Low Mass Transfer Rates Research Articles

When does an old nova become a dwarf nova? Kinematics and age of the nova shell of the dwarf nova AT Cancri

The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell, demonstrating that mass transfer in cataclysmic binaries decreases substantially after a CN eruption. The hibernation scenario of cataclysmic binaries predicts such a decrease, on a timescale of a few centuries. In order to measure the time since AT Cnc's last CN eruption, we have measured the radial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's recently commissioned imaging Fourier transform spectrometer. These range from -455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara 2012), the size of AT Cnc's shell, and a simple model of nova ejecta deceleration, we determine that the last CN eruption of this system occurred $330_{-90}^{+135}$ years ago. This is the most rapid transition from a high mass transfer rate, novalike variable to a low mass transfer rate, dwarf nova yet measured, and in accord with the hibernation scenario of cataclysmic binaries. We conclude by noting the similarity in deduced outburst date (within a century of 1686 CE) of AT Cnc with a "guest star" reported in the constellation Cancer by Korean observers in 1645 CE.

Outbursts in ultracompact X-ray binaries

Very faint X-ray binaries appear to be transient in many cases with peak luminosities much fainter than that of usual soft X-ray transients, but their nature still remains elusive. We investigate the possibility that this transient behaviour is due to the same thermal/viscous instability which is responsible for outbursts of bright soft X-ray transients, occurring in ultracompact binaries for adequately low mass-transfer rates. More generally, we investigate the observational consequences of this instability when it occurs in ultracompact binaries. We use our code for modelling the thermal-viscous instability of the accretion disc, assumed here to be hydrogen poor. We also take into account the effects of disc X-ray irradiation, and consider the impact of the mass-transfer rate on the outburst brightness. We find that one can reproduce the observed properties of both the very faint and the brighter short transients (peak luminosity, duration, recurrence times), provided that the viscosity parameter in quiescence is slightly smaller (typically a factor of between two and four) than in bright soft X-ray transients and normal dwarf nova outbursts, the viscosity in outburst being unchanged. This possibly reflects the impact of chemical composition on non-ideal MHD effects affecting magnetically driven turbulence in poorly ionized discs.

The awakening of a classical nova from hibernation

Cataclysmic variable stars-novae, dwarf novae, and nova-likes-are close binary systems consisting of a white dwarf star (the primary) that is accreting matter from a low-mass companion star (the secondary). From time to time such systems undergo large-amplitude brightenings. The most spectacular eruptions, with a ten-thousandfold increase in brightness, occur in classical novae and are caused by a thermonuclear runaway on the surface of the white dwarf. Such eruptions are thought to recur on timescales of ten thousand to a million years. In between, the system's properties depend primarily on the mass-transfer rate: if it is lower than a billionth of a solar mass per year, the accretion becomes unstable and the matter is dumped onto the white dwarf during quasi-periodic dwarf nova outbursts. The hibernation hypothesis predicts that nova eruptions strongly affect the mass-transfer rate in the binary, keeping it high for centuries after the event. Subsequently, the mass-transfer rate should significantly decrease for a thousand to a million years, starting the hibernation phase. After that the nova awakes again-with accretion returning to the pre-eruption level and leading to a new nova explosion. The hibernation model predicts cyclical evolution of cataclysmic variables through phases of high and low mass-transfer. The theory gained some support from the discovery of ancient nova shells around the dwarf novae Z Camelopardalis and AT Cancri, but direct evidence for considerable mass-transfer changes prior, during and after nova eruptions has not hitherto been found. Here we report long-term observations of the classical nova V1213 Cen (Nova Centauri 2009) covering its pre- and post-eruption phases and precisely documenting its evolution. Within the six years before the explosion, the system revealed dwarf nova outbursts indicative of a low mass-transfer rate. The post-nova is two orders of magnitude brighter than the pre-nova at minimum light with no trace of dwarf nova behaviour, implying that the mass-transfer rate increased considerably as a result of the nova explosion.

