Optimization of Steam Ejector Design and Performance Doniazed Sioud #1 , Raoudha Garma #2 , Ahmed Bellagi #3 # U.R. Thermique & Thermodynamique des Procédés Industriels Ecole Nationale d’Ingénieurs de Monastir-ENIM, University of Monastir, Monastir, Tunisia siouddoniazed@gmail.com raoudhagarma83@gmail.com Ahmedbellagi@enim.rnu.tn Abstract— This work presents a computer simulation model of steam ejector is used to enhance the performances of absorption chiller. The 1D model is developed based on thermodynamic equations governing perfect gas flow correlations is used in the current study to improve the ejector: design and performance. Actual study specifies the constant-pressure ejector flow model at critical operating mode for steam as working fluid. The effect of design parameters, particularly the primary nozzle area ratio and the ejector area ratio, and operating conditions of primary, secondary and back pressure are used to evaluate the ejector operating zone according to entrainment ratio calculations. Besides that, the effect of pressure exiting nozzle and the area ratio on ejector performance are discussed and optimized. Keywords—Ejector; Performance, Design, Steam, back pressure, and optimization. I. INTRODUCTION Steam ejectors are used in vapour compression refrigeration and absorption chillers technology to enhance machines performances [1-5]. Ejectors are classified based on the state of the working fluid (gas-liquid ejector, gas-gas ejector) or based on geometry (constant area ejector [6] or constant pressure ejector as described below). Experimental works and a computational Fluid Dynamics (CFD) model are conducted to predict the ejector performances by studying the effect of the primary nozzle and the mixing chamber diameters [7] on the entrainment ratio. Other CFD works were conducted [8] to analyze ejector’s performance using different roughness nozzles levels with experimental values. It was find that the performance of the ejector is noticeably influenced by the friction also that the rise of roughness values will lead to increase in temperature, whereas the Mach number drops working flow in varying proportions and degrades the ejector performance. Other CFD studies, analyzing multi-factor effect on the performances of the ejector and its design [9], results show that after optimization, five-factor : the diameter of the nozzle outlet , the distance between the nozzle outlet to the inlet of the mixing chamber and diameters of the contraction section of the mixing chamber and the diffuser chamber and four-level orthogonal tests to gain the sensitivity for every factor to performances of the ejector, indicating mainly that an optimized ejector has much better performances The effect of back pressure, the throat diameter and the NXP was studied using CFD simulation [10]. It was found that the back pressure should not exceed a critical value, a shock wave can prevent the disturbance caused by back pressure by propagating upstream. Different ejector geometries are tested under different working conditions. A 1D analysis is presented [11] to evaluate ejector performance. The entrainment ratio at working conditions is investigated in order to validate analytically the experimental results of a steam ejector. Results show that the model predicts fairly the entrainment ratio of the ejector and the performances of many studied refrigerator machines. Experimental and theoretical studies [12] are investigated to study ejector working with various flow to establish its design and then optimize the chiller prototype. Experimental works are performed to study the effect of ejector geometries on the performances of a cooling system 13], Results showed the difficulty to reach the optimum of using one ejector under various operating conditions. A 3D ejector model [14] is developed using AutoCAD, meshed and simulated using Ansys CFX. for predefined inputs and boundary conditions, pressure, temperature, Mach number and velocity contours are analysed Parametric analysis was carried out to identify the convergence. A steam ejector [15] is investigated. Two theoretical approaches are discussed: ejector design for a fixed duty and performance ejector prediction for known geometry. Semi-empirical correlations are proposed for the design and performance prediction of steam ejectors. Investigations are carried out to design and optimize an ejector using ammonia [16] in order to find out the optimum operation conditions. A maximum entrainment ratio is found under various boundary conditions and for each value. An optimum area ratio is then concluded for each case. The purpose of the present work is to analyse theoretically the design under various operating conditions of steam ejector. Optimum operating conditions as function of thermodynamic and geometric parameters governing the ejector are discussed in order to optimize its performances and to evaluate its off design conditions.