Guo Model Research Articles

Impact of Climate Change on Spatiotemporal Patterns of Snow Hydrology: Conceptual Frameworks, Machine learning versus Nested Model

Snow accumulation in mountainous watersheds plays a paramount role in the hydrological cycle and environmental stability. In the current research, three different snow modeling approaches including conceptual models, Random Forest (RF) and their nested (Nested-RF) model have been implemented to project climate change. Also, three distinct calibration scenarios employing Snow Cover Area (SCA) and Snow Water Equivalent (SWE) have been used. These scenarios involve using SCA and SWE data individually or combined to calibrate both conceptual snowpack models and machine learning methods. Considering comparative analysis in the mountainous and complex topographic area of Tashk-Bakhtegan watershed as a case study, the Guo model (calibrated using both SCA and SWE data) achieves the highest prediction accuracy in predicting SCA/SWE using conceptual method. Considering various statistics, RF using the same calibration scenario demonstrates high accuracy in estimating SWE and shows promising results in detecting SCA. Considering the feature importance analysis and statistics of the RF and Nested-RF models indicate that the feeding conceptual outputs as extra information into the Nested-RF had minimal influence and even slightly reduced accuracy. Future projections using RF indicate significant reductions in mean annually SCA/SWE, especially under SSP8.5, with a 28.4% decrease in SCA and a reduction in SWE to 13.62 mm from a historical baseline of 19.4 mm. Lower emission scenarios (SSP2.6 and SSP4.5) show less drastic declines. While minor differences were observed between the best conceptual model and the RF approach in capturing spatiotemporal and annual snow patterns, these discrepancies did not reach statistical significance.

Experimental study and thermodynamic modeling of CO2+CH4 gas mixture hydrate phase equilibria for gas separation efficiency

Gas separation is a critical application of gas hydrates, and accurately predicting separation performance is crucial. In this study, we used thermodynamic calculations to predict the equilibrium phase of gas hydrates for various mole fractions of CO2 + CH4 gas mixtures. We also determined the mole fraction of each gas component trapped within the hydrate clathrate. To predict the equilibrium points, we used the Soave–Redlich–Kwong（(SRK) equation of state for the gas phase, the nonrandom two-liquid (NRTL)model for the liquid phase, and the Chen–Guo model for the hydrate phase. We modified the hydrate fugacity formula and introduced a new function to improve the accuracy of the Chen–Guo model. By incorporating experimental equilibrium results from our study and another study, we developed a correlation based on gas mixture composition and temperature, resulting in highly accurate predictions. The use of this new correlation for hydrate fugacity calculation significantly improved precision, as evidenced by an average absolute deviation percent of calculated pressures (AADP) of 1.34% for pure CO2 and 1.25% for CH4. When considering the 27 data points of different CO2 + CH4 mixtures, the AADP% was 1.98%.To implement the model to predict equilibrium phases, we used the Chen–Guo framework to determine the mole fraction of each gas component in the hydrate mixture. Interestingly, we discovered a linear correlation between the CO2 mole fraction in the hydrate and equilibrium pressure, with a slope of approximately 0.001 and a y-intercept of less than one, for all gas compositions. Therefore, we can conclude that low thermodynamic conditions (temperature and pressure) result in a high CO2 mole fraction in the hydrate phase and great separation efficiency.

Lifting relations for a generalized total-energy double-distribution-function kinetic model and their impact on compressible turbulence simulation

Recently, Qi et al. (2022) and Guo et al. (2023) proposed two alternative designs of an efficient mesoscopic method using the total-energy double-distribution-function (DDF) formulation, hereafter referred to as the Qi model and the Guo model. The two models share the same advantage of using only 40 discrete particle velocities to fully reproduce the Navier–Stokes-Fourier (NSF) system. However, the Guo model is based on a more rigorous kinetic consideration, while the Qi model relies on a more general design of the source term to allow for adjustable bulk-to-shear viscosity ratio. In this paper, we derive lifting relations for the Qi model based on two alternative approaches, namely, the Hermite expansion and the Chapman–Enskog expansion, which can be used to construct the boundary and initial conditions for the mesoscopic method. For three-dimensional compressible turbulence simulations, including compressible decaying homogeneous isotropic turbulence and Taylor–Green vortex flows, the derived two sets of lifting relations are applied to the initialization distribution function to study their impacts. Interestingly, for the Qi model, the two sets of lifting relations yield the same results without numerical artifacts, whereas for the Guo model, an appropriate lifting relation must be specified to avoid numerical artifacts resulting from the flow initialization (Qi et al., 2023).

