Measurement Of Mass Flow Rate Of Pneumatically Conveyed Particles Using An Electrostatic Sensor Array

On-line flow measurement of particles in a pneumatic conveying pipe is indispensable for the optimal control of industrial processes,enhancing productivity and reducing energy consumption.Measurement of the cross-sectional distribution of particle concentration and velocity is essential for the determination of the mass flow rate of pneumatically conveyed particles.The flow profile of solid particles in a dilute gas-solid transport pipe can be highly inhomogeneous depending upon the pipe orientation,measurement position,conveying air velocity etc.In consequence,incorrect quantification of the volumetric concentration,velocity and mass flow rate of conveyed particles may be obtained using most of the available measurement methods.In this study,an intrusive electrostatic sensor array is designed and implemented for measuring localised volumetric concentration and velocity profiles of pneumatically conveyed particles in a square-shaped pipe.The mean particle flow parameters are obtained based on the localised flow parameters over the whole pipe cross section.The main research includes the following aspects:(1)An electrostatic sensor array consisting of nine pairs of strip-shaped electrostatic electrodes is designed and implemented.The signal feature extraction and cross correlation velocimetry are performed to obtain the localised concentration and velocity of particles,respectively.The cross-sectional relative concentration and velocity profiles of particle flow are obtained using the measured localised particle parameters and the parameters of particles near pipe wall obtained from a non-intrusive electrostatic sensor array mounted on the pipe wall.(2)Experimental tests were conducted under sixteen test conditions,i.e.combinations of four air velocities and four mass flow rates.Experimental tests using plain flour were conducted on vertical and horizontal pipe sections(with 54 mm inner side)on a gas-solid two-phase test rig successively.Experimental results show that in horizontal and vertical pipes,more particles are transported at the bottom of the pipe and the region near pipe walls,respectively.Particles in the centre of both horizontal and vertical pipe cross sections travel faster compared with those close to the pipe walls.The concentration distributions of the particles in the pipe are more uniform under higher particle mass flow rate conditions.(3)The measurement accuracy of the non-intrusive electrostatic sensor array is essentially affected by the choice of weighting coefficient,indicating that the intrusive sensor array is more reliable when measuring the local parameters inside the pipe.Therefore,the newly-designed electrostatic sensor array can be used to calibrate other types of non-intrusive ones for flow parameter measurement in a square-shaped pipe.(4)Particle mass flow rate are obtained based on the calibration under sixteen test conditions.The accuracy of the measurment result from the a square-shaped electrostatic sensor array is the lowest.Under higher or lower mass flow rate conditions,the accuracy of the measurment results from the intrusive and non-intrusive electrostatic sensor arrays are the highest,respectively.