A NUMERICAL STUDY ON STEAM EJECTOR OPTIMUM PERFORMANCE

Document Type : Original Article

Authors

1 Lecture, Dept. of Mech. Power Engineering, Faculty of Engineering, Menoufia University, Shebin El-Kom, Egypt.

2 Professor, Dept. of Mech. Power Engineering, Faculty of Engineering, Menoufia University, Shebin El-Kom, Egypt.

Abstract

ABSTRACT
The present paper introduces a numerical study on the optimum performance of
steam ejector at constant pressure ratio. Both the suction and motive fluids are
assumed to be dry steam. As a result of the low pressure created at the exit of the
supersonic motive steam nozzle, a suction steam is entrained to be mixed with the
motive steam where both flows continue flowing towards the ejector exit. Mass ratio
of suction to motive flows is a vital parameter to enhance the ejector performance.
The objective of the present study is to maximize the steam ejector efficiency by
optimizing the ejector mass ratio. The effect of three different geometrical parameters
on ejector mass ratio and its efficiency is investigated at constant operating
conditions. These parameters are the ejector convergent section angle, the length of
the constant area mixing chamber and the ejector divergent section angle. The
theoretical model is formulated based on single phase (superheated steam), twodimensional
and compressible flow using the finite volume solver, FLUENT 6.3. In
addition, steady, axisymmetric horizontal ejector is considered. The realizable
k −e model is used to model turbulence in the present simulation. The proposed
numerical model is validated with the available experiments in literature. The results
showed that the ejector wall static pressure distributions were greatly affected by the
three investigated geometrical parameters. Furthermore, at constant operating
conditions (motive, suction and back pressures) separation in the ejector divergent
section started to take place at 10o at b =4.8o. In order to avoid separation, the
ejector divergent section angle must be selected carefully together with the operating
conditions. The ejector mass ratio and efficiency increased with increasing the
previously stated three geometrical parameters to gain there upper limit values,
subsequent to that, the efficiency and mass ratio decreased with increasing these
geometrical parameters. Moreover, it is finally concluded that there are certain
optimum ejector convergent, divergent angles and the length of the constant area
mixing chamber in order to optimize the ejector mass ratio and consequently its
efficiency at given constant operating condition.

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