Oxygen Concentration Distribution Research Articles

Numerical analysis of O2 concentration, gas-zeolite temperatures in two zeolite columns for an oxygen concentrator

In order to improve the performance of a compact adsorption-type oxygen concentrator, it is necessary to develop an analytical method for a compact concentrator having two zeolite columns of 15–30 cm length. A method which computes the velocity of gas flowing through the zeolite column was developed by assuming that the total gas pressure over the entire area of the column is spatially uniform during pressure swing adsorption (PSA) operation. The energy conservation equation for gas includes flow work and gas enthalpy transport which occurs when gas adsorbs/desorbs at a surface of a zeolite particle. Spatial distributions of gas velocity, oxygen concentration, and gas-zeolite temperatures were analyzed numerically using these equations. The numerical results of the time dependent changes in the discharged oxygen concentration and the temperature distribution of the zeolite column were in agreement with experiment.

Experimental investigations of oxyfuel burner for cement production application

The production of cement is one of the CO2 intensive processes, due to the inherent formation of CO2 in the calcination process by decomposition of limestone which is additional to the CO2 generated from fuel combustion. Carbon capture and storage technologies have been seen as a promising way to comply with CO2 reduction targets. As part of the objectives of the Horizon 2020 project CEMCAP, the retrofitting of key parts of the equipment of a conventional cement plant to oxyfuel combustion are investigated. The present study reports the results of several combustion tests employing a downscaled commercial kiln burner to determine its adequacy for oxyfuel operation mode. The investigations were carried out in the 500 kWth top-fired combustion facility at University of Stuttgart, which was previously adapted for these tests, including the installation of an electric preheating system to rise secondary gas temperature up to 800 °C. Fuel used is a German pre-dried lignite previously milled to required fineness in a separate location. A variety of in-flame measurements are performed at a dozen of ports located at different distances from burner outlet in order to characterize combustion behavior in each firing mode. It was observed that under oxyfuel mode additional parameters in burner configuration like total oxygen concentration and oxygen distribution in primary and secondary gas are key variables to adjust flame formation and obtain similar results as in conventional air firing.

Numerical analysis of parallel flow fields improved by micro-distributor in proton exchange membrane fuel cells

The flow field on bipolar plates of proton exchange membrane fuel cells (PEMFCs) is critical to flow distribution and overall pressure drop, both of which have great influence on cell performance. A micro-distributor was proposed to improve the uniformity of flow distribution in parallel flow field. The effects of micro-distributor size on output cell performance and pressure drop were systematically studied with computational fluid dynamics (CFD) simulations. To evaluate the competence of the modified parallel flow field, a serpentine flow field was also considered for comparison. The results suggest that the modification of the flow field is able to enhance the uniformity of flow distribution significantly. The maximum output power density increases when decreasing the size of micro-distributor. Compared with the serpentine flow field, the modified parallel flow field with micro-distributor enables the fuel cell to give nearly comparable output performance, but requires two orders of magnitude lower pressure. More generally, it was found that the flow uniformity could be simply and conveniently improved by enhancing the mean pressure drop in the sub-channels. The origin of non-uniform distribution of oxygen concentration in the interface of gas diffusion layer (GDL) and catalyst layer (CL) was also discussed. This work provides an alternative to conventional parallel and serpentine flow fields, and is helpful for the designing of high output PEMFCs.

Study on the influence of periodic weighting on the spontaneous combustion “three-zone” in a gob

The spontaneous combustion “three-zone” of a gob is one of the key fields in the study of the self-heating of residual coal and it is a coupled result of several factors. This paper studies the impact of periodical weighting by introducing weighting intervals into the coupled model of coal self-heating in gobs. The simulated result under field conditions matches well with the measured oxygen concentration distribution in situ. Further simulations of the validated model have been carried on under different weighting intervals, which reveals that the “three-zone” appears to be an asymmetric structure: it moves deeper on the air-intake side but closer to the working face on the air-return side, and the “three-zone” is wider in the middle and tapers when extending to the walls of the gob. The greater weighting interval makes the “three-zone” move deeper into the gob, and the spontaneous combustion zone declines in width. In addition, the highest temperature point proceeds into the depth of the gob at a decreasing speed as the weighting interval rises. This study may be a guide for the problem related to the spontaneous combustion of residual coal in gobs and for the optimization of the ventilation mode in the working face.

