that depends from the way you decide to model the nozzle,
I utilize the isentropic nozzle model
available in PRODE PROPERTIES , see

'http://www.egpet.net/vb/entries/82303-PSV-sizing-with-HEM-%28Homogeneous-Equilibrium-Model%29-limits-of-application'

this model for HEM adopts a mixed (isentropic + adiabatic) solution for outlet temperature,
according my experience the results are consistent with infield measurements.