Simulation And Experiment On Evaporation Process Of Single Droplet Of Alcohol

The phenomenon of combustion instability may occur in the working process of air heater.It is generally believed that the process of droplet evaporation is related to the excitation and maintenance of combustion instability.Based on this understanding,simulation and experimental studies on the evaporation process of a single alcohol droplet are carried out in this dissertation.The main contents and results are described as follows:An experimental study on the evaporation process of single alcohol droplet was carried out.The results show that there is an unsteady evaporation stage in which the droplet diameter changes little,and the heat absorbed by the droplet from the outside is mainly used for self-heating and less for evaporation.most of the time in the process of droplet evaporation is in good agreement with the classical D₂ law,and the evaporation rate will gradually decrease at the end of droplet evaporation.The ambient temperature has a significant effect on the droplet evaporation rate.The higher the ambient temperature is,the faster the droplet evaporation is,and the shorter the duration of the unsteady evaporation stage is.When the droplet evaporation rate is too fast,the flash phenomenon may occur;the higher the alcohol concentration,the faster the droplet evaporation.The evaporation of alcohol droplets is different from that of pure ethanol droplets.Ethanol with lower boiling point evaporates first,while water evaporates later,and ethanol evaporates faster and shorter.The strong convection environment will enhance the heat and mass transfer between the ambient gas and droplets,thus accelerating the evaporation rate of alcohol droplets.An unsteady evaporation model of alcohol droplets in oscillating environment is established,and the unsteady evaporation process of alcohol droplets in velocity oscillation environment and pressure oscillation environment is calculated by using this model.The open-loop response process of alcohol droplets to pressure oscillation is emphatically studied and analyzed.It is found that the relative velocity between alcohol droplets and ambient gas is an important factor affecting the speed of droplet evaporation.The greater the relative velocity between droplets and ambient gas is,the stronger the convective mass transfer and heat transfer is,the greater the evaporation rate of the droplet is.Changing the frequency and amplitude of pressure oscillation will affect the phase difference between droplet evaporation rate and pressure,and the relationship between them is nonlinear,they are different in the early and later stages of droplet evaporation.the thermal inertia of the droplet itself plays an important role in it.The evaporation process of alcohol droplets under different ambient pressure,ambient temperature and convection intensity is simulated by using the previously established evaporation model,and the simulation results are compared with the experimental results,and the results are good.