Jet Reactor Research Articles

Experimental investigation and simulation optimization of a pilot-scale supercritical water oxidation system

Supercritical water oxidation (SCWO) technology has an excellent performance in treating high concentration and refractory organic wastes. While the high treatment cost is one of the key drawbacks currently restricting its large-scale application. In this study, a SCWO pilot system with a novel jet reactor (treatment capacity of 200 kg/h) was experimentally investigated, and the process model was developed to optimize the system by Aspen Plus. The energy and exergy efficiency of the system was evaluated, and the wastewater treatment cost in different operating conditions was estimated. The results show that chemical oxygen demand (COD) removal efficiency could be increased with the increase of the temperature, pressure, and the excess oxygen coefficient. By locating the electric heater 1 (H1) before the heat exchanger 2 (H2), and improving the outlet temperature of the oxygen compressor (MP1), the wastewater treatment cost could be reduced to 53.5 $/t, and the energy and exergy efficiency of the SCWO system could be improved to 81.61% and 8.91%, which is 26.28% and 6.23% higher than that of the current system, respectively. Both the reaction temperature and COD concentration of the wastewater have positive effects on the wastewater treatment cost, e.g. the wastewater treatment cost could decrease from 80.88 $/t to 59.27 $/t when the reaction temperature increases from 380 °C to 420 °C, and the SCWO system could achieve the energy self-sufficient operation when the COD concentration is over 60,000 mg/L.

Generic residual charge based model for the interpretation of the electrohydrodynamic effects in cold atmospheric pressure plasmas

In cold atmospheric pressure plasmas (CAPPs), the residual charges that exist in the wake of the streamers play an important role in the acceleration of the working gas. This paper presents a model that links the drift of the net residual ionic charge density, under the effect of the local electric field, with the momentum increase of the gas. In the model, the ions and the neutrals are considered as separate phases and the conservation equations for the two phases are connected via the ionic pressure. The residual charge density is quantified through an approximate approach that considers the streamer events to be ‘instantaneous’, in order to avoid the excessive computational cost of resolving the propagation of each streamer. For the validation of the residual charge model with the ‘instantaneous’ streamer approach, comparisons are made with experimental data from three plasma jet reactors. The electrode configuration of the reactors and the varied parameters (applied voltage, gas flow rate) are chosen so as to cover a broad range of different cases, in order to assess the generality of the model. The comparisons concern the gas flow and visible plasma patterns. It is found that the numerically simulated flow structures are in agreement with the corresponding schlieren images and that the residual charge density is a fair indicator of the visible plasma channel.

Atmospheric-Pressure Microwave Plasma Torch for CVD Technology of Diamond Synthesis

An electrodeless microwave jet plasma source is considered, and its various applications in the technology of chemical vapor deposition of diamond films and dimension increasing of small diamond single crystals synthesized at high pressures and temperatures are discussed. The plasma jet is ignited in an atmospheric-pressure gas (argon) flow with hydrogen and methane additives. The operation of the microwave jet reactor is described, and the plasma characteristics measured using emission spectroscopy are presented. The brightly glowing atmospheric-pressure plasma jet is ignited and stably burns at a microwave power of ≤1 kW supplied from a microwave oven magnetron. The specific microwave power density absorbed by the compact plasma jet (≤104 W/cm3) is comparable with that absorbed by a dc arc. The growth rate of the polycrystalline diamond layer amounts to 40 µm/h. The process of film deposition on the substrate can be controlled by scanning the substrate surface with the jet.

Effect of ultrasonic intensification on synthesis of nano-sized particles with an impinging jet reactor

The preparation of nanoparticles can be conducted in a fast way by intensifying the micromixing due to the enhanced turbulence in an impinging jet Reactor (IJR) where the two linear liquid jets collide with high velocity to diminish the segregation. However, the micromixing is significantly affected by the occurrence of the stagnant region which may partially choke the reaction chamber. By imposing the ultrasound to the IJR, micro-scale turbulent eddies generated as the result of collapse of ultrasonically generated micro cavitation bubbles may generate a strong local shear. Such micro-scale turbulent vortices exert shear on the interface between the particles and surrounding fluid, resulting in uniform particle morphology and high surface area for chemical reaction. The paper aims to optimize the ultrasonic intensification effect on synthesis of nano-sized particles with desired homogeneity, reveal the governing mechanisms and present a kinetic model to describe the multiphase flow dynamics in the IJR. Except for the experimental method, numerical method was also used to demonstrate the impact of fluid dynamics on particle synthesis.

