41
The empirical function, B, depends upon whether or not the surface is
hydrodynamically smooth or rough. In general, if the Reynolds number
based upon the shear velocity and the roughness height is less than
0.13 then the surface is considered smooth and B is determined using
Equation (2-47). The surface is rough if the Reynolds number is
greater than 2.0 and Equation (2-48) is used to determine the value
of B.
%
B = 13.6 Sc J 13.5
% \
B = 7.3 Re 4 Sc 5.0
where
Sc Schmidt number
v
Dv
Re = Reynolds number
z0 U*
v
The dimensionless heat transfer coefficient or Stanton number
(Chr) can be determined by substitution of the Prandtl number for the
Stanton number for the Schmidt number in equations (2-47) and (2-48)
above. The surface heat transfer coefficient can then be determined by
(2-47)
(2-48)
hh = Chy. PgCpg WSp
(2-49)