Gas Flow Behavior Research Articles

COUPLED HYDRO-MECHANICAL MODELING OF GAS FLOW IN SHALE MATRIX CONSIDERING THE FRACTAL CHARACTERISTICS OF NANOPORES

To economically develop shale gas reservoirs, hydraulic fracturing treatments must be applied to artificially introduce pathways for gas to flow out. After hydraulic fracturing, both the induced hydraulic fractures and activated natural fractures provide high permeable channels for gas transport. However, the long-term production performance of shale gas reservoirs is determined by the physical properties of matrix instead of the fractures. In this work, a coupled hydro-mechanical model is developed to investigate gas flow in heterogeneous shale matrix at the microscale. This model considers the mechanical interaction and gas mass transfer between organic matter (OM) and inorganic matter (iOM) during gas depletion. The interesting results show that due to matrix heterogeneity, i.e. co-existence of OM and iOM, the gas flow and mechanical deformation behaviors in shale exhibit regional differences. Specifically, during reservoir depletion, pore pressure, Knudsen number and volumetric strain in iOM are smaller than that in OM while the intrinsic and apparent permeability of OM are smaller than that of iOM. Thus, matrix heterogeneity should be taken into account when characterizing shale gas flow. In addition, sensitivity analysis is conducted to study the influence of fractal parameters on shale apparent permeability evolution. These fractal parameters include nanopore radius fractal dimension, tortuosity fractal dimension and maximum nanopore radius. The analysis indicates that the variation of fractal parameters in iOM results in the change of apparent permeability of both OM and iOM, while the variation of fractal parameters in OM only leads to the change of apparent permeability of OM. The modeling results offer new insights into gas flow behaviors in shale matrix.

Study on Fluid Behaviors of Foam-Assisted Nitrogen Flooding on a Three-Dimensional Visualized Fracture–Vuggy Model

Tahe Oilfield, located in northwest China, is an unconventional fracture–vuggy carbonate reservoir. The foam-assisted nitrogen gas flooding technology has been proven to be a potential EOR technology. However, the flow behaviors of foam-assisted nitrogen gas in fracture–vuggy structures are not clear due to the complex fracture–vuggy structures and their strong heterogeneity. In this work, a three-dimensional visualized fracture–vuggy model is designed and fabricated to investigate the fluids behaviors of foam-assisted N2 flooding and classify the residual oil types after foam-assisted N2 flooding. Experimental results reveal that foam slug can enlarge the sweep efficiency, suppress the formation of nitrogen gas channeling, and detach the oil film. Additionally, the evolution processes of the gas–oil and oil–water interfaces are investigated and analyzed. Moreover, the residual oil types after foam-assisted N2 flooding and nitrogen gas flooding, respectively, are classified and summarized. Compared to nitrogen gas flooding after water flooding, 12.36% more oil can be recovered through foam-assisted N2 flooding. This work further studies the fluid flow behaviors of foam-assisted N2 in the three-dimensional visualized fracture–vuggy carbonate model and also confirms the previous achievements.

Nanoconfined methane flow behavior through realistic organic shale matrix under displacement pressure: a molecular simulation investigation

Academic investigations digging into the methane flow mechanisms at the nanoscale, closely related to development of shale gas reservoirs, had attracted tremendous interest in the past decade. At the same time, a good understanding of the complex essence remains challenging, while the broad theoretical scope, as well as application value, possesses great attraction. In this work, with the help of molecular dynamics methods nested in LAMMPS software, a fundamental framework is established to mimic the nanoconfined fluid flow through realistic organic shale matrix. Denoting evident discrepancy with existed contributions, shale matrix in this work is composed of specific number of kerogen molecules, rather than simple carbon-based nanotube. Recently, promotion efforts have been implemented in the academic community with the use of kerogen molecules, however, gas flow simulations are still lacking, and the pore shape in the current papers is always hypothesized as slit pores. The pore-geometry assumption seriously conflicts with the general observation phenomenon according to the advanced laboratory experiments, such as SEM image, AFM technology, that the organic pores tend to have circular pore geometry. In order to fill the knowledge gap, the circular nanopore with desirable pore size surrounded by kerogen molecules is constructed at first. The organic nanopore with various thermal maturity can be obtained by altering the kerogen molecular type, expecting to achieve more physically and theoretically similar to the realistic shale matrix. After that, methane flow simulation is performed by utilization of non-equilibrium molecular dynamics, the methane density as well as velocity distribution under different displacement pressures are depicted. Furthermore, detailed discussion with respect to the simulation results is provided. Results show that (a) displacement pressure acts as a dominant role affecting methane flow velocity and, however, fails to affect methane density distribution, a behavior mainly controlled by molecular–wall interactions; (b) the velocity distribution feature appears to be in line with the parabolic law under high atmosphere pressure, which can be attributed to small Knudsen number; (c) the simulation time will be prolonged with larger displacement pressure imposed on nanoconfined methane. Accordingly, this work can provide profound basis for accurate evaluation of nanoconfined gas flow behavior through shale matrix.

