Spray Drying Of Heat And Mass Transfer Characteristics Of Study

Through analyzing on the existing droplet evaporation models, such as droplet evaporation model in large space, droplet evaporation model in limited space, this paper discussed these models above whether to consider the temperature gradient of temperature and its application. Based on these previous models, through further analysis and discussion, we obtain a mathematical model for multi-component droplet evaporation process,which is suitable for spray drying process.The mathematical model of gas which flows in the spray dryer and the orbit model of particle are established,firstly. Next,By solving these equations,the flow field in spray dryer and the trajectory of particle are obtained,respectively. Meanwhile, the characteristics of heat and mass transfer of particles are obtained by coupling calculating of gaseous phase and moving particles. And the dynamic evaporation performance and the heat and mass transfer between gaseous phase and moving particles are also obtained in the whole process.The temperature field and relative humidity in spray dryer,and in the meantime,are also obtained bycoupling calculating of gaseous phase and moving particles. Access to track the motion process of some typical particles, the residual time of these particles are obtained.The process of droplet evaporation in the dry tower can be divided into several stages. Firstly,the droplets are heat up by the hot air and their temperture are rised.Next, by heat up for a short time,these droplets enter a rapid drying stage when the proper temperature is reached. At last, these droplets are in the stages of completion after a evaporation period. By numerical simulation,the cyclone zones are found which exist in the drying tower. And the existence of cyclone zones have a salutary effect on the particles drying process, because their can provide more time for particles when particles are drying in the spray dryer.But this phenomenon can also increse the energy consumption. The evaporation rate of droplet is increased with the increase of inlet and outlet air temperature. And this increase process becomes approximately a linear relationship within a certain temperature range. With the increase of inlet air velocity, the average air speed increases and the average particle residence time become shorter in the drying tower.The separating efficiency of cyclone separator which is used for spray drying process has a relationship with the physical model of cyclone separator, the inlet air speed and particle diameter.For a special cyclone separation equipment. To some degree, the separation efficiency can be improved with the increase of inlet air speed and particle size. But the increase of inlet air velocity can also lead to a rapid increase in wind resistance and power consumption. Thus,It is not appropriate to increase the inlet air velocity blindly to improve the separating efficiency.