Numerical investigation of the flow dynamics inside single fluid and binary fluid ejectors

Abstract

The present study describes the flow dynamics inside a supersonic ejector using Computational Fluid Dynamics (CFD) modelling. Numerical prediction of both the mass flow rates and the wall static pressure profiles are validated using experimental measurements. Air-Air, Argon-Argon and Argon-Air cases are investigated in term of fluid mixing and ejector performance for the same boundary conditions and ejector geometry. It is found that the molar entrainment ratio is higher for Argon-Air as compared to the single fluid cases due to the higher molecular mass ratio between the primary and the secondary fluids. It is also found that the mass entrainment ratio is lower when Air is replaced with Argon as a primary fluid. New flow physics findings based on analysis of flow momentum and turbulence quantities distribution are provided in this paper to explain such behavior.

Numerical Characterization of the Flow Dynamics and COP Estimation of a Binary Fluid Ejector Ground Source Heat Pump Cooling System

“…The uncertainty of the The convergence of the CFD simulations occurred when the residual for each governing equation reduced to a value less than 10 −6 . The same 2D-axisymmetric CFD model of the present investigation was used in our previous studies [2,15]. A good agreement was shown between the CFD and the experimental measurements.…”

“…Equation (2) shows that the smaller the difference between the evaporator and condenser temperatures, the higher the Carnot cycle efficiency. Increasing the temperature of the boiler also increases the COP; however, one must also consider the influence of such an increase on the specific heat of the primary fluid.…”

“…The entrainment ratio (ratio between the mass flow rate of the secondary fluid and that of the primary fluid) is one of the most important parameters that influences the COP of ejector refrigeration systems [1][2][3][4]. Many researchers have shown the need to improve the ejector performance in order to make ejector-based systems economically more attractive.…”

Numerical and Experimental Investigation of Supersonic Binary Fluid Ejector Performance

“…It can be seen that the SST k-ω model gives a good prediction of th static pressure distribution along the ejector wall and a good prediction of the exit tem perature and entrainment ratio. It should be noted that the SST k-ω model provides better prediction of the static pressure distribution for larger differences in molecul weight between the working fluids then in [5]. This could be related to the higher mole ular diffusion rates that exist for fluid pairs with a small difference in molecular mas Indeed, the SST k-ω model primarily focuses on capturing turbulent transport phenomen and may not adequately account for the influence of molecular diffusion.…”

“…Altering the distance between the primary steam nozzle's outlet section and the mixing chamber's inlet section can result in the relocation of the shock wave, which may improve or worsen the steam ejector's entrainment mechanism. As described in [5], the coefficient of performance (COP) for an ejector system is directly related to the mass entrainment ratio. Hence, the entrainment ratio is a standard measure of an ejector's efficiency.…”