scholarly journals Turbulent mixed convection in asymmetrically heated vertical channel

2012 ◽  
Vol 16 (2) ◽  
pp. 503-512 ◽  
Author(s):  
Ameni Mokni ◽  
Hatem Mhiri ◽  
Palec Le ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Vertical Channel ◽  
Channel Length ◽  
Forced Flow ◽  
Mean Velocity ◽  
Flow Development ◽  
Heated Channel ◽  
The Mean

In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.

Heat Transfer From an Oscillating Horizontal Wire to Water

1962 ◽  
Vol 84 (3) ◽  
pp. 251-254 ◽  
Author(s):  
F. K. Deaver ◽  
W. R. Penney ◽  
T. B. Jefferson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Low Frequency ◽  
Mean Velocity ◽  
Transfer Rates ◽  
Low Frequency Oscillations ◽  
The Mean ◽  
Horizontal Wire

An investigation has been made to determine the effect of low frequency oscillations of relatively large amplitude on the rate of heat transfer from a small horizontal wire to water. Frequencies from 0 to 4.25 cps and amplitudes to 2.76 in. were employed. Temperature differences up to 140 deg F provided heat flux from 2000 to 300,000 Btu/hr ft2. A Reynolds number was defined based on the mean velocity of the wire, and it was shown that heat-transfer rates may be predicted by either forced, free, or mixed convection correlations depending on the relative magnitudes of Reynolds and Grashof numbers.

Heat transfer and entropy generation analysis of Cu-water nanofluid in a vertical channel

2018 ◽  
Vol 15 (5) ◽  
pp. 604-613
Author(s):  
Essma Belahmadi ◽  
Rachid Bessaih
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Friction Factor ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Vertical Channel ◽  
Simple Algorithm ◽  
Content Type

Purpose The purpose of this study is to analyze heat transfer and entropy generation of a Cu-water nanofluid in a vertical channel. The channel walls are maintained at a hot temperature Tw. An up flow penetrates the channel at a uniform velocity v0 and a cold temperature T0 (T0 < Tw). The effects of Reynolds number Re, Grashof number Gr and solid volume fraction ϕ on streamlines, isotherms, entropy generation, friction factor, local and mean Nusselt numbers are evaluated. Design/methodology/approach The Cu-water nanofluid is used in this study. The software Ansys-fluent 14.5, based on the finite-volume method and SIMPLE algorithm, is used to simulate the mixed convection problem with entropy generation in a vertical channel. Findings The results show that the increase of Reynolds and Grashof numbers and solid volume fraction improves heat transfer and reduces entropy generation. Correlations for the mean Nusselt number and friction factor in terms of Reynolds number and solid volume fraction are obtained. The present results are compared with those found in the literature, which reveal a very good agreement. Originality/value The originality of this work is to understand the heat transfer and entropy generation for mixed convection of a Cu-water nanofluid in a vertical channel.

scholarly journals Turbulent mixed convection in heated vertical channel

2010 ◽  
Vol 14 (1) ◽  
pp. 125-135 ◽  
Author(s):  
Ameni Mokni ◽  
Hatem Mhiri ◽  
Palec Le ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Boundary Layers ◽  
Vertical Channel ◽  
Ambient Air ◽  
Forced Flow ◽  
Working Fluid ◽  
Heat Flow Rate ◽  
Maximum Heat ◽  
First Case

In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer enhancement obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Combined forced and free convection are studied in order to increase the cooling requirements. The study is conceded for two Rayleigh number. The first case corresponds to two separate boundary layers so the channel acts as two independent plates. For the second case the two boundary layers are attached. Calculations are carried out with air as the working fluid by changing the jet velocity in order to optimize the system to give the maximum heat flow rate over the chimney. The system of governing equations is solved with a finite volumes method and an implicit scheme. The results obtained show that the jet-wall activates the heat transfer, as does the drive of ambient air by the jet.

Numerical Analysis of Opposing Mixed Convection in Air in a Vertical Channel With a Moving Plate

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Analysis ◽  
Mixed Convection ◽  
Vertical Channel ◽  
Forced Flow ◽  
Uniform Heat Flux ◽  
Transition Flow ◽  
Moving Plate ◽  
Buoyancy Flow

In this study a numerical investigation of mixed convection in air due to the interaction between a buoyancy flow and a moving plate induced flow in a vertical channel is carried out. The moving plate has a constant velocity and moves in the opposite direction with respect to the buoyancy force. The channel principal walls are heated at uniform heat flux. The numerical analysis is obtained by means of the commercial code Fluent. The effects of the channel spacing, heat transfer and moving plate velocity are investigated and results in terms of the channel wall and moving plate temperatures and Nusselt numbers are given. The wall temperature profiles allow to observe different behaviors of the flow motion inside the channel, a buoyancy flow, a forced flow and a transition flow related to the velocity of moving plate. The transition velocity increases as the heat flux and the channel gap increase. Dimensionless heat transfer results, Nu/Re0.68 as a function of Richardson number, Ri, present a good agreement with two correlations obtained for the buoyancy dominant flow, at Ri &gt; 10, and forced dominant flow, at Ri &lt; 10−3.

