Thermal Precipitation Research Articles

Development of an efficient thermal management system for Vanadium Redox Flow Battery under different charge-discharge conditions

The temperature rise inside VRFB stack may exceed its safe limit at higher charging and discharging currents leading to thermal precipitation. A thermal management and control model of VRFB is developed in this paper for the first time in MATLAB/Simulink environment and experimentally validated in the lab. Online monitoring of VRFB stack temperature and flow rate control is executed by dsPIC microcontroller platform. The usual practice of applying higher flow rate by increasing pump speed during charging and discharging operations for keeping the stack temperature within safe limit leads to reduction of overall VRFB system efficiency due to higher pump power loss. In this work a model for determining the dynamic optimal flow rate is developed to ensure efficient thermal management and improvement of overall system efficiency of VRFB. The proposed thermal management scheme is validated by a practical 1 kW 6 h VRFB system operation. It is observed that at a lower flow rate of 180 ml/sec the stack temperature during fast charging and discharging at the rate of 60A rises up to 47 °C which is well above the specified safe limit of operating temperature of VRFB and leads to incomplete charging due to premature thermal shut down of the system. Increasing the flow rate to 300 ml/sec keeps the stack temperature within safe limit but the overall VRFB efficiency becomes around 83%. However, by applying dynamic optimal flow rate (160–300 ml/sec) over the range of SOC (10–90%), this is managed within the safe level of 35.8 °C and at the same time improving the overall VRFB system efficiency up to 88.55%. The model performance shows very good agreement with the experimental results having maximum error of 0.85%. The thermal management and control scheme demonstrated in this paper is a generalised one and hence very useful for large scale VRFB applications as well.

On osmotic heat engines driven by thermal precipitation-dissolution of saturated aqueous solutions

Cyclic thermal precipitation and dissolution of saturated aqueous solutions and its significance with regard to osmotic heat engines (OHEs) is discussed. Here, the thermal dependence of the solubility is harnessed by alternating thermal solute precipitation and dissolution when heat is either applied (by heating the solution) or extracted (by cooling the solution) depending of the given solution. Utilizing a simplified physical model, it is shown that by the proper choice of the concentration, a closed cycle seems feasible. In contrast with traditional OHEs which working with dilute ideal solutions, the proposed osmotic engine operates at saturation concentration level and therefore the approximation of ideal solution is no longer valid, and then, for a valid approach, an osmotic coefficient was included in the calculations to take account the deviation from the ideal case. The expression for the extractable energy per unit of volume of solution as well as the thermal efficiency of the heat engine were derived considering the spontaneous change in the Gibbs free energy and the enthalpy of precipitation. The specific case for Na2SO4 was analyzed and it was found a percentage of Carnot efficiency as high as 23% which is a little larger than the efficiencies reported by traditional OHEs. The proposed heat engine eliminates the need of evaporation to re-concentrate the draw solution and then the constraint of working with solutions with high vapor pressures.

Investigation of V(V)/V(IV) Redox Reaction in Mixed Acid Electrolyte Using X-Ray Absorption Spectroscopy

