## THERMAL SCIENCE

International Scientific Journal

### TURBULENT MIXED CONVECTION IN HEATED VERTICAL CHANNEL

**ABSTRACT**

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.

**KEYWORDS**

PAPER SUBMITTED: 2008-11-19

PAPER REVISED: 2009-04-05

PAPER ACCEPTED: 2009-04-14

**THERMAL SCIENCE** YEAR

**2010**, VOLUME

**14**, ISSUE

**1**, PAGES [125 - 135]

- Metais, B., Eckert, E. R. G., Forced, Mixed and Free Convection Regimes, Journal of Heat Transfer, 86 (1964), pp. 295-296
- Bar-Cohen, A., Rohsenow, W. M., Thermally Optimum Spacing of Vertical Natural Convection Cooled Parallel Plates, Journal of Heat Transfer, 106 (1984), 1, pp. 116-123
- Betts, P. L., Dafa'nela, A. A., Turbulent Buoyant Air Flow in a Tall Rectangular Cavity, Proceedings, (ASME HTD) Winter Annual Meeting, New York, USA, 1986, Vol. 60, p. 83
- Cheung, F. B., Sohn, D. Y., Numerical Study of Turbulent Natural Convection in An Innovative Air Cooling System, Numerical Heat Transfer, Part A , 16 (1989), 4, pp. 467-487
- Gebhart, B., et al., Buoyancy-Induced Flows and Transport, Hemisphere Publ. Corp., Washington, DC, 1987
- Hugot, G., Study of Laminar Natural Convection between Two Isothermal Vertical Parallel Plates (in French), Entropie, 46 (1972), pp. 55-66
- Miyamoto, M., et al., Turbulent Free Convection Heat Transfer from Vertical Parallel Plates, in: Heat Transfer (Eds. C. L. Tien, V. P. Carey, J. K. Ferrell) Hemisphere Publ. Corp., Washington DC, 1986, Vol. 4., pp. 1593-l598
- Auletta, A., Manca, O., Heat and Fluid Flow Resulting from the Chimney Effect in a Symmetrically Heated Vertical Channel with Adiabatic Extensions, International Journal of Thermal Sciences, 41 (2002), 12, pp. 1101-1111
- Korbut, V. P., Paladenko, Yu. V., Turbulent Natural Convection Flow and Heat Transfer in a Fat Vertical Slot with Asymmetrically Heated Walls, Heat Transfer Research, 25 (1993), pp. 313-320
- Fedorov, A. G., Viskanta, R., Turbulent Natural Convection Heat Transfer in an Asymmetrically Heated Vertical Parallel Plate Channel, International Journal of Heat Mass Transfer, 40 (1997), 16, pp. 3849-3860
- Versteegh, T. A. M., Nieuwstadt, F. T. M., Turbulent Budgets of Natural Convection in an Infinite, Differentially Heated, Vertical Channel, International Journal of Heat and Fluid Flow, 19 (1998), 2, pp. 135-149
- Versteegh, T. A. M., Nieuwstadt, F. T. M., A Direct Numerical Simulation of Natural Convection Between Two Infinite Vertical Differentially Heated Walls Scaling Laws and Wall Functions, International Journal of Heat and Mass Transfer, 42 (1999), 19, pp. 3673-3693
- Elenbas, W., Heat Dissipation of Parallel Plates by Free Convection, Physica, 9 (1942), 1, pp. 1-28
- Dalbert, A. M., Penot, F., Peube, J. L., Laminar Natural Convection in a Vertical Heated Channel (in French), International Journal of Heat and Mass Transfer, 24 (1981), 9, pp. 1463-1473
- Penot, F., Dalbert, A. M., Mixed Convection and Forced into a Vertical Thermosyphon (in French), International Journal of Heat and Mass Transfer, 26 (1983), 11, pp. 1639-1647
- Kheireddine, A. S., et al., Numerical Prediction of Pressure Loss Coefficient and Induced Mass Flux for Laminar Natural Convective Flow in a Vertical Channel, Energy, 22 (1997), 4, pp. 413-423
- Desrayaud, G., Fichera, A., Laminar Natural Convection in a Vertical Isothermal Channel with Symmetric Surface-Mounted Rectangular Ribs, International Journal of Heat and Fluid Flow, 23 (2002), 4, pp. 519-529
- Ben Maad, R., Natural Convection in Plane Wall with Prandtl High Numbers (in French), Ph. D. thesis, University of Pierre et Marie Curie, Paris VI, France, 1979
- Najam, M., et. al., Numerical Study of Mixed Convection in a T Form Cavity Subjected to a Constant Heat Flux and Ventilated by a Vertical Air Jet (in French), Compte Rendu de Mecanique, 330 (2002), 7, pp. 461-467
- Jones, W. P., Launder, B. E., The Calculation of the Low Reynolds Number Phenomena with a Two-Equation Model of Turbulence, International Journal of Heat and Mass Transfer, 16 (1973), 6, pp. 1119-1130