The soft X-ray spectrum of the high-mass X-ray binary V0332+53 in quiescence

The propeller effect should cut off accretion in fast-spinning neutron star high mass X-ray binaries (HMXBs) at low mass transfer rates. However, accretion continues in some HMXBs at $L_{x} < 10^{34}$ erg s$^{-1}$, as evidenced by continuing pulsations. Indications of spectral softening in systems in the propeller regime suggest that some HMXBs are undergoing fundamental changes in their accretion regime. A 39 ks \textit{XMM-Newton} observation of the transient HMXB V0332+53 found it at a very low X-ray luminosity ($L_{x} \sim 4\times 10^{32}$ erg s${^{-1}}$). A power-law spectral fit requires an unusually soft spectral index ($4.4^{+0.9}_{-0.6}$), while a magnetized neutron star atmosphere model, with temperature \lt\ 6.7$\pm 0.2$ K and inferred emitting radius of $\sim0.2-0.3$ km, gives a good fit. We suggest that the quiescent X-ray emission from V0332+53 is mainly from a hot spot on the surface of the neutron star. We could not detect pulsations from V0332+53, due to the low count rate. Due to the high $N_H$, thermal emission from the rest of the neutron star could be only weakly constrained, to \lt\ $<$6.14$^{+0.05}_{-6.14}$ K, or $<3\times10^{33}$ erg s${^{-1}}$.

Mass transfer kinetics using two-site interface model for removal of Cr(VI) from aqueous solution with cassava peel and rubber tree bark as adsorbents

Present study investigates the potential of cassava peel and rubber tree bark for the removal of Cr (VI) from aqueous solution. Removal efficiency of more than 99% was obtained during the kinetic adsorption experiments with dosage of 3.5 g/L for cassava peel and 8 g/L for rubber tree bark. By comparing popular isotherm models and kinetic models for evaluating the kinetics of mass transfer, it was observed that Redlich-Peterson model and Langmuir model fitted well (R2 > 0.99) resulting in maximum adsorption capacity as 79.37 mg/g and 43.86 mg/g for cassava peel and rubber tree bark respectively. Validation of pseudo-second order model and Elovich model indicated the possibility of chemisorption being the rate limiting step. The multi-linearity in the diffusion model was further addressed using multi-sites models (two-site series interface (TSSI) and two-site parallel interface (TSPI) models). Considering the influence of interface properties on the kinetic nature of sorption, TSSI model resulted in low mass transfer rate (5% for cassava peel and 10% for rubber tree bark) compared to TSPI model. The study highlights the employability of two-site sorption model for simultaneous representation of different stages of kinetic sorption for finding the rate-limiting process, compared to the separate equilibrium and kinetic modeling attempts.

Nickel-Rich Cathode Precursor Synthesis By Taylor Vortex Reactor

Progresses in lithium ion battery (LIB) materials are increasing by the development of new synthesis methods where the production of materials in a scalable and continuous route is very critical when the process development transfers to large scale quantities. In a LIB, one of the most performance limiting components is the cathode, which also limits the overall performance of the battery. Among the other synthesis methods, co-precipitation from aqueous processes is known to yield the best cation mixing within the structure, in particular for the synthesis of cathode precursors for batteries. Continuous stirred tank reactor (CSTR) is by far the most widely used systems utilized in battery industry, yet have low reproducibility, product efficiency, and undergo from very long stabilization times due to low mass transfer rate. Here, we report a new emerging technology, Taylor Vortex Reactor (TVR), for the cathode precursor synthesis which overcomes many complexities encountered in CSTRs. As current research in the field is trending towards exploring nickel-rich compositions, we produced Ni0.6Mn0.2Co0.2 (OH)2 precursors employing a continuous hydroxide route in a TVR which were then lithiated to form active cathode particles. The effect of rotation speed on the morphology, and particle size and distribution of the precursors were investigated and reported. In general, higher rotation speed favored spherical particle formation with a smooth surface morphology along with a narrow particle size distribution. Tap densities of 1.77 – 1.98 g/cc for the precursor and 2.02 – 2.24 g/cc for the active materials were achieved, delivering 173 – 186 mAh/g discharge capacities at the first cycle with a C-rate of 0.1C when cycled between 4.3 - 3.0V.

