Study On Mechanism Of Air Film Formation And Cooling For Large Span Air Conditioning Plant Roof

In summer,the roof of large-span air-conditioning plant is exposed to strong solar radiation.The temperature of the outer surface of the roof is high,and the roof area accounts for a large proportion of the area of the large-span air-conditioned building envelope structure.Therefore,the cooling load of the roof is cold in the large-span air-conditioned building envelope structure.The load accounts for a large proportion.Reducing the temperature of the outer surface of the roof and reducing the heat transfer temperature difference between the inner and outer surfaces of the roof can effectively reduce the cooling load.At present,the roof cooling methods include cold roof technology,green roof technology,and roof water spray technology.In this paper,based on the Coanda Air Inducer,combined with the air exhaust of large-span air-conditioned buildings,a large-span air-conditioning cooling system for roofs of air-conditioning plants wasdesigned to remove the heat from the roof surface by forming an adherent film on the outer surface of the roof.Reduce the temperature of the outer surface of the roof,reduce the heat transfer temperature difference between the inner and outer surfaces of the roof,and reduce the cooling load on the roof.The gas film formation mechanism and the ability of film cooling on the outer surface of a large-span air-conditioned powerhouse without or with natural wind were discussed.Developed a new air-film cooling technology for large-span air-conditioned factory roofs,supplementing existing roof cooling technologies.The specific research content is as follows:(1)On the basis of comprehensive analysis of relevant literature and actual measurement of the temperature of the roof surface,the ventilation requirements and roof structure of large-span air-conditioned buildings are mastered,and the existing roof cooling methods and energy consumption status are analyzed.(2)A mathematical model and a numerical simulation method were developed to consider the fluid-solid coupling heat transfer between the air film and the roof layer on the outer surface of the roof and the effect of solar radiation on the film formation ability and cooling effect on the outer surface of the roof.The validity of the numerical simulation method was verified.(3)Based on the Coanda Air Inducer,a Coanda Airfoil roof air film cooling system with air exhaust from a large-span air-conditioned buildingwas designed,and the Coanda surface was optimized based on the induction rate.(4)A physical model of the air-film cooling of a large-span air-conditioned factory roof without natural winds was established,and mesh-independence tests were performed.The influence of air speed and solar radiation intensity of the Coanda air-inducing device on the air film formation mechanism,the cooling effect of the air film and the temperature distribution inside the roof of the air-conditioning factory building with different spans are discussed.(5)A physical model of air-film cooling at the roof of a large-span air-conditioned factory building with natural winds was established,and mesh-independence tests were performed.The influence of the natural wind on the air supply speed of the Coanda Air Type Air Inducer and the influence of the natural wind speed on the air film formation mechanism,the roof cooling effect and the temperature distribution inside the roof of the large-span air-conditioned factory building were discussed.