building superior steam air heaters - pin fin tube · steam air heaters building superior. ......
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CONCEPT ENGINEERING INTERNATIONAL
COMPACT, LIGHTWEIGHT AND EFFICIENT SOLUTIONS.
STEAM AIR HEATERSBUILDING SUPERIOR
Saturated steam condensing in tubes has a very high heattransfer coefficient. To harness its true potential you need a very efficient fin tube as the airside is the limiting factor. Our PIN Fin tube fits the bill. It consists of wire loops fastened to the tube with a flattened wire soldered to the tube. The soldering(lead free solder is an option) gives 100% bondingand strength and the wire loops provide very high airside turbulence. The result is an extremely high airside coefficient enhancing significantly the overall heat transfer coefficient. These fin tubes can be provided with carbon steel, stainless steel or copper wire fins on steel, stainless steel or copper/copper alloy tubes. To demonstrate the performance of these tubes against helical fin tubes we have done the following:
1. Designed a 1 meter by 1 meter 3 row panel using ¾” OD steel tubes with 10 FPI L type Aluminum fins. We have used 57 tubes in this panel. (19 tubes/row) The fin thickness was 0.5 mm and the fin height was 13 mm giving a heat transfer area of 3.51 ft2/ft. The transverse pitch was 50.8 mm and the longitudinal pitch was 38 mmv
2. Using HTRI software, we calculated the heat transfer and pressure drop of this panel under different air flow rate conditions, 25 deg C ambient air temperature and saturatedsteam at 3 kg/cm2g pressure in the tubes. We calculated all the parameters like air outlet temperature, LMTD, linear heat transfer coefficient, heat load and airsidepressure drop. We also isolated the airside heat transfer coefficient.
3. We then repeated this exercise using the same tube size but substituting the L type fins with our Pin fins in 5 different wire-winding configurations. The design was done using our in house design data proven over 2 decades of use. Since Aluminum cannot be used in wire wound fin tubes, we have considered stainless steel wire fins.
4. We also used panels with the same 1 meter by one meter 3 row configuration but changed the tube OD. We have adjusted the number of tubes to fit this configuration. We have selected the most commonly used winding configuration for each tube OD selected. We thus had panels with 1” OD at 51 tubes per panel, 5/8” tubes at 60 tubes per panel and 3/8” tubes at 77 tubes per panel.
5. We thus arrived at 9 panels, One of ¾” L type fin tubes, five of different windings of ¾” wire wound fin tubes and one each of 3/8”, 5/8” & 1” tubes. The idea of comparing one meter by one-meter panels was to be able to compare the performance of similarly sized heat exchangers across the tube options.
6. When comparing coefficients we have decided to use a linear coefficient (Per length of tube) instead of the generally used surface area. This gives a more straightforward comparison between tubes and is easier to use.One must keep in mind that with lower OD tubes a larger number of tubes can be fitted in a panel which will gives a higher panel coefficient. (Linear coefficient x length of tube in panel).
7. Due to its fin geometry and efficiency the weight of the wire fin tube is very low both in absolute per meter terms andmore so when the total length is adjusted for higher performance. To compare, S1 and the higher efficiency S2 and S3 stainless steel fin tubes are lower in weight than the 10 FPI Aluminum fin steel tube combination. The S4 & S5 are only slightly higher. When comparing against the stainless steel L fin tube, the S1 is 40% of the weight. The S5 stainless steel is only 2.9 kgsvs. 4.7 kgs for the stainless steel fin L tube. When you consider that the S1 is 30% more efficient and the S5 is 3 times the efficiencyof the L tube great new possibilities open up. The weight chart that follows is worth studying.
