Venturi Ejector Research Articles

Research on a new-designed Venturi ejector and dazomet particle motion characteristics for dilute-phase pneumatic conveying systems based on CFD-DEM

To disperse dazomet, a commonly used soil fumigant for soil disinfection, over large soil surfaces, dilute-phase pneumatic conveying can be utilized. Currently, most research has focused on pneumatic conveying systems for large particles, such as coal conveying or pneumatic seeding However, there has been almost no research on the dilute-phase pneumatic conveying of dazomet particles. Therefore, a coupled simulation model based on computational fluid dynamics and discrete element method (CFD-DEM) was established to study the effect of the structural parameters of the Venturi ejector on the motion of particles and airflow fields variation characteristics for the pneumatic conveying system of dazomet particles. Based on the Box–Behnken experimental design method, a 3-factor and 3-level response surface simulation experiment was carried out by selecting the contraction angle, throat diameter, and diffusion angle of the Venturi ejector as factors. The suction-flow ratio, average velocity of particles, average coordinates of particles in the vertical direction, and corresponding standard deviation at the outlet of the pipeline were chosen as response indexes. Multiple linear regression models were established between each factor and response index. The simulation results showed that the impact of factors on the 4 response indexes from strong to weak were throat diameter, contraction angle, and diffusion angle. With decreasing throat diameter, the suction flow ratio and average velocity of the particles increased. The average coordinates of the particles in the vertical direction decreased, while the standard deviation increased, indicating that the pneumatic conveying performance of the system increased. The optimal structural parameters for the contraction angle, throat diameter, and diffusion angle were 34.5°, 15 mm, and 12.0°, respectively. The experimental results demonstrated that the application precisions of the optimised Venturi ejector were 99.23%, 98.46%, and 98.56% at application rates of 15, 20, and 25 g/s, respectively. The results provide a theoretical reference for the structural optimisation of the Venturi ejector and operational performance evaluation of the pneumatic conveying system for dazomet particles.

Optimization Design of an Alfalfa Seed Airflow Collection and Drainage System Based on Numerical Simulation

In order to improve the working performance of an Alfalfa air conveyor, a type of horizontal screw conveyor with a seed stirring function was designed. The working process of the horizontal screw conveyor was co-simulated by EDEM software and ADAMS software. The effects of a seed stirring mechanism on population movement characteristics, population stress, the seed mass flow rate and the variation coefficient of each index were obtained. The results showed that the stirring mechanism can effectively improve the mobility of the population, reduce the local dead zone of the population, and increase the material filling coefficient between the spiral blades. Under the same working conditions, the horizontal screw conveyor with a stirring mechanism has a higher conveying efficiency and better conveying uniformity. In order to optimize the structure parameters of the Venturi injector diffuser and improve seeding efficiency and uniformity, EDEM software and Fluent software were used to co-simulate the seeding process. The influence of diffuser structure parameters on the working performance of the Venturi injector was analyzed by taking the changes in pressure and velocity in the inner flow field of the pipeline and the velocity and force of seed particles as indices. The results showed that when the diffusion angle is 5°, the length of the diffusion section is 200 mm and the length of the mixing section is 50 mm, the pressure loss of the Venturi ejector is the smallest, the outlet air velocity is the largest, the uniformity of seed feeding is the best and the seed feeding efficiency is the highest. Taking the inlet air pressure and particle feeding efficiency as test factors and the variation number of ejector discharge as test index, a two-factor and five-level full factor test was carried out, and the range and variance analyses were carried out. The results showed that the seed feeding rate and the inlet wind pressure had significant effects on the coefficient of variation. The optimal combination of working parameters was 1.6 kpa inlet wind pressure and 1.8 g/s particle feeding efficiency.

