scholarly journals Numerical Simulation and Stability Study of Natural Convection in an Inclined Rectangular Cavity

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Hua-Shu Dou ◽  
Gang Jiang ◽  
Chengwang Lei
Keyword(s):  
Natural Convection ◽  
Inclination Angle ◽  
Flow Instability ◽  
Onset Time ◽  
Flow Time ◽  
Stability Study ◽  
Plate Length ◽  
Energy Gradient ◽  
Lower Left Corner ◽  
The Right

This paper examines the process of instability of natural convection in an inclined cavity based on numerical simulations. The energy gradient method is employed to analyze the physics of the flow instability in natural convection. It is found that the maximum value of the energy gradient function in the flow field correlates well with the location where flow instability occurs. Meanwhile, the effects of the flow time, the plate length, and the inclination angle on the instability have also been discussed. It is observed that the locations of instabilities migrate right as the flow time increased. With the increase of plate length, the onset time of the instability on the top wall of the cavity decreases gradually and the locations of instabilities move to the right side. Furthermore, the locations of instability move left with the increase of the inclination angle in a certain range. However, these positions move right as the accumulation of the heat flux is restrained in the lower left corner of the cavity once the inclination angle exceeds a certain range.

NUMERICAL SIMULATION OF FLOW INSTABILITY AND HEAT TRANSFER

2014 ◽  
Vol 34 ◽  
pp. 1460377
Author(s):  
HUA-SHU DOU ◽  
GANG JIANG
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Gradient Method ◽  
Physical Mechanism ◽  
Flow Instability ◽  
K Value ◽  
Energy Gradient ◽  
Efficient Heat Transfer ◽  
The Right ◽  
Fin Length

This paper numerically investigates the physical mechanism of flow instability and heat transfer of natural convection in a cavity with thin fin(s). The left and the right walls of the cavity are differentially heated. The cavity is given an initial temperature, and the thin fin(s) is fixed on the hot wall in order to control the heat transfer. The finite volume method with the SIMPLE scheme is used to simulate the flow. Distributions of the temperature, the pressure, the velocity and the total pressure are achieved. Then, the energy gradient method is employed to study the physical mechanism of flow instability and the effect of the thin fin(s) on heat transfer. Based on the energy gradient method, the energy gradient function K represents the characteristic of flow instability. It is observed from the simulation results that the positions where instabilities take place in the temperature contours accord well with those of higher K value, which demonstrates that the energy gradient method reveals the physical mechanism of flow instability. Furthermore, the effect of the fin length, the fin position, the fin number, and Ra on heat transfer is also investigated. It is found that the effect of the fin length on heat transfer is negligible when Ra is relatively high. When there is only one fin, the most efficient heat transfer rate is achieved as the fin is fixed at the middle height of the cavity. The fin blocks heat transfer with a relatively small Ra, but the fin enhances heat transfer with a relatively large Ra. The fin(s) enhances heat transfer gradually with the increase of Ra under the influence of the thin fin(s). Finally, it is observed that both Kmax and Ra can reveal the physical mechanism of natural convection from different approaches.

scholarly journals A Numerical Study of Natural Convection Heat Transfer in Fin Ribbed Radiator

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Hua-Shu Dou ◽  
Gang Jiang ◽  
Lite Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Instability ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Gradient Theory ◽  
Computational Domain ◽  
Energy Gradient ◽  
Gradient Function ◽  
Fin Shape

This paper numerically investigates the thermal flow and heat transfer by natural convection in a cavity fixed with a fin array. The computational domain consists of both solid (copper) and fluid (air) areas. The finite volume method and the SIMPLE scheme are used to simulate the steady flow in the domain. Based on the numerical results, the energy gradient functionKof the energy gradient theory is calculated. It is observed from contours of the temperature and energy gradient function that the position where thermal instability takes place correlates well with the region of largeKvalues, which demonstrates that the energy gradient method reveals the physical mechanism of the flow instability. Furthermore, the effects of the fin height, the fin number, and the fin shape on the heat transfer rate are also investigated. It is found that the thermal performance of the fin array is determined by the combined effect of the fin space and fin height. It is also observed that the effect of fin shape on heat transfer is insignificant.

