O2 Mass Research Articles

A NUMERICAL INVESTIGATION OF TURBULENT PREMIXED METHANE-AIR COMBUSTION IN A CYLINDRICAL CHAMBER

Turbulent premixed methane-air combustion in an axisymmetric cylindrical chamber is numerically simulated by a second-order finite volume method. Combustion chemistry is modeled by a reduced mechanism consists of 16 species and 31 elementary reactions, which includes some C1 and C2-chain species. Reaction rates are considered as minimum rates between Arrhenius rates and eddy break-up rates. Turbulent modeling is done via standard k-ϵ model with modified coefficients in flame cases and empirical inlet boundary conditions. All the numerical results were compared with experimental data for 3 turbulent premixed methane-air flames. Since combustion is occurred in distributed reaction zone, the turbulent intensities play an important role in prediction of the flame characteristics such as temperature and species mass fractions, specially when the flame occurs near the broken reaction zone. The results show the important role of C2-chain species in prediction of turbulent premixed flames behavior, especially in CO and O2 mass fractions and the temperature field.

The interaction of CO2 concentration and spatial location on O2 flux and mass transport in the freshwater macrophytes Vallisneria spiralis and V. americana

The biology of aquatic organisms determines the maximum rates of physiological processes, but the mass transport of nutrients determines the nominal rates at which these processes occur. Maximum O(2) flux (P(max)) at 17.1 mmol m(-3) CO(2) was higher for the leaves of the freshwater macrophyte Vallisneria spiralis [P(max)=0.013+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1) (mean +/- s.e.m.)] than for the closely related species, Vallisneria americana [P(max)=0.008+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1)]. The O(2) flux saturated at freestream velocities >4.5+/-1.2 cm s(-1) and was spatially invariant for both species. However, a tenfold decrease in CO concentration to 1.71 mmol m(-3) changed the nature of the relationship between O(2) flux and spatial location along the leaf surface, and reduced the O(2) flux of V. spiralis to values similar to V. americana. The O(2) flux [P(max)=0.007+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1)] saturated at the upstream location (i.e. 1 cm from the leading edge of the leaf) but was found to increase linearly with freestream velocity [slope=0.057+/-0.011 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1) (m s(-1))(-1)] at the downstream location (i.e. 7 cm from the leading edge) at freestream velocities >1.8+/-0.9 cm s(-1). Conversely, mass transfer rates did not vary with CO(2) concentration, and were characteristic of a laminar concentration boundary layer at the upstream location and a turbulent concentration boundary layer at the downstream location. Rates of mass transfer measured directly from O(2) profiles were not predicted by theoretical values based on hydrodynamic measurements. Moreover, the concentration boundary layer thickness (delta(CBL)) values measured directly from O(2) profiles were 48+/-2% and 21+/-1% of the predicted theoretical delta(CBL) values at the upstream and downstream locations, respectively. It is evident that physiological processes involving mass transport are coupled and vary in space. Mass transport investigations of biological systems based solely on hydrodynamic measurements need to be interpreted with caution.

Bioleaching of Heavy Metal Polluted Sediment: Influence of Temperature and Oxygen (Part 1)

