Page 150 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10D 5/30/2001 4:30 PM Page 114

114 Applied Process Design for Chemical and Petrochemical Plants

2
60 h o 46.4 Btu/hr (ft )(°F)
Water velocity 5.88 ft>sec
160217.48210.02272
Try to obtain a better coefficient by closer baffling,
5. Film coefficient, tube side, check extreme of 2-in. baffle spacing.
From Figure 10-50A and 10-50B, at 5.88 fps and 93°F, read: 7. Shell-side film coefficient based on 2-in. baffle spacing,
2
h i 1,340 Btu/hr (ft )(°F) 16,35021144211.252
2
G s 229,000 lb>hr 1ft 2
Correction for tube I.D. of 0.834 in., F w 0.94 110210.252122
Correction to outside of tube:
10.0621229,0002
2
h io (1,340)(0.94)(0.834)/1.0 1,050 Btu/hr (ft )(°F) R e 14,080
0.978
6. Film coefficient, shell side,
From Figure 10-54, read: From Figure 10-54,
j H 66
I.D.1c¿B2
Cross-flow area a s
p11442
166210.055211.812
h o 109.5 Btu>hr 1ft 21°F2
2
Assume baffle spacing of 10 in. B 0.06
I.D. shell I.D. 10 in.
c 1.25 1.0 0.25 in. 8. Assume fouling,
W 6,350 lb/hr
p 1.25 Shell side 0.002
Tube side 0.001
110210.2521102
a s 0.139 ft 2
11.25211442
9. Overall coefficient,
W 6,350
2
G s 45,700 lb>hr 1ft 2
a s 0.139
1
U
D e G s
Reynold’s number: Re 1 1
0.001 0.002
1,050 109.5
2
D e (0.72/12) 0.06 ft (Table 10-21) 76.2 Btu>hr 1ft 21°F2
(0.404)(2.42) 0.978 lb/ft (hr)
10. Area required,
10.062145,7002
R e 2,800
0.978 150,000
A 50 ft 2
176.52139.22
Reading Figure 10-54,
j H 28 (for 25% cut segmental baffles) 11. Area available in assumed unit,
From Figure 10-140, A (0.2618)(24)(8 6 in./12) 47 ft 2

f 0.0027 (for 25% cut segmental baffles)
Therefore, the assumed unit is too small.
Note: “f” from figure 10-140. is divided by 1.2 for plain tubes (not
finned).
12. Second trial,
Assume:
h o D e c 1>3 0.14
j H a b a b 28 12-in. I.D. shell, 44 tubes, 1-in. O.D. 14 BWG 8 ft
long on 1 / 4 -in. triangular pitch, 4 tube passes. For the
k a k a w 1
0.055 10.333210.404212.422 1>3 revised water rate, allow only 3°F rise.
h o 28a ba b 112
0.06 0.055
150,000
lb hr 50,000
11213°2
Note that ( / w ) is taken as 1.0 for fluids of low viscosity where
the change in temperature does not introduce a significant 50,000
gpm 100
increase in viscosity. 18.3321602