Conditions Of Low Concentration Research Articles

Highly Efficient Dopant-Free Cyano-Substituted Spiro-Type Hole-Transporting Materials for Perovskite Solar Cells

The hole-transporting material (HTM) is an important component of perovskite solar cells (PSCs) because it plays a crucial role in achieving high performance. The most frequently used HTM is 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD). Spiro-OMeTAD requires dopants such as Li(TFSI) to realize high power conversion efficiencies (PCEs). However, these dopants cause severe instability issues in PSCs. The Spiro-OMeTAD layer also tends to undergo severe morphological deformation at high temperature, which produces large voids and further reduces the cell performance. These drawbacks must be overcome for the commercialization of PSCs. Therefore, it is strongly desirable to develop high-performance dopant-free HTMs to replace Spiro-OMeTAD. Here, we synthesize two cyano-substituted spirobifluorene-based HTMs, SF27 and SF48, for this purpose. These compounds are derived from Spiro-N, which is a Spiro-OMeTAD analogue obtained via the replacement of the p-methoxy substituents with strong electron-donating p-N,N-dimethylamino groups. The influence of cyano substituents on the optoelectronic properties, PCEs, and charge transport behavior in PSCs are investigated. These compounds have a highest occupied molecular orbital energy level that is well-matched to the valence band of perovskite layers. The hole mobility of SF48 (o-cyano-substituted) was determined to be higher than that of SF27 (m-cyano-substituted), although it is lower than those of Spiro-OMeTAD and the reference compound Spiro-N. Mesoporous PSCs were fabricated using these new HTMs without dopants under relatively low HTM concentration conditions, and the cell performance was compared to that of devices with Spiro-OMeTAD and Spiro-N. The PSC with non-doped SF48 exhibited a high PCE of 18.7%, which is comparable to that of the reference PSCs with doped Spiro-OMeTAD (18.6%). In addition, the thermal stability of SF48 at 85 °C in air was superior to that of Spiro-OMeTAD, both with and without dopants. Therefore, the SF48 spirobifluorene-based compound is determined to be quite effective as a high-performance dopant-free HTM for PSCs.

Influence of radial fuel staging on combustion instabilities and exhaust emissions from lean-premixed multi-element hydrogen/methane/air flames

The utilization of hydrogen-blended hydrocarbon fuels, or even completely carbon-free fuels like pure hydrogen and ammonia, will be indispensable in the effort to reduce anthropogenic carbon dioxide emissions from heavy-duty land-based gas turbines. In order to make this energy transition, however, low emissions, low dynamics fuel-flexible gas turbine combustion systems will be required. To address some of the key technological obstacles in the development of such systems, we explore a prototype multi-element injector assembly devised to prevent flashback in extremely fast premixed hydrogen flames, paying particular attention to the impact of radial dual-fuel staging on the generation of self-induced instabilities and the formation of nitrogen oxides and carbon monoxide. In conjunction with phase-averaged OH*/CH* chemiluminescence and OH PLIF flame imaging, we carry out extensive measurements over the full range of 0 to 100% H2/CH4 fuel staging conditions, including even/uneven blends of H2/CH4 fuels between inner and outer nozzle groups, partial/complete fuel split cases, and pure H2 or CH4 fuel for all constituent flames, under a constant thermal power condition of 78 kW. Our measurements demonstrate that whereas carbon monoxide concentrations are largely unaffected by the radial fuel staging conditions except under high and pure hydrogen percentage conditions, there exists a strong correlation between total nitrogen oxides emissions and overall adiabatic flame temperature. Integrated analyses of isocontour instability maps reveal that near XH2,g = 0.50 a discontinuous mode transition takes place, where the intermediate-amplitude lower frequency oscillations associated with relatively low hydrogen concentration conditions give way to stronger, higher frequency instabilities under high hydrogen content conditions. While even-blend (non-staging) conditions are characterized by coherent oscillations of the constituent flames, the responses of clustered flames to radial fuel staging conditions are eccentric and complex, manifested as large-scale asynchronous modulations between inner- and outer-stage heterogeneous reaction zones. This observation suggests that in a multi-element injector environment spatiotemporal incoherence driven by inhomogeneous heat release can be used to neutralize self-excited pressure oscillations, by disrupting pressure-heat release coupling processes.