AbstractA remediation process for heavy metal polluted sediment has previously been developed in which the heavy metals are removed from the sediment by solid‐bed bioleaching using elemental sulfur (S0): the added S0 is oxidized by the indigenous microbes to sulfuric acid that dissolves the heavy metals which are finally extracted by percolating water. In this process, the temperature is a factor crucially affecting the rate of S0 oxidation and metal solubilization. Here, the effect of temperature on the kinetics of S0 oxidation has been studied: oxidized Weiße Elster River sediment (dredged near Leipzig, Germany) was mixed with 2 % S0, suspended in water and then leached at various temperatures. The higher the temperature was, the faster the S0 oxidized, and the more rapid the pH decreased. But temperatures above 35 °C slowed down S0 oxidation, and temperatures above 45 °C let the process – after a short period of acidification to pH 4.5 – stagnate. The latter may be explained by the presence of both neutrophilic to less acidophilic thermotolerant bacteria and acidophilic thermosensitive bacteria. Within 42 days, nearly complete S0 oxidation and maximum heavy metal solubilization only occurred at 30 to 45 °C. The measured pH(t) courses were used to model the rate of S0 oxidation depending on the temperature using an extended Arrhenius equation. Since molecular oxygen is another factor highly influencing the activity of S0‐oxidizing bacteria, the effect of dissolved O2 (controlled by the O2 content in the gas supplied) on S0 oxidation was studied in suspension: the indigenous S0‐oxidizing bacteria reacted quite tolerant to low O2 concentrations; the rate of S0 oxidation – measured as the specific O2 consumption – was not affected until the O2 content of the suspension was below 0.05 mg/L, i.e., the S0‐oxidizing bacteria showed a high affinity to O2 with a half‐saturation constant of about 0.01 mg/L. Stoichiometric coefficients describing the relationship between the mass of S0, O2 and CO2 consumed are scarcely available. The growth of S0‐oxidizing, obligate aerobic, autotrophic bacteria was, therefore, stoichiometrically balanced (by using a yield coefficient of YX/S = 0.146 g cells/g S0, calculated with data from the literature): 24.14 S0 + 29.21 O2 + 27.14 H2O + 5 CO2 + NO3–→ C5H7O2N + 24.14 SO42– + 47.28 H+, which resulted in Y = 1.21 g O2/g S0 and Y = 0.28 g CO2/g S0.

Wind-Driven Surficial Oxygen Transfer and Dinitrogen Gas Emission from Treatment Lagoons

Surficial oxygen transfer plays an important role, when analyzing the complex biochemical and physical processes responsible for ammonia and dinitrogen gas emission in animal waste treatment lagoons. This paper analyzes if currently known nitrogen biochemical pathways can explain the enigmatic dinitrogen gas emissions recently observed from the treatment lagoons, based on the amount of wind-driven oxygen that can be transferred through the air-water interface. The stoichiometric amounts of the maximum dinitrogen gas production potential per unit mass of O2 transferred were calculated according to three most likely biochemical pathways for ammonia removal in the treatment lagoons—classical nitrification-denitrification, partial nitrification-denitrification, and partial nitrification-Anammox. Partial nitrification-Anammox pathway would produce the largest N2 emission, followed by partial nitrification-denitrification pathway, then by classical nitrification-denitrification pathway. In order to estimate stoichiometric amount (i.e., maximum) of N2 emission from these pathways, we assumed that heterotrophic respiration was substantially inhibited due to high levels of free ammonia prevalent in treatment lagoons. Most observed N2 emission data were below the maximum N2 emission potentials by the classical nitrification-denitrification pathway. However, one value of observed N2 emission was much higher than that could be produced by even the partial nitrification-Anammox pathway. This finding suggests yet unknown biological processes and/or non-biological nitrogen processes such as chemodenitrification may also be important in these treatment lagoons.

On-line oxygen uptake rate and culture viability measurement of animal cell culture using microplates with integrated oxygen sensors.

O2 uptake rates of animal cells (Chinese hamster ovary-CHO) were measured in 96-well microtiter plates by integrating with fluorescent sensors thereby measuring fluorescence intensity ratios of an O2-sensitive and an insensitive fluorophor. O2 consumption rate was estimated from measured dissolved O2 and from O2 mass transfer coefficient determined in advance. Specific uptake decreased with time from 3.2 x 10(-13) mol O2 cell(-1) h(-1) at 15 h cultivation to 1.8 x 10(-13) mol O2 cell(-1) h(-1) at 48 h. Specific O2 uptake was also determined by sampling from a spinner-flask culture giving identical values. A cell viability assay for cultures based on O2 measurements is described in which cells are incubated outside the fluorescence reader and then the dissolved O2 is measured only once at a fixed time after the start of incubation. This protocol can be directly applied for high-throughput measurements.