Numerical investigation of lattice Boltzmann method-based large-eddy simulation in non-isothermal enclosed cavity airflow

This study implemented the lattice Boltzmann method-based large-eddy simulation (LBM-LES) in a wall-heated cavity turbulent flow problem with the Rayleigh number reaching 5.33 × 109. The effects of crucial parameters in LBM temperature simulation, including discrete time intervals, discrete external force models by temperature effect, and temperature discrete velocity schemes, were investigated to obtain the suggested values. In addition, the simulations' accuracy and computational efficiency were compared with those of FVM-LES. LBM-LES generally agreed with experiments, and the accuracy was comparable to FVM-LES. However, exceedingly small discrete time intervals induced numerical oscillations in velocity and temperature at high frequencies, yielding significant errors. The accuracy of the discrete external force model satisfied Guo model > primitive model > He model. For temperature particles' discrete velocity scheme, D3Q7 was already sufficiently accurate, and higher schemes (D3Q19 and D3Q27) did not increase the accuracy further. LBM-LES and FVM-LES were concordant with respect to predicting various physical quantities, and the accuracy of LBM-LES in the near-wall region was slightly higher than that of the FVM-LES. Single-core and multicore computational speeds of LBM-LES were 4–8 fold higher than FVM-LES. The multicore parallelism of LBM-LES also exceeded FVM-LES and became more evident as CPU cores increased.

A novel model to predict phase equilibrium state of hydrates from the relationship of gas solubility

The study of hydrate phase equilibrium is crucial for ensuring the safety of natural gas pipeline transportation and the process of hydrate recovery. While scientists typically focus on the chemical potential of hydrates, the role of gas solubility in hydrate phase equilibrium remains unclear, and this study fills this gap. This work investigated the solubility of gas at the equilibrium point of the hydrate phase through model calculations. Additionally, a new model of hydrate phase equilibrium is established based on the relationship between solubility. Firstly, a solubility model based on gas-liquid equilibrium theory showed higher prediction accuracy in comparison to the PR equation and Duan model and was then used to calculate gas solubility under hydrate phase equilibrium conditions. Afterwards, a novel model was developed to predict hydrate equilibrium state based on the relationship between gas solubility and hydrate phase equilibrium temperature, and it was further compared with the Chen–Guo model and CSMGem in terms of prediction accuracy under pure water and brine settings. The results showed: (a) The calculation deviation of the solubility model was 0.7–8.7% in pure water settings and 2.6–11.7% in brine settings; (b) A strong linear correlation between the phase equilibrium temperature of hydrates and gas solubility was also found; (c) This proposed model achieved over 10 times the accuracy of the Chen–Guo model and the CSMGem in predicting the phase equilibrium state of N2 and CO2 hydrates, and 3–10 times higher accuracy than that of the Chen–Guo model and CSMGem in brine. This work suggests that the gas solubility equilibrium theory can provide a more accurate prediction of hydrate states.

Cyclic Behavior and Stress-Strain Model of Nano-SiO2-Modified Recycled Aggregate Concrete.

Recycled aggregate concrete (RAC) possesses different mechanical properties than ordinary concrete because of inherent faults in recycled aggregates (RAs), such as the old interfacial transition zone (ITZ). However, the application of nano-SiO2 presents an effective methodology to enhance the quality of RA. In this study, nano-SiO2-modified recycled aggregate (SRA) was used to replace natural aggregate (NA), and the stress-strain relationships and cyclic behavior of nano-SiO2-modified recycled aggregate concrete (SRAC) with different SRA replacement rates were investigated. After evaluating the skeleton curve of SRAC specimens, the existing constitutive models were compared. Additionally, the study also proposed a stress-strain model designed to predict the mechanical behavior of concrete in relation to the SRA replacement rate. The results show that compared with RAC, the axial compressive strength of SRAC specimens showed increases of 40.27%, 29.21%, 26.55%, 16.37%, and 8.41% at specific SRA replacement rates of 0%, 30%, 50%, 70%, and 100%, respectively. Moreover, the study found that the Guo model's calculated results can accurately predict the skeleton curves of SRAC specimens.

