Abstract:During the operation of Venturi injector, when the negative pressure in throat portion gets lower, the suction flow rate will increase. But a lower negative pressure will cause cavitation easily, which may damage the surface of internal structures and finally affect the suction flow rate and the fertigation uniformity of micro-irrigation system. The internal flow of a Venturi injector with 1.5 inch dia-meter for both inlet and outlet was observed using high-speed photography technique. The relations between the cavitation characteristics, the inlet pressure, and pressure differences between inlet and outlet were analyzed. The impact of cavitation on the injection performance was also investigated. The results indicate that the cavitation occurred firstly in the junction of constriction and throat portions. With the increase of the pressure difference, cavitation gradually aggravated and the bubbles extended from the throat to the diffusion portion, meanwhile the growth rate of the suction flow rate decreased gradually. When the pressure difference increased to a certain value, the critical cavitation occurred, while the suction flow increased no longer. The increase of suction flow rate would impact on the working fluid, causing the bubbles to move toward the upper side of the diffusion portion and distributed unevenly. The reflux phenomenon occurred obviously in the rear of the diffusion portion leading the bubbles shed periodically.
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