Constant Pressure Method Research Articles

Development of microfluidic chip flowmeter-based constant pressure system for analysing the hydrogen adsorption performance of non-evaporable getters

BackgroundAs one of the primary residual gases in vacuum, hydrogen affects the performance of MEMS devices. It commonly uses a non-evaporable getter (NEG) to adsorb hydrogen in this case. One of the standard test methods for NEG is the constant pressure method. However, most constant pressure test systems control the intake flow by valves or small orifices. These methods are crude and limit the reliability of the result. Therefore, it is necessary to provide a stable intake flow method for the constant pressure test system to improve the accuracy of the test. ResultsWe demonstrate a constant pressure system based on the microfluidic chip flowmeter to evaluate the hydrogen adsorption performance of non-evaporable getters in this paper. The microfluidic chip features microchannels with a height of around 100 nm. It is encapsulated with standard tube fittings, with leakage of less than 1 × 10−13 Pa ∙ m3∙ s−1. The conductance of the flowmeter is 10−12 m3∙ s−1, and the upper-pressure limit of the molecular flow is 105 Pa. It can control the intake flow of the adapted constant pressure test system from 10−11 to 10−7 Pa ∙ m3∙ s−1. Using this system, we tested the hydrogen adsorption capability of the Zr–Fe getter at different working pressures/temperatures and the types of gas it adsorbs were analysed. The results showed that the adsorbent has a noticeable adsorption effect on H2 and a partial adsorption effect on H2O, CO and CO2. SignificanceThe microfluidic chip flowmeter can provide a stable intake molecular flow for the adapted constant pressure test system. It ensures the reliability of the measurement results. The ability of the flowmeter to offer tiny flow rates at 105 Pa can drastically simplify the test system and is more user-friendly for getters tests with poor adsorption performance. It has positive significance for industrial research on the non-evaporable getter.

Investigation on improvement potential of steam ejector performance in refrigeration cycle via constant rate of momentum change design method

In this paper, an ejector created by the constant rate of the momentum change method (CRMC ejector) was experimentally studied and compared with the widely used constant pressure method (CPM ejector) under the same ejector area ratio. The influence of the boiler temperature, evaporator temperature, and primary nozzle size on the ability to improve the performance of the CRMC ejector was examined. The results indicated that at the same ejector area ratio, the CRMC ejector always performed a higher mass entrainment ratio than the CPM ejector. However, the critical condenser pressure was similar. The average percent improvement of the entrainment ratio via the CRMC ejector was approximately 20%. Based on the photograph taken from the transparent ejector, a compression shock wave was still found in the flow process of the CRMC ejector. This shows that an improvement potential of the CRMC ejector does not concern the compression shock wave as proposed in the design theory. The key to improvement was believed to be its ability to mitigate the momentum loss during the mixing process. In such a case, some simulation works based on computational fluid dynamics (CFD) were employed for explanation. This can also confirm that the compression shock wave via CRMC ejector is still found. In addition, this paper compared the experimental results with the theoretical results obtained from 1-D theory and CRMC theory to alternatively discuss that an improvement potential of the CRMC ejector was mainly the cause of a lower mixing loss.

Influence of Barrier Layers on ZrCoCe Getter Film Performance.

Improving the vacuum degree inside the vacuum device is vital to the performance and lifespan of the vacuum device. The influence of the Ti and ZrCoCe barrier layers on the performance of ZrCoCe getter films, including sorption performance, anti-vibration performance, and binding force between the ZrCoCe getter film and the Ge substrate were investigated. In this study, the Ti and ZrCoCe barrier layers were deposited between the ZrCoCe getter films and Ge substrates. The microtopographies of barrier layers and the ZrCoCe getter film were analyzed using scanning electron microscopes. The sorption performance was evaluated using the constant-pressure method. The surface roughness of the barrier layers and the getter films was analyzed via atomic force microscopy. The binding force was measured using a nanoscratch tester. The anti-vibration performance was examined using a vibration test bench. The characterization results revealed that the Ti barrier layer significantly improved the sorption performance of the ZrCoCe getter film. When the barrier material was changed from ZrCoCe to Ti, the initial sorption speed of the ZrCoCe getter film increased from 141 to 176 cm3·s-1·cm-2, and the sorption quantity increased from 223 to 289 Pa·cm3·cm-2 in 2 h. The binding force between the Ge substrate and the ZrCoCe getter film with the Ti barrier layer was 171 mN, whereas that with the ZrCoCe barrier layer was 154 mN. The results showed that the Ti barrier layer significantly enhanced the sorption performance and binding force between the ZrCoCe getter film and the Ge substrate, which improved the internal vacuum level and the stability of the microelectromechanical system vacuum devices.