The performances of all-vanadium redox flow batteries (VRB) can be improved by increasing the electrode kinetics and/or by increasing the solubility of the electroactive species involved in the process [1]. The concentrations of vanadium species in the electrolyte determine the total electrolyte volume and energy density of the system, albeit relatively low for VRBs, between 30-50 Wh/kg [2]. Higher vanadium concentrations are desirable to achieve reasonable energy densities. It has been shown that the solubilities of V(II), V(III) and V(IV) species in H2SO4 increase with increasing temperature and decreasing acid concentration. Precipitation of V(II), V(III) and V(IV) have been reported at temperature below 10°C. V(V) however, does not precipitate as a sulphate but undergoes thermal precipitation by an endothermic reaction to form V2O5 at temperatures > 40°C. The maximum ion concentration is therefore set by the operating temperature of the VRB which lies between 10 and 40°C. The preferred electrolyte composition for this temperature range is a total vanadium ion concentration between 1.6-2 mol/L and a total sulfate concentration of 4-5 mol/L [3]. It is critical to stabilize V(V) species against thermal precipitation. One solution to increase both thermal stability and solubility of V(V) electrolyte is the use of a mixture of H2SO4 and HCl acids as supporting electrolyte [4], [5]. It has been reported that by using this electrolyte the V(V) solubility is increased to 2.5 mol/L while the electrolyte is stable in a temperature range between -5 and 50°C. Initially we investigated the kinetics of V(V)/V(IV) redox couple in sulfuric acid and mixed electrolyte (H2SO4+HCl) using oxidized glassy carbon electrode surface [6]. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used for the electrochemical investigation. Additionally, the thermal and chemical stability of the V(V) and V(IV) electrolytes in H2SO4 and mixed H2SO4 + HCl were investigated using X-Ray absorption spectroscopy. Detailed knowledge regarding the V(V) coordination sphere in H2SO4 and mixed acids are of significant interest for understanding electrolyte stability but also for elucidating the V(V) electrochemical reduction mechanism. Finally, the change in atomic coordination sphere of V(V) and V(IV) electrolytes in H2SO4 and H2SO4/HCl were investigated in fresh and aged samples using K-edge EXAFS, which is sensitive to both the electronic configuration and the atomic structure around the V, Cl and S atoms.

Synthesis, characterization and using a new terpyridine moiety-based ion-imprinted polymer nanoparticle: sub-nanomolar detection of Pb(II) in biological and water samples

A highly selective lead-imprinted polymer was synthesized via a thermal precipitation polymerization technique based on a terpyridine-based ligand as the complexing agent. The synthesized polymer was successfully incorporated in a graphite paste electrode (GPE) as the recognition element for lead ion (Pb2+). Differential pulse anodic stripping voltammetry (DPASV) technique was used to transduce the binding events at the modified electrode. The imprinted polymer nanoparticles (IP-NPs) were synthesized by precipitation polymerization of ethylene glycol dimethacrylate as the cross-linker, 2,2′-azobisisobutyronitrile as the free radical initiator and 2,2′:6′,6″-terpyridine (terpy) as the recognition element. The sensing procedure is based on the accumulation of lead ions at − 1.0 V vs. Ag/AgCl. Afterward, the DPV was recorded by the sweeping potential in a positive direction to oxidize the accumulated ions, leading to the appearance of a significant anodic peak. The constructed IIP–GPE revealed a linear response toward Pb2+ over the concentration range from 0.4 to 10 nM (with the sensitivity of 693.95 nA nM−1 cm−2) and 10 nM to 1.0 µM (with the sensitivity of 580.25 µA µM−1 cm−2). The limit of detection (LOD) was evaluated to be 0.11 nM (for S/N = 3). The accuracy of the sensor was explored by analysis of a quality control material (QCMs, Seronorm™ urine REF NO 1011645) and different water samples. Selectivity studies showed no particular interference for detection of Pb(II).

Design of Nanodispersed Magnetoactive Systems for Targeted Drug Delivery

Based on the method of thermal solvent precipitation, unique procedures for drug capsulation have been developed. Biodegradable polymers, polycaprolactone, and polyethylene glycol are used. Hydrosols and alcosols of various metals and their compounds have been obtained, which makes the targeted delivery of the desired substance using a magnetic field possible. The importance of magnetite hydrosol in the stability of colloidal systems has been shown. Experiments on the impact of doxorubicin and capsulated doxorubicin on the HeLa cell culture are carried out. The studies are conducted in laboratory mice and the possibility of controlling magnetoactive particles in vivo is demonstrated.

