Discharge coefficients of Venturi tubes with standard and non-standard convergent angles

Abstract This paper describes twenty one Venturi tubes manufactured in a range of diameter ratios from 0.4 to 0.75. Fifteen of them are standard, with a convergent angle of 21°, manufactured in a range of diameters from 50 mm to 200 mm and of diameter ratios from 0.4 to 0.75. Six are standard except for the convergent angles which are either 10.5° or 31.5°; they are of diameter 100 mm. They have all been calibrated in water and high-pressure gas. For the standard Venturi tubes an equation for the discharge coefficient in water has been obtained with an uncertainty of 0.74 per cent. Work on the physical basis of the equation for the discharge coefficient at high Reynolds number is described, and an equation fitting all the gas data from the standard Venturi tubes with an uncertainty of 1.23 per cent has been derived. It is clear that the data in gas from the Venturi tubes with a convergent angle of 10.5° are much smoother than those from Venturi tubes with the standard or the higher convergent angle: an equation fitting all the gas data from the three Venturi tubes with a convergent angle of 10.5° has been obtained with an uncertainty of 0.71 per cent.