Tube Experiments Research Articles

A comprehensive kinetic modeling study of hydrogen combustion with uncertainty quantification

A 19-reactions H2 oxidation chemical kinetic model has been optimized with uncertainty quantification. The uncertainties of the reaction rate constant (RRC) parameters have been first estimated based on the recommended direct measurements and review works. This deterministic approach was further combined with the probabilistic treatment of RRC to decrease the uncertainty intervals and to extend the temperature validity range for RRCs with the highest uncertainty level, for which two quantities, discrepancy measures and uncertainty contributions, were introduced in the developed framework. Monte Carlo simulations with randomly sampled RRCs and polynomial regression were performed to develop the response surface with high coefficients of determination to be utilized in the model optimization procedure.10 key channels were selected for further optimization, and the probability density functions were calculated on the basis of discrepancy measures for 4 channels to reduce their large uncertainty intervals. The training set was collected from carefully validated measured data following experiments of shock tubes, rapid compression machines, jet stirred reactors, plug flow reactors, and premixed laminar flames. Inconsistent experimental targets were fixed and excluded from considerations. The optimized chemical kinetic model demonstrates good predicting ability for the H2 combustion experimental data from both the training set and the conditions outside the tested range (blind modeling).

Improved Exploration-Enhanced Gray Wolf Optimizer for a Mechanical Model of Braided Bicomponent Ureteral Stents

Ureteral stent tubes are important medical devices used to repair ureteral obstruction or injury. However, relevant experiments of ureteral stent tubes are usually time-consuming and expensive. This research introduces a mechanical model that can simulate the force and deformation of ureteral stents. In addition, a novel optimization algorithm called improved exploration-enhanced gray wolf optimizer (IEE-GWO) is proposed to optimize parameters of the model. In order to balance exploration and exploitation of gray wolf optimizer (GWO), a dimension learning-based hunting (DLH) search strategy and a nonlinear control parameter strategy are integrated into the IEE-GWO. The experimental results show that the proposed IEE-GWO has better performance, such as fast convergence speed and high solution quality. Furthermore, the novel approach can improve the accuracy of the mechanical modal.

Amalgamation of stress wave force balance with artificial intelligence: An alternative way of drag force measurement in supersonic flows

The present investigation demonstrates the efficacy of strain gauge and piezofilm as a potential force measurement sensor and Adaptive Neuro Fuzzy Inference System (ANFIS) as a drag force prediction strategy in an impulse test facility. A stress-wave force balance (SWFB) system incorporated with a hemispherical model was intended to measure simultaneous strain histories during shock tube-based tests. Moreover, owing to the high blockage factor during actual experiments, almost unsteady drag force is expected; thereby, dynamic calibration experiments were also performed with impulse hammer. These calibration experiments aimed to estimate the system response function for de-convolution technique and obtain optimal network parameters in the case of the artificial intelligence architecture. Subsequently, the acquired responses at 125 kHz during dynamic calibration tests and shock tube experiments are analyzed in temporal as well as in frequency domain to assess the behavior of these sensors in a short duration environment. Afterward, using the experimentally acquired strain responses, the drag force acting on the model during the experiment was estimated through the usage of de-convolution algorithm and ANFIS. An in-house solver was also used to perform the numerical simulations to predict the temporal variation of the drag force. Encouraging agreement within the uncertainty band of ± 10% was perceived during the comparative assessment of the drag force. The numerical prediction and the drag force magnitude recovered from the piezofilm and the strain gauge response were estimated to be 334 N, 354 N, and 362 N, respectively. The findings designated piezofilm as a potential sensor for short-duration force measurements. Moreover, comparative assessment of the findings of ANFIS and de-convolution technique also turned out to be an encouraging exercise, as the ability of ANFIS to predict short-duration forces was established.

Excited-State N Atoms Transform Aromatic Hydrocarbons into N-Heterocycles in Low-Temperature Plasmas.