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Design ParameterDesign ParameterDesign ParameterDesign ParameterDesign ParameterDesign ParameterModel No Units
L 10, S1,S2,S3,S4,S5 T5 R2 P4
Air inlet temperature deg C 25 25 25 25Steam Pressure kg/cm^2g 3 3 3 3
Dirt factor outside (Rdo) hr. ft2 F/btu 0.002 0.002 0.002 0.002Dirt factor inside (Rdi) hr. ft2 F/btu 0.0005 0.0005 0.0005 0.0005
Face Area M^2 1 1 1 1
Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Heat Transfer Coefficient Tube side (hi) btu/hr. ft^2 F 1500 1500 1500 1500
When referred to tube ID/OD (hio) btu/hr. ft^2 F 1180 - - -
with dirt factor (hiod) btu/hr. ft^2 F 742 742 742 742linear heat transfer coefficient btu/hr. ft F 145.64 202.27 122.20 70.29
TubeTubeTubeTubeTubeTubeTubeTubeTubeTubeTubeTubeOD in 0.75 1 0.625 0.375thk in 0.08 0.08 0.064 0.048ID in 0.59 0.84 0.497 0.279
No.of rows 3 3 3 3No. of tubes 57 51 60 77
Pitch in row (pir) mm 50.8 57.2 48 38row pitch (Rp) mm 38 44 36 28
Weight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWeight of different fin configurations of fintubesWinding Code Tube OD Weight per meter (kg/mtr)Weight per meter (kg/mtr)Weight per meter (kg/mtr)Weight per meter (kg/mtr) Total
weightTube Fins Tension wire Solder wire Kg/mtr
S1 A ¾” 1.01 0.91 0.062 0.09 2.072S2 B ¾” 1.01 1.1 0.07 0.093 2.273S3 C ¾” 1.01 1.25 0.08 0.11 2.45S4 D ¾” 1.01 1.38 0.083 0.12 2.593S5 E ¾” 1.01 1.68 0.083 0.12 2.893P4 F 3/8” 0.16 0.45 0.05 0.06 0.72R2 G 5/8” 0.34 0.88 0.08 0.09 1.39T5 H 1” 0.75 1.63 0.12 0.14 2.64
L fins SS L 10 FPI ¾” 1.01 3.71 - - 4.72L fins AL L 10 FPI ¾” 1.01 1.41 - - 2.42
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www.conceptengg.com
Air
sup
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Udl
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Udl
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Air
coe
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Air
coe
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ient
Air
coe
ffic
ient
Air
coe
ffic
ient
velo
city
fpm
200
300
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500
600
700
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900
1000
1100
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1300
1400
1500
bt
u/hr
. ft
btu/
hr. f
tbt
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hr. f
t Fde
g C
deg
Cde
g C
deg
Cde
g C
deg
Cde
g C
deg
CP4
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finS1
S2S3
S4S5
T5P4
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37.3
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56.5
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79.7
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81.8
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67
Air
sup
velo
city
fpm
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Air
out
let
Air
out
let
Air
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kcal
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kcal
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kcal
/hr.
kcal
/hr.
kcal
/hr.
kcal
/hr.
kcal
/hr.
kcal
/hr.
P4R2
L fin
S1S2
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5.0
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59.6
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7.6
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8.9
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28.9
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88.4
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93.9
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2.3
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34.1
Air
sup
velo
city
fpm
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
LMTD
LMTD
LMTD
LMTD
LMTD
LMTD
LMTD
LMTD
LMTD
Air
side
Air
side
Air
side
Air
side
Air
side
Air
side
Air
side
Air
side
Air
side
pr
dro
ppr
dro
ppr
dro
ppr
dro
ppr
dro
ppr
dro
ppr
dro
ppr
dro
ppr
dro
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g C
deg
Cde
g C
deg
Cde
g C
deg
Cde
g C
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Cde
g C
in w
cin
wc
in w
cin
wc
in w
cin
wc
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cin
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finS1
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3
Air
sup
Velo
city
fp
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030
040
050
060
070
080
090
010
0011
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0013
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ud/p
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ud/p
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ud/p
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ud/p
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ud/p
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ud/p
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ud/p
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ud/p
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A
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A
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hr p
anel
F
btu/
hr p
anel
F
btu/
hr p
anel
deg
C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
bt
u/hr
pan
elde
g C
P4
R2L
finS1
S2S3
S4S5
T5P4
R2L
finS1
S2S3
S4S5
T531
8532
8431
4136
9445
6853
9660
1974
3853
3939
6038
8641
7343
9056
4869
2679
6710
600
6483
4161
4191
3814
4470
5483
6427
7129
8699
6661
5590
5225
5208
5531
7117
8728
1003
913
357
8541
4962
4942
4239
5093
6207
7231
7985
9649
7732
7138
6446
5837
6516
8385
1028
311
827
1573
710
387
5489
5585
4524
5617
6808
7892
8684
1041
086
3882
8275
8662
8874
0195
2211
676
1342
917
864
1208
959
6961
5048
0660
7273
2584
5792
7811
051
9423
9426
8666
6738
8208
1056
512
958
1490
719
839
1368
562
3966
9350
8064
7577
7989
4797
8811
592
1011
610
118
9787
7189
8964
1153
614
147
1627
321
653
1519
765
2970
1053
3368
3681
8493
8110
238
1206
410
736
1090
410
480
7638
9674
1244
815
264
1755
723
360
1664
167
8972
9555
7571
6585
4897
7010
641
1248
411
165
1164
711
129
8082
1034
513
312
1632
518
778
2498
617
694
7023
7554
5812
7467
8881
1012
311
005
1286
111
561
1235
511
743
8518
1098
414
136
1733
819
944
2654
118
711
7237
7792
6026
7745
9186
1044
411
333
1319
611
924
1303
312
328
8933
1159
914
925
1830
221
051
2800
819
680
7433
8012
6225
8004
9468
1074
011
636
1350
412
258
1368
312
887
9327
1218
915
684
1923
322
121
2943
020
609
7614
8216
6409
8245
9730
1101
411
916
1378
812
569
1431
113
424
9704
1275
716
417
2013
223
158
3081
421
502
7783
8407
6581
8472
9974
1126
912
175
1404
712
859
1491
713
941
1006
113
308
1712
521
000
2415
532
139
2236
379
4085
8667
4886
8510
204
1150
712
417
1429
013
130
1550
514
441
1040
413
840
1781
221
845
2512
933
440
2319
6
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Tables giving maximum air velocity and performance for various tubes at different pressure drop points. (Measured in inches of water column.) We have after analysis generated the following tables where we have generated the maximum airflow rate possible for every panel given a pressure drop limit. We have set the limit at .5”, 1”, 1.5” and 2” of water column. For this maximum airflow, we have given the corresponding heat transfer parameters. These tables allow us to optimize the tubes and airflow rates to get the desired results.
