Drying technology has a wide range of applications. In the face of numerous industries, physical and chemical properties, materials, product quality and other diverse requirements, drying technology is a cross-industry, interdisciplinary, experimental and scientific technology. Generally, three aspects of knowledge and technology are required in the development and application of drying technology. The first is to understand the physical and chemical properties of the material being dried and the characteristics of the product; the second is to be familiar with the principle of transfer engineering, namely the principle of mass transfer, heat transfer, fluid mechanics and aerodynamics; The means of implementation is the engineering design of the drying process, main equipment, and electrical instrument control. Obviously, these three aspects of knowledge and technology do not belong to a subject area. In practice, these three aspects of knowledge and technology are indispensable. So drying technology is a cross-industry, interdisciplinary technology.
Although modern drying technology has a history of more than one hundred years, it still belongs to the category of experimental science. Most drying technologies currently lack scientific theories and design methods that accurately guide practice. In practical applications, relying on empirical and small-scale experimental data to guide industrial design is still the main way, the reasons for this situation are as follows:
One of the reasons is that some basic disciplines relying on drying technology (mainly subject to the discipline of transfer engineering) have the characteristics of experimental science. For example, the development of aerodynamic research is driven by the “wind tunnel” experiment, which indicates that it has not deviated from the scope of experimental science, and the development level of these basic disciplines directly affects and determines the development level of drying technology.
The second reason is that many drying processes are the process of multi-disciplinary technology convergence, involving a wide range of factors, many changing factors, and complex mechanisms. For example, in the field of spray drying technology, the trajectory of atomized droplets in a drying tower is the key to engineering design. The trajectory of the droplet is related to its volume, mass, initial velocity and direction, and the flow and velocity of other droplets and hot air around it. However, due to the mass transfer and heat transfer processes, these parameters change all the time, and in the initial state, neither the size of the droplets nor the distribution of hot air can be uniform. Obviously, engineering design based on theoretical calculations for such complex and varied processes 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. The mass transfer and heat transfer rates of different materials may vary greatly even under the same drying conditions. If not treated differently, it may have unsatisfactory consequences. For example, the drying of some Chinese herbal medicines, although belonging to the same medicinal materials, only needs to change the drying conditions because of the difference in the origin or harvest period of the medicinal materials, otherwise the quality of the products will be affected.
The above three reasons determine that the development and application of drying technology should be based on experiments. However, these characteristics of dry search are often ignored by people intentionally or unintentionally. Manufacturers often avoid the drying experiments that should be done because of the lack of experimental devices or incomplete models (which is a common phenomenon in China), and users often give up the requirements of necessary experiments because they do not understand the characteristics of drying technology. The result is that the device is not working well and even causes the design failure. In China, such cases are not uncommon. There has been a lesson in the industrial drying unit worth 20 million yuan that was left unused because it could not meet the requirements for use. Therefore, before constructing industrial drying equipment, especially larger ones, it is necessary to conduct sufficient and convincing experiments, and use the experimental results as the basis for industrial equipment design. This is a distinctive feature of drying technology applications.