Influence of flight mode on loads from turbulent air

This paper investigated the influence of altitude and flight speed on the loads arising on the elastic wing of a turbojet aircraft of conventional layout, which falls into turbulent conditions. The aircraft structure is modeled by elastic beams with appropriate weight and stiffness distribution. Performed a modal analysis of the aircraft design and examined the influence of the number of calculated tones own oscillations on the loading of an aircraft wing. Aerodynamic forces and moments are determined by the dipole lattice and constant pressure method (DLM/CPM). Non-stationary characteristics are also taken into account, as required by certification specification. Determining the effect of flight speed showed the need to consider both the minimum and maximum speeds, because at minimum speed the end zone of the wing is loaded more, and at the cruise speed ‒ the root section. When analyzing the effect of flight altitude on the load, determined that the maximum values of transverse force and bending moment occur when flying at minimum altitude, and the torque on the wing reaches the maximum value at altitudes with the maximum Mach number. Separately highlighted loads of aircraft wing at horizontal balanced flight. Also showed that the speed of flight, namely the Mach number, significantly affects the torque that occurs on the wing.

Laminar burning characteristics of bio-aviation fuel candidate derived from lignocellulosic biomass

This study investigated the laminar burning characteristics of bio-aviation fuel candidate produced from corn stover lignin via catalytic hydrodeoxygenation (HDO). The experiments were conducted at equivalence ratios of 0.7–1.4, initial pressures of 1 bar, 2 bar, and 4 bar, and initial temperatures of 443 K and 473 K. The laminar burning velocity (LBV), explosion pressure, maximum pressure-rise rate, and combustion duration were studied. The LBV was studied using the constant volume (CVM) and constant pressure (CPM) methods. The CVM results were significantly higher than that of CPM in the presence of cellular flame. In other cases, the deviations of both were within 10 %. The analysis indicated that the LBV of the bio-aviation fuel candidate at certain equivalence ratios was lower than that of Jet A-1, RP-3, and n-decane. However, the LBV of the bio-aviation fuel candidate was greater than that of n-decane in fuel rich mixtures. A 12-term power-law correlation was determined to quantify the relationship between the LBV of the bio-aviation fuel candidate and the equivalence ratio, initial temperature, and initial pressure. The maximum deviation between the experimental data and the correlation was 11.85 %, and the average deviation was 2.95 %. Finally, the effects of the initial conditions on the explosion characteristics of the bio-aviation fuel candidate were analyzed. The explosion pressure, maximum pressure-rise rate, and deflagration index were linearly and positively correlated with the initial pressure; however, the latter two were insensitive to the initial temperature. Furthermore, a quantitative correlation between the explosion characteristics and the equivalence ratio and initial pressure was determined.

Evaluation of the effectiveness of poly (phenyl sulfone) / nanoclay mixed matrix membranes for carbon dioxide/methane separation

