Liquid Atomization by an Electrostatic Rotating Bell Atomizer and Spray Deposition on Solid Surfaces

In an electrostatic rotating bell (ESRB) atomizer, fluid is driven from a central orifice over the bell-cup’s surface towards its edge by the centrifugal force. After the fluid is ejected, it breaks up into droplets. Images of these spray droplets were captured using a DropSizer while operating the bell-cup at various angular frequencies (ω). After processing the images to obtain the droplet sizes, the Sauter mean diameter (SMD) was found to decrease as the angular frequency was increased. Furthermore, a stretching rate γ ̇=ω^2 R/U ̅, where R is the distance from the axis of rotation, was derived for ligaments ejected from a serrated bell-cup and it was shown that the SMD ∝ γ ̇^(-0.5).To determine how spray droplets cover a surface, images of an ESRB atomizer spraying a 20 wt% aqueous glycerol solution on a vertical glass substrate were captured from behind using a high-speed camera. The fraction of surface area coverage was obtained by processing each image. An analytical model was developed based on probability theory and used to predict, with good agreement, the fraction of surface covered by solely using the rate of droplet impingement and the droplet size. A minimum theoretical film thickness assuming full coverage was derived from the probabilistic model; when divided by the droplet diameter, it was found to be dependent only on the droplet spread factor. Droplet/surface interaction is not limited to spreading and drawback when spray droplets impinge on surfaces that are porous. As such, water was atomized using a full-cone nozzle and sprayed onto various vertical stainless-steel meshes. The mass of liquid that penetrated the mesh was measured using a scale, and images of each mesh surface were captured during droplet impingement. It was observed that droplets that landed near unblocked pores of a mesh were leached by neighbouring pools of liquid, delaying the blockage of some pores. A stochastic model, developed to determine the mass of liquid that penetrates a vertical mesh, compared well with experimental measurements. In the model, the volume required to block a pore was a function of the number of surrounding blocked pores and the mesh’s open-area ratio.

Department dc:contributor.department

Mechanical and Industrial Engineering

Year dc:date.issued

2022

Author dc:creator

• Sidawi, Khalil

Advisor dc:contributor.advisor

• Chandra, Sanjeev

• Atomization
• Coatings
• ESRB Atomizers
• Liquid Films
• Sprays
• Surface Coverage

Handle dc:identifier.uri

http://hdl.handle.net/1807/123346

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/123346