The direct formation of N-heterocycles from aromatic hydrocarbons has been observed in nitrogen-based low-temperature plasmas; the mechanism of this unusual nitrogen-fixation reaction is the topic of this paper. We used homologous aromatic compounds to study their reaction with reactive nitrogen species (RNS) in a dielectric barrier discharge ionization (DBDI) source. Toluene (C7H8) served as a model compound to study the reaction in detail, which leads to the formation of two major products at "high" plasma voltage: a nitrogen-replacement product yielding protonated methylpyridine (C6H8N+) and a protonated nitrogen-addition (C7H8N+) product. We complemented those studies by a series of experiments probing the potential mechanism. Using a series of selected-ion flow tube experiments, we found that N+, N2+, and N4+ react with toluene to form a small abundance of the N-addition product, while N(4S) reacted with toluene cations to form a fragment ion. We created a model for the RNS in the plasma using variable electron and neutral density attachment mass spectrometry in a flowing afterglow Langmuir probe apparatus. These experiments suggested that excited-state nitrogen atoms could be responsible for the N-replacement product. Density functional theory calculations confirmed that the reaction of excited-state nitrogen N(2P) and N(2D) with toluene ions can directly form protonated methylpyridine, ejecting a carbon atom from the aromatic ring. N(2P) is responsible for this reaction in our DBDI source as it has a sufficient lifetime in the plasma and was detected by optical emission spectroscopy measurements, showing an increasing intensity of N(2P) with increasing voltage.

The modeling of two-dimensional vortex flows in a cylindrical channel using parallel calculations on a supercomputer

Objectives . The study aimed to examine vortex structures formed during the interaction of incident and reflected shock waves in a cylindrical channel. The shock wave was described by the Hugoniot relations, which make it possible to determine the parameters of the gas behind the shock front by a given Mach number and the values of the gasdynamic parameters ahead of the pressure jump. The propagation of a strong shock wave (Mach number was 20) in argon was simulated. Methods . The methods of mathematical modeling were used. A parallel algorithm for solving two-dimensional equations of gas dynamics in cylindrical coordinates (r, z, t) was developed and a new version of the NUTCY_ps program created. The calculations were performed on an MVS-100K supercomputer. Results. Two methods of parallelization when solving a system of equations were considered. Using a specific task as an example, a comparison of the effectiveness of these methods was conducted. A parallel algorithm was developed and a program was upgraded for solving two-dimensional equations of gas dynamics in cylindrical coordinates (r, z are spatial coordinates, t is time). Numerical calculations were performed to simulate: 1) the shock wave incidence to and reflection from a metal screen; 2) the propagation of the shock wave through a hole in the screen; 3) the propagation of the shock wave through a cylindrical channel and its reflection from the bottom of the channel and interaction with the incident wave. The results obtained by the parallel supercomputer with different numbers of processors are presented. It is shown that using 16 processors, it is possible to reduce the computation time for getting a solution for the test problem by approximately 12 times. Conclusions . It is shown that the interaction of incident shock wave and the one reflected at an angle leads to the formation of regions with low and high gas densities, as well as vortex flows. The vortex interaction area (turbulence zone) gets a complex shape. The article discusses the possibility of carrying out full-scale experiments in shock tubes or using a laser shock tube. Such studies would make it possible to compare experimental data with the results of numerical simulation and, on their basis, to develop more advanced models of turbulent motions.

Deep learning-based symbol detection for time-varying nonstationary channels

The highly dynamic channel (HDC) in an extremely dynamic environment mainly has fast time-varying nonstationary characteristics. In this article, we focus on the most difficult HDC case, where the channel coherence time is less than the symbol period. To this end, we propose a symbol detector based on a long short-term memory (LSTM) neural network. Taking the sampling sequence of each received symbol as the LSTM unit's input data has the advantage of making full use of received information to obtain better performance. In addition, using the basic expansion model (BEM) as the preprocessing unit significantly reduces the number of neural network parameters. Finally, the simulation part uses the highly dynamic plasma sheath channel (HDPSC) data measured from shock tube experiments. The results show that the proposed BEM-LSTM-based detector has better performance and does not require channel estimation or channel model information.

