What problems have not been solved in the development of hot air circulation oven

Although modern hot air circulation oven technology has a history of more than 100 years, it still belongs to the category of experimental science At present, most of the drying technology can also guide the practice of microtubule scientific theory and design methods In practical application, it is still the main way to rely on the data of small-scale test in the whole province Some basic subjects that the drying technology of hot air circulation oven relies on are mainly subjects belonging to the transmission engineering category, which have the characteristics of experimental science For example, the research and development of aerodynamics should be promoted by "wind tunnel" test, which shows that it has not been separated from the scope of experimental science The development level of these basic disciplines directly affects and determines the development level of the drying technology of the hot air circulation oven A lot of drying processes of hot air circulation oven are the process of the intersection of the technology of sedimentation, involving a wide range, many variables and complex mechanism For example, in the field of spray drying technology, the running track of droplets in the drying tower is the key to engineering design The trajectory of droplets is related to their volume, mass, initial velocity and direction, and the flow direction and velocity of other droplets and hot air around them But these parameters are changing all the time because of the mass transfer and heat transfer And in the initial state, neither the size of droplets nor the distribution of hot air can be uniform Obviously, it is not reliable to design such a complex and changeable process only by theoretical calculation There are many kinds of materials dried by hot air circulation oven, and their physical and chemical properties are also different Even under the same drying conditions, the mass transfer and heat transfer rates of different materials may vary greatly If they are not treated differently, they may have unsatisfactory consequences For example, although some Chinese herbal medicines belong to the same kind of medicinal materials, the drying conditions must be changed only because of the differences in the origin or harvest time of the medicinal materials, otherwise the product quality may not be qualified.