Application of Machine Learning in Predicting Formation Condition of Multi-Gas Hydrate

Thermodynamic models are usually employed to predict formation condition of hydrates. However, these thermodynamic models usually require a large amount of calculations to approach phase equilibrium. Additionally, parameters included in the thermodynamic model need to be calibrated based on the experimental data, which leads to high uncertainties in the predicted results. With the rapid development of artificial intelligence (AI), machine learning as one of sub-discipline has been developed and been widely applied in various research area. In this work, machine learning was innovatively employed to predict the formation condition of natural gas hydrates to overcome the high computation cost and low accuracy. Three data-driven models, Random Forest (RF), Naive Bayes (NB), Support Vector Regression (SVR) were tentatively used to determine the formation condition of hydrate formed by pure and mixed gases. Experimental data reported in previous work were taken to train and test the machine learning models. As a representative thermodynamic model the Chen–Guo (C-G) model was used to analyze the computational efficiency and accuracy of machine learning models. The comparison of results predicted by C-G model and machine learning models with the experimental data indicated that the RF model performed better than the NB and SVR models on both computation speed and accuracy. According to the experimental data, the average AADP calculated by the C-G model is 7.62 times that calculated by the RF model. Meanwhile, the average time costed by the C-G model is 75.65 times that by the RF model. Compared with the other two machine learning models, the RF model is expected to be used in predicting the formation condition of natural gas hydrate under field conditions.

Hydrate phase equilibrium of hydrogen-natural gas blends: Experimental study and thermodynamic modeling

Blending hydrogen (H2) into natural gas pipelines has become an effective way to transport H2 on a large scale. Due to the difference in properties between H2 and natural gas, the natural gas hydrate (NGH) phase equilibrium will be changed after blending H2, which influences the flow assurance in pipelines. In this work, hydrate phase equilibrium for CH4 + H2, CH4 + C2H6 + H2, and CH4 + C2H6 + C3H8 + H2 multicomponent systems had been measured at a temperature range from 274.24 K to 289.59 K by the isochoric pressure-search method. The results show the inhibition effect on CH4 hydrate formation of blending H2 to 20% is a little better than the 5.0 wt.%CH3OH solution. In addition, the Chen–Guo model was adopted to predict hydrogen-natural gas blends (HNGB) hydrates formation conditions, and model results have a good agreement with the experimental data. Average enthalpies of HNGB hydrates dissociation were also calculated utilizing the Clausius-Clapeyron equation, which was in the range of 68.02 kJ/mol and 90.17 kJ/mol. These studies provide basic data for flow assurance when transporting HNGB in pipelines.

Integration of a dissipative contact force model into vehicle–track dynamics for analysing wheel–rail dynamic interaction under short-wavelength irregularity

Wheel–rail dynamic interaction under short-wavelength irregularity which has a detrimental effect on the service life of vehicle and track components, is of crucial importance to be estimated accurately. Aiming at this, dissipative contact force models are integrated into a validated vehicle–track coupled dynamics model, which enables to consider the energy dissipation at the wheel–rail interface. Wheel–rail interactions for different dissipative contact force models are evaluated, and the Hu–Guo model is selected as the most suitable one for wheel–rail interaction analysis. The wheel–rail interactions for the Hu–Guo model and Hertz theory are analysed under different track irregularities including sinusoidal rail corrugation and rail welded joints. The simulation results indicate that the Hu–Guo model has little effect on the normal interaction at low frequencies, but reduces the contact force fluctuation amplitude obviously at high frequencies above 600 Hz, with a more significant reduction at the resonance peak of high frequency range. The Hu–Guo model has an obvious contact force phase lead compared with the Hertz theory at higher frequencies above 1250 Hz. The Hu–Guo dissipative contact force model is needed for the wheel–rail interaction analysis at high frequencies above 600 Hz.

