Application of small size cavitating venturi as flow controller and flow meter

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. The flow rate is a function of the upstream pressure, the throat area, the density and saturation pressure of the liquid. An experimental setup with capability of supplying water flow rate and constant upstream pressure was designed and manufactured. Three cavitating venturis with throat diameter of 5, 2.5, and 1 mm were designed and built to investigate the effect of venturi size on its mass flow rate. Three different sets of experiments were conducted to investigate the performance of the venturis. In the experiments, the mass flow rates were examined under different downstream and upstream pressure conditions and time varying downstream pressure. The results show for the ratio of downstream pressure to upstream pressure less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever the pressure ratio exceeds 0.8, the venturi acts like an orifice. This pressure ratio has been predicted analytically to highlight the affecting parameters, mainly the geometry of the venturi and viscous losses. It is found that the venturi size has no effect on its expecting function to keep mass flow rate constant. Also, it is shown that by applying a discharge coefficient and using only upstream pressure, the cavitating venturi can be used as a flowmeter with a high degree of accuracy in a wide range of mass flow rate. (C) 2011 Elsevier Ltd. All rights reserved.