Types of finned tube heat exchangers and calculation of their return air temperature

- Oct 27, 2018-

Finned tube heat exchangers are widely used in gas and liquid heat exchangers. They are of many types and are basically distinguished according to the different shapes of the fins. Common arcs are used. Louver fins, rectangular louver fins, etc.


Heat exchangers in different fin forms have different air-side heat transfer coefficients and resistance characteristics. Through a large number of experiments, it is found that, while obtaining good heat exchange characteristics, the frictional resistance is inevitably increased. Under a given heat exchanger size and fan operating curve, an increase in pressure loss necessarily results in a decrease in air flow rate and, in turn, a reduction in the heat transfer temperature difference between the air and the fin wall.


Secondly, most of the fin-and-tube heat exchangers used in air-conditioning projects are alternately operated under dry and wet conditions, while the heat transfer and resistance characteristics of different fin-and-tube heat exchangers under wet conditions are dry. There are big differences compared to working conditions. Therefore, how to correctly select the fin form, the impact on the actual working characteristics of the heat exchanger can not be ignored.


In contrast, the fin-and-tube heat exchanger with curved louver fins has an ideal effect, followed by a rectangular louver type, a corrugated plate type, and a corrugated plate type. The louver-type fins greatly improve the heat exchange performance, especially the curved louver fins can obtain a very high heat transfer coefficient, which is almost twice that of the corrugated sheet.


Regardless of the type of finned tube heat exchanger, the corresponding return air temperature is calculated in the same way. Calculate the design temperature of the fin-and-tube heat exchanger according to the calculation of the new wind, that is, the air side inlet temperature is 108 ° C, the outlet temperature is required to be 160 ° C, and then the total heat exchange amount can be obtained according to the flow rate, density and specific heat. The logarithmic mean temperature difference can be determined by setting the steam temperature.