Influence of fluid dynamic conditions on enzymatic hydrolysis of lignocellulosic biomass: Effect of mass transfer rate

The effect of fluid dynamic conditions on enzymatic hydrolysis of acid pretreated corn stover (PCS) has been assessed. Runs were performed in stirred tanks at several stirrer speed values, under typical conditions of temperature (50°C), pH (4.8) and solid charge (20% w/w). A complex mixture of cellulases, xylanases and mannanases was employed for PCS saccharification. At low stirring speeds (<150rpm), estimated mass transfer coefficients and rates, when compared to chemical hydrolysis rates, lead to results that clearly show low mass transfer rates, being this phenomenon the controlling step of the overall process rate. However, for stirrer speed from 300rpm upwards, the overall process rate is controlled by hydrolysis reactions. The ratio between mass transfer and overall chemical reaction rates changes with time depending on the conditions of each run.

Liquid–liquid flow regimes and mass transfer in various micro-reactors

The flow regimes and mass transfer rates in five complex micro-reactors with different mixing mechanisms were investigated using the two-phase alkaline hydrolysis of 4-nitrophenyl acetate. n-Butanol and toluene were used as organic solvents. Using n-butanol in curvature-based micro-mixers, the flow regime evolved from slug to parallel to drop/dispersed flow with increasing flow rates. In obstacle-based micro-mixers, no parallel flow was observed. Using toluene, no parallel flow was observed for all reactors. The conversion of 4-nitrophenyl acetate was found to be strongly dependent on the flow regime. In slug and parallel flow, the conversion generally decreased with an increase in flow rate whereas it typically increased in drop flow and was constant or slightly decreased in dispersed flow. The different micro-mixers were compared using the overall volumetric mass transfer coefficient, Korga, which was primarily a function of the rate of energy dissipation within the dispersed flow regime. The geometry itself impacts the resulting flow regime and rate of energy dissipation at a given flow rate. The micro-reactors were then compared using modified Damköhler’s numbers. Curvature-based reactors were found to be inadequate for liquid–liquid reactions under the studied conditions, as they favor parallel flow patterns and yield relatively low interphase mass transfer rates.

Accelerated desulphurization of waste lead battery paste in a high-gravity rotating packed bed

Pb-paste as the major composition in waste lead acid battery has an important role in the process of lead recycling. However, low liquid-solid mass transfer rates in conventional reactors have a significant limitation for the industrial application of Pb-paste desulphurization using hydrometallurgical process. In this paper, a cost-effective mass-transfer intensified approach for Pb-paste desulphurization with Na2CO3 solution in a rotating packed bed (RPB) reactor was presented. The effects of various variables on the desulphurization degree of PbSO4 were firstly explored. The results indicated that the increases in rotating speed, Na2CO3 concentration and Na2CO3/PbSO4 molar ratio were beneficial to the process. Temperature and reactant flow rate had obvious effects on the desulphurization degree only at a low reactant concentration. Further, the desulphurization processes of the simulated Pb-pastes were comparatively investigated. It was found that the RPB reactor markedly intensified the process in a very short contact time (about 1s), thereby achieving a continuous desulphurization process. Only one cycle liquid-solid contact could make the desulphurization degrees of PbSO4, anode powder and cathode powder reach 99.7%, 98.9% and 97.2%, respectively. Compared to a stirred tank reactor, the desulphurization time was greatly shortened by at least 2 orders of magnitude.

The effect of microbubbles on gas-liquid mass transfer coefficient and degradation rate of COD in wastewater treatment.

