Analysis Of Heat Transfer Characteristics And Operation Optimization Of The Air-cooled Condenser

In recent years,China has got a sustained and rapid economic growth,and the demand for electricity has also continued to increase.Thermal power generation is still the most important way of power generation at present.Traditional thermal power generation consumes a huge amount of water.At present,as the most effective water-saving technology in thermal power plants,direct air-cooling technology has received more and more extensive attention and applications.The air-cooled condenser is the most important equipment in the direct air cooling system.Its heat transfer performance largely affects the efficiency of the direct air cooling system.Therefore,it is very necessary to study the heat transfer characteristics and operation optimization of the air cooled-condenser,The research results of this paper have certain guiding significance for the safe and efficient operation of air-cooled condenser.Firstly in this paper,the heat transfer process of the air-cooled condenser inner tube,tube wall and the outside of tube is analyzed,and five factors that mainly affect the condensation ability of the air-cooled condenser is found,namely environment temperature,environment humidity,environment lateral wind,solar radiation,and axial fan speed.At the same time,a one-dimensional simulation model was established based on the theoretical analysis,and the accuracy of the simulation model was verified through direct air-cooled condenser operation experiment,which proved that the error was within an acceptable range.Secondly,using the simulation model,the five factors influence rule on the air-cooled condenser are analyzed.(1)The change of environment temperature and axial fan speed has great influence on the condenser condensing ability.The condensing capacity of the fan at 1.1times rated speed is 1.6 times the condensing capacity at 0.5 times rated speed,and the condensing capacity of the air-cooled condenser at-25℃ is about 3.75 times that of the30-degree-thirry space-cooled condenser.(2)The effect of environment humidity and solarradiation has a little effect on the condenser condensing ability,both have a 0.3% impact on the condensing capacity of air-cooled condensers.(3)The low speed crosswind has a small influence,but the high speed crosswind has a obvious influence on the air-cooled condenser.When the crosswind speed is 4m/s,the condensing capacity of the air-cooled condenser decreases by only 1.2%.When the crosswind speed reaches 12m/s,the condensing capacity drops by 12.6%..Then,using CFD simulation software,the CFD simulations were performed on the external convection heat transfer process and the condensation heat transfer process of the air-cooled tube bundle.The study found that:(1)the air flows in the channel,and the temperature of the air rises continuously during the convection heat transfer with the high temperature wall.Because of the shape of the snake fins,the air velocity near the root part of the fin is low,which leads to the poor heat transfer effect.(2)The temperature difference between the finned tubes is small and the entire finned tube can be considered as isothermal.(3)in the process of condensation heat transfer,the volume fraction of vapor in the tube decreases constantly.However,befor the vapor is condensed completely,the temperature inside the tube contain the same,because the vapor condenses and releases a lot of energy.Finally,the operation of the air-cooled condenser was optimized.Through the analysis,the following are obtained:(1)When the turbine exhaust volume is constant,and the environment temperature changes,the adjustment plan of axial flow fan speed is obtained;(2)in summer high temperature,the peak heat exchanger is incorporated into the steam condensing system,and the combined operation plan of the air cooled condenser and the peak heat exchanger is obtained.