Abstract
When a fluid flows in a passage, the fluid in contact with the wall has been generally treated as no slip. We can, however, recognize some cases where the slippage occurs under certain conditions.
In order to obtain the slippage coefficient, it is usually necessary to measure the pressure difference, the fluid viscosity and so on, but their measurements are generally very troublesome.
In this paper the author deals with a useful method for the slippage measurement and the slippage effects on the flow velocity distribution in a circular pipe.
The main merit of the method is to be able to obtain the amount of slippage from the pipe radius, the flow rate and the maximum flow velocity independent of the pressure difference or the fluid viscosity.
As a kind of the physical quantity to express the slippage we propose a slippage index number which is obtained by the ratio of the slippage coefficient to the square of hydraulic mean depth.
When the water flows in circular pipe, the variation of the slippage coefficient is experimentally observed for the change of the pipe radii even if inside surface conditions of pipes are same finishing, but the slippage index number does not vary and is kept to be constant. Therefore, the usage of the slippage index number is very convenient because of getting generalized slippage.