A commonly used aeration device at present has the disadvantages of low mass transfer rate because the generated bubbles are several millimeters in diameter which are much bigger than microbubbles. Therefore, the effect of a microbubble on gas-liquid mass transfer and wastewater treatment process was investigated. To evaluate the effect of each bubble type, the volumetric mass transfer coefficients for microbubbles and conventional bubbles were determined. The volumetric mass transfer coefficient was 0.02905 s(-1) and 0.02191 s(-1) at a gas flow rate of 0.67 L min(-1) in tap water for microbubbles and conventional bubbles, respectively. The degradation rate of simulated municipal wastewater was also investigated, using aerobic activated sludge and ozone. Compared with the conventional bubble generator, the chemical oxygen demand (COD) removal rate was 2.04, 5.9, 3.26 times higher than those of the conventional bubble contactor at the same initial COD concentration of COD 200 mg L(-1), 400 mg L(-1), and 600 mg L(-1), while aerobic activated sludge was used. For the ozonation process, the rate of COD removal using microbubble generator was 2.38, 2.51, 2.89 times of those of the conventional bubble generator. Based on the results, the effect of initial COD concentration on the specific COD degradation rate were discussed in different systems. Thus, the results revealed that microbubbles could enhance mass transfer in wastewater treatment and be an effective method to improve the degradation of wastewater.

Effects of water acidification on element concentrations in natural waters of the Kola North

This study discusses the problem of evolution of water chemistry under the influence of acid loadings from copper–nickel smelters of the Kola mining and smelting company (“KGMK”). The natural waters of the Kola Peninsula are characterized by low contents of biogenic substances and mineral salts owing to low water temperatures and low mass transfer rates at high latitudes. Acid precipitation causes water acidification in regions made up by granite gneisses and sandy rocks. Unlike naturally acidic waters with high humic acid contents, these lakes have high-transparency waters. The results show that Cd, Bi, Se, and Re become involved in the transport fluxes irrespective of a natural or anthropogenic source of acidification. Acidified lakes have higher Zn, Pb, As, Bi, and Sb contents compared to neutral lakes. The high coefficient of aqueous migration of Se, Re, Bi, Sb, Cd, and Sn is indicative of the anthropogenically-induced dispersal of these elements.

Discovery of an eclipsing dwarf nova in the ancient nova shell Te 11

We report on the discovery of an eclipsing dwarf nova (DN) inside the peculiar, bilobed nebula Te 11. Modelling of high-speed photometry of the eclipse finds the accreting white dwarf to have a mass 1.18 M$_\odot$ and temperature 13 kK. The donor spectral type of M2.5 results in a distance of 330 pc, colocated with Barnard's loop at the edge of the Orion-Eridanus superbubble. The perplexing morphology and observed bow shock of the slowly-expanding nebula may be explained by strong interactions with the dense interstellar medium in this region. We match the DN to the historic nova of 483 CE in Orion and postulate that the nebula is the remnant of this eruption. This connection supports the millennia time scale of the post-nova transition from high to low mass-transfer rates. Te 11 constitutes an important benchmark system for CV and nova studies as the only eclipsing binary out of just three DNe with nova shells.

Continuous formation of N-chloro-N,N-dialkylamine solutions in well-mixed meso-scale flow reactors.

The continuous flow synthesis of a range of organic solutions of N,N-dialkyl-N-chloramines is described using either a bespoke meso-scale tubular reactor with static mixers or a continuous stirred tank reactor. Both reactors promote the efficient mixing of a biphasic solution of N,N-dialkylamine in organic solvent, and aqueous sodium hypochlorite to achieve near quantitative conversions, in 72–100% in situ yields, and useful productivities of around 0.05 mol/h with residence times from 3 to 20 minutes. Initial calorimetric studies have been carried out to inform on reaction exotherms, rates and safe operation. Amines which partition mainly in the organic phase require longer reaction times, provided by the CSTR, to compensate for low mass transfer rates in the biphasic system. The green metrics of the reaction have been assessed and compared to existing procedures and have shown the continuous process is improved over previous procedures. The organic solutions of N,N-dialkyl-N-chloramines produced continuously will enable their use in tandem flow reactions with a range of nucleophilic substrates.

