Counter Current Research Articles

Assessing the impact of environmental forcing on the condition of anchovy larvae in the Cadiz Gulf using nucleic acid and fatty acid-derived indices

Understanding the environmental processes affecting fish larvae survival is critical for population dynamics, conservation purposes and to ecosystem-based fishery management. Using anchovies (Engraulis encrasicolus) of the Cadiz Gulf as a study case and considering the “Ocean Triad” hypothesis, we investigate the larval ecophysiological status and potential survival in relation to oceanographic variables. Therefore, this study aims to describe the nutritional condition of anchovy larvae during spawning season (peak in summer) through nucleic acid- and fatty acid (FA)-derived indices and to analyze the effects of the major environmental parameters (Depth, Temperature, Salinity, Plankton biomass) on anchovy survival potential at early phases. Fish larvae were collected in August from 30 m to 400 m depth at 35 stations off the southern Iberian coast. A previous upwelling event influenced the oceanographic conditions of the more western stations off Cape São Vicente (CSV). Along the coast, the water became warmer from west to the east through Cape Santa Maria (CSM) ending at Guadiana estuary, where easterly winds originated the development of a counter current. The standardized RNA/DNA (sRD) of anchovy larvae decreased throughout larval ontogeny, reflecting a reduction of growth during the development. Essential FA concentrations also decreased, but docosahexaenoic acid (DHA) in particular was highly conserved even after the reduction of total FA concentration in anchovy larvae related to the onset of swimming abilities (post-flexion phase). The oceanographic conditions (west upwelling, east counter current, and stratification) led to a nearshore aggregation of plankton and anchovy larvae with good ecophysiological conditions in the central area of the southern coast, where an optimal range of temperature and chlorophyll, as an indirect food proxy for anchovy larval development, were registered. The study proves that the oceanographic conditions of the study area are putative drivers of the ecophysiological condition of anchovy larvae to guarantee potential survival, supporting the “Ocean Triad” hypothesis with major repercussions for recruitment and population dynamics.

Experimental and numerical investigations of a triple concentric-tube heat exchanger

The experimental and numerical investigations of the triple concentric-tube heat exchanger are presented with particular reference to double tube heat exchanger. The purpose is to present a clear view on the thermo-fluid characteristics of this type of heat exchangers with different key design parameters leading to design optimization. Three fluids being considered are chilled water in inner tube, hot water in inner annulus, and normal tap water in outer annulus. Numerical CFD model is developed using a finite volume discretization method. The numerical model is validated and then extended to cover more extra design parameters. Four flow patterns are conducted of counter current, co-current, counter current with co-current and co-current with counter current flow. Correlations of Nusselt number, friction factor and heat exchanger effectiveness with the dimensionless design parameters are also presented. The triple tube heat exchanger contributes higher heat exchanger effectiveness and more energy saving compared with double tube heat exchanger per unit length.

Efficient solvent-less separation of lipids from municipal wet sewage scum and their sustainable conversion into biodiesel

A very efficient separation of lipids from wet sewage scum was optimised and positively tested on samples taken from several wastewater treatment plants (WWTPs). By simply heating sewage scum at 353 K and centrifuging the heated mass at 4000 rpm per 1 min, a recoverability of 93–99% of total oils was always obtained. This procedure resulted to be effective on samples with very different starting water contents. In all cases, extracted lipids have a very similar composition in terms of free fatty acids (FFAs), calcium soaps (32–40%wt) and glycerides (mono-, di- and tri-glycerides were practically absents), as well as fatty acid profiles. Once separated, lipids were converted into biodiesel through a direct esterification process carried out by adopting three sequential batch reactors, in which methanol and catalysts were charged in counter current. In this way, the complete conversion (>99%) of starting FFAs into FAMEs was perfectly matched with using the minimum amount of reactants under very mild conditions (345 K, 2 h). The overall convenience of the process was completed by the anaerobic digestion of fibrous residues obtained from centrifugation of starting sewage scum: the final biogas resulted largely enough to sustain the heat of process.

