The Pressure Distribution in a Convergent-Divergent Steam Nozzle

Abstract

The paper describes experiments performed to determine the pressure distribution in a convergent-divergent steam nozzle of rectangular cross-section. By means of pressure tappings drilled along the axis, it was found that, in the course of its passage through the nozzle, initially superheated steam expanded continuously until condensation commenced, when a sharp rise of pressure (of the order of 1 lb. per sq. in.) occurred. Up to this point the observations were consistent with the predictions of Callendar's equation for the isentropic expansion of superheated and supersaturated steam: the friction loss was small as far as the throat of the nozzle, but in the divergent portion it was of appreciable magnitude.

The Wilson line was determined after allowances for the effects of friction had been made. The pressure rise was also investigated in detail and was found to be accompanied by a decrease of velocity and an increase of total heat. At the peak of the rise, where continuous expansion recommenced, the steam was probably not in thermal equilibrium.

Additional tappings were placed across the throat, where the pressure observations were in close agreement with the values demanded by Taylor's theory. This theory, which does not assume uniformity of conditions over cross-sections of the nozzle, is more accurate in the neighbourhood of the throat than the classical theory of Reynolds.

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