An experimental investigation of the electrospray characteristics of ethanol–R141b mixture under small flow rates

Electrospray refers to the electrohydrodynamic phenomenon where the electrified liquid is sprayed under a sufficiently strong electric field, which has been implemented in a variety of applications. One of the recently emerged applications is electrospray cooling, where the mixture of ethanol and another dielectric liquid of low boiling point is usually used as the working fluid for the thermal management of microelectronics. However, most of the previous electrospray cooling studies only focused on the cooling performance, while the electrospray characteristics of the mixed working fluid under different operating conditions have not been adequately investigated. In this work, we conducted an experimental investigation of the electrospray characteristics of an ethanol–R141b mixture under small flow rates, which is one of the most frequently used working fluids for electrospray cooling. We first analyzed the variations of electrospray regimes under different applied voltages, flow rates, and volume fractions of ethanol. Among the seven observed regimes, we identified a transitional regime between the pulsating jet and stable atomization regimes and named it pulsating atomization. This transitional regime is a new observation of an existing, previously described regime named pulsating emission. The probable cause of the pulsating atomization regime was identified, and its electrospray characteristics were compared with those of the stable atomization regime obtained in this work. Following previous electrospray studies, the electric Bond number and dimensionless flow rate were adopted for the analysis of the Taylor cone profile, liquid jet breakup length, liquid atomization angle, and area of these two regimes.