Electrodialysis treatment of secondary steam condensate obtained during production of ammonium nitrate. Technical and economic analysis

Abstract The process of electrodialysis desalination of secondary steam condensate produced during ammonium nitrate production using various anion-exchange membranes is studied in the laboratory and on pilot scale electrodialysis modules. The main parameters of the process: current efficiency, salt flux and power consumption, are studied. The membranes studied include three commercial heterogeneous anion-exchange membranes: Ralex AMH produced by Mega a.s.; MA-40 and MA-41 produced by JSC Szchekinoazot; and the homemade profiled membrane MA-41P. It is shown that the profiled membrane possesses the best mass transfer characteristics this is explained by the combined effects of several factors. These factors include a significant increase of the active membrane area available for mass transfer, intensive fluid mixing and a decrease in the water splitting rate. Among the smooth membranes the Ralex AMH shows the best performance due to its larger active area. The mass transfer properties of the membranes are explained with the help of scanning electron microscopy and voltammetry. The reason behind their behavior in the electrodialysis process is explained by the properties and morphology of their surfaces. An analysis of the economics of the desalination process is made. It is shown that from an economical point of view, MA-41 membranes can be successfully applied in the electrodialysis demineralization process despite their lower mass transfer characteristics compared to the Ralex AMH membranes. Due to their lower mass transfer rates, a larger number of modules is required to achieve the same goals. However, this is compensated for by their lower price.

Numerical Simulation of Laminar Film Condensation in a Horizontal Minitube with and Without Non-Condensable Gas by the VOF Method

Based on the volume of fluid (VOF) method, a steady three-dimensional numerical simulation of laminar film condensation of water vapor in a horizontal minitube, with and without non-condensable gas, has been conducted. A user-defined function defining the phase change is interpreted and the interface temperature is correspondingly assumed to be the saturation temperature. An annular flow pattern is to be expected according to a generally accepted flow regime map. The heat-transfer coefficient increases with higher saturation temperature and a smaller temperature difference between the saturation and wall temperatures, but varies little with different mass flux and degree of superheat. The existence of a non-condensable gas will lead to the generation of a gas layer between vapor and liquid, resulting in a lower mass-transfer rate near the interface and higher vapor quality at the outlet. In consequence, the heat-transfer coefficient of condensation with a non-condensable gas drops sharply compared with that of pure vapor condensation. Meanwhile, the non-condensable gas with a smaller thermal conductivity would cause a stronger negative effect on heat flux as a result of a higher thermal resistance of heat conduction in the non-condensable gas layer.

Maxwell–Stefan modeling of mass transfer in solvent impregnated resins

Solvent impregnated resins are promising for the removal of polar organic compounds from aqueous streams, but have low mass-transfer rates. A thorough understanding of the phenomena occurring inside the pores of the solvent impregnated resin is therefore required. In this study a mathematical model was developed to describe the simultaneous diffusion and reaction. The diffusion was described using the Maxwell–Stefan approach towards multi-component diffusion and included the volume-expansion of the organic phase. The model was validated using experimental data from the literature on the extraction of phenol by Cyanex923 impregnated in macro-porous polypropylene. The model described the experimental data as function of temperature and initial concentration accurately with an R2>0.96 and a regressed reaction rate constant with a confidence interval of ±6%. Analysis of the model results revealed that multi-component effects as described by the Maxwell–Stefan model were of limited importance whereas the volume expansion was essential to accurately describe the experimental data.

High‐resolution experiments on chemical oxidation of DNAPL in variable‐aperture fractures

AbstractChemical oxidation of dense nonaqueous‐phase liquids (DNAPLs) by permanganate has emerged as an effective remediation strategy in fractured rock. We present high‐resolution experimental investigations in transparent analog variable‐aperture fractures to improve understanding of chemical oxidation of residual entrapped trichloroethylene (TCE) in fractures. Four experiments were performed with different permanganate concentrations, flow rates, and initial TCE phase geometry. The initial aperture field and evolving entrapped‐phase geometry were quantified for each experiment. The integrated mass transfer rate from the TCE phase for all experiments exhibited three time regimes: an early‐time regime with slower mass transfer rates limited by low specific interfacial area; an intermediate‐time regime with higher mass transfer rates resulting from breakup of large TCE blobs, which greatly increases specific interfacial area; and a late‐time regime with low mass transfer rates due to the deposition of MnO2 precipitates. In two experiments, mass balance analyses suggested that TCE mass removal rates exceeded the maximum upper bound mass removal rates derived by assuming that oxidation and dissolution are the only mechanisms for TCE mass removal. We propose incomplete oxidation by permanganate and TCE solubility enhancement by intermediate reaction products as potential mechanisms to explain this behavior. We also speculate that some intermediate reaction products with surfactant‐like properties may play a role in lowering the TCE‐water interfacial tension, thus causing breakup of large TCE blobs. Our quantitative experimental measurements will be useful in the context of developing accurate computational models for chemical oxidation of TCE in fractures.

