Under what circumstances can a finned tube heat exchanger be used?

Under what circumstances can a finned tube heat exchanger be used?

The spacing and height of the finned tube heat exchanger mainly affect the finning ratio, which has a great relationship with the film heat transfer coefficient of the medium inside and outside the tube. If there is a large difference in the heat transfer coefficient between the inner and outer membranes of the tube, a finned tube with a relatively large finning ratio should be selected, such as steam heating air. When there is a phase change in one side of the medium, the difference in heat transfer coefficient will be large, such as the exchange of hot and cold air. When the hot air drops below zero, a finned tube heat exchanger can be used. In the case of air-to-air heat exchange without phase change, or water-to-water heat exchange, bare tubes are usually more suitable. Of course, low-finned tubes can also be used, because at this time it is a weak heat transfer coefficient, and strengthening any side of it has a positive effect. However, the effect of excessive finning ratio is not obvious. The best situation is that the internal and external contact areas of the tube are strengthened at the same time, and threaded tubes or corrugated tubes can be used.

The pitch of the fins is mainly to consider factors such as dust accumulation, dust accumulation, and easy cleaning, and at the same time, it must strictly meet the requirements of the equipment for pressure drop. When arranging, the distance between the tubes should not be too large, generally more than 1mm is suitable for tube layout. In the process of heat exchange, when the air flows through the finned tube heat exchanger, the front and back sides of the fins mainly participate in the 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. Because there is no fin at this position, there is no resistance, and the air is easy to penetrate. In the process of air heating, the cold air without heat exchange will neutralize the heated hot air passing through the middle of the fins, which reduces the effect of heat exchange. Compared with foreign finned tube heat exchangers, the tube The spacing is only 0.5mm larger than the outer diameter of the fins, which shows the importance of the spacing of the tubes when the finned tubes are arranged.