Determine the Fluid Grid Width in Near-Wall Region for Natural Convection

How can I calculate the fluid grid width in near-wall region for natural convection?

Unlike forced convection, in natural convection the width of the first fluid cell adjacent to the wall surface should be defined cautiously. This is because that in the numerical prediction of natural convection, it is important to solve accurately the viscous and thermal boundary layers. Furthermore, for turbulent flow, it is desirable that the first fluid cell adjacent to the wall surface be inside the viscous sublayer a thermal sublayer.

The attached PDF demonstrates a methodology to estimate the width of the first cell in order to solve a natural convection phenomena.