scholarly journals Moist Air Flow Analysis in an Open Enclosure. Part A: Parametric Study

2021 ◽  
Vol 11 (5) ◽  
pp. 7571-7577
Author(s):  
T. Chati ◽  
K. Rahmani ◽  
T. T. Naas ◽  
A. Rouibah
Keyword(s):  
Mass Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat And Mass Transfer ◽  
Surface Effect ◽  
Flow Behavior ◽  
Adiabatic Wall ◽  
Maximum Heat ◽  
Aspect Ratios ◽  
Maximum Heat Transfer

Heat and mass transfer in many systems are widely accomplished applying natural convection process due to their low cost, reliability, and easy support. Typical applications include different mechanisms in various fields such as (solar energy, solar distiller, stream cooling, etc…). Numerical results of turbulent natural convection and mass transfer in an open enclosure for different aspect ratios (AR = 0.5, 1, and 2) with a humid-air are carried out. Mass fraction and local Nusselt number were proposed to investigate the heat and mass transfer. A heat flux boundary conditions were subjected to the lateral walls and the bottom one make as an adiabatic wall, while the top area was proposed as a free surface. Effect of Rayleigh numbers (106≤????????≤108) on natural convection and mass flow behavior are analyzed. The governing equations are solved using CFD Fluent code based on the SIMPLE algorithm. The results showed that the cavity with an aspect ratio of AR = 2 has a significant enhancement to raise the rates of both heat and mass transfer. When the Rayleigh number increases, maximum heat transfer rates were observed due to the fluid flow becomes more vigorous. However, mass transfer improves as the Rayleigh number decreases.

scholarly journals NATURAL CONVECTION IN RECTANGULAR CAVITIES WITH DIFFERENT ASPECT RATIOS

2011 ◽  
Vol 10 (1-2) ◽  
pp. 44
Author(s):  
R. M. Nogueira ◽  
M. A. Martins ◽  
F. Ampessan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Flow Behavior ◽  
Heated Wall ◽  
Flow Profile ◽  
Height Ratio ◽  
Dimensionless Variable ◽  
Aspect Ratios ◽  
Wide Range

Natural convection in closed cavities has been extensively studied in recent decades. This spontaneous method of heat transfer has a wide range of applications in engineering. In the present work, natural convection was numerically analyzed in a rectangular cavity heated on one of the sides and cooled on the opposite side. Temperatures of the heated wall and of the cooled wall were assumed to be constant. The objective of these studies was to determine the effects of the aspect ratio and the Rayleigh number on flow behavior and heat transfer in the cavity. In the simulations, the Rayleigh number drastically influenced the flow profile and heat transfer inside de cavity, as well as the thickness of the thermal boundary layer. It was also verified that the Nusselt number is strongly dependent on the L/D (Length/Height) ratio, and that this dimensionless variable increases with the increase of the W/L. The simulation of natural convection problems in the CFD Studio satisfactorily described the studied situations.

Natural Convection Heat and Mass Transfer in the Vertical Cylindrical Porous Channel Under the Effects of Time-Periodic Boundary Condition

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Hayder I. Mohammed ◽  
Donald Giddings
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Boundary Condition ◽  
Porous Medium ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Heat And Mass Transfer ◽  
Vertical Wall

Abstract Heat and mass transfer are investigated numerically with steady-state laminar natural convection through a vertical cylindrical enclosure filled with a liquid-saturated porous medium. The vertical wall is under a constant magnetic field and various durations of periodic heating boundary condition; the top and bottom surfaces are kept at a constant cold temperature. Continuity, momentum, and energy equations are transformed to dimensionless equations. The finite difference approach with the line successive over-relaxation (LSOR) method is used to obtain the computational results. This study covers the heat transfer, the temperature distribution, and the velocity field in the domain under the variation of different parameters. The code used is validated by modifying it to analyze the Nusselt number in the existing experimental literature of Izadpanah et al. (1998, “Experimental and Theoretical Studies of Convective Heat Transfer in a Cylindrical Porous Medium,” Int. J. Heat Fluid Flow, 19(6), pp. 629–635). This work shows that Nusselt number decreases (with varying gradient) as the aspect ratio increases, and that it increases as the Rayleigh number increases. The centerline temperature has a proportional relationship with the heating amplitude and the heating period (as the system receives more heat) and is inversely proportional with Rayleigh number. Increasing the Rayleigh number causes increased convective velocity, which affects the position of the hot region, and causes a decrease in the temperature field. Increasing the aspect ratio results in a warm stream at the center of the cylinder, and when the time period of the heating increases, the circulation becomes faster and the intensity of the temperature contour layers decreases. In this work, a correlation for Nu as a function of the mentioned parameters is developed.

scholarly journals Laminar natural convection from a vertical array of horizontal heated cylinders inside a water-filled rectangular enclosure cooled at sides

