Real Gas Research Articles

Implementation and assessment of a low-dissipative OpenFOAM solver for compressible multi-species flows

An ever-increasing number of engineering problems regard the numerical simulation of fluid flows with high-density ratio, shock wave onset, and different chemical species. In such conditions, obtaining reliable results depends on the ability of the numerical algorithm to offer a stable and robust time and space discretization of the governing equations while simultaneously limiting the numerical diffusivity.This work presents the extension and the assessment of a low-dissipative Navier–Stokes solver for compressible, multi-specie flows. We first studied the Richtmyer–Meshkov instability to test the code on fluid flows involving shock waves and species interactions for ideal gas. Then, we simulated a benchmark case regarding a cryogenic coaxial injector often used in rocket engines to explore the solver’s capability in representing high-Reynolds-number supercritical flows of multi-species real gases with large density gradients. Finally, we studied the flow in complex geometries like a high-pressure gasoline injector for propulsion application. The results demonstrate the capability of the present approach in the cases investigated.

Efficient implementation of complex equations of state in a high-order framework

In the last decades, the interest in non-ideal compressible fluid dynamics (NICFD) flows and high-order accurate numerical methods, such as discontinuous Galerkin (dG), has quickly grown. In fact, advanced simulation capabilities are of paramount importance to develop new sustainable technologies with higher efficiency and low environmental impact, and to decrease the use of expensive experimental facilities. Nowadays however, the coupling of accurate Computational Fluid Dynamics (CFD) solvers with sophisticated thermodynamic models has been investigated mainly in the finite volume (FV) framework. Moreover, the solution of complex equations of state (EoS) has a too high computational cost for real-life use in industry, which is often overcome with the look-up table (LuT) interpolation approach. LuTs seem to be more suitable for FV solvers rather than high-order or finite element ones, since the interpolation error introduced may deteriorate the higher accuracy provided by these numerical methods. The novelty of this work lies in the assessment of an efficient implementation for real gas simulations in a high-order solver, by resorting to structured LuTs and automatic differentiation (AD). The proposed implementation is assessed with the computation of the inviscid and turbulent flow around a NACA0012. This approach guarantees an overhead of the computational cost around 17% with respect to an ideal gas solver with manually derived jacobian matrix.

Modeling and simulation for n-decane cracking flow based on detailed reaction kinetics and complete real gas thermodynamics under supercritical pressure

The real gas thermodynamics and the detailed reaction kinetics are two crucial components in studying the flow of hydrocarbon fuel with cracking reactions under supercritical pressure. However, these two aspects have not been effectively integrated to provide stable and accurate predictions of experimental results. This study combined a detailed cracking mechanism with a real gas thermodynamic model based on the Peng-Robinson equation of state, and introduced real gas chemical potential. By comparing with experimental measurement results, the impacts of the thermodynamic and reaction models on simulation accuracy were carefully studied. The results demonstrate that, within a wide range of conditions (pressure 3–10 MPa, flow rate 1–5 g/s, temperature 300–1004 K), the calculation model based on real gas thermodynamics predicts outlet temperatures and conversion rates with higher accuracy compared to ideal gas. The non-ideal gas effect of chemical potential at 3 MPa has a slight impact on the n-decane cracking reaction system. But this effect increases with increasing pressure. Under 10 MPa pressure, the real gas effects of chemical potential may result in changes reaching 40% in the rate of progress variables (ROPs). Furthermore, when using the same complete real gas thermodynamics, the Detailed mechanism has higher accuracy in predicting fuel temperature, conversion rate and product distribution, than PPD or Lumped mechanisms. The differences in the simulation results from different reaction models mainly due to the different descriptions of reaction rate rules and intermediate products. This work provides a more accurate method for simulating the supercritical pressure cracking process of fuel in cooling channels.

