Measurement of droplets size and temperature under different conditions by using rainbow technique

The precise measurement of particle size and temperature during the droplet evaporation process is critical yet remains challenging. A non-intrusive method named the rainbow technique is utilized to investigate the evaporation process of ethanol droplets. By analyzing the rainbow patterns captured in the vicinity of the rainbow angle, the average temperature and size of droplet can be simultaneously extracted. Then, the evaporation process of ethanol droplet stream is conducted under ambient temperatures of 293 K to 313 K. The results validate the accuracy of the rainbow technique in measuring the droplet size and refractive index. Furthermore, a higher ambient temperature and a smaller droplet induce a larger reduction rate in droplet diameter. Moreover, the experimental results are quantitatively compared with the simulation data. Both the numerical and experimental results exhibit a reduction tendency of temperature, revealing the cooling effect as a result of vaporization. Besides, it indicates that the measured temperature by the rainbow technique is the equivalent temperature in the liquid phase.