The Hagen-Poiseuille equation is not applicable for free-falling vertical jets due to the absence of a stationary solid pipe wall. Instead, the Navier-Stokes equations should be utilized to describe viscous incompressible flows in such scenarios. The discussion emphasizes the limitations of the Bernoulli equation when applied to liquids with low viscosity and suggests that the Hagen-Poiseuille equation may not effectively model flow in varying circular cross-sections. The participants are preparing an experiment to demonstrate these principles and explore the viscosity considerations involved.
PREREQUISITESFluid mechanics students, researchers in hydrodynamics, and engineers working on fluid flow applications will benefit from this discussion.
If the fluid is in free fall, the hagen poiseulle equation doesn't apply because there is no stationary solid pipe wall.ChaoY said:I honestly don't know what viscosity we should use yet. We're preparing a little experiment to show that Bernoulli equation can be used to calculate velocity for liquid with low viscosity. We also want to calculate the flow rate of the jet this time with viscous liquid. The idea is to show that the Bernoulli equation becomes less effective. Now we're wondering if we could use the Hagen-Poiseuille equation to do the job instead this time considering the viscosity. Do you know if this equation still works if the circular cross section varies from two points?