On the Reynolds-number independence of mixed convection in a vertical channel subjected to asymmetric wall temperatures with and without flow reversal

1992 ◽  
Vol 13 (4) ◽  
pp. 329-339 ◽  
Author(s):  
Yih Nen Jeng ◽  
Jiann Lin Chen ◽  
Win Aung
Keyword(s):  
Reynolds Number ◽  
Mixed Convection ◽  
Vertical Channel ◽  
Flow Reversal

scholarly journals Flow Reversal of Fully Developed Mixed Convection in a Vertical Channel with Chemical Reaction

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Habibis Saleh ◽  
Ishak Hashim ◽  
Sri Basriati
Keyword(s):  
Mixed Convection ◽  
Chemical Reaction ◽  
Buoyancy Force ◽  
Vertical Channel ◽  
Critical Values ◽  
Flow Reversal ◽  
Governing Equations ◽  
Reversed Flow ◽  
Exothermic Chemical Reaction

The present analysis is concerned with the criteria for the onset of flow reversal of the fully developed mixed convection in a vertical channel under the effect of the chemical reaction. The governing equations and the critical values of the buoyancy force are solved and calculated numerically via MAPLE. Parameter zones for the occurrence of reversed flow are presented. The exothermic chemical reaction is found to enhance the flow reversal and made flow reversal possible for symmetrical walls temperature.

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.

Stability of Mixed Convection in a Differentially Heated Vertical Channel

1998 ◽  
Vol 120 (1) ◽  
pp. 127-132 ◽  
Author(s):  
Y.-C. Chen ◽  
J. N. Chung
Keyword(s):  
Reynolds Number ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Local Minimum ◽  
Wave Speed ◽  
Vertical Channel ◽  
Shear Instability ◽  
Wave Number ◽  
Wave Numbers ◽  
Prandtl Numbers

In this study, the linear stability of mixed convection in a differentially heated vertical channel is investigated for various Prandtl numbers. The results indicate that this fully developed heated flow can become unstable under appropriate conditions. It is found that both the Prandtl number and Reynolds number hold very important effects on the critical Grashof number, wave number, wave speed, and instability mechanism for higher Prandtl numbers. For low Prandtl numbers, the effects from the Prandtl number and Reynolds number are relatively small. The most significant finding is that the local minimum wave numbers can be as high as eight for Pr = 1000, which is substantially higher than those found before for other heated flows. The existence of multiple local minimum wave numbers is responsible for the sudden jumps of the critical wave number and wave speed and the sudden shift of instability type for higher Prandtl numbers. The energy budget analysis shows that the thermal-shear and shear instabilities dominate at both low and high Reynolds numbers for Pr = 0.7 and 7. It is the thermal-buoyant instability for Re < 1365 and shear instability for Re ≥ 1365 for Pr = 100. The thermal-buoyant and mixed instabilities are the possible instability types for Pr = 1000. In general, for mixed convection channel flows, the instability characteristics of differentially heated flows are found to be substantially different from those of uniformly heated flows.

Simulation of Mixed Convection Air Cooling of Protruding Heat Sources Mounted on One Side of a Vertical Channel

2011 ◽  
Author(s):  
Rajat Dhingra ◽  
P. S. Ghoshdastidar
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Regression Analysis ◽  
Mixed Convection ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Vertical Channel ◽  
Separation Distance ◽  
Air Cooling ◽  
Heat Sources

A numerical study of steady, laminar, two-dimensional mixed convection air cooling of identical as well as non-identical rectangular protruding heat sources located on one side of a vertical channel is presented in this paper. The stream function-vorticity-temperature approach with the finite-difference-based methodology implementing higher order upwind scheme has been applied. Three cases have been considered, namely (i) when the number of identical chips is two; (ii) when the number varies from 3 to 10; and finally, (iii) when five chips of different heights but of same width are placed in various orders. For the case of two chips the effects of Re, Gr/Re2 (that is, Richardson number), dimensionless separation distance between the chips (d/H), dimensionless chip height (h/H) and width (w/H) on the average Nusselt number of each chip have been investigated. A correlation based on regression analysis is also presented for each parameter. With increase in Reynolds number the average Nusselt number of both chips increases. Similar trend is seen when the separation distance between two chips is raised. It is also observed that as the number of chips escalates from 2 to 10, the average Nusselt number of downstream chips becomes smaller than that of the upstream chips, the rate of drop being much sharper near the channel inlet. A regression-analysis based composite correlation each for average Nusselt number of Chip 1 (lower chip) and Chip 2 (upper chip) as a function of Reynolds number, Richardson number, separation distance between the chips, chip height and width has been obtained for the 2-chip case. The model also predicts maximum chip temperature in an array of ten chips. Finally, for five non-identical chips having same width but different heights the simulation reveals that the chips placed in increasing order of their heights in the direction of air flow are cooled better as compared to any other pattern of placement of the chips.

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.

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