NACA ARR No. E5I20                                              3
Tw
ro
Tg                                              Ta
where
Ta   cooling-air temperature
Tg   mean effective gas temperature
Tw   wall temperature
ql   coefficient of heat transfer from gas to wall
rf   thermal resistance of fins
ro   over-all thermal resistance from point on inside of cylinder
to cooling air
rw   thermal resistance of cylinder wall
When a heat balance is set up for a point on the inside surface
of the wall, the heat transferred to the wall H  is
H = ql A (Tg - T)                     (1)
where A   is the area considered. Heat transferred away from the
wall .H  is
H = - A (Tw - Ta)
ro
o (2)
= Ko A (Tw - Ta)
where Ko is the over-all conductivity from a point on the inside
of the wall to thu cooling air.