paraffin wax deposition and fouling

— A36 —
A74
Velocity Distribution if I’luid Properties are Constant
Doissler used velocity distribution data for flow without heat
transfer to evaluate the constants K and n.
Assuming T
= Tw and constant physical properties, a substitution
for cu/rw in equation A73.5 gives:
(1) Away from wall
+
+ y +
u = in —- - u1
.....(A7.4.i)
where y is the lowest
of y for which the equation applies and u
is the value o u at y1. From experimental data Deissier found K = 0.3
u
—
(2) Close to wall
y ÷
dy
+
(4
2 + + 2 + +
l+n u y 1-exp(—n u y)
J
From experimental data Deissler found n = 0.124. At small y (< 5) the
equation reduces to
+ +
u = y .....(A7.4.3
Equations A7.4.1 and A7.4.3 are the same as in the Universal
Velocity Profile.
Deissler found his data to Lit very well with these equations if
ttaay from the wall” was considered when y26, at which point u = 12.82.
A75
ueratur Distribution if Fluid ProDorties are Constant
Assuming q = q,,, and = 1 in the dimensionless form of the heat
flux equation A7.3.6, results in the following equation:
A
dT’
l=ç.+
__)
sucsti;ution for the dimensionless eddy diffusivity gives: