Impinging Stream Research Articles

An investigation into the potential large-scale continuous magnetite nanoparticle synthesis by high-pressure impinging stream reactors

Magnetite nanoparticle synthesis is becoming increasingly important in a variety of fields. Scale-up of current batch, laboratory magnetite precipitation techniques involving relatively small volumes may be problematic as large stirred vessels can yield areas of localized low pH upon addition of a base to an iron solution resulting in the precipitation of undesired non-magnetic iron oxides. We present the use of high-pressure impinging stream reactors of different designs for the potential large-scale continuous precipitation of magnetite nanoparticles. The experimental system described here is capable of producing up to 50 g/min predominantly magnetite precipitate of 8–12 nm particle diameter.

Pressure Fluctuation in the Submerged Circulative Impinging Stream Reactor

Pressure fluctuation in the submerged circulative impinging stream reactor (SCISR) is studied by measuring the dynamic pressure with micro pressure sensors of high accuracy, with water as the process material. Experimental results show that the maximum amplitude of fluctuation can be up to about 1.6kPa. On the power spectra the fluctuation is relatively concentrated in the range of <1000Hz, with some weak peeks in acoustic wave range. The space profile of intensive fluctuation region in the reactor is determined. The region is found to take the form of a couple truncated cones of empty core, with coincided bottoms, and is symmetrical with respect to the impinging plane and approximately symmetrical about the axis, essentially independent of u 0. The integral intensity of fluctuation increases as the impinging velocity, u 0 increasing.

Numerical simulation of flow and mixing behavior of impinging streams of shear-thinning fluids

Due to their high efficiency, impinging streams, which involve the use of two inlet streams that enter the system through two closely spaced inlets along the same axis in opposite directions, have recently found many applications in the chemical and food industry as alternatives to conventional mixing operations. However, there is no prior work that focuses on the flow and mixing behavior of non-Newtonian impinging streams. Numerical simulation was therefore performed to investigate the flow and mixing behavior of steady-state, two-dimensional laminar confined impinging streams of shear-thinning fluids. The coupled heat, mass and momentum balance equations were solved with the finite element method using commercial software FEMLAB ™ 3.0. The effects of various parameters, i.e., inlet jet Reynolds number based on the inlet slot width ( Re j ) in the range of 10–200 and the flow behavior index of the fluids in the range of 0.6161–1, on the flow and mixing behavior of impinging streams were then investigated. Temperature of the mixing fluid was used as a passive tracer to monitor mixing in this study. The results were also compared and discussed with those of Newtonian impinging streams.

Effects of geometry and operating conditions on the mixing behavior of an in-line impinging stream mixer

The present study investigated experimentally the effects of various geometric and operating parameters on the mixing characteristics of model liquids undergoing mixing in a novel in-line mixer, viz. an in-line impinging stream (IS) mixer. First, the mixer with one set of three inlet jets was used. Later two sets of inlet jets were used in order to increase the number of impingement zones and hence the mixing capability of the mixer. A statistical analysis was performed to indicate the best geometry of the mixer based on the data of both the mixing effectiveness and the pressure loss due to impingement of liquid streams.

Fundamental Research on Drying Process in Institute of Engineering Thermophysics, CAS

Some results of our fundamental research on drying processes are summed up in this article. It consists of three parts: (1) Multistage fluidized bed drying, including particle flowing characteristics, heat and mass transfer between particles and drying medium, drying characteristics of drying materials; (2) Impinging stream drying, the flowing and drying characteristics of a vertical impinging stream dryer, one-stage and multistage semi-circular impinging stream dryer and combined vertical and semi-circular impinging stream dryer are discussed; (3) The effects of rapid transient heat and mass transfer on drying processes, such as time and space scales for nonFourier or nonFickian and influence of extreme heat and mass transfer are also discussed.

Multi-phase flow and drying characteristics in a semi-circular impinging stream dryer

A physical model was proposed to describe granular material drying in a semi-circular impinging stream dryer, and the multi-phase flow characteristics as well as the heat and mass transfer were numerically investigated. Specially, the influence of various factors (inlet air temperature, mass flow-rate ratio, initial moisture content etc.) on drying process was inspected. The results indicate that constant drying rate period does not exist in a semi-circular impinging stream dryer. Appropriate curvature radius, flow-rate ratio, air velocity and higher inlet air temperature should be chosen for improving the drying performance, and decreasing the energy consumption and operation cost. The numerical predictions were compared with the available experimental results, and they are in quite good agreement with each other.

