Heterogeneous Gas Research Articles

Production Performance Analysis for Deviated Wells in Carbonate Gas Reservoirs With Multiple Heterogeneous layers

Deviated wells are used to improve the performance of carbonate reservoirs with multiple heterogeneous layers and penetrate the “sweet spot” of each layer, which is full of fractures and vugs. It is difficult to consider in-layer and inter-layer heterogeneities simultaneously, and predict the production performance for these wells accurately. Therefore, a semi-analytical model to analyze the production performance of deviated wells in a multilayer heterogeneous stress-sensitive carbonate gas reservoir is proposed. For each layer, the inner region is a fractured-vuggy porous medium, while the outer region is merely a tight formation with matrix and formation properties, and penetrated inclination angles may be distinct. Pseudo-time/pressure factors are introduced to consider fracture stress sensitivity. Through the application of Laplace transformation, Fourier transform and inverse, Duhamel convolution, and Stehfest numerical inversion, the presented model is solved. The validity of this model is verified through comparison with single-layer composite formation with different porous mediums and vertical well in a multilayer carbonate gas reservoir. Moreover, by matching bottom-hole pressure data collected from a slanted well in the Anyue gas field, the applicability of this model is validated. A synthetic case, which has two composite formations, the first (upper) layer is more permeable than the second (lower) layer, is used to study the variations of inner region radius, fracture/matrix permeability, and inclination angles on production behaviors. The results show the properties of the first layer determine well bottom-hole pressure, whereas the rise of permeability, inner region radius and penetrated angle for the second layer can improve the gas recovery of this layer. In practice, to maintain well bottom-hole pressure with a relatively high level and enhance gas recovery of the tight layer, the inclination angle should be larger than 60° for each layer, and be increased to as large as possible. The findings of this study can help for a better understanding of the production behaviors of deviated wells in multilayer heterogenous reservoirs and could provide some guidance for the design of well trajectory.

Permeability prediction of heterogeneous carbonate gas condensate reservoirs applying group method of data handling

Carbonate petroleum reservoirs typically have lower permeabilities and recovery factors than sandstone reservoirs, so the natural fractures they often incorporate have positive impacts on resource recovery and fluid production rates. Quantifying effective permeability, incorporating contributions from pores and fractures, is therefore essential in the reservoir characterization and flow-regime modelling of carbonate reservoirs. This research applies a robust machine-learning forecasting model to predict permeability (K) for heterogeneous carbonate gas condensate reservoirs. A 212-point dataset from six gas-condensate carbonate reservoirs (Russia and Iran) is compiled. The input variables considered are porosity (Φ, %), specific surface area (Sp, 1/cm) and irreducible water saturation (Swir, %). These variables are assessed using four machine learning models: group method of data handling (GMDH), polynomial regression (PR), support vector machine (SVR), and decision tree (DT) to predict permeability. The GMDH algorithm, a polynomial neural network with a customized architecture is developed, such that it displays increased prediction accuracy and improved learning capabilities. All four models developed in this study substantially improve upon K predictions derived from established empirical correlations. The GMDH model also outperforms the other models in respect of K prediction accuracy using Φ, Swir, and Sp as input variables. It achieves permeability prediction accuracy for the multi-field dataset evaluated with a root mean squared error (RMSE) and coefficient of determination (R2) for the training and testing of the best model (GMDH) of RMSE = 9.2 mD and R2 = 0.9988; RMSE = 0.4 mD and R2 = 0.9972, respectively. The model can be readily adapted for application to other field datasets to estimate K from limited well-log and/or core data.

In-situ X-ray tomographic imaging study of gas and structural evolution in a commercial Li-ion pouch cell

Gas generation within Li-ion batteries (LIB) can lead to an increase in resistance, thereby, reducing their cycle lifetime. The chance of catastrophic failure via internal gas evolution may increase as a function of cell size and capacity. However, in-situ studies of gas evolution at the cell level are very limited due to limited number of techniques that can effectively probe this. Hence, for the first time, we employed high-energy X-ray tomography to non-destructively observe the structural evolution (gas and electrodes) as a function of cycle numbers for a 400 mAh commercial Li-ion pouch cell. Gas agglomeration led to cell deformation in different areas were observed in 4D (3D + time), the subsequent quantification including the volume fraction, surface area and thickness showed a heterogeneous gas distribution, revealing the degradation mechanism involving the coalescence of gas. This study demonstrates a feasible case of the use of lab-based X-ray to investigate the cell degradation and monitor state of health (SOH) by tracking the thickness in-situ, providing practical guidance for designing safer pouch cells.