Oxidation of Carbon Particles in Supercritical Water: Rate and Mechanism

Oxidation of a carbon particle in supercritical water was studied in a flow-type reaction cell by directly observing the change in the size and shape of the particle through a sapphire window attached to the cell. Three types of carbon were investigated: activated carbon, synthetic graphite, and highly oriented pyrolytic graphite (HOPG). The reaction was observed at a pressure of 23−30 MPa and a temperature of 673−873 K. The spherical particles (3−4 mm in diameter) of both the activated carbon and the synthetic graphite became smaller while maintaining their shape, indicating that the reaction occurred nearly at the surface of the sphere. The reaction was first order with respect to O2 concentration. The rate of the decrease in the radius was in the order of μm s-1 for the activated carbon, and the rate was about an order of magnitude slower for the synthetic graphite. The rate of O2 mass transfer was estimated by computational fluid dynamics (CFD) calculations, showing good agreement with the reaction r...

PERFORATION-MEDIATED MODIFIED ATMOSPHERE PACKAGING: INFLUENCE OF PACKAGE GEOMETRY AND PERFORATION LOCATION ON OXYGEN AND CARBON DIOXIDE TRANSFER

ISHS VIII International Controlled Atmosphere Research Conference PERFORATION-MEDIATED MODIFIED ATMOSPHERE PACKAGING: INFLUENCE OF PACKAGE GEOMETRY AND PERFORATION LOCATION ON OXYGEN AND CARBON DIOXIDE TRANSFER

Shadowgraph Observation of Supercritical Water Oxidation Progress of a Carbon Particle

Supercritical water oxidation (SCWO) progress for a spherical activated carbon particle was pursued using a flow-type reaction cell equipped with sapphire windows, where the change in the size and shape of the particle inside the cell was observed in real time by means of a shadowgraph. While maintaining its shape, the particle radius decreased almost linearly with time at a rate on the order of micrometers per second. Phenomenologically, the reaction occurred at the surface of the sphere. The decreasing rate of the radius was nearly first order with respect to the O2 concentration and was almost independent of the temperature and pressure in the cell. On the other hand, the rate increased with the flow rate of the supercritical water. These trends suggested that the reaction was almost limited by the mass transfer of O2 from the bulk to the surface of the particle. The observed rate roughly agreed with the rate of O2 mass transfer which was estimated using empirical relations.

Preparation and properties of rf sputtered Pb(Mg1/3Ta2/3)O3 thin films

Abstract Radio frequency magnetron sputter deposition of Pb3MgTa2O9 (PMT) thin films on n-type (1 0 0) Si wafers is investigated in a low pressure ambient of Ar and O2. The process is optimized with process variables including rf power density, substrate temperature, ambient pressure, O2 mass flow and target composition. The properties of the films including refractive index, morphology, composition, crystallinity, microstructure and electrical properties are characterized as functions of the process parameters and correlated. The films as grown at 300°C are amorphous and become polycrystalline upon annealing at 600°C and above. The dielectric constants are between 29 and 129. The leakage current densities are below 1×10−7 A cm−2 at 1×106 V cm−1 and further improved after annealing.

The Sulfur-Isotopic Composition of Cenozoic Seawater Sulfate: Implications for Pyrite Burial and Atmospheric Oxygen

The availability of high-temporal-resolution C- and S-isotope curves for the Cenozoic permit for the first time modeling of the influence of the C and S cycles on the partial pressure of atmospheric O2 on comparable time scales. A simple isotope mass-balance model was used to calculate atmospheric O2 levels from the burial rates of organic C and pyrite S. Burial rates were derived from the C- and S-isotope records of seawater-dissolved inorganic C and sulfate. Results indicate that in the early Cenozoic atmospheric O2 levels were about 16% higher than current levels. Extension of the model to Phanerozoic time scales yields atmospheric O2 levels that are inconsistent with geological evidence that suggests that the mass of atmospheric O2 has not changed by more than a factor of two from the present atmospheric level since the Cambrian (Berkner and Marshall, 1974; Watson et al., 1978; Jones and Chaloner, 1991). These results indicate that either our knowledge of the parameters controlling atmospheric O2 is incomplete, or that the assumptions used in such models inadequately represent the complexity of the natural systems. Here we critically examine the assumptions inherent in isotope mass-balance models to determine whether they may be the source of the model-data discord. A major problem with these models is the extreme sensitivity of the mass of atmospheric O2 to very small changes in the much larger masses of oxidized and reduced C and S reservoirs. For example, small variations in continental weathering fluxes and the associated isotope ratios of river input have profound effects on calculated O2 levels and need to be accounted for. Similarly, variations in the isotopic composition of pyrite and organic C buried in sediments, which are strongly influenced by changes in isotopic fractionation, dramatically influence calculated O2 concentrations. Thus, constant fractionation factors should not be applied in such models. In addition, the assumption that the isotopic composition of dissolved inorganic C is controlled only by the relative amounts of reduced and oxidized C buried in sediments and their respective isotope ratios is questionable when relatively short time scales are considered. Isotope mass-balance models do not adequately encompass and simulate the actual processes being modeled because of the simplifications and assumptions made. More “realistic” models are required to achieve stabilization of atmospheric O2 over geological time.

