Abstract
In the present paper, a series of numerical simulations of wet steam flows within ejectors distinguished by four primary nozzle contours have been carried out with the objective to evaluate the overall ejector performance. The studied primary nozzle contours are the following: a standard Laval nozzle (LAVAL); a nozzle that is designed in order to provide Constant Expansion Rate (CER); and two nozzles (MOC_SHORT, MOC_LONG) that are designed by employing axisymmetric Method of Characteristics. At first, the wet steam flow simulation throughout solely nozzles are carried out. Within the CFD simulations routines most valuable flow parameters are compared: expansion rates, boundary layer displacement and momentum thicknesses; entropy generation rate from various thermodynamic forces; thrust and liquid mass fraction across the nozzle exit plane. A comprehensive analysis of solely nozzles revealed that the CER nozzle contour is the most aerodynamically efficient design, which provides the minimum liquid mass fraction by the nozzle exit and possess the minimum entropy generation rate. The CFD results analysis of a full ejector domain revealed that an ejector with a MOC_SHORT primary nozzle contour provides the maximum performance in terms of secondary mass flow rate. At that, the secondary mass flow rate in MOC_SHORT nozzle contour case is almost 4% greater than for the CER nozzle design case.
Highlights
Steam ejectors are widely used in metallurgy, oil and gas industry, etc
A series of numerical simulations of wet steam flows within ejectors distinguished by four primary nozzle contours have been carried out with the objective to evaluate the overall ejector performance
The studied primary nozzle contours are the following: a standard Laval nozzle (LAVAL); a nozzle that is designed in order to provide Constant Expansion Rate (CER); and two nozzles (MOC_SHORT, MOC_LONG) that are designed by employing axisymmetric Method of Characteristics
Summary
Steam ejectors are widely used in metallurgy, oil and gas industry, etc. On power plants, steam ejectors are used to utilize non-condensable gases from low-pressure parts of steam turbines. As with any jet pump, the main device component of the ejector is the primary nozzle, in which the potential energy of the vapor (pressure) is converted into kinetic energy of the jet (momentum). In this case, the supersonic primary flow involves a static secondary flow through a turbulent interaction in the free shear layer in the ejector’s mixing chamber. [3], where comprehensive data are given both on the geometry of the experimental ejector and on the operating modes studied (initial steam parameters, mass flow rates of the motive and suction flows, distribution of static pressure along the wall of the mixing chamber and diffuser). In Ref. [3] author does not take into account the condensation that is the flow feature of all devices with water vapour as a fluid
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