Film lifting and drainage of third-grade fluid on a vertical belt with surface tension.

Understanding the film lifting and draining of fluid on a vertical belt with surface tension is crucial for improving predictive models in coating and lubrication processes. This paper presents a theoretical study on the film lifting and drainage of a third-grade fluid with surface tension. The driving mechanisms on a vertical belt are the belt’s upward movement, the gradient of surface tension, and gravity. The formulated nonlinear ordinary differential equation (ODE) is solved for a series-form solution using the Adomian decomposition method. Numerical computations are used to determine the stationary point placements and the thickness of the uniform film. The study elucidated that lift velocity shows a decreasing trend, while drainage velocity exhibits an increasing trend with increasing values of inverse capillary number <italic>C</italic> and Stokes number St. The lift velocity shows an increase, whereas the drainage velocity demonstrates a decrease with an increase in the Deborah number <italic>De</italic>. With increasing values of St and <italic>C</italic>, the stationary points shift away from the fluid–air interface, while an increase in <italic>De</italic> causes them to move towards the interface. Surface tension plays a role in supporting drainage and leads to a shift in the stationary points towards the belt. Newtonian and third-grade fluids are also compared in terms of velocity, stationary points, uniform film, and surface tension, providing insight into their behavior. [ABSTRACT FROM AUTHOR]