Calculation of the Gas Injection Rate and Pipe String Erosion in Nitrogen Drilling Systems

Detailed information is provided for the design and construction of nitrogen drilling in a coal seam. Two prototype wells are considered. The Guo model is used to calculate the required minimum gas injection rate, while the Finnie, Sommerfeld, and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings. The calculated minimum gas injection rates are 67.4 m3/min (with water) and 49.4 m3/min (without water), and the actual field of use is 90–120 m3/min. The difference between the calculated injection pressure and the field value is 6.5%–15.2% (formation with water) and 0.65%–7.32% (formation without water). The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam. The Finnie, Sommerfeld, and Tulsa models have different sensitivities to cutting densities, particle size, impact velocity and angle, and pipe string hardness.

Natural Gas Hydrate Prediction and Prevention Methods of City Gate Stations

During the process of distributing natural gas to urban users through city gate stations, hydrate is easy to form due to the existence of throttling effect which causes safety risks. To handle this problem, a program to quickly calculate hydrate prediction and prevention methods for city gate stations is developed. The hydrate formation temperature is calculated through the Chen–Guo model, and the Peng–Robinson equation of state combined with the balance criterion is used to analyze the water condensation in the throttling process. The Wilson activity coefficient model is used to calculate the mass fraction in the liquid phase of thermodynamic inhibitors for preventing hydrates. Considering the volatility of inhibitors, the principle of isothermal flash has been utilized to calculate the total injection volume of the inhibitor. Moreover, the effects of commonly used methanol and ethylene glycol inhibitors are discussed. In terms of safety and sustainability, the ethanol inhibitor, which is considered for the first time, exhibited better prevention and control effects under conditions with relatively high temperature and low pressure after throttling. Combined with the actual working conditions of a gate station, methanol has the best inhibitory effect, followed by ethylene glycol. From an economic point of view, the benefits of the gas phase of the inhibitor during the delivery of natural gas are obvious; therefore, the method of methanol injection is recommended for hydrate prevention. If the gas phase benefits of the inhibitor are not considered, the ethylene glycol injection method becomes more economical.

Pore-scale study of non-ideal gas dynamics under tight confinement considering rarefaction, denseness and molecular interactions

Non-ideal gas flow behaviors are investigated by an Enskog-Vlasov type kinetic model considering the simultaneous effects of gas molecule size (volume exclusion) and long-range intermolecular attractions at the molecular level, which corresponds to the real gas equation of state at the macroscopic level. The Knudsen minimum is captured and a local Knudsen maximum may appear if gas molecule sizes or intermolecular attractive forces are considered. Although the Boltzmann equation is applicable to all the flow regimes in rarefied gas dynamics, it is invalid for a dense gas system, such as a tight or a shale gas reservoir. The Boltzmann-BGK model and the Enskog-BGK model overestimate and underestimate the mass flow rate of real gases, respectively, while Guo's model is more accurate to investigate real gas dynamics under tight confinements from a physical perspective. As the channel width increases or the solid fraction decreases, the impact of intermolecular interactions reduces. An anomalous slip regime occurs if both the volume exclusion and long-range intermolecular attraction are considered. Although the rarefaction effect is more prominent at larger Knudsen numbers, the flow at a smaller Knudsen number (a larger solid fraction or channel width) contributes to more practical gas production. The effect of long-range intermolecular attractions on gas dynamics decreases with temperature for real gases. This paper provides a novel insight into the real gas flow characteristics in a dense gas system, such as tight and shale gas reservoirs, from molecular natures of fluids.

Review on the Applications and Modifications of the Chen–Guo Model for Hydrate Formation and Dissociation

Research on gas hydrates is relevant to many industrial issues including flow assurance in oil and gas production and transportation, exploitation of new energy deposits in the form of natural gas ...

