Reactant Stream Research Articles

Ignition-delay measurement for drop test with hypergolic propellants: Reactive fuels and hydrogen peroxide

Green hypergolic propellants have been extensively studied. In the present study, we attempted to improve the measurement technique for the ignition delay in hypergolic reactions by using a drop-test apparatus. The evaluation method for the hypergolicity is important because an increase in the diversification of green hypergolic combinations is inevitable. Hydrogen peroxide (90 wt%) was used as an oxidizer, and six different reactive fuels were prepared. Sodium borohydride was utilized as an ignition source for the fuels. Optical and acoustic sensors were employed to reliably measure the ignition delay. The proposed measurement technique used in this study accurately reflected the physical phenomena of the hypergolic interactions. The technical limitations in the conventional measurement technique using a high-speed camera were experimentally investigated. Liquid-phase reactions were dominant in the hypergolic reactions of the glyme-based reactive fuels. Gas-phase reactions significantly influenced the hypergolic reactions of most of the amine-based reactive fuels. The pyridine-based reactive fuel had a longer delay time for the gas-phase reaction process than the liquid-phase reaction process. Recognizing the rate-determining step of the hypergolic ignition is necessary for not only designing a rocket injector but also reducing combustion instability, e.g., reactive stream separation.

A New Mathematical Model for the Prediction of Internal Recirculation in Impinging Streams Reactors

A mathematical model for the prediction of internal recirculation of complex impinging stream reactors has been presented. The model constitutes a repetition of a series of ideal plug flow reactors and CSTR reactors with recirculation. The simplicity of the repeating motif allows for the derivation of an algebraic relation of the whole system using the Laplace transform. An impinging streams reactor system with one axial and two tangential inlet fluid streams was constructed and considered as a case study. The model predicts satisfactorily the complex and flow rate dependent experimental residence time distribution functions obtained employing a pulse tracer method for different total flow rates of the incoming feed. The variation of the controlling parameters with changing the total inlet flow rate is discussed. The presented model can predict complex internal recirculation streams within the impinging streams reactor system.

Effects of interchange ratio on sludge reduction and microbial community structures in an anaerobic/anoxic/oxic process with combined anaerobic side-stream reactor.

Oxic-settling-anaerobic (OSA) process is effective in minimizing sludge production, by inserting an anaerobic side-stream reactor (ASSR) in the recycling bypass. Interchange ratio (IR), the quantity ratio of sludge entering the ASSR to the sludge in the main stream reactors, is one of the most important parameters for OSA process. In the present study, a laboratory-scale anaerobic/anoxic/oxic (A2/O) process combined with an ASSR (A2/O-ASSR) was operated for 366 days in parallel with a conventional A2/O process to investigate the effects of IR on sludge reduction. IR was assigned values of 5%, 8%, 10%, and 15%, and the A2/O-ASSR process achieved 14.0%, 16.0%, 24.1%, and 13.7% of sludge reduction, respectively. At the optimum IR of 10%, high through-put sequencing analysis showed that the microbes responsible for pollutant removal and ubiquitous in wastewater treatment remained predominant in the two systems, and slow-growing microbes related to hydrolysis, nitrogen and phosphorus removal increased in the A2/O-ASSR process, which probably played a key role in sludge reduction. 40.6-58.6% of sludge reduction was caused by sludge decay in the ASSR. The tiny amount of extracellular polymeric substance released in the A2/O-ASSR process was subthreshold to cause remarkable sludge reduction.

Kinetics Investigation of Carbon Dioxide Hydrate Formation Process in a New Impinging Stream Reactor

Abstract The absorption of carbon dioxide by hydrates is considered as one of the potential methods for carbon capture and storage. In this work, a new impinging stream reactor was designed to investigate the characteristics of carbon dioxide hydrate formation process. The experiments were carried out at different pressure, temperature and impinging strength. It was shown that the carbon dioxide hydrate formation process could be enhanced by the impinging stream technique. With the increased of impinging strength, both gas consumption and hydration rate were increased. In addition, initial pressure and temperature also had an effect on the carbon dioxide hydrate formation process. Moreover, the kinetics of carbon dioxide hydrate formation was discussed. When the initial pressure was 3.5 MPa and impinging strength was 0.21, the activation energy was 24.74 kJ/mol, which was similar to the experimental data available in the literature.

Heterogeneous Cu-Fe oxide catalysts for preferential CO oxidation (PROX) in H2-rich process streams.