Numerical study on the flow characteristics of ultrahigh pressure gas affected by valve opening time based a real gas model

Numerical study on the flow characteristics of ultrahigh pressure gas affected by valve opening time based a real gas model

Reducing Environmental Impact of Jet Engines by Hydrogen Co-combustion

Due to the need to mitigate global warming, there is a growing interest in alternative fuels for various means of transport, including aviation gas-turbine engines. The work aimed to check the impact of hydrogen co-combustion on the performance and emissions of aircraft engines. Zero-dimensional models of JetCat P140 RXI and DGEN 380 engines developed in the GSP (Gas Turbine Simulation Program) program were used in the research. Combustion calculations in GSP are based on the real gas model and NASA Chemical Equilibrium Applications (CEA) equations. The performance of the engines fueled by Jet A-1 and blends containing hydrogen or methane were calculated. The simulations were performed at the design point on the ground, and then in flight for selected altitudes and flight speeds. With an increase in the gas content in the blend, the thrust and temperature behind the turbine slightly increase, and the specific fuel consumption decreases, because hydrogen and methane have a higher calorific value. The performance of JetCat and DGEN 380 engines was calculated for blends of kerosene with methane or hydrogen. This knowledge will be used to convert these engines to gaseous fuels. In terms of fuels and emissions, GSP has limitations related to the set of available chemicals and the zero-dimensional model of the combustor.

Performance of a supercritical carbon dioxide compressor using a streamline curvature based throughflow method

Supercritical carbon dioxide (sCO2) has emerged as a promising working fluid for the Brayton power cycle, offering enhanced efficiency due to its high density and low viscosity near the critical point. A critical component of the sCO2 Brayton cycle is the turbomachinery, namely the compressor. The pronounced sensitivity of the thermophysical properties of sCO2 in the vicinity of the critical point where the compressor operates can significantly impact the performance characteristics of sCO2 compressors. This study presents a two-dimensional (2D) streamline curvature-based throughflow method, considering real gas thermophysical properties, to analyze a centrifugal compressor operating with sCO2 at near-critical inlet conditions. The method’s validity is established through comparisons of the predicted performance characteristics with those of the Sandia National Laboratories compressor and by comparing the predicted flow field with the pitch-averaged flow field obtained from computational fluid dynamic (CFD) analysis. Moreover, various compressor intake conditions including subcritical vapor, supercritical vapor, supercritical liquid, and near-critical conditions are investigated to explore their impact on compressor performance. The streamline curvature-based throughflow method demonstrates its effectiveness by achieving significant agreement between the flow field and performance characteristics, both at design and off-design conditions where efficiency predictions were within 5.84% near the best efficiency point compared to CFD simulations. At near critical conditions, a maximum of 3201% increase the computational run-time required for CFD based computation was observed compared to superheated conditions while only a maximum of 164% increase in run-time was observed in the throughflow based computations as a result of the numerical under-relaxation required.

Virial equation of state for a granular system.

The equation of state for an ideal gas is simple, which is . In the case of imperfect gases where mutual interactions among the constituents are important, pressure P can be expressed as the series expansion of density n with appropriate coefficients, known as virial coefficients . In this paper, we have obtained the first four virial coefficients for a model interaction potential using multidimensional Monte-Carlo integration and importance sampling methods. Next, we perform molecular dynamics simulations with the same for a many-particle system to obtain P as a function of T and n. We compare our numerical data with the virial equation of state.

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Uniqueness of a Generalized Solution for a One-Dimensional Thermal Explosion Model of a Compressible Micropolar Real Gas

In this paper, we analyze a quasi-linear parabolic initial-boundary problem describing the thermal explosion of a compressible micropolar real gas in one spatial dimension. The model contains five variables, mass density, velocity, microrotation, temperature, and the mass fraction of unburned fuel, while the associated problem contains homogeneous boundary conditions. The aim of this work is to prove the uniqueness theorem of the generalized solution for the mentioned initial-boundary problem. The uniqueness of the solution, together with the proven existence of the solution, makes the described initial-boundary problem theoretically consistent, which provides a basis for the development of numerical methods and the engineering application of the model.

Ultrathin PEI-functionalized carboxyl covalent organic framework membranes for efficient CO2/N2 separation

Covalent organic frameworks (COF) are deemed as disruptive membrane materials owing to their versatile functionalities, high stability and ordered nanochannels. However, the size mismatch between the COF intrinsic pore and gas molecules becomes a grand challenge when using COF membrane for carbon capture. Herein, we propose a new type of polymer-functionalized COF laminar membranes through grafting CO2-phlic polyethyleneimine (PEI) polymer onto carboxylic acid COF (cCOF) laminar membranes. The cCOF nanosheets with high density of carboxyl groups are prepared via modified single phase solution method and then assembled to fabricate membranes. Further, the cCOF membranes are functionalized with PEI using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS) coupling chemistry. The introduction of abundant amino groups from PEI afford the affinity of membranes toward CO2. Meanwhile, the graft of the PEI polymers reduces the defects or pinholes on the membrane surface. As a result, the PEI functionalized cCOF membranes exhibit a high CO2 permeance of 1004 GPU and a CO2/N2 selectivity of 33.7, which reach the carbon capture target performance and show great prospect for treating real flue gas. Our approach of functionalizing cCOF membranes with tailored functionalities may inspire the design of molecule-selective COF membranes.

