Holographic deflection imaging measurement of electric charge on aerosol particles

Hydrodynamic interactions and extreme particle clustering in turbulence

“…To verify that the level of charge was similar in our full-scale HIT chamber with the conductive shielding paint, we also measured the electric charge on particles in situ. We used a dynamic charge measurement strategy (Brown 1997) like that of Hammond, Liang & Meng (2019), designed to simply observe the presence or lack of deflection of particle trajectories in a strong electric field. When an electric field is applied instantaneously, the difference of HIT chamber particle velocity before and after the electric field is applied can be used to estimate the Coulomb drift velocity v x required to estimate charge (equation (1) of Hammond et al 2019), since the flow velocity from turbulence at the scale of the particle is tied to τ η τ e , where τ e ≈ O(100 μs) is the response time of the particle to the electric field.…”

“…We used a dynamic charge measurement strategy (Brown 1997) like that of Hammond, Liang & Meng (2019), designed to simply observe the presence or lack of deflection of particle trajectories in a strong electric field. When an electric field is applied instantaneously, the difference of HIT chamber particle velocity before and after the electric field is applied can be used to estimate the Coulomb drift velocity v x required to estimate charge (equation (1) of Hammond et al 2019), since the flow velocity from turbulence at the scale of the particle is tied to τ η τ e , where τ e ≈ O(100 μs) is the response time of the particle to the electric field. To instantaneously generate an electric field to the flow facility centre, we connected a 5000 volt high voltage power supply with a < 1 ms rise time to a pair of parallel wires separated by 1.8cm that spanned the HIT chamber which could be triggered to turn on and off at will.…”

“…We found that the resulting charge distribution was bipolar, with a mean of (C: Coulomb) and standard deviation ; hence, the charge level was of the order . To verify that the level of charge was similar in our full-scale HIT chamber with the conductive shielding paint, we also measured the electric charge on particles in situ. We used a dynamic charge measurement strategy (Brown 1997) like that of Hammond, Liang & Meng (2019), designed to simply observe the presence or lack of deflection of particle trajectories in a strong electric field. When an electric field is applied instantaneously, the difference of HIT chamber particle velocity before and after the electric field is applied can be used to estimate the Coulomb drift velocity required to estimate charge (equation (1) of Hammond et al.…”

“…When an electric field is applied instantaneously, the difference of HIT chamber particle velocity before and after the electric field is applied can be used to estimate the Coulomb drift velocity required to estimate charge (equation (1) of Hammond et al. 2019), since the flow velocity from turbulence at the scale of the particle is tied to , where is the response time of the particle to the electric field. To instantaneously generate an electric field to the flow facility centre, we connected a 5000 volt high voltage power supply with a ms rise time to a pair of parallel wires separated by that spanned the HIT chamber which could be triggered to turn on and off at will. To perform this test, we used the STB experimental set-up shown in figure 1 and the particles listed in table 1.…”

On the charged aerosols generated by atmospheric pressure non‐equilibrium plasma

“…The more economic method, holographic deflection imaging, is also used to measure electric charge on individual aerosol particles. This method uses common optical hardware and a novel particle sizing algorithm for poly‐dispersed size distributions [87]. A charged particle sample is introduced into a vertical channel air flow and a horizontal electric field, simultaneously, in‐line digital holography is used to simultaneously track particle position and decode size information.…”