463
13.1 Mean Line Analysis
So, the conventional loss is the loss the flow would be subjected to, if density were
constant.
In order to express the conventional loss with a compressible fluid, a process
average density may be defined by
In a compression process, this average density only slightly deviates from the arithmetic average density.
or
= −
−
= −
irr
irr
1
1
0 dh
dp dq
dq
dh
dp.
r
r
For = con
r
stant :
o
=
=
s
s
1
1
dh
dp,
h
p.
D
D
r
r
r
So :
=
−
=
−
irr
s
1
q
h
p
h
h .
D
D
D D
r
or
.
∆
∆
∆ =
= ∆
s
m
m
s
p
p
h
h
r
r
As
,
1 n
n
2
2
1
1
p
p ~
p
 
→
=  
 
r
r
r
1/
1
2
1
2 1
it follows
1/2 (
) 1/2 (1
), with
/ .
n
r
r
r p p
r
r r
r
=
+
=
+
=
( 1)/
2
2
1
1
1
1
From
1
(
1),
−


− =
− =
−




s
s
h
h
h h
h r
h
g
g
1
1
( 1)/
( 1)/
1
( 1)
1
1
it follows
.
(
1)
1
−
−
−
−
−
=
=
−
−
m
p
p r
r
C T r
r
g
g
g
g
g
r
r g
Fig. 13.3 h-s diagram of a
compressor stage