Biogas Upgrading to Biomethane by CO2 Removal using Water Absorber with Microbubble Technique

Biogas upgraded to biomethane can be utilized as a renewable energy source to substitute LPG in households and industry. This study explored biogas upgrading by CO2 removal from 20 - 75 % CO2-N2 simulated biogas mixture. The experimental unit using the microbubble technique combined with the water absorption column was set up and used for CO2 removal from the gas. Microbubble sizes of 20 - 30 µm were generated by a venturi ejector and measured with an automated bubble size measurement. The experiments confirmed that a microbubble with an inline mixer could enhance the effectiveness of the absorption process. The tests demonstrated over 85.80 % removal of CO2 from the simulated biogas by the experimental unit. The effects of various parameters, including the size of venturi ejector, gas flow rate, water flow rate, liquid-gas ratio, and initial concentration of CO2, were investigated. The results revealed that 2 L/min gas flow rate, 15 L/min water flow rate, L/G ratio 7.5, and venturi ejector size 0.50 inches are the optimum conditions. The use of the tube absorber gave much higher CH4 recovery than an absorption column. The appropriate operating conditions gave over 96 % CH4 concentration or less than 4 % CO2 concentration, matching the CH4 purity required by biomethane specifications. The results indicated that the new technique demonstrated in this study can upgrade biogas to biomethane.

Optimizing conical nozzle of venturi ejector in ejector loop reactor using computational fluid dynamics

The structure of a conical nozzle is critical to the gas induction of a venturi ejector. In this work, the effect of nozzle structure on the gas induction was investigated by means of multiphase CFD and validating experiments. Under different structures, the maximal gas induction was obtained through analyzing the nozzle outlet velocity (NOV), nozzle inlet velocity (NIV), as well as nozzle shrinking angle (NSA). The simulated inlet pressure is positively proportional to inlet flow rate, which is in good agreement with experimental results. The simulated results reveal that the inlet pressure and gas induction increase with the increasing NOV. Considering the operational characteristics of centrifugal pump, the recommended NOV is about 21.8 m/s. NIV and NSA show little impact on gas induction and inlet pressure. Based on the pipeline energy consumption, the recommended NIV is the same as the outlet velocity of centrifugal pump. The recommended NSA is about 20o to obtain the maximal gas induction.

Numerical investigation into hydrogen supply stability and I-V performance of PEM fuel cell system with passive Venturi ejector

In traditional PEM fuel cells (PEMFCs), the unreacted hydrogen gas at the anode outlet is recovered using a mechanical pump or centrifuge and returned to the inlet side for reuse. However, the energy consumed by the pump reduces the system efficiency. Accordingly, the present study considers a 3-kW PEMFC in which the unreacted hydrogen gas is recovered passively from the exhaust stream using a Venturi ejector. An integrated simulation framework is constructed consisting of a COMSOL model of the ejector unit and a MATLAB/Simulink model of the hydrogen recovery system. The simulation framework is used to examine the temperature, pressure and velocity distributions within the ejector for various values of the inlet hydrogen pressure. The stability of the hydrogen supply in PEMFC systems incorporating a passive ejector system and a traditional mechanical hydrogen recovery system, respectively, is then investigated and compared. It is shown that the ejector stabilizes the hydrogen supply more quickly than the traditional mechanical system. As a result, it not only improves the hydrogen utilization rate and environmental safety of the PEMFC system, but also reduces the overall hydrogen consumption. The simulation results for the I-V performance of the PEMFC with the Venturi ejector are shown to be in good qualitative agreement with the experimental results. Overall, the numerical framework constructed in the present study provides a useful tool for exploring the effects of the ejector design parameters on the hydrogen recovery performance and determining the operating conditions which maximize the performance of the PEMFC system.