An analysis method of injection and production dynamic transient flow in a gas field storage facility

A dynamic transient flow analysis method considering complex factors such as the cyclic injection and production history in a gas field storage facility was established in view of the limitations of the existing methods for transient flow analysis and the characteristics of the injection-production operation of strongly heterogeneous gas reservoirs, and the corresponding theoretical charts were drawn. In addition, an injection-production dynamic transient flow analysis model named “three points and two stages” suitable for an underground gas storage (UGS) well with alternate working conditions was proposed. The “three points” refer to three time points during cyclic injection and production, namely, the starting point of gas injection for UGS construction, the beginning and ending points of the injection-production analysis stage; and the “two stages” refer to historical flow stage and injection-production analysis stage. The study shows that the dimensionless pseudo-pressure and dimensionless pseudo-pressure integral curves of UGS well flex downward in the early stage of the injection and production process, and the dimensionless pseudo-pressure integral derivative curve is convex during the gas production period and concave during the gas injection period, and the curves under different flow histories have atypical features. The new method present in this paper can analyze transient flow of UGS accurately. The application of this method to typical wells in Hutubi gas storage shows that the new method can fit the pressure history accurately, and obtain reliable parameters and results.

The Fourier transform infrared spectroscopy (FTIR) analysis for the clay mineralogy studies in a clastic reservoir

The complete characteristics knowledge of clay minerals is necessary in the evaluation studies of hydrocarbon reservoirs. Ten samples taken from two wells in a heterogeneous clastic gas reservoir formation in NE Iran were selected to conduct the transmission Fourier transform infrared spectroscopy (FTIR) tests for the clay mineralogy studies. The FTIR analysis showed that there were clear signs of clay minerals in all samples. The wavenumber region of the clay minerals in FTIR tests was detected to be 3621, 3432, 1034, and 515 cm−1 for illite, 3567, 3432, 1613, 1088, 990, 687, 651, and 515 cm−1 for magnesium-rich chlorite, 3700, 3621, 3432, 1034, 687, and 463 cm−1 for kaolinite, and 3567, 1088, 990, and 463 cm−1 for glauconite. After screening of samples by the FTIR method, the samples were then analyzed by powder X-ray diffraction (PXRD), wavelength dispersive X-ray fluorescence (WDXRF), and scanning electron microscopy (SEM). The PXRD and SEM result showed illite was by far the most common clay present. Kaolinite, magnesium-rich chlorite, and traces of smectite and the mixed-layer clays of both the illite–smectite and chlorite-smectite types were also recognized. The combination of PXRD and WDXRF results could quantify the clay abundances in the each well too. It was concluded that the FTIR analysis successfully could show the absorption bonds of all constituent clays. However, the infrared absorption spectra of mixed-layer clays overlapped those of the respective constituents of each mixed-layer minerals. This can be considered as the evidence of the usefulness of FTIR technique in the screening of the samples for the clay mineralogy studies.

Introduction to in silico synthesis of polymers via PySIMM [Article v1.0

Pysimm is a framework for molecular simulations of polymers and polymer-based nanostructures, which enables their direct chemical synthesis and preparation. Pysimm facilitates the understanding of novel, amorphous, processable materials for a broad range of applications, including heterogeneous catalysts, adsorbents and gas storage materials, as well as protein-polymer conjugates. This tutorial provides a detailed guide on the construction of atomistic and united-atom models of polymers using Pysimm: an open-source Python Application Programming Interface for atomistic molecular simulations. The API complements and simplifies the work of widely known molecular simulation software, such as LAMMPS, CASSANDRA, NAMD and Amber. Readers should be familiar with the basic concepts of atomistic molecular simulations, as well as the basic knowledge of Python programming language, before attempting to follow this tutorial. This work is separated into 3 main sections. First, the process of building an atomic-level model of a polymer chain from its repetitive units is described. The second section shows how to work with existing forcefields, and how Pysimm can automatically read, recognize, and assign appropriate Force Field parameters to a molecule. The final section discusses how to use Pysimm to construct polymer chains with pre-specified tacticity. The section is also available in the form of an interactive Jupyter notebook tutorial outlining simple guidelines to construct polymer models.

