Modern drying technology lacks precision guidance

China's modern drying technology has gradually developed from the 1950s, but most drying technologies currently lack scientific theories and design methods that can accurately guide practice. In practical applications, relying on data from experience and small-scale experiments to guide industrial design is the main method. The reasons for this situation are as follows:

One of the reasons is that some of the basic disciplines on which drying technology is based (mainly the disciplines that belong to the category of transmission engineering) have their own characteristics of experimental science. For example, the development of aerodynamic research is also driven by “wind tunnel” experiments, which shows that it has not yet broken away from the scope of experimental science, and the development level of these basic disciplines directly influences and determines the development level of drying technology.

The second reason is that many drying processes are the process of convergence of multiple disciplines. They involve a wide range of factors, many factors of change, and complex mechanisms. For example, in the field of spray drying technology, the trajectory of atomized droplets in the drying tower is the key to engineering design. The trajectory of the droplet is related to its own volume, mass, initial velocity and direction, and the flow and velocity of other droplets and hot air around it. However, due to mass transfer and heat transfer processes, these parameters do not change all the time. In the initial state, neither the droplet size nor the distribution of hot air can be uniform. Obviously, engineering design based on theoretical calculations for such a complex and varied process is not reliable.

The third reason is that the types of materials to be dried are various and their physical and chemical properties are also different. Different materials, even under the same dry conditions, may have large differences in mass transfer, heat transfer rate, and heat transfer. If you do not treat them differently, you may have unsatisfactory results. For example, the drying of some Chinese herbal medicines, although belonging to the same kind of medicinal materials, only needs to change the drying conditions because of differences in the origin or harvest period of the medicinal materials, otherwise the quality of the products will be affected.