CFD study of the transient wet gas flow behavior through orifice plate flow meters

Differential pressure flow meters are widely used in wet gas flow measurement, typically, combined with a method to determine the liquid fraction. An alternative with significant advantages for industry, in term of cost, operation and maintenance, is determining the liquid fraction based on its relation with the statistical parameters of transient differential pressure signal fluctuations. In this way, a single measurement device can provide mass flow rate and liquid fraction simultaneously. For this method to be more feasible in the wet gas flow measurement, it is essential to understand how the differential pressure signal fluctuations and the gas–liquid flow behavior at the restriction are correlated. On this basis, this paper presents a transient 3D Computational Fluid Dynamics (CFD) study of the wet gas flow through an orifice plate, operating under field conditions, using the two-fluid model. Steady-state results, calculated from the time averaging of the transient solution, for the over-reading OR parameter were validated with experimental field data and results obtained by correlations available in the literature, showing very good agreement. The transient results from simulations presented a trend in agreement with experimental data from the literature, showing a positive correlation of the standard deviation of differential pressure signal with liquid fraction upstream of the orifice plate. However, these results should be analyzed qualitatively due to model limitations, mainly related to the interfacial transfer closure in gas–liquid flows with changing phase morphologies. Despite this fact, some important insights regarding the 3D transient flow structure with a practical value were obtained from the model.

Goaf gas drainage and its impact on coal oxidation behaviour: A conceptual model

In gassy underground and spontaneous combustion prone coal mines, goaf management is a challenging task to reduce the risks of gas explosion and spontaneous combustion to acceptable levels. Goaf gas drainage via vertical surface goafholes is a primary control method to manage gas emissions in Australian coal mines. However, the operation of vertical surface goafholes maybe significantly impacted by insufficient understanding of goaf gas flow and coal self-heating behaviour, especially under different goaf gas drainage operating conditions. This paper focuses on analysing the field monitoring data collected from 161 goaf drainage holes at two coal mines in Australia. The data formed the basis to develop a conceptual model, which represents the changes of goaf atmosphere during the longwall retreat along with goaf drainage operations. The results indicate that the goaf drainage operating conditions may significantly affect goaf gas composition, which contributes to a different goaf atmosphere in comparison to existing models without goaf drainage. Within the studied longwall goaf, the ‘oxidation zone’ and ‘inert zone’ are identified with different carbon monoxide (CO) and oxygen (O2) trends, and the ‘oxidation zone’ is conceptually further divided into the ‘heat accumulation zone’, ‘elevated oxidation zone’ and ‘slow oxidation zone’ based on the variation of gas composition and potential degree of oxidation of residual coal. The coal oxidation potential risk and corresponding goaf gas drainage strategies at these conceptual zones are also evaluated in this paper. The results of this study are expected to act as a guideline for future goaf gas drainage operations.

Shale gas transport through the inorganic cylindrical and conical nanopores: A density gradient driven molecular dynamics

Pores heterogeneity is an essential part of porous media, however, the effect of the changeable pore is usually overlooked in studies on the shale gas transport in inorganic nanopores. Research currently focuses on inorganic nanoslits that fail to simulate the realistic methane transport through cylindrical and conical inorganic nanopores because variable apertures are not captured in the simulation. However, the impact of such varied apex angles and diameters on methane transport capacity in nanopores has not been studied yet in inorganic shale nanopores. To compensate for the defect, density gradient-driven molecular dynamics (DGD-MD) are used to study the methane transport behavior through the cylindrical and conical inorganic nanopores. The clay material (Ca-montmorillonite) is used to establish the conical nanopores with different apex angles and the cylindrical inorganic shale nanopores with different diameters. Main results show that the permeability of methane increases with enlarged nanopores diameter in cylindrical inorganic nanopores and can be described by the Hagen-Poiseuille (HP) equation with the effective viscosity. However, the flux of methane through cylindrical nanopores is greater than that obtained by using the HP equation under high pressure drop owing to the intensive surface diffusion of gas and positive slippage. Methane is most readily absorbed in the conical nanopores with an apex angle of 9.6°. The flow behavior of methane molecules gradually changes from negative slippage to positive slippage through the conical nanopores and this will result in the overestimation flux obtained by the HP equation. The flow capacity of confined methane predicted by the modified HP equation combining with apex angle is in good agreement with the simulation results. This study provides a molecular-level understanding of the key relationship between variable apex angles and permeability through the cylindrical and conical nanopores, and it can apply to the flow behavior of gas at the nanoscale in biological, chemical, medical, and physical fields.

