Gasdynamic Analysis Research Articles

Reinforced Membranes with PTFE Matrix and Sulfonated Hydrocarbon Electrolyte for PEM Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have emerged as a promising technology for clean energy conversion with various potential applications. Due to its cost-effectiveness, sulfonated hydrocarbon has been researched as an alternative to Nafion, a commercial proton exchange membrane. However, sulfonated hydrocarbon's mechanical and chemical stability remains a critical challenge that needs to be addressed, as the membrane must withstand harsh operating conditions, such as wet-dry mechanisms in high-temperature operations. To compete with perfluorosulfonic acid (PFSA), sulfonated hydrocarbon should be reinforced with a polytetrafluoroethylene (PTFE) substrate. However, there are significant issues with incompatibility between sulfonated hydrocarbon and PTFE substrate.To improve the impregnation, simple and reproducible chemical treatment has been developed to enhance the hydrophilicity of PTFE using a mixture of acids and oxidizing agents. Moreover, surfactant was added to increase compatibility and improve impregnation. After the reinforced membrane was fabricated, the membranes were characterized, including their water uptake and dimensional stability. The reinforced membrane also showed superior mechanical properties, including gas permeability, tensile strength, and dynamic mechanical analysis. To evaluate the degree of impregnation, the transparency of the reinforced membrane was checked for haziness and further analyzed with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping to quantify the impregnation degree. Finally, the performance and durability of the reinforced membrane were measured by single-cell and wet-dry cycling tests.

3D numerical study of neutral gas dynamics in the DTT particle exhaust using the DSMC method

Recently the design of the divertor tokamak test (DTT) Facility divertor has been modified and consolidated. The new divertor design presents significant geometrical differences compared to the previous ITER-like one, including the presence of a more flattened dome shape. This paper presents a complete 3D numerical analysis of the neutral gas dynamics inside the DTT subdivertor area for the latest divertor design. The analysis has been performed based on the direct simulation Monte Carlo method by applying the DIVGAS simulator code. SOLEDGE2D-EIRENE plasma simulations have been performed for a deuterium plasma scenario at the maximum additional power in partially detached condition achieved by neon impurity seeding and the extracted information about the neutral particles has been imposed as incoming boundary conditions. The pumping efficiency of the DTT divertor is examined by considering various cases with respect to the pumping probability and the effect of the toroidal and poloidal leakages is quantified. The results show that a significant percentage of the incoming flux of neutrals returns back to the plasma site through the entry gaps (60% for deuterium and 40% for neon), and, consequentially, only a small percentage (∼2%–15%) of the incoming flux can be pumped out from the system. The toroidal leakages affect significantly the pumping performance of the divertor causing a significant decrease in the pumped flux (and also in the pressure at the pumping opening) about 37%–47% and 43%–56% for deuterium and neon respectively. It is discussed how many pumping ports are needed depending on the achievable pumping performance per port. The number can be reduced by closing the toroidal gaps. The analysis shows that enlarging the poloidal gaps by a factor of two causes a significant increase in the poloidal flux losses by a factor 1.7. It is also illustrated how the presence of the cooling pipes leads to conductance losses.

Monitoring and Characterization of Gas Migration in Oil-Based Mud Using Fiber-Optic DAS and DTS

Summary Understanding gas dynamics in mud is essential for planning well control operations, improving the reliability of riser gas handling procedures, and optimizing drilling techniques, such as the pressurized mud cap drilling (PMCD) method. However, gas rise behavior in mud is not fully understood due to the inability to create an experimental setup that approximates gas migration at full-scale annular conditions. As a result, there is a discrepancy between the gas migration velocities observed in the field as compared to analytical estimates. This study bridges this gap by using distributed fiber-optic sensors (DFOS) for in-situ monitoring and analysis of gas dynamics in mud at the well scale. DFOS offers a paradigm shift for monitoring applications by providing real-time measurements along the entire length of the installed fiber at high spatial and temporal resolution. Thus, it can enable in-situ monitoring of the dynamic events in the entire wellbore, which may not be fully captured using discrete gauges. This study is the first well-scale investigation of gas migration dynamics in oil-based mud with solids, using optical fiber-based distributed acoustic sensing (DAS) and distributed temperature sensing (DTS). Four multiphase flow experiments conducted in a 5,163-ft-deep wellbore with oil-based mud and nitrogen at different gas injection rates and bottomhole pressure conditions are analyzed. The presence of solids in the mud increased the background noise in the acquired DFOS measurements, thereby necessitating the development and deployment of novel time- and frequency-domain signal processing techniques to clearly visualize the gas signature and minimize the background noise. Gas rise velocities estimated independently using DAS and DTS showed good agreement with the gas velocity estimated using downhole pressure gauges.