Broad-Spectrum Ultrathin-Metal-Based Oxide/Metal/Oxide Transparent Conductive Films for Optoelectronic Devices.

High-quality transparent conductive materials are beneficial to improve the charge transfer and light transmittance and reduce the interface defects as well as the production cost of optoelectronic devices. A high threshold thickness of metal layer in oxide/metal/oxide (OMO) compound thin films leads to strong reflectance, especially in the near-infrared region, limiting the broad-spectrum device applications. Here, we propose a novel Zn doping strategy using the low-cost single-target sputtering technology to achieve the growth of Ag-Zn thin films (i.e., Zn-doped Ag) and introduce a trace amount of O2 to further obtain ultrathin Ag-Zn(O) films (thin-film thickness d ≤ 5 nm), which greatly improves the broad-spectrum characteristics of OMO films. Heterogeneous metal and gas doping technology effectively promotes the formation of two-dimensional continuous film growth. By combining the ultrathin Ag-Zn(O) layer with the MGZO (i.e., Mg- and Ga co-doped ZnO) oxide film grown by reactive plasma deposition, a typical broad-spectrum MGZO/Ag-Zn(O)/MGZO (50/5/50 nm)-OMO compound thin film exhibits an average transmittance of 91.6% in the wavelength range of 400-1200 nm and low sheet resistance. The broad-spectrum organic solar cells based on MGZO/Ag-Zn(O)/MGZO electrodes present a high power conversion efficiency of 15.35%, superior to those devices based on single-layer oxide electrodes. The distinguished performances are attributed to the ultrathin Ag-Zn(O) films in OMO, paving the way for applications in broad-spectrum optoelectronic and flexible electronic devices.

Patterns of carbon footprints of main grains production in China: a comparison between main and non-main producing areas.

Understanding the spatiotemporal patterns of carbon footprints (CFs) of grains production is important to formulate regional heterogeneous greenhouse gas (GHG) mitigation strategies. This study evaluates the CFs, farm CFs (FCFs: CFs of per unit area), and production CFs (PCFs: CFs of per unit yield) of main grains production in China based on a new scale data set: agricultural statistics data of over 300 prefecture-level regions. A comparison of CFs of main grains production between main producing area (MPA) and non-main producing area (NMPA) are firstly discussed on a totally new scale. Results show that the CFs of main grains production of MPA accounts for 54-57% of country's total although the area of farmland of MPA only accounts for 42%. The PCF and FCF of rice production are higher in MPA, while those of wheat and maize production are lower in MPA. It implies that there are less GHG emission of rice (main paddy grain) productions in NMPA and less GHG emission of wheat and maize (main dryland grains) production in MPA. In additional, the PCF of rice shows growth, while that of wheat and maize shows decline from 2008 to 2017. The growth of PCF of rice is mainly driven by the rise of PCF in MPA. Findings are expected to improve the understanding patterns of China's CF of main grains production and subsequently contribute to GHG mitigation.