Phase conversion and removal of impurities during oxygen-rich alkali conversion of high titanium slag

In order to achieve high-efficiency alkali conversion and impurity removal of high titanium slag under the condition of low alkali concentration, a new way of oxygen-rich alkali conversion in KOH solution was proposed. The conversion law of element occurrence state and the influence of the conversion conditions on the titanium conversion rate and removal rate of silicon and aluminum were studied. The results showed that the KOH solution converted the titanium oxide in high titanium slag into whisker-like potassium titanate. Silicon and aluminum elements were dissolved into the solution. Under the following conditions, KOH concentration of 6 mol/L, conversion temperature of 260 °C, initial oxygen partial pressure of 2 MPa, liquid−solid ratio of 35 mL/g, conversion time of 4 h, and high titanium slag particle size of 48−74 μm, the conversion rate of titanium was 97.0%, and the removal rates of silicon and aluminum were 90.2% and 76.2%, respectively. Oxygen-rich alkali conversion product was converted to rutile with a TiO2 grade of 99.1% by acid hydrolysis conversion.

Chemically Stable Guanidinium Covalent Organic Framework for the Efficient Capture of Low-Concentration Iodine at High Temperatures

The capture of radioactive I2 vapor from nuclear waste under industrial operating conditions remains a challenging task, as the practical industrial conditions of high temperature (≥150 °C) and low I2 concentration (∼150 ppmv) are unfavorable for I2 adsorption. We report a novel guanidinium-based covalent organic framework (COF), termed TGDM, which can efficiently capture I2 under industrial operating conditions. At 150 °C and 150 ppmv I2, TGDM exhibits an I2 uptake of ∼30 wt %, which is significantly higher than that of the industrial silver-based adsorbents such as Ag@MOR (17 wt %) currently used in the nuclear fuel reprocessing industry. Characterization and theoretical calculations indicate that among the multiple types of adsorption sites in TGDM, only ionic sites can bond to I2 through strong Coulomb interactions under harsh conditions. The abundant ionic groups of TGDM account for its superior I2 capture performance compared to various benchmark adsorbents. In addition, TGDM exhibits exceptionally high chemical and thermal stabilities that fully meet the requirements of practical radioactive I2 capture (high-temperature, humid, and acidic environment) and differentiate it from other ionic COFs. Furthermore, TGDM has excellent recyclability and low cost, which are unavailable for the current industrial silver-based adsorbents. These advantages make TGDM a promising candidate for capturing I2 vapor during nuclear fuel reprocessing. This strategy of incorporating chemically stable ionic guanidine moieties in COF would stimulate the development of new adsorbents for I2 capture and related applications.

Effect of solid wettability on three-phase hydrodynamic cavitation

In many modern industrial applications such as mineral flotation and water treatment, microbubbles have been used as an efficient aid for increasing the collision and attachment efficiencies and enhancing the recovery of valuable fine minerals. One technique to produce such micro-bubbles is to use the hydrodynamic cavitation process when gas cavities in water nucleate under low hydrodynamic pressure. To better understand the cavitation behavior in the presence of solids with different surface properties, we present an experimental study of a multi-phase system. The characteristics of hydrodynamic cavitation with a Venturi tube were experimentally investigated using acoustic detection. The effect of both particle and tube wall surface hydrophobicity and surface structure on the inception of hydrodynamic cavitation were considered. Results demonstrated that particles with lower wettability promoted hydrodynamic cavitation by efficiently trapping gas pockets that facilitate bubble nucleation. In addition, in the condition of low particle concentration (5 g/L) and fine particle size range (D50 < 20 µm), parameters including size and roughness did not play a critical role in affecting cavitation inception. Finally, tests using Venturi tubes of different surface properties showed that the wall surface behaves similarly as particles. Hydrodynamic cavitation was promoted by a more hydrophobic Venturi tube which screened the effect of particle surface properties.