Self-similar analysis of gas dynamics for van der Waals gas in slipping flow after normal shock wave

A self-similar model of gas dynamics and heat transfer behind the shock wave was developed with allowance for the effects of slippage and dissipation. The model takes into account the impact of the following factors: shock wave intensity (U∞/Us), physical properties (Prandtl number Pr), thermodynamic gas properties (van der Waals numbers Waa, Wab), slippage effects (Knundsen number Kn), and dissipation (Brinkman number Br), as well as the relation of the temperatures of the flow and the wall (T0/Tw). The numerical solution was performed with the help of MATLAB software, as well as an in-house code written using the programming language C++ to verify the accuracy of calculations. The study demonstrated that for the case at hand, the Reynolds analogy holds under the influence of all mentioned factors provided that Pr = 1, except for the conditions when the effects of mechanical energy dissipation become significant. The paper presents the results of calculations of the velocity and temperature profiles, friction, and heat transfer coefficients (Nusselt numbers).

Tip clearance irregularity influence on the flow simulation around the turbine blade end face

A modern gas turbine engine must meet high requirements for fuel efficiency, determined by the engine components efficiency. The tip clearance presence in the working crowns and the losses generated by it, which make up about 25-30% of the total losses, have the greatest influence on the turbine efficiency. A change in tip clearance of 0.25% in relative terms corresponds to a turbine efficiency change of approximately 1% for an aircraft engine. Therefore, flow simulation in the tip clearance and its effect on the turbine working process efficiency is a rather important aspect in gas turbine engines efficiency improving.Based on axisymmetric thermal calculations with the subsequent determination of the SSS, the radial displacements of the turbine rotor and stator were found. When summing up the stationary three-dimensional calculation results of the blade thermal state and SSS with displacements of the rotor and stator, the tip clearance actual shape determined, the value of which along the leading edge is 2.4 times greater than along the trailing edge.Based on the results of three-dimensional gas-dynamic analysis, it was determined that taking into account the tip clearance actual shape in the rotor blade model leads to an increase in the efficiency of the turbine stage by 0.40%, a decrease in kinetic energy losses by more than 5% and an increase in torque by 0.28%. The obtained effects are achieved due to the reduced value of the actual gap in the zone of maximum pressure gradient between the trough and the back of the blade, which leads to the sealing of the gap and a decrease in the flow rate of the working fluid through it by 20%.

Gas dynamic analysis of the modern single shaft gas turbine engine flow path

Abstract The paper outlines a finite volumes refined mathematical model of the working gas flow in the flow path of the three stage modern single shaft gas turbine engine that can be used in floating power plants. Such mathematical model based on the finite volumes of hexagonal-type was constructed using the three-dimensional Navier–Stokes equations for the case of viscous working fluid flow. For the problem solution such boundary conditions as “inlet’, “outlet” and “wall” have been used. The calculation is carried out in a non-stationary setting with a time step of 1.5974 × 10−6 s, which corresponds to the angle of rotation of the rotor, relative to the stator, of 0.09°. The total number of time iterations is 350. Also, it was shown that the variation field of pressure on the blades feather surfaces and the gas flow velocity due to rotation are the critical factors, causing the blades vibration. The result was confirmed with the experiment. The obtained results would be used as a base for further investigations of gas flow pressure field on the blades surface, because the gas flow pressure are key factors, causing the rotor forced vibration, and as initial data for their fatigue strength and crack study.

Gas dynamic analysis of the modern single shaft gas turbine engine flow path

Abstract The paper outlines a finite volumes refined mathematical model of the working gas flow in the flow path of the three stage modern single shaft gas turbine engine that can be used in floating power plants. Such mathematical model based on the finite volumes of hexagonal-type was constructed using the three-dimensional Navier–Stokes equations for the case of viscous working fluid flow. For the problem solution such boundary conditions as “inlet’, “outlet” and “wall” have been used. The calculation is carried out in a non-stationary setting with a time step of 1.5974 × 10−6 s, which corresponds to the angle of rotation of the rotor, relative to the stator, of 0.09°. The total number of time iterations is 350. Also, it was shown that the variation field of pressure on the blades feather surfaces and the gas flow velocity due to rotation are the critical factors, causing the blades vibration. The result was confirmed with the experiment. The obtained results would be used as a base for further investigations of gas flow pressure field on the blades surface, because the gas flow pressure are key factors, causing the rotor forced vibration, and as initial data for their fatigue strength and crack study.