Poly (phenyl sulfone) (PPSU) is a recently introduced poly (aryl sulfone) polymer that has attracted much attention for membrane fabrication. PPSU could fabricate both porous and non-porous membranes. Intrinsic gas permeability of pure PPSU is low, but it has good selectivity for CO2/CH4 separation. Therefore, this study aimed to investigate the effect of adding a layered nanoclay material to PPSU on CO2 permeability and CO2/CH4 selectivity. The fabricated membranes were characterized by FTIR, FESEM, XRD, DSC, EDS, Contact angle, gas solubility, and gas permeability. The permeability of each gas was measured by the constant volume-variable pressure method, and ideal selectivity was determined. The effect of nanoclay loading (1-3 wt.%) and feed pressure (2-8 bar) on the gases' permeability and CO2/CH4 selectivity was investigated at a constant temperature of 27 ± 2°C. The results showed that the addition of the nanoclay to PPSU has a considerable effect on CO2 permeability (up to 52% increase) while CO2/CH4 selectivity remains nearly unchanged or slightly decreases (down to 6%). Solubility measurement results revealed that adding the nanoclay to the PPSU polymer increases the solubility selectivity by 22%, while the diffusivity selectivity is decreased by 23%, revealing the formation of an intercalated morphology, confirmed by XRD analysis.

Synthesis, characterization, and gas separation properties of novel fluorinated co-polyimides with bulky side groups

A series of random 6FDA-MFPAP/BAMF co-polyimides with different MFPAP:BAMF molar ratios (2:1, 1:1, 1:2, and 1:3) were synthesized from a novel diamine, 4-(3-methoxy-4-(difluoromethoxy)-phenyl)-2,6-bis(4-aminophenyl)pyridine (MFPAP); a commercial fluorene diamine (BAMF); and a dianhydride, 4,4'-(hexafluoroiso-propyl)diphthalic anhydride (6FDA). The prepared co-polyimides exhibited outstanding thermal performances ( T g > 345 °C, T d > 509 °C), good optical properties (λ cut-off > 342 nm, λ 80% > 410 nm), and hydrophobic properties (contact angle >91.8°). They also showed excellent solubility in both high and low boiling point organic solvents. The pure gas (He, CO 2 , O 2, and N 2 ) permeability of the co-polyimide membranes was measured using the constant volume-variable pressure method. The gas permeabilities of the membranes were superior to those of the commercial Kapton, Matrimid and P84, where the He permeability coefficient of 6FDA-MFPAP/BAMF (2:1) was 55.39 barrer. This can be reasonably explained and supported by the fractional free volume and molecular chain spacing of the polyimides. In addition, the gas transport performances of the copolymers have significantly improved over their corresponding homopolymers (6FDA-MFPAP and 6FDA-BAMF). And the 6FDA-MFPAP/BAMF co-polyimides with 2:1 and 1:1 M ratios of MFPAP/BAMF had the best gas separation performance for the gas pairs He/CO 2 and O 2 /N 2 , respectively, which was close to the Robeson upper limit in 1991. A series of containing bulky side group novel fluorinated co-polyimides with outstanding thermal performances, excellent solubilities, good optical properties, and hydrophobic properties were synthesized based on a novel diamine MFPAP, fluorene diamine BAMF and dianhydride 6FDA, they exhibit good gas separation properties and show the potential of application in gas separation field. • A series of novel fluorinated co-polyimides with bulky were designed and synthesized. • Polymers exhibited excellent soluble, thermal, optical and hydrophobic properties. • Diamine MFPAP effectively modulate the FFV and gas transport performance of PIs. • Gas transport performance of MFPAP/BAMF (1:1) and (2:1) PIs are closest to the 1991 upper bond.

Step-by-step CO2 injection pressure for enhanced coal seam gas recovery: A laboratory study

With the objective of achieving an ‘emission peak and carbon neutrality’, the injection of CO2 into deep unmineable coal seams or abandoned mines can enhance the methane recovery from coalbeds and can realise CO2 geological sequestration. Traditionally, Constant CO2 injection pressure method（Const-CO2） is expensive and low injection capacity of coal seam. Therefore, this study proposes an SBS-CO2 method that steps the CO2 injection pressure. The results revealed that compared with const-CO2 method, the total recovery rate of CH4 was increased by 9.148% by SBS-CO2 method, with the largest increase (7.933%) in the stage II. The injection-production ratio of SBS-CO2 injection method was always smaller than Const-CO2. At the stage I, CO2 injected amount was reduced by 9.54%. CO2 injection amount of unit mass coal was reduced by 1.211 mL/g. The lower the injection pressure was, the higher was the permeability. In the proposed method, each pressurisation was followed by a temporary recovery in permeability, and the critical CO2 injection time of 140.83 min. The SBS-CO2 injection method can effectively improve the recovery efficiency of coalbed methane and CO2 injection efficiency, greatly reduce the risk of CO2 consumption and outburst, and significantly reduce the injection and time cost.

