Free Convection in a Discretely Heated Vertical Enclosure: Effects of Prandtl Number and Cavity Size

Natural convection in a discretely heated vertical cavity by three uniform flux heat sources on one side wall is experimentally and numerically investigated. The other vertical wall is considered to be isothermally cooled and the ends are adiabatic. The flow visualization pictures for the ethylene glycol-filled cavity reveal a multicellular flow pattern consisting of primary, secondary, and tertiary flows. The growth of these secondary and tertiary cells with Rayleigh number and aspect ratio is well-demonstrated by the numerical results for Prandtl number of 25. Although the flow structure varies significantly when the Prandtl number is reduced from 25 to 1, the variation is negligible for an increase in Pr from 25 (dielectric liquid) to 166. The numerically obtained temperature fields indicate that the temperature of the heated sections are strongly influenced by the thermal stratification and the flow pattern in the cavity. Numerical predictions are in excellent agreement with the flow visualization pictures and the measured heat transfer coefficients. The effect of aspect ratio on Nusselt number is minimal in the case of tall cavities, A ≥3. Bounds for minimum and maximum temperatures are discussed and several Nusselt number correlations are presented.