A Detailed PAH and Soot Model for Complex Fuels in CFD Applications

A model to predict soot evolution during the combustion of complex fuels is presented. On one hand, gas phase, hbox {polycyclic aromatic hydrocarbon (PAH)} and soot chemistry are kept large enough to cover all relevant processes in aero engines. On the other hand, the mechanisms are reduced as far as possible, to enable complex computational fluid dynamics (CFD) combustion simulations. This is important because all species transport equations are solved directly in the hbox {CFD}. Moreover, emphasis is placed on the applicability of the model for a variety of fuels and operating conditions without adjusting it. A kinetic scheme is derived to describe the chemical breakdown of short- and long-chain hydrocarbon fuels and even blends of them. hbox {PAHs} are the primary soot precursors which are modeled by a sectional approach. The reversibility of the interaction between different hbox {PAH} classes is achieved by the introduction of hbox {PAH} radicals. Soot particles are captured by a detailed sectional approach too, which takes a non-spherical growth of particles into account. In this way the modeling of surface processes is improved. The applicability and validity of the gas phase, hbox {PAH}, and soot model is demonstrated by a large number of shock tube experiments, as well as in atmospheric laminar sooting flames. The presented model achieves excellent results for a wide range of operating conditions and fuels. One set of model constants is used for all simulations and no case-dependent optimization is required.

Effect of secondary water body on the in-situ combustion behaviors

In-situ combustion (ISC) is an effective alternative method for the development of heavy oil reservoirs, especially in the later stage of steam injection and a large majority of high water-saturated channels have been formed during this phase. The water-saturated channels, also known as secondary water body (SWB), is regarded as a sensitive factor to the ISC performance. The effect of the SWB with different scales and locations was investigated by using combustion tube experiments. Results show that the existence of SWB is conducive to improving the propagation speed of combustion front combined with the reduction of combustion stability during the ISC process. As combustion front propagates to the SWB, the temperature is quickly decreased accompanied by an unstable propagation process, which inevitably induces the significant reduction of the O2 availability and COx emission concentration. Additionally, oversized SWB would lead to a worse combustion process with much lower COx concentration and O2 availability or even fall into an extinguishment process. Better combustion performance and oil recovery factor are obtained when SWB has large spacing to the gas injection well or exists in the lower layer. Whereas the premature O2 breakthrough and unstable fire front propagation are generated if the SWB is close to the gas injection well or forms in the upper layer. The findings of this study are significant for better understanding the ISC performance with the consideration of SWB in heavy oil reservoirs.

The Effect of Calcium Source on Pb and Cu Remediation Using Enzyme-Induced Carbonate Precipitation.

Heavy metal contamination not only causes threat to human health but also raises sustainable development concerns. The use of traditional methods to remediate heavy metal contamination is however time-consuming, and the remediation efficiency may not meet the requirements as expected. The present study conducted a series of test tube experiments to investigate the effect of calcium source on the lead and copper removals. In addition to the test tube experiments, numerical simulations were performed using Visual MINTEQ software package considering different degrees of urea hydrolysis derived from the experiments. The remediation efficiency degrades when NH4 + and OH− concentrations are not sufficient to precipitate the majority of Pb2+ and Cu2+. It also degrades when CaO turns pH into highly alkaline conditions. The numerical simulations do not take the dissolution of precipitation into account and therefore overestimate the remediation efficiency when subjected to lower Pb(NO3)2 or Cu(NO3)2 concentrations. The findings highlight the potential of applying the enzyme-induced carbonate precipitation to lead and copper remediations.

Design and analysis of monolithic integrated MEMS vector hydrophone micro-array

Based on the high sensitivity and miniaturization advantages of MEMS vector hydrophone, we proposed and designed a monolithic integrated micro-array vector hydrophone composed of multiple sensor units. The theoretical model shows that the micro-array can improve the structural sensitivity and output signal-to-noise ratio while eliminating the problem of port and starboard ambiguity. Meanwhile, the micro-array structure clearly reduces the installation error of conventional vector array and improve the directional accuracy. Taking 5-element micro-array as an example, the resonance frequency in wet mode reaches 956 Hz that meets the requirement of test frequency band. Through theoretical and computational analysis, the sensitivity of micro-array is increased 14 dB and the SNR is increased 3.1 dB compared with that of the single vector hydrophone. The standing-wave tube experiment verified the directional effect of vector micro-array. The research of vector hydrophone micro-array is helpful to the application of underwater acoustic engineering.