Effect of cellular mass on chondrogenic differentiation during embryoid body formation.

One approach to cell differentiation is to use the natural capacity of pluripotent stem cells to form three germ layers via embryoid bodies (EB). However, unification of this process during in vitro culture remains challenging and many microenvironmental factors including the number of cells in the culture can influence differentiation patterns. The number of cells serves a crucial role as it determines access to nutrients, the distribution of oxygen concentration and cellular interactions, all of which influence the fate of the differentiated cells. The influence of EBs derived from human pluripotent cells on the chondrogenic potential of such cells is not well understood. For this reason, the present study sought to determine the effect of varying amounts of cells on the properties of EBs derived from human embryonic stem cells (BG01V cell line). In the present study, 500–2,000 cells per well were cultivated from 5 to 15 days in suspension cell culture. Expression of pluripotency genes and germ layer markers were evaluated in order to determine the EBs with the greatest and least mesodermal properties. Genes associated with pluripotency and chondrogenesis were also evaluated to assess the influence of suspension culture duration and EB size on chondrogenic differentiation. Immunofluorescence staining for pluripotent and chondrocyte-associated proteins confirmed successful differentiation into chondrocyte-like cells. Alcian blue staining confirmed deposition of proteoglycans. These results suggested that EBs formed in 500-cell wells possess the highest mesodermal and prochondrogenic properties. Differentiation of EBs into chondrocytes on day 5 in 500-cell wells was more efficient than in that observed in larger and older EBs.

Stability and dynamics of a chemotaxis system with deformed free-surface in a shallow chamber

Complex bioconvection patterns have been studied analytically, experimentally, and numerically previously only for a flat free-surface of a suspension of chemotaxis bacteria in a shallow/deep chamber. In this paper, we have considered a two-dimensional chemotaxis-diffusion-convection system with a deformed free-surface. The influence of aggregation of chemotactic cells on the deformed free-surface of a shallow chamber is studied analytically. The aim of this paper is to investigate the nature of the instability in the chemotaxis-diffusion-convection system. We performed a detailed linear stability analysis of a steady-state cell and oxygen concentration distribution. The system becomes dominated by nonlinear convection terms beyond a critical Rayleigh number Raτ, which also depends on the critical wavenumber k as well as the other parameters. We have investigated that how the critical Rayleigh number in this system varies with three different sets of parameters. A weakly nonlinear analysis is carried out as well to determine the relative stability of the pattern formation at the onset of instability. A reactance between rolls, squares, hexagons, and mixed mode pattern is investigated in detail. Further research should link the weakly nonlinear analysis with the bifurcation analysis. Some important direct numerical simulation results have been presented in the support of linear stability analysis. Comparison of the analytical steady-state solution shows good agreement with the numerical result.

Optimization-based image reconstruction from sparsely sampled data in electron paramagnetic resonance imaging

Electron paramagnetic resonance imaging (EPRI) can yield information about the 3-dimensional (3D) spatial distribution of the unpaired-electron-spin density from which the spatial distribution of oxygen concentration within tumor tissue, referred to as the oxygen image or electron paramagnetic resonance (EPR) image in this work, can be derived. Existing algorithms for reconstruction of EPR images often require data collected at a large number of densely sampled projection views, resulting in a prolonged data-acquisition time and consequently numerous practical challenges especially to in vivo animal EPRI. Therefore, a strong interest exists in shortening data-acquisition time through reducing the number of data samples collected in EPRI, and one approach is to acquire data at a reduced number of sparsely distributed projection views from which existing algorithms may reconstruct images with prominent artifacts. In this work, we investigate and develop an optimization-based technique for image reconstruction from data collected at sparsely sampled projection views for reducing scanning time in EPRI. Specifically, we design a convex optimization program in which the EPR image of interest is formulated as a solution and then tailor the Chambolle-Pock (CP) primal-dual algorithm to reconstruct the image by solving the convex optimization program. Using computer-simulated EPRI data from numerical phantoms and real EPRI data collected from physical phantoms, we perform studies on the verification and characterization of the optimization-based technique for EPR image reconstruction. Results of the studies suggest that the technique may yield accurate EPR images from data collected at sparsely distributed projection views, thus potentially enabling fast EPRI with reduced acquisition time.