Flame-synthesized nickel-silver nanoparticle inks provide high conductivity without sintering

A new concept for the synthesis of conductive metal nanoparticle inks (nano-inks) is introduced using a one-step continuous flame-based process. Bimetallic nickel (Ni)-silver (Ag) nanopowders are simultaneously produced and functionalized in a High Temperature Reducing Jet (HTRJ) reactor. The HTRJ process allows rapid aerosol (gas phase) formation of multicomponent metal nanoparticles with relatively high production rates from low-cost metal precursors. Octylamine, a volatile aliphatic amine, is sprayed into the reactor effluent after the particle formation zone to cap nanoparticles as they form. Ni-Ag Functionalized Nano Powders (FNPs) were characterized and compared with Bare Nano Powders (BNPs) to verify that in situ ligand attachment was successful. Nano-inks were prepared by dispersing FNPs in an organic solvent. Conductive films were fabricated using different nano-ink compositions starting from pure Ni to 50 wt% Ni. With the use of a small capping agent, films containing 50 wt% (65 at%) Ni provide an electrical conductivity of 5.14 × 104 S m−1 without any post-processing. Conductivity increased to 4.22 × 105 S m−1 after thermal annealing in an inert environment. These sintering-free bimetallic conductive nanoparticles can be used as a lower cost replacement for current silver inks for single-step printing of conductive traces without post-processing.

Development of DDBD and plasma jet reactors for production reactive species plasma chemistry

A novel Double Dielectric Barrier Discharge (DDBD) and an atmospheric pressure plasma jet (APPJ) was generated with a dielectric barrier discharge (DBD) column by AC high voltage have been developed. This reactor can produce cold atmospheric plasmas (CAP) that formed in air reactive oxygen species (ROS). These species among others are O3, H2O2, was quantified in the outlet of reactors. The analysis for ROS has been conducted by using medium that we call Plasma-Activated Medium (PAM). Some analysis conducted including variation of exposure times by ROS to the plasma-activated medium. In addition, concentration-voltage characteristics of ozone production. Peroxide Value, Acid Value and Viscosity of virgin coconut oil (VCO, as PAM) increased with increasing exposure time of O3. The concentration of hydrogen peroxide in water (as PAM) has been measured. The concentration of H2O2 179 μM with exposure time for 1 minute. The concentration of H2O2 in the study is quite high when compared with some other research results. The results showed that increased exposure time resulted in increased concentrations of ozone and hydrogen peroxide.

One-dimensional drift-flux model of gas holdup in fine-bubble jet reactor

A one-dimensional drift flux model of the gas holdup in the fine-bubble jet reactor (for short FJR) was developed and experimentally verified. The model consists of three key sub-models (bubble Sauter mean diameter, bubble average rising velocity and energy dissipation rate). Effects of downcomer length, liquid dynamic viscosity and surface tension on the bubble Sauter mean diameter, energy dissipation rate, and gas holdup were discussed theoretically. Furthermore, three kinds of systems (air-tap water, air-aqueous ethanol, and air-aqueous glycerol) were chosen to validate the model under different conditions including liquid flow rate, nozzle diameter, downcomer length, and temperature. Theoretical results indicated that the energy dissipation rate in the downcomer of FJR was the critical factor influencing gas holdup in the column of FJR. It is also found that gas holdups predicted by the model were roughly identical to experimental results and errors were within ±15%.

Antisolvent based precipitation: Batch, capillary flow reactor and impinging jet reactor

A method for continuous antisolvent precipitation of ammonium perchlorate (AP) using a confined impinging jet reactor (CIJR) is studied. The geometry of the CIJR was optimized to achieve excellent mixing with a significant reduction in the particle deposition on walls. Initially, the experimental conditions were optimized in a batch system and then in a continuous capillary reactor. Later those conditions extended for antisolvent precipitation of AP in an impinging jet reactor using water and n-butyl alcohol as a solvent and antisolvent, respectively for optimum performance. The performance was compared with the experiments in batch mode as well as and in a continuous capillary reactor. Over a range of inlet jet velocity that corresponded to 1792 < Re < 7193 for the saturated aqueous solution of AP and 1135 < Re < 4553 for the antisolvent butanol phase, 8.98–16.98 µm Ammonium perchlorate particles were attained.

