Drop Diameter Prediction Model for Liquid Phase Dispersion In A Supersonic Nozzle with Wet Steam Flow


This paper is an attempt to obtain a prediction model for the drop diameter for the liquid phase dispersion in a supersonic nozzle with wet steam. The dispersion of liquid phase and gas dynamic characteristics of the flow of wet steam in Laval nozzles were first studied. A measuring method for dispersion was applied for subsonic and supersonic speeds. A single channel with a model that approximates to what exists between the turbine blades (Laval Nozzle) with different dimensions was designed. An optical unit was also designed on the basis of the work within the small angles method. At the end of the measuring processes for the intensity of the scattered light by laser scattering small angles method, the drop diameter was calculated and all results were analyzed using “DESIGN EXPERT 8” experimental design software. The experimental design used was based on the response surface methodology (RSM) using a central composite design (CCD). A mathematical model of the response (drop diameter) as function of the conditions used (light intensity, pressure ratio, and moisture ratio) was obtained and studied.It is found that the calculated diameter of the drops of the condensed steam along the longitudinal axis of the channelvaries between (40-110μm) according to the pressure ratio change. Also, the diameter of the steam drops is within (40-110μm) according to the variation of the moisture ratio that, where the error is not more than (15%). The geometry of Laval nozzle has a great influence on the nature of the flowing steam through the channel (diameter of drops, compressive shock). The resultant predicted two-factor interaction (2FI) model with a 95%confidence level showed that the pressure ratio, the interaction of pressure ratio and moisture ratio, and their squares were significant terms. According to the results obtained, the predicted model indicated that both pressure ratio and moisture ratio had a significant effect on drop diameter, but pressure ratio had the highest impact, whereas, variation of the light intensity factor had insignificant influence on drop diameter.