Page 179 - Chemical Process Equipment - Selection and Design

. Performance Characteristics of Fans”
I
Quantity Diameter
(1000adm9 Head Opt. (in.)
Inches V Max Peak
Description Min Max Water (fps) ad Min Max Ns 0, Eff.
Axial propeller 8 20 10 410 0.13 23 27 470 0.63 77
Axial propeller 20 90 8 360 0.12 27 72 500 0.60 80
Axial propeller 6 120 2.5 315 0.10 27 84 560 0.50 84
Raldial air foil 6 100 22 250 0.45 18 90 190 0.85 88
Radiai BC 3 35 18 260 0.63 18 90 100 1.35 78
Raldial open MH 2 27 18 275 0.55 18 66 97 1.45 56
Raldial MH 2 27 18 250 0.55 18 66 86 1.53 71
Radial IS 2 27 18 250 0.55 18 66 86 1.53 66
Vane 51 flat 1 10 12 250 0.43 10 30 210 0.81 70
Wane FC 1 10 2 65 1.15 10 30 166 0.65 66
I-
aqad = 32.2H/p, N, = IVQ~”/~”~ (specific speed), D, = Db@’5/Qo.5 (specific diameter), where
D = diameter (ft), H = head (ft), 0 =suction flow rate (cfs), V= impeller tip speed (fps), and N = rotation speed
(rpm).
(Evans, 1979).

I I I

14 TABLE 7.5. Fan Lawsa
Fan Variables
Law
Head-Capacity at 12 Number Ratio of - Ratio X Ratio Ratio
\ 900 rprn
l a cf m size’ X rpm 1
500 b press - size’ X rprn‘ X 6
C HP size5 X rpm3 6
2 a cfm size’ X press”* 1/6’/‘
b rpm - l/size X press”’ X 1/6’“
C HP size‘ X press”’ 1/6’12
3 a rp m size' X cfm ?
b press - l/size4 X cfm2 X 6
C HP l/size4 X cfm3 6
4 a cfm sizew3 X H P1I3
* BHP at 900 rprn
b press - 1/sizew3 X H Pz3 X
C rpm 1 /sizeY3 X HP’I3
5 a size cfm’/’ X 1/pressli4
b rpm - l/cfm”* X pressw4 X
C HP cf m X press
I
0 0 6 a size cfm’I3 X l/i-pm’13
0 25 50 75 100 I2j 150 b press - cfmz3 X rPm;; X
Capacity, KCFM C HP cfmS3 X rPm
Control CointroU Required Power Advantages (A), and 7 a size press”’ X l/rpm
3w Cost input Disadvantages (D) b cfm - press”’ X l/rpm’ X
a low high (A) simplicity; (D) C HP pressY’ X l/rpmz
high power input 8 a size 1/HPlf4 X cfmZ4
b moderate moderate (A) lower input b rpm - H P3/4 X 1 /c~m514 X
power; (D) higher C press HP X l/cfm
cost
c low moderate (A) simplicity; (D) 9 a size HP”* X l/press3I4
fan erosion b rpm - 1/HP”’ X pressY4 X
d moderate moderate (D) complex; also C cfm HP X l/press
needs dampers
e high low (A) simple; no dampers 10 a size HP1I5 X l/rpmZ5
needed b cfrn - HPw5 X l/rpmE X
C press HPa5 X wm
Figure 7.23. Performances of fans with several kinds of controls
(American Standard Co. Znc.). (a) A damper in the duct with = 6 = P/gc
constant-speed fan drive, (b) two-speed fan driver, (c) inlet vanes or For example, the pressure P varies as D2N’p/g, line l(b),
inlet louvers with a constant-speed fan drive, (d) multiple-step Qz(p/g,)/D4 line 3(b), ,Pz3(p/gc)1f3/Dw3 line 4(b), Qa3Af4/’p/g, line
variable-speed fan drive, and (e) hydraulic or electric coupling with 6(b), PI0 line 8(c), and Pa5Nw5(p/gc)”5 line lO(c).
constant-speed. driver giving wide control over fan speed. (R.D. Madison, 1949).

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