Modeling transient flow behavior with the high velocity non-Darcy effect in composite naturally fractured-homogeneous gas reservoirs

A gas reservoir with composite properties contains two distinct regions, where one develops natural fractures and the other does not. To investigate the pressure transient behavior of the non-Darcy flow in composite naturally fractured-homogeneous gas reservoirs, a radial bi-zonal composite non-Darcy flow model was developed based on Izbash's equation. The inner region was considered as a dual-porosity medium to simulate the non-Darcy flow, whereas the outer region was considered as a homogeneous medium to simulate the Darcy flow. This model was solved using the Laplace transform, linearization and Stehfest numerical inversion. Then, the standard bi-logarithmic characteristic curves of the non-Darcy flow model were plotted. The flow stages were recognized and the influence of vital characteristic parameters on the transient behavior was analyzed and discussed in detail, such as the empirical constant, radius of the non-Darcy region, storage ratio, crossflow coefficient, etc. It is found that the values of the empirical constant n have a significant influence on the pressure transient behavior of the non-Darcy region. Moreover, three reduced models of the model proposed in this study were analyzed and discussed. Finally, it was found from the field application that this model had an excellent agreement between the measured and simulated pressure responses. The research results can be a helpful guide for researchers in the related fields when studying the transient behavior of high-velocity non-Darcy gas flow in composite naturally fractured-homogeneous gas reservoirs.

Characterization of anisotropic coal permeability with the effect of sorption-induced deformation and stress

Changes in permeability are related to coalbed methane (CBM) production activities, and to coal mining safety. However, inherent properties, i.g. anisotropy and heterogeneity make the gas flow mechanism more complex. In this work, an anisotropic coal permeability model with synergistic stress compression and gas adsorption was constructed to simulate gas flow behavior in all directions in coal. Changes in coal anisotropic permeability are restricted by the fracture deformation in coal in all directions. Wherein, the fracture deformation in coal is controlled by the effective volume strain coordinated by gas adsorption and stress. The influence of stress can be expressed by employing the generalized Hooke’s law. Then, based on the coal matrix bridge structure, an internal swelling coefficient has been proposed to assess the control of the matrix swelling on fracture width during the gas adsorption process to further obtain the fracture deformation caused by gas adsorption. The anisotropic coal permeability model was verified by laboratory test data under different effective stresses, gas pressures, with respect to their combined influences. Subsequently, based on the experimental conditions of uniaxial strain, the permeability model of anisotropic coal during gas depletion was further deduced, and changes in anisotropic coal permeability under uniaxial strain were also calculated. In addition, the sensitivity of the reduction rate of the elastic modulus, and the internal swelling coefficient was also studied, to reveal the matrix-fracture interaction mechanism.

Stress-dependent fluid dynamics of shale gas reservoirs: A pore network modeling approach

In this study, the pore network modeling approach is implemented to study the flow behavior of the methane gas in shale reservoirs in the presence of slip flow and gas desorption under different effective stress conditions through the effect on apparent permeability. A single pore and a pore network are constructed using a down-scaled Berea sandstone image. The compressible Stokes is applied with proper boundary conditions to capture slip flow and gas desorption effects. To include the effect of stress, poroelasticity principles are applied to describe the interaction between fluid flow and solid deformation. The model performance is verified against an experimental data taken from the literature. Both models show a negative effect of stress on gas flow when slip flow and desorption mechanisms are activated in the models. In the single pore model, slip has a positive and complementary effect on desorption at a specific stress value when their coupled contributions are summative. However, the results of pore network model show that slip has a destructive effect on desorption contribution specially at low effective stress values. That is, the changes in pore pressure induced by the slip mechanism act to limit the desorption contribution. This is clearly noted with the consideration of stress effects. At high effective stress values, the slip effect is limited due to the increase in pore pressure by compression, hence a closer matching between the permeability enhancement produced by the desorption mechanism alone and the coupled effect of desorption and slip can be noticed. Stress acts to limit the slip flow and also the desorption mechanism as they both are a function of pore pressure, however, as stress increases the contribution of desorption no longer would be reduced by slip flow. This study provides insights into stress role in multiphysics gas flow in shale reservoirs.