The influence of Fe loading in Cu–Fe phases and its effect on carbon monoxide (CO) oxidation in H2-rich reactant streams were investigated with the catalyst material phases characterized by Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction (XRD) studies and Mössbauer Spectroscopy (MS). There was no change in the oxidation state of the Fe ions with copper or iron loading. The catalytic activity was examined in the feed consisting of H2, H2O and CO2 for the preferential CO oxidation (PROX) process. These catalysts showed an optimized performance in converting CO in WGS streams in the temperature range of 80–200 °C. In addition to the formation of the CuFe2O4 phase, the Fe and Cu were found to be incorporated into a Cu–Fe supersaturated solid solution which improved CO oxidation activity, with carbon dioxide and water produced selectively with high catalytic activity in depleted hydrogen streams. Relatively high conversion of CO was obtained with high Fe metal loading. In addition to their catalytic efficiency, the employed heterogeneous catalysts are inexpensive to produce and do not contain any critical raw materials such as platinum group metals.

Regeneration of deactivated CeCoxO2 catalyst by simple thermal treatment

Active species loss owing to reactant stream washing is a general problem which industrial catalysts suffer from. In case of catalysts synthesized by co-precipitation method, which have active species unused in bulk phase, can be regenerated by a simple thermal treatment that leads to active species in bulk phase migration to surface of the deactivated catalysts. In this work, the influence of regeneration temperature was investigated by employing ammonium hydroxide washing to simulate reactant stream washing of CeCoxO2 catalysts for NO + CO reaction. It is found that the deactivated catalyst can be regenerated by simple thermal treatment and increasing calcination temperature could accelerate the Co species migration from the bulk phase to surface of catalysts.

Development of Combustor for a Hybrid Turbofan Engine

Abstract A promising method of reducing NOx emissions in combustion systems is the Flameless oxidation (FO), which is based on significant dilution of the oxygen concentration in the reactant stream and elevating its temperature to above auto ignition level. The present work is aimed at developing an FO based combustor for a sequential combustion turbofan engine, where the primary combustor is fuelled with H2 and the secondary combustor with hydrocarbon (jet or bio-jet) fuel. The work was performed within the framework of the European project AHEAD (www.ahead-euproject.eu). Being situated between the high pressure and the low pressure turbines, the inlet conditions to the FO combustor are non-conventional. CHEMKIN simulations revealed the theoretical feasibility of a combustion system to operate in the FO mode of combustion under the specific Take-off and Cruise operating conditions. Several design iterations were conducted to find an appropriate geometrical configuration that would allow for such a system to operate in a stable manner. The design iterations were followed by CFD simulations (FLUENT) and a final design was an achieved where the predictions indicated nearly uniform internal temperature distribution with low mass fraction of CO and NOx at the exhaust.

Applying a new approach to predict the residence time distribution in impinging streams reactors

ABSTRACT Different configurations of impinging streams (IS) reactors are designed and widely applied in multiphase reactions. The great properties of IS reactors is to enhance the reaction kinetics by attenuating mass transfer resistances. It is highly important to have information on the residence time distribution (RTD) of fluid elements inside these devices to determine the kinetic behavior of the multiphase reactions performed in IS reactors. Herein, the RTD of fluid inside a two tangentially IS reactor is experimentally measured and theoretically modeled using simple conventional models like the stirred tank in series model. A new and more realistic model is presented that predicts the RTD of such IS reactors with larger precision. It consists of an ideal PFR reactor followed by a recycle reactor consisting of a cascade of tank in series reactor with a recycle stream.

Cooperative Catalysis of Methane Oxidation through Modulating the Stabilization of PdO and Electronic Properties over Ti-Doped Alumina-Supported Palladium Catalysts.

Poor low-temperature catalytic activity and durability are the main drawbacks of palladium-based catalysts for methane combustion. Herein, stable and active PdO particles are constructed by incorporating Ti into an alumina support, which makes the catalysts exhibit satisfactory methane combustion activity. The results of comprehensive characterization reveal that an appropriate amount of Ti doping induces the optimization of electron transfer and distribution, thus contributing to the construction and stabilization of active PdO lattices. The reactive oxygen mobility is improved and the optimal PdO/Pd0 combination is achieved, thanks to the amplified PdO–support interaction. In addition, the acid–base properties are regulated and Brønsted acid sites are generated by virtue of the adjustment of electronic properties, which facilitate stabilization of PdO as well. Hence, the Ti-containing catalyst exhibits superior activity for methane oxidation at low temperatures. Notably, the activity and cyclic performance of the catalyst can be further enhanced when undergoing long-term and isothermal heat treatment under the reactant stream and methane, and it demonstrates a high performance with 90% CH4 conversion at 340 °C.

