Date of Award

2015

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

Keywords

evaporation, paint spray, PDA, RBA

Supervisor

Paul Henshaw

Rights

info:eu-repo/semantics/openAccess

Abstract

Evaporation of paint solvents is a significant part of a automobile's environmental footprint. Relationships between evaporation of droplets and application parameters were developed to optimize the spray process and reduce the environmental footprint by reducing paint waste in the booth. A Phase Doppler Anemometer (PDA) was used to calculate the evaporation of spray from a rotary bell atomizer (RBA). The change in volume flux between consecutive planes was found to be significant. The total evaporation when spraying water was 0.93 cm3/s and 0.46 cm3/s between 22.5-30.0 cm and 30.0-37.5 cm axial distances, respectively. Tests were performed to determine the effects on evaporation of water spray for three rotary bell atomizer operational parameters: shaping air flow rate, bell speed and liquid flow rate. Evaporation rate increased with higher flow rate and bell speed, but no statistically significant effects were obtained for shaping air flow rate or interactions between parameters. For clearcoat sprays, evaporation increased with increasing bell speed and increase of flow rate from 100 to 200 cm3/s. The combination of higher electrostatic potential and lower flow rate decreased the mean particle diameter. Particle mean velocity increased with increasing bell speed and flow rate. The trend of mean diameter decreasing with an increasing bell speed that was found in water and clearcoat, was also found for basecoat. However, the measurements with basecoat had a low statistical viability, and were deemed unsuitable for calculating the flux through parallel planes, which is required for calculating the evaporation. A model was proposed by combining two existing models from the literature; and the RBA nozzle parameter, K1, and the evaporation rate, K, were calculated for water and clearcoat at 24°C. K1 was found constant for clearcoat but was flow rate and bell speed dependent for water. The value of K was found to be between 860-1270 μm2/s and 1300-2000 μm2/s for water and clearcoat, respectively. The initial particle diameter for different bell speeds and flow rates can be calculated using this RBA constant and the model. A model for the evaporation of droplets at any axial distance was also development.

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