Enhanced Evaporation of Microscale Droplets With an Infrared Laser

Enhancement of water droplet evaporation by added infrared radiation was modeled and studied experimentally in a vertical laminar flow channel. Experiments were conducted on droplets with nominal initial diameters of 50 lm in air with relative humidities ranging from 0% to 90% RH. A 2800 nm laser was used with radiant flux densities as high as 4 Â 10 5 W/m 2 . Droplet size as a function of time was measured by a shadowgraph technique. The model assumed quasi-steady behavior, a low Biot number liquid phase, and constant gas-vapor phase material properties, while the experimental results were required for model validation and calibration. For radiant flux densities less than 10 4 W/m 2 , droplet evaporation rates remained essentially constant over their full evaporation, but at rates up to 10% higher than for the no radiation case. At higher radiant flux density, the surface-area change with time became progressively more nonlinear, indicating that the radiation had diminished effects on evaporation as the size of the droplets decreased. The drying time for a 50 lm water droplet was an order of magnitude faster when comparing the 10 6 W/m 2 case to the no radiation case. The model was used to estimate the droplet temperature. Between 10 4 and 5 Â 10 5 W/m 2 , the droplet temperature changed from being below to above the environment temperature. Thus, the direction of conduction between the droplet and the environment also changed. The proposed model was able to predict the changing evaporation rates for droplets exposed to radiation for ambient conditions varying from dry air to 90% relative humidity

LASER SPECTROSCOPY OF HYDROGEN PEROXIDE EMBEDDED IN HELIUM NANODROPLETS

Author Institution: Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2G2Helium nanodroplets provide a gentle matrix in which to isolate reactive species for spectroscopic investigations. In our ongoing effort to generate radical species in helium nanodroplets, we have recently focused our attention on the highly reactive hydrogen peroxide (H$_2$O$_2$) molecule, a potential precursor for the hydroxyl radical. The infrared spectrum of hydrogen peroxide was measured in helium nanodroplets using a \textit{cw} OPO infrared laser in the OH stretching region. Several rovibrational transitions in the $v_5$ band of hydrogen peroxide (and HOOD) were recorded and assigned. Intensities, shapes, and assignments of lines will be discussed, as will prospects for the use of hydrogen peroxide in the production of hydroxyl radicals in helium droplets using laser photolysis