylindrical enclosure with an isothermal bottom heating/cooling surface. Cold/hot air was injected at several positions with varying pipe diameters and injection orientations, and was removed from the top of the enclosure. Under natural convection, the mean Nusselt number was correlated by the enclosure Rayleigh number RaD1/3, and under strong forced convection, by the jet Reynolds number Rej2/3. A combining rule for mixed convection was found for both the stabilizing (cooled surface) and destabilizing (heated surface) density gradients. Using the ratio of forced and free convection Nusselt numbers, this correlation could be further reduced to predict forced-jet augmentation as a function of the Archimedes number, with a correction factor to account for jet orientation and enclosure aspect ratio.

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43

Sheikholeslami, M., Hakan F. Öztop, Nidal Abu-Hamdeh, and Zhixiong Li. "Nanoparticle transportation of CuO-H2O nanofluid in a porous semi annulus due to Lorentz forces." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 1 (January 7, 2019): 294–308. http://dx.doi.org/10.1108/hff-01-2018-0014.

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PurposeThe purpose of this paper is to research on CuO-water nanofluid Non-Darcy flow because of magnetic field. Porous cavity has circular heat source and filled with nanofluid. Lattice Boltzmann Method (LBM) has been used to simulate this problem.Design/methodology/approachIn this research, LBM has been applied as mesoscopic approach to simulate water-based nanofluid free convection. Koo–Kleinstreuer–Li model is used to consider Brownian motion impact on nanofluid properties. Impacts of Rayleigh number, Darcy number, nanofluid volume fraction and Hartmann number on heat transfer treatment are illustrated.FindingsIt is found that temperature gradient decreases with rise of while it enhances with augment of Ha. Darcy number can enhance the convective flow.Originality/valueThe originality of this work is to analyze the to investigate magnetic field impact on water based CuO-H2O nanofluid natural convection inside a porous cavity with elliptic heat source.

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44

Stewart, W. E., and J. L. Verhulst. "Experimental Free Convection From Piping in District Heating Utilidors." Journal of Energy Resources Technology 108, no. 2 (June 1, 1986): 173–78. http://dx.doi.org/10.1115/1.3231258.

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Experiments were performed to study the two-dimensional natural convection heat transfer from two heated isothermal horizontal cylinders to an isothermal-cooled rectangular enclosure. The experiments were designed to simulate the heat transfer encountered in underground heat distribution systems where steam and condensate lines are routed through underground or in-ground corridors (utilidors) from a central plant. The steam supply and condensate return lines were simulated with two copper cylinders. The fluid between the cylinders and enclosure was distilled water to simulate the Rayleigh number range encountered with air in actual utilidors. Results were obtained for the overall heat transfer coefficient between the two cylinders and the enclosure. The data was correlated over a Rayleigh number, RaL, range of 2.1 × 108 to 4.8 × 109 representative of the Rayleigh number, based upon a hypothetical gap width, in a typical utilidor exposed to extreme enclosure to piping temperature differential boundary conditions. The corresponding Nusselt numbers, NuL, ranged from 21 to 59 when both cylinders were heated for water as the intermediate fluid. Corresponding heat transfer coefficients calculated for the utilidor case with air as the intermediate fluid were found to be smaller compared to some other correlations for concentric cylinders.

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45

Massoudi, Mohamed Dhia, Mohamed Bechir Ben Hamida, Mohammed A. Almeshaal, Yahya Ali Rothan, and Khalil Hajlaoui. "Numerical analysis of magneto-natural convection and thermal radiation of SWCNT nanofluid inside T-inverted shaped corrugated cavity containing porous medium." International Journal of Numerical Methods for Heat & Fluid Flow 32, no. 3 (October 10, 2021): 1092–114. http://dx.doi.org/10.1108/hff-02-2021-0095.

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Purpose The purpose of this paper is to examine numerically the magnetohydrodynamic (MHD) free convection and thermal radiation heat transfer of single walled carbon nanotubes-water nanofluid within T-inverted shaped corrugated cavity comprising porous media including uniform heat source/sink for solar energy power plants applications. Design/methodology/approach The two-dimensional numerical simulation is performed by drawing on Comsol Multiphysics program, based on the finite element process. Findings The important results obtained show that increasing numbers of Rayleigh and Darcy and the parameter of radiation enhance the flow of convection heat. Furthermore, by increasing the corrugation height, the convection flow increases, but it decreases with the multiplication of the corrugation height. The use of a flat cavity provides better output than a corrugated cavity. Originality/value The role of surface corrugation parameters on the efficiency of free convection and heat transfer of thermal radiation within the porous media containing the T-inverted corrugated cavity including uniform heat source/sink under the impact of Lorentz forces has never been explored. A contrast is also established between a flat cavity and a corrugated one.

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46

Adeyinka, O. B., and G. F. Naterer. "Particle Image Velocimetry Based Measurement of Entropy Production With Free Convection Heat Transfer." Journal of Heat Transfer 127, no. 6 (June 1, 2005): 614–23. http://dx.doi.org/10.1115/1.1863272.

