Free convection from a horizontal heated cylinder located below a ceiling

Steady two-dimensional laminar free convection from a horizontal heated cyl inder located beneath a wide ceiling at ambient temperature has been studie d. A finite element numerical solution has been obtained for a Prandtl numb er of Pr = 0.7 and a Rayleigh number range (based on the cylinder diameter) of 10(2) less than or equal to Ra less than or equal to 10(5). Numerically predicted temperature field and local Nusselt number distributions were co mpared to experimental measurements made in air using a Mach-Zehnder interf erometer. For cylinder-to-ceiling spacings greater than about one diameter, the ceiling was found to have almost no influence on the heat transfer rat e from the cylinder. At very close cylinder-to-ceiling spacings, the averag e Nusselt number increased substantially because of conduction effects. How ever, for 10(3) less than or equal to Ra less than or equal to 10(5), the e ffect of the ceiling on the numerically predicted overall heat transfer rat e was less than +/- 10%, provided the cylinder was more than about one quar ter of a diameter away form the ceiling.