In the range of very low specific speed, such as ns < 80 [min.−1, m3/min., m], or Ns < 533 [min.−1, USGPM, ft.], stable head-capacity curve is one of the most important issues. The head-capacity curve of a conventional closed impeller tends to be unstable with a positive slope characteristic in such a very low ns range. To solve this problem, a new type of centrifugal pump “J-groove pump” is proposed and tested in this study. The J-groove pump is composed of a rotating disk mounted with many shallow radial grooves and a circular casing. The experimental results reveal that the proposed J-groove pump is quite effective in the very low specific speed range. The pump head is about 1.2 times higher than that of a conventional centrifugal pump and the head-capacity curve is almost stable, though the efficiency becomes a little lower because of a large friction power of the stationary wall. The cavitation performance is also measured and is shown to be almost same as that of a conventional centrifugal pump. This pump is applicable to high speed pump, as it has no small clearance, high strength due to simple impeller configuration, and easy to assemble. In order to determine the internal flow characteristics of the J-groove pump, CFD simulation is carried out. It is revealed that the high head of the J-groove pump is caused by a strong vortex flow existing in both clearances near the impeller tip over the whole flow range.

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