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A twin-head electrospray (THES) aerosol generation system with one spray head producing positively charged particles and the other producing negatively charged ones has been constructed and its performance has been experimentally evaluated in this study. The charge-enhanced coagulation between oppositely charged droplets generated by the THES was verified by the measuring the resultant particle size distributions via a scanning mobility particle sizer (SMPS), the imaging of dye-labeled coagulated particles via a fluorescence microscope and the chemical composition characterization of generated particles via high-efficiency liquid chromatography (HPLC). The characterization time of charge-enhanced coagulation in our study's generator was estimated to be in the order of 10 −5 s under the tested operational conditions. The size evolution due to charge-enhanced coagulation was studied for particles with initial sizes ranging from 10 to 710 nm. Compared with those prior to the coagulation, the size distributions of particles upon coagulation became broader. Further, regardless the initial charge levels, the peaks of resultant particle size distributions were about 1.3 times larger than the corresponding ones before coagulation, indicating the collision of two oppositely charged particles. As expected, the number of charges on the resultant particles was significantly reduced in the THES generation system. However, only a small fraction of resultant particles carried zero electrical charge. Our study also evidenced that a maximal 70% transmission efficiency can be achieved for the THES system. It is therefore concluded that the twin-head ES technique makes it feasible to take unique advantage of electrosprayed particles without any charge reduction scheme. |
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