Occurrence-Time-Ratio Measurements on Air Entrainment in a Suction Sump

In order to get accurate measurements of air entrainment in a suction sump, we design a new and simple conductance-type electric bubble sensor, which can detect the existence of air bubbles inside a suction pipe with no disturbances by the sensor and with a fine spatial resolution. We focus on occurrence-time ratio γ of the air entrainment, and compare the result by the present sensor with those by conventional two methods, namely, visual and auditory ones. As a result, we show the criteria which specify lower-accuracy conditions in the conventional methods. By the visual method, the accuracy of γ becomes low, when γ is less than 0.05. By the auditory method, the accuracy of γ becomes low, when submergence depth S of the suction pipe is close to the critical one Sc.