Measurement of the Velocity of Sound Through Resonance in Air Columns as a Homemade Experiment

In recent years, with the more powerful functions of smartphones, the use of sensors integrated by mobile phones as an auxiliary tool for physical experiment teaching has become more popular. Combined with the related mobile phone apps, people easily can develop and expand the physical experiment contents of mechanics, optics, acoustic phenomena, and so on. These experiments not only help students master the relevant laws of physics, but also permit or encourage students to carry out experimental research, greatly increase students’ interest in learning, and meet the training requirements of the Next Generation Science Standards. Recently, some experiments about measurement of speed of sound have been introduced. It is amazing and interesting that people can use simple tools to measure the speed of sound.­ This kind of experiment is very helpful to improve students’ practical ability in experiment design, data acquisition, and analysis. Inspired by the above experiments, especially the Kundt’s tube experiment, we demonstrate the acoustic resonance in an air column using a plastic tube, a mobile phone, a loudspeaker, and a tape measure. Through the resonance phenomenon of an air column, the speed of sound in air can be calculated conveniently. The experimental results are in good agreement with the reference value. This kind of homemade experiment can provide guidance for students to carry out relevant research in a non-laboratory environment.

Development of computer code and calculation of the propagation of sonic boom to the ground in a real atmosphere

One of the main problems in the development of a supersonic aircraft of the second generation is to ensure a safe level of the sonic boom impact on the environment. Achieving such level at the preliminary design stage is possible with the help of reliable methods for calculating the characteristics of the sonic boom due to impossibility of tube experiments at far field and expensiveness of real flight tests. This paper presents method for determining the shape of the overpressure signatures in the generalized form of an augmented Burgers equation for the case of disturbances propagation in a moving medium (atmosphere with wind). Based on the presented method, the computer code “vBoom” has been developed. The calculation results of the sonic boom characteristics (overpressure waveforms, the loudness in different metrics and the sonic boom carpet on the ground) are presented in comparison with the results obtained by NASA within the international seminar SBPW3 [1] (Sonic Boom Prediction Workshop).

Effect of NO 2 on ignition characteristics of methanol and chemical kinetics analysis

Based on the shock tube experiments, the influence of NO2 on the ignition characteristics of methanol fuel was systematically studied. The ignition delay time of the CH3OH/NO2/O2/Ar mixture with equivalence ratios of 0.5, 1, and 1.5 was measured at the reflected shock temperatures of 1100 ~ 1650 K and the reflected shock pressure of 0.20 MPa. The methanol–NO2 mechanism was newly constructed based on previously developed mechanisms for methanol and NO2 reaction pathways. The new combined reduced mechanism could well predict the ignition delay time of the CH3OH/NO2/O2/Ar mixture. Based on the newly constructed methanol–NO2 mechanism, the reaction path, sensitivity, and important elementary reactions of the stoichiometric mixture were analyzed, and the reasons why NO2 promoted the ignition of methanol fuel were found out: the increase of OH radicals generation and rapid accumulation in the early ignition stage enhanced the activity of the reaction system, interfered the ignition process of CH3OH/NO2/O2/Ar mixture in advance, and promoted the ignition of methanol fuel.

Controllable morphology CoFe2O4/g-C3N4 p-n heterojunction photocatalysts with built-in electric field enhance photocatalytic performance

CoFe2O4/g-C3N4 p-n heterojunction photocatalysts have been successfully synthesized. The formation of p-n heterojunction and the unique morphology of g-C3N4 enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. 5-CoFe2O4/CNS not only had a high photocatalytic hydrogen evolution rate of 18.9 mmol·g−1·h−1, but also possessed an efficient photocatalytic fluoroquinolone antibiotics removal efficiency. A smaller band gap in 5-CoFe2O4/CNS photocatalyst promoted more light generated electrons under visible light irradiation. An internal electric field at the contact interface accelerated the accumulation of electrons and holes in the valence band of g-C3N4 and conduction band of CoFe2O4, thereby revealing a higher separation efficiency and noticeable inhibited recombination rate of the photoinduced electrons and holes. Also, improved removal efficiency for fluoroquinolone antibiotics was attained in the self-designed acousto-optic microreactor, which was 7.2 and 30 times higher than quartz glass tube and batch experiment, respectively.

