Electrostatic sensors – Their principles and applications

Online Measurement of the Size Distribution of Pneumatically Conveyed Particles Through Acoustic Emission Detection and Triboelectric Sensing

“…For years, various on-line measurement techniques have been proposed to realize particle sizing, including laser diffraction, digital imaging, electrostatic sensing, microwave scattering and acoustic emission detection [4][5][6][7][8]. However, as the particle flow in a pneumatic pipeline is very complex in terms of gas-solids two-phase flow nature, such as inhomogeneous particle distributions, irregular velocity profiles, variable particle size and shape distributions, moisture content and etc., the particle flow measurement is recognized as a longstanding industrial problem [9,10]. Due to the inherent complexity of gas-solids two-phase flow in a duct, harsh environmental conditions and high installation and maintenance costs, there have been very few on-line particle sizing instruments currently operating in industry.…”

“…Triboelectric phenomenon exists widely in our daily lives or industrial activities [19,20]. The transportation of particles in a pipe generates triboelectric charges on the particles due to interparticle interactions, particle-air frictions and particle-wall collisions [9]. For the particle velocity measurement, triboelectric sensing is regarded as the most cost-effective method [9,16].…”

“…The transportation of particles in a pipe generates triboelectric charges on the particles due to interparticle interactions, particle-air frictions and particle-wall collisions [9]. For the particle velocity measurement, triboelectric sensing is regarded as the most cost-effective method [9,16]. Hu et al [8] and Zhang et al [15] used a set of ring-shaped electrodes to measure the particle impact velocity.…”

“…However, the impacting area of the AE probe occupies only a very small fraction of the pipe cross section. In view of the complex nature of particle flow in a pneumatic conveying pipeline, in particular, inhomogeneous particle distribution and irregular velocity profile [9], the circumferentially averaged particle velocity is different from the particle impact velocity which is local to the waveguide. Therefore, the use of air velocity or circumferentially averaged particle velocity as the particle impact velocity will introduce significant errors in particle size measurement.…”

“…Firstly, two sets of arc-shaped triboelectric sensor arrays next to the waveguide are used for the first time to measure the impact velocity of particles close to the waveguide. Arc-shaped electrodes are suitable for the measurement of local particle velocities as they are sensitive to particles in its vicinity [9], which is more representative of the particle impact velocity than that from the ring-shaped electrodes. Secondly, the Gaussian model is used for the first time to predict peak distribution generated by large and small particles in order to reduce the deviation between the detected peak distribution and expected distribution due to overlapping impacts and environmental noise.…”