Sa. Theerthan et Jh. Arakeri, Planform structure and heat transfer in turbulent free convection over horizontal surfaces, PHYS FLUIDS, 12(4), 2000, pp. 884-894
This paper deals with turbulent free convection in a horizontal fluid layer
above a heated surface. Experiments have been carried out on a heated surf
ace to obtain and analyze the planform structure and the heat transfer unde
r different conditions. Water is the working fluid and the range of flux Ra
yleigh numbers (Ra) covered is 3x10(7)-2x10(10). The different conditions c
orrespond to Rayleigh-Benard convection, convection with either the top wat
er surface open to atmosphere or covered with an insulating plate, and with
an imposed external flow on the heated boundary. Without the external flow
the planform is one of randomly oriented line plumes. At large Rayleigh nu
mber Ra and small aspect ratio (AR), these line plumes seem to align along
the diagonal, presumably due to a large scale flow. The side views show inc
lined dyelines, again indicating a large scale flow. When the external flow
is imposed, the line plumes clearly align in the direction of external flo
w. The nondimensional average plume spacing, Ra-lambda(1/3), varies between
40 and 90. The heat transfer rate, for all the experiments conducted, repr
esented as Ra-delta T(-1/3), where delta(T) is the conduction layer thickne
ss, varies only between 0.1-0.2, showing that in turbulent convection the h
eat transfer rates are similar under the different conditions. (C) 2000 Ame
rican Institute of Physics. [S1070-6631(00)00903-X].