ALGAS MARINAS BENTICAS INDICADORAS DE UN AREA AFECTADA POR AGUAS DE SURGENCIA FRENTE A LA COSTA CARIBE DE COLOMBIA

The present paper is the result of a study undertaken to establish the relationship of certain marine envlromental factors and the benthic flora of the Caribbean littoral of Colombia. For the purpose of this study this coastal bands has been divided in two Areas. Area 1 is found between Cabo Tiburón and the mouth of the Río Magdalena, and is characterized by warm waters with very small fluctuations of the surface temperature. Area 2 ranges from the mouth of the Río Magdalena to Castilletes, and its waters are affected by a coastal upwelling with a locality of maximum intensity at the West of Península de Guajira. As a result of the presence of this upwelling there are considerable variations in the physical and chemical factors acting upon the benthic flora, there established for very short periods or all year round, as well as determining the absence of some genera and species typical of these latitudes. The parameters used for detecting this oceanographic phenomenon are given by Díaz-Piferrer (1967 a) for Venezuela. To the biological indicators cited by this author for Venezuela, the present writer adds the brown alga Ectocarpus confervoides (Roth) Le Jolis, which was found in the area of upwelling in Colombia. A comparative study of these indicators plants with those of Venezuela is given in the present paper. Similarities and differences were found to be caused by the over-run of the warm counter current on the Colombian upwelling; by the different forces of the Caribbean Current and Guayana Current, all of which lead to the related oceanographic phenomenon; tfie climatic factors; the topography of the sea bottom and the influence of the continental waters over these upwelling.

The mechanism of flecainide action in CPVT does not involve a direct effect on RyR2.

Flecainide, a class 1c antiarrhythmic, has emerged as an effective therapy in preventing arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) refractory to β-adrenergic receptor blockade. It has been proposed that the clinical efficacy of flecainide in CPVT is because of the combined actions of direct blockade of ryanodine receptors (RyR2) and Na(+) channel inhibition. However, there is presently no direct evidence to support the notion that flecainide blocks RyR2 Ca(2+) flux in the physiologically relevant (luminal-to-cytoplasmic) direction. The mechanism of flecainide action remains controversial. To examine, in detail, the effect of flecainide on the human RyR2 channel and to establish whether the direct blockade of physiologically relevant RyR2 ion flow by the drug contributes to its therapeutic efficacy in the clinical management of CPVT. Using single-channel analysis, we show that, even at supraphysiological concentrations, flecainide did not inhibit the physiologically relevant, luminal-to-cytosolic flux of cations through the channel. Moreover, flecainide did not alter RyR2 channel gating and had negligible effect on the mechanisms responsible for the sarcoplasmic reticulum charge-compensating counter current. Using permeabilized cardiac myocytes to eliminate any contribution of plasmalemmal Na(+) channels to the observed actions of the drug at the cellular level, flecainide did not inhibit RyR2-dependent sarcoplasmic reticulum Ca(2+) release. The principal action of flecainide in CPVT is not via a direct interaction with RyR2. Our data support a model of flecainide action in which Na(+)-dependent modulation of intracellular Ca(2+) handling attenuates RyR2 dysfunction in CPVT.

Study of Plate and Frame Heat Exchanger Performance : The Effects of Mass Flow Rate, Inlet Temperature and Type of Flow Againts The Overall Heat Transfer Coefficient

The purpose of this study is to know the effects of mass flow rate, inlet temperature and type of flow againts overall heat transfer coefficient (U). Heat exchanger used in this study was plate and frame type of TRIMGS 10. Mass flow rate of hot fluida was variated into 0.3 and 0.253 kg/s; mass flow rate of cold fluida was variated into 0.276 and 0.22 kg/s; inlet temperature of hot fluida was variated into 40, 45, 50 o C; type of flow was variated into co-current and counter current. The results show that the faster mass flow rate hot and cold fluida, the bigger overall heat transfer coefficient obtained. Also, the higher inlet temperature, the the bigger overall heat transfer coefficient obtained. In this study, the biggest of U value was obtained with variable of inlet temperatur 50°C, mass flow rate of cold fluid 0.276 kg/s, mass flow rate of hot fluid 0.3 kg/s, which were 140.6532 W/m 2 °C using type of counter-current flow and 135.4576 W/m 2 °C using type of co-current flow. Type of counter-current flow gave more satisfactory result of U value than type of co-current flow

Heat transfer enhancement by multiple twisted tape inserts and TiO2/water nanofluid