Study of flow instability in a centrifugal fan based on energy gradient theory

2016 ◽  
Vol 30 (2) ◽  
pp. 507-517 ◽  
Author(s):  
Meina Xiao ◽  
Qing Xiao ◽  
Hua-Shu Dou ◽  
Xiaoyang Ma ◽  
Yongning Chen ◽  
...  
Keyword(s):  
Flow Instability ◽  
Gradient Theory ◽  
Centrifugal Fan ◽  
Energy Gradient Theory ◽  
Energy Gradient

Effects of Viscous Dissipation and Radiation on MHD Natural Convection in Oblique Porous Cavity with Constant Heat Flux

2017 ◽  
Vol 9 (2) ◽  
pp. 463-484 ◽  
Author(s):  
Ammar I. Alsabery ◽  
Habibis Saleh ◽  
Ishak Hashim
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Inclination Angle ◽  
Hartmann Number ◽  
Constant Heat Flux ◽  
Governing Equations ◽  
Constant Heat ◽  
Left Wall ◽  
Porous Cavity

AbstractEffects of viscous dissipation and radiation on MHD natural convection in oblique porous cavity with constant heat flux is studied numerically in the present article. The right inclined wall is maintained at a constant cold temperatureTcand the left inclined wall has a constant heat fluxqwith lengthS, while the remainder of the left wall is adiabatic. The horizontal walls are assumed to be adiabatic. The governing equations are obtained by applying the Darcy model and Boussinesq approximations. COMSOL's finite element method is used to solve the non-dimensional governing equations together with specified boundary conditions. The governing parameters of this study are Rayleigh number (Ra=10,100,200,250,500 and 1000), Hartmann number (0≤Ha≤20), inclination angle of the magnetic field (0° ≤ω≤π/2), Radiation (0≤R≤15), the heater flux length (0.1≤H≤1) and inclination angle of the sloping wall (–π/3≤ϕ≤π/3). The results are considered for various values of the governing parameters in terms of streamlines, isotherms and averageNusselt number. It is found that the intensity of the streamlines and the isotherm patterns decrease with an increment in Hartmann number. The overall heat transfer is significantly increased with the increment of the viscous dissipation and the radiation parameters.

scholarly journals Stability study of rock slope in fractured quartzite at right side of spillway, Middle Marsyangdi Hydroelectric Project, Nepal

2003 ◽  
Vol 28 ◽  
Author(s):  
Kaustubh Mani Nepal ◽  
Roger Olsson
Keyword(s):  
Rock Slope ◽  
Stability Study ◽  
Cut Slope ◽  
Stability Studies ◽  
Hydroelectric Project ◽  
The Stability ◽  
The Right ◽  
Cut Slopes

A 120 m long and 68 m high rock cut slope is designed at the right side of spillway of Middle Marsyangdi Hydroelectric Project. This paper describes the stability studies performed for the rock cut slopes in jointed quartzite for foundation of spillway.

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.

Transient Natural Convection Between Two Zones in an Insulated Enclosure

1988 ◽  
Vol 110 (1) ◽  
pp. 116-125 ◽  
Author(s):  
P. A. Litsek ◽  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Experiments ◽  
Thermal Stratification ◽  
Convection Flow ◽  
Natural Convection Flow ◽  
Flow And Heat Transfer ◽  
Vertical Opening ◽  
The Right ◽  
Rayleigh Numbers

The natural convection flow and heat transfer between two enclosures that communicate through a vertical opening is studied by considering the evolution of an enclosed fluid in which the left half is originally at a different temperature than the right half. Numerical experiments show that at sufficiently high Rayleigh numbers the ensuing flow is oscillatory. This and other features are anticipated on the basis of scale analysis. The time scales of the oscillation, the establishment of thermal stratification, and eventual thermal equilibrium are determined and tested numerically. At sufficiently high Rayleigh numbers the heat transfer between the communicating zones is by convection, in accordance with the constant-Stanton-number trend pointed out by Jones and Otis (1986). The range covered by the numerical experiments is 102 < Ra < 107, 0.71 < Pr < 100, and 0.25 < H/L < 1.

Lattice Boltzmann Computations of Natural Convection Heat Transfer of Nanofluid in a Square Cavity Heated by Protruding Heat Source

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Mustapha Faraji ◽  
El Mehdi Berra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Inclination Angle ◽  
Lattice Boltzmann ◽  
Base Fluid ◽  
Numerical Code ◽  
Convection Flow ◽  
Square Enclosure ◽  
Rayleigh Numbers

Abstract This paper reported the mathematical modeling and numerical simulation of natural convection flow of Cu/water nanofluid in a square enclosure using the lattice Boltzmann method (LBM). The cavity is heated from below by heat source and cooled by the top wall. The vertical walls are adiabatic. After validating the numerical code against the numerical and experimental data, simulations were performed for different Rayleigh numbers (104–0.5 × 107), nanoparticles volume fractions (0–8%), and cavity inclination angle (0 deg–90 deg). The effects of the studied parameters on the streamlines, on isotherms distributions within the enclosure, and on the local and average Nusselt numbers are investigated. It was found that heat transfer and fluid flow structure depend closely on the nanoparticle concentration. Results show differences in stream separation between a base fluid and the nanofluid. Also, adding small nanoparticles fractions, less than 6%, to the base fluid enhances the heat transfer for higher Rayleigh numbers and cavity inclination angle less than 30 deg. It is concluded that the optimal dilute suspension of copper nanoparticles can be applied as a passive way to enhance heat transfer in natural convection engineering applications.

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