Some fundamentals for comprehending the Finned boiler tube principle
Following an understanding of the principles and functions of finned tube for boiler, the following principles for finned tube selection apply.
(1) If the heat transfer coefficients on the two sides of the tube differ significantly, the fins should be installed on the side with the lower heat transfer coefficient.
Example 1: In a boilers economizer, water flows into the tube and flue gas flows out. On the flue gas side, fins should be used.
Example 2: For the air cooler, liquid flows into the tube and air flows out. On the air side, fins should be added.
Example 3: In a steam generator, the flue gas flows outside the tube while the water boils inside. The flue gas side should have fins added. It should be noted that to make installing fins easier, the design calls for placing the side with the lowest heat transfer coefficient outside the tube.
(2) Fins should be put on both sides of the tube at the same time if the heat transfer coefficient on both sides of the tube is very low. Fins cannot be added to both sides of a complicated construction. If only one side of the fin is added in this situation, the increased heat transmission wont be noticeable.
Example 1: Flue gas flows outside the tube as air circulates inside it in a conventional tubular air preheater. We must utilize bare tube since the heat transfer coefficient is so low on both sides due to the gas to gas heat transfer and it is very challenging to add fins to the tube.
Example 2: Even though the heat pipe air preheater still uses flue gas to heat the air, it is practical to use finned tubes on both the flue gas side and the air side because both flow outside the pipe. This significantly improves heat transmission.
(3) It is not required to use finned tube if the heat transfer coefficient on both sides of the tube is high.
Example 1: In a water-to-water heat exchanger, finned tubes are not required when hot water is used to warm cold water since the heat transfer coefficient on both sides is sufficient. However, the screw tube or corrugated tube can be utilized in place of the smooth tube to further improve heat transfer.
Example 2: In a condenser at a power plant, water condenses on the exterior of the tube. Finned tubes do not have to be used in general because of the high heat transfer coefficient on both sides.