2019 ◽  
Vol 30 (5) ◽  
pp. 2607-2623 ◽  
Author(s):  
Marta Cianfrini ◽  
Massimo Corcione ◽  
Alessandro Quintino ◽  
Vincenzo Andrea Spena
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Control Volume ◽  
Maximum Heat ◽  
Content Type ◽  
Rectangular Enclosure ◽  
Cylinder Diameter ◽  
Maximum Heat Transfer ◽  
Laminar Natural Convection

Purpose The purpose of this study is to investigate numerically the laminar natural convection from a pair of horizontal heated cylinders, set one above the other, inside a water-filled rectangular enclosure cooled at sides, with perfectly insulated top and bottom walls, through a control-volume formulation of the finite-difference method, with the main aim to evaluate the effects of the center-to-center cylinder spacing, the size of the cavity and the temperature difference imposed between the cylinders and the cavity sides. Design/methodology/approach The system of the conservation equations of the mass, momentum and energy, expressed in dimensionless form, is solved by a specifically developed computer code based on the SIMPLE-C algorithm for the pressure-velocity coupling. Numerical simulations are executed for different values of the Rayleigh number based on the cylinder diameter, as well as the center-to-center cylinder spacing and the width of the cavity normalized by the cylinder diameter. Findings The main results obtained may be summarized as follows: the existence of an optimum cylinder spacing for maximum heat transfer rate is found at any investigated Rayleigh number; as a consequence of the downstream confinement, a periodic flow arises at sufficiently high Rayleigh numbers; the amplitude of oscillation of the periodic heat transfer performance of the cylinder array decreases as the cylinder spacing is increased and the cavity width is decreased, whereas the frequency of oscillations remains almost the same; at very small cavity widths, a transition from the typical two-cell to a four-cell flow pattern occurs. Originality/value The computational code used in the present study incorporates an original composite polar/Cartesian discretization grid scheme.

Thermo-Solutal Natural Convection in an Anisotropic Porous Enclosure Due to Non-Uniform Temperature and Concentration at Bottom Wall

2015 ◽  
Vol 7 (5) ◽  
pp. 644-662 ◽  
Author(s):  
Ashok Kumar ◽  
Pravez Alam ◽  
Prachi Fartyal
Keyword(s):  
Mass Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat And Mass Transfer ◽  
Numerical Study ◽  
Orientation Angle ◽  
Darcy Number ◽  
Bottom Wall ◽  
Transfer Rates ◽  
The Impact

AbstractThis article summaries a numerical study of thermo-solutal natural convection in a square cavity filled with anisotropic porous medium. The side walls of the cavity are maintained at constant temperatures and concentrations, whereas bottom wall is a function of non-uniform (sinusoidal) temperature and concentration. The non-Darcy Brinkmann model is considered. The governing equations are solved numerically by spectral element method using the vorticity-stream-function approach. The controlling parameters for present study are Darcy number (Da), heat source intensity i.e., thermal Rayleigh number (Ra), permeability ratio (K*), orientation angle (ϕ). The main attention is given to understand the impact of anisotropy parameters on average rates of heat transfer (bottom,Nub, sideNus) and mass transfer (bottom,Shb, side,Shs) as well as on streamlines, isotherms and iso-concentration. Numerical results show that, for irrespective value ofK*, the heat and mass transfer rates are negligible for 10−7≤Da≤ 10−5,Ra= 2 × 105andϕ= 45°. However a significant impact appears on Nusselt and Sherwood numbers whenDalies between 10−5to 10−4. The maximum bottom heat and mass transfer rates (Nub, Sub) is attained atϕ= 45°, whenK*=0.5 and 2.0. Furthermore, both heat and mass transfer rates increase on increasing Rayleigh number (Ra) for all the values ofK*. Overall, It is concluded from the above study that due to anisotropic permeability the flow dynamics becomes complex.

scholarly journals Dimensionless Correlations for Natural Convection Heat Transfer from a Pair of Vertical Staggered Plates Suspended in Free Air

2021 ◽  
Vol 11 (14) ◽  
pp. 6511
Author(s):  
Alessandro Quintino ◽  
Marta Cianfrini ◽  
Ivano Petracci ◽  
Vincenzo Andrea Spena ◽  
Massimo Corcione
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
Separation Distance ◽  
Vertical Alignment ◽  
Maximum Heat ◽  
Plate Length ◽  
Optimal Separation ◽  
Maximum Heat Transfer ◽  
Free Air

Buoyancy-induced convection from a pair of staggered heated vertical plates suspended in free air is studied numerically with the main scope to investigate the basic heat and momentum transfer features and to determine in what measure any independent variable affects the thermal performance of each plate and both plates. A computational code based on the SIMPLE-C algorithm for pressure-velocity coupling is used to solve the system of the governing conservation equations of mass, momentum and energy. Numerical simulations are carried out for different values of the Rayleigh number based on the plate length, as well as of the horizontal separation distance between the plates and their vertical alignment, which are both normalized by the plate length. It is observed that an optimal separation distance between the plates for the maximum heat transfer rate related to the Rayleigh number and the vertical alignment of the plates does exist. Based on the results obtained, suitable dimensionless heat transfer correlations are developed for each plate and for the entire system.

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