A numerical study of confined turbulent jets for homogeneous combustion with oxygen enrichment

Homogeneous Combustion (HC) and its variants (MILD, FLOX, CDC etc.) have emerged as attractive techniques to abate NOx emissions. The underlying theory is the arrest of Damköhler number (Da) to values close to unity by intense dilution (internal or external) of the reactant streams. The main research problem addressed in this work is the attainment of HC with enriched oxidizers (XO2>21%). The complex and three-dimensional in-furnace flow is described by breaking it down into a set of canonical flows and using parameters related to the latter. Further, jet-momentum ratio and stagnation length are used to characterize the flow-field and their effect on NOx emissions is explained. Unlike oxidizer-jet momentum, fuel-jet (<5% inert content) momentum is seen to have a nuanced effect on reaction zone homogeneity and NOx emissions; while reactant inlet temperature is seen to have little effect. Stagnation distance is also suggested as a length scaling parameter to describe arrangements with multiple confined turbulent jets. It is shown to perform well for flows under the jets by yielding velocity curves which are independent of chemistry. CO and hydrocarbon emissions are found to be dependent only on equivalence ratio. Volumetric standard deviation of Heat Release Rate is used to quantify the tendency of transition to the conventional mode of combustion due to oxidizer enrichment.

Improvement of Methane Combustion Activity for Pd/ZrO2 Catalyst by Simple Reduction/Reoxidation Treatment

The improvement of methane combustion activity was observed in cyclic temperature-programed and isothermal reactions over Pd/ZrO2 catalysts by simple reduction/reoxidation treatment. The catalytic activity increased during the initial stages of isothermal reaction, and the light-off temperature was lowered as the number of cycles increased in the cyclic temperature-programed reaction. To reveal the origin of activation, variations in the reduction properties after the activation period were carefully investigated through CH4 temperature-programed reduction (TPR) measurements. From the CH4-TPR results, it was confirmed that the reduction temperature decreased significantly after activation. The observation of the CH4-TPR peak at relatively low temperatures is directly proportional to the catalytic activity of CH4 combustion. It was therefore concluded that repeated reduction/reoxidation occurred in the reactant stream, and this phenomenon allowed the combustion reaction to proceed more easily at lower temperatures.

Direct preparation of drug-loaded mesoporous silica nanoparticles by sequential flash nanoprecipitation

The present work demonstrates how drug-loaded mesoporous silica nanoparticles (MSNPs) can be prepared by a sequential flash nanoprecipitation (FNP) technique. A sequential FNP technique is developed relying on a combination of two multi-inlet vortex mixers (MIVM), by which a continuous process that involves the formation of micelle-based templates followed by an in situ formation of MSNPs is achieved. Moreover, a widely used biological nematicide, abamectin (Abm), is added during the formation of micelles, ultimately leading to Abm-loaded MSNPs with high encapsulation efficiency. The obtained Abm-loaded MSNPs show excellent stability and inhibition activity against the livability of Meloidogyne incognita. Importantly, the parameters of the resulting MSNPs, such as silica shell thickness and inner cavity size of MSNPs, can be easily controlled by tuning the compositions of the reactant streams. We believe that such a simple approach towards direct preparation of drug-loaded MSNPs would find promising up-scale applications in various fields, such as drug delivery, bioimaging, and formulation technology.

Plasma in situ gas–liquid nitrogen fixation using concentrated high-intensity electric field

The environmental issues associated with the Haber–Bosch industry urges research on alternative nitrogen fixation processes. The efficiency of the plasma-based nitrogen fixation process could be greatly enhanced by eliminating hydrogen from the reactant stream and directly fixing nitrogen into the water-based solution. In this study, we present a novel non-thermal plasma gas–liquid nitrogen fixation process that generates plasma in situ within the liquid body using concentrated high-intensity electric field (CHIEF). The CHIEF system also avoided discharge at the electrode, which could help reduce electrode corrosion. The effects of input power and conductivity on discharge performance and nitrogen product composition were analyzed. The CHIEF system achieved a fixation rate as high as 11.2 µmol min−1. This system improved the selectivity towards nitrate compared with plasma generation at the water surface.