Quantitative investigation of gas flow, powder-gas interaction, and powder behavior under different ambient pressure levels in laser powder bed fusion

The powder motion in laser powder bed fusion (LPBF) processes causes defect and variability issues in the built products. It has been reported that the ambient pressure has a significant influence on the powder motion, but the physical effects of the ambient pressure on the gas flow, powder-gas interaction, and powder behavior are not quantitatively understood. In this work, we have developed the first three-dimensional multiphysics model for LPBF to simulate the molten pool dynamics, depression zone evolution, gas flow structure, and powder motion in a fully coupled manner. The model enables the first quantitative investigation of the gas flow, powder-gas interaction, and powder behavior in LPBF with different ambient pressure levels, all of which are difficult to measure by experiments. The simulation results show a consistent gas flow structure for all different pressure levels, but the gas flow parameters (temperature, velocity, Reynolds number, and Knudsen number) vary significantly with the ambient pressure. Four powder-gas interaction modes are defined by the gas flow around the particle and the gas-induced forces on the particle, and the interaction modes, individually or collectively, control the motion of each particle. With the changes in the ambient pressure and the gas flow parameters, the significance of the four modes to the powder motion varies, and the powder behavior (temperature, force, velocity, and ejection angle) becomes different. A new strategy is proposed to mitigate the powder motion based on the modeling results.

STUDY ON GAS ADSORPTION AND TRANSPORT BEHAVIOR IN SHALE ORGANIC NANOPORE

The characteristics of shale gas reservoir are expressed in terms of complex pore structure and multiple gas occurrence pattern. Adsorbed gas and bulk gas coexist in nano-scale organic pores. The influence of organic pore shape on confined gas adsorption and flow behavior is not clear, which consequently causes the inaccuracy to understand gas transport mechanisms in shale gas reservoir. To solve this problem, different shapes of organic pore (circular pore, slit pore, triangle pore, square pore) are constructed in this study and Grand canonical Monte Carlo method is first applied to simulate gas adsorption process in different shapes of organic pore across different pore pressure. We found that gas adsorption behavior in different shapes of pores conforms well with the Langmuir adsorption pattern. The absolute adsorption, excess adsorption and gas adsorption parameter change with pore size and pore pressure is analyzed and the influence of pore shape on gas adsorption is studied on this basis. The mathematical model of adsorbed gas surface diffusion and free gas slip flow in different shapes of organic pore is established based on the understanding of thermodynamic gas adsorption pattern in different shapes of organic pore. The respective contribution of adsorbed gas flow and free gas flow on total gas permeability is studied in organic pores with different pore shape and pore size combining molecular simulation results with established gas transport models. The results indicate that the slit pore exhibits the largest value of maximum gas concentration, Langmuir pressure and the weakest adsorbed gas surface diffusion capacity compared with the other three pore shapes. The adsorbed gas surface diffusion influence on gas permeability can be neglected at pore radius larger than 5 nm for different pore shapes. This study reveals the influencing mechanism of organic pore shape on gas adsorption and flow ability during practical shale gas reservoir production.

Self-diffusion flow and heat coupling model applicable to the production simulation and prediction of deep shale gas wells

