The Field Investigation of Dimensionless Convection Heat Transfer Coefficient in the Inclined Roof Solar Chimney

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Sudaporn Chungloo


The objectives of this paper are to study the free convection in the air gap of a 45-degree inclined roof
solar chimney and to experimentally determine the correlation of Nusselt number (Nu). The experiment was
carried out in an open-ended air gap between the corrugated roof tile and the gypsum board attached
to a detached building with the inner width and length of 18 and 160 cm. located outdoor under the hot
and humid climate. The surface temperatures of the corrugated roof tile are between 35-45°C during
the daytime of May and June, exposed to the solar intensity of 200-1,000 W/m2. The data reduction using
linear regression analysis yields linear relationships of mean bulk temperature, temperature difference of air
at inflow and outflow, heat transfer rate and mass flow rate of the solar chimney against the temperature
difference of hot roof surface and the mean bulk temperature (Th–Tb). Employing the derived linear
relationships, the correlation between the Nusselt number, Nus, Rayleigh number, Ras, and the aspect
ratio (air gap/length) are derived for 3°C≤Th–Tb≤ 9°C as Nus = 1.444⋅ [(S/L) Ras sin 45°] 0.249. It is the correlation
that could be used for determination of mean convection heat transfer coefficient of the roof solar chimney with
similar geometry applied in the hot and humid climate, provided that it is in the same range of Ra value and the
same range of Ra (S/L) value.


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