Large eddy simulations of variable property turbulent flow in horizontal and vertical channels with buoyancy and heat transfer effects

2007 ◽  
Vol 221 (4) ◽  
pp. 429-441 ◽  
Author(s):  
J S Lee ◽  
R H Pletcher
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Vertical Channel ◽  
Large Eddy Simulations ◽  
Mean Flow ◽  
Mean Velocity ◽  
Velocity Fluctuations ◽  
Combined Flow ◽  
Large Eddy ◽  
The Mean

Turbulent combined flow of forced and natural convection was investigated using large eddy simulations for horizontal and vertical channels with significant heat transfer. The walls were maintained at constant temperatures, one heated and the other cooled, at temperature ratios of 1.01, 1.99, and 3.00, respectively. Results showed that with increasing the Grashof number, large-scale turbulent motions emerged near the wall, resulting in significant changes in turbulent intensities for the horizontal channel flow case. Aiding and opposing flows, however, for the vertical channel, emerge near the heated and cooled walls, respectively, while the pressure gradient drives the mean flow upwards. Buoyancy effects on the mean velocity, temperature, and turbulent intensities were observed near the walls. In the aiding flow, the turbulent intensities and heat transfer were suppressed and the flow was relaminarized at large values of the Grash of number. In the opposing flow, however, turbulence was enhanced with increasing velocity fluctuations.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

High-Fidelity Simulations of a High-Pressure Turbine Stage: Effects of Reynolds Number and Inlet Turbulence

2021 ◽  
Author(s):  
Yaomin Zhao ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Suction Side ◽  
Rotor Blades ◽  
High Fidelity ◽  
Mean Flow ◽  
High Pressure Turbine ◽  
Flow Shear ◽  
Phase Lock ◽  
The Mean

Abstract We present the first wall-resolved high-fidelity simulations of high-pressure turbine (HPT) stages at engine-relevant conditions. A series of cases have been performed to investigate the effects of varying Reynolds numbers and inlet turbulence on the aerothermal behavior of the stage. While all of the cases have similar mean pressure distribution, the cases with higher Reynolds number show larger amplitude wall shear stress and enhanced heat fluxes around the vane and rotor blades. Moreover, higher-amplitude turbulence fluctuations at the inlet enhance heat transfer on the pressure-side and induce early transition on the suction-side of the vane, although the rotor blade boundary layers are not significantly affected. In addition to the time-averaged results, phase-lock averaged statistics are also collected to characterize the evolution of the stator wakes in the rotor passages. It is shown that the stretching and deformation of the stator wakes is dominated by the mean flow shear, and their interactions with the rotor blades can significantly intensify the heat transfer on the suction side. For the first time, the recently proposed entropy analysis has been applied to phase-lock averaged flow fields, which enables a quantitative characterization of the different mechanisms responsible for the unsteady losses of the stages. The results indicate that the losses related to the evolution of the stator wakes is mainly caused by the turbulence production, i.e. the direct interaction between the wake fluctuations and the mean flow shear through the rotor passages.

A Study of Three-Dimensional Mixed Convective Heat Transfer From Short Vertical Cylinders in a Horizontal Forced Flow

2000 ◽  
Author(s):  
David A. Scott ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Forced Flow ◽  
Low Velocity ◽  
Buoyancy Forces ◽  
The Mean ◽  
Mixed Convective Flow ◽  
Comparison Of The Results

Abstract Heat transfer from relatively short vertical isothermal cylinders in a horizontal forced fluid flow has been considered. The flow conditions are such that the buoyancy forces resulting from the temperature differences in the flow are in general significant despite of the presence of a horizontal forced flow of air, that is, mixed convective flow exists. Because the cylinders are short and the buoyancy forces act normal to the forced flow, three-dimensional flow exists. The experiments were performed in a low velocity, open jet wind tunnel. The study involved the experimental determination of the mean heat transfer coefficient and a comparison of the results with a previous numerical analysis. Mean heat transfer rates were determined using the ‘lumped capacity’ method. The mean Nusselt number has the Reynolds number, Grashof number and the height to diameter ratio of the cylinders as parameters. The results have been used to determine the conditions under which the flow departs from purely forced convection and enters the mixed convection regime, i.e., determining the conditions for which the buoyancy effects should be included in convective heat transfer calculations for short cylinders.

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