The aim of this present work is to enhance thermal performance characteristics in a heat exchanger tube by studying: (i) multiple twisted tapes in different arrangements; (ii) TiO2 nanoparticles with different concentrations as the working fluid. The tube inserted the multiple twisted tapes showed superior thermal performance factor when compared with plain tube or the tube inserted a single twisted tape, due to continuous multiple swirling flow and multi-longitudinal vortices flow along the test tube. The higher number of twisted tape inserts led to an enhancement of thermal performance that resulted from increasing contact surface area, residence time, swirl intensity and fluid mixing with multi-longitudinal vortices flow. Moreover, arrangement of twisted tapes in counter current was superior energy saving devices for the practical use, particularly at low Reynolds number. This was especially the case for quadruple counter tapes in the cross directions (CC-QTs) where heat transfer enhancement with relatively low friction loss penalty was deserved. The use of CC-QTs led to the highest thermal performance factor up to 1.45. Using water with TiO2 nanoparticle as a working fluid yielded a higher thermal performance than using pure water. The tube inserted CC-QTs with TiO2/water nanofluid at concentration of 0.21% by volume provided the highest thermal performance factor 1.59, where heat transfer rate and friction factor increased to 3.52 times and 11.7 times of those in the plain tube with water as the working fluid.

Experimental Study of an Air Tube-cavity Solar Receiver

A tube-cavity solar receiver was designed to obtain high temperature air for the micro gas turbine in a two-stage dish system. Experiments were conducted under both fair and counter currents with the inlet temperature of ∼20°C and the flow rate of 1∼5m3/h. The average flux on the aperture was ∼267kW/m2. Under the fair current situation, the outlet temperature ranged from 559°C to 583°C. Under the counter current situation, the outlet temperature ranged from 589°C to 661°C. The glass cover was proved useful for the receiver's performance.

An Overview of Welding Aspects and Challenges during Manufacture of Intermediate Heat Exchangers for 500mwe Prototype Fast Breeder Reactor

Prototype Fast Breeder Reactor (PFBR) is first of its kind 500MWe pool type, sodium cooled nuclear reactor which is presently in advanced stage of construction at Kalpakkam, India. Intermediate Heat Exchanger (IHX) is a shell and tube type, counter current, sodium to sodium heat exchanger. IHX is a very important, massive, over dimensional (∼42 tones in weight, ∼2 meters in diameter and ∼18 meters in length) and critical component of reactor, as it transfers heat from the radioactive primary circuit sodium to non-radioactive secondary circuit sodium forming the boundary between these two circuits. The principal material of construction of IHX is austenitic stainless steel grade 316LN. Each IHX has 3600 nos. of straight seamless tubes which are rolled and then welded to the either ends of top and bottom tubesheets by autogenous pulsed Gas Tungsten Arc Welding (GTAW) process. The shell welding around the tube bundle is extremely difficult and challenging task due to small gap between the tube bundle and shell inside diameter. Special arrangements were made to avoid arc strike or fusion on the tube during shell welding around the tube bundle.A mechanical hardfaced seal arrangement at the interface of the IHX outer shell and the inner vessel stand pipe is the chosen design concept to ensure leak tightness in the IHX penetrations. Based on radiation dose rate & shielding considerations during maintenance, handling and decommissioning, nickel based ENiCr-B hard facing alloy (Colmonoy-5) was chosen to replace the traditionally used cobalt based stellite alloys to improve the resistance to high temperature wear, especially galling of mating surfaces in sodium environment. The more versatile Plasma Transferred Arc Welding (PTAW) and Gas Tungsten Arc Welding (GTAW) were used for deposition of Colmonoy-5. The hardfacing on the seal ring is really challenging task, as the diameter is too large and thickness & width is too small and which has hardfacing on all mating surfaces. Extensive varieties of trials were conducted on the mockup to optimize the hardfacing process along with heat treatment cycle to obtain minimum distortion deploying special tools and fixtures.Intermediate Heat Exchanger involves 10mm and 28mm thick borated stainless steel components around the tube bundle and bottom portion confirming to ASTM 887, Type 304 B4, Grade B classification to reduce the radiation level in secondary sodium system while flowing through the IHX. Various types of welding trials were conducted on the test coupons for welding procedure qualification of borated stainless steel components using versatile grades of welding consumables. More than hundred nos. of trial coupons welded using 10 varieties of welding consumables have shown fissures and cracks in weld, as these welding consumables found not having good compatibility with SS 304 B4, Grade B borated steel. Special development work was taken-up for the first time in the country by developing a special grade ∼1% borated welding consumable (GRINOX-308BRN electrode) specifically for welding of borated steel components of IHX. This paper highlights on welding aspects and challenges during fabrication of Intermediate Heat Exchangers for 500MWe Prototype Fast Breeder Reactor.

