Heat Transfer Due to Natural Convection in a Periodically Heated Slot

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
M. Z. Hossain ◽  
J. M. Floryan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Field ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Horizontal Direction ◽  
Wave Number ◽  
Lower Wall ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Heat transfer resulting from the natural convection in a fluid layer contained in an infinite horizontal slot bounded by solid walls and subject to a spatially periodic heating at the lower wall has been investigated. The heating produces sinusoidal temperature variations along one horizontal direction characterized by the wave number α with the amplitude expressed in terms of a suitably defined Rayleigh number Rap. The maximum heat transfer takes place for the heating with the wave numbers α = 0(1) as this leads to the most intense convection. The intensity of convection decreases proportionally to α when α→0, resulting in the temperature field being dominated by periodic conduction with the average Nusselt number decreasing proportionally to α2. When α→∞, the convection is confined to a thin layer adjacent to the lower wall with its intensity decreasing proportionally to α−3. The temperature field above the convection layer looses dependence on the horizontal direction. The bulk of the fluid sees the thin convective layer as a “hot wall.” The heat transfer between the walls becomes dominated by conduction driven by a uniform vertical temperature gradient which decreases proportionally to the intensity of convection resulting in the average Nusselt number decreasing as α−3. It is shown that processes described above occur for Prandtl numbers 0.001 < Pr < 10 considered in this study.

Effect of Periodicity of Non-Uniform Sinusoidal Side Heating on Natural Convection in an Anisotropic Porous-Enclosure

2011 ◽  
Vol 110-116 ◽  
pp. 1613-1618 ◽  
Author(s):  
S. Kapoor ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Stream Function ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Porous Enclosure

A comprehensive numerical study on the natural convection in a hydrodynamically anisotropic as well as isotropic porous enclosure is presented, flow is induced by non uniform sinusoidal heating of the right wall of the enclosure. The principal directions of the permeability tensor has been taken oblique to the gravity vector. The spectral Element method has been adopted to solve numerically the governing differential equations by using the vorticity-stream-function approach. The results are presented in terms of stream function, temperature profile and Nusselt number. The result show that the maximum heat transfer takes place at y = 1.5 when N is odd.. Also, increasing media permeability, by changing K* = 1 to K* = 0.2, increases heat transfer rate at below and above right corner of the enclosure. Furthermore, for the all values of N, profiles of local Nusselt number (Nuy) in isotropic as well as anisotropic media are similar, but for even values of N differ slightly at N = 2.. In particular the present analysis shows that, different periodicity (N) of temperature boundary condition has the significant effect on the flow pattern and consequently on the local heat transfer phenomena.

Enhancement of Heat Transfer to an Air Jet Impinging on a Flat Plate

Volume 1 ◽  
2004 ◽  
Author(s):  
D. P. Mishra ◽  
D. Mishra
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flat Plate ◽  
Average Nusselt Number ◽  
Cooling System ◽  
Reynolds Numbers ◽  
Heated Plate ◽  
Maximum Heat ◽  
Air Jet ◽  
Maximum Heat Transfer

An experimental investigation of the impinging jet cooling from a heated flat plate has been carried out for several Reynolds numbers (Re) and nozzle to plate distances. The present results indicate that the maximum heat transfer occurs from the heated plate at stagnation point and decreases with radial distances for all cases. The maximum value of the stagnation as well as average Nusselt number is found to occur at separation distance, H/D = 6.0 for Re = 55000. An attempt is also made to study effects of nozzle exit configuration on the heat transfer using a sharp edged orifice for same set of Reynolds numbers and nozzle to plate distance. The stagnation Nusselt numbers of sharp orifice jets are found to be enhanced by around 16–21.4% in comparison to that of square edged orifice. However, the enhancement in the average Nusselt number of sharp orifice is found to be in the range of 7–18.9% as compared to the square edged orifice. The maximum enhancement of 18.9% in average Nu is achieved for Re = 55 000 at H/D = 6. Two separate correlations in terms of Nuo, Re, H/D for both square and sharp edged orifice are obtained which will be useful for designing impinging cooling system.

