Unsteady characteristics of a screw-type centrifugal pump operated under the sinusoidal flow rate were investigated experimentally. In order to produce the pulsating lfows of peirod 0.1s approx 100s, three types of oscillatoryflow generators were used in this study. An AC-type electromagnetic flow meter was utilized for the measurement of the instantaneous flow rate, and the suction head and the discharge head of a pump were measured by high frequency response pressure transducers. For the calculation of an apparent total head rise, and equivalent pipe length of the pump was decided experimental tally by using the measured head difference at the pump rests. A true total head rise by the pumping action when the pump was operated under the unsteady flow rate was calculated by substracting an apparent total head rise from a measured ottal head rise. And then, a ratio of the true total head amplitude of the unsteady state to that of the steady state and a phase lag of the true total head rise to the flow rate were obtained as a function of the period of the simusoidal flow rate. As a result, it was found that the unsteady phenomenon on the screw-type centrifugal pump occurs more readily than conventional cen-trifugal pumps with the same specific speed of the screw-type.
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