Abstract:

The tank drainage problems in the experiment measuring the flow velocity of small holes are systematically，theoretically and experimentally studied by taking water as the ideal fluid and considering head loss and or ifice contraction effect. The analytical solution of the cylindrical tank drainage time is theoretically obtained for the first time. Furthermore，the variation of drainage time with free surface velocity and flow coefficient is discussed.Based on this，the equivalent interval of drainage time is proposed. In the experiment，large cylindrical tanks with different sized exit orifice locating at the bottom are designed and fabricated. The tank drainage time varying with the height of liquid surface is measured. The flow coefficient is calculated from the experimental data and the proposal of equivalent time interval is further validated. The experimental results are in good agreement with theoretical calculations.

Key words: tank drainage time, free surface velocity, flow coefficient, head loss, orifice contraction