Mesoscale Reactor Research Articles

Three-Dimensional Model for Bioventing: Mathematical Solution, Calibration and Validation

Bioventing is an established technique extensively employed in the remediation of soil contaminated with petroleum hydrocarbons. In this study, the objective was to develop an improved foundational bioventing model that characterizes gas flow in vadose zones where aqueous and non-aqueous phase liquid (NAPL) are present and immobile, accounting for interphase mass transfer and first order biodegradation kinetics. By incorporating a correlation for the biodegradation rate constant, which is a function of soil properties including initial population of petroleum degrader microorganisms in soil, sand content, clay content, water content, and soil organic matter content, this model offers the ability to integrate a specific biodegradation rate constant tailored to the soil properties for each site. The governing equations were solved using the finite volume method in OpenFOAM employing the “porousMultiphaseFoam v2107” (PMF) toolbox. The equation describing gas flow in unsaturated soil was solved using a mixed pressure-saturation method, where calculated values were employed to solve the component transport equations. Calibration was done against a set of experimental data for a meso-scale reactor considering contaminant volatilization rate as the pre-calibration parameter and the mass transfer coefficient between aqueous and NAPL phase as the main calibration parameter. The calibrated model then was validated by simulating a large-scale reactor. The modelling results showed an error of 2.9% for calibrated case and 4.7% error for validation case which present the fitness to the experimental data, proving that the enhanced bioventing model holds the potential to improve predictions of bioventing and facilitate the development of efficient strategies to remediate soil contaminated with petroleum hydrocarbons.

Unbaffled mesoscale reactor coupled oscillatory flow-enhanced liquid–solid two–phase flow

Unbaffled U-shaped mesoscale oscillatory flow reactors (meso-OFRs) were developed to prevent solid deposition and prepare uniform barium sulfate (BaSO4) nanoparticles with environmental protection function. The results showed that the oscillation significantly reduced granular deposition; the greater the intensity of the oscillation, the faster it reached uniformity, and the less likely the granules were to be deposited. These results can be explained by the formation of a larger vortex size, which can strengthen the turbulent mixing of fluid in the reactor, promote the interaction and forced mixing between the liquid phase and solid particles, enhance the internal shear stress of the fluid, and contribute to the secondary suspension of solid particles and the disintegration of particle agglomeration. The prepared BaSO4 nanoparticles with oscillation were smaller in size and lower in pressure drop than those produced without oscillation, which conclusively illustrated that oscillation effectively prevented channel deposition and clogging.

Continuous Fatty Acid Decarboxylation using an Immobilized Photodecarboxylase in a Membrane Reactor.

The realm of photobiocatalytic alkane biofuel synthesis has burgeoned recently; however, the current dearth of well-established and scalable production methodologies in this domain remains conspicuous. In this investigation, we engineered a modified form of membrane-associated fatty acid photodecarboxylase sourced from Micractinium conductrix (McFAP). This endeavour resulted in creating an innovative assembled photoenzyme-membrane (protein load 5 mg cm-2 ), subsequently integrated into an illuminated flow apparatus to achieve uninterrupted generation of alkane biofuels. Through batch experiments, the photoenzyme-membrane exhibited its prowess in converting fatty acids spanning varying chain lengths (C6-C18). Following this, the membrane-flow mesoscale reactor attained a maximum space-time yield of 1.2 mmol L-1 h-1 (C8) and demonstrated commendable catalytic proficiency across eight consecutive cycles, culminating in a cumulative runtime of eight hours. These findings collectively underscored the photoenzyme-membrane's capability to facilitate the biotransformation of diverse fatty acids, furnishing valuable benchmarks for the conversion of biomass via photobiocatalysis.

Effects of hydrogen-addition on the FREI dynamics of methane/oxygen mixture in meso-scale reactor

FREI (Flame with Repetitive Extinction and Ignition) is a unique flame dynamic in the micro or meso combustor due to the scale effect of the combustor. To further understand the flame dynamics of the FREI, the flame propagating process of the methane-oxygen premixed gas with hydrogen addition is visualized and analyzed experimentally in a rectangle combustor with transparent wall. The equivalence ratio regimes of different flame behaviors are obtained by varying the hydrogen addition. The effect of hydrogen addition on the flame propagation speed, the flame amplitude and the frequency of the FREI is discussed in terms of methane and hydrogen properties, as well as combustor wall temperature. The results indicate that increasing the hydrogen addition will enlarge the amplitude and decrease the frequency of the FREI. However, the effects of hydrogen addition on the flame properties in the upstream and downstream parts of the combustor vary. When the hydrogen addition is increased under the FREI condition, the temperature profile becomes more uniform upstream. Meanwhile, the flame propagates faster with higher hydrogen addition. However, due to the combined effect of wall temperature and the hydrogen property, increasing the hydrogen addition will decrease the wall temperature and the flame propagating velocity at the downstream part when the equivalence ratio is less than 1.9.

