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How to Choose a Finned Heat Exchanger?

Date:2022-01-11

Normally, the spacing and piece height of finned tube heat exchangers mainly affect the finned 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 between the heat transfer coefficient of the membrane inside and outside the tube, the finned tube with a larger finned 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 greater, such as the exchange of hot and cold air, when the hot air is reduced to below the dew point, the finned tube heat exchanger can be used. In the case of heat exchange between air and air without phase change, or heat exchange between water and water, a bare tube is usually more suitable. Of course low finned tubes can also be used, as this is a weak heat giving coefficient at this point, and strengthening either side of it is of some effect. However, too large a finned ratio is not obvious, try to make the tube inside and outside the contact area at the same time to strengthen, you can use the threaded tube or grooved tube. The spacing of the fins is mainly a consideration for the accumulation of ash, dust, easy cleaning and other factors, and also needs to be strictly in line with the requirements of the equipment for pressure drop etc. When arranging, the spacing between the tubes is not easy to be too large, generally >1mm above the suitable layout can be. In the process of heat exchange, the air flows through the finned tube heat exchanger, mainly the fins are involved in heat exchange on both sides. The middle part of the two finned tubes has only a small amount of radiation heat transfer, and the heat transfer effect is not obvious. This part has no fins and no resistance, so the air can easily penetrate. In the process of heating the air, the unheated cold air will be neutralised with the heated hot air passing through the middle of the fins, which in turn reduces the effect of heat transfer, compared to foreign finned tube heat exchangers, where the tube spacing is only 0.5mm greater than the outside diameter of the fins.

The same as the general radiator, only the material is different, generally applicable to the air with corrosive gases or heat media with corrosive places heating, such as chemical plants, smelters, etc., if the appearance requirements are high also available stainless steel radiator. The main performance is still corrosion resistance, beautiful and generous. Due to the characteristics of the material itself, aluminium alloy is resistant to acid and oxidation, but prone to alkaline corrosion; steel has high strength and can withstand certain alkaline, but prone to oxidative corrosion; copper has better overall performance such as corrosion resistance, but too much sulphide in the water or miscellaneous copper will also corrode, and the mechanical strength of copper is low. Aluminium radiators and steel radiators with a wall thickness of 2.5mm or less must be treated with internal corrosion protection, coated with an internal corrosion protection coating, and aluminium radiators must use special non-metallic or bimetallic composite fittings, which must not be directly connected to steel pipes with aluminium threads to prevent electrochemical corrosion. The radiator is attached to the heat generating equipment on a layer of good thermal conductivity medium, playing as if the role of the intermediary, sometimes on top of the thermal conductivity medium will also add fans and other things to speed up the cooling effect. But sometimes the radiator also plays the role of a robber, as in the case of a refrigerator where the heat is forcibly drawn off to achieve a lower temperature than the room temperature.