Integration of an oxygen sensor into a polydymethylsiloxane hepatic culture device for two-dimensional gradient characterization

This paper presents a new hepatic culture device, in which oxygen concentration gradient formed by cellular respiration can be visualized as a two-dimensional optical image. An oxygen sensor layer containing Pt (II) octaethylporphyrin (PtOEP) was embedded at the bottom of the device, allowing visualization of oxygen concentration distribution over the cell culture area. Oxygen concentration was determined by analyzing the modulation of fluorescence intensity emitted by the sensor, which is negatively correlated to the concentration. The results in HepG2 cell culture showed that the oxygen gradient and local oxygen partial pressure could be regulated by controlling the perfusion flow rate in the device. The local and physiological oxygen gradient comparable to the in vivo liver lobules can successfully be reproduced in the device. Therefore, periportal and perivenous hepatic like-zones were successfully realized in vitro. The present device would be helpful in the development of novel in vitro methods recapitulating the liver physiology for investigation of hepatic zonation and drug screening system recapitulating the liver physiology.

Effects of agglomerate model parameters on transport characterization and performance of PEM fuel cells

A three-dimensional, non-isothermal and two-phase flow model for proton exchange membrane (PEM) fuel cells is developed. In the cathode catalyst layer, a spherical agglomerate model with consideration of catalyst layer structure and liquid water effect is applied to determine the electrochemical kinetics. The size and structure of the agglomerates are determined by the following parameters, i.e., the agglomerate radius (ragg), the volume fraction of ionomer within the agglomerate (Li,agg), and the thickness of the ionomer film over the agglomerate (δi). It is noted that a random combination of the three above parameters is widely used in agglomerate models by researchers. In this paper, the effects of ragg and Li,agg on the cell performance and local transport characteristics are numerically investigated by using the developed model with consideration of the relationships between agglomerate parameters. It is concluded that the cell performance is significantly improved by decreasing ragg and increasing Li,agg at medium and high current densities when the volume fractions of the solid phase (LPt/C) and ionomer phase (Li) are maintained constant. In addition, the distributions of oxygen concentration, liquid water saturation, volumetric current density and effectiveness factor are also strongly influenced by the variation of the two parameters.

Developing transmission line equations of oxygen transport for predicting oxygen distribution in the arterial system

The oxygen content in the arterial system plays a significant role in determining the physiological status of a human body. Understanding the oxygen concentration distribution in the arterial system is beneficial for the prevention and intervention of vascular disease. However, the oxygen concentration in the arteries could not be noninvasively monitored in clinical research. Although the oxygen concentration distribution in a vessel could be obtained from a three-dimensional (3D) numerical simulation of blood flow coupled with oxygen transport, a 3D numerical simulation of the systemic arterial tree is complicated and requires considerable computational resources and time. However, the lumped parameter model of oxygen transport derived from transmission line equations of oxygen transport requires fewer computational resources and less time to numerically predict the oxygen concentration distribution in the systemic arterial tree. In this study, transmission line equations of oxygen transport are developed according to the theory of oxygen transport in the vessel, and fluid transmission line equations are used as the theoretical reference for the development. The transmission line equations of oxygen transport could also be regarded as the theoretical basis for developing lumped parameter models of other substances in blood.

Prediction of Necrotic Core and Hypoxic Zone of Multicellular Spheroids in a Microbioreactor with a U-Shaped Barrier.

