NATURAL-CONVECTION IN A HEMISPHERICAL ENCLOSURE HEATED FROM BELOW

Natural convection in a hemisphere heated from below was studied experimentally. Correlation between heat transfer rate and Rayleigh number was obtained on a hemispherical surface over wide parameter ranges: 10(6) less-than-or-equal-to Ra less-than-or-equal-to 6 x 10(10) and 6 less-than-or-equal-to Pr less-than-or-equal-to 13000. The exponent of Nu against Ra changes from 1/4 to 1/3 at about Ra approximately 10(9). Flow patterns in a hemisphere were observed for 2 x 10(5) less-than-or-equal-to Ra less-than-or-equal-to 2 x 10(9) and 6 less-than-or-equal-to Pr less-than-or-equal-to 13000. The patterns were classified into several flow regimes. i.e. steady circulating flow, flow with periodic thermal plumes, flow with irregular thermal plumes and turbulent flow regime. Experimental results show that fully turbulent flow regime occurs at Ra approximately 10(9).