INTERFERENCE EFFECT BETWEEN SONIC NOZZLES

Calibration of a large capacity gas flow meter may be accomplished wit h a sonic nozzle bank as a reference system. For the design of a compa ct movable prover which is made with many nozzles, the nozzles should be installed as close as possible. The interference effect between nei ghbouring nozzles can be an additional error source for prediction of the mass flow of the assembly from the calibration of individual nozzl es. A nozzle bank was assembled from seven toroidal throat nozzles wit h a nominal throat diameter (d) of 4.3 mm in a hexagonal pattern, it w as calibrated by a primary gas flow system at stagnation pressures fro m 0.5 to 2 MPa and throat Reynolds number from 0.4 to 1.2 x 10(6). Thr ee installation plates of sonic nozzles were fabricated with distances between nozzles of 16-81 mm (L/d of 3.7 to 9.5). The average discharg e coefficient of the seven nozzles in a nozzle bank was calculated fro m the discharge coefficients of the individually measured sonic nozzle s. The differences from the directly measured results were within +/-0 .05% for all test cases. Also, the proximity of the wall for the six o uter nozzles located at 2.3 d from the pipe wall had no influence on t he experimental results. The discharge coefficients as a function of t hroat Reynolds number were in agreement with the recommended equation of ISO 9300. (C) 1998 Elsevier Science Ltd. All rights reserved.