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ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
Section
Page
IX-H
1 of 28
December, 2001 Changes shown by ➧
CONTENTS Section
Page
SCOPE ............................................................................................................................................................3 REFERENCES.................................................................................................................................................3 EQUIPMENT TYPES AND APPLICATIONS...................................................................................................3 DOUBLE PIPE UNITS.............................................................................................................................3 MULTITUBE UNITS ................................................................................................................................4 DESIGN CONSIDERATIONS..................................................................................................................4 CALCULATION PROCEDURE................................................................................................................4 VENDORS...............................................................................................................................................4 NOMENCLATURE...........................................................................................................................................5 SINGLE PHASE CALCULATION PROCEDURE..........................................................................................14 A.
PROCESS DATA...........................................................................................................................14
B.
PHYSICAL PROPERTIES .............................................................................................................14
C.
EXCHANGER GEOMETRY...........................................................................................................15
D.
TUBESIDE HEAT TRANSFER ......................................................................................................16
E.
ANNULUS HEAT TRANSFER .......................................................................................................16
F.
FIN EFFICIENCY...........................................................................................................................17
G.
OVERALL HEAT TRANSFER COEFFICIENT...............................................................................17
H.
ITERATE FOR WALL TEMPERATURE.........................................................................................18
I.
REQUIRED SURFACE ..................................................................................................................18
J.
TUBESIDE PRESSURE DROP .....................................................................................................19
K.
ANNULUS PRESSURE DROP......................................................................................................20
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION).............................................21 A.
PROCESS DATA...........................................................................................................................21
B.
PHYSICAL PROPERTIES .............................................................................................................21
C.
EXCHANGER GEOMETRY...........................................................................................................22
D.
TUBESIDE HEAT TRANSFER ......................................................................................................23
E.
ANNULUS HEAT TRANSFER .......................................................................................................23
F.
FIN EFFICIENCY...........................................................................................................................24
G.
OVERALL HEAT TRANSFER COEFFICIENT...............................................................................24
H.
ITERATE FOR WALL TEMPERATURE.........................................................................................24
I.
REQUIRED SURFACE ..................................................................................................................25
J.
TUBESIDE PRESSURE DROP .....................................................................................................25
K.
ANNULUS PRESSURE DROP......................................................................................................26
ExxonMobil Research and Engineering Company – Fairfax, VA
ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 2 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
CONTENTS (Cont) Section
Page
TABLES Table 1A Table 1B Table 2A Table 2B Table 3A Table 3B Table 4
Data for Bare and Finned Double Pipe Sections (Customary).......................................7 Data for Bare and Finned Double Pipe Sections (Metric) ..............................................8 Data for Bare Multitube Sections (3 - 16 in.), Customary...............................................9 Data for Bare Multitube Sections (76 - 406 mm), Metric ..............................................10 Data for Bare Multitube Sections (18 - 30 in.), Customary...........................................11 Data for Bare Multitube Sections (457 - 762 mm), Metric ............................................12 Geometric Constants For Double Pipe And Multitube Sections...................................13
FIGURES Figure 1 Figure 2
Typical Hairpin Section ................................................................................................27 Fin Efficiency For Longitudinally Finned Tubes ...........................................................28
Revision Memo 12/01
Reaffirmation of previous revision of DP IX-H, December, 1995, with minor editorial changes.
ExxonMobil Research and Engineering Company – Fairfax, VA
ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
Section IX-H
Page 3 of 28
December, 2001
SCOPE This section presents a brief description and a single phase calculation procedure for double pipe and multitube hairpin heat exchangers.
REFERENCES GLOBAL PRACTICE GP 6-2-1
Double Pipe and Multitube Hairpin Heat Exchangers
OTHER LITERATURE Hagner, R. C., Petro/Chem Engineer, 27, August 1968 Kern, D. Q., Process Heat Transfer, McGraw Hill, New York 1950 McDonough, M. J., Chemical Engineering, July 20, 1987
EQUIPMENT TYPES AND APPLICATIONS Double pipe and multitube heat exchangers consist of one or more pipes or tubes inside a pipe shell. The units usually consist of two straight tube lengths connected at one end to form a U or “hairpin". A sketch of a typical hairpin section is shown in Figure 1. The two straight shell lengths are connected by a return bend cover referred to as the “bonnet". These exchangers are also available without the hairpin - i.e., a straight section. The use of the hairpin construction rather than a straight length allows the ability to handle differential thermal expansion. One advantage of Hairpins is that the tube bundle is removed from the bonnet end which does not require the disassembly of the piping connections on the other end. Another advantage is that because of the large U-bend diameters even on the smallest U's, it is possible to use a flexible cleaning tool to clean the inside of the tubes. This is difficult to do in the inner tubes of a TEMA type shell-and-tube exchanger. Although some double pipe sections have bare tubes, the majority have longitudinal fins on the outside of the inner tubes. The fins are sometimes slotted to provide enhancement to the outside heat transfer coefficient. Hairpins are available in all the common materials of construction and can be built to the most severe design temperature and pressure requirements expected in petroleum refining. Also, the tubes, fins, and shell can be of different materials. However, since the fins are normally welded to the tubes, the fin and tube materials must be compatible. The use of fin tubes in hairpin sections is normally economical if the annular (shell side) heat transfer coefficient is less than 75% of the tube side coefficient. This is not a hard and fast rule because the break even point is a strong function of the annular heat transfer coefficient and fin material, both of which affect the fin efficiency. The fin efficiency increases with decreasing annular coefficient and increasing fin thermal conductivity. In addition, shorter fins have higher fin efficiencies. Hairpin sections can be combined in a variety of series or parallel arrangements to provide the required surface area while maintaining pressure drop limitations. Sections installed in series are normally mounted one on top of the other. Sections can also be connected in series/parallel (unbalanced) arrangements which are obtained using a combination of side-by-side and stacked mountings.
DOUBLE PIPE UNITS Double pipe sections contain a single inner pipe or tube inside a pipe shell. Commercially available single tube sections have shells ranging from 2 through 6 in. pipe sizes (50 to 150 mm). The inner tube, which may be bare or longitudinally finned, is available with outside diameters of 1/2 to 4-1/2 in. (12 to 114 mm). The fins, 12 to 72 per tube, are 1/2 to 1 in. high (12 to 25 mm), and 35 to 50 mils thick (0.9 to 1.3 mm). For change of phase services, the fins frequently contain holes to allow for fluid redistribution along the length of the tube. Double Pipe sections can be economically justified if the equivalent shell and tube surface area required is less than approximately 400 ft2 (40 m2). However, this criteria is not firm since the relative economics are a function of the service, materials, and installation costs.