Numerical and experimental studies on transport properties of powder ejector based on double venturi effect

The venturi ejector can form vacuum fields to transport particles due to venturi effect. The transportation performance of powder ejectors based on single- and double-venturi effect and the influence of nozzle position on the transportation performance were respectively investigated by the experimental method and the numerical simulation based on the CFD-DEM coupling method. The present results show the wind speed of the particle inlet increases due to the double-venturi effect, which is beneficial for particles into the injector; the driving force exerting on particles by fluid increases, meaning that particles can be transported to a long distance; the closer the nozzle is to the export, the greater the wind speed of the particle inlet is and the greater the suction force exerting on particles is; the closer the nozzle is to the export, the less the deposition number of particles in the injector is; however, particles can be hindered into the venturi tube if the nozzle is very close to the export. Additionally, in order to reduce the particle deposition, the optimal solution is presented here, namely, the nozzle position away from the export, y∗ = 30 mm.

Assessment of the Aerosol Generation and Toxicity of Carbon Nanotubes.

Current interest in the pulmonary toxicity of carbon nanotubes (CNTs) has resulted in a need for an aerosol generation system that is capable of consistently producing a CNT aerosol at a desired concentration level. This two-part study was designed to: (1) assess the properties of a commercially-available aerosol generator when producing an aerosol from a purchased powder supply of double-walled carbon nanotubes (DWCNTs); and (2) assess the pulmonary sub-acute toxicity of DWCNTs in a murine model during a 5-day (4 h/day) whole-body exposure. The aerosol generator, consisting of a novel dustfeed mechanism and venturi ejector was determined to be capable of producing a DWCNT consistently over a 4 h exposure period at an average level of 10.8 mg/m3. The count median diameter was 121 nm with a geometric standard deviation of 2.04. The estimated deposited dose was 32 µg/mouse. The total number of cells in bronchoalveolar lavage (BAL) fluid was significantly (p < 0.01) increased in exposed mice compared to controls. Similarly, macrophages in BAL fluid were significantly elevated in exposed mice, but not neutrophils. All animals exposed to CNT and euthanized immediately after exposure had changes in the lung tissues showing acute inflammation and injury; however these pathological changes resolved two weeks after the exposure.

Numerical simulation of Venturi ejector reactor in yellow phosphorus purification system

A novel type of Venturi ejector reactor, which was used in a pilot plant test in a factory in Guizhou in China, was developed to overcome the insufficiency of chemical reaction in the stirred-tank reactor in yellow phosphorus purification system. The effects of different working medium, the changes of vacuum region, and the performances of the Venturi ejector reactor with different operating pressure were investigated by FLUENT. Results show that the absolute value of vacuum pressure of single-phase flow was smaller than two-phase flow at the same operating conditions, which meat two-phase flow has a higher suction capability. Reflow phenomena occurred near the exit of suction pipe and nozzle. The former reflow which leads to energy loss of vacuum region was undesirable, and the latter was beneficial to the dispersion of liquid yellow phosphorus. With a flow rate ratio below 0.45, the performance of the Venturi ejector reactor was effective. By adjusting the operating pressure, a proper flow rate ratio could be satisfied to meet the production needs in yellow phosphorus purification system.

Optimization of oxygen transfer through venturi‐based systems applied to the biological sweetening of biogas

AbstractBACKGROUND: Dissolved oxygen is a key parameter in the biological removal of gaseous H2S since sulfide‐oxidizing bacteria convert H2S into elemental sulfur instead of sulfate under limiting dissolved oxygen concentrations. Elemental sulfur is insoluble in water and accumulates in the packing material in biotrickling filters, increasing the pressure drop and operating costs. A set of mass transfer tests was performed in a versatile pilot plant to supply the necessary oxygen for the biological oxidation of H2S. The plant can be operated with three different commercial gas–liquid contactor devices: a venturi ejector, a jet‐venturi and a diffuser. The effects of different geometric and operating parameters have been tested for each device (including pressure rise and sulfate content to mimic real wastewater treatment plant conditions).RESULTS: Results showed that the bioreactor pressure has a strong influence on the mass transfer characteristics of the three oxygenation devices. In addition, the ionic strength of the solution has a low influence on the mass transfer process.The SOTE values obtained for the diffuser, jet‐venturi and venturi ejector were 8.7%, 7.2% and 6.0%, respectively (pure water experiments), while SAE values were in the range 6.3–5.5 × 10−2, 4.1–4.8 × 10−1 and 3.1–3.7 × 10−1 kg O2 kW−1 h−1, respectively.CONCLUSIONS: The jet‐venturi offers the best oxygen transfer with lower power consumption compared with the diffuser and venturi ejector. The practical implementation of the most efficient aeration technology is possible from both technical and economical perspectives. Copyright © 2012 Society of Chemical Industry