Evaluation of spacecraft smoke detector performance in the low-gravity environment

In the interest of fire prevention, most materials used in the interior construction of manned spacecraft are non-flammable, however, they do produce smoke when overheated. Spacecraft smoke detectors will ideally detect smoke generated by oxidative pyrolysis (such as smoldering) in order to allow the maximum time for the crew to respond before a larger flaming fire develops. An experiment on the International Space Station (ISS) was performed to characterize smoke particles generated from the oxidative pyrolysis of five common spacecraft materials. The following parameters were controlled: heating temperature, air flow past the samples and duration of aging. Two different spacecraft smoke detectors were included in the instrumentation and their performance with different smoke types has been evaluated. Additional equipment in the experiment included a thermal precipitator to sample particles for microscopic analysis upon return to Earth, and two commercial-off-the-shelf real-time instruments to measure particle mass and number concentration, and an ionization detector calibrated to estimate the first moment of the size distribution. Results from the ISS experiment show that smoke particles vary in morphology and average diameter, however, they are not significantly different from smoke particles generated in equivalent experiments performed in normal gravity. The two spacecraft smoke detectors did not successfully detect every type of smoke, which demonstrates that the next generation of spacecraft fire detectors must be improved and tested against smoke from relevant space materials.

Thermally promoted evolution of open-volume defects and Cu precipitates in the deformed FeCu alloys

We have studied the effect of isothermal annealing on the evolution of the open-volume defect and the Cu precipitate in deformed Fe0.15Cu, Fe0.3Cu and Fe0.6Cu alloys. Using the coincidence Doppler broadening, positron annihilation lifetime and the S-W couples, the evolution of local electronic circumstance around the annihilation sites, open-volume defects and interaction between open-volume defects and Cu precipitates were measured as a function of the isothermal annealing temperatures. Cold rolling deformation induced an obvious increment in S parameters due to the formation of open-volume defects. Annealing not only resulted in gradual recovery of open-volume defects and Cu thermal precipitation, but also promoted the combination and interaction between defects and Cu precipitates. The interaction between open-volume defects and Cu precipitates was revealed clearly by the view point of S-W relationship. The S-W interaction for the different CumVn complexes was also calculated theoretically by MIKA-Doppler, which supports our experimental observations qualitatively. The results indicate that open-volume defects were formed first after cold rolling, followed by the Cu precipitation and recovery of open-volume defects, Cu precipitates recovered at the end. It is interesting that the trajectory of (S, W) points with increasing annealing temperature formed a similar closed “Parallelogram” shape. It is benefit for revealing the behavior of Cu thermal precipitation and their evolution in various Cu-bearing steels under thermal treatment. In addition, we also investigated the Cu content effect on the Cu precipitation in FeCu alloys, and the Cu precipitate phenomenon was enhanced in higher Cu content alloys.

Energy deposition and ion production from thermal oxygen ion precipitation during Cassini’s T57 flyby

Cassini’s Radio Science Investigation (RSS) and Langmuir Probe observed abnormally high electron densities in Titan’s ionosphere during Cassini’s T57 flyby. We have developed a three-dimensional model to investigate how the precipitation of thermal magnetospheric O+ may have contributed to enhanced ion production in Titan’s ionosphere. The three-dimensional model builds on previous work because it calculates both the flux of oxygen through Titan’s exobase and the energy deposition and ion production rates in Titan’s atmosphere. We find that energy deposition rates and ion production rates due to thermal O+ precipitation have a similar magnitude to the rates from magnetospheric electron precipitation and that the simulated ionization rates are sufficient to explain the abnormally high electron densities observed by RSS and Cassini’s Langmuir Probe. Globally, thermal O+ deposits less energy in Titan’s atmosphere than solar EUV, suggesting it has a smaller impact on the thermal structure of Titan’s neutral atmosphere. However, our results indicate that thermal O+ precipitation can have a significant impact on Titan’s ionosphere.

Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

Microstructural properties of a dissimilar friction stir welded thick aluminum aa6082-t6 and aa7075-t6 alloy

Friction stir welding is a severe plastic deformation process. This solid state welding procedure has recently received a general acceptance in the aerospace industry for joining difficult to weld aluminum alloy using the conventional method. A 10mm thick AA6082 and AA7075 in tempered form (T6) were friction stir welded in butt configuration as against the previous research on 4mm, 6mm and 8mm thicknesses respectively. The response of the stir zone (SZ) microstructure to processing parameters was evaluated using optical microscope (OM), Stereo microscope (SM) and scanning electron microscope (SEM) respectively. The magnitude forge force (kN) at the tool shoulder directly affect the flow of the extruded materials through the tool probe. The distribution of thermal energy, dissolution, precipitation and re-precipitation of solute influences the materials flow and properties evolution. Hence, equiaxed grain structures observed were due to the dynamic recrystallization mechanism at the weld nugget. Some microstructure imperfection were observed at the weld nugget when AA6082 aluminum plates were clamped on the retreating side to the backing plate. However, the material flow and mixing was not sufficient to establish good bonding and quality welds due to deviation in the positioning of the aluminum plates.

Water-Soluble Polymeric Probe for the Selective Sensing and Separation of Cu(II) Ions in Aqueous Media: pH-Tunable Detection Sensitivity and Efficient Separation by Thermal Precipitation

A thiosemicarbazone-based water-soluble polymeric probe was developed for the selective colorimetric detection of Cu(II) ions with pH-tunable sensitivity. The successful separation of Cu(II) ions from several alkali and transition metal cations by thermal precipitation was demonstrated. N,N-Dimethylacrylamide (DMA) and 3-vinylbenzaldehyde (VBA) were copolymerized by reversible addition–fragmentation chain transfer (RAFT) polymerization to produce p(DMA-co-VBA), herein P1. The aldehyde group of P1 was reacted with 4-phenylthiosemicarbazide to yield poly{DMA-co-[N-phenyl-2-(3-vinylbenzylidene)hydrazinecarbothioamide]}, [p(DMA-co-PVHC)], herein P2. Upon the addition of Cu(II) ions to an aqueous solution of P2, the color of the solution turned from colorless to yellow due to the formation of a coordination complex between the Cu(II) ions and phenylthiosemicarbazone units of P2, herein P2–Cu(II). The availability of the electron-rich imino nitrogen in the thiosemicarbazone units allowed P2 to show excellent se...

Kinetics of sub‐ion scale magnetic holes in the near‐Earth plasma sheet

AbstractIn collisionless space plasmas, the energy cascade from larger to smaller scales requires effective interactions between ions and electrons. These interactions are organized by sub‐ion scale plasma structures in which strong electric fields connect demagnetized ions to magnetized electrons. We consider one such structure, magnetic holes, observed by THEMIS spacecraft in the dipolarized hot plasma sheet. Magnetic holes are localized depressions of the magnetic field with strong currents at their boundaries. Taking advantage of slow plasma convection (∼10–20 km/s), we reconstruct the electron velocity distribution within magnetic holes and demonstrate that the current at their boundaries is predominantly carried by magnetized thermal electrons. The motion of these electrons is the combination of diamagnetic drift and E × B drift in a Hall electric field. Magnetic holes can effectively modulate the intensity of electron cyclotron harmonic waves, and thus the spatial distribution of thermal electron precipitation. They may also contain field‐aligned currents with magnitudes of ∼5 nA/m2 (1 order of magnitude smaller than the cross‐field current density). Therefore, sub‐ion scale magnetic holes can be important for ionosphere‐magnetosphere coupling.

Acid Rock Drainage Treatment Using Membrane Distillation: Impacts of Chemical-Free Pretreatment on Scale Formation, Pore Wetting, and Product Water Quality.