Time-dependent O2 mass balance change and target surface oxidation during mode transition in Ti–O2 reactive sputtering

Time-dependent O2 mass balance change among the amounts injected into the chamber, pumped out from the chamber, gettered by sputtered Ti metal, residing in the chamber, and consumed to oxidize the target surface has been investigated as a function of time elapsed after the discharge ignition in Ti–O2 reactive sputtering. From the mass balance results obtained, target surface coverage has been estimated. In the period of up to 10 s after discharge ignition, the gettering of O2 by sputtered Ti dominated the process change. In this period, the target surface oxidation rate was low. In the period of 20–50 s, the amount of O2 consumed to target surface oxidation surpassed the amount of O2 gettered by deposited Ti, resulting in a drastic increase in the target coverage. After the target surface oxidation was completed, the process became stable. In this period, the amount of O2 pumped out without causing any process changes increased and a very small amount of O2 was consumed to oxidize the target surface. The equilibrium in the balance between the formation and sputter etching of the oxide layer on the target surface resulted in the stable condition. Calculated target coverage achieved more than 250 monolayers at 600 s after the glow discharge ignition. This value equated with the oxide thickness of about 100 nm. It is concluded that the nonlinear target surface oxidation process causes a nonlinear process change occurring during the mode transition.

Oxygen and carbon dioxide mass balance for the estuarine‐intertidal marsh complex of five rivers in the southeastern U.S.

We measured dissolved O2 concentrations, pCO2 values, and respiratory rates in five estuaries of the southeastern U.S. in October 1995 and July 1996. In the low‐salinity sections of the coastal plain rivers, dissolved O2 saturation states were typically only 50%, while pCO2 values were over 4,000 matm. Respiratory rates measured concurrently in estuarine water averaged 8 and 23 mmol m−3 d−1 in October 1995 and July 1996, but they showed little variability either within or among the five estuaries. Benthic chamber incubations in the adjacent intertidal marshes indicated fluxes of 30–40 mmol m−2 d−1 and 50–120 mmol m−2 d−1 for O2 and total dissolved inorganic carbon (DIC), respectively. For the Satilla River estuary, simple calculations revealed that neither respiratory activity in estuarine waters and sediments nor any other within‐estuary process (not including the intertidal marsh system) was sufficient to account for the observed O2 concentrations and pCO2 values. Dissolved oxygen concentrations in four other southeastern U.S. estuaries fit the same general pattern as the Satilla, and likewise, within‐estuary processes could not explain observed gas concentrations. Measured O2 concentrations, pCO2 values, pelagic respiratory rates, and benthic fluxes were used to construct a mass‐balance model, focusing on the influence of the extensive intertidal marshes on O2 and CO2 mass balance and water‐atmosphere gas exchange in the five estuaries. Results indicate that respiratory activity in the sediments and overlying water of the marshes during high tide leaves a signal that is funneled back to the estuary during ebb tide and can account for the estuarine gas concentrations and fluxes. Both experimental and modeling approaches argue that the intertidal marshes of the southeastern U.S. export considerable amounts of inorganic respiratory products to the estuaries and that “outwelling” of organic matter to the estuaries is a minor process by comparison. The DIC exported to the coastal ocean, however, is only a small fraction of the total gas mass flow between the marsh, estuary, and atmosphere.