Next generation of ceramic hot gas filter with safety fuses integrated in venturi ejectors

The next generation of ceramic hot gas filter system of Pall Corporation with advanced venturi ejector blowback system, longer filter candles and safety fuses integrated in the venturi ejector is presented. The cleaning performance of the advanced venturi ejector blowback system has been investigated using filter candles of 1.5m length with additionally installed safety fuses and with 2m long filter candles with and without safety fuses. Measurements of the pressure profiles in the filter elements have been performed for a group of 48 filter elements. The results of these measurements are reported and discussed. The results are compared to reference measurements using the previous standard venturi ejector blowback system with 1.5m long filter elements.

Evaluation of the effects of water agitation by air injection and water recirculation on the heat transfer coefficients in immersion cooling

Most industrial food cooling is performed by air blast, water spraying and immersion cooling. Immersion cooling is simple, with low operational cost and leads to food quick cooling. The objective of this work was to investigate the influence of water agitation method (water injection, air injection and water injection coupled to a Venturi ejector) on the average heat transfer coefficient ( h ¯ ) between food and cooling water. Time–temperature evolutions of a sphere immersed in the cooling media were used to determine the heat transfer coefficients at different positions in a cooling tank. Air injection and water injection coupled with a Venturi ejector significantly increased the heat transfer coefficient between food and cooling water. For the investigated conditions, h ¯ was increased up to eight times, when air injection was used. However, the complex flow of bubbles and water inside the tank created heterogeneous water agitation, creating zones with different heat transfer coefficients. Furthermore, the use of water recirculation coupled with a Venturi ejector can be very convenient for cases where pressurized air is not available, but the best agitation solution depends on each case.

Studies on ejector-venturi fume scrubber

Experimental studies on diesel fume scrubbing have been conducted in a down-flow type liquid-jet ejector-venturi scrubber. The fume particulates have been captured in the throat of the ejector-venturi by a mechanism involving inertial impaction and impingement. The effect of nozzle geometry and the motive fluid flow rates on the suction created and the volumetric fume aspiration rates have been analyzed, in order to select the optimum nozzle geometry. Using the optimum nozzle geometry the efficiency of fume collection has been experimentally investigated as function of various hydrodynamic parameters. A theoretical analysis has been performed to interpret the experimental findings and determination of nozzle loss coefficients.

THE SPLIT OF THE LIQUID PHASE IN DROPS AND FILM IN AN EJECTOR-VENTURI SCRUBBER

Liquid distribution along an ejector-Venturi scrubber was determined experimentally in an industrial-scale pilot plant. The effects of geometry as well as flow rates were studied. The results showed that a significant fraction of the liquid travels as a film. Therefore, it should be taken into consideration in mass transfer studies, where usually it is neglected. The data were used to test a model, that allows for interchange of liquid between drops and film flowing on the Venturi walls. There was good agreement between experiment and predictions.

Fluid flow and pumping efficiency in an ejector-venturi scrubber

The air self-entrainment by a liquid jet is investigated in an industrial scale ejector-venturi scrubber. A mathematical model based on steady-state macroscopic mechanical energy balances is formulated and arranged in order to obtain simple equations useful for design purposes. Experiments are carried out in order to evaluate empirical values for the frictional coefficients. Gas entrainment and void pressure measurements are presented by using different geometric combinations for the venturi tube throat and the pressure-swirl atomizer used for inducing the gas flow rate.