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ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 4 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
EQUIPMENT TYPES AND APPLICATIONS (Cont) MULTITUBE UNITS Multitube hairpin sections contain from 7 to 750 tubes, bare or longitudinally finned. Section shells range from 4 through 30 in. (200 to 760 mm) pipe or shell sizes. The inner tubes are available with outside diameters of 5/8 in. to 1-1/4 in. (16 to 37 mm). The fins, 12 to 20 per tube, are nominally 1/4 in. high (6 mm) and 35 mils thick (0.9 mm). The surface area available in multitubes varies from approximately 40 ft2 (3.75 m2) to 7000 ft2 (650 m2). The larger hairpins can economically compete with TEMA type shell-and-tube heat exchangers when multiple shells in series are required due to a temperature cross.
DESIGN CONSIDERATIONS Considerations like fluid placement, fouling factors, minimum velocities are the same as shell-and-tube heat exchangers. Therefore recommendations in Sections IX-B and IX-C should be followed. If the shell-side heat transfer coefficient is small compared to the tubeside, finned tubes should be considered. These exchangers are also available with segmental baffles like a shell-and-tube. To rate exchangers with baffles, refer to Section IX-D.
CALCULATION PROCEDURE The calculation procedure is based on single phase flow in both the tubes and the shell. If the flow on either side is changing phase (vaporization or condensation), follow the tube side calculation procedure in the appropriate subsection (Section IX-E or IX-F) to evaluate the heat transfer coefficient and pressure drop. When the change of phase stream is in the shell, use the hydraulic diameters. The procedure should be used for rating existing equipment and checking vendor calculations. For new designs, it is common practice to supply the process data to the vendor and ask them to provide a design. Geometry parameters of some commonly available sections are given in Tables 1, 2, and 3. This information was provided by Brown Fintube Co. Geometry parameters for sections not listed can be calculated using Table 4, and the vendors listed below may have other standard sizes.
VENDORS The following vendors (all in the USA) may be contacted for additional information and quotations. A Specification Sheet is available in GP 6-2-1. 1.
Brown Fintube Houston, Texas (713) 466-3535
2.
Alco Products Wichita Falls, Texas (940) 723-6366
3.
R. W. Holland Tulsa, Oklahoma (918) 664-7822
ExxonMobil Research and Engineering Company – Fairfax, VA
ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS NOMENCLATURE ft2
(m2)
A Ai Ao Ar As AA AF
= = = = = = =
Total exchanger area, Inside surface area per unit tube length, ft2/ft (m2/m) Outside surface area per unit tube length, ft2/ft (m2/m) Required surface area, ft2 (m2) Surface area of one section, ft2/f (m2/m) Annular flow area, ft2 (m2) Finned surface area per unit tube length, ft2/ft (m2/m)
Cp
=
Fluid specific heat, Btu/lb-°F (kJ/kg-°C)
di do dsni dsno d2 Dhh Dhp
= = = = = = =
Inside diameter of inner tube, in. (mm) Outside diameter of inner tube, in. (mm) Inside diameter of shell inlet nozzle Inside diameter of shell outlet nozzle Inside diameter of shell (or outer pipe), in. (mm) Hydraulic diameter for heat transfer calculations, in. (mm) Hydraulic diameter for pressure drop calculations, in. (mm)
hi
=
Inside film coefficient, based on inside area, Btu/hr-ft2-°F (W/m2-°C)
ho Hf
= =
Annular film coefficient, Btu/hr-ft2-°F (W/m2-°C) Fin height, in.
k
=
Fluid thermal conductivity, Btu/hr-ft-°F (W/m-°C)
kf
=
Thermal conductivity of fin material, Btu/hr-ft-°F (W/m-°C)
kw L
= =
Thermal conductivity of tube wall, Btu/hr-ft-°F (W/m-°C) Straight tube length, ft (m)
LMTD Nf Ns NT
= = = =
Log Mean temperature difference, °F (°C) Number of fins per tube Number of sections in series Number of tubes per section
Pr
=
Prandtl Number, (2.42 µ Cp/k or 1000 µ Cp/k)
∆Pta
=
Total annular pressure drop, psi (kPa)
∆Ptt
=
Total tube side pressure drop, psi (kPa)
∆Pf
=
Pressure drop due to friction, psi (kPa)
∆Pn
=
Pressure drop in the nozzles, psi (kPa)
∆Pe
=
Pressure drop due to expansion, contraction, entrance, psi (kPa)
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Section IX-H
Page 5 of 28
December, 2001
ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT
Page
Section IX-H
6 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS NOMENCLATURE (Cont)
Q
=
Rate of heat transfer (Heat Duty), Btu/hr (W)
rf
=
Inside fouling resistance based on inside surface area, hr-ft2-°F/Btu (m2-°C/W)
rw
=
Tube wall resistance, hr-ft2-°F/Btu (m2-°C/W)
Rf
=
Annular fouling resistance, hr-ft2-°F/Btu (m2-°C/W)
Rio
=
Inside film resistance corrected to outside area, hr-ft2-°F/Btu (m2-°C/W)
Ro
=
Annular film resistance, hr-ft2-°F/Btu (m2-°C/W)
Rt
=
Total resistance to heat transfer, hr-ft2-°F/Btu (m2-°C/W)
Re
=
Reynolds number (dimensionless)
ti
=
Inlet temperature of tubeside fluid, °F (°C)
to
=
Outlet temperature of tubeside fluid, °F (°C)
Tf
=
Fin thickness, in. (mm)
Ti
=
Inlet temperature of annulus fluid, °F (°C)
To
=
Outlet temperature of annulus fluid, °F (°C)
Uo
=
Overall heat transfer coefficient, Btu/hr-ft2-°F (m2-°C/W)
V W X
= = =
Velocity, ft/sec (m/s) Mass flow rate, lb/hr (kg/s) Fin efficiency factor
ρ
=
Fluid density, lb/ft3(kg/m3)
η
=
Fin efficiency
η′
=
Surface efficiency
µ
= Subscripts
Fluid viscosity, cP (Pa•s)
a t w av
annulus tube wall average
= = = =
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DESIGN PRACTICES
ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
Section IX-H
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
Page 7 of 28
December, 2001
TABLE 1A DATA FOR BARE AND FINNED DOUBLE PIPE SECTIONS (CUSTOMARY) SHELL
TUBE
FINS
NOMINAL SIZE
ID d2
NOM. OD
ACTUAL OD, do
THICK.
ID di
(in.)
(in.)
(in.)
(in.)
(in.)
(in.)
