Harvesting Downstream Energy to Improve Efficiency: Creating Apparent Discharge Coefficients of Jet Nozzles Greater Than 1.3

Abstract

Fluid movement devices use upstream energy to move fluid from one location to another. Flow nozzles that slightly accelerate fluid motion, especially into the same direction, often exhibit discharge coefficients greater than 1.0. Jet nozzles, however, by definition, create a jet stream that is much faster than the upstream fluid, often exceeding 100-fold higher velocities. Energy used to move this fluid is often very high; jetting efficiencies are generally less than 1.0 and will only approach 1.0 if the shape of the entrance is such that there is no “vena contracta” within its flow regime inside the nozzle. High-pressure nozzles require high horsepower to generate high-velocity fluids. As is commonly performed, power is created using high-powered pumping equipment. Oftentimes, nozzles are used to jet in locations that have high ambient pressures, such as at the bottom of the ocean or inside a deep oil well. At these locations, the hydrostatic pressures could be very high. Pressure at the upstream side of the nozzle would be even higher. This paper discusses the design and use of a unique nozzle that uses the hydrostatic (potential) energy to accelerate the fluid velocity of the jet. In essence, the nozzle uses the downstream energy to perform part of its job, thus, substantially reducing the upstream pressure requirement. This phenomenon was proven to occur using CFD analysis. Laboratory tests have shown apparent discharge coefficients between 1.38 and 1.69, depending on the downstream pressure.