Dynamic Behavior and Deformation Characteristics of Oil Droplets in Spiral Flow Field

The spiral flow field is the key to ensuring the performance of centrifugal and cyclonic separation equipment. The migration and deformation dynamics of oil droplets in a spiral flow field are a crucial topic to guide the design of separation equipment and parameter optimization. However, the droplet dynamics especially in a two-phase nonlaminar flow field is challenging and meaningful due to its complex interfaces and deformation behaviors. The deformation, migration, and breakup dynamic behaviors of discrete-phase oil droplets in the spiral flow field were innovatively investigated via numerical simulation and high-speed photography methods. Two distinct breakup modes─tensile breakup and impact breakup─were clearly identified by analyzing the morphological evolution of droplets in the spiral flow field. Simultaneously, through flow field analysis and the construction of oil droplet mechanical models, a predictive model was established and validated to describe the relationship among the inlet Reynolds number, pitch, and critical droplet breakup diameter. Results show that in the five-stage spiral tube, the peak tangential velocity migrates from the tube center to the outer wall between the first and second stages (where the initial droplet breakup occurs) and then stabilizes in the subsequent stages. Furthermore, the effect of the Reynolds number on droplet breakup shows that as the Reynolds number increases droplets are prone to undergo impact breakup. When Re ranges from 1000 to 60,000, the critical value for impact breakup increases from 2.4 to 5.5 mm. Further investigation into the effect of pitch on droplet breakup showed that increasing the pitch promotes breakup until the critical value of 60 mm, beyond which further increases inhibit breakup. This research provides new insights into the interface behavior of discrete phases in complex spiral flow fields and offers a practical reference for enhancing the performance of related separation equipment.