Targeting glutamine metabolism exhibits anti-tumor effects in thyroid cancer

BackgroundEffective treatment for patients with advanced thyroid cancer is lacking. Metabolism reprogramming is required for cancer to undergo oncogenic transformation and rapid tumorigenic growth. Glutamine is frequently used by cancer cells for active bioenergetic and biosynthetic needs. This study aims to investigate whether targeting glutamine metabolism is a promising therapeutic strategy for thyroid cancer.MethodsThe expression of glutaminase (GLS) and glutamate dehydrogenase (GDH) in thyroid cancer tissues was evaluated by immunohistochemistry, and glutamine metabolism-related genes were assessed using real time-qPCR and western blotting. The effects of glutamine metabolism inhibitor 6-diazo-5-oxo-l-norleucine (DON) on thyroid cancer cells were determined by CCK-8, clone formation assay, Edu incorporation assay, flow cytometry, and Transwell assay. The mechanistic study was performed by real time-qPCR, western blotting, Seahorse assay, and gas chromatography–mass spectrometer assay. The effect of DON prodrug (JHU-083) on thyroid cancer in vivo was assessed using xenograft tumor models in BALB/c nude mice.ResultsGLS and GDH were over-expressed in thyroid cancer tissues, and GLS expression was positively associated with lymph-node metastasis and TNM stage. The growth of thyroid cancer cells was significantly inhibited when cultured in glutamine-free medium. Targeting glutamine metabolism with DON inhibited the proliferation of thyroid cancer cells. DON treatment did not promote apoptosis, but increased the proportion of cells in the S phase, accompanied by the decreased expression of cyclin-dependent kinase 2 and cyclin A. DON treatment also significantly inhibited the migration and invasion of thyroid cancer cells by reducing the expression of N-cadherin, Vimentin, matrix metalloproteinase-2, and matrix metalloproteinase-9. Non-essential amino acids, including proline, alanine, aspartate, asparagine, and glycine, were reduced in thyroid cancer cells treated with DON, which could explain the decrease of proteins involved in migration, invasion, and cell cycle. The efficacy and safety of DON prodrug (JHU-083) for thyroid cancer treatment were verified in a mouse model. In addition to suppressing the proliferation and metastasis potential of thyroid cancer in vivo, enhanced innate immune response was also observed in JHU-083-treated xenograft tumors as a result of decreased expression of cluster of differentiation 47 and programmed cell death ligand 1.ConclusionsThyroid cancer exhibited enhanced glutamine metabolism, as evidenced by the glutamine dependence of thyroid cancer cells and high expression of multiple glutamine metabolism-related genes. Targeting glutamine metabolism with DON prodrug could be a promising therapeutic option for advanced thyroid cancer.

Numerical Simulation of the Chemical Reaction on Faraday MHD Accelerator

Magnetohydrodynamic (MHD) is one of the most promising novel propulsion technologies with the advantages of no pollution, high specific impulse, and high acceleration efficiency. As the carrier of this technology, the MHD accelerator has enormous potential for applications in hypersonic wind tunnels, supersonic ramjet engines, and deep space propulsion. In this study, a three-dimensional numerical simulation of an ideal Faraday magnetohydrodynamic (MHD) accelerator is conducted to assess the effect on performance with respect to applied potential and magnetic field intensity. The study is performed by employing a low magnetic Reynolds number MHD model coupled with a 7-component chemical reaction model to simplify the impact of real gas effects. The chemical reaction exhibits an increasing trend with rising applied potential and a decreasing trend with diminishing magnetic field strength. This variation influences the gas conductivity, subsequently affecting the velocity and thrust of the system. Specifically, at a magnetic field intensity of 2.0 T and an applied potential of 600 V, the accelerator exhibits maximum velocity and thrust growth rates of 18.6% and 59.8%, respectively.

