چكيده به لاتين
One of the important requirements in contracts between buyers and sellers of gas is to calculate the overall uncertainty of metering systems, which according to the relevant standards and instructions, is a function of the uncertainty of each component affecting the measurement. In this research, a overall uncertainty model for gas metering stations with turbine meters is presented and the sources of uncertainty are identified. The contributions of each variable are combined and the overall uncertainty of the studied station is calculated. In the following, using CFD simulation, the effects of installation conditions on the overall uncertainty of the sample station are investigated. Typical configurations at natural gas metering stations are in five different scenarios. The first scenario is a straight pipe, the second and third scenarios are one elbow, and the fourth and fifth scenarios are two elbows out-of-plane. To calculate the torque on the rotor blades, a function code was created in UDF and added to the software. To validate the model, the simulation results and the experimental data of the manufacturer were compared. The relative error of the results was about 0.35%, which for the 8-inch turbine meter shows good simulation performance. The overall uncertainty of the studied station was equal to 0.903%, which has the highest effect of uncertainty related to pressure uncertainty (0.584%). After this parameter, temperature uncertainty (0.544%), compressibility coefficient (0.305%), K-factor (0.293%) and generated pulse frequency (0.00423%) have the highest uncertainty, respectively. The results show that climate change and seasonal changes can affect the overall uncertainty of the sample station. The values of overall uncertainty in the minimum and maximum temperature and pressure of the inlet gas are equal to 1.572% and 0.763%, respectively, and the changes of these two parameters are about 0.8%. Comparing the results of the installation effects, the first scenario (without elbows) has the lowest overall uncertainty (0.903%) and the fifth scenario with out-of-plane two elbows has the highest overall uncertainty (0.956%). Numerical results show that the use of two elbows upstream has the greatest effect on increasing the overall uncertainty of the sample station. Keywords: metering station, overall uncertainty, gas turbine meter, CFD simulation, ISO-5168 standard.