Nanoindentation creep testing: Advantages and limitations of the constant contact pressure method

Different loading protocols have been developed in the past to investigate the creep properties of materials using instrumented indentation testing technique. Recently, a new indentation creep method was presented, in which the contact pressure is kept constant during the creep test segment, similar to the constant stress applied in a uniaxial creep experiment. In this study, the results of constant contact pressure creep tests are compared to uniaxial and constant load hold indentation creep experiments on ultrafine grained Cu and CuAl5. The constant contact pressure method yields similar stress exponents as the uniaxial tests, down to indentation strain rates of 10–6 s−1, whereas the constant load hold method results mainly in a relaxation of the material at decreasing applied pressures. Furthermore, a pronounced change in the power law exponent at large stress reductions is found for both uniaxial and constant contact pressure tests, indicating a change in deformation mechanism of ultrafine grained metals.Graphical abstract

Hydrogen absorption performance and mechanism of low-temperature activated Ti-Co-Ce bulk getter

In this paper, a new type of non-evaporable low-temperature activated Ti-Co-Ce bulk getter was prepared. The phase structure, morphology and composition of this getter were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques, respectively. Under the activation condition of 350 °C for 30 min, its hydrogen absorption performance at room temperature was measured through the constant pressure method. The initial hydrogen pumping speed and cumulative absorption capacity within 2 h of Ti80Co15Ce5 (in the following, all alloy compositions, unless otherwise stated, are composition by weight) getter are 2700 ml/s·g and 4000 Pa·ml/g, respectively, which are more than twice those of Zr80.8Co14.2Ce5 (Zr-Co-Ce) and even greater than those of Zr70V24.6Fe5.4 (Zr-V-Fe) under the same preparation, activation and measurement conditions. XRD analysis shows that Ti-Co-Ce getter is mainly composed of (α-Ti) solid solution and Ti2Co intermetallic compound two phases. (α-Ti) instead of Ti2Co plays a more important role in hydrogen absorption. The hydrogen absorption performance of Ti-Co (Ti70.9Co29.1) getter even without rare earth addition is superior to Zr-Co-Ce, single Ti2Co or α-Ti phase. Measured by the constant volume method, the saturated hydrogen absorption capacity of 0.6 g Ti80Co15Ce5 is 143.6 Torr·L or 15.5 mg H2, higher than that of Zr-Co-Ce, intermetallic compounds Zr3Co and Ti2Co.

Application of fluorescent dextrans to the brain surface under constant pressure reveals AQP4-independent solute uptake.

Extracellular solutes in the central nervous system are exchanged between the interstitial fluid, the perivascular compartment, and the cerebrospinal fluid (CSF). The "glymphatic" mechanism proposes that the astrocyte water channel aquaporin-4 (AQP4) is a major determinant of solute transport between the CSF and the interstitial space; however, this is controversial in part because of wide variance in experimental data on interstitial uptake of cisternally injected solutes. Here, we investigated the determinants of solute uptake in brain parenchyma following cisternal injection and reexamined the role of AQP4 using a novel constant-pressure method. In mice, increased cisternal injection rate, which modestly increased intracranial pressure, remarkably increased solute dispersion in the subarachnoid space and uptake in the cortical perivascular compartment. To investigate the role of AQP4 in the absence of confounding variations in pressure and CSF solute concentration over time and space, solutes were applied directly onto the brain surface after durotomy under constant external pressure. Pressure elevation increased solute penetration into the perivascular compartment but had little effect on parenchymal solute uptake. Solute penetration and uptake did not differ significantly between wild-type and AQP4 knockout mice. Our results offer an explanation for the variability in cisternal injection studies and indicate AQP4-independent solute transfer from the CSF to the interstitial space in mouse brain.