Main performance analysis of kitchen waste gasification in a small-power horizontal plasma jet reactor

Plasma gasification technology has been demonstrated in recent studies as one of the most effective and environmentally friendly methods for solid waste treatment, which could be attractive for resource and energy recovery from kitchen waste. This study focuses on the effects of plasma gasification of kitchen waste replaced by 85% flour and 15% vegetables (Mass Fraction), including dimensionless operation parameters, ER (equivalence ratio), SFR (steam to feedstock ratio) and the gasification efficiency. The Horizontal plasma jet reactor is employed in the experiments. It is found that the influence of the equivalence ratio on syngas can be divided into positive and negative parts. And the steam injection is conducive to improving the yield of syngas, which mainly results from the heterogeneous water gas shift reaction. The optimal experimental parameters can be obtained at ER = 0.095 and SFR = 0.084. Besides, the maximum first and second efficiency of plasma gasification during these cases occurs in SFB = 0.084, accounting for 28.2% and 23.0%, respectively, which needs to study further to get improvement. The XRD and Raman spectra are applied to characterize the residual char, which may illustrate that the degree of graphitization is competing with a high yield of syngas during plasma gasification.

An innovative photoreactor, FluHelik, to promote UVC/H2O2 photochemical reactions: Tertiary treatment of an urban wastewater

An innovative photoreactor, FluHelik, was used to promote the degradation of contaminants of emerging concern (CECs) by a photochemical UVC/H2O2 process. First, the system was optimized for the oxidation of a model antibiotic, oxytetracycline (OTC), using both ultrapure water (UPW) and a real urban wastewater (UWW) (collected after secondary treatment) as solution matrices. Following, the process was evaluated for the treatment of a UWW spiked with a mixture of OTC and 10 different pharmaceuticals established by the Swiss legislation at residual concentrations (∑CECs <660 μg L−1). The performance of the FluHelik reactor was analyzed both at lab and pre-pilot scale in multiple and single pass flow modes.The efficiency of the FluHelik photoreactor, at lab-scale, was evaluated at different operational conditions (H2O2 concentration, UVC lamp power (4, 6 and 11 W) and flow rate) and further compared with a conventional Jets photoreactor. Both photoreactors exhibited similar OTC removal efficiencies at the best conditions; however, the FluHelik reactor showed to be more efficient (1.3 times) in terms of mineralization when compared with the Jets reactor. Additionally, the efficiency of the UVC/H2O2 photochemical system using the FluHelik photoreactor in reducing the toxicity of the real effluent containing 11 pharmaceuticals was evaluated through zebrafish (Danio rerio) embryo toxicity bioassays. FluHelik scale-up from laboratory to pre-pilot to promote UVC/H2O2 photochemical process proved to be feasible.

Selecting the best piping arrangement for scaling-up an annular channel reactor: An experimental and computational fluid dynamics study

This study is focused on the selection of the best piping arrangement for a pilot scale annular channel reactor intended for the remediation of waters and wastewaters. Two annular channel reactors composed of a single UV lamp and distinct piping arrangements were considered: (i) a novel reactor with tangential inlet/outlet pipes – the FluHelik reactor, and (ii) a conventional Jets reactor. These two reactors were manufactured at lab scale and characterized in terms of residence time distribution (RTD), radiant power and ability to degrade aqueous solutions spiked with a model compound – 3-amino-5-methylisoxazole (AMI) – by H2O2/UVC and UVC processes. Computational fluid dynamics (CFD) simulations were used to assess the hydrodynamics, RTD and UV radiation intensity distribution of both reactors at pilot scale. In general, experimental results at lab scale revealed quite similar RTDs, radiant powers and AMI degradation rates for both reactors. On the other hand, CFD simulations at pilot scale revealed the generation of a helical motion of fluid around the UVC lamp in the FluHelik reactor, inducing: (i) a longer contact time between fluid particles and UV light, (ii) more intense dynamics of macromixing as a result of larger velocity gradients, turbulent intensities and dispersion of RTD values around the peak, and (iii) a more homogeneous UV radiation distribution. In addition, the design of the FluHelik reactor can favor the implementation of various reactors in series, promoting its application at industrial scale. The FluHelik reactor was chosen for scaling-up. A pre-pilot scale treatment unit containing this reactor was constructed and its feasibility was proven.