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Local entropy production rates are determined from a numerical and experimental study of natural convection in an enclosure. Numerical predictions are obtained from a control-volume-based finite element formulation of the conservation equations and the Second Law. The experimental procedure combines methods of particle image velocimetry and planar laser induced fluorescence for measured velocity and temperature fields in the enclosure. An entropy based conversion algorithm in the measurement procedure is developed and compared with numerical predictions of free convection in the cavity. The predicted and measured results show close agreement. A measurement uncertainty analysis suggests that the algorithm postprocesses velocities (accurate within ±0.5%) to give entropy production data, which is accurate within ±8.77% near the wall. Results are reported for free convection of air and water in a square cavity at various Rayleigh numbers. The results provide measured data for tracking spatial variations of friction irreversibility and local exergy losses.

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47

Ghalambaz, Mohammad, Mahmoud Sabour, Ioan Pop, and Dongsheng Wen. "Free convection heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a porous complex shaped cavity with MHD and thermal radiation effects." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 11 (November 4, 2019): 4349–76. http://dx.doi.org/10.1108/hff-04-2019-0339.

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Purpose The present study aims to address the flow and heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a complex shape enclosure filled with a porous medium. The enclosure is subject to a uniform inclined magnetic field and radiation effects. The effect of the presence of a variable magnetic field on the natural convection heat transfer of hybrid nanofluids in a complex shape cavity is studied for the first time. The geometry of the cavity is an annular space with an isothermal wavy outer cold wall. Two types of the porous medium, glass ball and aluminum metal foam, are adopted for the porous space. The governing equations for mass, momentum and heat transfer of the hybrid nanofluid are introduced and transformed into non-dimensional form. The actual available thermal conductivity and dynamic viscosity data for the hybrid nanofluid are directly used for thermophysical properties of the hybrid nanofluid. Design/methodology/approach The governing equations for mass, momentum and heat transfer of hybrid nanofluid are introduced and transformed into non-dimensional form. The thermal conductivity and dynamic viscosity of the nanofluid are directly used from the experimental results available in the literature. The finite element method is used to solve the governing equations. Grid check procedure and validations were performed. Findings The effect of Hartmann number, Rayleigh number, Darcy number, the shape of the cavity and the type of porous medium on the thermal performance of the cavity are studied. The outcomes show that using the composite nanoparticles boosts the convective heat transfer. However, the rise of the volume fraction of nanoparticles would reduce the overall enhancement. Considering a convective dominant regime of natural convection flow with Rayleigh number of 107, the maximum enhancement ratio (Nusselt number ratio compared to the pure fluid) for the case of glass ball is about 1.17 and for the case of aluminum metal foam is about 1.15 when the volume fraction of hybrid nanoparticles is minimum as 0.2 per cent. Originality/value The effect of the presence of a variable magnetic field on the natural convection heat transfer of a new type of hybrid nanofluids, MgO-MWCNTs/EG, in a complex shape cavity is studied for the first time. The results of this paper are new and original with many practical applications of hybrid nanofluids in the modern industry.

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48

Wyczółkowski, Rafał, and Dorota Musiał. "Analysis of the occurrence of natural convection in a bed of bars in vertical temperature gradient conditions." Archives of Thermodynamics 34, no. 1 (March 1, 2013): 71–83. http://dx.doi.org/10.2478/aoter-2013-0005.

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Abstract The reason for undertaking this study was to determine the possible involvement of natural convection in the global heat transfer, that occurs in the heated steel rods bed. This problem is related to the setting of the effective thermal conductivity of the bars bed. This value is one of the boundary conditions for heating modeling of steel rods bundles during heat treatment. The aim of this study was to determine for which geometry of the bed bars, there will be no free convection. To analyze the problem the Rayleigh criterion was used. It was assumed that for the value of the number Ra < 1700 convection in the bed bars does not occur. For analysis, the results of measurements of the temperature distribution in the unidirectionally heated beds of bars were used. It has been shown, that for obtained, during the test, differences of temperature between the surfaces of adjacent rods, convection can occur only when the diameter of the rod exceeds 18 mm.

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49

Medebber, Mohamed A., and Noureddine Retiel. "Numerical Study of Natural Convection in a Vertical Cylindrical Partially Annular." Mechanics and Mechanical Engineering 22, no. 1 (August 12, 2020): 77–92. http://dx.doi.org/10.2478/mme-2018-0008.

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AbstractA study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103 to 106 and height ratios of 0 to 1. The influence of physical and geometrical parameters on the streamlines, isotherms, average Nusselt has been numerically investigated.

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50

Abu-Mulaweh, H. I., B. F. Armaly, and T. S. Chen. "Laminar Natural Convection Flow Over a Vertical Backward-Facing Step." Journal of Heat Transfer 117, no. 4 (November 1, 1995): 895–901. http://dx.doi.org/10.1115/1.2836308.

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Measurements and predictions of laminar boundary-layer air flow in natural convection over a vertical two-dimensional backward-facing step are reported. The upstream and downstream walls and the step itself were heated to a uniform and constant temperature. The experiment was carried out for the ranges of step heights 3.5 mm ≤ s ≤ 9 mm, temperature differences of 5.8°C ≤ ΔT ≤ 23°C between the heated wall and the free stream (corresponding to 2.238 × 107 < Grxi < 8.877 × 107), and reference velocities of 0.24 m/s ≤ u* ≤ 0.47 m/s. Laser-Doppler velocimeter and cold-wire anemometer were utilized to measure, respectively, the velocity and the temperature distributions simultaneously. Flow visualization was also performed to determine the reattachment length. Measurements compare favorably with predictions. These results reveal that the step height significantly affects the velocity and temperature distributions, the friction coefficient, and the rate of heat transfer downstream of the backward-facing step.

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