Effect of Process Management on the Emission of Organosulfur Compounds and Gaseous Antecedents from Composting Processes

Pilot-scale studies were performed to assess the effects of aeration rate and initial moisture content on the emissions of odorous organosulfur compounds and nonodorous gaseous antecedents from synthetic food waste (SFW) and biosolids composting processes. In the SFW studies peak organosulfur emissions occurred at an airflow rate of 0.16 L/min-kg VS. Emission rates (mol/time) and total aerobic biological activity (cumulative mass of O2 consumed) were lower at 0.07 L/min-kg VS, possibly because the slightly higher temperatures encountered at this rate suppressed microbial activity. Emission rates were progressively lower at 0.32 and 0.65 L/min-kg VS, likely because of higher oxygen levels. As moisture content increased from 45 to 55% (H2O/g wet weight), peak emission rates generally increased. In the biosolids studies organosulfur emissions decreased as aeration rate increased. In both the SFW and biosolids studies CO was emitted prior to the detection of organosulfur compounds. Additionally, average correlation coefficients relating the emission rate of CO with the emission rate of organosulfur odors were 0.67 for the SFW trials and 0.75 for the biosolids trials. These results suggest that CO may be a good antecedent compound for the early warning of odors from composting processes.

Evolution of the Abundance of CO, O 2 , and Dust in the Early Universe

We present a general set of calculations describing the chemical evolution of young massive galaxies and predict the evolution of the CO, O2, and dust abundances as a function of age and metallicity. Over a wide range of input parameters, the models predict that (1) the total mass in gaseous metals peaks at early epochs (z ~ 1-3) when approximately half the total baryonic mass is in stars and half is in gas; (2) at its extreme, the mass of gaseous metals ranges from a few to more than 10 times larger than the mass of gaseous metals at the current epoch; (3) owing to the larger O/C ratios in chemically young systems, the O2/CO ratio may be of order unity within dark molecular clouds at early cosmological epochs; and (4) at early epochs, the global volume-weighted O2/CO abundance ratios corrected for photodissociation are lowered significantly compared to the dark cloud solutions owing to the lower metallicities and the higher UV fields. For a variety of models, we calculate the evolution of the mass of CO, O2, and dust. We also compute the CO(1 ? 0) and O2(1, 1 ? 1, 0) line intensities and the thermal dust emission as a function of redshift. The model calculations suggest that both redshifted thermal dust emission and CO line emission will be easily observable in young massive galaxies with the next generation of millimeter- and submillimeter-wavelength telescopes. Although more challenging, the O2 lines may be observable in chemically young galaxies. Even though molecular oxygen has yet to be observed outside the solar system, and hence is much less abundant than CO in the Milky Way, the models indicate that O2 may be significantly more abundant in the early stages of galaxy evolution.

Maximal work capacity in relation to nutritional status in children with cystic fibrosis.

In children with cystic fibrosis, objective parameters of exercise tolerance are needed which are easy to measure in nonspecialized centres. We investigated maximal workload (W'max) in children with cystic fibrosis in relation to body weight and fat-free mass, and compared this with results for maximal oxygen consumption (V'O2,max). Fourteen patients with cystic fibrosis performed an incremental maximal exercise test on a bicycle ergometer. W'max, V'O2,max, body weight and fat-free mass were measured. W'max and V'O2,max were significantly correlated (r = 0.91; p < 0.001). Using standard deviation scores in relation to reference values, W'max and V'O2,max per kilogram body weight were significantly higher than uncorrected W'max and V'O2,max (mean difference (95% CI) 0.63 (0.24-1.01) and 0.91 (0.32-1.49) SD units, respectively). There was no such difference after correction for fat-free mass. Standardized V'O2,max was significantly higher than standardized W'max (mean difference (95% CI): 1.59 (1.14-2.04)), also after correction for body weight and fat-free mass. In children with mild-to-moderate cystic fibrosis, maximal workload per kilogram fat-free mass, but not per kilogram body weight, is a useful parameter to correct for diminished nutritional status. In these patients, maximal workload is consistently lower than maximal oxygen consumption. Taking into account this difference, maximal workload and maximal workload per kilogram fat-free mass can be used for follow-up of paediatric patients with cystic fibrosis in nonspecialized settings.

