2025 Volume 64 Issue 2 Pages 166-174
The evaporation rates of pico-liter droplets of water are measured with a visualization system to verify an estimation model and to investigate the effect of surrounding droplets. The visualization system consists of a piezo inkjet head with a linear actuator, camera, LED (light emitting diode) light, media, and thermo-hygrometer, and can measure the contact radius and the volume of a droplet. The evaporation rate can be estimated from the evolution of the droplet volume. The experimental results are compared with an existing evaluation model and simulation results. In the case of a single droplet evaporation, the effect of latent heat due to evaporation is discussed with the comparison among the experiment, estimation model and simulation. With the consideration of droplet cooling that is estimated from the simulation, estimated evaporation rate and evolution of droplet volume show good agreement with the experiment. Temperature cooling due to evaporation is an important factor for a droplet evaporation. In the case of multi-droplet evaporation, the effect of surrounding droplets is investigated with the consideration of droplet cooling due to evaporation. The results confirm when the distance between droplets becomes closer, the effect of surrounding droplets becomes greater.