Investigations on laminar premixed flame characteristics of ethyl acetate

Ethyl acetate (EtOAc) has the potential as an alternative fuel or fuel additive in internal combustion engines (ICEs). Therefore, it is important to have a good understanding of its combustion characteristics. In this regard, this study investigated the burning characteristics of EtOAc at the initial temperature of 358–418 K and the initial pressure of 1–4 bar over a wide range of equivalence ratio (0.8–1.4) using experimental and numerical analysis. The burning velocity of EtOAc was measured using the constant pressure method (CPM) and constant volume method (CVM) of the spherically expanding flame (SEF) method. The linear approximation and analytical two-zone burned mass fraction correlation were used to determine the burning velocity in the CVM analysis. Generally, the linear approximation burning velocity was almost 11% higher than the analytical two-zone burning velocity. The difference between the CVM and CPM burning velocity was nearly 24%. Laminar burning velocity at an elevated pressure of 11.2 bar was obtained using the CVM analysis. Finally, the experimental and theoretical Markstein length and number of EtOAc were also investigated and discussed.

Effect of new metal–organic framework (zeolitic imidazolate framework [ZIF-12]) in mixed matrix membranes on structure, morphology, and gas separation properties

Abstract In our study, the synthesis of zeolitic imidazolate framework (ZIF-12) crystals and the preparation of mixed matrix membranes (MMMs) with various ZIF-12 loadings were targeted. The characterization of ZIF-12 and MMMs were carried out by Fourier transform infrared spectroscopy analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and thermomechanical analysis. The performance of MMMs was measured by the ability of binary gas separation. Commercial polyetherimide (PEI-Ultem® 1000) polymer was used as the polymer matrix. The solution casting method was utilized to obtain dense MMMs. In the SEM images of ZIF-12 particles, the particles with a rhombic dodecahedron structure were identified. From SEM images, it was observed that the distribution of ZIF-12 particles in the MMMs was homogeneous and no agglomeration was present. Gas permeability experiments of MMMs were measured for H2, CO2, and CH4 gases at steady state, at 4 bar and 35 °C by constant volume-variable pressure method. PEI/ZIF-12-30 wt% MMM exhibited high permeability and ideal selectivity values for H2/CH4 and CO2/CH4 were P H 2 / CH 4 = 331.41 ${P}_{{\text{H}}_{2}/{\text{CH}}_{4}}=331.41$ and P CO 2 / CH 4 = 53.75 ${P}_{{\text{CO}}_{2}/{\text{CH}}_{4}}=53.75$ gas pair.

Cellularization characteristics of ethyl acetate spherical expanding flame

The cellular instability of ethyl acetate (EA) premixed flame has been studied theoretically and experimentally under different initial temperature, pressure and equivalence ratio. The constant pressure method (CPM) was used to determine the laminar burning velocity of EA spherical expanding flame in this research. In addition, the cellular evolution image of EA spherical expansion flame surface was obtained using high-speed schlieren technology. The image processing technology combined with three-dimensional reconstruction algorithm was used to extract and reconstruct the flame surface crack length, the number of cells on the flame surface, cellular area and cellular length scale. From the quantitative analysis of surface crack and cellular structure of EA flame, it can be seen that the evolution of flame surface crack and surface cellular structure is largely affected by equivalence ratio and initial pressure. With the increase of initial pressure or equivalence ratio, the earlier the flame surface cracks and cell formation. Furthermore, according to the cellular length scale in different radius, the wavenumber was deduced, and compared with the theoretical curve, it is found that the experimental wave numbers have the same evolution trend. Although, when the equivalence ratio is 1.4 with high Peclet number, the experimental wave numbers are somewhat beyond the boundary of the peninsula curve due to the influence of the nonlinear effects, the trend is consistent with the theoretical results.

