Vertical gas holdup distributions in ambient gassed, hot sparged and boiling systems in stirred tanks using multiple 6 hollow blade disc turbines(CD-6)are reported.The local gas holdup in the boiling system is dramati...Vertical gas holdup distributions in ambient gassed, hot sparged and boiling systems in stirred tanks using multiple 6 hollow blade disc turbines(CD-6)are reported.The local gas holdup in the boiling system is dramatically different from that in the ambient gassed or hot sparged system whether in terms of value or distribution.Under the same total gas flow rate and impeller speed,the local gas holdup is much smaller in the boiling system than that in the ambient gassed or hot sparged system.The hot sparged system has similar vertical gas holdup distributions,with maxima in similar locations but with smaller local gas holdup overall,to those of the ambient gassed system.The designs of existing hot sparged and boiling reactors are based on the ambient gassed system and not optimal.The results are of particular relevance to the design and operation of reactors with hot sparged or boiling liquids.展开更多
The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas hold...The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas holdup, relative power demand, and volumetric mass transfer coefficient under different conditions were compared. The results show that, the increasing stirring power or gas flow rate is beneficial in promoting the overall gas holdup and volumetric mass transfer coefficient, while the increasing system viscosity weakens the mass transfer in a shearing–thinning system. Among the three turbines, the six curved-blade disc turbine(BDT-6) exhibits the best gas pumping capacity; the six 45° pitched-blade disc turbine(PBDT-6) has the highest volumetric mass transfer coefficient at the same unit volume power.展开更多
Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux(RMF) model....Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux(RMF) model.With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerically. The modeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation,while the modeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model, simulation is carried out for CO2 absorption into aqueous Na OH solutions in a packed column(0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are compared with the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.展开更多
文摘Vertical gas holdup distributions in ambient gassed, hot sparged and boiling systems in stirred tanks using multiple 6 hollow blade disc turbines(CD-6)are reported.The local gas holdup in the boiling system is dramatically different from that in the ambient gassed or hot sparged system whether in terms of value or distribution.Under the same total gas flow rate and impeller speed,the local gas holdup is much smaller in the boiling system than that in the ambient gassed or hot sparged system.The hot sparged system has similar vertical gas holdup distributions,with maxima in similar locations but with smaller local gas holdup overall,to those of the ambient gassed system.The designs of existing hot sparged and boiling reactors are based on the ambient gassed system and not optimal.The results are of particular relevance to the design and operation of reactors with hot sparged or boiling liquids.
基金Supported by the Zhejiang Provincial Natural Science Foundation of China(LY16B060003)the National Natural Science Foundation of China(21776246)
文摘The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas holdup, relative power demand, and volumetric mass transfer coefficient under different conditions were compared. The results show that, the increasing stirring power or gas flow rate is beneficial in promoting the overall gas holdup and volumetric mass transfer coefficient, while the increasing system viscosity weakens the mass transfer in a shearing–thinning system. Among the three turbines, the six curved-blade disc turbine(BDT-6) exhibits the best gas pumping capacity; the six 45° pitched-blade disc turbine(PBDT-6) has the highest volumetric mass transfer coefficient at the same unit volume power.
基金Supported by the National Natural Science Foundation of China(21376163)
文摘Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux(RMF) model.With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerically. The modeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation,while the modeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model, simulation is carried out for CO2 absorption into aqueous Na OH solutions in a packed column(0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are compared with the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.
