  While there are studies of mixed convection heat transfer from a smooth
plate, studies of this phenomenon from an external rough plate are absent.
  The derivation by Jaffer (2023) of the heat transfer formula for natural
convection from an external plate implies a simple relation between heat
transfer and fluid velocity. This relation leads to formulas for mixed
convection from horizontal and vertical rough plates; these formulas are then
combined to predict the mixed convection heat transfer at any plate
inclination.
  Heat transfer measurements of a 30.5 cm square rough plate with forced air
velocities between 0.1 m/s and 2.5 m/s were made in each orthogonal combination
of plate and airflow direction, and of a tilted downward-facing plate. Each
data-set matches the present theory with root-mean-squared relative error
between 1.4% and 4%.
