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the inlet velocity is 3.33m/s (Reynolds number
Re =
which causes the pressure drop in a downwards serra-
5.531×104), and outlet pressure is 243 kPa. The pre- ssure loss coefficient is 12.96 and 12.26, respecti-
vely.
ted way. As the pressure drop in Case 1 is the largest among the 3 cases, it is selected to study the relation- ship between the pressure drop and the geometry con-
figuration of the passage. The calculated average pre- ssure is based on a cross section normal to the flow
Table 3 The geometroc parameters , and the calcula-
direction and the curve is plotted by connecting the representative value, as shown in Fig.8.
Fig.8 The downwards serrated pressure drop in Case 1
As the expanding section is followed by a right angle turn, so the pressure will be partly recovered after each drop. Each expanding section will generate a recovery and for a total of 9 times during the thro- ttling process. Thus it prevents the continuous and steep pressure drop and keeps the velocity in a rea- sonable level.
The downwards serrated curve also indicates that the most pressure drop is generated in the “series pa- ssage”, and the pressure differences between the peak and the valley are much greater than those in the “pa- rallel passage”.
ted
pn , ,
The pressure drop
pn
is defined as:
The and are the key parameters in the
p1 = p0 pA
for
n =1
(1)
passage design, which determine the recovery ampli- tude. From the calculated value of in Table 3, the
pn = pn pn1
for
n = 2 to 9 (2)
pressure recovery ratio is changed from 29% to 51% in the “series passage” section and just 9% to 38% in
The ratio of the pressure recovery n
as in Table 3.
is defined
the “parallel passage” even with the value of grea-
ter than the former. The reason might lie in the fact
The parameters and are introduced to de-
scribe the geometric characteristics and are defined as:
that the flow rate in the “series passage” is pided into two parts after the inlet of the “parallel passage” so
L
= n, D
Sn1
for
n = 1 to 6 (3)
the velocity is reduced, as shown in Fig.5(b), and the velocity of the water do not exceed 10 m/s through the main path. The other reason is that the value of in
the “parallel passage” are smaller than that in the
= Ln, D ,
Sn1, R
= Sn ,
Ln, D
L
= n, R ,
Ln, D
n = 7 to 9 (4)
n = 1 to 6 (5)
n = 7 to 10 (6)
“series passage”.
4. Discussions
The labyrinth passage studied in this paper has three advantages. Firstly, it is composed of many right angle turns, which can generate a great pressure drop and dissipate the energy of the fluid. And secondly, the pressure drops in a downwards serrated way. Lastly, there are many stages during the pressure dropping,