On the Influence of Low-power Laser Source on the Evaporation of Single Droplets: Experimental and Numerical Approaches

This work investigates the influence of laser power on an evaporating single droplet made from an H2O and NaCl mixture. Heat and mass transfer of a single droplet with the presence of a low-power laser source (as He-Ne laser) is studied both numerically and experimentally in this article. A new model is presented to simulate water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. Moreover, laser energy is taken into consideration as a source term which is a function of the wave length of the source beam and refractive index of the droplet. Considering the involved parameters, the model is implemented in a MATLAB code and validated using experimental data obtained in this study on top of those already available in the literature. Experimental data were collected for droplets with an initial radius of 500μm at room temperature for three initial concentrations of 3%, 5%, and 10% (by mass) of NaCl in water as well as pure water droplet to provide a comprehensive validation dataset. It is shown that low-power laser source significantly increases the evaporation rate (2.7 to 5.64 for 0% and 10% initial concentration of salt, respectively) which must be taken into consideration while using laser based measurement techniques.status: publishe

An investigation on spray cooling using saline water with experimental verification

© 2015 Elsevier Ltd. All rights reserved. A natural draft dry cooling tower rejects heat in a power plant. Spray cooling of the inlet air to the cooling tower improves the total efficiency of the power plant. To overcome the scarcity of natural water sources, this research is studying the usage of saline water in spray assisted dry cooling towers. A nozzle is analysed experimentally. It is shown that the CFD model captures the spray well. A full cone spray is simulated in a vertical cylindrical domain representative of cooling tower flows. To investigate the influences of initial and ambient conditions on the spray performance, fourteen different cases are simulated and trends analysed. It is shown that the distances from the nozzle, after which the dry stream starts (wet lengths), are in the range of 4.3-5.25 m depending on the test conditions. A dimensionless study is performed on the wet length and cooling efficiency as the two main parameters. Finally, to predict the wet length and cooling efficiency, two dimensionless correlations are presented and their impact on cooling tower operation is discussed.status: publishe