An Investigation of the Kinetic Modeling and Ignition Delay Time of Methanol—Syngas Fuel

The recycling of exhaust heat in internal combustion engines to dissociate the methanol, followed by its blending with methanol to produce engine fuel, is promising for improving the efficiency of engines, and reducing emissions. The kinetic model MEOHSYNGAS1.0 for the methanol–syngas fuel is proposed by reducing the detailed chemical kinetic model (Mech15.34). Shock tube experiments are conducted to measure the ignition delay time of methanol blended with dissociated methanol gas at different dissociated methanol ratios (0, 30, 50, and 100%). The model is validated by the experimental data of the present work and with data from the literature. The effects of the equivalence ratio, pressure, and dissociated methanol ratio on the ignition delay time are investigated through reaction path analysis and sensitivity analysis. When the dissociated methanol ratio does not surpass 50%, the ignition delay time increases with the increase in the dissociated methanol ratio, which is more obvious in the low temperature range, and but decreases with the increase in temperature.

Experiments and simulations on factors affecting the stereoscopic fire flooding in heavy oil reservoirs

In-situ combustion (ISC) or fire flooding (FF) technology had been widely applicated in developing heavy oil reservoirs. Due to the complex physical and chemical processes, it is not easy to guarantee the high oil recovery. For thin layer reservoirs, vertical well mode of FF can achieve good results, but for thick layer reservoirs, the vertical producing degree of FF under vertical well pattern is low. Therefore, it is necessary to deepen the basic understanding of fire flooding under different well patterns and study the influencing factors for thick heavy oil reservoir. Stereoscopic fire flooding (SFF) mode is proposed in this paper, and the one-dimensional combustion tube and differential scanning calorimetry (DSC) experiments were introduced and designed. The heavy oil samples of G block in Liaohe oilfield in China were studied and the oxidation kinetic parameters were obtained by experiments. The applicability of oil samples for fire flooding was tested. The different fire flooding modes was compared and the influencing factors of SFF were analyzed through simulations. The results indicated that the temperature of high temperature oxidation (HTO) was above 450 °C. The CO2 content of the produced gas was more than 13% and the apparent HC atomic ratio was 1.28. DSC experiments showed the activation energy of HTO stage was 1.40 × 105 J/mol. The results indicated that the heavy oil samples can reach a high temperature combustion state. The SFF mode was simulated by CMG-STARS module based on the experimental results. The simulation results showed that SFF had better performance than FF of only vertical wells in oil recovery. The important factors of SFF, such as gas-injection rate, reservoir thickness, transverse permeability, vertical permeability, crude oil viscosity, formation dip angle and relative position of horizontal wells and the applicable conditions of SFF mode were analyzed and the optimum condition for SFF mode for each influencing factor was analyzed, and the conclusions were obtained.

Numerical studies on weak and strong ignition induced by reflected shock and boundary layer interaction

In shock tube experiments, the interaction between the reflected shock and boundary layer can induce shock bifurcation and weak ignition. The weak ignition can greatly affect the ignition delay time measurement in a shock tube experiment. In this work, two-dimensional simulations considering detailed chemistry and transport are conducted to investigate the shock bifurcation and non-uniform ignition behind a reflected shock. The objectives are to interpret the formation of shock bifurcation induced by the reflected shock and boundary layer interaction and to investigate the weak ignition and its transition to strong ignition for both hydrogen and dimethyl ether. It is found that the non-uniform reflection of the incident shock at the end wall produces a wedge-shaped oblique shock foot at the wall. The wedge-shaped structure results in strong interactions between reflected shock and boundary layer, which induces the shock bifurcation. It is demonstrated that the local high-temperature spots at the foot of the bifurcated shock is caused by viscous dissipation and pressure work. As the post-reflected shock temperature increases, the transition from weak ignition to strong ignition in a stoichiometric hydrogen/oxygen mixture is observed. The relative sensitivity of ignition delay time to the post-reflected shock temperature is introduced to characterize the appearance of weak ignition behind the reflected shock. Unlike in the hydrogen/oxygen mixture, weak ignition is not observed in the stoichiometric dimethylether/oxygen mixture since it has a relatively longer ignition delay time and smaller relative sensitivity.