Accelerating Laminar Flame Speed of Hydrous Ethanol via Oxygen-Rich Combustion

To investigate the laminar flame characteristics of hydrous ethanol, experiments were conducted in a constant volume combustion chamber. The laminar burning velocity and Markstein length of ethanol with water content from 0 to 20% by volume were measured over a wide range of equivalence ratios from 0.7 to 1.4 under the initial condition of 388 K and 0.1 MPa. Calculations of the laminar burning velocity with the constant pressure method (CPM) and constant volume method (CVM) were compared and discussed. Apart from experiments, numerical studies were carried out in CHEMKIN based on the Marinov’s and Olm’s ethanol oxidation mechanism. Moreover, the combustion of hydrous ethanol with 20% water by volume in oxygen-enriched air (O2 = 23% by volume) was also studied. Results indicated that the overall trends of laminar burning velocity versus the equivalent ratio were basically consistent between the experiment and the simulation, but the results obtained by CVM were larger than those obtained by CPM and closer to the simulation results. The peak value of laminar burning velocity decreased from 0.638 to 0.591 m/s when the water content increased from 0 to 20% in CVM calculation, but the peak laminar burning velocity of hydrous ethanol with 20% water in oxygen-enriched air enhanced to 0.771 m/s, meaning that the oxygen-enriched air can effectively offset the negative impacts of water. Moreover, the Markstein length of hydrous ethanol decreases with increasing equivalence ratios.

Combined isochoric and isobaric acquisition methodology for accurate flame speed measurements from ambient to high pressures and temperatures

The present paper addresses measurement techniques of the most important fundamental property of a combustible mixture, the laminar flame speed. The accurate determination of this parameter has been investigated carefully using two different approaches: the constant pressure method based on the flame front trajectory obtained by means of a Schlieren optical technique, and the constant volume method based only on the pressure-time history recorded during the combustion process. Methane/air flames are selected, because they are relevant for many technical applications and believed to be well understood. Measurements were performed using two high-pressure, high-temperature constant volume vessels at RWTH and ICARE. First, uncertainties stemming from experiments are quantified, and the different sources of errors are identified. Second, the assumption that the unburned gas is compressed isentropically due to the burned gas expansion is verified experimentally for the first time to the authors’ knowledge. More importantly, it was found that combining the two approaches can provide high-fidelity data w.r.t. stretch, radiative heat loss, and instabilities. The data will be very helpful for mechanism development and combustion modeling. Ideally, both approaches are applied simultaneously in the same vessel to obtain a high confidence level in the measured data. Finally, a methodology is proposed to provide flame speeds over a wide range of pressures and temperatures up to 14 bars and 620 K, close to engine-relevant conditions.

Experimental, algorithmic, and theoretical analyses for selecting an optimal laboratory method to evaluate working fluid damage in coal bed methane reservoirs

The existing laboratory methods have limitations that make it very difficult to select the most suitable method for obtaining precise permeability measurements for evaluating reservoir formation damage. To date, there has been no research critically addressing this issue. In this study, the permeabilities of core or cuttings samples taken from No.15 Reservoir in the Qinshui Basin before and after damage caused by drilling and fracturing fluids were randomly measured using six general laboratory methods. Their average permeability values, as well as the extent of absolute and relative formation damage, were calculated and analyzed using a simple ranking method, statistical screening algorithm, and theoretical method. The results show that, first, there is a regular distribution of absolute reservoir damage measured by the laboratory methods; and second, the application priority of permeability measurement methods for formation damage evaluation in coal bed methane reservoirs is as follows: cuttings pulse decay method > constant flow rate method > nuclear magnetic resonance method > plunger pulse decay method = pressure oscillation method = constant pressure method. The cuttings pulse decay method is therefore recommended for measuring core matrix damage, while the constant flow rate method is suggested for measuring overall damage to core samples.

Effect of CO2 Dilution on the Laminar Burning Velocities of Premixed Methane/Air Flames at Elevated Temperature