A numerical study of mixing in a novel impinging stream in-line mixer

Numerical simulations were performed to study fluid mixing in a novel two-dimensional in-line mixer utilizing multiple impinging stream inlets operated in the laminar flow regime. Effects of the inlet jet Reynolds number as well as mixer geometry on the mixing characteristics are investigated and discussed. Offsetting the top and bottom inlet jets is effective in improving the quality of mixing due to the presence of intense mixing zones between the inlet jets. It is found that the operating as well as geometric parameters affect mixing differently in different zones of the mixer. Results show that excellent fluid mixing is achievable over a rather short axial distance in this mixer.

Novel Type of Impinging Streams Contactor for Liquid−Liquid Extraction

An experimental study was conducted on liquid-liquid extraction of succinic acid by means of normal butanol from its aqueous solution (BSW), iodine from its aqueous solution by means of kerosene (KIW), and acetic acid by means of distilled water from kerosene (WAK) in a novel type of contactor based on an impinging streams technique. This high-intensity jet contactor provides significant improvement over the conventional extractor because of the impingement of high-velocity feed streams upon one another in a relatively small contactor volume, resulting in a high-turbulent mixing of two phases. As a result of both the impinging process and shear forces exerted on the phases, the overall volumetric (capacity) mass-transfer coefficients, K L a, of up to 15, 23, and 26 min -1 have been obtained for BSW, KIW, and WAK, respectively. The order of magnitudes of the latter coefficients are higher than typical values obtained by conventional extractors. In addition, the effects of the upper disk speed, solution flow rate, disk diameter, distance between disks and the enhancing effect of impinging streams have been investigated. These experimental results verify the capability of the new contactor in liquid-liquid extraction.

Atomization characteristics of a double impinging F-O-O-F type injector with four streams for liquid rockets

This paper presents atomization characteristics of a double impinging F-O-O-F type injector with four streams. A phase Doppler particle analyzer was employed to measure the droplet-size and water was used as the inert simulant liquid instead of reactive propellant liquids. The droplet mean diameter (SMD) and size distribution were measured to investigate the effects of the momentum ratio and pressure drop variations. This experimental results can be used during the preliminary design stage of a impinging stream type injector for liquid rockets.

The development and modelling of high-intensity impinging stream jet reactors for effective mass transfer in heterogeneous systems

A novel type of phase-contacting device has been researched and is currently being developed at this institution. These high-intensity jet reactors provide significant improvement over conventional phase-contacting equipment due to the impingement of high-velocity feed streams upon each other in relatively small reactor volumes, resulting in a highly turbulent mixing of phases. Due to this intimate contact between phases, mass transfer coefficients ( k L ) of up to 1.5×10 −3 m/s have been realised, which, coupled with values of the specific interfacial area (a) of 8–18 000 m 2/m 3, have yielded volumetric mass transfer coefficients ( k L a) of up to 22 s −1 which are orders of magnitude higher than typical values obtained by conventional systems. A model for the prediction of the interfacial area production in these new reactors has also been proposed. It is implemented in the form of a Monte Carlo simulation, based on the fact that bubble breakup in a turbulent environment is governed by the interactions of bubbles with turbulent eddies. Although the model is only a first attempt, it has proved to be highly practical and flexible, reasonably predicting trends in the experimental data.

EXPERIMENTAL INVESTIGATION ON FLOW AND DRYING CHARACTERISTICS OF A VERTICAL AND SEMI-CYCLIC COMBINED IMPINGING STREAMS DRYER

Flow characteristics of a vertical and semi-cyclic combined impinging streams dryer(VSCIS) was investigated. Results show that centrifugation and gravity have obvious influences on pressure drop and on momentum commutation between gas and particles in impingement zones. The effects of various operating parameters on water removal from particles have been studied experimentally. It is found that initial hot air temperature Tin, μ and initial moisture content of particles X0 play important roles on water removal from particles. Based on the experimental data, dimensionless correlations for flow and drying characteristics in the system were obtained. VSCIS has shown to be a good way to overcome the shortcomings of single configuration of either vertical or semi-cyclic impinging streams. It can take full advantages of both arrangement to remove more water from particles.

