Optimum Shape of Critical Nozzles on Low Reynolds Numbers

Abstract

For toroidal throat Venturi nozzles with various diffuser lengths and half angles, the behaviors of their critical back pressure ratios were experimentally investigated on the Reynolds number less than 2×104 . The results showed that the diffuser shapes provided in JIS Z 8767(2006) are not always adequate for flow measurements under the above Reynolds number range. The toroidal throat Venturi nozzle used for flow measurements under the Reynolds number less than 2×104 is desirable to have longer diffuser than 10 times of its throat diameter and its diffuser half angle should be around 3.5 degrees.