On the absence of nova shells

We present our wide field Halpha+N[II] observations of 15 cataclysmic variables to search for remnant nova shells. Such shells have been found around other cataclysmic variables that were hitherto not known as novae. Our candidates were selected as objects in the period regime of high-mass transfer systems that experience - at least occasionally - low mass transfer rates. The fact that we find no indication of a nova shell in any of these systems allows us to set a lower limit of 13000 years to the recurrence time of these objects.

Preparation of NMC622 Cathode Materials Using a Cost Effective Circular Type Reactor for Li-Ion Battery Application

Li(Ni0.6Mn0.2Co0.2)O2 (NMC622) cathode materials have been recognized as the next generation cathode materials due to its higher capacity and lower raw material cost than commercialized cathode materials such as NMC532. Thus, many industrial companies have been made every effort to commercialize and apply the NMC622 to lithium ion battery system such as energy storage system (ESS). However, production cost of NMC622 still has been recognized as expensive material to be applied in the industrial field and it becomes main issues to be overcome. CSTR (Continuous Stirred Tank Reactor) has been widely applied in the industrial field to produce the NMC622 precursor but it has initial long stabilization time as well as low production efficiency. This is caused by the original limitation of CSTR such as the low mass transfer rate and required complete mixing zone to stabilize the system. Thus, in this study, we suggest the novel reactor system that shows the higher mass transfer rate as well as higher production rate than those of CSTR. Developed novel reactor system uses the taylor-couette flows to induce higher mass transfer rate and production efficiency with uniform particle size distribution.In this study, we synthesized NMC622 using taylor-couette reactor to understand the function and mechanism of the operation. The effect of operating parameters, i.e. pH, operating rpm, and feed retention time, in the taylor-couette reactor, was investigated thoroughly to evaluate the feasibility to produce NMC622 precursor. Produced precursors are characterized using SEM, XRD, ICP, FIB, PSA. Then, cathode materials are prepared and tested using a galvanostatic intermittent titration method (GITT) to understand the electrochemical properties. This study verified that taylor couette reactor is feasible process to be applied to the commercial NMC622 production.Acknowledgement - This work was supported by the Korea Institute of Energy Technology Evaluation and Planning under the Energy Technology Development Program (20132020101750)

Exploring the long-term variability and evolutionary stage of the interacting binary DQ Velorum

To progress in the comprehension of the double periodic variable (DPV) phenomenon, we analyse a series of optical spectra of the DPV system DQ Velorum during much of its long-term cycle. In addition, we investigate the evolutionary history of DQ Vel using theoretical evolutionary models to obtain the best representation for the current observed stellar and orbital parameters of the binary. We investigate the evolution of DQ Vel through theoretical evolutionary models to estimate the age and the mass transfer rate which are compared with those of its twin V393 Scorpii. Donor subtracted spectra covering around 60% of the long-term cycle, allow us to investigate time-modulated spectral variations of the gainer star plus the disc. We compare the observed stellar parameters of the system with a grid of theoretical evolutionary tracks computed under a conservative and a non-conservative evolution regime. We have found that the EW of Balmer and helium lines in the donor subtracted spectra are modulated with the long-term cycle. We observe a strenghtening in the EWs in all analysed spectral features at the minimum of the long-term cycle which might be related to an extra line emission during the maximum of the long-term variability. Difference spectra obtained at the secondary eclipse support this scenario. We have found that a non-conservative evolutionary model is a better representation for the current observed properties of the system. The best evolutionary model suggests that DQ Vel has an age of 7.40 x 10^{7} yr and is currently in a low mass transfer rate (-9.8x10^{-9} Msun/yr) stage, after a mass transfer burst episode. Comparing the evolutionary stages of DQ Vel and V393 Sco we observed that the former is an older system with a lower mass transfer rate. This might explain the differences observed in the physical parameters of their accretion discs.