Analysis of Mixed Convection in Vertical Convergent Channels

Volume 1 ◽  
2004 ◽  
Author(s):  
Nicola Bianco ◽  
Oronzio Manca ◽  
Alfonso W. Mauro ◽  
Vincenzo Naso
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Flow ◽  
Uniform Heat Flux ◽  
Turbulent Model ◽  
Flat Plates ◽  
Convergent Channel ◽  
Converging Angle

Air mixed convection in a convergent channel with the two principal flat plates at uniform heat flux is analyzed numerically. In the considered system two parallel adiabatic extensions are placed downstream the convergent channel. The forced flow is obtained by imposing a pressure drop between the inlet and the outlet of the channel. The flow in the channel is assumed to be two-dimensional, turbulent and incompressible. A k-ε turbulent model is employed. Results in terms of dimensionless wall temperature distribution as a function of the walls converging angle, the Grashof number and the pressure drop are presented in the ranges: 0 ≤ ΔP ≤ 2.2·107, 2.8·104 ≤ Gr ≤ 2.1·105. Results show that increasing the angle of converging the Reynolds number increases at the same pressure drop. The larger the pressure drop the smaller the contribution of the free convection to the Reynolds number. Increasing the converging angle only slightly increases the ΔP value for which the effect of free convection is negligible.

Effect of Channel Spacing on Mixed Convection in Vertical Convergent Channels

2006 ◽  
Author(s):  
Nicola Bianco ◽  
Giovanni Lacasa ◽  
Oronzio Manca
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Mixed Convection ◽  
Wall Temperature ◽  
Forced Flow ◽  
Flat Plates ◽  
Convergent Channel ◽  
Aspect Ratios ◽  
Converging Angle

Mixed convection in air in a convergent channel with the two principal flat plates at uniform heat flux is analyzed numerically by Fluent code. In the considered system two parallel adiabatic extensions are placed downstream of the convergent channel. The forced flow is obtained by imposing a pressure drop between the inlet and the outlet of the channel. The flow in the channel is assumed to be two-dimensional, turbulent and incompressible. A k-ε turbulent model is employed. Results in terms of dimensionless wall temperature distribution as a function of the walls converging angle, the Grashof number, the pressure drop and the channel aspect ratio are presented in the ranges: 0° ≤ θ ≤ 10°; 4.10 102 ≤ Gr ≤ 32.1 105, 0 ≤ ΔP ≤ 8.82·107, 10.15 < Lw/bmin < 58.0. Results show that Reynolds number, and then the mass flow rate flowing in the channel, increases at decreasing aspect ratios, Lw/bmin. The converging angle that optimizes the fluid-dynamic within the channel is equal to 5°. Dimensionless maximum wall temperature values decreases at increasing Reynolds number and the larger the aspect ratio, the larger the decrease. The Reynolds number over which natural convection become negligible, with respect to forced convection, increases at increasing converging angle and at decreasing aspect ratio.

Correlations for Laminar Mixed Convection Flows on Vertical, Inclined, and Horizontal Flat Plates

1986 ◽  
Vol 108 (4) ◽  
pp. 835-840 ◽  
Author(s):  
T. S. Chen ◽  
B. F. Armaly ◽  
N. Ramachandran
Keyword(s):  
Free Convection ◽  
Mixed Convection ◽  
Forced Flow ◽  
Flat Plates ◽  
Maximum Increase ◽  
Nusselt Numbers ◽  
Laminar Mixed Convection ◽  
Wide Range ◽  
Flow Configurations ◽  
Prandtl Numbers

Local Nusselt numbers for laminar mixed convection flows along isothermal vertical, inclined, and horizontal flat plates are presented for the entire mixed convection regime for a wide range of Prandtl numbers, 0.1 ≤ Pr ≤ 100. Simple correlation equations for the local and average mixed convection Nusselt numbers are developed, which are found to agree well with the numerically predicted values and available experimental data for both buoyancy assisting and opposing flow conditions. The threshold values of significant buoyancy effects on forced convection and forced flow effects on free convection, as well as the maximum increase in the local mixed convection Nusselt number from the respective pure convection limits, are also presented for all flow configurations. It is found that the buoyancy or forced flow effect can increase the surface heat transfer rate from pure forced or pure free convection by about 20 percent.

