Patent ID: 8011599

Claim:
A method of controlling evaporation of droplets of a liquid nebulised as a spray of droplets from a liquid droplet spray device, wherein said liquid droplet spray device comprises a reservoir for containing the liquid, a perforate membrane plate, fluid interface means for feeding the liquid from the reservoir to the membrane plate, ultrasound generating means arranged to act on the supplied liquid to cause the liquid to vibrate and to be expelled as a spray of droplets through orifices of the membrane plate, and electronic control means for controlling activation of the ultrasound generating means, wherein the method comprises the steps of: (a) providing the liquid droplet spray device; (b) supplying the liquid to a space below the perforated membrane plate; (c) providing a pulsed driving signal having a period T for activating the ultrasound generating means; (d) activating the ultrasound generating means for a period of time T on so the ultrasound generating means acts on the liquid and vibrates the liquid so as to cause the spray of droplets to be expelled at a maximum spray cloud height, wherein T on consists of T ona and T onb , and wherein vibration of the liquid by the ultrasound generating means heats the liquid; (e) de-activating the ultrasound generating means for a period of time T off , where T off ≧T on +T evap , wherein T evap is the time required for the sprayed cloud of a given liquid produced during T on to fully evaporate, and wherein T ona is the time required to ultrasonically heat the liquid, T onb is the time to spray the liquid, and T ona lasts from less than tens of milliseconds to several seconds, whereby an amount of unevaporated liquid that falls back on a surface surrounding the liquid droplet spray device is minimised.