Behaviors of discharge coefficients of small diameter critical nozzles

The discharge coefficients of 59 small diameter toroidal throat Venturi critical nozzles were measured by the static gravimetric method. The throat diameter is from 0.014 mm to 2.35 mm and the Reynolds number is 4 × 102 to 2 × 105. These nozzles were manufactured by the normally processing method base on the same design drawing, but their discharge coefficients were scattered widely. The purpose of this paper is to explain the behavior of discharge coefficient scattered. In the correction procedure used here, while comparing the discharge coefficient obtained experimentally and the reference theoretical model, the throat diameter is corrected and the optimal radius of curvature of nozzle inlet is determined so that both discharge coefficients match. Resultantly, most of the behaviors of the discharge coefficient of 59 critical nozzles could be explained well.