LOCAL HEAD LOSS IN PLASTIC PIPELINE JOINT WELDED BY ...

very good agreement between measured values of
the friction factor, λ, and computed ones from Eq.
(3). The results in Fig. 7 show practically constant
value of the local loss coefficient ζ = 0.6 for measured
values of the Reynolds number within a range
of 6.10 4 < Re < 5.10 5 and/or flow velocity 0.77
m s -1 < c < 6.39 m s -1 . According to Kolář and Vinopal,
(1963) value of the local loss coefficient for
a sharp-edged normalised orifice with the same
ratio d0/d = 0.87 is around 1.0, which is by 67 %
greater than the actual measured values of the tube
joints with butt welds. However, according to Idelčik
(1960) this value is only 0.6. It must be pointed
out that the sharp-edged normalised orifice and the
tube joints are quite different pipeline elements and
hence using of more accurate measured value is
justified.
In design practice it may be much easier to work
with equivalent pipe length, le. This is the length of
straight pipeline of the same diameter as the fitting,
which would have the same pressure drop as the
fitting, in our case the pipeline joint with the inner
butt weld. Considering the condition Yz f = Yz l from
Eqs. (1) and (8) the equivalent pipeline length can
be computed as follows:
ζ
le = . d.
(10)
λ
Using Eqs. (10) and (3) for the friction factor λ
and considering pipe diameter and experimentally
0.04
0.03
λ (1) 0.02
Local head loss in plastic pipeline joint welded by butt fusion
determined value ζ = 0.6 the equivalent length of
pipe can be computed. For the above-mentioned
range of flow velocity c through pipeline 90 x 8.2
βPP-H S5/SDR11 the value of the equivalent pipe
length varied from le = 2.23 to 3.33 m. These values
show that the local losses represent important part
of the total losses. This is significant in particular
for long PP pipeline systems. For examples in pipeline
90 x 8,2 βPPH S5/SDR11 with the length of
100 m inner projections of nineteen butt-welded
joints may cause the increase of head losses from
42 to 63 % for the above-mentioned Reynolds
numbers in comparison with the same pipeline
without butt welds.
The geometry of inner projections of the buttwelding
joints in PE tube is rather different. The
ration of d/d0 is approximately the same as for PP
tube joints. The expected projection width b depends
on wall thickness and for the same inner
diameter and wall thickness is for PP tube and PE
tube approximately identical. However, the PE tube
projections have more rounded edge, which leads to
assumption of lower basic local loss coefficient
value in the PE tube joints. It should be pointed out
that correct values of the local loss coefficient ζ
could be determined only experimentally using the
PE tube etalon joints.
Experimental data
Advani Eq. 3
Blasius Eq. 2
5x10
Re (1)
4 5x105 105 0.01
Fig. 6. Measured and computed values of the friction factors in straight pipeline test section of length l 12 in dependence on the
Reynolds number.
Obr. 6. Porovnání naměřených a vypočtených hodnot součinitelů tření v přímém potrubí délky l 12 v závislosti na Reynoldsově čísle.
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