0.5” Water Column0.5” Water Column0.5” Water Column0.5” Water Column0.5” Water Column0.5” Water Column0.5” Water Column0.5” Water Column
Tube
P4R2
L finS1S2S3S4S5T5
Tube
P4R2
L finS1S2S3S4S5T5
Tube
P4R2
L finS1S2S3S4S5T5
Tube
P4R2
L finS1S2S3S4S5T5
Air Air side Air Udlinear LMTD Heat Load Outlet Velocity Pr Drop Co efficient temp
700 0.463 40.06 24.70 85.95 218207.2 82.5600 0.430 44.04 31.25 82.02 206876.7 88.6700 0.471 38.45 27.17 88.40 203700.0 77.3700 0.440 47.95 34.63 84.81 225038.0 84.3600 0.430 56.51 39.18 76.94 231272.5 96.1500 0.394 62.45 42.21 68.79 222815.3 107.20500 0.473 71.83 46.45 65.61 233657.9 111.20400 0.432 84.17 51.61 54.17 214466.5 123.90400 0.446 62.09 46.22 61.92 196467.8 115.60
1” Water Column 1” Water Column 1” Water Column 1” Water Column 1” Water Column 1” Water ColumnAir Air side Air Udlinear LMTD Heat Load Outlet
Velocity Pr Drop Co efficient temp 1100 0.994 51.60 28.65 93.00 274317.6 71.0
900 0.954 56.55 37.07 88.14 263475.0 79.01100 0.996 47.78 32.23 94.80 259350.0 67.31100 1.070 62.04 41.43 91.38 290418.9 73.7
900 0.944 71.20 45.72 84.10 294701.7 85.4800 0.973 81.65 50.17 78.18 300556.7 94.30700 0.900 87.04 52.35 72.79 291828.4 101.90600 0.930 106.12 59.11 63.63 288196.1 113.60600 0.990 81.81 56.33 69.02 266402.5 106.90
1.5” Water Column 1.5” Water Column 1.5” Water Column 1.5” Water Column 1.5” Water Column 1.5” Water ColumnAir Air side Air Udlinear LMTD Heat Load Outlet
Velocity Pr Drop Co efficient temp 1400 1.495 59.06 30.82 96.39 305110.6 65.21100 1.414 62.64 39.59 91.26 291611.6 73.91400 1.505 53.82 35.20 97.80 291900.0 62.41300 1.485 68.23 44.10 93.65 316441.1 69.91100 1.393 79.83 49.13 87.40 329181.2 80.21000 1.493 92.73 54.15 82.35 342083.8 88.10
900 1.453 100.44 56.92 77.91 340078.0 94.70800 1.598 124.94 64.53 70.33 347830.4 105.20700 1.341 90.85 60.47 71.68 297520.8 103.40
2” Water Column 2” Water Column 2” Water Column 2” Water Column 2” Water Column 2” Water ColumnAir Air side Air Udlinear LMTD Heat Load Outlet
Velocity Pr Drop Co efficient temp 1500 1.681 61.39 31.44 97.25 314706.3 63.7 1300 1.963 68.21 41.75 93.71 315736.3 69.8 1500 1.695 55.65 36.09 98.60 301350.0 61.1
1500 1.968 74.02 46.45 95.46 339915.3 66.81300 1.927 87.81 52.04 89.99 359432.0 76.01200 2.118 102.87 57.45 85.64 377322.3 83.01100 2.128 112.60 60.62 81.88 380466.6 88.80
900 1.994 133.64 66.77 73.01 373744.2 101.60900 2.195 105.78 66.74 76.45 350324.2 96.80
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Analysis of the Data generated:
Performance of any Fin tube cooler is a combination of its Air side Coefficient and tubeside coefficient as given by the general formula:
Ud = h’fi*h’i/h’fi+h’i
Where:Ud = overall heat transfer Coefficienth’fi = Heat transfer coefficient on fin side of the tube.h’i = Heat transfer coefficient inside the tube
From this formula we can see that any increase of the coefficient on one side (Air or tube) will lead to a less than proportional increase in the overall coefficient.