Multiple porosity model of a heterogeneous layered gas hydrate deposit in Ulleung Basin, East Sea, Korea: A study on depressurization strategies, reservoir geomechanical response, and wellbore stability

Precise simulation of the geomechanical response is crucial for the gas hydrate production such as from the deposits in Ulleung Basin, East Sea, Korea, which exhibit severe vertical heterogeneity of the hydrate-bearing sand and mud layers. Physically, depressurization causing hydrate dissociation can induce critical subsidence. Meanwhile, it is numerically cumbersome to apply the fine-scale single porosity model to the heterogeneous layered system particularly for geomechanics. In this study, to investigate geomechanical responses of the intercalated layer system based on various depressurization scenarios, we employ a multiple porosity (MP) model with upscaled geomechanical properties while flow variables kept in the fine-scale. For the rigorous two-way coupling between the fluid flow and geomechanics, the fixed-stress sequential method is employed with two individual simulators, the TOUGH+HYDRATE for the flow and an in-house code (called the ROCMECH) for the geomechanics. Specifically for the ROCMECH, we applied axisymmetric geomechanics for more precise calculation of deformation near the wellbore. Numerical experiments of field-wide simulations are about two different comparison studies for depressurization: a constant bottom hole pressure (BHP) and several different BHPs cases. For a constant BHP case, gas production periods, i.e., 14- and 100-days productions representing short- and long-term, respectively, are compared, while several different BHPs case including continuous and periodic depressurizations is focused on the comparison of the productivity and geomechanical stability. From the case of constant BHP, we confirm significant vertical displacement due to the weaker stiffness of the formation after hydrate dissociation, which can aggravate as the production continues. Among the cases with varying BHP, the periodic depressurization scenario exhibits superiority with significantly small subsidence despite similar productivity. The MP model employed in this study can help devise depressurization strategies for gas hydrate reservoirs, especially for the precise and efficient calculation of the geomechanical responses of the intercalated layer system.

Air Pollutant Concentration Prediction Based on a CEEMDAN-FE-BiLSTM Model

The concentration series of PM2.5 (particulate matter ≤ 2.5 μm) is nonlinear, nonstationary, and noisy, making it difficult to predict accurately. This paper presents a new PM2.5 concentration prediction method based on a hybrid model of complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and bi-directional long short-term memory (BiLSTM). The new method was applied to predict the same kind of particulate pollutant PM10 and heterogeneous gas pollutant O3, proving that the prediction method has strong generalization ability. First, CEEMDAN was used to decompose PM2.5 concentrations at different frequencies. Then, the fuzzy entropy (FE) value of each decomposed wave was calculated, and the near waves were combined by K-means clustering to generate the input sequence. Finally, the combined sequences were put into the BiLSTM model with multiple hidden layers for training. We predicted the PM2.5 concentrations of Seoul Station 116 by the hour, with values of the root mean square error (RMSE), the mean absolute error (MAE), and the symmetric mean absolute percentage error (SMAPE) as low as 2.74, 1.90, and 13.59%, respectively, and an R2 value as high as 96.34%. The “CEEMDAN-FE” decomposition-merging technology proposed in this paper can effectively reduce the instability and high volatility of the original data, overcome data noise, and significantly improve the model’s performance in predicting the real-time concentrations of PM2.5.

Theoretical insights into the gas/heterogeneous phase reactions of hydroxyl radicals with chlorophenols: Mechanism, kinetic and toxicity assessment

Emission of 2-chlorophenols (2-CPs) can cause serious air pollution and health problems. Here, the reaction kinetics and products of key radicals in 2-CPs photo-oxidation are explored in both gaseous and heterogeneous reactions. Quantum chemical calculations show that •OH-addition pathways are more preferable than H-abstraction pathways in gas phase, while that is opposite in heterogeneous phase. At 298 K, the overall rate coefficients of the title reactions in gas and heterogeneous phases are 3.48 × 10−13 and 2.37 × 10−13 cm3 molecule−1 s−1 with half-lives of 55.3 h and 81.2 h, respectively. The strong H-bonds between linear Si3O2(OH)8 and 2-CPs change the energy barriers of initial •OH-addition and H-abstraction reactions, resulting in the competition between heterogeneous reactions and gas phase reactions. The products in heterogeneous reactions are chloroquinone and HONO, which can cause atmospheric acid deposition and eco-toxicity. In gas phase, self-cyclization of alkoxy radical (RO•) leads to formation of •HO2 and highly‑oxygenated molecules, which cause formation of secondary organic aerosol. It is emphasized that oxidation of 2-CPs by •OH leads to formation of more toxic products for aquatic organisms. Therefore, more attention should be focused on the products originated from •OH-initiated reactions of (2-)CPs in gaseous and heterogeneous reactions.

