**ABSTRACT**

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, CT for the thermal boundary layer and Ca for constrained thermal deformation of throat area. Firstly, using the similarity solution, the formula for correction factor CT over wall temperature range from 0.8T0 to 1.2T0 was obtained. For g = 1.33, CT = 1 - 3.800Re-1/2DT/T0; for g = 1.4, CT = 1 - 3.845Re-1/2DT/T0; for g = 1.67, CT = 1 - 4.010Re-1/2DT/T0. Secondly, thermal and stress models for partially constrained expansion were built. Unlike the free expansion, truth slopes of Ca for three nozzles are +1.74×10-6, -2.75×10-5 and -3.61×10-5, respectively. Lastly, the experimental data of copper nozzle was used to validate present results. It revealed that modified experimental values are in good agreement with the present result.

**KEYWORDS**

PAPER SUBMITTED: 2015-11-04

PAPER REVISED: 2016-06-14

PAPER ACCEPTED: 2016-06-23

PUBLISHED ONLINE: 2016-07-12

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