Liquid Jet Ejector Research Articles

Investigation of two phase liquid jet ejector with simultaneous air and water suction in fresh water distillation system

Liquid jet ejectors can be utilized to generate vacuum in thermal desalinations, power plant applications and chemical industries. Liquid jet ejectors have no moving parts and have the advantage of reliability and low maintenance cost and also entrainment of non-condensable gas and brine simultaneously relative to pumps. The aim of this work is to model a liquid jet ejector with mixed air and water suction, applicable in fresh water distillers. The design is numerically simulated by two-phase Eulerian model and Realizable k-ε turbulence model. The results of the numerical model of liquid jet-air ejector are compared with experimental data and good agreement is achieved with deviation of about 7.4 % and 11.2 % for flow ratio and maximum discharge pressure respectively. In order to study robustness of the design, the value of suction entrainment and motive load of ejector is studied for different values of brine and suction pressure (8–12.5 kPa) of a 12 m3/day fresh water distiller. The results show constant air entrainment in off-design condition. In addition, mixing behavior and hydrodynamics of the flow in such ejector is studied by the parameters of pressure, velocity, flow and turbulent intensity distribution and compared with the ejector with air-only suction.

Optimization of liquid jet ejector geometry and its impact on flow fields

Liquid jet liquid (LJL) ejectors have wide industrial application and the improvement in their efficiency is sought to increase the viability of their use. This study performs the optimization of the entire geometry of an LJL ejector with multiple parameters to maximize energy efficiency. The approach with multiple parameters allows to identify key geometrical features and interdependent parameters, like nozzle position and mixing chamber length, with respect to performance. Computational fluid dynamics (CFD) and optimization simulations were performed to optimize the parameters of Bézier curves that characterize the device's geometry. The optimization results showed that the ejector efficiency curve is sensitive to the nozzle and the suction chamber geometries. Simulations that consider the nozzle diameter and the nozzle position along ejector axis (NXP) as parameters of the optimization process resulted in higher efficiency values than those that kept these parameters fixed. The optimization of the diffuser curve, including the diameter of the diffuser and the length of the mixing chamber, also contributed to increase the efficiency of the device. It was observed that the increase in the length of the mixing chamber and the spacing of the nozzle imply similar effects in the efficiency and in the pressure, velocity and energy dissipation rate profiles confirming some correlation of these parameters on the performance. One may observe the effect of geometry modification through optimization on the flow profiles in key sections of the ejector: the flow profiles in the optimized geometry tend to be more homogenous, hence less dissipative, and it is also confirmed by local energy dissipation rate.

Effect of turbulent dispersion on hydrodynamic characteristics in a liquid jet ejector

Gas induction using a liquid jet is an extensively studied phenomenon. Many studies have been published detailing various hydrodynamic and mass transport aspects of gas induction in ejectors. Conversely, multiple studies have been published detailing jet dynamics, jet break up, nozzle geometry, effects of turbulence etc. In the modelling of the jet ejector systems CFD framework is used as the flow of gas is coupled with the liquid flow and the flow parameters like volume fraction, pressure drop/profile and velocity profiles both local and average are highly interdependent. Hence, it becomes important to capture all the flow physics in the simulations in order to understand the hydrodynamics. In the previous models the effect of turbulent dispersion was not included which led to incorrect calculation of phase profile, and other related parametric values. In the present work, the turbulence effects and its impact on the jet dynamics and gas induction rate in an ejector have been studied. Capturing the correct phase as well as velocity profile is imperative for the extension of the model to mass transfer and reactions. Lastly, other hydrodynamic properties like pressure drop, phase hold up and pressure profile help better the design correlations for jet ejectors.

Modelovanje simulacija i upravljanje postrojenja za desalinizaciju vode

In this paper, modelling, simulation and control of water desalination plant is presented. The desalination plant is based on vapour compression method acquired utilizing a liquid jet ejector. Nonlinear steady-state model is developed in order to verify simplified dynamic model for control purposes. Furthermore, to design PI controller capable of guiding the system through desired states under the influence of disturbances, the linearized model of the plant has been developed and verified applying the nonlinear dynamical model. It is shown that presented approach can deliver satisfying model and tracking results.

