A model for predicting bubble rise velocity in a pulsed gas solid fluidized bed

Bed stability, and especially the bed density distribution, is affected by the behavior of bubbles in a gas solid fluidized bed. Bubble rise velocity in a pulsed gas-solid fluidized bed was studied using photographic and computational fluid dynamics methods. The variation in bubble rise velocity was investigated as a function of the periodic pulsed air flow. A predictive model of bubble rise velocity was derived: ub=ψ(Ut+Up-Umf)+kp(gdb)(1/2). The software of Origin was used to fit the empirical coefficients to give ψ = 0.4807 and kp = 0.1305. Experimental verification of the simulations shows that the regular change in bubble rise velocity is accurately described by the model. The correlation coefficient was 0.9905 for the simulations and 0.9706 for the experiments.

CFD-DEM investigation into flow characteristics in mixed pulsed fluidized bed under electrostatic effects

Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance.In the process of fluidization,electrostatic interaction between particles will obviously accelerate particle agglomerate formation,which consequently reduces the fluidization performance.Pulsed gas flow injection is an efficient method to enhance particle mixing,thereby weakening the occurrence of particle agglomerate.In this study,the two-dimensional hybrid pulsed fluidized bed is established.The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects.Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition.Results show that in the presence of static electricity,the bubble generation position is lower,which is conducive to the particle flow.Pulsed gas flow can increase the particle velocity and improve the diffusion ability.The bubble generation time is different at different frequencies,and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics.Different gas flow ratios have significant impacts on the particle movement amplitude.When the pulse gas flow accounts for a large ratio,the particle agglomerate tends to be larger.Therefore,in order to improve the fluidization effect,the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.

Apparent viscosity of mixed particle system in pulsed gas-solid separation fluidized bed

The apparent viscosity reflects the resistance of the fluidized medium in the bed to the beneficiation particles,which directly affects the separation time and mismatch content.So,the falling-ball method was used to measure the apparent viscosity of a binary medium in a pulsed fluidized bed by varying the gas velocity,pulsation frequency,and fine particle content.The results show that with increasing gas velocity and fine particle content,the apparent viscosity of the bed gradually decreased,whereas it first decreased and then increased with pulsation frequency increasing and achieved a minimum value in the range of 4-6 Hz.Within limits,the adjustment of gas velocity and fine content can effectively reduce the apparent viscosity and improve the separation process.A model for predicting the apparent viscosity in a pulsation separation fluidized bed was established with good accuracy.