Prediction of refractive index profiles within evaporating droplets

Spray evaporation is a complex thermophysical process. An important parameter controlling the evaporation and chemical reactions within and at the surface of the liquid phase is the droplet temperature. To measure the droplet temperature Laser Light Scattering techniques are expedient. However, strong gradients of the refractive index in the droplet can lead to erroneous measurements. To assess the influence of refractive index profiles inside the droplets on the measurement accuracy numerical simulations are performed whereby the 1D spherical symmetric distribution of droplet temperature is resolved. The light scattering of droplets with the inferred refractive index profiles was studied to evaluate the influence on the temperature measurement. Then, based on this information the measurement positions along the droplet trajectories where it is possible to measure the droplet temperature were determined. Measured droplet temperatures were compared with the predicted droplet temperatures.