Liquid Jet Ejector Efficiency Improvement

The issues of application of an agitator, a diffuser, and a vertical pipe in a liquid jet ejector are considered. Possible versions of an agitator as a rotating nozzle with blades are recommended. A physical and mathematical model based on fundamental equations, which reflect the operating process of the device, is developed. The estimated dependencies and restrictive conditions of operation of the electrically driven rotating nozzle and blades ejector are provided. The increase in the efficiency of application of the agitator, diffusor, and vertical pipe is numerically quantified by means of extreme characteristics. Thus, a maximum efficiency gain of 37% after agitator is installed; 13% when diffuser is installed; 5% when vertical pipe is installed can be reached. The characteristics that reflect the relationship of maximum attainable operating parameters and the corresponding values of optimum relative nozzle area are obtained. The constancy of the optimum relative nozzle area in a wide range of operating parameters, while using the agitator alongside the diffuser and the vertical pipe, is revealed. Hence, if the agitator is applied, the optimum relative nozzle area is 0.29 ... 0.30, if the diffusor and vertical pipe are added, then – 0.40 ... 0.41. The recommendations on the implementation of the obtained results are made.

Rate of absorption and interfacial area of chlorine into aqueous sodium hydroxide system

Due to excellent mass transfer characteristics with energy efficiency jet ejectors can be used in place of conventional countercurrent systems, namely, packed bed contactors as well as venturi scrubbers, cyclones and airlift pumps. The removal of chlorine from certain gases by absorption in aqueous solutions of sodium hydroxide is industrially important in several chemical processes particularly in pollution control. Although, a number of papers have been published in the past, none of them provided a theoretical basis for the prediction of rate of absorption of chlorine from certain gases by absorption in aqueous solutions of sodium hydroxide in jet ejector. In this work, the rates of absorption of chlorine from different concentration of gas into aqueous sodium hydroxide solutions of various concentrations were measured at 30°C using a liquid jet ejector. The experimental results were analyzed on the basis of the penetration theory for gas absorption. The theoretical model to calculate rate of absorption is developed. The rate of absorption predicted from developed model is compared with experimental results. They were in good agreement. In this work, an attempt also has been made to develop mathematical model to estimate enhancement factor for jet ejector applying Higbie penetration theory. Key words : Higbie penetration theory, jet ejector, chlorine, aqueous solutions, gases.

Influence of pressure on the gas hold-up of aqueous activated carbon slurries in a down flow jet loop reactor

The hydrodynamics of a loop venturi reactor was studied using a down flow liquid jet ejector. The influence of the pressure, P, the superficial gas velocity, V g,sup , and the presence of small activated carbon particles on the gas hold-up, ε g , of aqueous systems in the main holding vessel was investigated. For the 2-phase system water–N 2 gas the influences of V g,sup (in m s −1 ) and the gas density ρ g (in kg m −3 ), on the observed ε g (in m 3 m −3 ) correlates as follows: ε g=0.873 V g, sup 0.55 ρ g 0.17 where V g, sup <0.14 m s −1 and 2.3 kg m −3⩽ρ g⩽17 kg m −3. The 3-phase experiments were performed with the system water–N 2 gas-activated carbon particles. Values of the solids fraction, ε s , ranged up to 4.8 wt% . In these systems qualitatively similar results were observed regarding the influence of V g,sup and P on ε g . However, the effect of the fine carbon particles on the porosity is much more complex. The presence of a low solid content increases the gas hold-up, whilst a higher solid content reduces the porosity sharply. The positive influence of carbon fines on the porosity diminishes at higher gas pressures. Based on these results it is suggested that for the design of jet loop reactors for 3-phase aqueous systems with a low content of active carbon fines the effects of V g,sup , P and ε s should be taken into account.