Acid rock drainage (ARD) is a metal-rich wastewater that forms upon oxidation of sulfidic minerals. Although ARD impacts >12,000 miles of rivers in the U.S. and has an estimated cleanup cost of $32-$72 billion, the low pH and high metal concentrations in ARD make rapid, high volume treatment without chemical addition difficult. This research focuses on a novel method of ARD treatment, membrane distillation (MD). In MD, heated ARD is separated from a cooled distillate by a hydrophobic, water-excluding membrane. Because water only passes through the membrane in the vapor phase, nonvolatile sulfate and heavy metals are retained in the concentrate stream. A preliminary in silico analysis using an electrolyte thermodynamic model indicated that MD of 10 different mine wastes yields product water containing no contaminants at concentrations >0.2 ppm. MD tests of synthetic ARD used a ∼34 °C temperature difference, operated at 80% recovery, and produced an initial flux of 38.4 ± 1.1 L·m-2·h-1. This flux decreased slightly after scaling by iron oxyhydroxide; however, membranes maintained >99% dissolved solids rejection. Both flux decline and membrane scale formation decreased after a chemical-free, thermal precipitation pretreatment. These results indicate that MD can purify contaminated, acidic wastewater using low-grade heat sources, such as geothermal energy, without chemical addition.

Thermodynamics of vacancies and clusters in high-entropy alloys

By means of thermodynamic analyses, we provide the intriguing evidence that the equilibrium vacancy concentrations and their clusters in high entropy alloys (HEAs) are substantially larger than those in pure metals and simple binary alloys. The increased defect concentrations strongly change the thermodynamic and kinetic properties of the HEAs. With these findings, we predict a strong recombination tendency of vacancies and interstitials after excitation from radiation bombardments, and the results are favorably compatible with very recent experiments on the superior radiation resistance of HEAs. The thermodynamics of vacancies and clusters in HEAs will be of great interest to the design of advanced materials involving many thermodynamic and kinetic properties such as thermal conductivity, diffusivity, precipitation, creep, and irradiation damage.

Microstructural Improvement of Hydroxyapatite-ZrO2 Composite Ceramics via Thermal Precipitation Techniques.

Hydroxyapatite-ZrO2 composite ceramic were synthesized using a thermal precipitation techniques. The chemical precursors were prepared from di-ammonium hydrogen orthophosphate, calcium oxide (CaO) derived from chicken eggshell, zirconium dioxide (ZrO2) and distilled water. The mixture were heated at the various temperatures from 100 to 700 °C in the furnace with an incremental temperature of 100 °C. The ZrO2 contents in the composite ceramic were varied from 0 to 15 percent weight of CaO. The prepared composites were then annealed at 300, 600 and 700 °C for 4 h in air. The crystal structure, function group and morphology of all samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and universal testing machine (UTM), respectively. The results indicated that the undoped-ZrO2 samples hydroxyapatite phase with a hexagonal structure. However, the hydroxyapatite was transformed to the tri-calcium phosphate after thermal treatment at 700 °C. For the doped-ZrO2 samples, the hydroxyapatite and ZrO2 phases were found. Moreover, the result showed that the compressive strength of hydroxyapatite-ZrO2 composite ceramic increased with increasing the ZrO2 content.

Evaluation of preparation methods for suspended nano-objects on substrates for dimensional measurements by atomic force microscopy.

Dimensional measurements on nano-objects by atomic force microscopy (AFM) require samples of safely fixed and well individualized particles with a suitable surface-specific particle number on flat and clean substrates. Several known and proven particle preparation methods, i.e., membrane filtration, drying, rinsing, dip coating as well as electrostatic and thermal precipitation, were performed by means of scanning electron microscopy to examine their suitability for preparing samples for dimensional AFM measurements. Different suspensions of nano-objects (with varying material, size and shape) stabilized in aqueous solutions were prepared therefore on different flat substrates. The drop-drying method was found to be the most suitable one for the analysed suspensions, because it does not require expensive dedicated equipment and led to a uniform local distribution of individualized nano-objects. Traceable AFM measurements based on Si and SiO2 coated substrates confirmed the suitability of this technique.

