Title:
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A novel, biomimetically inspired, flash evaporation liquid atomization system
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The increasing demands placed on conventional methods of liquid
atomization, in terms of spray quality, now mean that there is a need for a
new, disruptive, liquid atomization technology which can rapidly improve
spray performance to meet the growing sophistication required of modern
liquid spray systems. This thesis details an investigation into the mode of
action of a liquid atomization system (pMISTe) which shows promise to be
able to provide this disruptive new spray technology. Influenced by the
defence mechanism of the bombardier beetle, this atomization method
produces a large amount of volumetric shear in a body of liquid, by inducing
a flash evaporation of a proportion of the total liquid mass in an enclosed
chamber. The flash evaporation is created firstly by heating the liquid far
above its saturation temperature at an ambient external pressure - in a
chamber cavity sealed by an electronically controlled ejection valve. This
valve is released very rapidly, causing the liquid in the chamber to suddenly
`see' the ambient external pressure. It is this sudden exposure of a
superheated liquid to the low external ambient pressure that drives the flash
evaporation and the atomisation.
The atomization system was investigated using a staged experimental
method, including a mixture of Taguchi Design of Experiment (DoE) and full
factorial techniques. From these investigations the main characteristics of
the mode of action of the system were identified. These were that, in
general, increases in chamber liquid temperature caused decreasing
average droplet size, and that increases in refill flow rate caused increasing
droplet size; due to the primary flash evaporation mechanism. In addition
more complex secondary behaviours, attributed to the fluid dynamic
properties of the system, were discovered. The performance of the system is
also discussed with reference to its suitability for a range of spray
applications
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