Efficiency of a flashing flow nozzle

The efficiency of a flashing flow nozzle using R134A in an energy system using geothermal high pressure hot water, is calculated from a combination of thrust, flow, pressure, and temperature measurements. In order to promote nucleation within the nozzle, the inlet flow is seeded with small bubbles. Nozzle efficiencies are found to range from 33 to 47%. Increasing total mass of seeding bubbles (increasing inlet quality) and decreasing size of seeding bubbles is found to increase nozzle efficiency. Thermodynamic nonequilibrium in the nozzle is evaluated by comparing the flow rate to that predicted by homogenous equilibrium and frozen flow models. The same inlet flow changes that increase efficiency decrease thermodynamic nonequilibrium. The measured nozzle efficiencies are much higher than predicted by a homogenous equilibrium model with a normal shock in the diverging section.