A simulation and experimental verification of the operation of the oxidising catalytic converter in diesel engine.

This paper investigates an oxidizing catalytic converter in a diesel engine's particulate filter system, focusing on simulations and empirical studies. The converter, with a 1.4 dm3 volume and 400 cpsi channel density, features a platinum coating of 2.5 g/dm3. Scanning electron microscopy (SEM) examined its surface, revealing platinum and a highly porous structure with randomly distributed Pt crystallites. Simulations were conducted using AVL Boost, utilizing real exhaust gas concentrations to assess various converter volumes and channel densities for CO, HC, and NO2 conversion in NOX. These simulations were paralleled with empirical tests on an engine dynamometer. The comparison of simulation and experimental data showed that the simulation algorithm could accurately predict the converter's performance in reducing CO and HC levels and NO2 in NOX. This suggests that simulations can partly replace costly empirical research, offering a preliminary evaluation of the converter's future effectiveness.

Fluorinated Biphenyl Aromatic Polyimides for Gas Separation Applications: Real Gas Mixture Study

Fluorinated Biphenyl Aromatic Polyimides for Gas Separation Applications: Real Gas Mixture Study

Performance prediction and loss evaluation of the carbon dioxide supersonic nozzle considering the non-equilibrium condensation

Carbon dioxide (CO2) is being considered as a promising working medium in energy conversion and refrigeration cycles due to its unique properties. When carbon dioxide flows with supersonic in turbo machinery (compressor), the non-equilibrium effect is enhanced due to the large change of fluid velocity, resulting in non-equilibrium condensation of the blade, which will seriously affect the performance of the compressor. Considering the similarities in flow characteristics between the nozzle and the compressor blade, the condensing flow of the blade can be predicted by simulating in a nozzle. The real gas model is used. The pressure and the nucleation rate are predicted based on the modified model, and the flow losses and thermal efficiency are analyzed in different states. The results show that the pressure variation in the nozzle aligns well with the experimental data. When the fluid transitions from subcritical to supercritical, the condensation interval decreases and the peak of the nucleation rate increases. The maximum supercooling decreases gradually. The flow losses are relatively large, and the thermal efficiency is low.

The Entropy of van der Waals Fluid.

Thermodynamic state functions are fundamental quantities in many fields. In this work, the van der Waals (vdW) equation of state and calculation formulas of state functions are derived with statistical thermodynamic method in three-dimensional (3D) and two-dimensional (2D) spaces. The heat capacity at constant volume (CV,m ) or area (CA,m ) is exactly the same as that of ideal gas, but the heat capacity at constant pressure (Cp,m ) and other state functions are different from those of ideal gas. The vdW equation of state is a cubic equation, which leads to the fact that the entropy and free energy changes of vdW fluid can be expressed as explicit expressions of volume rather than pressure. Therefore, the adsorbate entropy at constant area can still be theoretically proven to have a linear relationship with the gas-phase entropy at constant volume. However, the linear correlation between it and gas-phase entropy at constant pressure is no longer strictly true in theory. In addition, since the vdW equation of state is applicable to both gas and liquid, the linear correlation between adsorbate entropy and liquid-phase entropy can also be found. At last, the reference state for real gas or fluid at a constant molar volume is suggested.

Use of near-infrared spectroscopy for the online monitoring of natural gas composition (hydrocarbons, water and CO2 content) at high pressure

The natural gas production from Brazilian pre-salt fields imposed new challenges for petrochemical industry. Actual treatment facilities are not adequate for this new scenario and studies have been conducted to apply new adsorbents materials and membranes for water and CO2 removal from natural gas at high pressures. To better develop such investigations, sensors for on-line monitoring of natural gas properties like CO2 and water content are important, since their presence affects the quality of the final product. Near infrared (NIR) spectroscopy associated to chemometric models (partial least squares) were employed for on-line monitoring of representative natural gas systems (methane/CO2, methane/water and methane/CO2/water) and a real natural gas at temperature and pressure ranges from 20 to 60 °C and 10 to 200 bar, respectively, water content up to gas saturation and CO2 content up to 50 wt%. Water solubility values used as reference for NIR Spectrometer calibration in model systems were taken from the literature and for real natural gas calculated with Cubic Plus Association (CPA) Equation of State (EoS), while CO2 content was experimentally controlled aiming to calibrate the chemometric models in the full range of pressure and temperature. Several strategies were adopted for the chemometric model’s development to obtain the best correlation between NIR spectra and experimental data. Results indicate good correlation in both calibration and validation steps attaining linear correlation coefficients (R2) higher than 0.96 for all systems investigated. The proposed methodology is a potential tool for on-line monitoring of natural gas composition, including CO2 and water content, at high-pressures and can be applied at petrochemical industries or in laboratories, dispensing sampling or any sample preparation.

