Abstract
A method using a steel ball as a float in water flow, as in the float-type variable-area flowmeter, was adopted to measure the mean inner diameter of a tube. The experiment was carried out first by employing gauge glasses and steel balls to obtain some informations with regard to the fundamental relation between flow rate and gap area. Several items that should be noticed in case of performing the measurement were found. Those are : (1) Reynolds' number should not exceed 3000 ; (2) the ratio of tube diameter to ball diameter should not exceed 1.5 ; (3) the rotation of a ball should be avoided ; and (4) the water temperature or viscosity should be maintained constant throughout the measurement.
Finally, it was shown that the tube inner diameter can be measured within an accuracy of ±0.01mm under the satisfactory conditions.