1
2.0
2.067
1.0
1.000
0.109
0.782
2
2.0
2.067
1.0
1.000
0.109
3
2.0
2.067
1.0
1.000
4
3.0
3.068
1.5
5
3.0
3.068
1.5
6
3.0
3.068
7
3.0
8
HGT. Hf
ANNULUS AA
FINS AF
TOTAL Ao
(in.)
(ft2)
(ft2)
(ft2)
0
0.50
0.018
0.000
0.782
16
0.50
0.016
0.109
0.782
24
0.50
0.015
1.900
0.145
1.610
0
0.50
0.032
0.000
0.497
0.00
1.18
1.900
0.145
1.610
16
0.50
0.030
1.333
1.831
0.73
4.35
1.5
1.900
0.145
1.610
28
0.50
0.028
2.333
2.831
0.82
6.72
3.068
1.5
1.900
0.145
1.610
36
0.50
0.027
3.000
3.497
0.86
8.30
4.0
4.026
1.5
1.900
0.145
1.610
0
1.00
0.069
0.000
0.497
0.00
1.18
9
4.0
4.026
1.5
1.900
0.145
1.610
16
1.00
0.065
2.667
3.164
0.84
7.51
10
4.0
4.026
1.5
1.900
0.145
1.610
28
1.00
0.062
4.667
5.164
0.90
12.26
11
4.0
4.026
1.5
1.900
0.145
1.610
36
1.00
0.060
6.000
6.497
0.92
15.42
12
4.0
4.026
2.0
2.375
0.154
2.067
0
0.75
0.058
0.000
0.621
0.00
1.15
13
4.0
4.026
2.0
2.375
0.154
2.067
16
0.75
0.055
2.000
2.621
0.76
4.85
14
4.0
4.026
2.0
2.375
0.154
2.067
28
0.75
0.053
3.500
4.121
0.85
7.62
15
4.0
4.026
2.0
2.375
0.154
2.067
40
0.75
0.050
5.000
5.621
0.89
10.39
16
4.0
4.026
2.5
2.875
0.203
2.469
0
0.50
0.043
0.000
0.752
0.00
1.16
17
4.0
4.026
2.5
2.875
0.203
2.469
16
0.50
0.041
1.333
2.086
0.64
3.23
18
4.0
4.026
2.5
2.875
0.203
2.469
32
0.50
0.039
2.667
3.419
0.78
5.29
19
4.0
4.026
2.5
2.875
0.203
2.469
48
0.50
0.037
4.000
4.752
0.84
7.36
20
5.0
5.047
3.0
3.500
0.216
3.068
0
0.688
0.072
0.000
0.916
0.00
1.14
21
5.0
5.047
3.0
3.500
0.216
3.068
28
0.688
0.067
3.208
4.124
0.78
5.14
22
5.0
5.047
3.0
3.500
0.216
3.068
40
0.688
0.065
4.583
5.499
0.83
6.85
23
5.0
5.047
3.0
3.500
0.216
3.068
56
0.688
0.063
6.417
7.333
0.88
9.13
24
6.0
6.065
4.0
4.500
0.237
4.026
0
0.688
0.090
0.000
1.178
0.00
1.12
25
6.0
6.065
4.0
4.500
0.237
4.026
36
0.688
0.084
4.125
5.303
0.78
5.03
26
6.0
6.065
4.0
4.500
0.237
4.026
56
0.688
0.081
6.417
7.594
0.84
7.21
27
6.0
6.065
4.0
4.500
0.237
4.026
72
0.688
0.078
8.250
9.428
0.88
8.95
NO.
NO. Nf
AREAS RATIO AF/Ao
RATIO Ao/Ai
0.262
0.00
1.28
1.333
1.595
0.84
7.79
2.000
2.262
0.88
11.05
Notes: 1. Total surface area (A) for a straight section: As = Ao (L) 2. Total surface area (A) for a hairpin section: As = Ao (2L) 3. GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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Section IX-H
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CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
December, 2001
DESIGN PRACTICES
TABLE 1B DATA FOR BARE AND FINNED DOUBLE PIPE SECTIONS (METRIC) SHELL
TUBE
FINS
NOMINAL SIZE
ID d2
NOM. OD
ACTUAL OD, do
THICK.
ID di
(mm)
(mm)
(mm)
(mm)
(mm)
(mm)
1
50.8
52.5
25.4
25.4
2.769
19.86
2
50.8
52.5
25.4
25.4
2.769
3
50.8
52.5
25.4
25.4
4
76.2
77.9
38.1
5
76.2
77.9
6
76.2
7
HGT. Hf
ANNULUS AA
FINS AF
TOTAL Ao
RATIO AF/Ao
RATIO Ao/Ai
(mm)
(m2)
(m2/m)
(m2/m)
0
12.70
0.0017
0.000
0.080
0.00
1.28
19.86
16
12.70
0.0015
0.406
0.486
0.84
7.79
2.769
19.86
24
12.70
0.0014
0.610
0.689
0.88
11.05
48.3
3.683
40.89
0
12.70
0.0029
0.000
0.152
0.00
1.18
38.1
48.3
3.683
40.89
16
12.70
0.0028
0.406
0.558
0.73
4.35
77.9
38.1
48.3
3.683
40.89
28
12.70
0.0026
0.711
0.863
0.82
6.72
76.2
77.9
38.1
48.3
3.683
40.89
36
12.70
0.0025
0.914
1.066
0.86
8.30
8
101.6
102.3
38.1
48.3
3.683
40.89
0
25.40
0.0064
0.000
0.152
0.00
1.18
9
101.6
102.3
38.1
48.3
3.683
40.89
16
25.40
0.0060
0.813
0.964
0.84
7.51
10
101.6
102.3
38.1
48.3
3.683
40.89
28
25.40
0.0057
1.422
1.574
0.90
12.26
11 12
101.6
102.3
38.1
48.3
3.683
40.89
36
25.40
0.0056
1.829
1.980
0.92
15.42
101.6
102.3
50.8
60.3
3.912
52.50
0
19.05
0.0054
0.000
0.189
0.00
1.15
13
101.6
102.3
50.8
60.3
3.912
52.50
16
19.05
0.0051
0.610
0.799
0.76
4.85
14
101.6
102.3
50.8
60.3
3.912
52.50
28
19.05
0.0049
1.067
1.256
0.85
7.62
15
101.6
102.3
50.8
60.3
3.912
52.50
40
19.05
0.0047
1.524
1.713
0.89
10.39
16
101.6
102.3
63.5
73.0
5.156
62.71
0
12.70
0.0040
0.000
0.229
0.00
1.16
17
101.6
102.3
63.5
73.0
5.156
62.71
16
12.70
0.0038
0.406
0.636
0.64
3.23
18
101.6
102.3
63.5
73.0
5.156
62.71
32
12.70
0.0037
0.813
1.042
0.78
5.29
19
101.6
102.3
63.5
73.0
5.156
62.71
48
12.70
0.0035
1.219
1.448
0.84
7.36
20
127.0
128.2
76.2
88.9
5.486
77.93
0
17.46
0.0067
0.000
0.279
0.00
1.14
21
127.0
128.2
76.2
88.9
5.486
77.93
28
17.46
0.0063
0.978
1.257
0.78
5.14
22
127.0
128.2
76.2
88.9
5.486
77.93
40
17.46
0.0061
1.397
1.676
0.83
6.85
23
127.0
128.2
76.2
88.9
5.486
77.93
56
17.46
0.0058
1.956
2.235
0.88
9.13
24
152.4
154.1
101.6
114.3
6.020
102.26
0
17.46
0.0084
0.000
0.359
0.00
1.12
25
152.4
154.1
101.6
114.3
6.020
102.26
36
17.46
0.0078
1.257
1.616
0.78
5.03
26
152.4
154.1
101.6
114.3
6.020
102.26
56
17.46
0.0075
1.956
2.315
0.84
7.21
27
152.4
154.1
101.6
114.3
6.020
102.26
72
17.46
0.0073
2.515
2.874
0.88
8.95
NO.