Mixed Convection From a Cylinder With Low Conductivity Baffles in Cross-Flow

2002 ◽  
Vol 124 (6) ◽  
pp. 1064-1071
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Cross Flow ◽  
Maximum Heat ◽  
Buoyancy Parameter ◽  
Maximum Heat Transfer ◽  
Laminar Mixed Convection

The problem of laminar mixed convection from an isothermal cylinder with low conductivity baffles in cross flow was solved numerically. The average Nusselt number was calculated at different combinations of number of baffles, baffle height, Reynolds number, and buoyancy parameter. The reduction in the Nusselt number is as much as 75 percent. When using a small number of baffles at low values of buoyancy parameter, an odd number of baffles reduced the Nusselt number more than an even number of baffles, especially at high values of Reynolds number. This is not the case at high values of buoyancy parameter. There is an optimal baffle height, Reynolds number dependent, for maximum heat transfer reduction beyond which an increase in baffle height does not result in further decrease in heat transfer.

scholarly journals Natural convection in a differentially heated enclosure with triangular roof

1970 ◽  
Vol 39 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Sumon Saha ◽  
Noman Hasan ◽  
Chowdhury Md Feroz
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Element Analysis ◽  
Left Wall ◽  
Square Enclosure

A numerical study has been carried out for laminar natural convection heat transfer within a two-dimensional modified square enclosure having a triangular roof. The vertical sidewalls are differentially heated considering a constant flux heat source strip is flush mounted with the left wall. The opposite wall is considered isothermal having a temperature of the surrounding fluid. The rest of the walls are adiabatic. Air is considered as the fluid inside the enclosure. The solution has been carried out on the basis of finite element analysis by a non-linear parametric solver to examine the heat transfer and fluid flow characteristics. Different heights of the triangular roof have been considered for the present analysis. Fluid flow fields and isotherm patterns and the average Nusselt number are presented for the Rayleigh numbers ranging from 103 to 106 in order to show the effects of these governing parameters. The average Nusselt number computed for the case of isoflux heating is also compared with the case of isothermal heating as available in the literature. The outcome of the present investigation shows that the convective phenomenon is greatly influenced by the inclined roof height. Keywords: Natural convection, triangular roof, Rayleigh number, isoflux heating. Doi:10.3329/jme.v39i1.1826 Journal of Mechanical Engineering, vol. ME39, No. 1, June 2008 1-7

Enhancement of Natural Convection Heat Transfer by a Staggered Array of Discrete Vertical Plates

1980 ◽  
Vol 102 (2) ◽  
pp. 215-220 ◽  
Author(s):  
E. M. Sparrow ◽  
C. Prakash
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Convection Heat Transfer ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Parameter Ranges

An analysis has been performed to determine whether, in natural convection, a staggered array of discrete vertical plates yields enhanced heat transfer compared with an array of continuous parallel vertical plates having the same surface area. The heat transfer results were obtained by numerically solving the equations of mass, momentum, and energy for the two types of configurations. It was found that the use of discrete plates gives rise to heat transfer enhancement when the parameter (Dh/H)Ra > ∼2 × 103 (Dh = hydraulic diameter of flow passage, H = overall system height). The extent of the enhancement is increased by use of numerous shorter plates, by larger transverse interplate spacing, and by relatively short system heights. For the parameter ranges investigated, the maximum heat transfer enhancement, relative to the parallel plate case, was a factor of two. The general degree of enhancement compares favorably with that which has been obtained in forced convection systems.

