Performance measurements of a flashing flow nozzle

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Virginia Tech


The performance of a flashing flow nozzle was quantified by efficiency and metastability measurements. Efficiency was calculated over a range of operating conditions, by using both inlet and exit conditions and the nozzle thrust. Metastability was quantified by a parameter that compared the experimental mass flow rate with homogeneous equilibrium and frozen state flow rates. The efficiency of the flashing flow nozzle was found to be less than half the efficiency of the nozzle while operating at near thermodynamic equilibrium. Attempts were made to improve nozzle performance by lowering the piping diameter immediately upstream of the nozzle to increase flow turbulence and encourage a uniform bubbly flow. Bubbly flow helps two-phase flows become less metastable, by generating a uniform distribution of bubbles that act as nucleation sites for flashing inception. Low flow metastabilities were found with high inlet qualities and small upstream piping diameters. These conditions also resulted in the highest flashing flow nozzle efficiencies; however, the efficiency showed a much less pronounced response to upstream piping diameter. The homogeneous equilibrium model was found to be an inaccurate predictor of nozzle performance. To satisfy this model, a shock must be positioned in the nozzle's divergent section, severely limiting nozzle efficiency. The effects of phase slip on nozzle efficiency were investigated with recommendations made for further research in this area.



refrigeration, two-phase