Microfluidic devices have been widely used for biological and cellular studies. Microbioreactors for three-dimensional (3D) multicellular spheroid culture are now considered as the next generation in in vitro diagnostic tools. The feasibility of using 3D cell aggregates to form multicellular spheroids in a microbioreactor with U-shaped barriers has been demonstrated experimentally. A barrier array is an alternative to commonly used microwell traps. The present study investigates oxygen and glucose concentration distributions as key parameters in a U-shaped array microbioreactor using finite element simulation. The effect of spheroid diameter, inlet concentration and flow rate of the medium are systematically studied. In all cases, the channel walls are considered to be permeable to oxygen. Necrotic and hypoxic or quiescent regions corresponding to both oxygen and glucose concentration distributions are identified for various conditions. The results show that the entire quiescent and necrotic regions become larger with increasing spheroid diameter and decreasing inlet and wall concentration. The shear stress (0.5–9 mPa) imposed on the spheroid surface by the fluid flow was compared with the critical values to predict possible damage to the cells. Finally, optimum range of medium inlet concentration (0.13–0.2 mM for oxygen and 3–11 mM for glucose) and flow rate (5–20 μL/min) are found to form the largest possible multicellular spheroid (500 μm), without any quiescent and necrotic regions with an acceptable shear stress. The effect of cell-trap types on the oxygen and glucose concentration inside the spheroid was also investigated. The levels of oxygen and glucose concentration for the microwell are much lower than those for the other two traps. The U-shaped barrier created with microposts allows for a continuous flow of culture medium, and so improves the glucose concentration compared to that in the integrated U-shaped barrier. Oxygen concentration for both types of U-shaped barriers is nearly the same. Due to the advantage of using U-shaped barriers to culture multicellular spheroids, the results of this paper can help to choose the experimental and design parameters of the microbioreactor.

Modelling for reactor-style aerobic composting based on coupling theory of mass-heat-momentum transport and Contois equation

This study establishes an optimal mathematical modelling to rationally describe the dynamic changes and spatial distribution of temperature and oxygen concentration in the aerobic composting process using coupling mass-heat-momentum transfer based on the microbial mechanism. Two different conditional composting experiments, namely continuous aeration and intermittent aeration, were performed to verify the proposed model. The results show that the model accurately predicted the dynamic changes in temperature (case I: R2 = 0.93, RMSE = 1.95 K; case II: R2 = 0.86, RMSE = 4.69 K) and oxygen concentration (case I: R2 = 0.90, RMSE = 1.26%; case II: R2 = 0.75, RMSE = 2.93%) in the central point of compost substrates. It also systematically simulated fluctuations in oxygen concentration caused by boundary conditions and the spatial distribution of the actual temperature and oxygen concentration. The proposed model exhibits good applicability in simulating the actual working conditions of aerobic composting process.

Analytical solution of coal self-heating characteristics incorporating the effect of oxygen concentration

A novel analytical solution, which included the effects of temperature distribution and oxygen concentration distribution on coal self-heating system, was presented. It was derived by combining the travelling wave reduced form method and the intermediate variable method. Coal self-heating results were consistent between theory and experiments. Using the analytical solution, the effects of kinetic parameters on coal self-heating were explicitly discussed. For Killoch6015 coal, an increase of pre-exponential and a decrease of other parameters (i.e., activation energy and inlet velocity) was observed at a reference temperature of 350K, and the temperature and oxygen consumption within the coal self-heating system raised in varying degrees. However, an increase in porosity had almost no influence on the coal self-heating process, only exhibiting a weak increase in oxygen concentration and temperature within the system. Finally, the evolution processes of the temperature and oxygen concentration distributions were discussed. [Received: May 24, 2017; Accepted: October 10, 2017]

Analytical solution of coal self-heating characteristics incorporating the effect of oxygen concentration

A novel analytical solution, which included the effects of temperature distribution and oxygen concentration distribution on coal self-heating system, was presented. It was derived by combining the travelling wave reduced form method and the intermediate variable method. Coal self-heating results were consistent between theory and experiments. Using the analytical solution, the effects of kinetic parameters on coal self-heating were explicitly discussed. For Killoch6015 coal, an increase of pre-exponential and a decrease of other parameters (i.e., activation energy and inlet velocity) was observed at a reference temperature of 350K, and the temperature and oxygen consumption within the coal self-heating system raised in varying degrees. However, an increase in porosity had almost no influence on the coal self-heating process, only exhibiting a weak increase in oxygen concentration and temperature within the system. Finally, the evolution processes of the temperature and oxygen concentration distributions were discussed. [Received: May 24, 2017; Accepted: October 10, 2017]

Numerical simulation of the oxygen distribution in silicon melt for different argon gas flow rates during Czochralski silicon crystal growth process

The effects of argon gas flow rate on the oxygen concentration in Czochralski (CZ) grown silicon crystal were examined. To analyze the influence of the argon gas flow rate in CZ growth process, a 200 mm length silicon single crystal was grown. Different argon gas flow rates are considered. The melt flow pattern, temperature and oxygen concentration distributions in the melt and crystal-melt interface are calculated. The results show that the transport of oxygen impurity is quite dependent on the flow motion in the melt. As the argon gas flow rate increases, there is no fundamental change in flow motion of the melt and the oxygen concentration decreases to a minimum value. When the argon gas flow rate increases further, the flow pattern under the melt-crystal interface starting changes and the oxygen concentration has increased after. Therefore, there is an optimum value for the argon gas flow rate for obtaining the lowest oxygen concentration in the melt.