Natural convection in differentially heated enclosures subjected to variable temperature boundaries

2019 ◽  
Vol 29 (11) ◽  
pp. 4130-4141 ◽  
Author(s):  
Abdulmajeed Mohamad ◽  
Mikhail A. Sheremet ◽  
Jan Taler ◽  
Paweł Ocłoń
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Uniform Heating ◽  
Content Type ◽  
Left Hand ◽  
Heating And Cooling ◽  
Right Hand ◽  
The Right

Purpose Natural convection in differentially heated enclosures has been extensively investigated due to its importance in many industrial applications and has been used as a benchmark solution for testing numerical schemes. However, most of the published works considered uniform heating and cooling of the vertical boundaries. This paper aims to examine non-uniform heating and cooling of the mentioned boundaries. The mentioned case is very common in many electronic cooling devices, thermal storage systems, energy managements in buildings, material processing, etc. Design/methodology/approach Four cases are considered, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature is kept at a constant, cold temperature. In the second case, the left-hand wall’s temperature linearly increases along the wall, while the right-hand wall’s temperature is kept a constant, cold temperature. The third case, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature linearly increases along the wall. In the fourth case, the left-hand and the right-hand walls’ temperatures decrease along the wall, symmetry condition. Hence, four scenarios of natural convection in enclosures were covered. Findings It has been found that the average Nusselt number of the mentioned cases is less than the average Nusselt number of the uniformly heated and cooled enclosure, which reflects the physics of the problem. The work quantifies the deficiency in the rate of the heat transfer. Interestingly one of the mentioned cases showed two counter-rotating horizontal circulations. Such a flow structure can be considered for passively, highly controlled mechanism for species mixing processes application. Originality/value Previous works assumed that the vertical boundary is subjected to a constant temperature or to a sinusoidal varying temperature. The subject of the work is to examine the effect of non-uniformly heating and/or cooling vertical boundaries on the rate of heat transfer and flow structure for natural convection in a square enclosure. The temperature either linearly increases or decreases along the vertical coordinate at the boundary. Four scenarios are explored.

Thermal Behavior of Silicon Heat Spreader Coated With Diamond Film

2004 ◽  
Author(s):  
T. W. Lin ◽  
M. C. Wu ◽  
C. H. Peng ◽  
P. L. Chen ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Silicon Wafer ◽  
Diamond Film ◽  
Silicon Surface ◽  
Average Nusselt Number ◽  
Diamond Surface ◽  
Heat Spreader ◽  
Heat Spreaders

In the present study, an experimental setup with stringent measurement methods for performing the natural convection from a horizontal heated chip mounted with a silicon heat spreader coated with diamond film has been successfully established. The parametric studies on the local and average effective heat transfer characteristics for natural convection from a horizontal smooth silicon wafer, rough silicon wafer or silicon wafer coated with diamond film spreader have been explored. The influencing parameters and conditions include Grashof number and spreader material with different surface treatment conditions. From the results, an axisymmetric bowl-shaped Nu profile is achieved, and the highest heat transfer performance occurs at the location near the rim of the heated surfaces for various heat spreaders. The local Nusselt number for a specified convective heat flux decreases along the distance from the disk rim toward the center. The local or average Nusselt number increases with increasing Grashof number for various heat spreaders. As compared with the average Nusselt number for smooth water surface (Ra=5.69nm), the heat transfer enhancements for rough silicon surface (Ra=516.61nm) and rough diamond surface (Ra=319.51nm) are 10.42% and 7.69%, respectively. Furthermore, new correlations for local and average Nusselt numbers for various heat spreaders are presented, respectively. As compared with the smooth silicon surface, the external thermal resistance for rough silicon surface and rough diamond surface are reduced to 91.18% and 90.73%, respectively; and the maximum thermal resistances for rough silicon wafer and silicon wafer coated with diamond film are reduced to 90.43% and 92.61%, respectively.