The characteristics of methane/oxygen premixed flame dynamics in a meso-scale reactor under fuel rich condition

The high surface-to-volume ratio of a micro combustor causes the flame motion to vary from that of a large-scale combustor. The effects of the length and height of the combustor on the flame behaviors are studied to revel the flame pattern. Five flame regimes are observed, namely diffusion flame, steady flame, partly RERI flame, fully RERI flame and flame flashback and extinction. The equivalence ratio range of each flame regime in several combustors is measured. The flame position of the steady flame and the corresponding wall temperature as well as the frequency and propagating distance of the RERI flame are investigated. The results show that the change of combustor length has a significant effect on the extinction area and the increase and decrease of the height of the combustor channel lead to a shift towards fuel rich side and fuel lean side respectively. Longer combustor broadens the low equivalence ratio limit of the steady flame. Higher combustor channel increases the effect of inlet Reynolds Number on the high equivalence limit of steady flame. Combustor length has little effects on the RERI flame, whereas higher channel height of combustor increases the propagating distance of the RERI flame but decreases the frequency.

Multiscale Simulations of Thermal Transport in W-UO2 CERMET Fuel for Nuclear Thermal Propulsion

Nuclear thermal propulsion (NTP) provides a consistent source of thrust for long space missions. However, fuel development for NTP reactors is a major technological hurdle. Existing modeling and simulation tools developed by the U.S. Nuclear Engineering Advanced Modeling and Simulation (NEAMS) program for power reactors can be leveraged to help accelerate the fuel development. This work is a preliminary demonstration of the application of NEAMS tools to model NTP fuel. Specifically, the fuel performance tool BISON and the mesoscale reactor materials tool MARMOT are used to develop a multiscale model of thermal transport in a W-UO2 CERMET fuel element for NTP reactors. Three-dimensional simulations in MARMOT are used to estimate the effective thermal conductivity (ETC) of fresh CERMET fuel at temperatures ranging from 1500 K to 3000 K. The ETC values from MARMOT are then used in BISON simulations that predict the steady-state temperature profile throughout a 61-subchannel hexagonal fuel element. The temperature varies by 83 K throughout the fuel element, with the highest temperature occurring near the outer edges of the element. BISON is also used to show that the temperature profile in prototype fuel elements with fewer subchannels does not vary significantly from that in the 61-subchannel element.

Combustion of Lean Methane–air Flames in Mesoscale Reactor with Opposite Gas Flows

ABSTRACT In this work, we study a countercurrent premixed rich-lean coaxial reactor to realize an overall lean combustion of hydrocarbon fuels. Flame topology and stability of the axially symmetric reaction fronts of methane-air mixtures are investigated both numerically and experimentally. These studies show that depending on the equivalence ratio of the mixture fed into the inner tube, playing the role of supporting a pilot burner, there can occur two or three-layered stable flame structures. It is demonstrated that flames can be stabilized over a wide range of mixture compositions and flow rates. In particular, it is possible to stabilize methane-air flames with the overall equivalence ratio below the lean flammability limit for this mixture due to the existence of the weak supporting flame and combined effect of the flame stretch and heat recirculation realized in the examined configuration. The diverse unsteady combustion modes, including flame oscillations and flame periodic extinction and ignition, are also found. The prospects of further investigations are discussed.

Purification of Forest Clear-Cut Runoff Water Using Biochar: A Meso-Scale Laboratory Column Experiment

Biochar can be an effective sorbent material for removal of nutrients from water due to its high specific surface area, porous structure, and high cation and anion exchange capacity. The aim of this study was to test a biochar reactor and to evaluate its efficiency in runoff water purification and consecutive nutrient recycling in clear-cut peatland forests. The goodness of the method was tested in a meso-scale (water volume thousands of liters) reactor experiment by circulating runoff water through wood biochar-filled columns and by determining water nutrient concentrations in the column inlet and outlet. The pseudo-first and second order kinetic models were fitted to the experimental data and the adsorption rate (Kad) and maximum adsorption capacity (Qmax) of the biochar reactor were quantified. The concentration of total nitrogen (TN) decreased by 58% during the 8-week experiment; the majority of TN adsorption occurred within the first 3 days. In addition, NO3-N and NH4-N concentrations decreased below the detection limit in 5 days after the beginning of the experiment. The maximum adsorption capacity of the biochar reactor varied between 0.03–0.04 mg g−1 biochar for NH4-N, and was equal to 0.02 mg g−1 biochar for TN. The results demonstrated that the biochar reactor was not able to adsorb TN when the water TN concentration was below 0.4 mg L−1. These results suggest that a biochar reactor can be a useful and effective method for runoff water purification in clear-cut forests and further development and testing is warranted. Unlike traditional water protection methods in peatland forestry, the biochar reactor can effectively remove NO3-N from water. This makes the biochar reactor a promising water protection tool to be tested in sites where there is the risk of a high rate of nutrient export after forest harvesting or drainage.

