A study on the measurement of charge and surface potential of charged liquid droplets in spray painting
Rito Jin1, Yuta Kurihara1, Masatoshi Daikoku1, *, Minori Shirota2, Taimei Miyagawa2, Takahiro Okabe2, Yoshiya Matsukawa3, Hideyuki Aoki3, Yasuhiro Saito4, Junichi Fukuno5
* The author to whom correspondence should be addressed.
1 Hachinohe Institute of Technology, Japan
2 Hirosaki University, Japan
3 Tohoku University, Japan
4 Kyushu Institute of Technology, Japan
5 Honda Motor Co., Ltd., Japan
Abstract
The charge and surface potential of liquid droplets falling from a nozzle were measured in order to clarify the charging and discharging properties of droplets formed under an applied voltage during automotive spray painting. The charge per droplet was found to initially increase with increasing voltage regardless of the test liquid used but then began to decrease due to a reduction in droplet size, the generation of satellite droplets, and electrical discharging. The ‘electrical surface tension’ was also determined and was found to be nondimensionally correlated with the surface charge density. The surface potential for moving droplets, stationary metallic disks, and spheres was measured using an electrostatic sensor, whose principles were applied in an attempt to correct the displayed values based on the size of the droplets. A regression analysis was also used to correct the displayed surface potentials. It was found that accurate measurement of the surface potential may be possible even for small particles.
Keywords - Charge, surface potential, liquid droplets, spray painting.