Empirical study on a coefficient of discharge μ from the flexible ducts

•Values of the coefficient of discharge μ for flexible and stiff conduits differ.•Empirical study show that coefficient of discharge μ flexible ducts was in 0.96–0.99.•Values differ about 30–60% and using incorrect parameter case huge errors in results.

The paper discusses issues connected with a coefficient of discharge μ and elements which provide a fluid flow regulation. The measurements were carried out for a few flexible conduits which differed in a perforation extent but had the same size (diameter and length). The outlets were located equally along the length of the pipe – the first one was 1.0 m from the place where the duct was attached to the hopper, while the last outlet was 1.0 m from the end of conduit. The outlets in each test had different diameters and were located in three distances. The results from 13 series of measurements showed that the coefficient of discharge was in range μ = 0.96–0.99, so it differed significantly from values recommended for the stiff conduits.