Aminated substrate based thin film composite nanofiltration membrane with high separation performance by chemically inhibiting the intrusion of polyamide

In this study, aminated PES substrates were prepared and applied for the investigation on the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricarbonyl trichloride (TMC) thereon, with relatively low (PIP: 0.1 wt%, TMC: 0.01 wt%) and high (PIP: 0.5 wt%, TMC: 0.05 wt%) monomer concentration. In low concentration condition, thin, dense, and defect-free selective layers were synthesized on the aminated substrates. In high concentration condition, thin film composite (TFC) membranes with thin selective layers and without the intrusion of polyamide into the substrates were formed. The reactions between the aminated substrate and selective layer were confirmed by XPS analysis on the back surface of the selective layer. The aminated substrates based TFC membrane (TFC-48-H) showed high separation performance, including high water permeability as 20.6 ± 0.1 L/m2 h bar and high Na2SO4 to NaCl selectivity as 86.7, indicating the application potential in divalent to monovalent salts separation process. A conceptual model was proposed to highlight the role of the aminated substrates in the interfacial polymerization process as (1) PIP loaders, (2) PIP diffusion hinders, and (3) polyamide intrusion chemically inhibitors in high monomer concentration condition.

Multifunctional sodium Alginate@ urushiol fiber with targeted Antibacterial, acid corrosion resistance and flame retardant properties for personal protection based on wet spinning

The protective clothing may face acid, high temperature, and bacterial attack in the process of use, affecting its protection efficiency, and multifunctional protective clothing that can meet a variety of needs appear more potential applications. However, multifunctional personal protection clothing has remained an unmet challenge. Here we report a new type of multifunctional clothing via a simple, environmentally friendly wet spinning method to load the urushiol with acid corrosion and antibacterial functions on sodium alginate fiber. This structure uniformly disperses a certain content of urushiol in sodium alginate solution, allowing alginate fibers to have flame retardant properties while having high acid resistance and excellent targeted antibacterial properties. Compared to alginate fibers, the fabricated fibers were treated with different concentrations of sulfuric acid, although the strength was reduced to a certain extent, the fibers retained their original shape and were not dissolved. The thermal analysis showed the fiber also has good flame retardant better than viscose fiber. In addition, the fabricated fiber has targeted antibacterial properties, with an efficiency of 99.99% against Staphylococcus aureus (S. aureus) and bacteriostatic effect on Escherichia coli (E. coli), and good biocompatibility under low concentration conditions. Our work may provide new insights for the development of “green” multifunctional protective clothing. It also provides a research possibility for absorbable surgical sutures.

Synergistic effect of F and triggered oxygen vacancies over F-TiO2 on enhancing NO ozonation

Oxidation-absorption technology is a key step for NOx removal from low-temperature gas. Under the condition of low O3 concentration (O3/NO molar ratio = 0.6), F-TiO2 (F-TiO2), which is cheap and environmentally friendly, has been prepared as ozonation catalysts for NO oxidation. Catalytic activity tests performed at 120°C showed that the NO oxidation efficiency of F-TiO2 samples was higher than that of TiO2 (about 43.7%), and the NO oxidation efficiency of F-TiO2-0.15 was the highest, which was 65.3%. Combined with physicochemical characteristics of catalysts and the analysis of active species, it was found that there was a synergistic effect between F sites and oxygen vacancies on F-TiO2, which could accelerate the transformation of monomolecular O3 into multi-molecule singlet oxygen (1O2), thus promoting the selective oxidation of NO to NO2. The oxidation reaction of NO on F-TiO2-0.15 follows the Eley-Rideal mechanism, that is, gaseous NO reacts with adsorbed O3 and finally form NO2.

Airborne Ultrafine Particle and Acute Physiological Effects during Maximal Aerobic Power Test

BACKGROUND: The practice of physical exercise in polluted areas could lead to adverse health effects that may contribute to the incidence and/or worsening of respiratory and cardiovascular diseases and some types of cancer. METHODS: Male recreational cyclists performed tests in a manner randomized crossover in two environmental conditions: low (environmental noise exposure) and high ultrafine particle concentration. For each trial, oxygen consumption ((VO) ̇_2), carbon dioxide production (VĊO2), respiratory frequency (Rf), tidal volume (Vt), pulmonary ventilation ((VE) ̇), and mechanical workload (WL) was measured. Gross efficiency (GE) was determined using the ratio between mechanical power output and metabolic power input. Repeated-measures ANOVA was applied to evaluate differences (P < 0.05) between physiological and mechanical parameters and compare oxygen consumption trends in the two scenarios. RESULTS: HR, Rf, and VE values do not show any significant difference. On the contrary, (VO) ̇2peak increased (P < 0.05) under high exposure (41.6 ± 4.31 mL kg-1 min-1), during high-intensity exercise, compared to a low exposure (38.4 ± 4.05 mL kg-1 min-1). VO2 and GE show differences (p < 0.05) between low and high ultrafine particle concentration conditions during exercise above 80% WLpeak. CONCLUSIONS: Present data suggest that high airborne UFPs levels impair recreational cyclists' gross efficiency.

