The present work described experimental and numerical investigations of ejectors using water as the motive fluid and water and gas as the entrained fluid. These ejectors are used in low temperature thermal desalination systems to entrain the brine and non-condensable gases to keep the desalination systems operating on condition of the vacuum. The numerical simulations were based on the Euler-Euler multiphase model, with a simplified slip velocity ratio, determined by comparing the experimental and the simulation results. The simulations showed that the slip velocity between phases is 11% and 12%. The simulations examined the influence of several variables, including the primary fluid pressure, the suction fluid pressure and the discharge pressure, on the volumetric entrainment ratio and efficiency. The results show that, if the structural variables are fixed, the volumetric entrainment ratio is determined by the pressure ratio Delta p(p)/Delta p(c) with the maximum efficiency obtained for a pressure ratio equal to the throat aspect ratio (D-T/D-N)(2). (C) 2011 Elsevier B.V. All rights reserved.