抄録
Discharge coefficients of 10 super-accurate nozzles whose machining error were smaller than ±1μm were measured using a constant volume tank system at absolute pressures of 100 to 500kPa with the Reynolds number of 4×104 to 1.2×106. The measured discharge coefficients agreed within ±0.1% with a reference curve, which had been measured using other 24 super-accurate critical nozzles at the atmospheric pressure or lower. Discharge coefficients of one nozzle among the 10 showed a sudden decrease by 0.1% at the Reynolds numbers around 106, which was caused by a boundary layer transition and defined the valid maximum Reynolds number of the reference curve. All of the equations and constants needed to calculate a flow rate using the reference curve are listed. An uncertainty analysis of the constant volume tank system, developed as the national standard and used to calibrate the nozzles, is described.