On ensuring the safe movement of emergency service vehicles under hazardous driving conditions

Introduction. The relevance of the study is substantiated by the need for a safe and timely arrival of an emergency service vehicle (firefighters, police, paramedics, gas service teams) to the place of call under the conditions of poor road visibility due to smoke, fog, snowfalls, the night time in the absence of illumination.Ensuring safe movement under the conditions of poor visibility. In case of smoke and insufficient visibility due to wildfires, safe movement is possible, if the air pressure in the cabin is excessive and the driver uses a thermal imager by. When a car is driven under the conditions of fog, a snowfall or the lack of illumination, a thermal imager can also be used. The gas-dynamic analysis of air supply to the cabin and its schemes are provided. The co-authors made a gas-dynamic assessment of the air flow rate if the cabin is not hermetically sealed and the crew stay inside.The car movement in case of floods and damaged roads. The structural layout diagram of an emergency service vehicle designed to move through flooded areas and along damaged roadbeds is provided.Conclusions. The novelty and expediency of the above technical solutions are confirmed by the RF patents. Their implementation will allow emergency services to arrive safely to the place of call, regardless of the road conditions.

Special aspects of numerical simulation of a two-stage axial-flow compressor with defective blades

The paper presents the results of a stage of development of an analytical model for assessing the impact of various defects on the operation of an axial-flow compressor. Some recommendations on setting the numerical models for carrying out gas dynamic and strength analysis of compressor stages and blades with account for various defects are proposed. Verification was carried out for the models presented: the results are also presented in the paper. On the basis of the verification results some special aspects of CFD-modeling are discussed. The requirements for the defects under investigation are defined. A classification of the defects that can be analyzed with the use of the developed mathematical description of the geometry of airfoils and blades with account of all proposed recommendations for the setting of the numerical model is presented.

Microscopic seepage mechanism of shale gas reservoir

<p indent=0mm>The percentage of nanopores in shale gas reservoirs is quite high, and their structure is complex. The gas flow mechanism in nanopores is different from macroscopic fluid flow. Therefore, understanding the flow mechanism of shale gas in nanopores is of the utmost importance for its efficient production. Several factors affect the permeability of nanopores in shale gas exploitation. These include adsorption and desorption of nanopores, stress sensitivity, and slippage. Therefore, we capitalize on the capillary model and consider adsorption deformation. We establish a shale apparent permeability model to describe the gas flow considering the influence of the slip-off effect. The model is validated experimentally, and the influence of model parameters on apparent permeability is discussed. We demonstrate that our model can reasonably describe the gas flow under the real shale gas reservoir conditions. More specifically, we consider microscopic mechanisms of adsorption deformation, stress sensitivity, and nanoporous gas slippage effect under stress changes. We demonstrate that when constant confining pressure is applied, theoretical predictions are in good agreement with the measured values. As the pore pressure increases, the apparent permeability of shale decreases exponentially. The apparent permeability of the two gases increases with the increase of the average molecular free path. In particular, the larger the pore size, the higher the permeability in the pressure range, and as the pore pressure increases, the permeability gradually decreases. The apparent permeability of shale is more sensitive to the elastic modulus, and the increase of the elastic modulus leads to higher permeability at a given pressure stage. Moreover, the smaller the fracture compression coefficient, the higher the permeability. Finally, the apparent permeability of shale increases as so does the temperature. The proposed model provides guidance for shale gas production and dynamics analysis, capacity prediction, and production system optimization.

