THERMAL EFFECT ON MASS FLOW-RATE OF SONIC NOZZLE

Sonic nozzles are widely used as flow measurement and transfer standard. The thermal effect of sonic nozzle is significant at low Reynolds number. It includes two correction factors, C-T for the thermal boundary-layer and C-alpha for constrained thermal deformation of throat area. Firstly, using the similarity solution, the formula for correction factor C-T over wall temperature range from 0.8T(0) to 1.2T(0) was obtained. For gamma = 1.33, C-T = 1 - 3.800 Re-12 Delta T/T-0; for gamma = 1.4, C-T = 1 - 3.845 Re-12 Delta T/T-0; for gamma = 1.67, C-T = 1 - 4.010 Re-12 Delta T/T-0. Secondly, thermal and stress models for partially constrained expansion were built. Unlike the free expansion, truth slopes of C alpha for three nozzles are +1.74.10(6), -2.75.10(5) and -3.61.10(-5), respectively. Lastly, the experimental data of Cu nozzle was used to validate present results. It revealed that modified experimental values are in good agreement with the present result.