Entropy Generation in Laminar and Turbulent Natural Convection Heat Transfer From Vertical Cylinder With Annular Fins

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Jnana Ranjan Senapati ◽  
Sukanta Kumar Dash ◽  
Subhransu Roy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Vertical Cylinder ◽  
Turbulent Regime ◽  
Maximum Heat ◽  
Turbulent Natural Convection ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
Annular Fins

Entropy generation due to natural convection has been calculated for a wide range of Rayleigh number (Ra) in both laminar (104 ≤ Ra ≤ 108) and turbulent (1010 ≤ Ra ≤ 1012) flow regimes, for diameter ratio of 2 ≤ D/d ≤ 5, for an isothermal vertical cylinder fitted with annular fins. In the laminar regime, the entropy generation was predominantly caused by heat transfer (conduction and convection) and the viscous contribution was negligible with respect to heat transfer. But in the turbulent regime, entropy generation due to fluid friction is significant enough although heat transfer entropy generation is still dominant. The results demonstrate that the degree of irreversibility is higher in case of finned configuration when compared with unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to delineate the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned. The ratio (I/Q)finned/(I/Q)unfinned gets its minimum value at optimum fin spacing where maximum heat transfer occurs in turbulent flow, whereas in laminar flow the ratio (I/Q)finned/(I/Q)unfinned decreases continuously with the increase in number of fins.

scholarly journals ISPH simulations of natural convection from heated rotating paddles on a circular cylinder inside a cross-shaped cavity filled with a nanofluid

2020 ◽  
Author(s):  
Abdelraheem Mahmoud Aly ◽  
Ehab Mahmoud
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Circular Cylinder ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Heterogeneous Porous Media ◽  
Convection Flow

The numerical simulations of the uniform circular rotation of paddles on circular cylinder results natural convection flow of Al2O3-water in a cross-shaped porous cavity were performed by incompressible representation of smoothed particle hydrodynamics entitled ISPH method. The two vertical area of a cross-shaped cavity is saturated with homogeneous porous media and the whole horizontal area of a cross-shaped cavity is saturated with heterogeneous porous media. The inner paddles on the circular cylinder are rotating around their center by a uniform circular velocity. The whole embedded body of paddles on a circular cylinder has temperature Th. The wall-sides of a cross-shaped cavity are positioned at a temperature Tc. The current geometry can be applied in analysis and understanding the thermophysical behaviors of the electronic motors. The angular velocity is taken as ! = 7:15 and consequently the natural convection case is only considered due to the low speed of inner rotating shape. The performed simulations are represented in the graphical for the temperature distributions, velocity fields and tabular forms for average Nusselt number. The results revealed that an augmentation on paddle length rises the heat transfer and speed of fluid flow inside a cross shaped cavity. Also, an incrementation on Rayleigh number augments the heat transfer and speed of the fluid flow inside a cross-shaped cavity. The fluid flow is circulated only around the rotating inner shape when Darcy parameter decreases to Da = 105. Average Nusselt number Nu enhances by an increment on the paddle lengths and nanoparticles volume fraction

scholarly journals Prediction of Natural Convection Heat Transfer Phenomena of Nanofluids in Corrugated Annulus

2020 ◽  
Author(s):  
Sattar Aljobair ◽  
Akeel Abdullah Mohammed ◽  
Israa Alesbe
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Outer Cylinder ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Abstract The natural convection heat transfer and fluid flow characteristic of water based Al2O3 nano-fluids in a symmetrical and unsymmetrical corrugated annulus enclosure has been studied numerically using CFD. The inner cylinder is heated isothermally while the outer cylinder is kept constant cold temperature. The study includes eight models of corrugated annulus enclosure with constant aspect ratio of 1.5. The governing equations of fluid motion and heat transfer are solved using stream-vorticity formulation in curvilinear coordinates. The range of solid volume fractions of nanoparticles extends from PHI=0 to 0.25, and Rayleigh number varies from 104 to 107. Streamlines, isotherms, local and average Nusselt number of inner and outer cylinder has been investigated in this study. Sixty-four correlations have been deduced for the average Nusselt number for the inner and outer cylinders as a function of Rayleigh number have been deduced for eight models and five values of volume fraction of nano particles with an accuracy range 6-12 %. The results show that, the average heat transfer rate increases significantly as particle volume fraction and Rayleigh number increase. Also, increase the number of undulations in unsymmetrical annuli reduces the heat transfer rates which remain higher than that in symmetrical annuli. There is no remarkable change in isotherms contour with increase of volume fraction of nanofluid.

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