Venturi nozzles allow a fast moving, or motive, gaseous stream to entrain a nearly quiescent, or suction, gaseous stream. In a Venturi nozzle, the motive stream is accelerated by flowing through a converging nozzle. The highest velocity is achieved at the throat of the nozzle. The high velocity of the fluid creates a region of low static pressure and therefore a pressure difference between the nozzle and the surroundings. The pressure difference allows for flow into the nozzle where the suction and motive streams mix before leaving the nozzle.Supersonic thermal ejectors and high pressure Venturi nozzles have been well studied and their performance characterized based on geometry and operating conditions. Additionally, large and high-pressure Venturi nozzles are extensively studied but there is a gap in engineering design knowledge for small scale design. The purpose of this work is to analyze small scale, subsonic, low pressure Venturi mixing nozzles in order to similarly characterize their performance. The use of small scale, subsonic, low pressure Venturi nozzles allows for two streams to mix while only using a compressor to move one of the streams, thus reducing the necessary energy input to operate a system.&nbsp;In subsonic Venturi nozzles, the suction flow rate is a function of the low pressure region, and therefore, the high velocity in the nozzle. The velocity and pressure are dictated by the geometry of the nozzle and the motive stream flow rate. The pressure at the suction inlet also has an effect on the suction flow rate; increased pressure at the suction inlet increases the suction flow rate. A parametric study was conducted to determine the effect of three different geometric parameters on the suction flow rate: the throat diameter; the diameter through which the suction stream enters the nozzle, or the suction diameter; and the distance between the throat and outlet of the nozzle, or the mixing length.Fifteen different Venturi nozzles were designed and simulated in Ansys Fluent to determine the effect of the geometry and operating conditions on the suction flow rate for a total of 55 simulations. The geometries were simulated with different suction pressure inlet and motive mass flow inlet boundary conditions. In all cases, it was assumed that the outlet of the nozzle was at ambient pressure. Experimental validation was conducted to ensure the validity of the simulations. The experimental and simulated results matched within 10% for each case. In this study both the motive and suction streams were air.Dimensional analysis was completed to determine functional relationship between the ratio of the suction mass flow rate to the motive mass flow rate, or suction ratio, and the geometry, suction inlet pressure, and fluid properties. A global minimization regression analysis was then done on the simulated data to determine the dependency on each dimensionless group. The result is a correlation equation for the suction ratio as a function of the dimensionless groups formed from the geometric parameters, operating conditions, and fluid properties.This correlation can be used as a design guide for Venturi nozzles. If operating conditions dictate an optimum suction ratio, the ideal nozzle geometry can be determined. Alternatively, based on the geometry of a given nozzle, the resulting suction ratio can be determined.

Effect of Geometry on Small Scale Venturi Nozzle Performance

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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