Synthesis of Carbon Fibers in the Decomposition of Acetylene and Propane–Butane Mixture in a Plasma Jet

Carbon fibers are prepared during the conversion of acetylene and propane–butane mixture in a jet of the helium and argon plasma without using catalysts. The synthesis is carried out in a plasma jet reactor. The synthesis products are studied by electron microscopy, synchronous thermal analysis and energy dispersive X-ray spectroscopy. The effect of the synthesis parameters on the structure and properties of the carbon fibers prepared in the volume is established. When the propane–butane mixture is decomposed in an inert medium, conditions are found for the synthesis of cylindrical carbon nanofibers of a tortuous shape with a diameter of up to 20 nm and a length-to-diameter ratio of up to 1000. The decomposition of acetylene at 350 Torr produces nanofibers formed by a chain of straight cylinders with a diameter of up to 20 nm, and cylindrical fibers are synthesized in the form of spirals of up to 200 nm in diameter at 150 Torr.

Experimental and numerical investigation on performance of a swirling jet reactor

In this work, a three-dimensional Computational Fluid Dynamic (CFD) analysis of a swirling jet reactor was implemented to gain a better understanding of fluid dynamics into the reactor. The effect of different geometries of the reactor, by considering different diameters of the injection slots of the reactor, on flow velocity and flow pressure distributions was investigated. Firstly, a one-phase model was implemented by considering only water into the reactor. Then, a two-phase model was defined including dissolved air into the water. The inlet flow pressure was set to 0.25 bar to consider non-cavitating conditions and, then, to get more accurate results on fluid dynamics into the reactor due to the absence of cavitating conditions. Data collected from experimental tests were used to calibrate and validate the model. Results of numerical simulations were in good agreement with experimental data, showing for all the geometries a rotating flow around the central axis of the reactor and at the exit of the double cone. The highest flow velocities and flow pressure drops were observed for the reactor geometry with the smallest injection slots diameters. Finally, noise measurements were performed during another set of experimental tests by considering different inlet flow pressures.

Lagrangian mixing simulation and quantification of scales

This paper introduces Lagrangian Mixing Simulation (LMS), which is a new method that uses particles to track the flow front between two fluids in a mixer. The line formed by an ensemble of particles enables the calculation of the instantaneous rate of interfacial area generation between the fluids and the computation of segregation scales. LMS uses the Eulerian velocity field from CFD simulation, which has a spatial resolution determined from the flow dynamics, for the simulation of mixing at scales that are several orders of magnitude below the CFD gridscale. Since only the interface between the two fluids is simulated, the LMS is orders of magnitude faster than the flow field simulation. In this work, LMS is applied to 2D CFD simulations of the flow in Confined Impinging Jets (CIJ) reactors for Re = 100, 300 and 500. LMS shows that the interfacial area generation is exponential for chaotic flow regimes (Re = 300 and 500) and linear for steady flows (Re = 100). Moreover, LMS is able to simulate segregation scales smaller than 10−8 m, i.e., LMS result spans and overcomes the entire range of spatial scales that have physical meaning.

Experimental investigation of flow and reacting characteristics in asymmetric confined impinging jets reactor

Impinging jet is one of the process intensifications. In order to investigate the flow characteristics and micromixing efficiency in asymmetric CIJR and provide fundamental data for optimizing existing reactors and improving the development of new reactors, 2D PIV system and iodide-iodate system were used. The result shows that in the high range of Re , Reynolds number has little difference on mean velocity, root mean square, turbulence kinetic energy. The distance between horizontal axis of jets and top wall of the mixing chamber L had a very complicated effect on the flow field and stagnation point. The increase of L within a certain range could increase TKE and enhance the micromixing efficiency in the impinging zone. The position of the stagnation point in asymmetric CIJRs is significantly related to the jet velocity ratio. Changes in the ratio of 10% affected changes in stagnation point offset of 35%. Therefore, the jet velocity ratio must be carefully adjusted to ensure that the stagnation point is in the center of mixing chamber. Both the PIV and reacting data could be applied to further understand the mixing performance in the asymmetric CIJRs and made optimization of the reactor.