NO. Nf
AREAS
Notes: 1. 2. 3.
Total surface area (A) for a straight section: As = Ao (L) Total surface area (A) for a hairpin section: As = Ao (2L) GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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December, 2001
TABLE 2A DATA FOR BARE MULTITUBE SECTIONS (3 - 16 IN.), CUSTOMARY SHELL
TUBE
NOMINAL SIZE
ID d2
OD do
THICK.
(in.)
(in.)
(in.)
(in.)
28
3.0
3.068
0.750
0.109
29
4.0
4.026
0.750
30
4.0
4.026
1.000
31
5.0
5.047
32
5.0
33
6.0
34
AREAS ID di
ANNULUS AA
TOTAL AoNT
U BEND
(in.)
(ft2)
(ft2/ft)
(ft2)
7
0.532
4.30
1.37
1.09
1.41
0.109
10
0.532
8.31
1.96
1.93
1.41
0.109
7
0.782
7.23
1.83
1.80
1.28
0.750
0.109
19
0.532
11.61
3.73
4.39
1.41
5.047
1.000
0.109
8
0.782
13.72
2.09
2.47
1.28
6.065
0.750
0.109
24
0.532
18.28
4.71
7.40
1.41
6.0
6.065
1.000
0.109
13
0.782
18.67
3.40
5.35
1.28
35
8.0
7.981
0.750
0.109
48
0.532
28.81
9.42
16.50
1.41
36
8.0
7.981
1.000
0.109
24
0.782
31.16
6.28
11.00
1.28
37
10.0
10.020
0.750
0.109
85
0.532
41.28
16.68
38.22
1.41
38
10.0
10.020
1.000
0.109
42
0.782
45.84
10.99
25.19
1.28
39
12.0
11.938
0.750
0.109
121
0.532
58.45
23.75
62.18
1.41
40
12.0
11.938
1.000
0.109
64
0.782
61.63
16.75
43.87
1.28
41
16.0
15.000
0.750
0.109
199
0.532
88.75
39.05
132.95
1.41
42
16.0
15.000
1.000
0.109
109
0.782
91.06
28.52
97.12
1.28
43
4.0
4.026
0.750
0.109
9
0.532
8.75
1.77
1.11
1.41
44
5.0
5.047
0.750
0.109
12
0.532
14.70
2.36
2.78
1.41
45
5.0
5.047
1.000
0.109
9
0.782
12.93
2.36
2.78
1.28
46
6.0
6.065
0.750
0.109
21
0.532
19.60
4.12
6.48
1.41
47
6.0
6.065
1.000
0.109
12
0.782
19.46
3.14
4.93
1.28
48
8.0
7.981
0.750
0.109
37
0.532
33.66
7.26
12.72
1.41
NO.
NO. NT
RATIO Ao/Ai
49
8.0
7.981
1.000
0.109
24
0.782
31.16
6.28
11.00
1.28
50
10.0
10.020
0.750
0.109
61
0.532
51.88
11.97
27.43
1.41
51
10.0
10.020
1.000
0.109
37
0.782
49.77
9.68
22.19
1.28
52
12.0
11.938
0.750
0.109
89
0.532
72.58
17.47
45.74
1.41
53
12.0
11.938
1.000
0.109
57
0.782
67.13
14.92
39.07
1.28
54
16.0
15.000
0.750
0.109
148
0.532
111.27
29.05
98.88
1.41
55
16.0
15.000
1.000
0.109
97
0.782
100.48
25.38
86.43
1.28
Notes: 1. 2. 3. 4.
Section No. 28-42 are for triangular layout; 43-55 are for rotated square layout. Total surface area (A) for a straight section: As = AoNT (L) Total surface area (A) for a hairpin section: As = AoNT (2L) + U bend area GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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DESIGN PRACTICES
TABLE 2B DATA FOR BARE MULTITUBE SECTIONS (76 - 406 MM), METRIC SHELL
TUBE
NOMINAL SIZE
ID d2
OD do
THICK.
