Abstract
In electrostatic atomization, the input electrical energy causes breaking up of the droplet surface by utilizing a mutual repulsion of net charges accumulating on that surface. In this work a number of key parameters controlling the bio-oil droplet breakup process are identified and these correlations among the droplet size distribution, specific charges of droplets and externally applied electrical voltages are quantified. Theoretical considerations of the bag or strip breakup mechanism of biodiesel droplets experiencing electrostatic potential are compared to experimental outcomes. The theoretical analysis suggests the droplet breakup process is governed by the Rayleigh instability condition, which reveals the effects of droplets size, specific charge, surface tension force, and droplet velocities. Experiments confirm that the average droplet diameters decrease with increasing specific charges and this decreasing tendency is non-monotonic due to the motion of satellite drops in the non-uniform electrical field. The measured specific charges are found to be smaller than the theoretical values. And the energy transformation from the electrical energy to surface energy, in addition to the energy loss, Taylor instability breakup, non-excess polarization and some system errors, accounts for this discrepancy. The electrostatic force is the dominant factor controlling the mechanism of biodiesel breakup in electrostatic atomization.
Highlights
Bio-oils derived from the pyrolysis of biomass or Fischer–Tropsch processes are considered as one of the major future renewable energy sources [1,2,3,4]
This paper aims to interpret the electrostatic breakup mechanism for a single droplet which possesses net charges on the whole surface or partial areas using the Rayleigh instability condition
In 1964, Ryce and Wyman used the minimum energy method originated by Vonnegut and Neubauer to analyze the energy variation before and after the breakup of droplets [19,21]. In their surface-charged droplets breakup analysis they assumed: (a) that two spherical drops for the electrical interaction to be negligible in the final state; (b) that the division takes place so as to make the surface energy and electrical energy of electrical energy of final state reach a minimum; (c) that there is a possibility of division with an electrical charge less than that given by the Rayleigh instability conditions; (d) that the permittivity of the surrounding air is uniform
Summary
Bio-oils derived from the pyrolysis of biomass or Fischer–Tropsch processes are considered as one of the major future renewable energy sources [1,2,3,4]. The implementation of electrostatic atomization can separate a bio-oil stream into fine droplets with a narrow size distribution. This process does not require a high air pressure like conventional atomization techniques do The previous excellent work has determined the highest possible specific charge and the theoretical interpretation of the breakup mechanism(s) of hydrocarbons using the Rayleigh limit or other energy conservation methods for diesel and other hydrocarbons have been done, the current literature does not contain fundamental understanding of the electrostatic breakup mechanism of bio-oils in sprays.
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