Experimental Study of Mixed Convection in an Enclosure with a Cold Movable Top Wall and Hot Bottom Wall (original) (raw)
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A Study of Mixed Convection in an Enclosure with Different Inlet and Outlet Configurations
SIJ transactions on computer networks and communication engineering, 2016
A constant flux heat source was heated vertical wall with the fluid considered being air. The other side walls including the top and bottom of the enclosure were assumed to be adiabatic. The inlet opening, located on the left vertical wall, was placed at varying locations. The outlet opening was placed on the opposite heated wall at a fixed location. The basis of the investigation was the two-dimensional numerical solutions of governing equations by using Finite Difference Method (FDM).Significant parameters considered were Richardson number (Ri) and Reynolds number (Re). Results are presented for Richardson number 0 to 10 at Pr=0.71 and Re=50,100,200.The effects of Richardson number and position of the inlet on dimensional temperature inside the enclosure was investigated. The resulting interaction between forced external air stream and buoyancy-driven flow by the heat source are presented in the form of velocity profile and temperature distribution within the enclosure by patterns of graphs. The computational results indicate that heat transfer is strongly affected by Reynolds and Richardson numbers. As the value of Ri increases, there occurs a transition from forced convection to buoyancy dominated flow at Ri>1. A detailed analysis of flow pattern shows that natural or forced convection is based on the parameter Ri.
Anbar Journal of Engineering Sciences, 2017
Laminar natural convection heat transfer and fluid flow due to the heating from below at variable heat source length inside two dimensional enclosure has been analyzed numerically in this study. The enclosure has filled with air as a working fluid. The vertical inclined walls of the enclosure are maintained at lower temperature while the remaining walls are insulated. The value of Rayleigh number from (1x10 3 ≤ Ra ≤ 4x10 4), the inclination angle at (γ = 0 o , 22.5 o , 45 o) and dimensionless heat source length at (S = 1 and 0.5). The continuity, momentum and energy equations have been applied to the enclosure and solved by using finite difference method. The results showing that the average Nusselt number increases with the increasing of the heating source length and decreases with the increasing in an inclination angle of the vertical walls.
Numerical Simulation on Mixed Convection in a Parallelogrammic Ventilated Enclosure
A parametric numerical investigation is carried out on steady, laminar mixed convection heat transfer in a parallelogrammic ventilated enclosure with a uniform heat source applied on the horizontal bottom wall. Inclined side walls and upper horizontal wall are kept insulated and adiabatic. An external air flow enters the enclosure through an opening located at the bottom of the left vertical wall and exits from an opening located at the top of the opposite wall. The developed mathematical model is governed by the two dimensional continuity, momentum and energy equations. The governing equations, written in non-dimensional form are solved by using Galerkin finite element method. A triangular grid system has been employed for discretization of the computational domain. The Reynolds number is fixed at 100 and the working fluid is considered as air. Parametric studies of the effect of mixed convection parameter, Gr/Re2 (also referred to as Richardson number, Ri), in the range of 0 ~ 10, on the fluid flow and heat transfer are performed for each inclination angle, α of the side walls of the parallelogrammic enclosure. The results are presented in terms of streamlines, isotherms, average Nusselt number and maximum non-dimensional temperature profile. Results show that average Nusselt number increases with the increase of the Richardson number for lower values of positive and negative inclination angle whereas, it remains invariant of Richardson number at higher values of positive and negative inclination angles.
Opposing Mixed Convection in a Vented Enclosure: Effects of Inlet Port Location and Prandtl Number
The effects of inlet port location and Prandtl number on the opposing mixed convection inside a vented square enclosure are investigated numerically. An external fluid flow enters the enclosure through an opening in the left vertical wall and exits from another opening in the right vertical wall. Various inlet port configurations are extensively studied with the change of governing parameters. Numerical solutions of the governing equations are obtained using the finite element method. The solutions are expressed in terms of the average fluid temperature and Nusselt number against the Richardson number in the range [0, 10] at a fixed Reynolds number of 100. Variations of the computed results are explained using temperature contour and streamline plots. From the present analysis it is found that the rate of heat transfer from the heated wall is significantly depended on the position of the inlet port and higher Nusselt number is observed at very large Prandtl number. Empirical correlations are designed to express the above relation mathematically.
International Communications in Heat and Mass Transfer, 2015
Entropy generation during the mixed convection process have been studied in a square enclosure for various 15 moving horizontal (cases 1a-1d) or vertical wall(s) (cases 2a-2c) where the bottom wall of the cavity is isother-16 mally hot, side walls are cold, and the top wall is adiabatic. Simulations have been performed for Prandtl number 17 Pr = 0.026 and 7.2, Reynolds number Re = 10 − 100, and Grashof number Gr = 10 3 − 10 5. Results show that, in 18 the case of the horizontally moving wall(s) (cases 1a-1d), the overall heat transfer rate ðNu b Þ and total entropy 19 generation (S total) are identical for cases 1a-1d and the cup-mixing temperature (θ cup) is high for case 1b at Pr = 20 0.026, Re = 100, and Gr = 10 5. Similarly, in the case of the vertically moving wall(s) (cases 2a-2c), Nu b and S total 21 are identical for cases 2a-2c with the maximum θ cup occurring for the case 2a. At Pr = 7.2, Gr = 10 5 , and Re = 10, 22 case 1a and case 1c are preferable for horizontally moving wall(s) and either of case 2a-2c is preferable for 23 vertically moving wall(s). At Pr = 7.2, Gr = 10 5 , and Re = 100, case 1d may be preferable for the horizontally 24 moving wall(s) and case 2a may be preferable for the vertically moving wall(s).
