Material Normalised RMS (mV/g-1s) Lactose 200M 121 ± 15% Avicel PH102 30 ± 3% Avicel PH101 23 ± 8% Maize Starch 12 ± 7% Lactose #316 Fast Flo 4 ± 7% Feasibility study on the in-line measurement of pharmaceutical powder mass flow rate and charging characteristics using an electrostatic powder flow sensor (EPFS). Hill-Izani, N.Y., Smith, G., Armitage. D.A., Polygalov, E. Pharmaceutical Technologies, School of Pharmacy, De Montfort University, Leicester LE1 9BH Results 16.548 33 21.998 62 26.308 28 30.601 90 R² = 0.88 0 5 10 15 20 25 30 35 40 0 1 2 3 4 5 6 7 8 9 Mean RMS (mV) Mean mass flow rate (g/s) 100 rpm 120 rpm 160 rpm 140 rpm 380.82 116 521.37 139 572.27024 673.21 304 R² = 0.96 0 200 400 600 800 0 1 2 3 4 5 6 7 Mean RMS (mV) Mean mass flow rate (g/s) 100 rpm 120 rpm 140 rpm 160 rpm 38.974 25 51.094 51 60.149 30 65.85456 R² = 0.92 0 20 40 60 80 100 0 1 2 3 4 5 6 7 Mean RMS (mV) Mean mass flow rate (g/s) 100 rpm 120 rpm 140 rpm 160 rpm 60.377 08 55.837 13 60.326 07 63.922 40 R² = -7.16 0 20 40 60 80 100 0 1 2 3 4 5 6 7 Mean RMS (mV) Mean mass flow rate (g/s) 100 rpm 120 rpm 140 rpm 160 rpm 74.520 38 81.850 41 75.881 74 76.844 03 R² = -15.13 0 50 100 150 200 0 1 2 3 4 5 6 7 Mean RMS (mV) Mean mass flow rate (g/s) 100 rpm 120 rpm 140 rpm 160 rpm Lactose #316 Fast Flo Lactose 200M Maize starch Avicel PH101 Avicel PH102 Powder mass flow rate vs RMS signal Fig. 5. Mean powder mass flow rate and mean RMS signal correlation, recorded for five pharmaceutical powders conveyed using the twin screw feeder across a range of screw speeds. Powder mass flow rate vs powder velocity Conclusions Table 3. Ranking in the normalised charges recorded for five pharmaceutical powders conveyed at 100rpm. Introduction Materials & Methods Fig. 2. EPFS and measurement electronics principle of operation. References DAQ PC Balance - + - e- + + Charge output Inverting input of Op. Amp. Flow of current Summing point (virtual ground) EPFS Charged particle Flow direction Induced charge • Electrostatic induction sensors are widely used to measure in-line particle flow parameters in pneumatic conveying processes [1], but are rarely utilised in pharmaceutical flow regimes. • Triboelectrification may result in powder adhesion to processing equipment [2]. Material charging differences are typically measured using tribo-series and Faraday Cup [3]. However, tribo-series only qualitatively ranks charging behaviour specific to the conditions at which the measurements were performed, whereas the Faraday Cup cannot be integrated into processes. • In this study, an electrostatic powder flow sensor (EPFS) was developed to directly measure in-line flow parameters and charging behaviour of powders conveyed in a pharmaceutical process. EPFS Volumetric twin screw feeder (T20, K-Tron) Solid-state balance Fig. 3. Lean phase conveying system, (measurement electronics not shown). • Electrostatic and gravimetric measurements were recorded for five “as received” powders and one oven-dried powder, which were conveyed using a twin screw feeder. • Particle velocity was obtained via cross-correlation algorithm (1), using the upstream and downstream electrostatic signals. • RMS signal was calculated by averaging values across consecutive 0.05s (20Hz) intervals over the entire electrostatic dataset. • Charging behaviour was analysed by normalising the RMS of the electrostatic signal against the mass flow rate. Fig. 4. Powder deposition behaviour for a) Avicel PH102; b) Lactose #316 Fast Flo; c) Avicel PH101; d) Lactose 200M and e) maize starch. • Particle velocity was independent of the screw speed (Table 1). • Differences in the particle velocities were thought to be influenced by powder deposition sizes (Fig. 4), which resulted from differences in the cohesivity of the entrained powder. • Similar rankings were shown between particle velocity and the cohesivity dependant FT4 parameters (Table 2). • Reasonable correlation was shown (R2 > 0.88) between the mass flow rate and RMS obtained