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M. Nitsche, R.O. Gbadamosi, in , 2016
Finned Tube Calculations 251
12.3.1
Calculation of the fin efficiency ηF 251
12.3.2
Calculation of the weighted fin efficiency ηW 251
12.3.3
Calculation of the overall for the inner tube surface area Ai without
12.3.4
Calculation of the overall heat transfer coefficient Uo based on the outer tube area Ao without fouling 254
12.3.5
Calculation of the overall heat transfer coefficient Uo based on the finned outer surface area Ao considering the fouling factors ro and ri 255
12.3.6
Calculation of the overall heat transfer coefficient Ui for the inner tube surface area Ai considering the fouling factors ro and ri 256
12.3.7
Fouling and Temperature Gradient 256
12.3.8
Comparison of the specific heat duties Ui × Ai (W/m K) of different tubes 258
Finned tubes are almost always used in air-cooled exchangers to compensate for the low air-side. Radial (annular) fins arranged in a helical pattern along the tube are used. The fin heigh is significantly larger than that of the low-fin tubes used in Hence, this type of tubing is referred to as high-fin tubing.
Various types of high-fin tubing are available, including:
•
Integrally finned
GEWA-D finned tubes made of copper and copper alloys are available in a wide range of sizes and withstand the highest mechanical and thermic stress. They are specially made for the individual geometries of complex heat exchangers. Copper offers the highest heat conductivity of all technical metals. It is superior in processing, hygienic and a corrosion resistant solution.
GEWA-D finned tubes made of aluminium are specifically used in light-weight applications. Aluminium combines highest ductility with reasonable heat conductivity.
GEWA-D finned tubes made of carbon steel can be used in applications such as solid-fuel boilers or storage tanks. The significantly enlarged surface area compared to plain tubes allows compact solutions. Ready to install heat exchangers can be an interesting alternative solution for heat exchangers made of costly materials.
GEWA-D medium-high finned tubes made of stainless steel can be used for condensing boilers or domestic hot water applications. Due to the enlarged outside heat transfer surface area the required tube length can be reduced and thus costly material can be saved.
Table 12.1. Characteristics of Typical High-Fin Tube Arrays
| Root tube OD (in.) | 1.0 | 1.0 |
| Fin height (in.) | 0.500 | 0.625 |
| Fin OD (in.) | 2.00 | 2.25 |
| Average fin height (in.) | ||
| Tension wound or embedded | 0.012–0.014 | 0.012–0.014 |
| Bimetallic or integral* | 0.015–0.025 | 0.015–0.025 |
| Fins per inch | 9 | 10 |
| Tube layout angle | 30° | 30° |
| Tube pitch (in.) | 2.25 | 2.50 |
| ATot/L | 3.80 | 5.58 |
| ATot/Ao | 14.5 | 21.4 |
| ATot/Ai | ||
| 13 BWG | 17.9 | 26.3 |
| 14 BWG | 17.4 | 25.6 |
| 16 BWG | 16.7 | 24.5 |
| External surface area per unit bundle face area | ||
| Three tube rows | 60.6 | 80.4 |
| Four tube rows | 80.8 | 107.2 |
| Five tube rows | 101.0 | 134.0 |
| Six tube rows | 121.2 | 160.8 |