Numerical Simulation of the Behavior of Toroidal and Spheroidal Multicellular Aggregates in Microfluidic Devices with Microwell and U-Shaped Barrier.

A microfluidic system provides an excellent platform for cellular studies. Most importantly, a three-dimensional (3D) cell culture model reconstructs more accurately the in vivo microenvironment of tissue. Accordingly, microfluidic 3D cell culture devices could be ideal candidates for in vitro cell culture platforms. In this paper, two types of 3D cellular aggregates, i.e., toroid and spheroid, are numerically studied. The studies are carried out for microfluidic systems containing U-shaped barrier as well as microwell structure. For the first time, we obtain oxygen and glucose concentration distributions inside a toroid aggregate as well as the shear stress on its surface and compare its performance with a spheroid aggregate of the same volume. In particular, we obtain the oxygen concentration distributions in three areas, namely, oxygen-permeable layer, multicellular aggregates and culture medium. Further, glucose concentration distributions in two regions of multicellular aggregates and culture medium are investigated. The results show that the levels of oxygen and glucose in the system containing U-shaped barriers are far more than those in the system containing microwells. Therefore, to achieve high levels of oxygen and nutrients, a system with U-shaped barriers is more suited than the conventional traps, but the choice between toroid and spheroid depends on their volume and orientation. The results indicate that higher oxygen and glucose concentrations can be achieved in spheroid with a small volume as well as in horizontal toroid with a large volume. The vertical toroid has the highest levels of oxygen and glucose concentration while the surface shear stress on its surface is also maximum. These findings can be used as guidelines for designing an optimum 3D microfluidic bioreactor based on the desired levels of oxygen, glucose and shear stress distributions.

Oxide Dissolution and Oxygen Diffusion in Solid-State Recycled Ti-6Al-4V: Numerical Modeling, Verification by Nanoindentation, and Effects on Grain Growth and Recrystallization

The oxide dissolution and oxygen diffusion during annealing of Ti-6Al-4V solid-state recycled from machining chips by equal-channel angular pressing (ECAP) have been investigated using nanoindentation and numerical modeling. The hardness profile from nanoindentation was converted into the oxygen concentration distribution using the Fleisher and Friedel model. An iterative fitting method was then employed to revise the ideal model proposed previously, leading to correct predictions of the oxide dissolution times and oxygen concentration profiles and verifying nanoindentation as an effective method to measure local oxygen concentrations. Recrystallization started at the prior oxide boundaries where local strains were high from the severe plastic deformation incurred in the ECAP recycling process, forming a band of ultrafine grains whose growth was retarded by solute dragging thanks to high oxygen concentrations. The recrystallized fine-grained region would advance with time to eventually replace the lamellar structure formed during ECAP.

Oxygen Concentration Measurement in the Porous Cathode of Aqueous Lithium–Air Battery By Fine Optical Fiber

