Finned heat exchanger
Fin type radiator is a widely used heat exchange device in gas and liquid heat exchangers. It achieves the purpose of enhancing heat transfer by adding fins to ordinary base pipes. The base pipe can be made of steel pipe; Stainless steel pipe; Copper pipes, etc. Fins can also be made of steel strips; Stainless steel strip, copper strip, aluminum strip, etc.
Fin type heat exchangers are mainly used for air heating in drying systems and are the main equipment in hot air devices. The heat medium used for radiators can be steam or hot water, or thermal oil. The working pressure of steam generally does not exceed 0.8 Mpa, and the temperature of hot air is below 150 ℃.
detailed explanation
The finned radiator is mainly composed of three rows of parallel spiral finned tube bundles in the air flow direction. The processing technology of the SRZ type heat dissipation finned tube bundle is to use mechanical winding method to wrap a 0.5 * 10mm steel strip around an 18mm seamless steel tube, and then hot-dip galvanized. It can also be made of stainless steel tube and stainless steel strip to achieve full stainless steel heat dissipation. The SRL type radiator is a finned radiator rolled from steel tube and aluminum strip, with a larger heat dissipation area per unit length than the SRZ type.
The finned heat exchanger adopts mechanical winding, and the contact surface between the heat dissipation fins and the heat dissipation tubes is large and tight, resulting in good and stable heat transfer performance. The resistance of air passing through is small, and steam or hot water flows through the steel tube. The heat is transferred to the air passing between the fins through the fins tightly wound on the steel tube, achieving the effect of heating and cooling the air.
Selection of pipe spacing and sheet spacing
In general, the spacing and height of finned tube heat exchangers mainly affect the fin ratio, which is closely related to the membrane heat transfer coefficient of the medium inside and outside the tube. If there is a significant difference in the heat transfer coefficient between the inner and outer membranes of the tube, a finned tube with a relatively high fin ratio should be selected, such as steam heated air. When there is a phase change in the medium on one side, the difference in heat transfer coefficient will be significant, such as in the exchange of hot and cold air. When the hot air drops below the dew point, a finned tube heat exchanger can be used. In the case of heat exchange between air without phase change, or between water and water, bare tubes are usually more suitable. Of course, low finned tubes can also be used, as this is a weak heat transfer coefficient, and strengthening either side has a certain effect. However, excessive wing ratio does not have a significant effect. A good contact area between the inside and outside of the tube can be strengthened simultaneously, and threaded or grooved tubes can be used.
The spacing between fins is mainly considered for factors such as dust accumulation, dust deposition, and ease of cleaning, while strictly meeting the equipment's requirements for pressure drop. When arranging, the spacing between pipes should not be too large, generally>1mm or more is suitable for laying pipes. During the heat exchange process, air mainly participates in heat transfer on the front and back surfaces of the fins when passing through the finned tube heat exchanger. There is only a small amount of radiative heat transfer in the middle of the two finned tubes, and the heat transfer effect is not significant. Due to the absence of fins and resistance, this area is easily penetrated by air. During the process of air heating, the cold air without heat exchange will neutralize the heated air passing through the middle of the fins, which actually reduces the heat transfer effect. Compared with foreign finned tube heat exchangers, the tube spacing is only 0.5mm larger than the outer diameter of the fins, indicating the importance of tube spacing when arranging finned tubes.