Hydrodynamics and mass transfer characteristics of a loop-venturi reactor with a downflow liquid jet ejector

The hydrodynamics and mass transfer characteristics of a loop-venturi reactor have been investigated using a downflow liquid jet ejector. The specific interfacial area of the ejector and the main holding vessel were determined separately. The cobalt catalyzed sulfite oxidation was used as a model system. The measured values of the interfacial area were in the range of 40,000 to 70,000 m 2/m 3 in the ejector and 500 to 2500 in the total system. From this it can be concluded that the Loop-venturi reactor is particularly suitable for very fast reactions, in which the liquid phase mass transfer is the reaction limiting step of the process. Further it was demonstrated that the flow regime in the ejector has a huge influence on the mass transfer characteristics of the total system. From the results it is concluded that for a proper design of a loop-venturi reactor, the ejector and the main holding vessel should be considered as two reactors in series, which require individual modeling.

Influence of the gas density on the gas entrainment rate and gas hold-up in loop-venturi reactors

The hydrodynamics of a loop-venturi reactor were investigated using a downflow liquid jet ejector. Both the gas entrainment rate of the ejector and the gas hold-up in the main holding vessel were shown to be influenced by the gas density. The amount of volumetrically entrained gas as well as the gas hold-up increase, whilst the average gas bubble diameter in the main holding vessel decreases with higher gas densities. The influence of the gas density on the gas entrainment rate could be explained from the Kelvin-Helmholtz stability analysis. This analysis showed that the initial amplitudes of the surface instabilities on the liquid jet surface ‘are influenced’ by the aerodynamic forces, i.e. a higher gas density results in an increase of the jet width at the plunging point. The increased gas flow observed at higher gas densities could be well explained by this theory.

Mass transfer and hydrodynamic characteristics of loop reactors with downflow liquid jet ejector

The mass transfer and hydrodynamic characteristics of a loop reactor have been investigated using downflow liquid jet ejectors fitted with straight- and venturi-type throats. The entrainment rate of the liquid jet and the gas holdup were shown as functions of power input per unit volume of the liquid. Similarly, the interfacial area and volumetric mass-transfer coefficient were correlated with the power input. The interfacial areas achieved with a venturi ejector are far superior to those obtained with a straight throat ejector. For the liquid-side mass transfer coefficient, the trend was found to be reversed within the range of the operating variables studied in this work. The gas—liquid behaviour inside the ejectors was analysed qualitatively for a better understanding of the phenomenon.

Momentum transfer in a vertical down flow liquid jet ejector: case of self gas aspiration and emulsion flow

Momentum transfer in a vertical liquid jet contactor consisting of an ejector supported in a vertical column has been studied, using three different liquids as motive fluids, and air as the entrained gas. On the basis of macroscopic momentum and energy balance, an overall loss factor is derived. Moreover, an empirical correlation is proposed to predict the mass flow rate of entrainment by the liquid jet system. Finally, an expression to predict the volumetric flow rate of the carried fluid available at a pressure higher than atmospheric, is given.

Gas-liquid mass transfer in the jet reactor with liquid jet ejector.

Liquid-side volumetric mass transfer coefficients and effective gas-liquid specific interfacial areas were measured from the longitudinal distribution of oxygen concentration in gas phase by catalytic sulfite oxidation with air in the spouting and the calm sections, which were the lower and upper regions respectively in the jet reactor with liquid jet ejector. Both liquid-side volumetric coefficients and effective gas-liquid specific interfacial areas increased with the kinetic energy of the liquid jet, and their values in the spouting section were larger than those in the calm section. Further, effective gas-liquid specific interfacial area showed greater values than in other types of reactors, at a similar power supply per unit reactor volume.

Liquid phase mixing in the gas-liquid jet reactor with liquid jet ejector.

The liquid-phase mixing pattern and dispersion coefficients were studied by the tracer concentration distribution at steady state and the impulse response method for the gas-liquid jet reactor with liquid jet ejector. The longitudinal liquid-phase mixing pattern was quite different between the spouting section and the calm section. In the spouting section, which was the lower region in the column, the liquid phase was regarded as almost completely mixed flow. By contrast, in the calm section, which was the upper region, the value of the dispersion coefficient was fairly smaller than that in bubble columns and back-mixing of the liquid phase was suppressed.

Flow Pattern and Gas Hold-Up in Bubble Column with Liquid Jet Ejector

Flow Pattern and Gas Hold-Up in Bubble Column with Liquid Jet Ejector

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Dispersion of Gas by a Liquid-Jet Ejector

Dispersion of Gas by a Liquid-Jet Ejector