Отходы нефтегазового комплекса как технологический индикатор геоэкологического состояния регионов России

This publication addresses a issue of heterogeneous waste products oil and gas sphere of society activity leaves behind, first of all about drilling or oil sludge — colloidal system that consists of high-molecular compound of oil, mineral particles of different composition and oilfield water. These large-scale waste products of oil-producing and oil-processing industries significant due to the complexity of chemical composition and are in process of constant transformation. Accumulating of waste products goes with large-scale pollution of the regions and creates ecological risks.

Semi-analytical modeling for multi-wing fractured vertical wells in a bilaterally heterogeneous gas reservoir

Many prolific hydrocarbon reservoirs show the lateral heterogeneity of rock properties, where the formation is composed of several regions with different rock properties separated by linear interfaces. Although there have been many studies on laterally heterogeneous reservoirs by linear composite models, most of them focus on vertical well without hydraulic fracturing. The modeling for fractured vertical wells in laterally heterogeneous reservoirs remains limited. The goal of this study is to develop a semi-analytical three-region linear composite model for multi-wing fractured vertical (MWFV) wells in a bilaterally heterogeneous gas reservoir. This model can take into account the common situation in practice, where the heterogeneity occurs on both sides of the reservoir region with the MWFV well. Based on the point-source function method, a semi-analytical modeling for an MWFV well in a bilaterally heterogeneous gas reservoir is developed by using pressure drop superposition, fracture wing discretization, and Stehfest algorithm. Compared with the simplified semi-analytical and numerical models, the correctness of the present model is verified. Log-log type curves for MWFV wells in a bilaterally heterogeneous gas reservoir are drawn. The flow regimes of the MWFV well in a bilaterally heterogeneous gas reservoir are identified. The influences of some well and reservoir parameters on the pressure response and rate decline of MWFV wells are investigated thoroughly. It is found that the pressure response and rate decline of MWFV wells are significantly affected by the well location, fracture wing properties, and reservoir heterogeneity.

Effect of Geological Heterogeneity on the Production Performance of a Multifractured Horizontal Well in Tight Gas Reservoirs

AbstractMultifractured horizontal wells are widely used in the development of tight gas reservoirs to improve the gas production and the ultimate reservoir recovery. Based on the heterogeneity characteristics of the tight gas reservoir, the homogeneous scheme and four typical heterogeneous schemes were established to simulate the production of a multifractured horizontal well. The seepage characteristics and production performance of different schemes were compared and analyzed in detail by the analysis of streamline distribution, pressure distribution, and production data. In addition, the effects of reservoir permeability level, length of horizontal well, and fracture half-length on the gas reservoir recovery were discussed. Results show that the reservoir permeability of the unfractured areas, which are located at both ends of the multifractured horizontal well, determines the seepage ability of the reservoir matrix, showing a significant impact on the long-term gas production. High reservoir permeability level, long horizontal well length, and long fracture half-length can mitigate the negative influence of heterogeneity on the gas production. Our research can provide some guidance for the layout of multifractured horizontal wells and fracturing design in heterogeneous tight gas reservoirs.

Simulation on Effects of Injection Parameters on CO2 Enhanced Gas Recovery in a Heterogeneous Natural Gas Reservoir

AbstractCO2 enhanced gas recovery (CO2‐EGR) is a promising technology to extract additional natural gas from depleted reservoirs with storing CO2 into underground formations. This work conducted CO2‐EGR simulations in a heterogeneous gas reservoir by using isothermal and non‐isothermal models and systematically analyzed the effects of various CO2 injection parameters on natural gas recovery, CO2 storage, and their comprehensive benefits. The results indicate that the CO2 injection well should be perforated in the lower position, whose overlaid layers with low permeability hinder the upward migration of CO2, and the larger natural gas recovery and CO2 storage can be achieved simultaneously for better comprehensive benefits. The optimal injection rate is 137.29 m3·d−1 to achieve the highest recovery factor of 64.87%. The decrease in injection temperature and the increase in injection pressure are averse to the enhancement of recovery but beneficial to larger CO2 storage. The comprehensive benefits of natural gas recovery and CO2 storage are insensitive to the change of injection pressure and temperature, despite that every single one of them is more subjective to injection pressure than temperature. It's hoped that the findings of this work provide some theoretical guidance for the application of CO2‐EGR.

