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MODELLING OF THE OPPOSING MIXED CONVECTION HEAT TRANSFER IN A ONE-SIDE HEATED VERTICAL FLAT CHANNEL IN THE TRANSITION REGION

DOI: 10.1615/ICHMT.2008.CHT.600
9 pages

Povilas Poskas
Lithuanian Energy Institute, Branduolines inzinerijos problemas laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania

Robertas Poskas
Lithuanian Energy institute; Kaunas Univerity of Technology, Kaunas, Lithuania

Arunas Sirvydas
Lithuanian Energy Institute, Branduolinës inþinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas

Abstrakt

In this paper we present results on the numerical investigation of the local opposing mixed convection heat transfer in a vertical flat channel with one-side heating in the laminar and vortex (transitional) regions using FLUENT 6.2 code. The investigations have been performed in airflow of different pressures (0.1, 0.2 and 0.4 MPa) in the range of Re from 1.5 · 103 to 2.5 · 103 and Grq from 1.8 · 105 to 2.6 · 107. The cross-section of the test section was 400 mm wide and 40.8 mm high. Channel's heated length was 3890 mm (x/de about 50). A hydrodynamic stabilization length of 2370 mm (x/de about 25) preceded the heated part of the test section. The value of heat flux on the wall was widely varied in order to achieve different buoyancy effect.
Performed numerical modelling with one-side heating demonstrates that under small buoyancy effect, as in the case of symmetrical heating, there are only small transformations in the velocity profile but flow is oriented downwards. With increase of buoyancy forces, the flow separation from the heated wall occurs at some distance from the beginning of the heated channel section. With further increase of buoyancy, the position of flow separation moves towards the beginning of the heated section. Channel wall temperature noticeably decreases at the flow separation point. For the vortex region characteristic sinusoidal flow in the central part of the channel was noticed with the vortices at the heated wall.
Correlations for the determination of the position of flow separation from the wall (loss of stability of the flow) in case of one-side heating are suggested. The results of one-side heating have been compared with earlier received results by Poskas et al. [2005] in the vertical flat channel with two-side heating.

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