2-4 Shell and Tube Heat exchanger - PowerPoint PPT Presentation

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2-4 Shell and Tube Heat exchanger

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2-4 Shell and Tube Heat exchanger Author: ws Last modified by: Ahmed Hassam Khan Created Date: 3/12/2009 7:15:12 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: 2-4 Shell and Tube Heat exchanger


1
2-4 Shell and Tube Heat exchanger
2
Outline
  • 2-4 Shell and tube heat exchanger
  • Why we use it ?
  • Problem 8.1

3
Problem Statement
  • 33,114 lb/hr of n-butyl alcohol at 210 0F is to
    be cooled to 105 0F using water from 95 to 115
    0F. Available for the purpose is a 19¼ in. ID,
    two- pass shell exchanger with 204 tubes ¾. OD ,
    16 BWG, 160 long on 1-in .square pitch
    arranged for four passes. Vertically cut baffles
    are spaced 7 in. apart. Pressure drops of 10psi
    are allowable.
  • What is the Dirt factor ?

4
SOLUTION
5
Data Available
  • Shell Side Data
  • Inside Shell Diameter 19¼ in
  • Number of Passes 2
  • Baffle spacing 7 in
  • Baffle type Vertically Cut
  • Allowable Pressure Drop 10psi

6
Data Available
  • Tube Side Data
  • Outside Diameter of Tubes ¾ in
  • BWG 16
  • Length of tubes 160
  • Tubes Pitch 1 in. Square
  • Number of tubes 204
  • Number of tube passes 4
  • Allowable Pressure Drop 10psi

7
Location of Fluids
  • Tube Side Fluid
  • As water has more scaling tendency than n-butyl
    alcohol that is why it is taken in tube side
  • Shell Side Fluid
  • n-butyl alcohol certainly

8
Data Available
  • Hot Fluid (n-butyl alcohol)
  • Inlet temperature (T1) 210 0F
  • Outlet temperature (T2) 105 0F
  • Mass Flow rate (mh) 33114 lb/hr
  • Cold Fluid (Water)
  • Inlet temperature (t1) 95 0F
  • Outlet temperature (t2) 115 0F

9
Diagram
  • mh 33114 lb/hr
  • (n-butyl alcohol) 210 0F 105 0F
  • (Water) 115 0F 95 0F

Temperature Profile
L
10
Step 1
  • Heat Duty
  • Qh mhCph(T1 - T2) (1)
  • mh 33,114 lb/hr
  • Cph 0.69 Btu/lboF (from fig.2)
  • Qh 33114(0.69)(210-105) Btu/hr
  • 2399109.3 Btu/hr

11
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12
Step 1 contd.
  • Mass flow rate of water
  • As Qh Qc
  • mc Qh / Cpw(t2 t1)
  • 2399109.3 / 1(115 - 95)
  • 119955.46 lb/hr

13
Step 2
  • LMTD Calculation
  • (n-butyl alcohol) 210 0F 105 0F
  • (Water) 115 0F 95 0F
  • LMTD (T1-t2) (T2-t1)
  • ln(T1-t2)/(T2-t1)
  • (210 115 ) (105 - 95)
  • ln(210 115 )/(105 - 95)
  • 37.75 0F

14
True temperature Difference
  • ?t FT LMTD
  • R T1 T2 210 - 105
  • t2 t1 115 95
  • 5.25
  • S t2 t1 115 - 95
  • T1 t1 210 95
  • 0.174
  • FT 0.95 (from fig 19)
  • ?t 0.95 37.75 35.860F

15
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16
Step 3
  • Tc and tc
  • These liquids are not viscous and the viscosity
    correction will be negligible
  • (µ/µw)s (µ/µw)t 1
  • Average temperatures can be used

17
Step 4a


  • Shell Side Calculations
  • Hot Fluid (n-butyl alcohol)
  • Flow area (as) I.DCB
  • nPT144
  • as (19.25)(.25)(7)
  • (2)(1)144
  • 0.117 ft2

18
Step 5a
  • Mass velocity
  • Gs W/as
  • 33114
  • 0.117
  • 283025.6 lb/hr.ft2

19
Step 6a
  • Reynold Number Res
  • Res De Gs / µ
  • De 4(PT2 (3.14/4)do2)
  • 3.14 do
  • 4 (12 (3.14/4)0.752)
  • 3.14 0.75
  • 0.95/12 0.0789ft
  • from figure 14
  • µ 1cp 2.42 2.42
  • Re 9356

20
Step 7a
  • jH Factor
  • from figure 28
  • jH 54
  • Step 8a
  • ho jH (k / De) (C µ / k)1/3
  • from Table 4
  • k 0.096 Btu/ft.0F
  • ho 54(0.096 / 0.0789)(0.692.42/0.096)1/3
  • 170 Btu / hr.ft2.0F

21
Step 4b
  • Tube Side Calculations
  • Tubes flow area
  • from Table 10
  • at 0.302 in2 / tube
  • 204 (0.302) / (144 4)
  • 0.1069 ft2

22
Step 5b
  • Mass velocity Gt
  • Gt w/at
  • 119955.46
  • 0.1069
  • 1122127.78 lb / hr ft2

23
Tube Side Velocity
  • V Gt / p
  • 1122127.78
  • 62.5 3600
  • 4.987 fps
  • OR
  • 1.52 ms-1

24
Step 6b
  • Reynold Number Ret
  • Ret di Gt / µ
  • from figure 17
  • µ 0.7 2.42 1.694 lb / ft hr
  • from table 10
  • di 0.620 in 0.0516 ft
  • Ret 34180.5

25
Step 7b
  • Tube side heat transfer coefficient hi
  • from Figure 25
  • hi 1240 Btu / hr ft2 0F
  • hio 1240 ID / OD
  • 1240 0.620 / 0.75
  • 1025 Btu / hr ft2 0F

26
Step 8
  • Clean Overall Coefficient Uc
  • Uc hio ho
  • hio ho
  • 145.8 Btu / hr ft2 0F

27
Step 9
  • Design Overall Coefficient UD
  • from Fourier Equation
  • UD Q/A. ?t
  • From Table 10
  • a 0.1963 ft2/ lin. Ft
  • A 204 0.1963 16
  • 640.72 ft2
  • UD 2399109.3 / 640.72 35.86
  • 104.47 Btu / hr . Ft2 .0F

28
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29
Step 10
  • Rd Uc-Ud
  • UcUd
  • 145.8 - 104.47
  • 145.8 104.47
  • .0027 hr ft2 0F/Btu

30
Step 11a
  • Pressure drop (on shell side
  • For Res 9356
  • (from fig.29)
  • f0.0035 ft2/in.2
  • No of crosses, N112L/B
  • N1(12 16)/7
  • N127.42 ( Say,28)
  • Ds19.25 in./12
  • Ds1.604 ft
  • s?

31
Step 11a
32
Step 11a
33
Step 11a
  • ?Ps fGs2Ds(N1)
  • 5.221010DesFs
  • ?Ps 0.0035 283025.6 21.60428
  • 5.221010 0.0789ft ?1
  • ?Ps 7.0psi (allowable10psi

34
Step 11b
  • Pressure drop (on tube side)
  • Ret 34180.5(from fig.26)
  • f0.0002ft2/in.2
  • ?Pt(fGt2Ln)/(5.221010DsFt)
  • ?Pt 4 psi
  • Gt973500,v2/2g0.13 (from fig.)
  • ?Pr(4nv2)/(2gs)
  • ?Pr3.2 psi
  • ?PT?Pt?Pr7.2psi(allowable10psi)

35
Step 11b
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