Experimental Study On The Unsteady Flow Pattern Of Dense Gas-solid Jet In Nozzle

Dense gas-solid jets are the key scientific problem in coal gasification,which is of vital reference value for the efficiency and stable operation of gasifier.In current thesis,a high-speed camera is used to film the gas-solid jets,and the PV6D and a micro pressure sensor are used to measure jet velocity at nozzle exit and the instantaneous pressure pulsation in the nozzle respectively,and the gas-solid jets are simulated by CPFD.The jet flow patterns and stability of dense gas-solid jets in pressurized nozzle are studied,and propose regulation methods.The main contents are as follows:(1)The unsteady flow patterns of dense gas-solid jets in plane nozzle are studied by using a high-speed camera.Effects of hopper pressure,particle diameter and nozzle structure parameters on the jet flow patterns are investigated.Results show that for the gas-solid jet with a particle diameter of 78 ?m,an unsteady bubble-type flow pattern appears when the hopper pressure is greater than 0.02 MPa.With the increase of particle diameter,solid fraction of gas-solid jet decreases,and the unsteady flow pattern changes from bubble-type to particle cluster.The formation frequencies of bubbles and particle cluster are in the range of 100-600 Hz,and increase with the increase of hopper pressures.There is slight effect on the jet flow of unsteady pattern when the nozzle convergence angles change.Micro pressure sensors are used to measure the pressure at different positions in the nozzle.Results show that the average pressure decreases as the flow distance increases,and the instantaneous pressure pulsation is mainly caused by the formation and evolution of bubbles and particle cluster.(2)The unsteady flow patterns of dense gas-solid jets in a circular nozzle are experimentally studied.Results show that for the gas-solid jet with small particle size,the critical hopper pressure of the unsteady flow pattern inside the nozzle is 0.02 MPa,when the hopper pressure is greater than 0.02 MPa,an unsteady flow pattern of particle cluster appears.When the particle sizes increase from 78?m to 350 ?m,the solid fraction of the gas-solid jet decreases,but all of them display the particle cluster unsteady flow patterns.The formation frequencies of particle cluster increase with the increase of hopper pressures,which are about 400-800 Hz.By changing the hopper pressure,the length of the nozzle and adding a sieve into the nozzle,the solid fraction of the gas-solid jet can be adjusted so as to effectively regulate the flow patterns of the gas-solid jets in the nozzle.(3)CPFD numerical simulation is used to simulate the dense gas-solid jet in a plane nozzle,and the important parameters such as average pressure drop,velocity and solid fraction of gas-solid jet in the nozzle are obtained,which are in good agreement with the experimental results.The results show that,from the hopper to the outlet of the nozzle,the gas pressure decreases continuously,and the momentum and energy between the gas and the particles transform each other,and the velocities of gas and particles increase continuously,and the solid fraction decreases gradually.In the connection area between the hopper cone angle and the nozzle,the gas pressure gradient is the largest,and the particle and gas velocity sharply increases,and the velocity difference between the two phases increases,and the solid fraction of gas-solid jet decrease sharply.The gas-solid interaction is violent,and the gas-solid jet becomes unstable.