Study On Optimization Of Heat Transfer Surface Structure And Material Of Direct Air-cooled Condenser

At present,the operation of large thermal power plants in China relies mainly on coal resources and water resources.In Three-North Regions with abundant coal resources,the shortage of water has seriously restricted the development of large scale power plants.In order to alleviate the increasingly serious water shortage in power plants,a lot of direct air cooling technology of water saving has been rapidly popularized and used.Air-cooled condenser is the core part of the direct air cooling system.Finned tubes are important heat exchange elements for direct air-cooled condensers.Since the 70s of last century,the fin tubes used in direct air-cooled condensers have undergone four rows of equal-diameter continuous fin structures,double row elliptical tubes with rectangular fin structures,three rows of elliptical tubes with elliptical fin structures and single row flat tube serpentine fin structure.Because of its advantages of large heat exchange area,small flow resistance,good anti-freeze performance,and high heat transfer coefficient,the large-diameter single-row tube of the serpentine fin becomes the main direction for research and application of direct air-cooled heat exchange elements.In this paper,the serpentine finned flat tube heat exchanger is studied.Gambit software was used to build geometric models and grid division.After that,the model is imported into Fluent for simulation calculations.From the view of manufacturing materials and geometry,the effects of the changes in the fin and flat tube materials,the increase of the spoiler holes and cylindrical convexes on the fins on the heat transfer performance,flow resistance and overall heat transfer performance of the finned tubes are explored.The results show that the heat exchange amount and heat transfer coefficient of finned tube of different materials increase with the increase of wind speed and fin efficiency decrease.At different frontal wind speeds,the overall heat transfer performance of aluminum-fins steel pipe and aluminum-fin aluminum tube are similar,and the overall heat-exchange performance of steel-fin steel pipe is greatly different from them.It shows that the heat transfer performance of finned tube can be improved greatly by changing fin material.In terms of fin geometry,the heat transfer coefficient of the finned tube is increased by 1%-18%after the spoiler is increased compared to the serpentine finned flat tube,and the increase is gradually weakened with the increase of the frontal wind speed and the fin spacing.The spoiler hole has little effect on the flow resistance of the finned tube.Compared with the serpentine finned tube,the heat transfer amount,Nu and the overall heat transfer performance Nu/f1/3 of the cylindrical convex finned tube increase with the increase of the frontal wind speed,and the extent also increases.Under the same pressure drop and pump work,the heat transfer performance of the cylindrical convex finned tube is better than that of the perforated finned tube in the same dimensions.