Drying technology has a wide range of application fields. Facing numerous industries, materials with different physical and chemical properties, and various requirements for product quality and other aspects, drying technology is a cross-industry and cross-disciplinary technology with experimental scientific nature. Generally, in the development and application of drying technology, three aspects of knowledge and technology are required. The first is to understand the physical and chemical properties of the material to be dried and the usage characteristics of the product; The second is to be familiar with the principles of transfer engineering, namely the principles of energy transfer such as mass transfer, heat transfer, fluid mechanics and aerodynamics. Thirdly, there must be implementation means, that is, the ability to conduct engineering design in aspects such as the drying process, main equipment, and electrical and instrument control. Obviously, the knowledge and techniques in these three aspects do not belong to the same disciplinary field. In practice, the knowledge and skills in these three aspects are all indispensable. Therefore, drying technology is a cross-industry and cross-disciplinary technology.
Although modern drying technology has a development history of more than a hundred years, it still belongs to the category of experimental science to this day. Most drying technologies currently lack scientific theories and design methods that can precisely guide practice. In practical applications, relying on experience and data from small-scale experiments to guide industrial design remains the main approach. The reasons for this situation are as follows:
One of the reasons is that some of the basic disciplines on which drying technology relies (mainly those belonging to the category of transfer engineering) inherently possess the characteristics of experimental science. For instance, the fact that the research and development of aerodynamics still rely on "wind tunnel" experiments to drive it indicates that it has not yet deviated from the scope of experimental science. Moreover, the development level of these basic disciplines themselves directly affects and determines the development level of drying technology.
The second reason is that many drying processes are carried out through the intersection of multiple disciplinary technologies, involving a wide range of aspects, numerous changing factors, and complex mechanisms. For instance, in the field of spray drying technology, the movement trajectory of the atomized liquid droplets within the drying tower is a key factor in engineering design. The trajectory of a droplet is related to its own volume, mass, initial velocity and direction, as well as the flow direction and velocity of other droplets and hot air around it. However, these parameters are constantly changing due to the progress of mass transfer and heat transfer processes. Moreover, in the initial state, neither the size of the droplets nor the distribution of hot air can be uniform. Obviously, it is unreliable to conduct engineering design solely based on theoretical calculations for such a complex and variable process.
The third reason is that the types of materials to be dried are diverse, and their physical and chemical properties are also different. Even under the same drying conditions, the rates of mass transfer and heat transfer of different materials may vary significantly. If not treated differently, it may lead to unsatisfactory consequences. For instance, in the drying of certain Chinese herbal medicines, even though they all belong to the same type of medicinal material, the drying conditions need to be changed merely due to differences 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 techniques are often intentionally or unintentionally overlooked by people. Manufacturers often avoid the necessary drying experiments due to the lack of experimental equipment or incomplete models (which is a common phenomenon in our country), and users often give up the requirement to conduct necessary experiments because they do not understand the characteristics of drying technology. The outcome is that the device performs poorly and even leads to the failure of the scheme design. In China, such cases are not uncommon. There was once a lesson that an industrial drying device worth 20 million yuan was left idle because it failed to meet the usage requirements. Therefore, before building an industrial drying facility, especially a larger one, it is essential to conduct thorough and convincing experiments, and use the experimental results as the basis for the design of the industrial facility. This