Long Wave Resonance in Tropical Oceans and Implications on Climate: the Atlantic Ocean

Based on the well established importance of long, non-dispersive baroclinic Kelvin and Rossby waves, a resonance of tropical planetary waves is demonstrated. Three main basin modes are highlighted through joint wavelet analyses of sea surface height (SSH) and surface current velocity (SCV), scale-averaged over relevant bands to address the co-variability of variables: (1) a 1-year period quasi-stationary wave (QSW) formed from gravest mode baroclinic planetary waves which consists of a northern, an equatorial and a southern antinode, and a major node off the South American coast that straddles the north equatorial current (NEC) and the north equatorial counter current (NECC), (2) a half-a-year period harmonic, (3) an 8-year sub-harmonic. Contrary to what is commonly accepted, the 1-year period QSW is not composed of wind-generated Kelvin and Rossby beams but results from the excitation of a tuned basin mode. Trade winds sustain a free tropical basin mode, the natural frequency of which is tuned to synchronize the excitation and the ridge of the QSWs. The functioning of the 1-year period basin mode is confirmed by solving the momentum equations, expanding in terms of Fourier series both the coefficients and the forcing terms. The terms of Fourier series have singularities, highlighting resonances and the relation between the resonance frequency and the wavenumbers. This ill-posed problem is regularized by considering Rayleigh friction. The waves are supposed to be semi-infinite, i.e. they do not reflect at the western and eastern boundaries of the basin, which would assume the waves vanish at these boundaries. At the western boundary the equatorial Rossby wave is deflected towards the northern antinode while forming the NECC that induces a positive Doppler-shifted wavenumber. At the eastern boundary, the Kelvin wave splits into coastal Kelvin waves that flow mainly southward to leave the Gulf of Guinea. In turn, off-tropical waves extend as an equatorially trapped Kelvin wave, being deflected off the western boundary. The succession of warm and cold waters transferred by baroclinic waves during a cycle leaves the tropical ocean by radiation and contributes to western boundary currents. The main manifestation of the basin modes concerns the variability of the NECC, of the branch of the South Equatorial Current (SEC) along the equator, of the western boundary currents as well as the formation of remote resonances, as will be presented in a future work. Remote resonances occur at midlatitudes, the role of which is suspected of being crucial in the functioning of subtropical gyres and in climate variability.

Optimising the design and operation of semi-continuous affinity chromatography for clinical and commercial manufacture

This paper presents an integrated experimental and modelling approach to evaluate the potential of semi-continuous chromatography for the capture of monoclonal antibodies (mAb) in clinical and commercial manufacture. Small-scale single-column experimental breakthrough studies were used to derive design equations for the semi-continuous affinity chromatography system. Verification runs with the semi-continuous 3-column and 4-column periodic counter current (PCC) chromatography system indicated the robustness of the design approach. The product quality profiles and step yields (after wash step optimisation) achieved were comparable to the standard batch process. The experimentally-derived design equations were incorporated into a decisional tool comprising dynamic simulation, process economics and sizing optimisation. The decisional tool was used to evaluate the economic and operational feasibility of whole mAb bioprocesses employing PCC affinity capture chromatography versus standard batch chromatography across a product's lifecycle from clinical to commercial manufacture. The tool predicted that PCC capture chromatography would offer more significant savings in direct costs for early-stage clinical manufacture (proof-of-concept) (∼30%) than for late-stage clinical (∼10–15%) or commercial (∼5%) manufacture. The evaluation also highlighted the potential facility fit issues that could arise with a capture resin (MabSelect) that experiences losses in binding capacity when operated in continuous mode over lengthy commercial campaigns. Consequently, the analysis explored the scenario of adopting the PCC system for clinical manufacture and switching to the standard batch process following product launch. The tool determined the PCC system design required to operate at commercial scale without facility fit issues and with similar costs to the standard batch process whilst pursuing a process change application. A retrofitting analysis established that the direct cost savings obtained by 8 proof-of-concept batches would be sufficient to pay back the investment cost of the pilot-scale semi-continuous chromatography system.