Study of Tribological Properties of Fullerenol and Nanodiamonds as Additives in Water-Based Lubricants for Amorphous Carbon (a-C) Coatings.

The tribological performances of fullerenol and nanodiamonds (NDs) as additives in water-based lubricants for amorphous carbon (a-C) coatings are investigated to avoid disadvantage factors, such as chemical reactions and deformation of particles. The effects of size and additive amount on tribological properties of nanoparticles are studied by rigid nanoparticles within the dot size range. The results show that owing to its small particle size (1–2 nm), fullerenol cannot prevent direct contact of the friction pair at low concentration conditions. Only when the quantity of fullerenol increased to support the asperity contact loads in sufficient concentration did nano-bearings perform well in anti-friction and anti-wear effects. Unlike fullerenol, nanodiamond particles with a diameter of about 5–10 nm show friction-reducing effect based on the nano-bearing effects at ultra-low concentration (0.01 wt.%), whereas particles at higher concentration block the rolling movement, hence increasing the coefficient of friction (COF) and wear. As a result of the effect of difference in size, fullerenol provides a better overall lubrication, but it is hard to reach a friction coefficient as low as NDs even under the optimal conditions.

In-situ utilization of membrane foulants (FeOx+MnOx) for the efficient membrane cleaning

Preoxidation-ultrafiltration process is an effective method for Fe2+ and Mn2+removal, in which Fe2+ (Mn2+) are firstly oxidized to FeOx (MnOx), then collected by the ultrafiltration membrane. However, the simultaneous presence of Fe2+, Mn2+, and organics in feed can cause severe membrane fouling, which inhibits the overall performance of this method prominently. In this study, a novel FeOx+MnOx+H2O2 membrane cleaning method is proposed based on the idea of turning in-situ generated membrane foulants, i.e., FeOx+MnOx, into the catalysts for membrane cleaning. The results demonstrate that the FeOx+MnOx+H2O2 system can achieve more than 95% membrane flux recovery and remove almost all irreversible membrane foulants within only 5 min and with only 0.5%wt% H2O2 solution. The outstanding performance of the system is mainly attributed to the catalytic decomposition of H2O2 to generate both highly reactive radicals, such as hydroxyl radicals (·OH), and abundant oxygen. In addition, when the membrane is loaded by only MnOx, polyaluminium chloride (PAC) as the coagulator demonstrates prominent influence on the performance of membrane cleaning. However, PAC makes almost no contribution to membrane cleaning when the membrane is loaded by FeOx. This is because coagulation induced by PAC exerts more prominent impact on the particle size distribution of MnOx than that of FeOx. In conclusion, the catalytic decomposition of H2O2 by in-situ generated FeOx+MnOx is a promising advanced oxidation process to achieve outstanding membrane cleaning performance under the condition of low H2O2 concentration and no extra dosage of catalysts. The novel membrane cleaning system exhibits high potential for the practical membrane treatment processes to treat water with high contents of Fe and Mn.

Role of Hypoxia on Growth and Differentiation of Human Adipose Derived Stem Cells Grown on Silk Fibroin Scaffold Induced by Platelet Rich Plasma

Previous research has proven that 10% platelet-rich plasma (PRP) can enhance growth and differentiation of human adipose derived stem cells (hADSC) grown on silk fibroin scaffold into chondrocytes. A low oxygen concentration (hypoxia) condition is an important factor that potentially affects the ability of hADSC to grow and differentiate. The objective of this research was to analyze the difference in growth and differentiation capacity of hADSC grown on salt leached silk fibroin scaffold supplemented by 10% PRP under normoxic and hypoxic conditions. The growth capacity of the hADSC was determined by MTT assay and differentiation was tested using glycosaminoglycan (GAG) content analysis, while chondrocyte markers were visualized with the immunocytochemistry (ICC) method. This research observed hADSC proliferation under normoxic and hypoxic conditions for 21 days. Visualization of type 2 collagen showed that it was more abundant under hypoxia compared to normoxia. HIF-1α was only detected in the hADSC cultured in hypoxic conditions. In conclusion, culture under hypoxic conditions increases the capacity of hADSC to grow and differentiate into chondrocytes. This is the first study that has shown that hypoxia is able to enhance the proliferation and differentiation of hADSC grown on 3D salt leached silk fibroin scaffold supplemented by 10% PRP.