Experimental Analysis of Opposing Flow in Mixed Convection in a Channel With an Open Cavity Below

2005 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Kambiz Vafai
Keyword(s):  
Reynolds Number ◽  
Mixed Convection ◽  
Flow Visualization ◽  
Vortex Structure ◽  
Open Cavity ◽  
Forced Flow ◽  
Heated Wall ◽  
Heated Plate ◽  
Thermal Plume ◽  
Recirculation Flow

In this paper mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The cavity has the heated wall on the opposite side of the forced inflow. The results are reported in terms of wall temperature profiles of the heated wall and flow visualization for Reynolds number (Re) from 100 to 2000 and Richardson number (Ri) in the range 4.3–6400; the ratio between the length and the height of cavity (L/D) is in the range 0.5–2.0 and the ratio between the channel and cavity height (H/D) is equal to 1.0. The present results show that at the lowest investigated Reynolds number the surface temperatures are lower than the corresponding surface temperature for Re = 2000, at same the ohmic heat flux. The flow visualization points out that for Re = 1000 there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100 the effect of a stronger buoyancy determines a penetration of thermal plume from the heated plate wall into the upper channel. Moreover, the flow visualization points out that for lower Reynolds numbers the forced motion penetrates inside the cavity and a vortex structure is adjacent to the unheated vertical plate. At higher Reynolds number the vortex structure has a larger extension at same L/D value.

Numerical Study on Mixed Convection in Porous Media in a Channel With an Open Cavity Below

2010 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Paolo Mesolella ◽  
Sergio Nardini
Keyword(s):  
Mixed Convection ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Vertical Wall ◽  
Open Cavity ◽  
Temperature Fields ◽  
Forced Flow ◽  
Heated Wall ◽  
Local Thermal Equilibrium ◽  
Uniform Heat Flux

A numerical analysis of mixed convection in gas saturated metal foam in a horizontal channel with an open cavity heated at uniform heat flux on a vertical wall is studied numerically. Non-local thermal equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 PPI and ε = 0.909, the fluid is air and for the assisting case. Results, for different Peclet and Rayleigh numbers, are given in terms of solid and fluid wall temperatures and local Nusselt numbers and stream function and temperature fields. Results show that diffusive effect determined lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. The interaction between the forced flow in the channel and the buoyancy due to the heated wall determines different thermal and fluid dynamic behaviors.

scholarly journals Effect of Reynolds and Prandtl Numbers on Mixed Convection in an Obstructed Vented Cavity

2011 ◽  
Vol 3 (2) ◽  
pp. 271-281
Author(s):  
M. M. Rahman ◽  
M. M. Billah ◽  
M. A. Alim
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Reynolds Number ◽  
Finite Element ◽  
Free Convection ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Forced Convection ◽  
Thermal Field ◽  
Heat Transfer Characteristics

A numerical investigation is conducted to analyze the steady flow and thermal fields as well as heat transfer characteristics in a vented square cavity with a built-in heat conducting horizontal solid circular obstruction. Hydrodynamic behavior, thermal characteristics and heat transfer results are obtained by solving the couple of Navier-Stokes and energy equations by using a weighted residuals Finite element method. The computation was made for different Reynolds number, Prandtl number ranging from 50 to 200 and from 0.71 to 7.1 at the three different convective regimes. Three different regimes are observed with increasing Ri: forced convection (with negligible free convection), mixed convection (comparable free and forced convection) and free convection dominated region (with higher free convection). The results are presented to show the effects of the Reynolds number, Prandtl number on flow pattern, thermal field and heat transfer characteristics at the three convective regimes. It is found that the flow and thermal field strongly depend on the Reynolds number, Prandtl number as well as Richardson number. As the Reynolds number and Prandtl number increase, the heat transfer rate increases but average fluid temperature in the cavity and temperature at the cylinder center decrease at the three convective regimes.Keywords: Mixed convection; Finite element method; Obstructed vented cavity; Prandtl number.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i2.4344                J. Sci. Res. 3 (2), 271-281 (2011)