(mm)
(mm)
(mm)
(mm)
28
76.2
77.9
19.1
2.8
29
101.6
102.3
19.1
30
101.6
102.3
25.4
31
127.0
128.2
32
127.0
33
152.4
34
AREAS NO. NT
ID di
ANNULUS AA
TOTAL AoNT
U BEND
(mm)
(m2)
(m2/m)
(m2)
7
13.51
0.0028
0.42
0.10
1.41
2.8
10
13.51
0.0054
0.60
0.18
1.41
2.8
7
19.86
0.0047
0.56
0.17
1.28
19.1
2.8
19
13.51
0.0075
1.14
0.41
1.41
128.2
25.4
2.8
8
19.86
0.0088
0.64
0.23
1.28
154.1
19.1
2.8
24
13.51
0.0118
1.44
0.69
1.41
152.4
154.1
25.4
2.8
13
19.86
0.0120
1.04
0.50
1.28
35
203.2
202.7
19.1
2.8
48
13.51
0.0186
2.87
1.53
1.41
36
203.2
202.7
25.4
2.8
24
19.86
0.0201
1.91
1.02
1.28
37
254.0
254.5
19.1
2.8
85
13.51
0.0266
5.08
3.55
1.41
38
254.0
254.5
25.4
2.8
42
19.86
0.0296
3.35
2.34
1.28
39
304.8
303.2
19.1
2.8
121
13.51
0.0377
7.24
5.78
1.41
40
304.8
303.2
25.4
2.8
64
19.86
0.0398
5.10
4.08
1.28
41
406.4
381.0
19.1
2.8
199
13.51
0.0573
11.90
12.35
1.41
42
406.4
381.0
25.4
2.8
109
19.86
0.0587
8.69
9.02
1.28
43
101.6
102.3
19.1
2.8
9
13.51
0.0056
0.54
0.10
1.41
44
127.0
128.2
19.1
2.8
12
13.51
0.0095
0.72
0.26
1.41
45
127.0
128.2
25.4
2.8
9
19.86
0.0083
0.72
0.26
1.28
46
152.4
154.1
19.1
2.8
21
13.51
0.0126
1.26
0.60
1.41
47
152.4
154.1
25.4
2.8
12
19.86
0.0126
0.96
0.46
1.28
48
203.2
202.7
19.1
2.8
37
13.51
0.0217
2.21
1.18
1.41
49
203.2
202.7
25.4
2.8
24
19.86
0.0201
1.91
1.02
1.28
50
254.0
254.5
19.1
2.8
61
13.51
0.0335
3.65
2.55
1.41
51
254.0
254.5
25.4
2.8
37
19.86
0.0321
2.95
2.06
1.28
52
304.8
303.2
19.1
2.8
89
13.51
0.0468
5.32
4.25
1.41
53
304.8
303.2
25.4
2.8
57
19.86
0.0433
4.55
3.63
1.28
54
406.4
381.0
19.1
2.8
148
13.51
0.0718
8.85
9.19
1.41
55
406.4
381.0
25.4
2.8
97
19.86
0.0648
7.74
8.03
1.28
NO.
RATIO Ao/Ai
Notes: 1. 2. 3. 4.
Section No. 28-42 are for triangular layout; 43-55 are for rotated square layout. Total surface area (A) for a straight section: As = AoNT (L) Total surface area (A) for a hairpin section: As = AoNT (2L) + U bend area GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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Page 11 of 28
December, 2001
TABLE 3A DATA FOR BARE MULTITUBE SECTIONS (18 - 30 IN.), CUSTOMARY SHELL
TUBE
NOMINAL SIZE
ID d2
OD do
THICK.
(in.)
(in.)
(in.)
(in.)
56
18.0
17.250
0.750
0.109
57
18.0
17.250
1.000
58
20.0
19.250
59
20.0
60
AREAS NO. NT
ID di
ANNULUS AA
TOTAL AoNT
U BEND
(in.)
(in.2)
(ft2/ft)
(ft2)
241
0.532
127.17
47.30
161.00
1.41
0.109
130
0.782
131.54
34.02
116.00
1.28
0.750
0.109
304
0.532
156.66
59.66
234.40
1.41
19.250
1.000
0.109
163
0.782
162.94
42.65
168.00
1.28
22.0
21.250
0.750
0.109
380
0.532
186.68
74.58
322.30
1.41
61
22.0
21.250
1.000
0.109
208
0.782
191.20
54.43
235.00
1.28
62
24.0
23.250
0.750
0.109
463
0.532
219.90
90.86
428.40
1.41
63
24.0
23.250
1.000
0.109
253
0.782
225.74
66.20
312.00
1.28
64
26.0
25.250
0.750
0.109
559
0.532
253.65
109.70
488.50
1.41
65
26.0
25.250
1.000
0.109
301
0.782
264.20
78.76
351.00
1.28
66
28.0
27.250
0.750
0.109
649
0.532
296.34
127.37
600.50
1.41
67
28.0
27.250
1.000
0.109
361
0.782
299.53
94.46
446.00
1.28
68
30.0
29.125
0.750
0.109
752
0.532
333.83
147.58
879.00
1.41
69
30.0
29.125
1.000
0.109
421
0.782
335.40
110.16
650.00
1.28
NO.
RATIO Ao/Ai
Notes: 1. 2. 3. 4.
Data are for triangular layout. Total surface area (A) for a straight section: As = AoNT (L) Total surface area (A) for a hairpin section: As = AoNT (2L) + U bend area GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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TABLE 3B DATA FOR BARE MULTITUBE SECTIONS (457 - 762 MM), METRIC SHELL
TUBE
NOMINAL SIZE
ID d2
OD do
THICK.
(mm)
(mm)
(mm)
(mm)
56
457.2
438.2
19.05
2.8
57
457.2
438.2
25.40
58
508.0
489.0
59
508.0
60
AREAS NO. NT
ID di
ANNULUS AA
TOTAL AoNT
U BEND
(mm)
(m2)
(m2/m)
(m2)
241
13.51
0.082
14.42
14.96
1.41
2.8
130
19.86
0.085
10.37
10.78
1.28
19.05
2.8
304
13.51
0.101
18.18
21.78
1.41
489.0
25.40
2.8
163
19.86
0.105
13.00
15.61
1.28
558.8
539.8
19.05
2.8
380
13.51
0.120
22.73
29.94
1.41
61
558.8
539.8
25.40
2.8
208
19.86
0.123
16.59
21.83
1.28
62
609.6
590.6
19.05
2.8
463
13.51
0.142
27.70
39.80
1.41
63
609.6
590.6
25.40
2.8
253
19.86
0.146
20.18
28.99
1.28
64
660.4
641.4
19.05
2.8
559
13.51
0.164
33.44
45.38
1.41
65
660.4
641.4
25.40
2.8
301
19.86
0.170
24.01
32.61
1.28
66
711.2
692.2
19.05
2.8
649
13.51
0.191
38.82
55.79
1.41
67
711.2
692.2
25.40
2.8
361
19.86
0.193
28.79
41.43
1.28
68
762.0
739.8
19.05
2.8
752
13.51
0.215
44.98
81.66
1.41
69
762.0
739.8
25.40
2.8
421
19.86
0.216
33.58
60.39
1.28
NO.
RATIO Ao/Ai
Notes: 1. 2. 3. 4.
Data are for triangular layout. Total surface area (A) for a straight section: As = AoNT (L) Total surface area (A) for a hairpin section: As = AoNT (2L) + U bend area GP 6-2-1 requires a minimum Schedule 40 shell for carbon and low alloy steel, and Schedule 10 for high alloy and non-ferrous material.
