Referring to regulation of ISO 9300, the discharge coefficients of 2mm, 5mm and 10mm nozzles with 2.5°, 4.0° and 6.0° diffuser angle were measured, respectively. Through comparisons among experimental results, simulation results and prediction results of empirical equations, it was clear that the discharge coefficients were the same for the nozzles with the same throat diameter and were in good agreement with the results of the empirical equations for 10mm nozzles, while that changed with different diffuser angle for other two sets of nozzles. The influence of throat diameter, surface roughness and entrance contour on discharge coefficient was analyzed one by one. The results showed the large out-of-roundness of entrance contour might be the most important reason resulted in the experimental results.

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