Experimental study on the effect of external thermal pattern on the dynamics of methane-oxygen and methane-oxygen[sbnd]carbon dioxide premixed flames in non-adiabatic meso-scale reactors

In the current study, the effect of external thermal pattern on the dynamics and characteristics of methane-oxygen and methane-oxygen-carbon dioxide premixed flames in non-adiabatic meso-scale cylindrical reactors is investigated experimentally. In this regard, two different external thermal patterns were imposed on the outer surface of the reactors. The results showed that imposing method/direction and also temperature level of the external thermal pattern have impressive effect on flame dynamics and chemiluminescence in the non-adiabatic meso-scale reactors. Also, it was shown that increasing the temperature level of the external thermal pattern could significantly extend the flame stability and its presence range in the meso-scale reactors, especially for the vitiated mixtures (methane-oxygen-carbon dioxide). Moreover, the results demonstrated that decreasing the inner diameter of a meso-scale reactor, which was subjected to an external thermal pattern, could increase the flame controllability and its presence range in the non-adiabatic meso-scale reactors.

Non-catalytic ethane cracking using concentrated solar energy

Non-catalytic ethane cracking – a highly endothermic process – was carried out using simulated, concentrated sunlight. A mesoscale reactor suitable for the direct utilization of solar thermal energy for the purpose of ethane cracking was designed, built and tested. The effect of different process conditions (temperatures of 800–1000 °C, steam-to-ethane ratios of 0–3.3, and mean residence times of 0.14–0.44 s) on the system performance was investigated using a dilute mixture of ethane (3%) in nitrogen. Single-pass, ethane conversions as high as 69% were observed with high selectivity towards ethylene. The efficiency of chemical conversion was calculated to be within 1–2%. The reported efficiency is low due to the dilute system used and the relatively low temperature of the inlet gas; however, efficiency can be greatly improved through use of a more concentrated feed stream and enhanced gas recuperation. This work demonstrates a new and promising approach to effective utilization of solar thermal energy for value added chemical production.

Continuous-flow solid-phase peptide synthesis: a revolutionary reduction of the amino acid excess.

A highly efficient continuous-flow technique for the synthesis of peptides was developed. The method allows the application of only 1.5 equivalents of amino acids during coupling, while yielding virtually quantitative conversions. A mesoscale reactor was constructed which permits the use of high temperature and pressure during the synthesis. A complete reaction parameter optimization was carried out. Under the optimum conditions, the couplings of all 20 proteinogenic amino acids were achieved with 1.5 amino acid equivalents with quantitative conversions. As a demonstration of the efficiency of the methodology, difficult sequences and β-peptide foldamers with alicyclic side-chains were synthetized in excellent yields and with lower costs thanks to the lower amounts of amino acid and solvent used. By this the synthesis is highly economic and sustainable. Importantly, exotic and expensive artificial amino acids were incorporated into peptidic sequences by the utilization of a reasonable number of amino acid equivalents. The synthesis can be performed in quantities of microgram to gram in an automated way.

An experimental study of the effects of equivalence ratio, mixture velocity and nitrogen dilution on methane/oxygen pre-mixed flame dynamics in a meso-scale reactor

At the present study, the effects of nitrogen dilution, equivalence ratio and inlet mixture velocity on methane–oxygen premixed flame dynamics in a meso-scale reactor with inner diameter of 5mm has been investigated experimentally. The methane–oxygen premixed flame formation zones and also dynamical behavior of the established flames in a meso-scale reactor have been explored. In this research, the presence of five flame regimes of blow-off, blowout, normal asymmetric, repetitive extinction and re-ignition (RERI), and flashback have been observed. Based on the results of this study, it can be inferred that by increasing the inlet mixture velocity, the equivalence ratio should be decreased from fuel rich values toward the stoichiometric value for establishing the flame in a meso-scale reactor. In addition, it has been shown that by increasing the inlet mixture velocity more than a critical value, RERI type of flame may occur. Moreover, increasing the dilution percent at a constant flow rate of oxygen restricted the asymmetric stable flame region and simultaneously extended RERI and blowout regions for the various values of entrance mixture velocities versus equivalence ratio. On the contrary, decreasing the dilution percent (to lower than a critical value) could lead the flame to flashback. Also, it was shown that only the asymmetric flame could be formed as a stable flame in such a meso-scale reactor. Moreover, increasing the equivalence ratio to the fuel rich side moved the flame location toward the reactor outlet.

Undulating topography of HfO2 thin films deposited in a mesoscale reactor using hafnium (IV) tert butoxide

AbstractHfO2 was deposited by chemical vapor deposition on Si, native SiO2, and borosilicate glass surfaces using hafnium (IV) tert butoxide in a mesoscale flow reactor. Undulating thin film topographies were observed by atomic force microscopy on all substrates with peak‐to‐peak periods between 10 and 25 nm in the presence of a temperature gradient perpendicular to flow of 25°C/mm. A computational fluid dynamic model suggests the phenomenon originates from buoyancy driven roll type flow. The thickness uniformity and roughness of the films depended on the flow rate, reactor temperature, and the substrate type. © 2011 American Institute of Chemical Engineers AIChE J, 2011