Geometry dimension optimization of a liquid–gas vacuum ejector for MED-TVC system

Abstract

• Establishing the 3D model for the design and optimization of liquid–gas ejector. • The internal fluid flow characteristics of liquid–gas ejector was investigated. • The optimal NXP, area ratio and the length of mixing chamber were obtained. • A correlation between geometric parameters and ejector performance is developed. A liquid–gas ejector is designed to entrain the non-condensable gas accumulating in the condenser without power consumption in the multi-effect distillation with a thermal vapor compression desalination system and the geometry dimensions are optimized by the optimization method provided in this paper for their vital influence on liquid–gas ejector performance. In this paper, the effects of nozzle exit position, area ratio, and the mixing chamber length on liquid–gas ejector are investigated simultaneously using numerical simulations. The results show that: the mass flow rate ratio and efficiency increase within a certain range and then decrease while the nozzle exit position increases; the mass flow rate ratio increases with the increasing of area ratio, meanwhile, the efficiency increases until reaching a maximum value and then decreases; there is no obvious effect on system vacuum degree as the mixing chamber length increases. Following this, the optimal geometry parameters including nozzle exit position, area ratio, and mixing chamber length are determined. When NXP is 16.95 mm, the area ratio is 4.45 and the length of the mixing chamber is 92.5 mm, the liquid–gas ejector has the best performance with the efficiency, mass flow rate ratio, and vacuum degree of 0.5, 2.02, and 0.18 atm, which satisfies the design requirements. Through the geometry optimization method, the liquid–gas ejector can effectively remove the non-condensable gas from the condenser instead of the mechanical pump in the vacuum system under a typical working condition of the multi-effect distillation with thermal vapor compression desalination system.