New Technologies in the Research of Aluminum Tubes and Aluminum Tube Production Lines After nearly a century of experimental research and theoretical exploration, aluminum tube technology has entered a period of rapid development, accumulating a wealth of design experience and correlations applicable to the analysis and prediction of mixed systems. However, due to the diversity of fluid mixing systems and the complexity of material rheological properties, the selection and design of mixing equipment currently still mainly rely on experience and experiments. It is difficult to theoretically predict their advantages and disadvantages, and the energy consumption and production cost can only be compared after a certain scale of production equipment is established. In addition, there is still insufficient understanding of the scaling laws for mixing equipment, lacking theoretical guidance. Therefore, from a more microscopic and essential perspective, using advanced testing methods and computational fluid dynamics methods to obtain the velocity field, temperature field, and concentration field in the mixing equipment not only has significant economic significance for the optimal design of mixing and mixing equipment but also has practical theoretical significance for the basic research of scaling and mixing. 1

Early velocity measurement methods, such as Pitot tubes, electromagnetic flow meters, piezoelectric probes, and hot-wire or hot-film anemometers, all disturbed the flow due to probes inserted into the flow field. Since the 1980s, Laser Doppler Velocimetry (LDV) has been used domestically and internationally to measure the flow field in stirred tanks. LDV measurements are performed at a certain measuring point over a period of time; therefore, the measured velocity is a time-averaged value. By measuring each point in the stirred tank, the entire flow field can be obtained. However, since these measurements cannot be performed simultaneously, LDV cannot be used to study unsteady flow. To study time-varying flow, a more advanced Particle Image Velocimetry (PIV) must be used, which can instantaneously obtain the entire flow field distribution. Its principle is that the mixing equipment is irradiated by a narrow slit laser beam, and two pulsed light sources are used to obtain two exposure images of the particle field. Then, the velocity field is calculated from the displacement of the particles within the exposure time. However, the development of PIV technology is still not perfect and is still in its early stages of application; at present, it cannot accurately measure turbulence parameters under high-speed turbulence.

Using LDV measurement technology, abundant information such as the time-averaged velocity field, turbulence intensity field, Reynolds stress field, and shear rate field in the stirred tank can be accurately obtained, and macroscopic characteristic parameters such as displacement and power consumption can be further calculated. Therefore, a main current application of LDV measurement data is to verify the simulation results of CFD (Computational Fluid Dynamics) models and provide model boundary conditions. In recent years, LDV has also been used to measure the mixing characteristics of multi-layer impellers, such as displacement and circulation flow. Because the particle tracking method used to measure displacement under single-layer impeller conditions is not applicable under multi-layer impeller conditions. 2 CFD Simulation Technology LDV only provides some important parameters such as the displacement number, the distribution of time-averaged velocity and fluctuating velocity, but cannot fundamentally understand mixing and flow, and cannot change the current situation of relying on experience for scaling. Therefore, using computational fluid dynamics methods to simulate and predict the detailed flow and mixing characteristics in mixing equipment with different geometric sizes and operating conditions is the development trend of fluid mixing technology.