INFLUENCE OF A HORIZONTAL FLOW ON THE PERFORMANCE OF FINE-BUBBLE DIFFUSED AIR SYSTEMS

The horizontal rotation of water in an oxidation ditch by separate agitation improves the oxygen transfer of diffused air aeration systems. This can be explained by the modifications. due to the horizontal flow. of several parameters that play a role in the oxygen transfer. An experimental study was performed on a 1400m3 annular ditch fitted with fine bubble diffusers and mixers to quantify this empirical knowledge. The initial findings of this research are presented. Compared to the absence of an imposed horizontal flow, the O2 mass transferred per hour, in clean water, is increased by 40% to 50% for a horizontal water flow of 0.4 to 0.5 m/s. This improvement may be explained by the prolongation of air bubble contact time (modification of spiral flow phenomena) for 10% at the most, by the increase of the exchange surface for the most part, due, not to the shear or to the elimination of the coalescence of air bubbles, (insignificant phenomena in this case). but to the deformation of air bubbles for 17% at the most and especially to the decrease of the diameter of the nascent bubbles. Moreover, the renewal of the liquid layer around the air bubbles could be considered as insignificant.

Multiphoton dissociative ionization of O2: Competition between dissociation and ionization in excited states

A mass and energy resolved photoion spectrum of O2 induced by 12 ns 193 nm radiation with an intensity of 1010–1011 W/cm2 is presented. The analysis of the spectrum gives (1) the two-photon ionization cross section (≊1.1×10−54 cm4 s) of the X 3Σ−g of O2 and (2) the intensity dependent branching ratios between photoionization and predissociation of the B 3Σ−u state of O2. The two-photon ionization cross section of O2 is linked to our ab initio calculation of the three-photon ionization cross section (≊7.5×10−84 cm6 s2) of atomic oxygen.

A novel membrane bioreactor for microbial growth

A novel membrane bioreactor, previously assessed for its gas transfer characteristics, was used in various size and membrane configurations for the growth of the strictly aerobic bacterium Pseudomonas aeruginosa. The bioreactor was found to readily support growth, and the initial growth rates showed the previously demonstrated enhanced effect in gas O2 mass transfer of the dimpled membrane bioreactor over flat membrane bioreactors. The production of a secondary metabolite by a Pseudomonas sp. following growth was demonstrated, as was the biotransformation of a nitrile by Nocardia rhodochrous with the removal of the biotransformation products across a membrane. The potential of the bioreactor, in terms of other applications in the field of biotechnology, is discussed.

On‐line Determination via Differential Electrochemical Mass Spectroscopy (DEMS) of Chemical Products Formed in Photoelectrocatalytical Systems

AbstractThe evolution of oxygen in acid aqueous solution on thin porous titanium dioxide (anatase) electrodes under illumination was monitored with DEMS. By adding Cl− in the electrolyte, a Cl2 mass signal is additionally observed. This latter increases as a function of Cl− concentration while O2 mass signal decreases, although the photocurrent‐potential characteristics remain unchanged. This example illustrates a competitive oxidation which cannot be discriminated by only recording photocurrent‐potential curves.

Arteriovenous oxygen diffusion shunt is negligible in resting and working gracilis muscles

Distribution of O2 within and among arterioles and venules was determined in dog and rat gracilis muscles with a cryospectrophotometric method. Saturation in 40-microns arterioles was not demonstrably different from saturation in the aorta even when flow was abnormally low. Arterioles greater than 40 microns ran parallel to venules. Measurements and a mathematical model indicate that diffusive shunting is negligible for typical separation distances between arterioles and venules. Most separation distances were greater than 30 microns. In some venule segments less than 15 microns from an arteriole, saturation within 10 microns of the wall facing the arteriole was higher than at other locations within the venule. However, saturation in the population of venules did not increase with venule diameter, and mean venular saturation was not different from saturation in effluent blood. We make the following conclusions: 1) a small arteriovenous diffusive O2 flux exists in postural muscles; 2) contribution of this flux to O2 mass balance is negligible; 3) O2 diffusivity of the arteriolar wall and surrounding tissue in vivo cannot be much higher than O2 diffusivity determined in vitro; and 4) effluent PO2 closely approximates mean end-capillary PO2.