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DESIGN PRACTICES
IX-H
Page 13 of 28
December, 2001
TABLE 4 GEOMETRIC CONSTANTS FOR DOUBLE PIPE AND MULTITUBE SECTIONS Annular flow area, AA, ft2 (m2)
[
(
C1 π d22 − NT π d 20 + 4 Nf Hf Tf
)]
C1 =
1 (Customary ) or 2.5 × 1 0−7 (Metric ) 576
C2 =
1 (Customary ) or 10 −3 (Metric ) 12
Finned surface area per unit tube length, AF, ft2/ft (m2/m)
[
C2 NF (2Hf + Tf )
]
Inside surface area per unit tube length, Ai, ft2/ft (m2/m) C2 [π d i ]
tside surface area per unit tube length, Ao, ft2/ft (m2/m) C2 [π do + 2 Nf Hf ] Area of one section, As, ft2 (m2) Straight:
Ao NT L
Hairpin:
Ao NT (2L) + U-bend
If U-bend surface is not known, use 5% of AoNT (2L) as an estimate. Hydraulic diameter for heat transfer calculations, Dhh, in. (mm) é AA ù C3 ê ú ë NT A o û
C3 = 48 (Customary ) or 4000 (Metric )
Hydraulic diameter for pressure drop calculations, Dhp, in. (mm) é ù AA C3 ê ú êë NT A o + C2 π d2 úû
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CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE Exch No.:
Plant:
Date:
Service:
A.
Done By:
PROCESS DATA CUSTOMARY UNITS 1.
2.
B.
METRIC UNITS
Tubeside ti, Inlet temperature
°F
to, Outlet temperature
°C
°F
°C
Wt, Flow rate
lb/hr
kg/s
tav, Average bulk temp., (ti + to)/2
°F
°C
rf, fouling factor
hr-ft2-°F/Btu
m2-°C/W
kw, wall thermal conductivity
Btu/hr-ft-°F
W/m-°C
Annulus side Ti, Inlet temperature
°F
°C
To, Outlet temperature
°F
°C
Wa, Flow rate
lb/hr
kg/s
Tav, Average bulk temp., (Ti + To)/2
°F
°C
Rf, fouling factor
hr-ft2-°F/Btu
m2-°C/W
µi, Viscosity @ inlet
cP
Pa•s
µo, Viscosity @ outlet
cP
Pa•s
µav, t Viscosity @ tav
cP
Pa•s
Cpt, Specific heat @ tav
Btu/lb-°F
kJ/kg-°C
kt, Thermal conductivity @ tav
Btu/hr-ft-°F
W/m-°C
ρt, Density @ tav
lb/ft3
kg/m3
µi, Viscosity @ inlet
cP
Pa•s
µo, Viscosity @ outlet
cP
Pa•s
µav, a Viscosity @ Tav
cP
Pa•s
Cpa, Specific heat @ Tav
Btu/lb-°F
kJ/kg-°C
ka, Thermal conductivity @ Tav
Btu/hr-ft-°F
W/m-°C
ρa, Density @ Tav
lb/ft3
kg/m3
PHYSICAL PROPERTIES 1.
2.
Tubeside
Annulus side
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IX-H
15 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (Cont) 3.
Heat duty and heat balance Qt = W t Cpt (to - ti)
Btu/hr
kW
Qa = W a Cpa (To - Ti)
Btu/hr
kW
Btu/hr
kW
Qav =
Q t + Qa 2
If Qt and Qa differ by more than 10%, check the data or recalculate one of the outlet temperatures so that the two duties are equal.
C.
EXCHANGER GEOMETRY Select from Table 1, 2, or 3, or calculate using Table 4. 1.
Number of sections in series, Ns Nominal straight length, L
ft.
m
Height, Hf
in.
mm
Thickness, Tf
in.
mm
Thermal Conductivity, kf
Btu/hr-ft-°F
W/m-°C
Outside Diameter, do
in.
mm
Inside Diameter, di
in.
mm
Surface area, Ai
ft2/ft
m2/m
Inside Diameter, d2
in.
mm
Flow area, AA
ft2
m2
Fin area, AF
ft2/ft
m2/m
Tube Outside area, Ao
ft2/ft
m2/m
Total surface area of one section, As
ft2
m2
Total surface area of all sections, A = AsNs
ft2
m2
Hydraulic diameter for heat transfer, Dhh (use Table 4)
in.
mm
Hydraulic diameter for pressure drop, Dhp (Use Table 4)
in.
mm
Number of tubes per section, NT 2.
Fins Number, Nf
3.
4.
Tubeside
Annulus Side
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CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (Cont) D.
TUBESIDE HEAT TRANSFER Follow the procedure for tubeside calculation in Section IX-D, beginning with the step to calculate the velocity Vt. Velocity, Vt
ft/s
m/s
Btu/hr-ft2-°F
W/m2-°C
Reynolds No., Ret For water
Coefficient, hi
Other than water
Prandtl No., Prt
2.42 µ Cp / k
Coefficient, hi (Use di not do) Resistance, Rio =
E.
1 hi
æ Ao ö ç ÷ çA ÷ è i ø
1000 µ Cp / k
Btu/hr-ft2-°F
W/m2-°C
hr-ft2-°F/Btu
m2-°C/W
ANNULUS HEAT TRANSFER Velocity, Va
Wa 3600 ρ A A
Wa ρ AA ft/s
m/s
Now follow the same procedure as for the tubeside except use Dhh instead of di in all equations. Reynolds No., Rea For water
Coefficient, ho
Btu/hr-ft2-°F
W/m2-°C
Btu/hr-ft2-°F
W/m2-°C
hr-ft2-°F/Btu
m2-°C/W
Other than water Prandtl No., Pra Coefficient, ho Resistance, Ro =
1 ho
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IX-H
FIN EFFICIENCY
ha =
1 Ro + R f
X= Hf
ha 6 k f Tf
Hf
ha 500 k f Tf
η, fin efficiency, read from Figure 2 η′, surface efficiency = η
G.
æ AF A ö + çç1 − F ÷÷ Ao Ao ø è
OVERALL HEAT TRANSFER COEFFICIENT rw, Tubewall resistance
æd ö do In çç o ÷÷ 24 k w è di ø
æd ö do In çç o ÷÷ 2000 k w è di ø hr-ft2-°F/Btu
m2-°C/W
hr-ft2-°F/Btu
m2-°C/W
R1, total resistance = Rio + rf
æ R + Ro ö Ao ÷÷ + rw + çç f Ai η′ è ø
Uo, overall heat transfer coefficient, based on surface area A =
1 Rt
Btu/hr-ft2-°F
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17 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (Cont) F.
Page
W/m2-°C
ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 18 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (Cont) H.
ITERATE FOR WALL TEMPERATURE
tw, average tubeside wall temperature æ A ö = tav + Uo çç Rio + rf o ÷÷ (Tav − tav ) Ai ø è
°F
°C
°F
°C
Tw, average annulus side wall temperature æ R + rf ö ÷÷ (Tav − tav ) = Tav − Uo çç o η è ø
Return to item D to correct the wall viscosity, µw, and repeat if necessary.
I.
