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1、一类反常弹流油膜出现的实验研究IntroductionIn this study, we aimed to investigate the occurrence of a reverse transition from laminar to turbulent flow during the flow of non-Newtonian fluids. This phenomenon is commonly known as Anti-Spitting or Anti-Dribbling flow, and it has been observed in several fluids, incl
2、uding polymer melts, suspensions of particles, and liquid crystals. The Anti-Spitting flow is characterized by the sudden formation of a thick flow layer, also known as an oil-film, on the surface of the flowing fluid, which then separates the fluid from the solid surface. This process significantly
3、 alters the flow characteristics of the fluid and can affect the quality of the final product in certain industries, such as polymer processing and transportation of slurries. In this paper, we present the experimental observations of Anti-Spitting behavior in shear thinning polymer solutions.Experi
4、mental setup and methodologyThe experimental setup consisted of a parallel plate rheometer with a fixed top plate and a movable bottom plate. The plates had a diameter of 25mm and a gap between them of 1mm. The bottom plate was driven by a motor, and the speed was adjusted using a rheometer control
5、unit. The temperature of the system was controlled using a Peltier-controlled water bath. The rheometer was equipped with a video camera to visualize the flow behavior of the fluid.The fluid used for the experiments was a 0.5% w/w solution of Polyethylene oxide (PEO) in water. PEO is a well-studied
6、shear thinning polymer that exhibits weak thixotropic behavior. Initially, the rheometer was operated in the linear viscoelastic region, and the shear stress-shear rate data was recorded. The flow behavior of the fluid was then changed by increasing the shear rate above a critical value, and the dev
7、elopment of the Anti-Spitting flow was recorded using the video camera.Results and discussionThe rheological data of the PEO solution showed a typical shear thinning behavior with a consistent decrease in viscosity with increasing shear rate. At low shear rates, the fluid was in the linear viscoelas
8、tic regime, and the viscosity remained constant. However, when the shear rate was increased to a critical value, the viscosity of the fluid dropped significantly, indicating the onset of the Anti-Spitting flow. The video footage of the flow showed the formation of a thick layer of the fluid on the s
9、urface. This layer separated the fluid from the solid surface, and the shear stress drastically decreased due to the reduction of the contact area between the fluid and the surface. The formation of the oil-film on the surface of the PEO solution can be attributed to the shear-induced instability of
10、 the fluid. The shearing action causes the fluid to thin out, creating a lower viscosity boundary layer close to the surface. The lower viscosity layer destabilizes, leading to deformation and the formation of the oil-film. The appearance of the Anti-Spitting behavior in our experiment is consistent
11、 with previous studies of polymer melts and liquid crystals. This phenomenon is an important consideration in designing and optimizing the processing of these fluids.ConclusionIn conclusion, we have demonstrated the occurrence of Anti-Spitting flow in shear thinning polymer solution, PEO. The phenom
12、enon can significantly alter the flow characteristics of the fluid and affect the quality of the end product in certain applications. The shear-induced instability of the fluid leads to the formation of an oil-film that separates the fluid from the solid surface. This study highlights the importance
13、 of considering Anti-Spitting flow in the design and optimization of the processing of polymer solutions, suspensions of particles, and liquid crystals. Further studies in this area can help understand the underlying mechanisms of Anti-Spitting behavior and aid in developing mitigation strategies.An
14、ti-Spitting flow is a complex phenomenon that can be observed in various types of non-Newtonian fluids. In polymer processing, Anti-Spitting can lead to defects in the products, leading to waste and production losses. To mitigate the occurrence of Anti-Spitting flow, various strategies have been pro
15、posed, such as surface modification or addition of small amounts of additives to the fluid. These approaches aim to stabilize the boundary layer of the fluid and reduce the likelihood of instability and the formation of the oil-film on the surface.Understanding the underlying mechanisms of Anti-Spit
16、ting behavior is crucial for the development of effective mitigation strategies. Several theoretical and numerical models have been proposed to explain the phenomenon, including the lubrication theory, the hydrodynamic stability analysis, and the surface energy-based models. However, these models can be challenging to validate experimentally due to the complex nature of the Anti-Spitting phenomenon.Future studies can focus on developing advanced experimental
