| Evaporation process is widely used in liquid atomization and related industries.Single droplet evaporation is an important evaporation research method.High-speed photography is the most common measurement method for the single droplet evaporation.Currently,its diameter resolution is the order of 10?m.However,high-speed,high-resolution imaging systems are expensive,but its acquisition speeds are still unable to meet the rapid changes in the size of high-evaporation liquids at high temperatures.The rainbow refractometry measurement method measures the droplet diameter and the corresponding phase difference when the ripple structure is translated by the first rainbow ripple structure to achieve a small change in droplet diameter.Rainbow refractometry method has the characteristics of simple method and high measurement accuracy.In this paper,the rainbow refractometry measurement method is used to measure the temperature characteristics of droplet evaporation.Firstly,the relationship between the ripple frequency of the first rainbow intensity distribution of the droplet and the diameter is calculated by the Mie scattering theory of the spherical particle.The measurement accuracy of the droplet with diameter of 2 mm is 5 ?m.A period change of the first rainbow ripple structure of water and alcohol corresponding to diameter changes of 0.256?m and 0.242?m,respectively.The results show that the rainbow method can measure the diameter variation by a few nanometers.The measurement method only needs to use the linear array CCD to collect the one-dimensional rainbow intensity distribution on the meridional surface of the droplet.There is no need to quantitatively calibrate the first rainbow angle,which greatly simplifies the measurement system structure while reducing the requirements of the light intensity acquisition system.The above analysis results provide theoretical guidance for the design and experimental measurement of the droplet evaporation experimental system.This paper designs and builds a droplet evaporation measurement system based on highspeed linear array CCD to collect rainbow signal intensity.Change the beam of the system in order to apply millimeter-level droplet rainbow,it can effectively improve the signal-tonoise ratio of the rainbow signal.The integrated design of the optical path contributes to the integration of the overall system.In this paper,the droplet generation heating and temperature control device is designed.The temperature range of the droplet heating is from room temperature to 200 °C,and the temperature control precision is ±1 °C,which satisfies the measurement of temperature characteristics of droplet evaporation under different conditions.Rapid evaporation of the lower droplets,using a high-speed linear array CCD with 68 KHz to collect rainbow signals,in order to achieve rapid data acquisition and processing,based on the CCD software development kit,developed high-speed processing and acquisition software,the software can be at high speed The acquisition simultaneously achieves a fast calculation of the signal cross-spectral density.Based on the rainbow measurement theory and the rainbow system,we studied the evaporation temperature characteristics of water droplets and alcohol droplets.When the water droplets are in the range from 18.9 °C to 80 °C and the alcohol droplets are in the temperature range from 18.9 °C to 60 °C,the rainbow measurement method obtains the instantaneous continuous change of the droplet diameter,and the water and alcohol droplets are obtained at different temperatures by the instantaneous diameter change.In the end,we can obtain evaporation constants and evaporation rates. |
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