Ultrasound-modulated two-fluid atomization

The present invention is a dramatic enhancement of the two-fluid atomization art through the discovery of a method of causing resonance between capillary waves in the ultrasound range in a flowing liquid stream and the waves created at the surface of that stream of liquid by an impinging gas stream. In the present invention, the surface of a stream of liquid issuing from the outlet or nozzle of an ultrasonic atomizer is impinged upon by a stream of gas. That impinging stream of gas then develops, at the surface of the liquid stream already sustaining its own wave motion, a flow of gas substantially parallel to the flow of the liquid stream that moves faster than that surface of the liquid stream. The flow of the gas at the surface of the liquid stream moves sufficiently faster than the surface of the liquid stream to generate waves at the surface of the liquid stream. The wavelength of the waves generated by the impinging gas on the surface of the liquid stream are modulated by velocity control of the impinging gas stream and resonate with the liquid stream waves. The resonance results in an atomization wherein the droplets are smaller and the droplet size distribution is reduced over prior art ultrasonic atomizers.

The effect of jet reactors on the leaching of gold from ores

The extraction of metals from ores by means of appropriate solvents has been practised for many years. A number of methods involve leaching of crushed ores held in tanks or ponds in which the solvent is sprayed over the ore, of which effectiveness is enhanced by mechanical agitation and increased temperature and pressure. In contrast, this investigation uses a high-velocity impinging stream reactor to induce micro-cracking in the ore phase, and consequently enhance leaching kinetics by improved solvent/ore contact. Initial tests show that jet reactor leaching of a free milling ore can increase gold recovery by 10% while decreasing leaching time by up to 90%. Further investigation is required regarding refractory ores, taking into account the complex mineralogy of each ore. The three refractory ores that were tested, all behaved very similarly when subjected to jet reaction. There is no apparent improvement in recovery. However, leaching kinetics are dramatically increased when these ores are subjected to jet reaction prior to agitation.

Experimental investigation of phosphate dust collection in impinging streams (IS)

AbstractAn experimental study on collection of dry phosphate dust and coalescence of moistened phosphate dust in an Impinging‐stream (IS) collector has been conducted in the presence and in the absence of a water spray.The total collection efficiency with a water spray of specific consumption of 0.3 kg water/kg dust was 95–97%. Air velocity at the inlet pipes varied between 10–30 m/s and the inclination angle with respect to the horizontal, a, of the IS was 40−60°. The water spray increased the collection efficiency by 5–20% in comparison to dry collection.In the coaxial configuration, α = 0°, it has been obtained that in the presence of a water spray, up to 55–85% of the dust accumulated on the walls of the collector, which was undesirable. Applying the inclined IS decreased the above quantities up to 5–15% with an optimal inclination angle of α = 40°.A simple model for collection of the particles has been established, showing a satisfactory agreement with experimental results.

Optimal Spacing Between Pin Fins With Impinging Flow

This is an experimental numerical and theoretical study of the heat transfer on a pin-finned plate exposed to an impinging air stream. The pin fins are aligned with the air approach velocity. The base plate and the fin cross section are square. It is demonstrated experimentally that the thermal conductance between the plate and the air stream can be maximized by selecting the fin-to-fin spacing S. Next, a simplified numerical model is used to generate a large number of optimal spacing and maximum heat transfer data for various configurations, which differ with respect to fin length (H), fin thickness (D), base plate size (L), fluid type (Pr), and air velocity (ReL). Finally, the behavior of the optimal spacing data is explained and correlated theoretically based on the intersection of asymptotes method. The recommended correlations for optimal spacing, Sopt/L ≅ 0.81 Pr−0.25 ReL−0.32, and maximum thermal conductance, (q/ΔT)max/kaH ≅ 1.57 Pr0.45 ReL0.69 (L/D)0.31, cover the range D/L = 0.06 − 0.14, H/L = 0.28−0.56, Pr = 0.72−7, ReD = 10−700, and ReL = 90−6000.