A Global Model for Circumgalactic and Cluster-core Precipitation

Abstract We provide an analytic framework for interpreting observations of multiphase circumgalactic gas that is heavily informed by recent numerical simulations of thermal instability and precipitation in cool-core galaxy clusters. We start by considering the local conditions required for the formation of multiphase gas via two different modes: (1) uplift of ambient gas by galactic outflows, and (2) condensation in a stratified stationary medium in which thermal balance is explicitly maintained. Analytic exploration of these two modes provides insights into the relationships between the local ratio of the cooling and freefall timescales (i.e., t cool / t ff ), the large-scale gradient of specific entropy, and the development of precipitation and multiphase media in circumgalactic gas. We then use these analytic findings to interpret recent simulations of circumgalactic gas in which global thermal balance is maintained. We show that long-lasting configurations of gas with 5 ≲ min ( t cool / t ff ) ≲ 20 and radial entropy profiles similar to observations of cool cores in galaxy clusters are a natural outcome of precipitation-regulated feedback. We conclude with some observational predictions that follow from these models. This work focuses primarily on precipitation and AGN feedback in galaxy-cluster cores, because that is where the observations of multiphase gas around galaxies are most complete. However, many of the physical principles that govern condensation in those environments apply to circumgalactic gas around galaxies of all masses.

Anti-precipitation effects of TiO2 and TiOSO4 on positive electrolyte of vanadium redox battery

In this study, the effects of TiO2 and TiOSO4 on the precipitation of the positive electrolyte of vanadium redox battery (VRB) systems were investigated. TiO2 and TiOSO4 were used as anti-precipitating agents for V(V) ions at 40 and 60 °C. The optimum amounts and electrochemical properties of additives were determined by electrochemical methods such as cyclic voltammetry and electrochemical impedance spectroscopy. The optimum amount of additives was identified as wt% 0.004 and 0.003 for TiO2 and TiOSO4, respectively. The structural features and composition of electrodes were investigated by scanning electron microscopic and energy-dispersive X-ray analysis. A plausible reaction mechanism was also proposed for redox reaction occurring on the positive electrode of a VRB. The concentration of V(V) ions in the additive including electrolyte were higher than that of blank solution at the end of the thermal precipitation tests. According to thermal and electrochemical studies, TiO2 and TiOSO4 can be useful additives for the positive electrolyte of a VRB.

Triggering and Delivery Algorithms for AGN Feedback

Abstract We compare several common subgrid implementations of active galactic nucleus (AGN) feedback, focusing on the effects of different triggering mechanisms and the differences between thermal and kinetic feedback. Our main result is that pure thermal feedback that is centrally injected behaves differently from feedback with even a small kinetic component. Specifically, pure thermal feedback results in excessive condensation and smothering of the AGN by cold gas because the feedback energy does not propagate to large enough radii. We do not see large differences between implementations of different triggering mechanisms, as long as the spatial resolution is sufficiently high, probably because all of the implementations tested here trigger strong AGN feedback under similar conditions. In order to assess the role of resolution, we vary the size of the “accretion zone” in which properties are measured to determine the AGN accretion rate and resulting feedback power. We find that a larger accretion zone results in steadier jets but can also allow too much cold gas condensation in simulations with a Bondi-like triggering algorithm. We also vary the opening angle of jet precession and find that a larger precession angle causes more of the jet energy to thermalize closer to the AGN, thereby producing results similar to pure thermal feedback. Our simulations confirm that AGNs can regulate the thermal state of cool-core galaxy clusters and maintain the core in a state that is marginally susceptible to thermal instability followed by precipitation.

Regional climatic changes and small river’s water quality in Republic of Moldova’s south (Danube River basin)

Abstract Climate variability in decades requires detailed research aspect basin in order to take account of climate change attested, both in making various decisions applicative and at proper adaptation to these changes. Previous research results obtained in this section indicates that territory most vulnerable to climate change is largely located within the Danube basin within the territory of the Republic of Moldova. Therefore, the purpose of the proposed research in this paper was to record some changes in the current period and which are forecasts on thermal regime and precipitation in the scale time 2016-2035.