Gas pollutants removal in a single- and two-stage ejector–venturi scrubber

The absorption of SO 2 and NH 3 from the flue gas into NaOH and H 2SO 4 solutions, respectively has been studied using an industrial scale ejector–venturi scrubber. A statistical methodology is presented to characterise the performance of the scrubber by varying several factors such as gas pollutant concentration, air flowrate and absorbing solution flowrate. Some types of venturi tube constructions were assessed, including the use of a two-stage venturi tube. The results showed a strong influence of the liquid scrubbing flowrate on pollutant removal efficiency. The initial pollutant concentration and the gas flowrate had a slight influence. The use of a two-stage venturi tube considerably improved the absorption efficiency, although it increased energy consumption. The results of this study will be applicable to the optimal design of venturi-based absorbers for gaseous pollution control or chemical reactors.

Removal of SiO2 particles with an ejector venturi scrubber

Removal of SiO₂ particles with an ejector venturi scrubber

Behavior of Mercury in High-Temperature Vitrification Processes

The Pacific Northwest Laboratory (PNL) has evaluated the waste processing behavior of mercury in simulated defense waste. A series of tests was performed under various operating conditions using an experimental-scale liquid-fed ceramic melter (LFCM). This solidification technology had no detectable capacity for incorporating mercury into its product, borosilicate glass. Essentially all the mercury fed to the melter was lost to the off-gas system as gaseous effluent. An ejector venturi scrubber condensed and collected 97% of the mercury evolved from the melter.Chemically, the condensed mercury effluent was composed almost entirely of chlorides, and except in a low-temperature test, Hg2Cl2 was the primary chloride formed. As a result, combined mercury accounted for most of the insoluble mass collected by the process quench scrubber. Although macroscopic quantities of elemental mercury were never observed in process secondary waste streams, finely divided and dispersed mercury that blackened all condensed Hg2Cl2 residues was capable of saturating the quenched process exhaust with mercury vapor. The vapor pressure of mercury, however, in the quenched melter exhaust was easily and predictably controlled with the off-gas stream chiller.These tests followed 12 earlier experiments performed at PNL to study the behavior of mercury during vitrification of simulated typical defense waste. The experiments were conducted using an experimental-scale spray calciner/in-can melter (SC/ICM) system plus a very similar off-gas system. Results with both the LFCM and SC/ICM technologies were essentially the same. Just as with the LFCM, the mercury was completely volatilized from the in-can melter system in all experiments. It reacted predominantly with halogens to form a fine particulate solid, most of which was deposited in the off-gas system piping.

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.

Fluid flow and gas absorption in an ejector venturi scrubber

AbstractEmpirical models were developed to describe the fluid flow characteristics and gas absorption efficiency of an ejector venturi scrubber. The empirical constants were determined experimentally using stop action photographs of the spray, static pressure measurements, and sulfur dioxide absorption efficiencies.Experiments were conducted on a commercial scrubber, 24 inches (61 cm) high, with a 4 inch (10 cm) diameter gas inlet and outlet. Liquid flow rates varied from 3 to 8 gallons/min (.0114 to .0303 m3/min) in the atomizing range of the scrubber, and gas flows from 24 to 64 cubic feet/min (.680 to 1.81 m3/min). The liquid‐to‐gas ratio was constant at .0167.Droplet sizes ranged from 34 to 563 microns, with a volume mean diameter of 155 microns, at a liquid rate of 6 gpm (.0227 m3/min).The sulfur dioxide mass transfer coefficient varied from 25 to 800 lb‐mole/hr‐ft3 (400 to 12,800 kg‐mole/hr‐m3).

Energy and Efficiency Characteristics of the Ejector Venturi Scrubber

The scrubbing and pumping actions in the Ejector Venturi Scrubber are two separate phenomenon occurring simultaneously. Each phenomenon requires energy and has efficiency of operation and collection efficiency. These energy and efficiency relationships are discussed and illustrated in form of numerous graphs. The scrubbing energy requirements and how they vary with particle sizes down to one micron are also discussed and presented in form of numerous graphs.