Several methods to improve the total heat transfer coefficient of finned tube heat exchanger
Not all heat exchange occasions are suitable for the use of finned tube heat exchangers, when the heat transfer coefficient on the inside and outside of the tube is comparable, finned tube heat exchangers can be dispensed with, such as oil-oil, water-water, gas-gas heat exchange.
When the heat transfer film coefficient on the two sides of the heat transfer surface is very different, it is suitable to use a finned tube heat exchanger, because at this time, the smaller side becomes the main aspect of controlling heat transfer. When designing a finned tube heat exchanger, the heat transfer coefficient on the smaller side should be increased as much as possible. The membrane coefficients on both sides are roughly equal, and the main ones are more favorable.
The methods for increasing the membrane coefficient mainly have the following aspects;
1. Reduce the cross-sectional area of the passage to increase the flow rate, add baffles in the passage or promote turbulence, which is generally used in the pipe structure of finned tube heat exchangers.
2. Adding fins on the tube wall can not only improve the degree of turbulence, but also increase the heat transfer area, and the main heat exchange effect of the finned tube heat exchanger is based on this.
3. Use a strengthened heat transfer surface, such as a groove surface of various shapes, or a porous surface, which can obtain a considerable heat transfer film coefficient for the heat transfer process with phase change such as condensation and boiling.
Because this type of enhanced heat transfer reduces metal consumption, but also increases processing difficulty and production cost, it is less used in finned tube heat exchangers, unless there is a specific installation space limitation.
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