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 / meter | Total
weight |
Tube | Fins | Solder wire kg/mtr |
S1 | A | 3/4" | 1.01 | 0.91 | 0.152 | 2.072 |
S2 | B | 3/4" | 1.01 | 1.1 | 0.163 | 2.273 |
S3 | C | 3/4" | 1.01 | 1.25 | 0.190 | 2.45 |
S4 | D | 3/4" | 1.01 | 1.38 | 0.203 | 2.593 |
S5 | E | 3/4" | 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 | H | 1" | 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 velocity | Air 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 |
200 | 0.055 | 0.049 | 0.07 | 0.038 | 0.051 | 0.067 | 0.081 | 0.115 | 0.113 |
300 | 0.11 | 0.11 | 0.128 | 0.083 | 0.112 | 0.147 | 0.178 | 0.25 | 0.253 |
400 | 0.18 | 0.194 | 0.194 | 0.147 | 0.196 | 0.257 | 0.309 | 0.432 | 0.446 |
500 | 0.262 | 0.301 | 0.273 | 0.227 | 0.302 | 0.394 | 0.473 | 0.66 | 0.692 |
600 | 0.357 | 0.43 | 0.368 | 0.325 | 0.43 | 0.56 | 0.671 | 0.93 | 0.99 |
700 | 0.463 | 0.583 | 0.471 | 0.44 | 0.58 | 0.753 | 0.9 | 1.243 | 1.341 |
800 | 0.58 | 0.758 | 0.587 | 0.572 | 0.751 | 0.973 | 1.161 | 1.598 | 1.743 |
900 | 0.708 | 0.954 | 0.711 | 0.721 | 0.944 | 1.22 | 1.453 | 1.994 | 2.195 |
1000 | 0.846 | 1.173 | 0.847 | 0.887 | 1.158 | 1.493 | 1.775 | 2.429 | 2.697 |
1100 | 0.994 | 1.414 | 0.996 | 1.07 | 1.393 | 1.792 | 2.128 | 2.904 | 3.25 |
1200 | 1.152 | 1.678 | 1.153 | 1.269 | 1.649 | 2.118 | 2.511 | 3.419 | 3.853 |
1300 | 1.319 | 1.963 | 1.323 | 1.485 | 1.927 | 2.47 | 2.926 | 3.974 | 4.506 |
1400 | 1.495 | 2.27 | 1.505 | 1.718 | 2.225 | 2.847 | 3.368 | 4.565 | 5.209 |
1500 | 1.681 | 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
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