ATOP - The Advanced Taiwan Ocean Prediction System Based on the mpiPOM. Part 1: Model Descriptions, Analyses and Results

A data-assimilated Taiwan Ocean Prediction (ATOP) system is being developed at the National Central University, Taiwan. The model simulates sea-surface height, three-dimensional currents, temperature and salinity and turbulent mixing. The model has options for tracer and particle-tracking algorithms, as well as for wave-induced Stokes drift and wave-enhanced mixing and bottom drag. Two different forecast domains have been tested: a large-grid domain that encompasses the entire North Pacific Ocean at 0.1° × 0.1° horizontal resolution and 41 vertical sigma levels, and a smaller western North Pacific domain which at present also has the same horizontal resolution. In both domains, 25-year spin-up runs from 1988 - 2011 were first conducted, forced by six-hourly Cross-Calibrated Multi-Platform (CCMP) and NCEP reanalysis Global Forecast System (GSF) winds. The results are then used as initial conditions to conduct ocean analyses from January 2012 through February 2012, when updated hindcasts and real-time forecasts begin using the GFS winds. This paper describes the ATOP system and compares the forecast results against satellite altimetry data for assessing model skills. The model results are also shown to compare well with observations of (i) the Kuroshio intrusion in the northern South China Sea, and (ii) subtropical counter current. Review and comparison with other models in the literature of ”(i)” are also given.

Transport and turbulence studies in the linear ohmic confinement regime in Alcator C-Mod

Transport in ohmically heated plasmas in Alcator C-Mod was studied in both the linear (LOC) and saturated (SOC) ohmic L-mode confinement regimes and the importance of turbulent transport in the region r/a = 0.5–0.8 was established. After an extensive analysis with TGLF and GYRO, it is found that using an effective impurity ion species with Zi = 8, and moderately high Zeff (2.0–5.6), in the LOC regime electron transport becomes dominant due to TEM turbulence. The key ingredient in the present results is the observation that dilution of the main ion species (deuterium) by impurity species of moderate charge state reduces dominant ITG turbulence, in contrast to the SOC regime with little, if any dilution. The turbulent spectrum measured with the phase contrast imaging (PCI) diagnostic is in qualitative agreement with predictions of a synthetic PCI diagnostic adopted to Global GYRO. The toroidal rotation in the low-density LOC regime is in the co-current direction but as the density is raised in the SOC regime the rotation reverses to the counter current drive direction. The impurity content of the plasma was measured recently and an effective Zi of 9 was deduced.

On the nonlinear Schrödinger equation for waves on a nonuniform current

A nonlinear Schrödinger equation with variable coefficients for surface waves on a large-scale steady nonuniform current has been derived without the assumption of a relative smallness of the velocity of the current. This equation can describe with good accuracy the loss of modulation stability of a wave coming to a counter current, leading to the formation of so-called rogue waves. Some theoretical estimates are compared to the numerical simulation with the exact equations for a two-dimensional potential motion of an ideal fluid with a free boundary over a nonuniform bottom at a nonzero average horizontal velocity.

CFD simulation of PEM fuel cell performance: Effect of straight and serpentine flow fields

In this study, a comprehensive non isothermal, 3-dimensional model has been established to investigate the performance of proton exchange membrane (PEM) fuel cells with straight and serpentine flow fields. The model considers the major transport phenomena in a fuel cell involving mass, heat and energy transport, electrode kinetics, and potential fields. Two flow patterns including co-current and counter current are considered for all flows in the cell. Oxygen and hydrogen mass fraction distributions, current density and temperature distribution has been determined. The activation overpotential is constant within anode and cathode. Modeling findings showed that profiles differ from those simulations that assume constant activation overpotential. Serpentine flow field shows better distribution of current density and temperature. Simulation results were compared with the experimental data reported in literature and global comparisons showed good agreement between the model and experimental results.

Modelling of a Catalytic Micro-Reactor Coupling Endothermic Methane Reforming and Combustion