Superheated Steam Drying of a Single Particle in an Impinging Stream Dryer

ABSTRACT Impinging stream contactors provide a novel configuration for drying and/or chemical reactions of particulates, pastes or suspensions which can be dispersed in a flowing gas stream. Essentially they consist of one or more highly turbulent “impingement” zones formed by collision of two opposing jets (OJ) in a confied channel or duct. The objective of this paper is to present computational fluid dynamic predictions for two-dimensional turbulent opposing jets over a range of nozzle-to-nozzle separations and jet Reynolds numbers for the simulation of single particle drying in these systems using superheated steam. A number of different turbulence models were tested ( e.g. high Reynolds, Lam-Bremhorst, Launder and Sharma models etc.). Predictions are performed in two distinct parts. In the first part a power law, finite volume method based on the “SIMPLEC” algorithm is used to solve the momentum and energy conservation equations for air in OJ systems in order to gain insight into their

Stochastic modelling of the effects of liquid droplet collisions in impinging streams absorbers and combustors

A stochastic model based on the Boltzmann kinetic equation and employing the comprehensive treatment of the dynamics of binary droplet collisions is suggested to describe the droplet size and spatial distribution in dense spray. The model is valid for highly non-equilibrium impinging sprays in which the inertia of the droplets is very high and dynamic coupling with the gas is low. A Monte Carlo simulation procedure is developed for the solution of the kinetic equation. A model is used to analyse the absorption of a gas in a liquid spray in an impinging streams absorber. It is demonstrated that droplet collisions result mainly in coalescence, and reduce the overall droplet concentration and the interphase area in the reactor. The results of the analysis of the vaporization of a pentane spray in an impinging streams combustor are presented. It is shown that while droplet collisions reduce the vaporization rate by deflecting droplets out of the reactor and by coalescence, collision-induced fragmentation strongly affects the droplet size distribution and increases the fuel vaporization rate. The obtained results indicate that in the high velocity combustion of light fuels the collision-induced fragmentation of fuel droplets has a profound effect on the droplet size and spatial distribution.

An impinging–Streams reactor with two pairs of tangential air feeds

AbstractThe original two–impinging steams devices have proved useful for processes in gas–solid Systems. A modified form of the original two–impinging–streams reactor, with two additional air streams, was explored. All four air streams are fed tangentially to the reactor. The Performance characteristics included the determination of the pressure drop on the reactor, limits of the gas and solid particle mass flow rate, the mean residence time of the particles, and the drying heat transfer, as a function of air flow rates of the secondary and major air streams.The behaviour of the particles and their residence time distribution was investigated by applying a stochastic Markov chain model.It was found that the secondary air stream increases the pressure drop on the reactor and the mean residence time of the particles along with their recycling in the reactor. On the other hand, the secondary air stream decreases the critical mass flow rate of the particles, delays their exit from the reactor and reduces the heat transfer coefficient in drying wet particles.

Monte Carlo simulation of gas-solids suspension flows in impinging streams reactors

Impinging streams reactors have been employed in various fields of chemical engineering, as a means of enhancing the rates of convective transfer processes. The analysis of the hydrodynamics of gas-solids suspension flows in these reactors requires that collisions between particles be taken into account. The stochastic model for gas-solids suspension flows, based on the Boltzmann transport equation, is presented. The system of nonlinear integro-differential transport equations is solved using the Monte Carlo method. A qualitative agreement is obtained between the predicted and experimental results for the particle concentration distribution in an impinging streams reactor. The particle concentrations in the impingement zone of two particle-laden jets are strongly reduced by the effects of inter-particle collisions. The analysis of laminar pipe flows in the absence of gravity and lift forces (Saffman force etc.) reveals a collision-induced migration of particles towards the pipe wall and, to a lesser extent, towards the core. In turbulent vertical pipe flow, particles migrate towards the pipe core and the laminar sublayer. Collison-induced effects become more pronounced in mixture flows with particles of different sizes and densities.

Application of Free Impinging Streams to the Combustion of Gas and Pulverized Coal

Abstract Combustion experiments of synthetic gas and pulverized coal were carried out by the method of two free-impinging-streams as shown schematically in configuration b of Figure I. In combustion of gas, the complete behaviour of impinging jets versus the fuel/air ratio was revealed and explained on the basis of the dependence of the burning velocity of the gas mixture on the above ratio. This behaviour consists of three distinct and stable modes of operation as follows: In mode I, no combustion takes place along the path of the free jets fed into the reactor (Figure 3a). In mode II, combustion begins roughly near the impingement plane of the two jets (Figures 3b, 4 and 6). Mode III is a third situation in which combustion takes place immediately at the entrance of the jets into the reactor (Figures 3c and 5). For combustion of pulverized coal, a correlation based on a diffusion-convection model was obtained for the prediction of the combustion efficiency as a function of available operational parame...