KURENAI : Kyoto University Research Information Repository

"1,5~c
for -ln[1-{1-exp(-4.91Pr x )}°•671 < t
h* =2 (39)
{ 1 - exp(-4.91 P1.5)}0,33
rxx
for -ln[1-{1-exp(-4.91Pr x1•s)}o,67~•
*
>t*
h,F — 2 ---------------------------------------------- (40)
{ 1 - exp(-t )}
The transient heat transfer coefficient calculated by Eqs.(39) and (40)
is shown in Fig.6 in hvs. xkPro•33 plot.
in Eq.(39)
orNu
The steady state heat transfer coefficient can be obtained by w } 0
h=2)~ ---------------------------1(41)
stf (4 .91)0•33Pr0•17(ua)
st= 0.480 RexPr0.33(42)
U x
whereRe =—(43)
x- •
The asymptotic value of transient heat transfer coefficient is given by
Eq.(39). Therefore, from Egs.(39) and (43), The ratio between the asym-
ptotic heat transfer coefficient and steady state one is given by
h a Nua0•17x*
is.h t - Nu t= 1.70{1
- exp(-4 .91 Pr xJ1•s)}o,33(44)
The value of h a/hst calculated by Eq.(44) is shown in Fig.4.
U. 5 LAMINAR FLOW FOR Pr = 1
When Prandtl number is order of unity or larger, The thickness of
boundary layers for velocity and temperature are comparable. Therefore,
velocity distribution given by Eq.(28), cannot be applied to this case.
Then, one,assumes the velocity distribution given by Eq.(45), which is ty-
pical in boundary layer analysis
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