In this study the mathematical modelling of a catalytic microstructured plate reactor for the production of hydrogen was performed in 2D and 3D geometry. The proposed reacting system uses the heat generated by an exothermic reaction (combustion) to sustain endothermic reforming reactions. Therefore, it pertains to those devices useful for producing the feed for fuel cell system for the remote generation of electrical power. However, because of the compactness of the reacting system it can also be considered in the context of apparatus aiming at process intensification. Within this frame the catalytic contribution of both exothermic and endothermic reactions was modelled considering the classic Langmuir-Hinshelwood surface kinetic theory. The advantage of using a real 3D geometry configuration consists in the possibility of considering the importance of the entering and boundary effects with particular attention to fluid stagnation and heat hot spots. The trade off of such a choice is certainly the huge increase of computing time and/or of the power of the computing facility. With respect to other works performed with similar reactor geometry and reacting systems this does not use simplifying assumptions such as catalyst layers modeled by one-dimensional approach, fully developed laminar flow or transverse heat and mass transfer taken into account through lumped heat and mass transfer coefficients. Results of simulations presented here concentrates on the comparisons between results of: countercurrent (CTC) and concurrent (CNC) flow patterns of the reactant streams; of simulations carried out with 2D and 3D models and of the influence of the thickness of the catalytic layers on the reactor performance. Simulations indicates that CNC flow pattern of reactants streams allows a better performance of the reactor since positive temperature differences between the catalyst layers and the gas in the channels maintain along the whole reactor and, consequently, there are not heat flux inversions, which occur under CTC flow pattern. Results also showed that as concerns an adiabatic reactor, whatever the operating conditions, 2D and 3D models yield substantially the same results. Finally, modelling demonstrated that for a realistic catalyst layer configuration thicknesses larger than 50 µm are useless for enhancing the reactor performance. The feasibility of the model proposed may show its potential in fast and easy implementation of several combustion and reforming fuels so to significantly enhance the performance prediction of real processes.

Uranium, plutonium and neptunium co-recovery with high nitric acid concentration in extraction section by simplified solvent extraction process

Abstract As a part of NEXT, the behavior of Np in a simplified solvent extraction process using TBP as an extractant for U, Pu and Np co-recovery was investigated. Two approaches to Np co-recovery with U and Pu in the irradiated fast reactor core fuel using a dissolver solution in a counter current were examined. One used a feed solution with a high HNO3 concentration, and the other used a scrubbing solution with a high HNO3 concentration. The leakages of Np to the raffinate were 1.1 and 4.7% using high HNO3 concentration feed and scrubbing solutions, respectively. Simulation results based on these experiments showed that high HNO3 concentration in the feed solution is advantageous for the Np extraction because Np oxidation progresses in the feed solution before being supplied into the centrifugal contactor, and there is less effect of HNO2 at the extraction section.

Effectiveness of fast electron retention in the magnetic cavern during disturbance of the magnetic field azimuthal symmetry

The loss rate of fast electrons (with an energy much higher than the energy of the plasma electron thermal motion), when they leave a magnetic cavern during a disturbance of the magnetic field azimuthal symmetry, is studied. The cases of point and volume sources of fast particles have been considered. The plasma density in the cavern is supposed to be low, so that collisions of fast electrons with plasma particles can be neglected. The effect of the electric field on particle motion is neglected because it is assumed that the electric charge particles outgoing from the cavern is compensated by the counter current of plasma conductivity electrons. The dependence of the loss value on the harmonic number and the amplitude of the cavern boundary radius disturbance has been obtained.

Transient Flow of Air through Rectangular Vents in a Horizontal Partition

Transient laminar flow of air through rectangular vents in a horizontal partition between two large chambers was investigated. For vent aspect ratios of 1, 0.5, and 2, three flow regimes were identified as the Rayleigh number (Ra) was varied from 1 × 103 to 5 × 104 based on flow parameters in the vent and the corresponding modes of heat transfer through it. The critical control parameter was found to be the Rayleigh number, which determined the flow regimes of conduction, counter current, and oscillatory flow regimes. As the effective driving potential decreased with time, flow changed from one regime to the other such that higher Rayleigh number results showed all the three regimes over time. The circulation patterns within the vent for conduction regime (Ra < 1500) appeared to follow Chandrasekhar's (1961) well-known linear stability results. The flow exchange increases with partition thickness L/D = 0.5 and decreases for L/D = 2. At higher Ra, sudden bursts of upflow with a corresponding downflow were documented and compared with experimental observations in the literature. The time traces of velocity and temperature fields for this flow regime reveal interesting mechanisms, which have been explained.

Autothermal operation of an adiabatic simulated counter current reactor

Periodic operation of several adiabatic fixed beds connected in series is an alternative to conventional steady-state fixed-bed operation or transient reverse flow reactor operation, e.g. to process lean waste gases or to perform efficiently slightly exothermic equilibrium limited reactions. This work explains the periodic operation of a multi-bed reactor network using both a simplified model assuming a true counter current of the phases involved and a more detailed dynamic model. An appropriate expression for relating the switching times and solid phase velocities is applied. The shapes of the thermal waves are studied in a range of relevant switching times. Results of a stability analysis considering both models reveal hysteresis for ignition and extinction of the reactor network. The accompanying regions of multiplicity provide insight in the potential of performing in such reactor networks exothermal reactions for certain ranges of the adiabatic temperature rise.