Evaporations rates of a fog in a cylindrical acoustic resonator

Motivated by the potential use of fog as a load or a source in two-phase thermoacoustic devices, evaporation rates of low-density water fog in a cylindrical acoustic resonator were investigated experimentally, using 2D mass flow visualization and PIV techniques . Evaporation rates were measured under the influence of a low frequency acoustic standing wave of various Acoustic Pressure Amplitude [APA] values. Fog evaporation and settling were monitored between the resonator’s pressure and velocity Anti-nodes . The results revealed two distinct regimes of acoustically enhanced evaporation rate: linear at Strouhal number (St) values 0.5<St<0.25 obtained at lower APA values, and exponential at 0.12<St<0.06 obtained at higher APA values. Such behavior is explained through combined influence of fluctuations of the boundary layer surrounding each droplet due to pressure fluctuations and the periodic fluctuations in droplets velocity. Phase lag between the pressure and velocity oscillations is shown to be the major factor in setting the evaporation rate.