Simultaneous degradation of amoxicillin and norfloxacin by TiO2@nZVI composites coupling with persulfate: Synergistic effect, products and mechanism

• Persulfate (PS) significantly enhanced AMX removal by TiO 2 @nZVI/UV process. • The decomposition rate of PS in TiO 2 @nZVI/PS/UV process was the highest. • Both HO• and SO 4 •− were the dominant radicals in TiO 2 @nZVI/PS/UV process. • AMX was effectively degraded through hydroxylation and deamination reactions. • A mechanism for the simultaneous removals of AMX and NOF was proposed. In recent years, a serious threat of antibiotic residues in aquatic environments to human health and ecological security has become increasingly widespread attention. In this study, this is the first report on an alternative strategy on enhanced degradation of amoxicillin (AMX) and norfloxacin (NOF) by TiO 2 @nZVI/persulfate (PS) process under UV irradiation. Results revealed that a signficantly synergistic effect on AMX degradation had been achieved in TiO 2 @nZVI/PS/UV process due to the photocatalysis and Fenton-like reactions. NO 3 – , HCO 3 – , PO 4 3- and humic acid exhibited inhibitory effects on AMX degradation, whereas Cl - was negligible on that. The degradation of AMX decreased as the addition of Cr(VI) concentrations increased, whereas the correspond values were enhanced when a low Cu(II) concentration was introduced. TiO 2 @nZVI/PS/UV process was the most efficient for activating PS decomposition. HO•, SO 4 •− and 1 O 2 were all generated in TiO 2 @nZVI/PS/UV process, but HO• and SO 4 •− were the dominant radical species for AMX degradation. The AMX intermediates products identified by LC-MS system confirmed AMX was effectively degraded through hydroxylation and deamination reactions. A better performance on the simultaneous removals of AMX and NOF by TiO 2 @nZVI/PS/UV process could be achieved at lower concentration conditions, and the simultaneous reaction mechanism was thereby proposed base on expriment results.

Atmospheric Autoxidation of Organophosphate Esters.

Organophosphate esters (OPEs), widely used as flame retardants and plasticizers, have frequently been identified in the atmosphere. However, their atmospheric fate and toxicity associated with atmospheric transformations are unclear. Here, we performed quantum chemical calculations and computational toxicology to investigate the reaction mechanism of peroxy radicals of OPEs (OPEs-RO2•), key intermediates in determining the atmospheric chemistry of OPEs, and the toxicity of the reaction products. TMP-RO2• (R1) and TCPP-RO2• (R2) derived from trimethyl phosphate and tris(2-chloroisopropyl) phosphate, respectively, are selected as model systems. The results indicate that R1 and R2 can follow an H-shift-driven autoxidation mechanism under low NO concentration ([NO]) conditions, clarifying that RO2• from esters can follow an autoxidation mechanism. The unexpected autoxidation mechanism can be attributed to the distinct role of the ─(O)3P(═O) phosphate-ester group in facilitating the H-shift of OPEs-RO2• from commonly encountered ─OC(═O)─ and ─ONO2 ester groups in the atmosphere. Under high [NO] conditions, NO can mediate the autoxidation mechanism to form organonitrates and alkoxy radical-related products. The products from the autoxidation mechanism have low volatility and aquatic toxicity compared to their corresponding parent compounds. The proposed autoxidation mechanism advances our current understanding of the atmospheric RO2• chemistry and the environmental risk of OPEs.

