The performance of the water-sand two phase jet pump has been evaluated for developing environmental sand purification systems. Three types of throat diameter, D = 26, 31, 37 mm, are tested with constant nozzle-exit diameter 20 mm in order to vary the cross section ratio of nozzle exit to throat, R = 0.59, 0.42 and 0.29. The coarse and fine natural sands extracted at Hirase-higashi beach and artificial crushed sand, of which the fineness modulus are 2.71, 2.03 and 2.88 respectively, are mixed in the secondary water flow. The concentration of sand is less than 18% in the present experiment. It is confirmed that the dependences of two-phase efficiency curve and of two-phase flow rate ratio curve upon cross section ratio R agrees with those of single phase flow. On the other hand, the effect of particle size appears in the range of decrement of pump efficiency. That is, it is found that the deviation between two phase and single phase efficiency is 10% on average for coarse sand, whereas the deviation is almost zero for fine sand.

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