Numerical Investigation On The Ash Deposition Characteristics Of Fin-tubes In Direct Air-cooled Condenser

Condenser is one of the important equipments in the direct air-cooled unit. Its working performance plays a decisive role for me safety and economy of the unit. The direct air-cooled condensers use air as cooling medium. The finned tube is the core element of the direct air-cooled condensers. At present, single row flat wave finned tube bundle are commonly used in the direct air-cooled condenser of power plant. Because of the small number of fin spacing, the number of large number, complex structure, the particles in the air can easily accumulate in the channel of the fin, and the surface area of the condenser can be accumulated. The heat transfer efficiency of the condenser is decreased and the back pressure of the steam turbine is increased, which seriously affects the efficiency of the steam turbine. So, study on the characteristics of the outer ash accumulation of finned tube, analysis the influence factors of the outer product of the tube has important practical significance to reduce the negative influence of the ash deposition.Based on the theory analysis of the micro process of particulate matter deposition, the Fluent software is used to simulate the gas-solid two-phase flow field and track the movement track of the particles in the fin.The effects of particle size, speed, and fin layout on the deposition rate of particles were analyzed. The results show that when the wind speed is 1-4m/s, the particle size of the particles is controlled by the movement of the gas; With the increase of the particle size, the trajectory of the particle is affected by the gravity and the gas flow.When the particle size is increased to a certain extent, the particle size is influenced by gravity, and when the wind speed is 1m/s, 2m/s, the deposition rate increases with the increase of particle size. When the wind speed is 3m/s, 4m/s, the deposition rate increases gradually with the increase of particle size. The particle size of 10μm, 20μm, 50μm particles deposition rate with the trend of the change of fin thickness is basically the same, while the particle size of 100μm particles with the trend of the fin thickness c hanges in different wind speed showed a greater difference.Compared with the arrangement of the 30°, the change of the particle deposition rate is basically the same, and the difference of the particle deposition rate is not significant.The heat transfer and flow of different thickness of fin tube bundles are obtained by numerical simulation. The correlating equations of the friction factor versus Reynolds number and the N usselt number versus Reynolds number were obtained by fitting. The results show that the convective heat transfer coefficient, heat transfer coefficient, and flow resistance before and after the deposition of ash are gradually increased with the increase of the wind speed; under the same windward velocity, convective heat transfer coefficient and flow resistance are enhanced and heat transfer coefficient is dropped with the increase of the thickness of the ash.