Clarifying the flow laws of shale gas under high temperature and high pressure is the prerequisite to accurately predicting the productivity of deep shale gas wells. In this paper, a self-diffusion flow model of flow field and temperature field coupling (referred to as self-diffusion flow and heat coupling model) was established based on the previously proposed self-diffusion flow model, while considering the influence of the temperature field change. Then, its calculation result was compared with that of the flow model based on Darcy's law and Knudsen diffusion (referred to as modified Darcy flow model). Based on the self-diffusion flow and heat coupling model, the self-diffusion flow behaviors of deep shale gas under the influence of temperature field change were analyzed, and the influence of bottomhole temperature on the degree of reserve recovery of deep shale gas was discussed. Finally, the self-diffusion flow and heat coupling model was applied to simulate the production of one shale-gas horizontal well in the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Changning Block of the Sichuan Basin. And the following research results were obtained. First, at the same parameters, the shale gas production calculated by the self-diffusion flow and heat coupling model is higher than the result calculated by the modified Darcy flow model. Second, when temperature field change is taken into consideration, the self–dviffusion coefficient profile presents a peak, the gas density profile presents a valley and the data points corresponding to the peak/valley move synchronously to the internal formation, which indicates that the self–diffusion coefficient influences the gas mass transfer rate, and the influence range of near well low temperature on gas self-diffusion increases continuously as the production continues. Third, when the bottomhole temperature is lower than the formation temperature, the self–diffusion coefficient of the gas near the well decreases and the gas is blocked near the well, which reduces the gas well production. Fourth, the production simulation result of the case well shows that the self-diffusion flow and heat coupling model can predict the production of deep shale gas more accurately if temperature field change is taken into consideration. In conclusion, the self-diffusion flow and heat coupling model established in this paper is of higher reliability and accuracy and can be used for productivity simulation and prediction of deep shale gas wells. The conclusion of this paper has certain guiding significance for deep shale gas production and gas well productivity prediction.

Influence of gas hydrate saturation and pore habits on gas relative permeability in gas hydrate-bearing sediments: Theory, experiment and case study

Gas relative permeability characterization is of key significance to model the behavior of gas flow in gas hydrate-bearing sediments. The present study proposes a novel model to relate gas relative permeability to gas hydrate saturation based on X-ray micro-CT imaging information of xenon hydrate pore-scale distribution in sand sediments. Lattice Boltzmann method (LBM) was used to obtain permeability values of xenon hydrate-bearing sediments via micro-CT data. The results showed that gas relative permeability (Kr) versus gas hydrate saturation (Sh) data are consistent with the new model and the imitative effect is relatively better than that of the simple Corey model. Besides, we calculated gas relative permeability versus gas hydrate saturation curves for various pore habits via idealized models. Experimental measurements and simulation results showed that the grain-coating gas hydrate exhibits the highest gas relative permeability, while pore-filling gas hydrate exhibits the lowest values of gas relative permeability, and the cementing gas hydrate ranges in between. We validated the new gas relative permeability calculation model by applying it to the well logging data of gas hydrate reservoirs. Our results showed that the novel model is beneficial for permeability characterization of gas hydrate reservoirs and gas relative permeability calculations.

Transverse permeability measurements of gas shales under replicated in-situ flow conditions: Mathematical modeling and laboratory testing

Fast and accurate characterization of unconventional gas reservoirs is of great significance for estimation of gas-in-place and enhancement of gas recovery; however, it remains a big challenge to efficiently and effectively determine the permeability of tight-structure reservoirs in the nano-Darcy scale, especially for those reservoirs with strong gas sorption potential. A novel pressure transient technique is proposed to replicate the in-situ gas flow behavior, and thus to reduce the permeability errors from gas compressive storage, gas sorption, and gas compressibility, which are the three primary error sources widely existing in various permeability measurement techniques. The feasibility of the technique is firstly verified via numerical solutions of a partial differential equation (PDE) model established to closely represent the proposed technique. The results of the numerical study showed that the effects of the error sources on the measured permeability can be minimized and meanwhile, high accuracy and efficiency can be achieved in comparison with the conventional method. A specially designed apparatus for experimental tests via the proposed technique is then used to investigate the stress-dependent permeability of gas shales. The consistency of the experimental results with the findings from the numerical study further validates the applicability of the technique. Considering the complexity of the analytical solution of the PDE model for experimental data interpretation, shale permeability is computed via a new data interpretation approach which is developed by combining the curve-matching and the finite difference method. The experimental results showed that shale permeability is strongly dependent upon the applied stresses and easily affected by gas sorption, gas compressibility and stress inhomogeneity. Without consideration of these factors, the permeability error can reach up to 28.1 % at low stresses. The proposed technique provides a great tool to get insights into the in-situ gas flow behavior and characterize tight-structure gas reservoirs.