Methodology for the large-eddy simulation and particle image velocimetry analysis of large-scale flow structures on TCC-III engine under motored condition

Large-eddy simulation has been increasingly applied to internal combustion engine flows because of their improved potential to capture the spatial and temporal evolution of turbulent flow structures compared with Reynolds-averaged Navier Stokes simulation. Furthermore, large-eddy simulation is universally recognized as capable of simulating highly unsteady and random phenomena, which drive cycle-to-cycle variability and cycle-resolved events such as knocks and misfires. To identify large-scale structure fluctuations, many methods have been proposed in the literature. This article describes the application of several analysis methods for the comparison between different datasets (experimental or numerical) and the identification of large-structure fluctuations. The reference engine is the well-known TCC-III single-cylinder optical unit from the University of Michigan and GM Global R&amp;D center; the analyses were carried out under motored engine conditions. A deep analysis of in-cylinder gas dynamics and flow structure evolution was performed by comparing the experimental results (particle image velocimetry of the velocity fields) with a dataset of consecutive large-eddy simulation cycles on four different cutting planes at engine-relevant crank angle positions. Phase-dependent proper orthogonal decomposition was used to obtain further conclusions regarding the accuracy of the simulation results and to apply conditional averaging methods. A two-point correlation and an analysis of the tumble center are proposed. Finally, conclusions are drawn to be used as guidelines in future large-eddy simulation analyses of internal combustion engines.

Features of heat and mechanical characteristics of pulsating flows in gas-air paths of piston engines with turbocharging

This article provides a comparative analysis of unsteady gas dynamics and instantaneous local heat transfer of pulsating flows in the intake and exhaust systems of reciprocating internal combustion engines in the case of a turbo-compressor installed without it and based on the results of experimental studies. Experimental studies were carried out on full-scale laboratory stands under the conditions of gas-dynamic nonstationarity. The article provides an original method for determining the instantaneous values of the local heat transfer coefficient in pipes, and describes the procedure for conducting experiments. It has been established that the presence of a turbo compressor in the gas-air system of a piston engine leads to significant differences in the patterns of changes in the gas-dynamic and heat exchange characteristics of pulsating flows. The obtained new data can be used to improve engineering methods for calculating the quality indicators of gas exchange processes, to refine the working processes of the engine when installing a turbocharger, as well as to develop advanced gas-air ICE systems with turbocharging.

An extended Kozeny-Carman-Klinkenberg model for gas permeability in micro/nano-porous media

Gas transport in micropores/nanopores deviates from classical continuum calculations due to nonequilibrium in gas dynamics. In such a case, transport can be classified by the Knudsen number (Kn) as the ratio of gas mean free path and characteristic flow diameter. The well-known Klinkenberg correction and its successors estimate deviation from existing permeability values as a function of Kn through a vast number of modeling attempts. However, the nonequilibrium in a porous system cannot be simply modeled using the classical definition of the Kn number calculated from Darcy’s definition of the pore size or hydraulic diameter. Instead, a proper flow dimension should consider pore connectivity in order to characterize the rarefaction level. This study performs a wide range of pore-level analysis of gas dynamics with different porosities, pore sizes, and pore throat sizes at different Kn values in the slip flow regime. First, intrinsic permeability values were calculated without any rarefaction effect and an extended Kozeny-Carman model was developed by formulating the Kozeny-Carman constant by porosity and pore to throat size ratio. Permeability increased by increasing the porosity and decreasing the pore to throat size ratio. Next, velocity slip was applied on pore surfaces to calculate apparent permeability values. Permeability increased by increasing Kn at different rates depending on the pore parameters. While the characterization by the Kn value calculated with pore height or hydraulic diameter did not display unified behavior, relating permeability values with the Kn number calculated from the equivalent height definition created a general characterization based on the porosity independent from the pore to throat size ratio. Next, we extended the Klinkenberg equation by calculating unknown Klinkenberg coefficients which were found as a simple first order function of porosity regardless of the corresponding pore connectivity. The extended model as a combination of Kozeny-Carman for intrinsic permeability and Klinkenberg for apparent permeability correction yielded successful results.

Analytical toolset to characterize polyurethanes after exposure to artificial weathering under systematically varied moisture conditions

Abstract Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography (SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands.

Specific aspects of the thermal and mechanic characteristics of pulsating gas flows in the intake system of a piston engine with a turbocharger system

In the article, the results of experimental studies on gas dynamics and the heat exchange of gas flows in the intake system of a turbocharged piston engine are presented. The studies were carried out on full-size experimental installations under the conditions of gas-dynamic unsteadiness. First, the authors analyzed the influence of the flow turbulence number on the heat exchange rate in the turbocharger compressor’s outlet channel. It was demonstrated that the heat exchange rate in the outlet channel decreased as the turbulence number increased from 0.008 to 0.016. Further, the authors evaluated the influence of external turbulence (the mechanical impact of the compressor’s blade row) on the thermal-mechanical characteristics of the pulsating flow in the intake system. A comparative analysis of gas dynamics and heat exchange in the intake systems of turbocharged and non-turbocharged engines was carried out. The obtained results can be used to design new intake systems for turbocharged engines.