Synthesis of mesoporous silica SBA-15 using a dropwise flow reactor

Generally, mesoporous silica materials, such as SBA-15, are hydrothermally synthesized in batch reactors. We synthesized SBA-15 in a dropwise flow reactor, which has several merits, such as short reaction times, continuous operation, and easy scale-up. The reaction system had three parts: a mixer and two reaction channels, one operated at a low temperature of 35 °C for the self-assembly of 2D hexagonal silica structures, and the other operated at a high temperature of over 80 °C to increase the stability of the silica structure. Two different operating schemes were used to mix the two immiscible reactant streams, one with a magnetically driven active mixer and the other with a direct supply of premixed reactants. The dropwise flow reactor with the active mixer instead of the low-temperature reaction channel produced fractured silica particles in the final product. However, when a premixed solution under hydrolysis conditions was employed, the synthesis of mesoporous silica SBA-15 was successful within 2.5 h in the dropwise flow reactor, showing close physical properties to the reference SBA-15 sample obtained in a conventional batch reactor.

In Situ Photophysical Characterization of π-Conjugated Oligopeptides Assembled via Continuous Flow Processing.

Bioinspired materials have been developed with the aim of harnessing natural self-assembly for precisely engineered functionality. Microfluidics is poised to play a key role in the directed assembly of advanced materials with ordered nano and mesoscale features. More importantly, there is a strong need for understanding the kinetics of continuous assembly processes. In this work, we describe a continuous microfluidic system for the assembly and alignment of synthetic oligopeptides with π-conjugated cores using a three-dimensional (3D) flow focusing of inlet reactant streams. This system facilitates in situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM), which can be used in unprecedented capacity to characterize the integrity of peptides during the assembly process. To achieve continuous assembly, we integrate chevron patterns in the ceiling and floor of the microdevice to generate a 3D-focused sheath flow of the reactant peptide. Consequently, the peptide stream is directed toward an acidic triggering stream in a cross-slot geometry which mediates assembly into higher-order fiber-like structures. Using this approach, the focused peptide stream is assembled using a planar extensional flow, which ensures high degrees of microstructural alignment within the assembled material. We demonstrate the efficacy of this approach using three different synthetic oligopeptides, and in all cases, we observe the efficient and continuous assembly of oligopeptides. In addition, finite element simulations are used to guide device design and to validate 3D focusing. Overall, this approach presents an efficient and effective method for the continuous assembly and alignment of ordered materials using microfluidics.

Fast coprecipitation of nickel-cobalt oxide in a micro-impinging stream reactor for the construction of high-performance asymmetric supercapacitors

Precipitation is a convenient process for the massive production of materials in industry due to its fast kinetics and mild reaction conditions. In this work, a micro-impinging stream reactor (MISR) was constructed as a process intensification equipment to synthesize transition metal oxides via ambient-temperature precipitation. The as-prepared Ni-Co-O composites showed a loose mesoporous structure consisting of aggregated spherical nanoparticles with a mean size of ∼50 nm, which exhibited much smaller particle size, larger BET surface area and superior electrochemical performance as compared to Co3O4 and NiO. Benefited from the enhanced micromixing performance and higher supersaturation level, the highly developed MISR (Reynold number (Rej) > 3000) could produce smaller and more uniform Ni-Co-O aggregates with larger BET surface area as well as higher specific capacitance than those prepared in traditional stirred tank reactor (STR) and in MISR at low Rej. The electrochemical measurements demonstrated that Ni-Co-O composites prepared in MISR at Rej = 3160 displayed a high specific capacitance of 2012 F g−1 at the current density of 1 A g−1 as well as good rate capability and cycle stability. Furthermore, a Ni-Co-O//AC asymmetric supercapacitor assembled with the Ni-Co-O composites and activated carbon exhibited remarkable performance with a high energy density of 48.3 W h kg−1, a maximum power density of 7.6 kW kg−1, and excellent capacitance retention of 90.2% after 3000 cycles. The results illustrated that MISR is a promising and powerful process intensification technology for the fast production of Ni-Co-O composites that can be used as high performance supercapacitor electrode materials.

Modelling of multispecies reactive transport on pore-space images

We present a new model, named poreReact, to simulate multispecies reactive transport on pore space images. We solve the Navier–Stokes equations and the advection-diffusion equation for concentration on an unstructured grid using the finite volume method implemented in OpenFOAM. We couple it with the chemical model Reaktoro, which we use to calculate the chemical equilibrium of homogeneous reactions in each grid cell, considered as a completely mixed batch reactor. We validate the model against analytical solutions and experimental data, and investigate, for a range of Péclet numbers, the interplay between transport and reaction for multispecies reactive transport in a 3D bead pack where two streams of reactants at different pH are injected in parallel. We analyse the distribution of species and the rates of formation and consumption in the pore space and find that, despite the relative homogeneity of the bead pack and symmetry in injection conditions, the concentration fields of the products can be asymmetric because of the interplay between transport and chemical equilibrium. For different Péclet numbers, we calculate relative yields (the ratio between the observed change in concentration and the change that would be obtained if the reactants were completely mixed). We observe that lower Péclet numbers give rise to higher relative yields because of increased transverse mixing by diffusion. However, higher absolute yields are obtained at higher injection velocities because of the larger amount of matter available for reaction in a given time. Reaction is more favoured in the faster-flowing regions of the pore space. However, this effect is more marked for species for which advection is the dominant mechanism of transport to reactive sites, as opposed to diffusion-mediated reactions where the full velocity distribution is sampled before reaction occurs.