Numerical and Experimental Analysis of Gas Flow in a Coaxial Nozzle Applied to Directed Energy Deposition (DED)

create a melt pool on the substrate. A nozzle is used to carry metal powder within a gas flow until the melt pool, concentrating the flow at the same point. Coaxial nozzles usually have also a shield gas flow to prevent oxidation and an internal flow to protect the optical system. A right flow configuration must be selected to avoid high turbulence at the nozzle exit, leading to an efficient, inexpensive, and high-quality process. Due to the complexity of the process, CFD – Computer Fluid Dynamics are becoming necessary to understand the behaviour of those gas flows in DED processes. CFD can offer results close to reality and may allow an optimization of the whole nozzle designs, besides selecting the best gas flows for each application. The present work develops a CFD simulation of the gas flow behaviour in a coaxial nozzle with three internal annular channels (internal, carrier and shield). An initial set of gas flow was selected, based on previous experience of the manufacturer, and then improved. It searches for the low gas consumption, to form a focal point coinciding with the laser focus and a low velocity, which favours the deposition quality. To check the accuracy of the proposed CFD model, experimental measurements of gas velocity were performed and compared with simulated results.

Hybrid physical and data driven transient modeling for natural gas networks

With the development of gas-fired generators, the increasing gas-electricity systems bring a new challenge to accurately analyze pressure or flow rate fluctuation in gas pipeline networks caused by gas-fired generators ramping. This paper proposes a hybrid physical and data driven modeling approach, which can take full advantage of physical laws and measurement data to characterize the transient behavior of gas flow in pipeline networks. Based on the linear graph theory, the gas flow dynamics and network topology are uniformly represented in the directed graph, so that the state-space model can be extracted automatically. Considering that the increasing number of model parameters with networks scale, a decentralized parameters identification algorithm is designed to enhance computational efficiency. The overall network is partitioned into a certain number of non-overlapping subnetworks, and each one formulizes the parameter identification as a nonlinear optimization problem solved by an iterative Levenberg-Marquardt algorithm. To demonstrate the effectiveness of the proposed method, a real-world gas network from a steel industrial park in China is studied, and simulation results are compared with the commercial simulation software Apros™. The results indicate that the proposed method improves the accuracy in gas network transient modeling markedly.

Derivation of a Closed Form Expression for Estimating the Reduced Flow Rate for Pressure Driven Rarefied Gas Flow Through Circular Nano/Micro Pores

In this paper, a new model to predict the gas flow rate through short tubes under rarefied condition based on the sigmoidal bahaviour of gas reduced flow rate (W) versus the rarefaction parameter (d) under rarefied condition was developed. The data produced by Varoutis et al. via Direct Simulation Monte Carlo (DSMC) method were utilised to obtain the model coefficients as functions of tube length to radius (w) and pressure ratio (Pr). Then, the model was tested against the published experimental data.There was a high degree of agreement between the model predictions and the experimental data. Moreover, the new model was capable to predict the reduced flow rate of rarefied systems, not only at free molecular region and hydrodynamic region, but also at transition region, hence covering all the Knudsen number domain within the utilised data. Therefore, the proposed model was capable to make predictions as well as meet all the criteria of the rarefied gas flow within the following conditions: 0<Pr<0.9, 0.01<d<1000 and 0.0<w<20. Thus, the proposed model provides a useful tool to make a valid prediction of the rarefied gas flow behavior in a wide range of gas transport regime.

Numerical Analysis of Flow Behavior in Gas–Liquid Cylindrical Cyclone (GLCC©) Separators With Inlet Design Modifications

Abstract The Gas–Liquid Cylindrical Cyclone (GLCC©) is a simple, compact, and low-cost separator, which provides an economically attractive alternative to conventional gravity-based separators over a wide range of applications. More than 6500 GLCC©’s have been installed in the field to date around the world over the past two decades. The GLCC© inlet section design is a key parameter, which is crucial for its performance and proper operation. The flow behavior in the GLCC© body is highly dependent on the fluid velocities generated at the reduced area nozzle inlet. An earlier study (Kolla et al., 2017, “Structural Integrity Analysis of GLCC© Separator Inlet,” ASME J. Energy Resour. Technol., 140(5), p. 052905) recommended design modifications to the inlet section, based on safety and structural robustness. It is important to ensure that these proposed configuration modifications do not adversely affect the flow behavior at the inlet and the overall performance of the GLCC©. This paper presents a numerical study utilizing specific GLCC© field applications working under three different case studies representing the flow entering the GLCC, separating light oil, steam flooded wells in Minas, Indonesia. Commercially available computational fluid dynamics (CFD) software is utilized to analyze the hydrodynamics of flow with the proposed modifications of the inlet section for GLCC© field applications.

