Research Of Flow And Heat Transfer Behaviors In The Three-phase Multi-pipe Circulating Fluidized Bed Evaporator

The vapor-liquid-solid (V-L-S) circulating fluidized bed evaporator can enhanceheat transfer and also defense and clean fouling effectively, which makes it occupy apromising application prospect. Research on the three-phase flow heat exchanger hasattracted wide attention. In order to research further about its performance, atransparent multi-tube three-phase forced-circulating fluidized bed evaporator wasbuilt and a circulating pump was used as forced-circulation equipment. The effects ofcirculating flow rate, heat flux of heating tubes, the volume and species of addedparticles on solid holdup of heating tube bundle, the thermal efficiency and powerconsumption of circulating pump were studied with six kinds of particles as the solidphase by using online data acquisition and processing system and the CCD imagegathering and processing system.The research about the solid holdup of heating tube bundle shows that solidholdup in heating tube bundle increases with the increase in the circulating flow rate,but the increase degree in each tube varies: a larger increase in No.1and No.5tube,and a relatively flat increase in No.24tube. Solid holdup in each tube of heating tubebundle shows a slight increase while the heat flux increases, indicating that theinfluence of heat flux on the solid holdup is very weak. Solid holdup in heating tubebundle increases clearly with the increment of volume of added particles, shows thatthe increase in the amount of added particles can effectively improve the solid holdupthe heating tubes. To different particle settling velocity of the particles, solid holdupin different tube show different trends: solid holdups in No.1and No.5tube dropdown as the particle settling velocity increases, while in No.24tubes, maximumsolid holdup appear when added particle is3.15mm POM.The investigation about the thermal efficiency of the evaporator shows that thethermal efficiency of the evaporator increases while the circulating flow rate increases.The thermal efficiency increases significantly with the increment of heat flux, whichindicates that heat utilization is better at high heat flux. The thermal efficiency growswith the growth of the amount of particles, and the increase tendency slows downgradually. The amount of particles has a more obvious effect on the thermal efficiency at low heat flux. As particles can be completely fluidized, it can be seen that thegreater particle density and thermal conductivity, the higher the thermal efficiency.A circulating pump was used as forced-circulation equipment, and the powerconsumption of pump increases modestly with the increment of the volume of addedparticles and particle settling velocity. The power consumption of pump is greater incold model than that in heating model.