Studies On Heat Transfer And Evaporation And Applications Of Wiped Thin-film Evaporator With An Inner Condenser

With the action of blades' wiping, the wiped thin-film evaporators are more suitable to deal with viscous and thermal instable materials than common evaporators. In the wiped thin-film evaporator with an inner-condenser, the distance from evaporating surface to condensing surface is obviously shortened, the driving force of mass transfer on evaporating surface increased, and the performance of heat transfer and evaporation strengthened. Recent research on the inner condensing wiped thin-film evaporator is mainly on the theoretical of the evaporating process, but unfortunately without certification by the experimental findings. On the other hand, the fluid for studying was always water, and seldom using viscous material in studying the characters of the wiped thin-film evaporators. Therefore, it is very important to study heat transfer and evaporation performance of pilot plant of wiped thin-film evaporator with an inner condenser and extend its applications.A self-established pilot plant of inner condensing wiped thin-film evaporator system is described first in detail in this paper. It has 3 features: (1) the jacket with agitators; (2) the back-pressure valve in the pipeline of outlet of metering pump that guarantees high vacuum degree; (3) single stage that can fulfill multistage operation.Evaporating experiments are carried out with water in the self-established pilot plant. It is found that the feed rate and jacket heating temperature have more influence on the total heat transfer coefficient than wiper rotating speed, and that jacket heating temperature has more influence on evaporating rate than feed rate and wiper rotating. Feed temperature has great influence. The evaporating surface can be used effectively and heat transfer and evaporation performance can be improved when the feed temperature closes possibly to the evaporating temperature.Heat transfer and evaporation experiments are carried out with the viscous fluid of glycerol. It is found that the heat transfer coefficient of oil in jacket is determined 1.5 to 2.0 times that of fluid film when evaporating. This demonstrates that the heat transfer resistance mainly lies in the thin film. The total heat transfer coefficient and thin film heat transfer coefficient increase with the wiper rotating speed, vacuum degree, feed rate and feed temperature and decrease with the evaporating temperature. Each factor has little influence on the heat transfer coefficient of oil in jacket. The evaporating rate increases with the rotating speed, vacuum degree and feed...