Investigation of droplet distribution in electrohydrodynamic atomization (EHDA) using an ac-based electrical capacitance tomography (ECT) system with an internal-external electrode sensor

Electrohydrodynamic atomization (EHDA) has recently been applied to the fabrication of polymeric micro-or nano-particles or fibres for drug encapsulation. For in situ monitoring of pharmaceutical particle fabrication in an EHDA encapsulation chamber, electrical capacitance tomography (ECT) has been used as a non-invasive measurement technique. The key achievements made during this study include the successful monitoring of very dilute droplet and particle trajectories in different regions of the EHDA encapsulation chamber. The results of both a charge/discharge ECT system and an ac-based ECT system are compared. A new type of ECT sensor with internal and external electrodes is used to improve the sensitivity of ECT measurement for detection of the objects in the central area of the EHDA encapsulation chamber. The water-air and dicholoromethane (DCM)-air systems in the dripping and spray modes have been investigated to determine the feasibility of imaging water and DCM droplets of low concentration in the encapsulation chamber using ECT.