Na_(2)SO_(4)循环流化床蒸发器中的颗粒碰撞行为和传热性能

Particle collision behavior and heat transfer performance in a Na_(2)SO_(4)circulating fluidized bed evaporator

将流化床换热防垢节能技术和Na_(2)SO_(4)蒸发过程相结合,设计并构建了1套Na_(2)SO_(4)循环流化床蒸发装置。选用质量分数为20%的Na_(2)SO_(4)溶液作为液相工质,采用聚甲醛(POM)和碳化硅(SiC)颗粒作为惰性固体颗粒,考察了颗粒类型、颗粒加入量(1%~3%)、循环流速(0.37~1.78 m·s^(-1))和热通量(7.29~12.14 kW·m^(-2))等操作参数对于颗粒的碰撞行为和蒸发器传热性能的影响。研究结果表明,POM和SiC颗粒的加入均可以强化传热。实验范围内,POM和SiC颗粒的最大增强因子分别为9.5%和13.4%,所对应的操作参数分别为ε=1%,u=1.78 m·s^(-1),q=7.29 kW·m^(-2)和ε=3%,u=0.37 m·s^(-1),q=12.14 kW·m^(-2)。液相和固相碰撞加速度信号的特征频率范围分别为0~1000 Hz和6000~17000 Hz;汽相的产生可以显著增加其他相的碰撞强度。颗粒加入量增加,POM颗粒的标准偏差增大;SiC颗粒的标准偏差在循环流速较低时先减小、后增大,而在循环流速较高时增大。2种颗粒的流动沸腾传热系数受颗粒加入量的影响较小。循环流速增加,2种颗粒的标准偏差和传热系数均增大。热通量增加,2种颗粒的传热系数均明显减小。颗粒加入量较小时,2种颗粒的标准偏差随热通量的变化不明显。颗粒加入量较大时,POM颗粒的标准偏差随着热通量的增加而增大;SiC颗粒的标准偏差随热通量的变化受循环流速的影响。

A Na_(2)SO_(4)circulating fluidized bed evaporation apparatus is designed and built by combining the fluidized bed heat transfer and fouling prevention technology and the evaporation process of Na_(2)SO_(4)solution.20%(mass fraction)Na_(2)SO_(4)solution is selected as the liquid working medium.Polyoxymethylene(POM)and silicon carbide(SiC)particles are selected as the inert solid particles.The effects of the operating parameters,such as particle type,the amount of added particles(1%~3%),circulation flow velocity(0.37~1.78 m·s^(-1))and heat flux(7.29~12.14 kW·m^(-2)),on the particle collision behavior and heat transfer performance are investigated.The results show that the addition of the POM and SiC particles can enhance heat transfer.The maximum enhancement factors are 9.5%and 13.4%for the POM and SiC particles,respectively,and the corresponding operating parameters areε=1%,u=1.78 m·s^(-1),q=7.29 kW·m^(-2)和ε=3%,u=0.37 m·s^(-1),q=12.14 kW·m^(-2).The characteristic frequency ranges of the collision acceleration signals are 0~1000 Hz and 6000~17000 Hz for the liquid phase and solid phase,respectively.The generation of the vapor phase significantly strengthens the collision intensity of other phases.The standard deviation of the POM particles increases with the increase in the amount of added particles.The standard deviation of the SiC particles initially decreases and then increases at low circulation flow velocity but increases at high circulation flow velocity with the increase in the amount of added particles.The amount of added particles slightly influences the heat transfer coefficients of the two kinds of particles.The standard deviations and heat transfer coefficients of the two kinds of particles increase with the increase in circulation flow velocity.The heat transfer coefficients of the two kinds of particles obviously decrease with the increase in heat flux.The heat flux has no obvious effect on the standard deviation at low amount of added particles.At high amount of added particles,the standard deviation of POM particles increases with the increase in heat flux;however,the variation trend of the standard deviation of the SiC particles with heat flux is dependent on the circulation flow velocity.