A new semi-implicit pressure-based solver considering real gas effect

A new semi-implicit pressure-based solver considering the real gas effect is developed and tested. The advantage of the semi-implicit solver is that it can take a large time step, which makes the calculation speed faster than the classical density-based explicit solver. The comparison of the calculation speed between the explicit density-based solver and the new semi-implicit pressure-based solver is conducted by performing two-dimensional numerical simulations of a cryogenic nitrogen planar jet. Moreover, the developed pressure-based solver is validated by comparing the numerical results of a three-dimensional large-eddy simulation of a cryogenic nitrogen jet under the supercritical pressure condition with the experimental result. Results show that the developed pressure-based solver can calculate more than five times faster than the classical explicit density-based solver and accurately predict the jet behavior under the supercritical pressure condition.

Comprehensive Investigation of Cu2+ Adsorption from Wastewater Using Olive-Waste-Derived Adsorbents: Experimental and Molecular Insights.

This study investigates the efficacy of adsorbents from locally sourced olive waste-encompassing olive skins, leaves, and pits, recovered from the initial centrifugation of olives (OWP)-and a composite with sodium alginate (OWPSA) for the removal of Cu2+ ions from synthetic wastewater. Experimental analyses conducted at room temperature, with an initial Cu2+ concentration of 50 mg/L and a solid/liquid ratio of 1 g/L, showed that the removal efficiencies were approximately 79.54% and 94.54% for OWP and OWPSA, respectively, highlighting the positive impact of alginate on adsorption capacity. Utilizing statistical physics isotherm models, particularly the single-layer model coupled to real gas (SLMRG), allowed us to robustly fit the experimental data, providing insights into the adsorption mechanisms. Thermodynamic parameters affirmed the spontaneity and endothermic nature of the processes. Adsorption kinetics were interpreted effectively using the pseudo-second-order (PSO) model. Molecular modeling investigations, including the conductor-like screening model for real solvents (COSMO-RS), density functional theory (DFT), and atom-in-molecule (AIM) analysis, unveiled intricate molecular interactions among the adsorbent components-cellulose, hemicellulose, lignin, and alginate-and the pollutant Cu2+, confirming their physically interactive nature. These findings emphasize the synergistic application of experimental and theoretical approaches, providing a comprehensive understanding of copper adsorption dynamics at the molecular level. This methodology holds promise for unraveling intricate processes across various adsorbent materials in wastewater treatment applications.

Supercritical combustion instabilities of oxygen/kerosene mixture in a swirl coaxial injector

This study focuses on the fundamental combustion instability issues in staged combustion for liquid oxygen/kerosene rocket engines. A comprehensive and high-fidelity numerical simulation is conducted based on the Peng-Robinson real gas model. This involves combining the large eddy simulation (LES) method with the eddy-dissipation-concept (EDC) model. This study focuses on both the mixing and combustion processes within the gas-centered liquid-swirl coaxial injector and the influence of the swirl number. The results show that the numerical method can accurately predict the change of thermodynamic properties at transcritical conditions. For the injector under investigation, the dominant frequencies of near-field pressure, axial velocity, and radial velocity all coincide at 1,066 Hz. This indicates that these three parameters are coupled, but no periodic fluctuation processes are evident for tangential velocity and temperature. The time-domain pressure characteristics at monitoring points in various directions are compared and analyzed. These comparisons reveal a robust coupling relationship between pressure and axial velocity. Additionally, the numerical simulation results show that the change of the swirl number conditions at the fuel inlet has negligible effect on the evolutionary characteristics of the injector. It is confirmed that tangential velocity is not the cause of pressure fluctuations.