Non-isothermal electrochemically mediated amine regeneration for CO2 capture: Performance evaluation and optimization

Carbon dioxide emission is the main environmental impact of energy systems fed by carbon-intensive fuels. Developing CO2 capture systems can be an effective solution towards mitigating such detrimental impacts causing global warming. This study proposes a non-isothermal electrochemical CO2 capture and storage system operating based on ethylenediamine and copper ions. Also, the system is parametrically analyzed and optimized from an energy perspective. To conduct the parametric analysis, a mathematical model is developed based on the activities and equilibrium constants of the involved reactions. The influence of design variables on the system’s performance is investigated. The optimization study aims at minimizing the total electrical work consumed by the system via genetic algorithm. In both parametric and optimization studies, the impact of CO2 concentration in exhaust gases, varying from 4 % to 15 %, on the system’s performance is evaluated to measure the system’s ability to work under low CO2 concentration conditions. The results reveal that for the CO2 concentrations of 15 %, 10 %, and 4 %, the system’s minimum attainable total electrical work is 32.53, 32.9, and 34.18 kJ.mol−1CO2, respectively. These optimized works, however, are achieved at the cost of extra heating loads demanded by the system within the range of 152−156 kJ.mol−1CO2 that must be supplied at temperatures below 90 ℃.

Enhancement effect on adsorbent utilization rate based on Twin–Bed tandem adsorption

The actual adsorption loading of the adsorbent is usually less than the equilibrium capacity in the abatement of volatile organic compounds (VOCs) with industrial fixed-bed adsorption. In this study, the twin-bed tandem adsorption (TBTA) cycle was proposed. Adequate time was ensured for the upstream bed to adsorb and reach saturation via the take-up and protection of the downstream bed, thus utilizing the full capacity of the adsorbent. A mathematical model and an extended bed depth service time (BDST) model were developed to describe the characteristics of the TBTA. Then, fixed-bed adsorption experiments were performed to validate the accuracy of the aforementioned two models. Results of the parametric analysis showed that the best enhancement effect could be achieved at low packing height, low feed concentration and high superficial velocity conditions. By defining the unit energy consumption (UEC) as the fan power consumption for the recovery of contaminants per unit amount, suggestions for adsorption parameters were provided. Tracking the UEC at each concentration point on the breakthrough curve, the relative concentration of 70% to 80% was found to be the cost-efficient switch point for TBTA. This study demonstrated the operational dynamics of the TBTA and parametric effects on adsorption performance. Our findings can help to improve the adsorbent utilization rate in fixed-bed systems.

Characterization of clay-stabilized, oil-in-water Pickering emulsion for potential conformance control in high-salinity, high-temperature reservoirs

In this study, a Na-montmorillonite clay-stabilized, oil-in-water (O/W) Pickering emulsion system was prepared and tested under high-salinity and high-temperature conditions. The emulsifying ability of the clay particles, emulsion stability against creaming and coalescence, and emulsion rheological behavior at different NaCl concentrations and temperatures were investigated. The results showed that decane could be effectively emulsified by clay particles into small emulsion droplets at salinities up to 25 wt% NaCl. The emulsion had a relatively narrow drop size distribution. However, the emulsion stability against creaming decreased with increases in NaCl concentration. At low NaCl concentrations, clay particles connected with each other by edge-edge and edge-face interactions, forming a three-dimensional network that stabilized the emulsion against creaming. A higher concentration of NaCl caused some clay particles to connect through face-face interactions, forming clay clusters. At high NaCl concentrations, the temperature had only a slight effect on the emulsion stability against creaming. However, emulsion stability against coalescence decreased with increasing temperature due to increased droplet collision caused by Brownian motion. A higher concentration of NaCl moderated this temperature effect of coalescence. The viscosity of emulsion decreased with increased NaCl concentration. Temperature increases caused emulsion viscosity to decrease at low NaCl concentration conditions. When the NaCl concentration was higher than 10 wt%, the temperature had little effect on the viscosity. In summary, this study identifies an O/W Pickering system with the potential for conformance control in high-salinity and high-temperature reservoirs.

Mathematical Modelling of Turbulent Combustion of Two-Phase Mixtures of Gas and Solid Particles with a Eulerian–Eulerian Approach: The Case of Hydrogen Combustion in the Presence of Graphite Particles

The numerical modelling of turbulent combustion of H2–air mixtures with solid graphite particles is a challenging and key issue in many industrial problems including nuclear safety. This study presents a Eulerian–Eulerian model based on the resolution of the Navier–Stokes equations via large eddy simulation (LES) coupled with a system of ordinary differential equations (ODEs) of the detailed chemical kinetics to simulate the combustion of mixtures of gases and particles. The model was applied to predict the transient evolution of turbulent combustion sequences of mixtures of hydrogen, air and graphite particles under low concentration conditions. When applied to simulate lab-scale combustion experiments, the results showed a good agreement between experimental and numerical data using a detailed chemical kinetic model. Moreover, the model was able to predict some key experimental tendencies and revealed that the presence of a low concentration of graphite particles (~96 g/m3) in the scenario influenced the hydrogen combustion dynamics for mixtures of 20% (in volume) of hydrogen in air. Under these conditions, pressure levels reached at the walls of the sphere were increased and the combustion time was shortened. The results also showed the viability of using this kind of a model for obtaining global combustion parameters such as wall pressure evolution with time.

