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.

Three-Dimensional Numerical Investigation of Thermodynamic Performance Due to Conjugate Natural Convection From Horizontal Cylinder With Annular Fins

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Jnana Ranjan Senapati ◽  
Sukanta Kumar Dash ◽  
Subhransu Roy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Horizontal Cylinder ◽  
Diameter Ratio ◽  
Tube Diameter ◽  
Wide Range ◽  
Thermodynamic Performance ◽  
Annular Fins ◽  
Fin Spacing

Entropy generation due to natural convection has been computed for a wide range of Rayleigh numbers based on fin spacing, RaS in the entire laminar range 5≤RaS≤108, and diameter ratio 2 ≤ D/d ≤ 5 for an isothermal horizontal cylinder fitted with vertical annular fins. Entropy generation in the tube-fin system is predominantly due to heat transfer rather than fluid friction. The results demonstrate that the degree of irreversibility is higher in the case of the finned configuration when compared with the unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to show the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned which gets its minimum value at optimum fin spacing where heat transfer is maximum. A detailed view of the entropy generation around the finned cylinder has been shown for various S/d (fin spacing to tube diameter ratio) at a particular D/d (fin to tube diameter ratio) and Rayleigh number, which explains the nature and reason of entropy production.

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 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.

scholarly journals Investigation of the novelty of latent functionally thermal fluids as alternative to nanofluids in natural convective flows

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Zoubida Haddad ◽  
Farida Iachachene ◽  
Eiyad Abu-Nada ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Volume Fraction ◽  
Heat Of Fusion ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Thermal Fluids ◽  
Maximum Heat Transfer ◽  
Wide Range

AbstractThis paper presents a detailed comparison between the latent functionally thermal fluids (LFTFs) and nanofluids in terms of heat transfer enhancement. The problem used to carry the comparison is natural convection in a differentially heated cavity where LFTFs and nanofluids are considered the working fluids. The nanofluid mixture consists of Al2O3 nanoparticles and water, whereas the LFTF mixture consists of a suspension of nanoencapsulated phase change material (NEPCMs) in water. The thermophysical properties of the LFTFs are derived from available experimental data in literature. The NEPCMs consist of n-nonadecane as PCM and poly(styrene-co-methacrylic acid) as shell material for the encapsulation. Finite volume method is used to solve the governing equations of the LFTFs and the nanofluid. The computations covered a wide range of Rayleigh number, 104 ≤ Ra ≤ 107, and nanoparticle volume fraction ranging between 0 and 1.69%. It was found that the LFTFs give substantial heat transfer enhancement compared to nanofluids, where the maximum heat transfer enhancement of 13% was observed over nanofluids. Though the thermal conductivity of LFTFs was 15 times smaller than that of the base fluid, a significant enhancement in thermal conductivity was observed. This enhancement was attributed to the high latent heat of fusion of the LFTFs which increased the energy transport within the cavity and accordingly the thermal conductivity of the LFTFs.

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.

scholarly journals Numerical Analysis Natural Convection Heat Transfer from Vertical Cylinder Annular Fins with The Addition of Slits

2021 ◽  
Vol 9 (4) ◽  
pp. 405-409
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Simulation Method ◽  
Cylinder Length ◽  
Annular Fin ◽  
Annular Fins

One method of increasing the heat transfer rate of the fins is by adding slits to the fins. The purpose of this study was to analyze the heat transfer rate by adding slits in the annular fins with a vertical cylinder under natural convection conditions. The vertical cylinder length, cylinder diameter, fin diameter, and distance between the fins are 313 mm, 25 mm, 125 mm, and 7 mm, respectively. The number of slits varied from 2 slits and 4 slits and the spacing of the slits was kept constant by 5 mm. This research was conducted with a simulation method using Autodesk CFD 2019 software. As a result, fins with slits and fins without slits were compared. The value of the heat transfer rate that occurs and the heat transfer coefficient in the annular fin with slits is better than the fin without slits. The highest heat transfer rates were 142.928 W and 2.6022 W/m 2K for an annular fin with 2 slits

Numerical Analysis of Natural Convective Heat Transfer over a Vertical Cylinder Using External Fins

2015 ◽  
Vol 813-814 ◽  
pp. 707-712
Author(s):  
Anwesha Panigrahi ◽  
D.P. Mishra ◽  
Deepak Kumar
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Working Fluid ◽  
Natural Convection Heat Transfer ◽  
Maximum Heat ◽  
Optimum Parameters ◽  
Maximum Heat Transfer

The present numerical study deals with the natural convection heat transfer on the surface of a vertical cylinder with external longitudinal fins. The aim of the study was to determine the effects of geometric parameters like fin height, fin number and fin shape on the heat transfer and thus obtain the optimum parameters that will maximize the rate of heat transfer have been discussed. The numerical investigation consists of an aluminium cylinder of length 1m and diameter 0.07m with air as the working fluid. It has been seen from the numerical investigation that the heat transfer increases with fin height. It is also observed that there exists optimum fin number for maximum heat transfer. Keeping the fin number, fin height and volume fixed, it was found that the heat transfer is maximum for rectangular shaped fin.

Compounded Heat Transfer Enhancement in Enclosure Natural Convection by Changing the Cold Wall Shape and the Gas Composition

2006 ◽  
Vol 129 (7) ◽  
pp. 827-834 ◽  
Author(s):  
El Hassan Ridouane ◽  
Antonio Campo
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Gas Mixtures ◽  
Gas Mixture ◽  
Transfer Enhancement ◽  
Maximum Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Triangular Enclosure

This article addresses compound heat transfer enhancement for gaseous natural convection in closed enclosures; that is, the simultaneous use of two passive techniques to obtain heat transfer enhancement, which is greater than that produced by only one technique itself. The compounded heat transfer enhancement comes from two sources: (1) reshaping the bounded space and (2) the adequacy of the gas. The sizing of enclosures is of great interest in the miniaturization of electronic packaging that is severely constrained by space and∕or weight. The gases consist in a subset of binary gas mixtures formed with helium (He) as the primary gas. The secondary gases are nitrogen (N2), oxygen (O2), carbon dioxide (CO2), methane (CH4), and xenon (Xe). The steady-state flow is governed by a system of 2-D coupled mass, momentum, and energy conservation equations, in conjunction with the ideal gas equation of state. The set of partial differential equations is solved using the finite volume method, for a square and a right-angled isosceles triangular enclosure, accounting for the second-order accurate QUICK and SIMPLE schemes. The grid layouts rendered reliable velocities and temperatures for air and the five gas mixtures at high Ra=106, producing errors within 1% were 18,500 and 47,300 elements for the square and triangle enclosures, respectively. In terms of heat transfer enhancement, helium is better than air for the square and the isosceles triangle. It was found that the maximum heat transfer conditions are obtained filling the isosceles triangular enclosure with a He–Xe gas mixture. This gives a good trade-off between maximizing the heat transfer rate while reducing the enclosure space in half; the maximum enhancement of triangle∕square went up from 19% when filled with air into 46% when filled with He–Xe gas mixture at high Ra=106.

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