So to get a fair idea of the performance of a fin tube we have to look at both the Airside performance as well as the overall performance to see its individual impact as well as composite impact. We have accordingly in the interest of transparency given both the airside coefficient as well as the overall coefficient.
The lower material consumption per meter of tube offsets in part its greater labor cost giving a surprisingly economical tube. When the lower length of tube required in any equipment is factored in it becomes definitely very cost effective.
Now the findings:
1. In the general Airflow velocity range of 800 to 1200 the pressure drop of S1 pin fin tube is almost identical to the 10 FPI L fin tube. However the airside coefficient is higher by 26-30% similarly the overall coefficient is higher by 28% in the case of 3-bar steam in the tubes.
2. For S5 the overall coefficient is 220% and airside coefficient is 300% of the coefficient of the 10 FPI L fin tube. This implies a reduction to 40% in panel size for the same performance.
3. The wire fin tube hits the pressure drop limit at a lower airflow rate as compared to the L fin tube. However at this lower air flow it has a much higher coefficient than the L fin tube operating at the higher airflow rate giving a higher total heat load. This translates into significant power saving.
4. The outlet Air temperature achieved at different flow rates is higher for the S5 Panel by about 25 degrees centigrade. Again this implies that one can achieve the desired air temperature with a lower number of fin tube rows.
5. Again with the log mean temperature difference we are able to achieve an improvement of about 18-24 degrees between the 10 FPI L fin tube and S5. A tighter LMTD means a much more efficient heat exchanger.
6. Notwithstanding the tight LMTD achieved, the heat load for S5 is higher by 60-61% for S5 compared to the 10 FPI L panel.
7. While the difference is very large for S5 and 10 FPI L fin, it is also substantial when compared with S1, the lowest configuration.
8. Copper fins give a 15% higher airside coefficient and an 8-10% higher overall coefficient as compared to stainless steel or steel fins.
In a nutshell, we can achieve a reduction in number of rows of the steam air heater, by approximately 50%. We can achieve a further reduction in weight as the wire fin tube is much lighter than the L fin tube. (If the same metal is used by over 50%, In case the L fin is made of aluminum the weight may be about the same.) A significant reduction in power consumption is also achieved. We are able to substitute aluminum fins with stainless steel without an increase in cost or weight.
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Designing your own exchangers
We have made it easy to design your own exchangers by providing extensive data. Also by presenting the data in the form of 1x1 meter 3 row Panels, and expressing the coefficient in linear terms we have made it easy to predict performance by scaling up these panels in face area or number of rows. We have tried to make it intuitive.
For easy reference we have also given a graph comparing the same panel 3 kgs with 10 kgs steam.
By isolating the airside coefficient, we have made it possible for designers to use the data for any other type of heat exchanger like oil coolers, water coolers or any other air-cooled heat exchangers.
The Data tables have given a color code to values where the typical allowable pressure drops are reached. (.5, 1, 1.5 & 2) inches of water column. This allows you to select the most appropriate tube and airflow rate for a given allowable pressure drop. This allows you to easily optimize your tube type and panel sizing.
Assistance with design
We are willing to work together with you to design your equipment. We charge a very nominal design fee, which we are willing to rebate at the time of order conclusion. Our design capability covers all types of heat exchangers and fin tubes. We generally limit ourselves to process design but can also assist in mechanical design.
Partnership
Concept engineering wishes to work with local companies in all countries. We encourage our local partners to fabricate the heaters themselves using our fin tubes, turbulators, components and design capability. This makes it possible for companies with Fabrication capacity but limited heat exchanger design capability to partner with us to successfully make and market heat exchangers. Of course we are looking at sustained partnerships with a win win perspective.
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Concept Engineering International Turbulator Division, 2nd floor, KK Chambers, Sir P.T. Marg, Fort, Mumbai 400001.
Phone: +91-22-4353 3700-99Fax: +91-22-4353 3717
E-mail: [email protected]