REQUIRED SURFACE LMTD if countercurrent flow =
(Ti
− t o ) − (To − ti ) é T − to ù ln ê i ú ë To − ti û
°F
°C
°F
°C
ft2
m2
LMTD if cocurrent flow =
(Ti
− ti ) − (To − to ) é T − ti ù ln ê i ú ë To − t o û
Ar, required surface area Qav = Uo (LMTD )
Compare Ar to A. If Ar > A, then sufficient surface is available to perform the heat duty Qav. If Ar < A, then the surface is not sufficient, and either the area (A) or the coefficient (Uo) should be increased. A can be increased by selecting a larger shell size or by using finned tubes. Uo can be increased by using the heat transfer enhancement techniques described in Section IX-A.
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ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
Section
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
IX-H
Page 19 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (Cont) J.
TUBESIDE PRESSURE DROP Follow the procedure for tubeside calculation in Section IX-D, except Pe. ∆Pe, entrance, expansion, and turnaround pressure drop per section
æ 3 ρ Vt2 ö ç ÷ ç 9270 ÷ è ø
æ 3 ρ Vt2 ö ç ÷ ç 2000 ÷ è ø
psi
kPa
psi
kPa
psi
kPa
∆Pf, tube friction pressure drop per section (Use total hairpin length including U-bend and Number of tube passes, NTP = 1). ∆Ptt, total tubeside pressure drop = (∆Pe + ∆Pf) Ns
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ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 20 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (Cont) K.
ANNULUS PRESSURE DROP Follow the procedure for tubeside calculation in Section IX-D, beginning with step 13, except Pe. Use Dhp instead of di in all equations. Inlet nozzle size, dsni
in.
mm
Outlet nozzle size, dsno
in.
mm
Vn, nozzle velocity
ft/s
m/s
∆Pn, nozzle pressure drop per section
psi
kPa
∆Pe, entrance, expansion, and turnaround pressure drop per section
æ 3 ρ Va2 ö ç ÷ ç 9270 ÷ è ø
æ 3 ρ Va2 ö ç ÷ ç 2000 ÷ è ø
psi
Reynolds number for pressure drop, Reap
kPa
124 ρ Va Dhp
ρ Va Dhp
µav,a
1000 µav,a
∆Pf, annulus friction pressure drop per section (Use total hairpin length including U-bend and NTP =1)
psi
kPa
psi
kPa
∆Pta, total annulus pressure drop = (∆Pn + ∆Pe + ∆Pf) Ns
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ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
Section IX-H
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
Page 21 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) Exch No.:
Plant:
Date:
Service:
A.
Done By:
PROCESS DATA CUSTOMARY
1.
Tubeside
ti, Inlet temperature
86
°F
30
°C
to, Outlet temperature
120
°F
49
°C
Wt, Flow rate
30,650
tav, Average bulk temp., (ti + to)/2 rf, fouling factor kw, wall thermal conductivity 2.
B.
METRIC
103 0.002
lb/hr
3.86
kg/s
°F
39.5
°C
hr-ft2-°F/Btu
0.00035
m2-°C/W
26
Btu/hr-ft-°F
45
W/m-°C
Ti, Inlet temperature
181
°F
83
°C
To, Outlet temperature
104
°F
40
°C
Annulus side
Wa, Flow rate
20,000
lb/hr
2.52
kg/s
Tav, Average bulk temp., (Ti + To)/2
142.5
°F
61.5
°C
Rf, fouling factor
0.001
hr-ft2-°F/Btu
0.834
cP
8.34 x 10-4
Pa•s
10-4
Pa•s Pa•s
0.00018
m2-°C/W
PHYSICAL PROPERTIES 1.
Tubeside
µi, Viscosity @ inlet
2.
µo, Viscosity @ outlet
0.575
cP
5.75 x
µav, t Viscosity @ tav
0.678
cP
6.78 x 10-4
Cpt, Specific heat @ tav
1.00
Btu/lb-°F
4.19
kJ/kg-°C
kt, Thermal conductivity @ tav
0.364
0.63
W/m-°C
ρt, Density @ tav
61.8
Btu/hr-ft-°F lb/ft3
989.9
kg/m3
0.070
cP
7.0 x 10-5
Pa•s
10-4
Pa•s Pa•s
Annulus side
µi, Viscosity @ inlet µo, Viscosity @ outlet
0.116
cP
1.16 x
µav, a Viscosity @ Tav
0.098
cP
9.8 x 10-5
Cpa, Specific heat @ Tav
0.691
Btu/lb-°F
2.89
ka, Thermal conductivity @ Tav
0.079
Btu/hr-ft-°F
0.137
W/m-°C
ρa, Density @ Tav
29.9
lb/ft3
478.9
kg/m3
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kJ/kg-°C
ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 22 of 28
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
December, 2001
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) (Cont) 3.
Heat duty and heat balance Qt = W t Cpt (to - ti) Qa = W a Cpa (To - Ti) Qav =
1,042,100
Btu/hr
307.3
kW
1,064,140
Btu/hr
313.2
kW
1,053,120
Btu/hr
310.3
kW
Qt + Qa 2
If Qt and Qa differ by more than 10%, check the data or recalculate one of the outlet temperatures so that the two duties are equal. C.
EXCHANGER GEOMETRY Select from Table 1, 2, or 3, or calculate using Table 4. 1.
2.
Number of sections in series, Ns
3
Nominal straight length, L
20
Number of tubes, NT
7
7
20
20
6.1
m
Height, Hf
0.210
in.
5.334
mm
Thickness, Tf
0.035
in.
0.889
mm
Btu/hr-ft-°F
216.4
W/m-°C
Thermal Conductivity, kf
125
Tubeside
Outside Diameter, do
0.875
in.
22.225
mm
Inside Diameter, di
0.709
in.
18.009
mm
0.186
ft2/ft
0.0566
m2/m
Inside Diameter, d2
4.026
in.
102.26
mm
Flow area, AA
0.052
ft2
0.00483
m2
Fin area, AF
0.758
ft2/ft
0.231
m2/m
Tube Outside area, Ao
0.929
ft2/ft
0.283
m2/m
Total surface area of one section, As
273.1
ft2
25.38
m2
Total surface area of all sections, A = As Ns
819.4
ft2
76.14
m2
Hydraulic diameter for heat transfer, Dhh (use Table 4)
0.384
in.
9.75
mm
Hydraulic diameter for pressure drop, Dhp (Use Table 4)
0.330
in.
8.39
mm
Surface area, Ai 4.
ft.
Fins
Number, Nf
3.
3
Annulus Side
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ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
Section
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
IX-H
Page 23 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) (Cont) D.