Abstract With increased interest in reducing emissions, the staged combustion concept for gas turbine combustors is gaining in popularity. For this work, the effect of CO2 dilution on laminar burning velocities of premixed methane/air flames was investigated at elevated temperature through both experiments and numerical simulations. Validation of the experimental setup and methodology was completed through experimental testing of methane/air mixtures at 1 bar and 298 K. Following validation, high temperature experiments were conducted in an optically accessible constant volume combustion chamber at 1 bar and 473 K. Laminar burning velocities of premixed methane/air flames with 0%, 5%, 10%, and 15% CO2 dilution were determined using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front. Results show that laminar burning velocities of methane/air mixtures at 1 bar increase by 106–145% with initial temperature increases from 298 K to 473 K. Additions of 5%, 10%, and 15% CO2 dilution at 1 bar and 473 K cause a 30–35%, 51–54%, and 66–68% decrease in the laminar burning velocity, respectively. Numerical results were obtained with CHEMKIN (Kee et al., 1985, “PREMIX: A Fortran Program for Modeling Steady Laminar One-Dimensional Premixed Flames,”) using the GRI-Mech 3.0 (Smith et al., 2019) and the San Diego (“Chemical-Kinetic Mechanisms for Combustion Applications,” San Diego Mechanism Web Page, Mechanical and Aerospace Engineering (Combustion Research), University of California at San Diego, San Diego, CA) mechanisms. It is concluded that the GRI-Mech 3.0 (Smith et al.., 2019) better captures the general overall trend of the experimental laminar flame speeds of methane/air/CO2 mixtures at 1 bar and 473 K. Additionally, the dilution, thermal-diffusion, and chemical effects of CO2 on the laminar burning velocities of methane/air mixtures were investigated numerically by diluting the mixtures with both chemically active and inactive CO2 following the determination of the most important elementary reactions on the burning rate through sensitivity analysis. Finally, it was shown that CO2 dilution suppresses the flame instabilities during combustion, which is attributable to the increase in the burned gas Markstein length (Lb) with the addition of diluent.

Investigating CO[formula omitted], O[formula omitted] and N[formula omitted] permeation properties of two new types of nanocomposite membranes: Polyurethane/silica and polyesterurethane/silica

The current study presents a synthesis method of two new types of polyurethane-based nanocomposite membranes: polyurethane/silica and polyesterurethane/silica. The main difference between the membranes is the type of the polyol used in the synthesis of their polymers. The polymers were synthesized via two-step polymerization and then the polymeric membranes were prepared by solution casting-solvent evaporation. To prepare the nanocomposite membranes, silica nanoparticles were loaded into polyurethane matrices with different contents (5, 10, and 15 wt. %). In order to evaluate the chemical bond variations, glass transitions, crystalline structure and morphology of the membranes, the prepared membranes were characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM), respectively. Permeation properties of pure gases CO2, O2 and N2 through all the membranes were measured using a constant pressure method at different pressures (6, 8, and 10 bar) and temperatures (25, 35, and 45 °C). Acquired results of permeation experiments show that increasing of silica nanoparticles loading in matrices of both membrane types, decreases gases permeability values but increases ideal CO2/N2 and O2/N2 selectivity values. The results also revealed that the PU400-based nanocomposite membranes have higher performance for CO2/N2 separation, while the PU100-based nanocomposite membranes exhibit higher performance for O2/N2 separation.

Methods of determination of aerodynamic loads at flight in continuous turbulence

This paper investigates the loads which acting on the elastic high aspect ratio wing of a cargo aircraft flying in continuous turbulence. According to the requirements of CS-25, gusts that are normal to the flight path and uniform at spanwise are considered. Random gusts at continuous turbulence are described by the spectral density (PSD) of gusts suggested by Karman.The simulation of the flow around the calculated model aircraft are performed by the methods of computational aerodynamics: dipole lattice method (DLM), high order panel method (Panel), dipole lattice and constant pressure method (DLM/CPM), vortex frame method (VFM). Flow is accepted as quasi-stationary or non-stationary. The elastic mass model of the aircraft is described by beam. The discrepancies between the results of the load calculations from the continuous turbulence on the aircraft elastic wing are determined.The results show that taking into account the effects of non-stationary aerodynamics results in somewhat lower values of loads on the aircraft structure: up to 2% in the root sections of the wing and up to 5% in the end sections. The largest difference is observed using the dipole lattice method and the smallest one is in the panel method. The magnitude of the load increase from turbulence is almost the same for all the considered methods. Its main difference is observed when determining loads in horizontal flight, where the lowest values are obtained when using DLM / CPM.The main results are presented in graphical and tabular form.