To stretch the automatic thinning algorithm to problem of much greater difficulty, the following strategy was adopted. Instead of two, six independent view angles were considered. For each projection, the entire width of the cavity (namely 500mm) was scanned. The average Nusselt number obtained for each projection and for each wall is presented in Table 5. The total average Nusselt number seen here is lower than that predicated by the one-roll data. It is however within the experimental uncertainty of the reference value. As a second check on data reduction, experiments were conducted at a Rayleigh number of 40200. The Nusselt number calculated for the entire fluid layer using the automatic thinning algorithm was found to be 3.32. This value is within of the correlation given by Gebhart et al. [89]

Table5: Average Nusselt Number over the Full Width of the Cavity