Abstract
The magnitude of the effective diffusivity of carbon dioxide in the atmosphere through the oscillatory flow along a pipe for each condition presented in the former paper^<(1)> might be related with the state of the flow. To observe the state of the oscillatory flow, visualization of the oscillatory flow of water, which is similar to the flow of air, has been carried out for each condition of flow in a circular pipe with circumferential grooves and a smooth circular pipe, respectively. Transition from laminar to turbulent for the oscillatory flow in the straight pipe was observed as same as the former other studies. Even on the same condition on which the flow is laminar in the straight pipe, the vortices were generated in the pipe with circumferential grooves, mainly inside the grooves. Turbulent flows have been observed in the grooves almost in the whole case, especially at the dead points of the piston.