Analysis of mixed convection flows within a square cavity with linearly heated side wall(s)
International Journal of Heat and Mass Transfer, 2009
Finite element simulations have been performed to investigate the influence of linearly heated side wall(s) or cooled right wall on mixed convection lid-driven flows in a square cavity. It is interesting to note that multiple circulation cells appear inside the cavity with the increase of Pr for Re ¼ 10 and Gr ¼ 10 5 in the case of linearly heated side walls. For Pr ¼ 0:015, only two circulation cells are formed inside the cavity. As Pr increases to 0.7, three circulation cells are formed inside the cavity. Further increase in Pr to 10, leads to the formation of four circulation cells inside the cavity. On the other hand, only two circulation cells are formed inside the cavity for the case of cooled right wall. A detailed analysis of flow pattern shows that as the value of Re increases from 1 to 10 2 , there occurs a transition from natural convection to forced convection depending on the value of Gr irrespective of Pr. It is observed that the secondary vortex at the top left corner disappears for Re ¼ 10 2 and Gr ¼ 10 5 due to enhanced motion of the upper lid in the case of cooled right wall while a small secondary vortex exist at the bottom right corner in the case of linearly heated side walls. The local Nusselt number (Nu b ) plot shows that heat transfer rate is equal to 1 at the edges for the case of linearly heated side walls case and that is zero at the left edge and thereafter that increases for the case of cooled right wall. It is interesting to observe that Nu b is large within 0:4 6 X 6 0:6 due to compression of isotherms for Pr ¼ 0:7 and 10 in the case of linearly heated side wall. It is also observed that Nu r or Nu l exhibits oscillations especially for Pr ¼ 10 at higher Gr due to the presence of multiple circulations. It is also observed that Nu r or Nu l vs Gr plots show oscillation for two case studies. Average Nusselt numbers at the bottom and right walls are strong functions of Grashof number at larger Prandtl numbers whereas average Nusselt number at the left wall at a specific Pr is a weaker function of Gr.
Revista de Engenharia Térmica
In this work, the laminar natural convection in high aspect ratio three-dimensional enclosures has been numerically studied. The enclosures studied here were heated with uniform heat flux on a vertical wall and cooled at constant temperature on the opposite wall. The remaining walls were considered adiabatic. Fluid properties were assumed constant except for the density change with temperature on the buoyancy term. The governing equations were solved using the finite volumes method and the dimensionless form of these equations has the Prandtl number and the modified Rayleigh number as parameters. The influences of the Rayleigh number and of the cavity aspect ratio on the Nusselt number, for a Prandtl number of 0.7, were analyzed. Results were obtained for values of the modified Rayleigh number up to 106 and for aspect ratios ranging from 1 to 20. The results were compared with two-dimensional results available in the literature and the variation of the average Nusselt number with th...
On natural convection in a single and two zone rectangular enclosure
International Journal of Heat and Mass Transfer, 1992
Convective heat transfer was investigated numerically for rectangular enclosures both undivided and divided in two zones by a vertical partition, and having opposite isothermal walls at different temperatures. The aspect ratio was varied from 0. I to 16 and the Rayleigh number from 3.5 * lo3 to 3.5 * I O7 (non-partitioned enclosures) and from I .O * 10' to 1.6 * 10' (partitioned enclosures). The thickness and conductivity of the partition were varied. The end wall thermal boundary conditions were adiabatic or LTP (Linear Temperature Profile). The continuity, momentum and energy equations for a 2-D laminar steady flow were solved under the Boussinesq approximation by using a finite-difference method and the SIMPLEC pressure-velocity coupling algorithm. Grid-independent results indicate that the reduction in the Nusselt number caused by a thin central partition can be predicted within a few per cent (in the range investigated) by assuming the partition to be isothermal, i.e. infinitely conducting. The finite conductivity of the partition causes a temperature distribution along its length, resulting in an increase in Nu which depends on Rayleigh number, aspect ratio and end wall thermal boundary conditions.
International Journal of Heat and Mass Transfer, 1995
Abstraet--Steady natural convection in an enclosure heated from below and symmetrically cooled from the sides is studied numerically, using a streamfunction-vorticity formulation. The Allen discretization scheme is adopted and the discretized equations were solved in a line by line basis. The Rayleigh number based on the cavity height is varied from 103 to 10 7. Values of 0.7 and 7.0 for the Prandtl number are considered. The aspect ratio L/H (length to height of the enclosure) is varied from 1 to 9. Boundary conditions are uniform wall temperature and uniform heat flux. For the range of the parameters studied, a single cell is observed to represent the flow pattern. Numerical values of the Nusselt number as a function of the Rayleigh number are reported, and the Prandtl number is found to have little influence on the Nusselt number. A scale analysis is presented in order to better understand the phenomenon.