Study Of The Characteristics Of Bubbles In Fluidized Bed Through Electrostatic Sensor Arrays

Bubble is one of basic characteristics of gas-solid fluidized bed and has significant influences on the mechanics of the gas-solid flow in fluidized bed such as gas-solid mixing,mass and heat transfer within the fluidized bed.The bubble rising velocity and diameter are two important parameters characterizing bubble behaviors.Bubble rising velocity affects the turbulence and reaction time of the gas and solid phases while the mixing quality of gas and solid is dependent on the bubble diameter.Therefore,it is of great significance to measure the bubble rising velocity and diameter in practice.The present methods for the bubble parameters measurement are limited in industrial application.This paper proposes a measurement method for simultaneous measurement of the bubble rising velocity and diameter through electrostatic sensor arrays.Further the bubble behavior within a two-dimensional fluidized bed is investigated experimentally.A multi-channel cross-correlation velocity measurement system is developed to achieve the online measurement of the bubble rising velocity at various locations in the fluidized bed.The hardware system mainly includes the electrostatic signal conversion circuit,power supply and data acquisition system.A software program is designed for the data acquisition,calculation,storage and display.Bubble diameter can be calculated based on the measured bubble rising velocity with corresponding processing methods.The experimental results are compared with those obtained from optical imaging to verify the feasibility of the measurement method.A two-dimensional fluidized bed is built to carried out the bubble measurement experiments with three different kinds of solid particles.The bubble characteristics at different fluidization numbers are investigated.Experimental results show that bubbles appear when fluidization velocity exceeds the critical fluidization velocity of particles.During the rising process of bubble,its rising velocity and diameter increase.Besides,the bubble rising velocity and diameter increase with increasing fluidized air flow rate.Experimental results in the two-dimensional fluidized bed showed that the characteristics of bubbles is in agreement with the Davidson semi-empirical equation.The rising velocity of the bubble is linear with fluidized air velocity and square root of diameter.