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

The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na_(2)SO_(4) circulating fluidized bed evaporator.The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε(1%–3%),circulation flow velocity u(0.37–1.78 m·s^(-1)),and heat flux q(7.29–12.14 kW·m^(-2)).The results show that the enhancement factor reach up to 14.6%by adding polytetrafluoroethylene particles at ε=3%,u=1.78 m·s^(-1),and q=7.29 kW·m^(-2).Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles.The standard deviation increases with the increase in circulation flow velocity;however,the enhancement factor initially decreases and then increases.The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity,but initially increases and then decreases at high circulation flow velocity.The enhancement factor decreases with the increase in heat flux.The enhancement factor in Na_(2)SO_(4) solution is superior to that in water at high amount of added particles.The empirical correlation for heat transfer is established,and the model results agree well with the experimental data.