Spatial and temporal oxygen concentration distribution in the porous cathode of discharging aqueous lithium-air secondary battery was successfully measured. Lithium-air battery attracts great attention because of its high energy density. In this study, we focus on the aqueous lithium–air secondary battery. The aqueous electrolyte realizes cost reduction and ensures the safe use of a battery. On the other hand, low solubility of oxygen in aqueous electrolyte limits oxygen transport to the reaction site. To realize a more powerful aqueous lithium–air battery, it is necessary to clarify and improve the oxygen transport phenomena in the porous cathode. In this study, we developed the measurement technique of oxygen concentration in the porous cathode under operating condition by inserting a fine optical fiber oxygen sensor. In this study, platinum tetrakis pentrafluoropheny porphine (PtTFPP) was employed as oxygen indicator [1]. When the PtTFPP is exposed to excitation light (λ = 405 nm), phosphorescence emission (λ= 650 nm) is produced, and its intensity depends on oxygen partial pressure. Thus, quantitative oxygen concentration can be obtained by measuring phosphorescence intensity and using calibration data. The PtTFPP was painted at the edge of optical fiber of which diameter was 110 μm. In order to measure the phosphorescence intensity, bifurcated optical fibers were connected to excitation light source and spectrometer, respectively. As shown in Figure 1, phosphorescence intensity changed at 650 nm depending on oxygen concentration. The experimental setup is shown in Figure 2. The porous cathode (SIGRACET® 10AA, SGL Group, USA) was fixed near electrolyte interface horizontally. The tiny optical fiber sensor was moved up and inserted in the cathode. The temporal oxygen concentration change from the start of discharge was measured at arbitrary positions in the porous cathode. The composite anode was water-stable and had a multilayer structure for the aqueous lithium air battery [2]. Measurement of spatial and temporal distribution of oxygen concentration has been conducted under the assumption that discharge experiment had reproducibility. Initial position (z = 0 μm) was defined arbitrary, and the sensor was moved up each 70 μm. Time variation of oxygen concentration was measured at each point. Finally, spatiotemporal distribution of oxygen concentration for each current density was obtained. As shown in Figure 3, the spatial and temporal oxygen concentration distribution at 0.10 mA/cm2 was successfully observed. When the discharge was started, the oxygen concentration gradually decreased in the cathode, and finally, oxygen concentration reached considerably low value even in the condition of 0.10 mA/cm2. In this experiment, oxygen concentration gradients are present at both ends of the atmosphere side (0-140 μm) and electrolyte side (490-910 μm) of the cathode. Flux for both side of cathode, upper side and lower side, was discussed and comprehensible interpretation was obtained. Although dissolved oxygen that forms flux from the lower side of cathode has an effective supply to the porous electrode, electrolyte layer formed at between the atmosphere and the cathode causes oxygen transport resistance. Acknowledgement: This work was supported by JSPS KAKENHI Grant Number 15K13881, 15H02347. Reference: [1] CS Chu., CA Lin, Sensors and Actuators B: Chemica, 2014, 195, 259-265. [2] T. Zhang, N. Imanishi, S. Hasegawa, A. Hirano, J. Xie, Y. Takeda, O. Yamamoto, N. Sammes, J. Electrochem. Soc., 2008, 155, A965. Figure 1

Measurement of oxygen concentrations in bacterial biofilms using transient state monitoring by single plane illumination microscopy

Oxygen is required for respiration in aerobic bacteria and hence plays an essential role in the generation of energy necessary for cell maintenance and growth. The distribution of oxygen within a biofilm can be heterogeneous and may result in bacterial cells exhibiting distinct physiological states depending on their local oxygen availability. Here, we have employed transient state (TRAST) monitoring, a non-invasive method that can measure the relative populations of triplet states by time-modulated illumination, to determine the distribution of oxygen concentrations in biofilm colonies. The method was implemented on a single plane illumination microscope that can perform optical slicing, making it a suitable approach for imaging thick samples. We present a map of triplet relaxation times measured inside a Pseudomonas aeruginosa biofilm at micrometre resolution. We also provide a calibration method that can evaluate oxygen concentration based on TRAST contrast. Our results indicate that anoxic zones exist within the colonies, and oxygen consumption extends outside the areas of high cell densities, establishing a gradient until levels return to air saturation.

Numerical Modeling with Electrochemical Active Area (ECA) Distribution in the Lateral Direction in a PEM Fuel Cell

Abstract In a PEM fuel cell, local current density distribution is very critical to the overall cell performance. From our previous experimental research on the current performance between land and channel in a PEM fuel cell, current density under the land is significantly larger than that under the channel in the most operating voltage regions [1] . This could lead to very severe problems such as accelerating membrane and catalyst degradation, thus reduce the lifetime and durability of a PEM fuel cell. In order to understand the mechanism of the current density distribution in this lateral direction, and for the better future design of a PEM fuel cell with higher performance, we construct a three-dimensional CFD model with electrochemical active area (ECA) equation implemented, while the ECA distribution is directly from previous research. The numerical results coincide well with the experimental results, and the lateral current density distribution and oxygen concentration distribution have also been studied.