Transport behavior of pressure-driven gas flow in a nanochannel and the variation of thermal accommodation coefficient

A three-dimensional molecular dynamics simulation of a rarefied gas flow confined between two parallel solid walls has been carried out to study the gas transport behavior in nanoscale pressure-driven flows. To simulate the effects of pressure-driven flows in nanoscale systems; a reservoir is created at the beginning of the channel. A force, in the form of gravity, is applied to every gas molecule occupying a specific region in the reservoir thereby facilitating to establish a streamwise inhomogeneous flow in a finite length nanochannel. Further, the model is tested for its structural stability and steady-state characteristics. The flow characteristics are evaluated at various bins (A, B, C, and D) along the length of the channel. The presence of a pressure drop established along the length of the channel results in a significant variation of flow properties in the channel. The characteristics of the system are further studied using the spatial distribution of flow properties. To investigate the streamwise variation, thermal accommodation coefficients (TACs) at various sections of the channel are calculated. The results indicate that the TACs vary along the length. Further, the effect of pressure drop on TACs is also analysed. The effect of confinement is also studied with velocity autocorrelation function (VACF) and mean squared displacement (MSD). The effect of confinement is evident in the fluid region away from the wall too.

УДОСКОНАЛЕННЯ КОНСТРУКЦІЇ ГЛУШНИКІВ ДЛЯ ЗМЕНШЕННЯ РІВНЯ ЗВУКОВОГО ТИСКУ НА ОПЕРАТОРІВ МАЛОГАБАРИТНИХ ТРАКТОРІВ

Noise background, as an important factor in the working conditions of agricultural operators, has a direct impact on human health and productivity. This topic is especially relevant for small tractors, which in most cases are not equipped with cabs. One of the main means of reducing the sound pressure on the operator are the mufflers of exhaust gases, which mainly have a labyrinth-absorbing type of action. The paper proposes a fundamental approach to the design of the muffler by the criterion of reflection and scattering of sound waves with the verification of efficiency by computer simulation. The purpose of research: - to improve the working conditions of operators of small tractors that are not equipped with cabs, by reducing the sound pressure level from internal combustion engines; - to improve the noise-absorbing properties of mufflers of exhaust gases of engines with observance of requirements to manufacturability of process of their manufacturing; - to develop a structural scheme of the exhaust gases muffler based on the results of preliminary modeling and analysis of the trajectory of the gas flow in the cavity of its working part. Methods. Determination of the sound pressure level of the engine of a small tractor by mathematical (computer) modeling of the behavior of the exhaust gas flow in the muffler cavity in different frequency ranges. Results. The article analyzes the main sources of noise during the operation of agricultural machinery with internal combustion engines (ICE). On the basis of literature sources and methods, their separate degree of influence on the complex picture of noise pollution of the working space of the operator of a small tractor is established. A comparative analysis of the efficiency of mufflers, created on the generally accepted principles and approaches to the design of such devices. According to the results of previous tests, shortcomings and limitations in the application of design concepts were identified, an additional analysis of external causes and factors was made, and adjustments were made to the method of creating muffler designs. An alternative design approach to the creation of internal combustion engine mufflers of small tractors is proposed and computer modeling of the processes of sound pressure distribution and sound waves in their cavity is performed. Conclusions. 1. A layout diagram of the design of the exhaust muffler, containing a resonator chamber and a shell module, which is made in the form of a three-stage ribbed diffuser of oscillations of the exhaust flow pulses with an additional surface layer of the vibration absorber. The parameters of the exhaust flow of exhaust gases of a typical diesel engine of a small tractor with a capacity of 24 hp are calculated. (pressure - 11652 Pa, acceleration – 90-105 m / s2, frequency - 1950-3300 Hz), which performed computer simulations of the process of gas movement in the muffler cavity of the proposed layout. Optimal design parameters were selected to ensure the maximum possible noise absorption with a body diameter of 150 mm and a length of 600 mm. The calculated sound pressure when working at the crankshaft speed (1700-2000) rpm does not exceed 72 dB. At the same time, the design of the muffler is made in compliance with the requirements for economic feasibility, manufacturability and in accordance with the capabilities of industrial production. A further direction of research is the manufacture of an experimental sample of the muffler and testing for the efficiency of its noise absorption in the conditions of operation of small tractors.