Radiative Effects on Mixed Convection in a Uniformly Heated Vertical Convergent Channel with an Unheated Moving Plate

2011 ◽  
Vol 3 (3) ◽  
pp. 280-296
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Vincenzo Naso
Keyword(s):  
Mixed Convection ◽  
Heat Removal ◽  
Polymeric Materials ◽  
Temperature Fields ◽  
Uniform Heat Flux ◽  
Radiative Effects ◽  
Moving Plate ◽  
Convergent Channel ◽  
Research Attention ◽  
Channel Configuration

AbstractFluids engineering is extremely important in a wide variety of materials processing systems, such as soldering, welding, extrusion of plastics and other polymeric materials, Chemical Vapor Deposition (CVD), composite materials manufacturing. In particular, mixed convection due to moving surfaces is very important in these applications. Mixed convection in a channel, as a result of buoyancy and motion of one of its walls has received little research attention and few guidelines are available for choosing the best performing channel configuration, particularly when radiative effects are significant. In this study a numerical investigation of the effect of radiation on mixed convection in air due to the interaction between a buoyancy flow and an unheated moving plate induced flow in a uniformly heated convergent vertical channel is carried out. The moving plate has a constant velocity and moves in the buoyancy force direction. The principal walls of the channel are heated at uniform heat flux. The numerical analysis is accomplished by means of the commercial code Fluent. The effects of the wall emissivity, the minimum channel spacing, the converging angle and the moving plate velocity are investigated and results in terms of air velocity and temperature fields inside the channel and wall temperature profiles, both of the moving and the heated plates, are given. Nusselt numbers, both accounting and not for the radiative contribution to heat removal, are also presented.

Implication of geometrical configuration on heat transfer enhancement in converging minichannel using nanofluid by two phase mixture model: A numerical analysis

2020 ◽  
pp. 095440892096469
Author(s):  
Md. Faizan ◽  
Sukumar Pati ◽  
Pitamber R Randive
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Straight Channel ◽  
Particle Loading ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Phase Mixture ◽  
Converging Angle

In the present study laminar forced convective flow of nanofluid through a converging minichannel is investigated numerically by employing two phase mixture model. The heat transfer enhancement and the corresponding pressure drop are analyzed for the following range of parameters: Reynolds number (700 ≤ Re ≤ 1650), particle volume concentration (0% ≤ ϕ ≤ 4%) and converging angle (θ = 0.029°, 0.043° and 0.05°). The results indicate that there is a considerable increase in pressure drop coupled with enhancement in heat transfer rate with particle loading due to the improvement in the thermal properties of the resulting mixture. The pressure drop in the converging channel increases with the converging angle. The pressure drop augments as high as 2 times by advancing the particle loading from 0% to 4%. The wall temperature decreases appreciably by 34 K and heat transfer coefficient is enhanced by as high as 98% from Re =  700, ϕ = 0% and straight channel to Re =1650, Hout = 2.75mm and ϕ = 4%. The enhancement in heat transfer and corresponding increase in pressure drop as compared to equivalent straight channel is presented by the performance factor, which increases with decrease in converging angle. There is a significant concern of the pumping power with increase in converging angle, volume fraction and Reynolds number.

scholarly journals EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

2017 ◽  
Vol 60 (4) ◽  
pp. 352-366 ◽  
Author(s):  
A. B. Sukhotskii ◽  
G. S. Sidorik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Convection Flow ◽  
Single Bundle ◽  
Single Row

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

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