Various factors for fin tube selection

- Aug 09, 2019-

  Finned tube heat exchangers are widely used in power, chemical, petrochemical, air conditioning engineering and refrigeration engineering, such as surface air coolers, air heaters, and fan coils used in air conditioning projects. The chiller evaporator, frost-free refrigerator evaporator, etc. used in the refrigeration engineering are not only suitable for the flow of single-phase fluid, but also have great value for phase-change heat. At present, most fin-and-tube heat exchangers for clean gas use a new and efficient fin surface structure to achieve significant heat transfer enhancement.

Generally, the pitch and sheet height of the fin-and-tube heat exchanger mainly affect the winging ratio, and the winging ratio has a great relationship with the film heat transfer coefficient of the medium inside and outside the tube. If the heat transfer coefficient of the inner and outer membranes of the tube is quite different, a fin tube with a relatively large fin ratio, such as steam heating air, should be selected. When there is a phase change in the medium, the difference in heat transfer coefficient will be large, such as the exchange of hot and cold air. When the hot air is reduced below the dew point, a finned tube heat exchanger can be used. In the case of heat exchange without phase change between air and air, or heat exchange between water and water, it is usually suitable for bare tubes. It is of course also possible to use low finned tubes, since this is a weak heat transfer coefficient, and strengthening either side has a certain effect. However, the excessive winging ratio is not obvious, and the best inner and outer contact areas of the pipe are simultaneously strengthened, and a threaded pipe or a grooved pipe can be used.

The fin spacing is mainly considering factors such as dust accumulation, dusting, easy cleaning, etc., and it is necessary to strictly meet the requirements of equipment pressure drop. When arranging, the spacing between the tube and the tube is not too large, and generally more than 1 mm is suitable for the tube. In the process of heat exchange, when the air flows through the finned tube heat exchanger, the two sides of the fin are mainly engaged in heat exchange. There is only a small amount of radiation heat transfer in the middle part of the two finned tubes, and the heat transfer effect is not obvious. This part has no fins and no resistance, and the air is easy to penetrate. In the process of air heating, the cold air without heat exchange will form a neutralization with the heated hot air passing through the middle of the fin, which will reduce the heat exchange effect. Compared with the foreign finned tube heat exchanger, the tube The spacing is only 0.5 mm larger than the outer diameter of the fins, and the importance of the tube spacing when the finned tubes are aligned is seen.