PDPA Investigation on an Electrostatically-Assisted Twin-Fluid Atomization Flow

Abstract

The Phase Doppler Particle Analyzer (PDPA) technique is utilized for characterizing the droplet sizes and velocity profiles in an electrostatic spray flow which is atomized using the aerodynamic forces assisted with electrostatic forces. An electrostaticallyassisted twin-fluid atomization system is presented and spatial distributions of the droplet size and two-dimensional velocity components are measured simultaneously at each specified point. The droplets are firstly ejected from a liquid jet through the nozzle by aerodynamic shear forces, and the breakup mechanism of such an electrostatically-assisted twin-fluid atomization is investigated using the Rayleigh instability conditions through studying the specific surface charges on these droplets measured by a Faraday canister. The discrepancies between experiment data and Rayleigh limit for specific charges of droplets are presented and discussed due to energy transforming from electrical energy to surface energy, energy loss, Taylor instability breakup and nonexcess charge polarization. The measured average velocity profiles and their RMS (root mean square) velocity values for two different scale drops further reveal the effects of the aerodynamic and electrostatic forces on the atomization process.

A comparative study on droplet characteristics and specific charge of ethanol in two small-scale electrospray systems

“…D 32 can be defined as follows:where N is the total number of droplets ( N ≤ 2000), D i is the diameter of the individual droplets at the specific measuring position. D 32 is known as Sauter Mean Diameter (SMD) 12 . It is well known that droplet size is the most relevant parameter to evaluate the performance of the spraying.…”

“…The RMS velocity was derived from the PDA measured velocity profiles using the following equation 12 :where represents standard deviation of the axial velocity of the droplets, is mean velocity at the specific measurement point, v i is the velocity of individual droplet, N is the total number of droplets at the specific measurement point ( N ≤ 2000). It is well known that the lower RMS velocity indicates the more stable spraying process.…”

“…It has been applied in many areas such as fuel atomization in combustion systems 2,3 , controlled droplet generation 4,5 , electrospinning 6,7 , thin film deposition 8,9 and electrospray ionization-mass spectrometry applications 10,11 . Meanwhile more and more attention has been focused on the micro-power systems using micro-scale combustors due to the higher specific energy of liquid hydrocarbons than that of batteries 12,13 . But it is difficult to keep stable flame inside the micro-combustor, due to limitation by short residence time and high heat loss rate 14,15 .…”

Efficient Planar-Heterojunction Perovskite Solar Cells Fabricated by High-Throughput Sheath-Gas-Assisted Electrospray

“…The associated electrostatic free energy, which increases with V A , partly offsets the intrinsic molecular forces giving rise to surface tension, making it easier for the sheath gas to tear the solution into finer droplets . Moreover, as the charge-to-surface-area ratio of these droplets increases during solvent vaporization, which is accelerated by the dry ambient of the sheath gas, further disintegration of the droplets occurs via Coulomb fission. , The droplets deposited on the substrate are agglomerated into a film, and its drying rate is controlled by adjusting the substrate temperature, which determines the surface coverage, thickness uniformity, and crystallite size of the resulting MAPbI 3– x Cl x film.…”

“…Here, we demonstrate that efficient PSCs can be fabricated using an electrospray process, with a throughput that is several tens of times higher than that achieved using the conventional electrospray. This was enabled by using sheath-gas-assisted electrospraya technique that has previously been applied to electrospray ionization mass spectrometry, atomization of highly viscous and/or conductive liquids, − and generation of uniform nanoparticles, , where a strong aerodynamic force generated by the flow of a sheath gas having a high dielectric strength, such as N 2 , CO 2 , and SF 6 , pneumatically nebulizes the liquid, thus allowing for stable electrospray of high-σ liquids at high V A . Exploiting this unique feature, we show that a highly conductive precursor solution for CH 3 NH 3 PbI 3– x Cl x (MAPbI 3– x Cl x ) is successfully nebulized in a stable jet mode at high Q sol of 50 μL/min, ∼60 times higher than that achieved using the conventional electrospray .…”