(Invited) Strategies for Calibration Cost Reduction in Heterogeneous Chemical Sensor Arrays

Introduction Heterogeneous gas sensor arrays coupled with machine learning algorithms have been proposed for a wide range of applications. However, inherent sensor variability degrades the performance of calibration models when directly transferred to new replicates of the original system [1]. As a result, in order to fulfill industry requirements, very often, calibration needs to be performed individually for each unit, limiting mass-deployment [2]. Recently, calibration methodologies have been proposed to reduce calibration costs and extend lifetime of the models. Briefly, these strategies make use of calibration models built for a primary system, incorporate new information to the calibration model, or take advantage of nearby units. Calibration Transfer Calibration transfer relies on a primary unit, for which a calibration model is built using a full set of calibration samples. Then, the sensor space of the secondary unit is mapped to the space of the primary unit using a set of transfer samples. Finally, using the transfer function, the calibration model built for the primary can be used with the secondary instrument. Hence, the cost reduction can be estimated from the ratio between the full set of calibration measurements and the transfer samples.Different methodologies have been proposed to obtain the transfer function, with different assumptions. For example, Single Signal Standardization assumes that the differences between units are linear, with no shifts in the signal. On the contrary, Direct Standardization (DS) constructs the mapping between all signals and can capture shifts in the signal. DS, however, may incorporate unwanted sources of variability and may face highly underdetermined systems [3]. Piecewise Direct Standardization (PDS) operates locally and can overcome the computational limitations of DS. The mentioned techniques have been tested on heterogeneous MOX gas sensor arrays [4,5]. Results showed that variations in sensor operating temperature can be corrected by means of calibration transfer techniques. Moreover, aging and sensor drift can be also alleviated with calibration transfer methods [6]. Calibration Update Calibration update, instead, enriches the calibration dataset with new calibration examples (update samples). The model incorporates the update samples using a hyperparameter that controls the weight of the new samples. It can also be combined with system regularization, in which case the regularization parameter needs to be selected for each task. The method showed successful results when applied to potentiometric chemical sensors [7,8]. Nevertheless, the regularization parameter and the weight of the new samples significantly changed between calibration updates. After some time, new samples dominate the calibration model such that the original calibration dataset contributes scarcely to the model. Although calibration update was designed to adapt the calibration model of a sensing unit affected by drift, it can also be applied to other sensing units since, after some time, any sensing unit behaves like another unit. In-the-field calibration A background mismatch between laboratory calibration and in-the-field operation may render calibration models inefficient. In-the-field calibration takes advantage of on-site reference instrumentation to perform calibration and ensure same background during calibration phase and deployment. Usually, linear models are built, which can include additional terms to account for temperature, humidity and time effects [9]. Collocation, however, requires the installation of the sensing unit next to the reference instrumentation, time during which the system is not operational.Multi-hop calibration enables node-to-node calibration such that data stream is not interrupted (see Figure). This strategy is particularly appropriate in scenarios with moving units that encounter each other regularly. It provided higher accuracy than single collocation when implemented in public vehicles equipped with electrochemical sensors [10]. However, as the number of hops increases, the resulting calibration becomes less reliable. It has been suggested that a node redundancy of about 30% can keep calibration error contained [11]. Conclusions Very different methodologies have been proposed to reduce calibration costs and increase lifetime of heterogeneous chemical systems. However, the suitability of each method depends on the sensor technology and the required task. Further benchmark is still required to elucidate the methods that provide best results and under which conditions and environments. This work provides a discussion on the calibration methodologies that aim at reducing calibration costs and encourages researchers to share datasets for the benchmark of the different calibration strategies.