TUBESIDE HEAT TRANSFER Follow the procedure for tubeside calculation in Section IX-D, beginning with the step to calculate the velocity Vt. Velocity, Vt Reynolds No., Ret For water
7.18
ft/s
57553
2.19 57583
Btu/hr-ft2-°F
Coefficient, hi
m/s
W/m2-°C
Other than water
Prandtl No., Prt Coefficient, hi (Use di not do) Resistance, Rio =
E.
1 hi
æ Ao ö ç ÷ çA ÷ è i ø
4.51
4.51
1636
Btu/hr-ft2-°F
9040
W/m2-°C
0.00305
hr-ft2-°F/Btu
0.000553
m2-°C/W
ANNULUS HEAT TRANSFER Velocity, Va
Wa 3600 ρ A A 3.57
Wa ρ AA ft/s
1.09
m/s
Now follow the same procedure as for the tubeside except use Dhh instead of di in all equations. Reynolds No., Rea For water
51864
51934 Btu/hr-ft2-°F
Coefficient, ho
W/m2-°C
Other than water
Resistance, Ro =
1 ho
Prandtl No., Pra
2.07
Coefficient, ho
428
0.00234
2.07 Btu/hr-ft2-°F
2448
W/m2-°C
hr-ft2-°F/Btu
0.00041
m2-°C/W
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ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 24 of 28
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
December, 2001
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) (Cont) F.
FIN EFFICIENCY
ha =
1 Ro + R f
299.4
X=
Hf
η, fin efficiency, read from Figure 2
1695
ha 6 k f Tf
Hf
ha 500 k f Tf
0.709
0.709
0.86
0.86
0.89
0.89
η′, surface efficiency = η
G.
æ A ö AF + çç1 − F ÷÷ Ao Ao ø è
OVERALL HEAT TRANSFER COEFFICIENT rw, Tubewall resistance
æd ö do In çç o ÷÷ 24 k w è di ø
æd ö do In çç o ÷÷ 2000 k w è di ø
0.0003
hr-ft2-°F/Btu
0.000052
m2-°C/W
0.0171
hr-ft2-°F/Btu
0.00302
m2-°C/W
331.4
W/m2-°C
Rt, total resistance = Rio + rf
æ R + Ro ö Ao ÷÷ + rw + çç f Ai η′ è ø
Uo, overall heat transfer coefficient, based on surface area A =
H.
1 Rt
58.5
Btu/hr-ft2-°F
ITERATE FOR WALL TEMPERATURE
tw, average tubeside wall temperature æ A ö = t av + Uo çç Rio + rf o ÷÷ (Tav − t av ) Ai ø è
133
°F
56
°C
Tw, average annulus side wall temperature æR +r = Tav − Uo çç o f è η
ö ÷÷ (Tav − tav ) ø
134
°F
Return to item D to correct the wall viscosity, µw, and repeat if necessary. ExxonMobil Research and Engineering Company – Fairfax, VA
56
°C
ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
Section
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
IX-H
Page 25 of 28
December, 2001
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) (Cont) I.
REQUIRED SURFACE LMTD if countercurrent flow
=
(Ti − to ) − (To − ti ) éT − t ù ln ê i o ú ë To − ti û
35.2
°F
19.6
°C
LMTD if cocurrent flow
=
(Ti − ti ) − (To − to ) é T −t ù ln ê i i ú ë To − t o û
°F
Ar, required surface area
X
Qav × 1000 Uo (LMTD )
Qav Uo (LMTD )
511.4
°C
ft2
47.8
m2
Compare Ar to A. If Ar > A, then sufficient surface is available to perform the heat duty Qav. If Ar < A, then the surface is not sufficient, and either the area (A) or the coefficient (Uo) should be increased. A can be increased by selecting a larger shell size or by using finned tubes. Uo can be increased by using the heat transfer enhancement techniques described in Section IX-A.
J.
TUBESIDE PRESSURE DROP Follow the procedure for tubeside calculation in Section IX-D, except Pe. ∆Pe, entrance, expansion, and turnaround pressure drop per section
æ 3 ρ Vt2 ö ç ÷ ç 9270 ÷ è ø
æ 3 ρ Vt2 ö ç ÷ ç 2000 ÷ è ø
1.03
psi
7.12
kPa
5.97
psi
41.2
kPa
21.0
psi
145
kPa
∆Pf, tube friction pressure drop per section (Use total hairpin length including U-bend and Number of tube passes, NTP = 1). ∆Ptt, total tubeside pressure drop = (∆Pe + ∆Pf) Ns
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ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 26 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
SINGLE PHASE CALCULATION PROCEDURE (SAMPLE CALCULATION) (Cont) K.
ANNULUS PRESSURE DROP Follow the procedure for tubeside calculation in Section IX-D, beginning with step 13, except Pe. Use. Dhp instead of di in all equations. Inlet nozzle size, dsni
3.0
in.
76.2
mm
Outlet nozzle size, dsno
3.0
in.
76.2
mm
Vn, nozzle velocity
3.8
ft/s
1.15
m/s
0.083
psi
0.57
kPa
∆Pn, nozzle pressure drop per section ∆Pe, entrance, expansion, and turnaround pressure drop per section
æ 3 ρ Va2 ö ç ÷ ç 9270 ÷ è ø
0.123
Reynolds number for pressure drop, Reap
æ 3 ρ Va2 ö ç ÷ ç 2000 ÷ è ø
psi
0.85
124 ρ Va Dhp
ρ Va Dhp
µav,a
1000 µav,a
44570
kPa
44690
∆Pf, annulus friction pressure drop per section (Use total hairpin length including U-bend and NTP =1)
1.61
psi
11.12
kPa
5.4
psi
37.62
kPa
∆Ptt, total tubeside pressure drop = (∆Pn + ∆Pe + ∆Pf) Ns
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ExxonMobil Proprietary HEAT EXCHANGE EQUIPMENT DESIGN PRACTICES
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
Section IX-H
Tube Bundle Front End Closure
Shell
Movable Support
DP9HF01
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27 of 28
December, 2001
FIGURE 1 TYPICAL HAIRPIN SECTION
Bonnet
Page
ExxonMobil Proprietary Section IX-H
HEAT EXCHANGE EQUIPMENT
Page 28 of 28
December, 2001
CALCULATION PROCEDURE DOUBLE PIPE AND MULTITUBE HAIRPIN HEAT EXCHANGERS
DESIGN PRACTICES
FIGURE 2 FIN EFFICIENCY FOR LONGITUDINALLY FINNED TUBES 1.0
0.9
0.8
0.7
Fin Efficiency, Ef
0.6
0.5
0.4
0.3
0.2
0.1
0 0
1
2
3
X
ExxonMobil Research and Engineering Company – Fairfax, VA
4
5 DP9HF02