Influence of Reaction Conditions and Promoting Role of Ammonia Produced at Higher Temperature Conditions in Its Synthesis Process over Cs‐Ru/MgO Catalyst

AbstractCs promoted Ru/MgO catalyst was prepared by an impregnation method using Ru(NO3)3 and Cs(NO3)2 as precursor compounds. The activity measurements for ammonia (NH3) synthesis were carried out in a fixed‐bed flow reactor. A reactant stream of H2 and N2 was used for NH3 synthesis. The influences of reaction temperature, pressure and H2/N2 ratio on the performance of the catalyst were investigated in detail. The relative concentration of H2 and N2 in the reactant stream highly influenced the catalytic activity. The remarkably higher rate of NH3 synthesis was observed for the higher H2/N2 ratio at 400 °C and lower H2 concentration in the reactant stream improved the catalytic activity at lower temperature conditions. A sharp increase in the catalytic activity of Cs−Ru/MgO with an increase in pressure was observed at 400 °C for a reactant stream with higher H2 concentration. Relatively less interaction of H2 with the surface of the catalyst is suggested in the presence of NH3 produced during the reaction conducted at elevated temperature conditions. This less susceptibility for H2 adsorption on the active sites of the catalyst is a plausible reason for a higher rate of NH3 synthesis at higher temperature conditions. We modified the Temkin equation model by considering the adsorbed species on the surface of the catalyst affecting NH3 synthesis.

Chemiluminescence of Burner-Stabilized Premixed Laminar Flames

ABSTRACTThe OH*, CH* and CO chemiluminescence signals of methane/air premixed laminar flames stabilized over a nonadiabatic porous plug burner are compared to the signals measured from a nearly adiabatic conical flame in a series of experiments. The impact of reactant stream temperature is also characterized. A numerical study based on 1-D flame models then follows to support the experimental results. It is found both in experiments and in simulations that the linear relationship between the mixture flowrate and the chemiluminescence intensities is no longer valid when flames are closely attached to the burner surface due to the heat transfer between the flame and the burner. The transition between the linear and the nonlinear regimes is identified as the gas flow velocity drops below the adiabatic laminar burning velocity calculated at the bulk temperature of the flow leaving the burner. When the mass flowrate is kept constant, preheating of the reactant stream increases the chemiluminescence intensity for a freely propagating flame, but has almost no impact for a burner-stabilized flame. It is finally found that the OH* and CH* chemiluminescence intensities correlate with the burnt gas temperature for the adiabatic but also the nonadiabatic flames. The underlying physical mechanisms are discussed. Finally, the evolution of the CH*/OH* ratio with the inlet gas velocity is discussed.

Application of micro-impinging stream reactors in the preparation of Co and Al co-doped Ni(OH)2 nanocomposites for supercapacitors and their modification with reduced graphene oxide.

A micro-impinging stream reactor (MISR) consisting of a commercial T-junction and steel capillaries, which is of intensified micromixing efficiency as compared with traditional stirred reactors (STR), was applied for the preparation of Co and Al co-doped Ni(OH)2 nanocomposites and their modification with reduced graphene oxide (RGO). The co-precipitation preparation process was conducted under precisely controlled proportions and concentrations of reactants in the MISR. Therefore, element analysis showed a higher uniform distribution of metal ions within the nanocomposites obtained through the MISR. The structural characterization and electrochemical measurements also showed that the MISR-prepared metal-doped nanocomposites were of more uniform dispersion and superior electrochemical performance than those prepared with STR. In addition, by modifying with RGO in the MISR, the electrochemical performance of Co and Al co-doped Ni(OH)2 nanocomposites could be further improved. The Co and Al co-doped Ni(OH)2/RGO prepared under optimal conditions achieved an ultrahigh specific capacitance of 2389.5 F g−1 at the current density of 1 A g−1 and displayed an excellent cycling stability with 83.7% retention of the initial capacitance after 1000 charge/discharge cycles in 6 M KOH aqueous solution.