A Polytropic Approximation of Compressible Flow in Pipes With Friction

This paper demonstrates the usefulness of treating subsonic Fanno flow (adiabatic flow, with friction, of a perfect gas in a constant-area pipe) as a polytropic process. It is shown that the polytropic model allows an explicit equation for mass flow rate to be developed. The concept of the energy transfer ratio is used to develop a close approximation to the polytropic index. Explicit equations for mass flow rate and net expansion factor in terms of upstream properties and pressure ratio are developed for Fanno and isothermal flows. An approximation for choked flow is also presented. The deviation of the results of this polytropic approximation from the values obtained from a traditional gas dynamics analysis of subsonic Fanno flow is quantified and discussed, and a typical design engineering problem is analyzed using the new method.

Numerical 3D Simulation of Safety Valve Gas Dynamics

Рассмотрена модель газодинамических процессов в предохранительном клапане прямого действия, предназначенном для обеспечения безопасности трубопроводов и аппаратов высокого давления. Моделирование осуществлялось на основе метода контрольного объема и разностной схемы С. К. Годунова в трехмерной постановке. Внутреннее пространство клапана разделено на два блока, в каждом из которых строится структурированная разностная сетка. В первом блоке сетка является ортогональной. Параметры газа на границах контрольных объемов определяются на основе автомодельного решения задачи о распаде произвольного разрыва. Формирование газодинамических переменных для решения задачи о распаде произвольного разрыва с последующим восстановлением составляющих вектора скорости проводилось с применением преобразований векторов в локальной системе координат на каждой грани контрольного объема. Реализованный численный метод расчета нестационарной трехмерной газодинамики позволяет определять пространственную структуру потока в предохранительном клапане и его количественные характеристики (давление, плотность, скорость, температуру). Анализ результатов расчетов показал, что течение до нижней части диска близко к осесимметричному. Сравнение с результатами расчетов в осесимметричной и трехмерной постановках свидетельствует о том, что интегральная характеристика (газодинамическая сила) может рассчитываться для рассмотренных условий в осесимметричной постановке при соответствующем выборе эквивалентной конфигурации внутреннего контура клапана.

Development Features of Thermal and Gas-Dynamic Performance of Mineral Wool Cupola Furnace

Major unit for mineral melt production in industry is a shaft (cupola) furnace. Such type units are noted for the ease of fabrication and maintenance, high melting rate (up to 100-150 t/m2 per day), as well as high heat utilization efficiency (up to 60-80 % of the total supply). Design disadvantages may include inefficient workspace side-view, poor thermal and gas dynamic performance, lack of practical methods to impact the melting process. Another pressing problem is related to melt production in the amount of no more than 3 t/h, with the average coke consumption of up to 24-270 kg/t, and the overheating temperature level of no more than 1350-1400 °С. Thermal and gas dynamic performance analysis of mineral wool cupola furnace, based on evaluation of zone balance model demonstrated that mineral melt is produced under conditions of essential nonuniformity of the bed temperature, gas phase composition and heat exchange conditions, both throughout the bed height and the unit cross section.

Simulation of Sand Filling Process and Analysis of Flow Behavior with Different Binder Ratio

Core shooting process has a great influence on the quality of sand cores. At present, there are two computational fluid dynamic models applied to simulate the hydrodynamics of core shooting process. In this paper, a two-fluid model (TFM) simulation is made on fluid dynamic analysis. With validation of experimental results and discrete particle model (DPM) simulations, the TFM is able to predict a reasonable flow behavior of sand particles by gas dynamic pressure analysis. Residual gas distribution of sand filling process is analyzed and a good agreement is achieved between air volume fraction simulation based on TFM and experimental results. A comparison between different binder ratios is made. The binder ratio has a significant effect on sand hydrodynamic behavior and the sand volume fraction.

Molecular gas dynamics analysis on influence of non-condensable gas molecules on evaporation of vapor molecules

Molecular gas dynamics analysis on influence of non-condensable gas molecules on evaporation of vapor molecules