CHEMICAL ENGINEERING

160 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

be cooled from 420 to 380 K. There is available a tubular exchanger with an inside shell
diameter of 0.60 m, having one pass on the shell side and two passes on the tube side.
It has 324 tubes, 19 mm outside diameter with 2.1 mm wall and 3.65 m long, arranged
on a 25 mm square pitch and supported by baffles with a 25% cut, spaced at 230 mm
intervals. Would this exchanger be suitable?

Solution

Mean temperature of bottom productD 0. 5
420 C 380 D400 K.

Mean temperature of crude oilD 0. 5
330 C 295 D313 K.
For the crude oil at 313 K:CpD1986 J/kg K,D 0 .0029 N s/m^2 ,kD 0 .136 W/m K
andD824 kg/m^3.

For the bottom product at 400 K:CpD2200 J/kg K.

Heat loads:

tube side:QD 37. 5 ð 1. 986

330  295 D2607 kW.

shell side:QD 29. 6 ð 2. 20

420  380 D2605 kW.

Outside coefficient

Temperature of wallD 0. 5
400 C 313 D 356 .5K

and film temperature,TfD 0. 5
400 C 356. 5 D378 K.

At 378 K,D867 kg/m^3 ,D 0 .0052 N s/m^2 ,andkD 0 .119 W/m K

Cross-sectional area for flowD shell i.d.ðclearanceðbaffle spacing/pitch

D 

0. 60 ð 0. 0064 ð 0. 23 / 0. 025 D 0 .353 m^2

(assuming a clearance of 0.0064 m).

∴ G^0 maxD
29. 6 / 0. 0353 D 838 .5 kg/m^2 s

and: RemaxD
0. 019 ð 838. 5 / 0. 0052 D 306. 4

Therefore in equation 9.90, takingChD1:

hoð 0. 019 / 0. 119 D 0. 33 ð 1. 0

30640.^6

2200 ð 0. 0052 / 0. 1190.^3

or: hoD
2. 07 ð 125 ð 3. 94 D1018 W/m^2 Kor1.02 kW/m^2 K

Inside coefficient

Number tubes per passD
324 / 2 D162.

Inside diameterD[19. 0 
2 ð 2. 1 ]/ 1000 D 0 .0148 m