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Effect of fin pitch and fin height on fin ratio

Effect of fin pitch and fin height on fin ratio
Generally, the fin pitch and fin height mainly affect the fin ratio. The fin ratio is closely related to the film heat transfer coefficient of the medium on the surface of the tube. If the difference of heat transfer coefficient between the surface and inner film is large, the finned tube with larger fin ratio should be selected, such as steam heating air. When there is phase change in the side medium, the difference of heat transfer coefficient will be larger, such as the exchange of cold and hot air, when the hot air drops below the dew point, finned tube heat exchanger can be selected.
In the case of air to air heat exchange without phase change, or water to water heat exchange, usually bare tube is more suitable. Of course, low finned tube can also be used. Because of the weak heat transfer coefficient at this time, strengthening either side of the tube is effective.
However, too large wing ratio has little effect. If the inner touch area of the tube surface is strengthened together, threaded tube or grooved tube can be selected.
The fin spacing mainly considers the factors of ash deposition, dust deposition, easy cleaning, etc., and it needs to meet the requirements of the equipment on the pressure level. When placing, the distance between pipes is not easy to be too large, generally more than 1 mm is suitable for pipe laying. In the process of heat exchange, when the air flows through the finned tube heat exchanger, the positive and negative sides of the fin mainly participate in the heat exchange. Only a small amount of radiative heat transfer is needed in the center of the two finned tubes. Because there are no fins and resistance in this part, the air penetrates slightly. In the process of air heating, the unheated cold air will neutralize with the heated hot air passing through the center of the fin, which will affect the heat transfer.