(Invited) Role of Surface p-n Heterojunctions in the Gas Sensing with Smox Based Devices - Operando Studies Insights

In applications as well as in research, the majority of chemoresistive gas sensors developed for the detection of reducing gases is based on semiconducting metal oxides (SMOX), which are loaded or doped with an additional compound - typically noble or other transition metals. The introduction of these additives has proven to be the most suitable approach to overcome significant disadvantages of pristine SMOX gas sensing materials, namely the poor long-term stability, lack of selectivity, high operation temperature, i.e. energy consumption, and strong interference of humidity [1-4]. Because of their practical importance the understanding of the chemical and electrical role of additives is an essential topic of gas sensor research. The initial models, established in the 1980s [5-7], suffered because of the inability of the characterization methods to operate in conditions closed to the actual applications ones. Nevertheless, the proposed mechanisms based on solely chemical or electronic sensitization of SMOX by noble metal additives, namely the spillover or Fermi-level control sensitization mechanism, respectively, played an important role in the general advancement of the field. However, these models do not describe the complexity of the sensitization by metal or metal oxide additives, which arises from interplay of the materials reactivity and gas sensing performance and the mutual influence of surface chemistry and the electronic properties of the solid. Thus, in many cases one has to consider both, a chemical and an electronic contribution to the sensitization effect [8-10]. Besides the presence of a separate additive phase, doping, i.e. the presence of impurity atoms in the SMOX’s lattice, additionally influences the chemical and electrical properties of SMOX.Today, the development of in-situ and operando methods provides a large tool-box to probe structural, chemical and electrical properties and processes during gas sensor operation. These developments play a key role in improving the mechanistic understanding of gas sensing with loaded or doped SMOX and this contribution aims to present revised models based on reviewing and discussing current works on sensitization mechanisms in SMOX materials and to describe the complexity of sensitization mechanisms with regard to the chemical and electronic contributions [11]. A summary of findings shows that the sensitization mechanism of an additive will depend on the nature of the additive itself and the properties of the SMOX, i.e. the selection of the materials, as well as the structure of the additive, which can be controlled material synthesis or introduction procedure. In some cases, sensitization mechanisms will be additive, e.g. the introduction of additional electronic states and reactive surface sites by doping; but in other cases, one effect will dominate, e.g. electronically coupled additives, which deactivate the SMOX surface and control its space charge layer.In order to enable a knowledge-based design of SMOX gas sensing materials, it is important to obtain detailed synthesis-structure-function-relationships and concepts of selecting a combination of SMOX and additive, which allow tuning the gas sensing properties. Modern synthesis methods allow an unprecedented control of structural properties and state-of-the-art characterization techniques allow monitoring gas sensing materials under realistic operation conditions. Thus, it is possible to systematically extent synthesis-structure-function-relationships to a large set of gas sensing materials operation conditions and analytes. This will provide a profound basis to rationally design and optimize gas sensing materials based on the understanding of the fundamental mechanisms and how they are linked to the selected materials and structure. Moseley, P. T. Progress in the Development of Semiconducting Metal Oxide Gas Sensors: A Review. Meas. Sci. Technol. 2017, 28 (8), 082001.Yamazoe, N.; Sakai, G.; Shimanoe, K. Oxide Semiconductor Gas Sensors. Catal. Surv. from Asia 2003, 7 (1), 63–75. https://doi.org/10.1023/A:1023436725457.Jaaniso, R.; Tan, O. K. Semiconductor Gas Sensors; Woodhead Publishing Limited, 2013.Ihokura, K.; Watson, J. The Stannic Oxide Gas Sensor: Principles and Applications, first.; CRS Press, Inc., 1994.Yamazoe, N. New Approaches for Improving Semiconductor Gas Sensors. Sensors Actuators B Chem. 1991, 5 (1–4), 7–19. https://doi.org/10.1016/0925-4005(91)80213-4.Matsushima, S.; Teraoka, Y.; Miura, N.; Yamazoe, N. Electronic Interaction between Metal Additives and Tin Dioxide in Tin Dioxide-Based Gas Sensors. Jpn. J. Appl. Phys. 1988, 27 (10), 1798–1802. https://doi.org/10.1143/JJAP.27.1798.Morrison, S. R. Selectivity in Semiconductor Gas Sensors. Sensors and Actuators 1987, 12 (4), 425–440.Yamazoe, N.; Kurokawa, Y.; Seiyama, T. Effects of Additives on Semiconductor Gas Sensors. Sensors Actuators B Chem. 1983, 4, 283–289. https://doi.org/10.1016/0250-6874(83)85034-3.Degler, D.; Müller, S. A.; Doronkin, D. E.; Wang, D.; Grunwaldt, J.-D.; Weimar, U.; Barsan, N. Platinum Loaded Tin Dioxide: A Model System for Unravelling the Interplay between Heterogeneous Catalysis and Gas Sensing. J. Mater. Chem. A 2018, 6 (5), 2034–2046. https://doi.org/10.1039/C7TA08781K.Morrison, S. R. The Chemical Physics of Surfaces; Plenum Press, New York, 1977.D. Degler, U. Weimar, N. Barsan, Current Understanding of the Fundamental Mechanisms of Doped and Loaded Semiconducting Metal-Oxide-Based Gas Sensing Materials, ACS Sensors 4, 9 (2019) 2228-2249 DOI: 10.1021/acssensors.9b00975

