Handbook of Turbomachinery Second Edition Revised - Ventech!

calculate the correct head ðDh * isentropicÞ to use in Eq. (40):
Dh * " #
0:4=1:4
Btu
15:19
isentropic ¼ 0:24 ð760 RÞ 1
lbm R 44:1
¼ 47:88 Btu=lbm
The rotational speed is then
o ¼ NsðDh * isentropic Þ3=4
ðQ2Þ 1=2
¼ 4368 rad=sec
ft lbm
0:6 32:174 lbf s
¼
2
ft lbf 778:16 Btu 47:88 Btu
h i3=4 lbm
ð24:77 ft 3 =secÞ 1=2
The rotor inlet tip radius is found from Eq. (8):
r1 ¼ U1
o
1100 ft=sec in:
¼ 12 ¼ 3:023 in:
4368 rad=sec ft
The rotor inlet blade height h1, commonly referred to as the ‘‘bwidth,’’
is calculated from continuity at rotor inlet:
_m
1:693 lbm=sec
¼
r1Vr12pr1 ð0:1123 lbm=ft 3 in:
12
Þð268:0ft=secÞð2pÞð3:023 in:Þð1ft=12 in:Þ ft
¼ 0:426 in:
h1 ¼
The rotor exit geometry can be determined in several ways. A hub-totip
radius ratio can be assumed, the ratio of the exit tip radius to the inlet
radius can be specified, or the ratio of the rotor exit root-mean-squared
radius to the inlet radius can be chosen. Following Rodgers [27], we choose
r1=rrms2 ¼ 1:8. The root-mean-squared radius is that radius that divides the
flow area into two equal parts. The rotor exit hub and tip radius are
calculated from
A2
2 ¼ pðr2 rms2 r 2 h2 Þ¼pðr2 t2 r 2 rms2 Þ
The following results are obtained:
rrms2 ¼
rh2 ¼
rt2 ¼
Copyright © 2003 Marcel Dekker, Inc.
3:023 in:
¼ 1:680 in:
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1:8
ð1:680 in:Þ 2 10:80 in: 2
r
¼ 1:049 in:
2p
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð1:680 in:Þ 2 r
10:80 in:2
þ ¼ 2:131 in:
2p