THE EFFECTIVE VISCOSITY OF A SUSPENSION OF POROUS PARTICLES BASED ON THE DARCY-STOKES COUPLING MODEL

Particle suspensions exist widely in nature and engineering applications, and their viscous characteristics have an important influence on their flow behavior. Based on the Darcy-Stokes coupling model, the analytical formulas of effective viscosity of dilute suspensions containing porous particles are derived in this paper. Firstly, an auxiliary problem is solved, that is, the disturbance caused by porous media spheres in the flow field with linear distribution under the condition of low Reynolds number. The fluid flows in the free-flow domain and porous medium are governed by the Stokes equation and Darcy’ law, respectively. The mass conservation law, the balance of normal forces, and the Beavers-Joseph(-Saffman) interface condition are used at the fluid–porous interface. An analytical solution for the present coupled free-flow and porous-medium system is derived by using the undetermined coefficient method. Then the additional heat dissipation rate caused by the porous media particle is calculated. Intrinsic viscosity of the porous media suspension under the condition of low concentration is determined as a function of the Darcy number and the Beavers-Joseph coefficient, which is based on the additional heat dissipation rate under the condition of low concentration. It is found that the intrinsic viscosity increases with increasing the Beavers–Joseph coefficient, and the larger the Beavers–Joseph coefficient is, the slower the increase of the intrinsic viscosity. When Darcy number is in the range of \begin{document}${10^{ - 6}}$\end{document} to \begin{document}${10^{ - 4}}$\end{document} , the intrinsic viscosity is close to 2.5, which was consistent with the classical Einstein viscosity formula. When Darcy number is in the range of \begin{document}${10^{ - 4}}$\end{document} to \begin{document}${10^{ - 1}}$\end{document} , the intrinsic viscosity decreases rapidly, so the effective viscosity coefficient of porous media suspension is closer to the viscosity of the based fluid. At last, the present effective viscosity formula is compared with that obtained by the Darcy-Brinkman equation coupling with the shear stress jump condition. It can be found that the effective viscosities obtained two different models agree well with each other in the low Darcy number regime when the sum of the Beavers-Joseph coefficient and the shear stress jump coefficient is unity.

Influence of Free Fatty Acid Concentrations and Weight Loss on Adipose Tissue Direct Free Fatty Acid Storage Rates.

The factors that determine the recycling of free fatty acids (FFA) back into different adipose tissue depots via the direct storage pathway are not completely understood. To assess the interactions between adipocyte factors and plasma FFA concentrations that determine regional FFA storage rates. We measured direct adipose tissue FFA storage rates before and after weight loss under high FFA (intravenous somatostatin and epinephrine) and low (intravenous insulin and glucose) FFA concentrations. Mayo Clinic Clinical Research Unit. Sixteen premenopausal women, body mass index 30 to 37 kg/m2. Comprehensive lifestyle weight loss program. Direct FFA storage rates in upper and lower body subcutaneous fat. Over the entire range of FFA and under isolated conditions of elevated FFA concentrations, the storage rates of FFA into upper and lower body subcutaneous fat per unit lipid were associated with concentrations, not adipocyte fatty acid storage factors. Under low FFA conditions, direct FFA storage rates were related to adipocyte CD36 content, not tissue level content of fatty acid storage factors. Weight loss did not change these relationships. The regulation of direct FFA storage under low FFA concentration conditions appears to be at the level of the cell/adipocyte content of CD36, whereas under high FFA concentration conditions, direct FFA storage at the tissue level is predicted by plasma FFA concentrations, independent of adipocyte size or fatty acid storage factors. These observations offer novel insights into how adipose tissue regulates direct FFA storage in humans.