关键词: 蒸发, 水溶液, 选择性非催化还原, 对流, 尿素, 气泡

Abstract: The evaporation process of a single urea-aqueous-solution (UAS) droplet was observed by the hanging drop method in a quartz tube reactor. Also，the evaporation characteristics of droplets were compared under various ambient temperatures and initial droplet diameters. The results showed that UAS droplet revealed different evaporation behavior at 100—1300 ℃. At higher temperatures，it showed quite complicated behavior，such as bubble formation，distortion，and micro-explosion. However，with decreasing temperature，these phenomena became weak and finally disappeared. At the same time，the relationship between steady-state evaporation coefficient and temperature，initial droplet diameter was quantitatively analyzed. Under the condition of initial droplet diameter of 2.5 mm and temperature in the range of 100—600 ℃，the steady-state evaporation coefficient increased by about 10 times，from 0.02075 mm2/s to 0.23953 mm2/s. In addition，the evaporation characteristics of droplets were also investigated in the case of airflow velocity within 0.25—1.25 m/s. When there existed forced airflow，heat transfer between droplet and gas changed from heat conduction into heat convection，so as to enhance the capacity of the heat and mass transfer on the surface of the droplet，then the evaporation process would be promoted.

Key words: evaporation, aqueous solution, SNCR, convection, urea, bubble