The hydrocyclone generally exhibits limited separation efficiency and classification sharpness. As the discharge channel for fine particles, the vortex finder plays a critical role in influencing the classification performance through its structural parameters. However, the influence of vortex finder wall thickness on fly ash classification within the hydrocyclone has not yet been reported. In this study, computational fluid dynamics (CFDs) were employed to investigate the variations in pressure field, velocity field, and separation efficiency with respect to changes in vortex finder wall thickness. The results indicate that the radial velocity increases with vortex finder wall thickness, which facilitates the rapid formation of a particle-size stratification, thereby reducing the number of misclassified particles. The cut size initially decreases and then increases as the wall thickness of the vortex finder increases. A minimum cut size of 17.2 µm was observed when the wall thickness reached 10 mm. The classification sharpness improves progressively with increasing wall thickness. At a wall thickness of 15 mm, the steepness index reaches 0.68. Experimental results demonstrate that a thick-walled vortex finder structure can significantly enhance the classification sharpness of the hydrocyclone. Specifically, the content of −19 µm particles in the underflow decreased by 32.17% when the vortex finder wall thickness increased from 5 mm to 15 mm. Meanwhile, the proportion of −19 µm particles in the overflow increased by 12.72%. Therefore, employing a thick-walled vortex finder structure can not only enhance the cut size precision but also effectively improve the classification performance of the hydrocyclone.

To enhance the classification efficiency of hydrocyclones, this study introduces a novel hydrocyclone design featuring a composite curved-inlet-body structure. Through numerical simulations, the internal flow field characteristics of this structure are thoroughly investigated. The results reveal several key findings: when the diameter of the overflow tube is reduced below a critical threshold, the axial velocity exhibits predominantly downward movement within the outer cyclone, accompanied by substantial recirculation, leading to a loss of effective separation. Moreover, both static pressure and tangential velocity are largely independent of the insertion depth of the overflow tube. In contrast, the diameter of the bottom flow opening plays a crucial role in determining flow dynamics within the hydrocyclone. An excessively large or small bottom opening leads to flow instabilities, causing fluctuations that disrupt the uniformity of the flow field. Additionally, a small height-to-diameter ratio exacerbates flow instability, increasing turbulence intensity and resulting in irregular fluctuations in the LZVV. These findings provide important theoretical insights for the design of more efficient hydrocyclone separation structures.

The utilization of hydrocyclones dates back more than a century. As the key channel for multiphase flow, the inlet chamber exerts a notable influence on the separation efficiency of hydrocyclones. Conventional feed bodies mainly adopt straight lines as guidelines. During the transition of fluid from linear motion to circumferential motion, significant kinetic energy loss and particle misalignment are exhibited, resulting in relatively low classification accuracy of the hydrocyclone. Therefore, in this study, a hydrocyclone featuring a complex curved inlet chamber structure was designed, and numerical analysis was employed to examine the particle distribution and aggregation characteristics within both the inlet chamber and the hydrocyclone. Supplemented with RSM/VOF/TFM simulations and quartz sand experimental validation, this study compares the separation performance of the complex curved inlet with the conventional linear inlet. The results indicate the following: when particle sizes are small, particles are dispersed throughout the hydrocyclone and inlet chamber, exhibiting a disordered state, which leads to poor classification performance. As particle size increases, particles gradually form layers along the radial direction; larger particles tend to accumulate on the hydrocyclone wall. When the particle concentration is maintained within a specific range, it promotes the migration of fine particles toward the center, thereby reducing the likelihood of fine particles entering the outer vortex and allowing for more precise classification of fine particles. As the particle concentration increases, the cutting ability of the hydrocyclone progressively diminishes; when the concentration exceeds 20%, the maximum underflow recovery rate for particles smaller than 50 µm is only 60%, resulting in significant coarse overflow and a notable decrease in classification precision. Furthermore, as the inlet concentration increases, the dispersion index for 0.5 µm particles ranges from 0.6 to 1.6, for 4 µm particles from 0.6 to 1.4, and for 60 µm particles from 0.6 to 1. The decreasing dispersion index indicates an increasing classification force, which aids in the formation of a coarse particle layer on the wall. The conclusions and data obtained provide a theoretical foundation and empirical support for the design of innovative inlet chamber structures.

The application of cyclones can be traced back to 100 years ago. Salt, an important carrier of energy exchange in the human body, is one of the essential substances. Currently, salt surface impurities are mostly removed manually, resulting in low sorting efficiency. Cyclones, as important physical separation equipment, are widely used in separating different substances. This paper focuses on using cyclones for salt decontamination. However, due to the limitations of the cyclone’s structure, ensuring grading accuracy is challenging. The flow field, as the main power source in the cyclone grading process, significantly impacts the grading effect. The overflow pipe, where fine particles exit, has a significant effect on the internal flow field. To explore the impact of the overflow pipe structure on the cyclone’s internal flow field, five overflow pipe structures were designed and numerically analyzed. The results indicate that the improved overflow tube structure has higher static pressure than the conventional linear structure. Type 2 (Parabolic) has the highest tangential velocity, which is 27.7 percentage points higher than that of the conventional cyclone, while Type 3 (hyperbola) has the lowest axial velocity(minimum value is only 0.3 m/s) and turbulence intensity(minimum value of the cone segment is only 0.2), resulting in longer particle residence time in the cyclone for better separation. Additionally, vortices are effectively avoided, improving the stability of the flow field to some extent. The obtained data provide a theoretical basis and support for the structural design of new cyclones.