Mathematical modelling of uniaxial extension of a heterogeneous gas cell wall in bread dough: Stress fields and stress concentration analysis relating to the proving and baking steps

A mathematical model was developed to increase the understanding of stress concentrations within a gas cell wall (GCW) in bread dough during baking. The GCW was composed of a single A-type wheat starch granule surrounded by various proportions of gluten typical of GCWs when about to rupture. Finite element simulations were carried out in 2D using linear viscoelasticity and visco-hyperelasticity. Strain orders of magnitude and rates relevant to dough during baking were applied as boundary conditions for two plausible sets of mechanical properties before and after protein coagulation and starch gelatinization (T < 50–60 °C and T > 70–80 °C). The average stress within the GCW was found to be strongly dependent on the starch fraction. Gluten-starch interactions influenced average stress values considerably when the starch fraction was greater than 11% v/v. The locations within the GCW where rupture was most likely to be initiated were identified by mapping maximal stress points using stress field and triaxiality analysis and the findings were discussed. • A mathematical model has been developed to better understand Gas Cell Wall rupture at the scale of bread dough constituents. • Stress fields in an extending GCW composed of a single starch granule and gluten were mapped. • Locations for rupture initiation in GCWs at strain and strain rates relevant to bread baking were identified. • The effects of gluten-starch proportion and gluten-starch interactions on stress concentration were discussed. • Gluten-starch proportion influenced average stress when the proportion was greater than 11%.

Ce-doped LaCoO3 film as a promising gas sensor for ethanol

With increasing exposure to ethanol in various scenarios, including hand sanitizers that combat bacteria and viruses, energy-efficient miniaturized sensors capable of detecting excessive concentrations of ethanol are required in the fields of disinfection and chemical storage. Modified perovskite-type oxides with ABO3 structures are particularly attractive because they can be appropriately modified and have been used in heterogeneous catalysis and gas sensors. In this study, we designed and manufactured a novel thin-film-type LaCeCoO3 gas sensor using lithography technology and precursor-solution doping. The samples exhibited morphologies that contain randomly oriented nanostructures and short rods; the particle size was observed to decrease with Ce-addition. Room-temperature gas-sensing characterization studies revealed high reproducibility for the detection of ethanol. La0.96Ce0.04CoO3 exhibited superior stability and sensitivity, with a high impedance, |Z|, of ∼120 kΩ and a Δ|Z| of up to 77%, with response and recovery times of 16 and 8 s, respectively. This study provides a rational method for the development of LaCeCoO3 as a semiconducting material for ethanol gas-sensing applications.

Experimental Study on Areal Flowing During Depletion of a High-Pressure Heterogeneous Gas Reservoir

Experimental Study on Areal Flowing During Depletion of a High-Pressure Heterogeneous Gas Reservoir