PIV experiment and large eddy simulation of turbulence characteristics in a confined impinging jet reactor

Abstract Confined impinging jet reactor (CIJR) is a typical process intensification device used in the chemical industry. In this study, two dimensional Particle Image Velocimetry (PIV) and Large Eddy Simulation (LES) method were used to investigate the flow field in a CIJR with jets of diameter 3 mm under highly turbulent condition. The results showed LES can predict the velocity and Turbulence Kinetic Energy (TKE) distributions in the reactor well by comparing with the PIV results. In the CIJR, the stagnation point fluctuates with the turbulence, and its instantaneous position accords with the normal distribution. Three methods, including s–t representation, Lumley–Newman triangle and A–G representation, were used to compare the turbulence anisotropy in the mixing chamber. It was found that the anisotropy in the impinging area and at the edge of impinging jet was strong and the maximum deviation was up to 40%. The results from 2D PIV would lead to an overestimation of the turbulent kinetic energy as much as 20% to 30% than the results from the three dimensional numerical simulation.

Micromixing performance and the modeling of a confined impinging jet reactor/high speed disperser

In order to get a better micromixing performance, an intensification reactor that couples a confined impinging jet reactor and high speed disperser (CIJR-HSD) was designed. The influences of operating and structural parameters on the micromixing performance were investigated by using the iodide-iodate reaction system. The results showed that the segregation index decreased with the increase of both the rotational speed and the number of rotors; whilst there was little influence due to both inlet flow rate and the presence of packing. The coupling distance between the centre of the CIJR and the first rotor of the HSD also had a non-negligible effect on segregation index. The micromixing time was determined by the Engulfment model, and could also be evaluated by the energy dissipation model based on fluid energy transformation. It was found that the micromixing time for the CIJR-HSD device was in the range of 0.1–0.3 ms, while that for a single CIJR was in the range of 0.35–0.5 ms.

Surfactant-free synthesis of extremely small stimuli-responsive colloidal gels using a confined impinging jet reactor

Extremely small monodisperse stimuli-responsive poly(N-vinylcaprolactam) (PVCL) colloidal gels with a radius of 45 nm were synthesized for the first time by surfactant-free precipitation polymerization in a high-pressure confined impinging jet reactor. We demonstrate that high pressures, combined with high mechanical shear forces inside the reaction chamber, resulted in size reduction and improved stabilization of microgel precursors leading to extremely small and uniform colloidal gels.

On the reliable probing of discrete ‘plasma bullet’ propagation

This report is devoted to the imaging of the spatiotemporal evolution of ‘plasma bullets’ during their propagation at atmospheric pressure. Although numerous studies have been realized on this topic with high gating rate cameras, triggering issues and statistical analyses of single-shot events over different cycles of the driving high voltage have not been discussed properly. The present work demonstrates the related difficulties faced due to the inherently erratic propagation of the bullets. A way of capturing and statistically analysing discrete bullet events is introduced, which is reliable even when low gating rate cameras are used and multiple bullets are formed within the voltage cycle. The method is based on plasma observations by means of two photoelectron multiplier tubes. It is suggested that these signals correlate better with bullet propagation events than the driving voltage or bullet current waveforms do, and allow either the elimination of issues arising from erratic propagation and hardware delays or at least the quantification of certain uncertainties. Herein, the entire setup, the related concept and the limits of accuracy are discussed in detail. Snapshots of the bullets are captured and commented on, with the bullets being produced by a sinusoidally driven single-electrode plasma jet reactor operating with helium. Finally, the instantaneous velocities of bullets on the order of 104–105 m s−1 are measured and propagation phases are distinguished in good agreement with the bibliography.

Numerical Investigation of a Novel Microscale Swirling Jet Reactor for Medical Sensor Applications

A microscale swirler and corresponding reactor for a recent detection and analysis tool for healthcare applications, Fiber optic-surface plasmon resonance (FO-SPR), is presented in this study. The sensor is a 400 μm diameter needle that works as a detector for certain particles. Currently, the detection process relies on diffusion of particles towards the sensor and hence diagnostic time is rather long. The aim of this study is to decrease that diagnostic time by introducing convective mixing in the reactor by means of a swirling inlet flow. This will increase the particle deposition on the FO-SPR sensor and hence an increase in detection rate, as this rate strongly depends on the aimed particle concentration near the sensor. As the flow rates are rather low and the length scales are small, the flow in such reactors is laminar. In this study, robustly controllable mixing features of a swirling jet flow is used to increase the particle concentration near the sensor. A numerical analysis (CFD) is performed to characterize the flow and a detailed analysis of flow structures depending on the flow rate are reported.