Simultaneous measurement of particle size and electrostatic charge distribution in DC electric field using phase Doppler anemometry

The proposed noninvasive method of measurement of the charge level on a population of particles employs the phase Doppler anemometry (PDA) technique in conjunction with a high-resolution computer-controlled traversing system. The PDA system was used to track the motion of charged particles in the presence of a DC electric field. By solving the equation of particle motion in a viscous medium combined with the simultaneous measurement of its size and velocity, the magnitude as well as the polarity of the particle charge can be obtained. In order to detect particles with high electrical mobility and to cover the wide range of electrostatic charges the probe volume was moved mapping the velocity of the particles within the space between the parallel-plate electrodes. The preliminary experimental tests were carried out on dioctyl-phthalate aerosol droplets produced by nebulizing isopropanolic solutions using a Medic-Aid Sidestream nebulizer. The narrow size distribution, in the range from 0.5 to 3 μm, was achieved using this method of aerosolization. The experimental results show that inherent electrostatic charge on dioctyl-phthalate droplets ranged from -250 to 250 electrons with an average charge-to-mass ratio of 0.24 μC/g. After charging the aerosol using corona source the average charge-to-mass ratio increased to 20 μC/g. The results demonstrate the capability of the technique to allow real-time determination of particle size and charge with a high-particle-count rate on the order of several thousands particles per second.