Semi-clathrate hydrate phase stability conditions for methane + TetraButylAmmonium Bromide (TBAB)/TetraButylAmmonium Acetate (TBAA) + water system: Experimental measurements and thermodynamic modeling

One of the promising applications of clathrate/gas hydrates is the transport and storage of natural gas. Semi-clathrate hydrates have received more attention due to milder pressure/temperature stability conditions compared to ordinary clathrate hydrates. The most commonly reported semi-clathrate hydrates are formed from a combination of gas + water + quaternary ammonium salts. In this work, a total of 53 equilibrium data for semi-clathrate hydrates of methane + TetraButylAmmonium Bromide (TBAB)/TetraButylAmmonium Acetate (TBAA) aqueous solutions were experimentally measured. For TBAB, three concentrations including 0.0350, 0.0490, and 0.1500 mass fractions were used. For TBAA, a solution with a 0.0990 mass fraction was used. Additionally, the modified Chen–Guo model was applied to calculate the hydrate phase equilibrium conditions of methane + TBAB/TBAA aqueous solutions. The model can accurately calculate the aforementioned semi-clathrate hydrate phase equilibrium conditions with the Average Absolute Deviations ((AAD)T and (AAD)P) of 0.1 K and 0.08 MPa, respectively. The temperature increments for 0.0350, 0.0490, and 0.1500 mass fractions of TBAB are 7.7, 9.4, and 13.5 K, respectively. This value for 0.0990 mass fraction of TBAA is 6.2 K. Therefore, it is concluded that TBAB is a stronger hydrate promoter compared to TBAA.

Modeling Phase Behavior of Semi-Clathrate Hydrates of CO2, CH4, and N2 in Aqueous Solution of Tetra-n-butyl Ammonium Fluoride

Abstract Semi-clathrate hydrates are members of the class of clathrate compounds. In comparison with clathrate hydrates, where the networks are formed only by H2O molecules, the networks of semi-clathrate hydrates are formed by mixtures of H2O and quaternary ammonium salts (QASs). The addition of QASs to the solution enables to improve the formation of semi-clathrate hydrates at much milder conditions comparing to clathrate hydrates. In this work, we study the phase equilibria of semi-clathrate hydrates of CH4, CO2, and N2 gas in an aqueous solution of tetra-n-butyl ammonium fluoride (TBAF). An extension of the Chen–Guo model is proposed as a thermodynamic model. The Peng–Robinson equation of state (PREOS) was applied to calculate the fugacity of the gas phase and in order to determine the water activity in the presence of TBAF, a correlation between the system temperature, the TBAF mass fraction, and the nature of the guest molecules has been used. These equations were solved simultaneously and through optimizing tuning parameters via the Nelder–Mead simplex algorithm. The results are compared to experimental data and good agreement is observed.

A Semianalytical Productivity Model for a Vertically Fractured Well With Arbitrary Fracture Length Under Complex Boundary Conditions

Summary Vertically fractured wells are used widely to achieve efficient development of low-permeability reservoirs and unconventional tight reservoirs. Currently, there are some commonly adopted productivity models for a fractured vertical well, including the Giger (1985) model, the Economides model (Economides et al. 1989), the Joshi (1991) model, the Guo model (Guo and Evans 1993), the Zhang (1999) model, and others. However, these models are only suitable for either short fractures or long fractures, and thus cannot satisfy the need for arbitrary-length fracture selection. In addition, these models have certain requirements for boundary conditions, and few models consider the nonuniform flow in actual hydraulic factures. Therefore, it is desirable to establish a productivity model for vertically fractured wells with arbitrary fracture length under complex boundary conditions. In this paper, first, we evaluate the existing fractured-vertical-well productivity models in detail. After that, on the basis of the potential superposition principle and mirror-image method, we develop the productivity model for a fractured vertical well with arbitrary fracture length under different boundary conditions. Grounded in this model, further considering the frictional pressure drop caused by fracture-flow nonuniformity, we establish the productivity equation of a finite-conductivity-fracture vertical well with nonuniform flow in the fracture. Finally, after comparing with the existing model under certain conditions, the reliability of the proposed model is verified successfully. Results show that the Giger model assumes that the boundary in the fracture-extension direction is impermeable, and the pressure wave reaches the boundary earlier than the constant-pressure boundary, which is perpendicular to the extension direction of the fracture, whereas both the Economides model and the Joshi model assume that the boundary in the fracture-extension direction is far, and is always farther than the boundary perpendicular to the direction of the fracture extension. The results forecast by the previous models will deviate greatly from actual well-production performance, if the real field case cannot meet the requirements of these models. The proposed model is not only in good agreement with the previous models at given conditions, but is also suitable for fractured vertical wells under arbitrary-length fractures and complex boundary conditions. Compared with the existing models, the correctness and reasonableness of the model are shown, and the application of the proposed model is broadened. For the development of low-permeability and unconventional tight oil and gas reservoirs with fractured vertical wells or fractured horizontal wells, the establishment and application of this model have great theoretical significance and application value for production prediction. This model can be a foundation or reference for productivity prediction of low-permeability and unconventional tight oil and gas reservoirs with fractured vertical wells or fractured horizontal wells.