Sensitivity Analysis of Thermochemical Kinetics Modeling for Hypersonic Air Flows

A computational analysis is used to model Mach 5 and Mach 7 flows over a cylinder, where freestream properties are representative of experiments to be conducted in the Hypervelocity Expansion Tube at the California Institute of Technology. A sensitivity analysis is conducted using the polynomial chaos expansion method, and Sobol indices are used to determine which thermochemical nonequilibrium phenomena most affect various quantities of interest. The results show that the dissociation of molecular oxygen through interaction with molecular nitrogen and with atomic oxygen reactions dominates the determination of surface pressure, surface heat transfer, drag, heating rate, and rotational temperature, whereas the first two Zeldovich reactions dominate the surface number density of NO. The reaction is found to be less important than other reactions. Surface pressure and drag are also shown to be relatively insensitive overall. The results also indicate flow separation and recirculation near the trailing edge of the cylinder. These findings may help diagnostic developments to lower discrepancies between computation and experiments, and indicate that the Hypervelocity Expansion Tube experiments should be successful for the future evaluation of thermochemistry modeling.

Higher criteria for the regularity of a one-dimensional local field

A coupled problem of gasdynamics, vibrational relaxation, and dissociation in the flow of oxygen behind reflected shock waves is studied. The detailed state-to-state kinetic approach is used, which is based on a coupled solution of the momentum and energy conservation equations with the balance equations for molecular vibrational state populations and concentrations of oxygen atoms. Initial conditions corresponding to recent experiments in shock tubes are considered. For different models of physicochemical processes, a comparison is made with experimental data; varying the model parameters yields satisfactory agreement of all gas-dynamic parameters with the measured ones. The key feature of the proposed approach is the allowance for partial vibrational-chemical relaxation in the time interval between the incident and reflected shock waves. When relaxation between the shocks is not frozen, the reflected shock wave propagates through a vibrationally nonequilibrium gas, which significantly affects kinetics and gas dynamics. Accounting for partial relaxation ensures good agreement between the pressure calculated behind the front of the reflected shock wave and the pressure measured in the experiment. On the other hand, comparison with the vibrational temperature calculated indirectly from spectroscopic experimental data under the assumption of frozen relaxation shows noticeable differences near the shock wave front. We conclude that the technique for extracting gas-dynamic parameters fromspectroscopic data has to be improved by taking into account vibrational excitation before the reflected shock wave.

Acoustics Performance Research and Analysis of Light Timber Construction Wall Elements Based on Helmholtz Metasurface

Based on the efficient sound absorption characteristics of Helmholtz resonance structures in the range of medium and low frequency acoustic waves, this paper investigates an effective solution for light timber construction walls with acoustic problems. This study takes the light timber construction wall structure as the research object. Based on the Helmholtz resonance principle, the structure design of the wall unit, impedance tube experiment and COMSOL MULTIPHYSICS simulation calculation were carried out to obtain the change rule of acoustic performance of the Helmholtz resonance wall unit structure. The research results show that the overall stability of sound insulation of the structure is improved, and the frequency range with sound transmission loss more than 50 dB in the experimental group is 640–1600 Hz, while in the control group is 500–906 Hz and 1238–1600 Hz; the sound absorption performance of the structure is obviously better than that of the ordinary structure, especially in the low frequency acoustic wave range of 100–320 Hz, the sound absorption coefficient of the experimental group is more than 0.49, while the sound absorption coefficient of the control group is less than 0.1. It is expected that these results will contribute to the optimization of the acoustic performance of light timber construction walls and have high application and popularization value.