A water film cooling modular nozzle for high temperature testing of specimens or similar comprising a rather long divergent in relation to the throat diameter, consisting of a metal section including the convergent, the throat and the beginning of the divergent and one or several divergent sections also metallic, the various sections being end to end assembled, and in that the outer wall of each section is independently cooled with a thin water film, the unit consisting of the sections and the separators being enclosed in a fixed outer shell defining, opposite each section, an independent cooling fluid circulation chamber containing the separator, the arrangement being such that a clearance with respect to the longitudinal axis of said unit in relation with said shell is allowed in order to absorb the thermal expansion of the nozzle.