Progressive taxation and macroeconomic stability in two-sector models with social constant returns

It has been shown that, in the two-sector Benhabib–Farmer–Guo model with technologies of social increasing returns that exhibits indeterminacy, progressive income taxes de-stabilize the economy. This paper revisits the robustness of the tax implication in the two-sector Benhabib–Nishimura model with technologies of social constant returns that exhibits indeterminacy. We show that a progressive income tax stabilizes the economy against sunspot fluctuations, and thus the tax implication based on the two-sector Benhabib–Farmer–Guo model is not robust.

Thermodynamic modeling of equilibrium conditions of CH4/CO2/N2 clathrate hydrate in presence of aqueous solution of sodium chloride inhibitor

ABSTRACTIn this work, the effect of sodium chloride (NaCl) on thermodynamic properties of CH4+CO2+N2 hydrate formation and equilibrium condition has been studied. The three-phase (hydrate–liquid–gas) equilibrium calculation has been carried out using the Peng–Robinson equation of state (PR EoS) and Universal Quasi Chemical (UNIQUAC) activity coefficient models. The PR EoS coupled with classic mixing rule is applied for the vapor phase. The calculations of the gas hydrate formation pressures are performed in the absence and presence of sodium chloride inhibitor for the gas hydrate systems. The Chen–Guo model has been used for the hydrate phase and the UNIQUAC activity coefficient is applied for non-ideality of the liquid phase. To obtain higher accuracy, the solubility of the gases in the aqueous phase is also taken into account using pressure corrected Henry's law. Finally, the stepwise procedure has been followed to obtain the results and compared with the experimental results. The addition of 2% (by volume) sodium chloride to water results in large shifts in phase equilibrium boundary to increase pressure for the same temperature condition.

Phase equilibria prediction model for semiclathrate hydrates formed from CH4, CO2, and N2 in the presence of tetra-n-butyl ammonium bromide

ABSTRACTIn this work, a prediction model was studied and carried out to predict phase equilibrium conditions for semiclathrate hydrates formed from the ternary system of liquid water, tetra-n-butyl ammonium bromide, and CO2, CH4, or N2. Based on the Soave–Redlich–Kwong equation of state along with the Chen–Guo model, the predictions of phase equilibria of semiclathrates of CO2, CH4, and N2 + pure water/tetra-n-butyl ammonium bromide aqueous solution has been made. A new correlation for activity relating to the system temperature and tetra-n-butyl ammonium bromide concentration has been proposed. The prediction results were analyzed and showed good agreement with the experimental data.

Vapor–hydrate two-phase and vapor–liquid–hydrate three-phase equilibrium calculation of THF/CH4/N2 hydrates

Tetrahydrofuran (THF) is a popular thermodynamic promotor for gas hydrates. Nonetheless, the phase equilibrium calculations of THF hydrates are limited given the abundant experimental data. In this work, we successfully applied the Chen–Guo hydrate model to the THF/CH4/N2 system with different compositions of CH4/N2 gas mixtures. In consideration of various reaction conditions, we proposed the vapor–hydrate two-phase and vapor–liquid–hydrate three-phase models for the equilibrium separations of THF/CH4/N2 via hydrate formation. The hydrate formation condition and equilibrium separation of CH4/N2 in 6mol% THF solution were calculated and compared with experimental results. The average absolute relative deviations between the experimental and calculated data for hydrate formation pressure and equilibrium separation compositions are 6.86% and 7.56%, respectively. This demonstrates that the Chen–Guo model has relatively high accuracy for the equilibrium calculation of THF/CH4/N2 hydrates. This work provides an effective approach to predict the thermodynamic phase behavior of hydrates containing promotors or inhibitors.