Pin Fin Tubes

A division of Concept Engineering International, A Heat Transfer Focus Company
Heat Transfer Specialists, Manufacturers of Turbulators, Wire Wound Fin tubes, Brass and Naval Brass plates

Visit us at Stall C74 in the Thermal Processes Hall 6.1 at Achema, Frankfurt.






Basic curves on which all the different studies are based.


While we have done a rigorous analysis in the detailed sections, we have given in this section two very important set of curves and the parameters on which they are based.
These are:

1) Air Side Heat transfer coefficient for various sizes and configurations of wire wound fin tubes as compared to a 10 fins per inch standard L fin tube.
2) Air side Pressure drop for the same.

Methodology

To develop these we have done the following:

1. Designed a 1 meter by 1 meter 3 row panel using 3/4" OD steel tubes with 10 FPI L type Aluminium fins. We have used 57 tubes in this panel (19 tubes/row). The fin thickness considerd as 0.5 mm and the fin height as 13 mm giving a heat transfer area of 3.51 ft2/ft. The transverse pitch is 50.8 mm and the longitudinal pitch is 38 mm.

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 saturated steam 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 airside pressure 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 Aluminium 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 3/4" OD L type fin tubes, five of different windings of 3/4" OD wire wound fin tubes and one each of 3/8" OD, 5/8" OD & 1" OD 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 straight forward 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 and more 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 Aluminium 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 kgs vs. 4.7 kgs for the Stainless Steel L fin tube. When it is considered that the S1 is 30% more efficient and the S5 is 3 times the efficiency of the L fin tube, great new possibilities open up. The weight chart that follows is worth studying.

Weight of different fin configurations of fin tubes:-

Winding Code Tube OD Weight in kg / meterTotal weight
Tube Fins Solder wire
kg/mtr
S1 A3/4" 1.01 0.91 0.152 2.072
S2 B3/4" 1.01 1.1 0.163 2.273
S3 C3/4" 1.01 1.25 0.190 2.45
S4 D3/4" 1.01 1.38 0.203 2.593
S5 E3/4" 1.01 1.68 0.203 2.893
P4 F 3/8" 0.16 0.45 0.110 0.72
R2 G 5/8" 0.34 0.88 0.170 1.39
T5 H1" 0.75 1.63 0.260 2.64
L fins SS L 10 FPI- 1.01 3.71 - 4.72
L fins AL L 10 FPI- 1.01 1.41- 2.42

Design Parameters

Model No  L 10, S1,S2,S3,S4,S5 T5 R2 P4
Air inlet temperature deg C 25 25 25 25
Steam Pressure kg/cm^2g 3 3 3 3
Dirt factor outside (Rdo) hr. ft2 F/btu 0.002 0.002 0.002 0.002
Dirt 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
Tube side (hi) btu/hr.ft^2F 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 742 742 742 742
linear heat transfer coefficient btu/hr. ft F 145.64 202.27 122.20 70.29
Tube
OD in 0.75 1 0.625 0.375
thk in 0.08 0.08 0.064 0.048
ID in 0.59 0.84 0.497 0.279
No.of rows   3 3 3 3
No. of tubes  57 51 60 77
Pitch in row (pir) mm 50.8 57.2 48 38
row pitch (Rp) mm 38 44 36 28

Air sup velocityAir coefficient btu/hr. ft
fpm deg C
  P4 R2 L fin S1 S2 S3 S4 S5 T5
200 15.68 19.75 22.32 23.48 30.21 37.05 42.61 56.70 38.76
300 22.13 26.55 27.86 29.58 38.07 46.68 53.69 71.44 51.06
400 28.26 32.75 31.22 34.85 44.85 55.00 63.26 84.17 62.09
500 32.79 38.55 33.63 39.59 50.93 62.45 71.83 95.55 72.27
600 37.32 44.04 36.04 43.90 56.51 69.31 79.73 106.12 81.81
700 40.06 49.73 38.45 47.95 61.70 75.67 87.04 115.82 90.85
800 43.17 53.25 40.85 51.74 66.58 81.65 93.91 124.94 99.48
900 46.12 56.55 43.23 55.33 71.20 87.32 100.44 133.64 105.78
1000 48.92 59.67 45.56 58.75 75.61 92.73 106.68 141.96 111.85
1100 51.60 62.64 47.78 62.04 79.83 97.89 112.60 149.81 117.65
1200 54.18 65.48 49.89 65.20 83.89 102.87 118.32 157.42 123.20
1300 56.66 68.21 51.90 68.23 87.81 107.68 123.86 164.81 128.54
1400 59.06 70.84 53.82 71.18 91.60 112.32 129.20 171.90 133.69
1500 61.39 73.38 55.65 74.02 95.27 116.84 134.41 178.86 138.67


Air sup velocity Air side pr drop in wc
fpm
 P4 R2 L fin S1 S2 S3 S4 S5 T5
2000.055 0.049 0.07 0.038 0.051 0.067 0.081 0.115 0.113
3000.11 0.11 0.128 0.083 0.112 0.147 0.178 0.25 0.253
4000.18 0.194 0.194 0.147 0.196 0.257 0.309 0.432 0.446
5000.262 0.301 0.273 0.227 0.302 0.394 0.473 0.66 0.692
6000.357 0.43 0.368 0.325 0.43 0.56 0.671 0.93 0.99
7000.463 0.583 0.471 0.44 0.58 0.753 0.9 1.243 1.341
8000.58 0.758 0.587 0.572 0.751 0.973 1.161 1.598 1.743
9000.708 0.954 0.711 0.721 0.944 1.22 1.453 1.994 2.195
10000.846 1.173 0.847 0.887 1.158 1.493 1.775 2.429 2.697
11000.994 1.414 0.996 1.07 1.393 1.792 2.128 2.904 3.25
12001.152 1.678 1.153 1.269 1.649 2.118 2.511 3.419 3.853
13001.319 1.963 1.323 1.485 1.927 2.47 2.926 3.974 4.506
14001.495 2.27 1.505 1.718 2.225 2.847 3.368 4.565 5.209
15001.681 2.6 1.695 1.968 2.544 3.25 3.842 5.196 5.963

In our study we have isolated the airside and tube side coefficient and dealt with how to enhance both to get the optimum result.
The relevant literature can also be downloaded from the following websites

Stream Air Heater
catalog
Fin tube catalog Air cooled heat exchanger
catalog
Turbulators catalog