The temperature fields associated with natural convection heat transfer within enclosed plane air cells with diabatic vertical walls have been studied using a Mach Zehnder interferometer. From the information thus obtained the heat transfer coefficients have been determined on the vertical walls. The average values have been correlated by a relationship of the form
Nu = Nu (Ra, A) where Nu is the Nusselt number
Ra is the Rayleigh number
and A is the cell aspect ratio (height/width).
A variety of cell sizes was used giving a range of Rayleigh number, 10³ < Ra < 6.5 × 10⁵ and a range of aspect ratio, 1.25 < A < 20. Within these ranges of the variable5Ra and A there were distinct regimes of characteristic temperature distribution. The findings regarding these regimes and the associated heat transfer coefficients will be discussed in detail.