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  pn1

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  

Sn1

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     ,

Sn1, 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,