Abstract
The electro-spraying process can be regular and periodic, consisting of cyclical phases of initiation (meniscus, drop, and/or jet), pulsation, deformation and separation. This paper presents an experimental study on the repetition frequency of drop and/or jet ejection from the capillary end with various spraying modes during an electro-spraying process of deionized (DI) water. The influence of operating parameters such as applied voltage, liquid flow rate, electrical conductivity (DI) and the number of emitters is considered. The time evolution of drop and/or jet initiation, pulsation, deformation and separation from the capillary tip or meniscus was captured and analyzed in detail in different spraying modes. The repetition frequency was calculated offline based on the time-resolved images captured by a high-speed camera and was found to be highly affected by the electrical strength and dependent on the spraying mode. This frequency firstly increased and then decreased with an increase in applied voltage. Peak frequency and the applied voltage were related and both correlated to the liquid flow rate. The repetition frequency was very sensitive to the applied voltage at a low volume flow rate. Particular attention was given to the electro-spraying characteristics of single, double and triple emitters. The similarities and differences are discussed.
Highlights
Electro-spraying is a well-established technique that, by applying high voltage on the liquid surface at a nozzle outlet, a drop or jet is formed, which further disintegrates into fine drops due to electric stresses
It offers several benefits compared to other atomization methods where trajectory and size of the fine drops could be controlled by varying the applied voltage and adjusting the liquid flow rate (Chen et al, 1999; Wilhelm et al, 2003; Mei and Chen, 2008).As a result, electro-spraying has been widely used in medical protein production (Gomez et al, 1998), painting and printing (Lee et al, 2013), film coating (Miao et al, 2002), fuel injection (Waits et al, 2010; Gan et al, 2015, 2016), micro- and nano-particles generation (Jaworek and Sobczyk, 2008; Gañán-Calvo et al, 2013), and particle collection (Kim et al, 2010; Jaworek et al, 2013; Chen et al, 2017)
Time Resolved Spraying Mode Based on meniscus, drop and/or jet formation pattern, the electro-spraying could be classified into dripping, spindle, pulsating, cone-jet and multi-jets modes, under combined effects of liquid property, applied voltage, volume flow rate and background gas property
Summary
Electro-spraying is a well-established technique that, by applying high voltage on the liquid surface at a nozzle (capillary) outlet, a drop or jet is formed, which further disintegrates into fine drops due to electric stresses. Substantial works have been reported to study the effect of various parameters on the formation, characterization and control of the spraying modes. Among such parameters are the liquid type (Delamora and Loscertales, 1994; Lopez-Herrera et al, 2003), surface tension(Sato et al, 1998; Samalikova and Grandori, 2005), liquid conductivity(Tang and Kebarle, 1991; Modesto-Lopez and Biswas, 2010), nozzle diameter (Kim et al, 2011; Zhang et al, 2012), applied voltage (Marginean et al, 2009), power supply (Sung et al, 2004, Higashiyama and Saito, 2013) and the liquid volume flow rate (Lopez-Herrera et al, 2003)
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