چكيده به لاتين
Critical nozzles are widely used in gas flowmeters calibration. However, the critical nozzles standard (ISO 9300) and the presented formula for calculating discharge coefficient in this standard can not predict the discharge of sonic nozzles under different operating conditions. Due to mentioned reason, in this study, the numerical simulation of the flow in the sonic nozzles carried out and different factors affecting it were identified and understood correctly. The studied variables included the study of the pressure ratio, inlet temperature, throat diameter, divergence length, divergence angle, type of gas, wall roughness and moisture content in the fluid. The results showed that an increase in the throat diameter increased the discharge coefficient up to 13%. Also, study of the wall roughness effect on discharge coefficient showed when the relative roughness increased, the discharge coefficient has less values. On the other hand, the results showed when the amount of moisture in the air is higher, the amount of discharge coefficient is reduced. Finally, a new relationship has been proposed to predict discharge coefficient in order to correct existing relationships.
Keywords: Sonic Nozzle, Discharge Coefficient, Numerical Simulation, Wall Roughness, Moisture.
