Multi-field Coupling Research Articles

An advanced vortex-tube technology for pure ammonia combustion with clean and steady peculiarity

The present study investigates the combustion performance of pure ammonia in a stratified vortex-tube reactive flow (SVRF) concerning stability limits, flame topology, pressure fluctuations, and emissions. The results demonstrate that the SVRF enables efficient and stable combustion of ammonia, characterized by uniform flame topology, low NO emissions, and high combustion efficiency. The lean φg stability limits consistently remain below 0.32 within the qf range of 5.0–30.0 l/min. Moreover, the flame topology remains consistently smooth and uniform throughout the process while maintaining a peak heat release above 5.0 × 107 W/m3. Additionally, pressure fluctuation amplitude generally stays within 100 Pa, indicating a remarkably steady combustion process for ammonia burning in the SVRF. The investigation focuses on the multi-field cooperative coupling, which enhances species and enthalpy transport to increase combustion strength, thereby contributing to a larger stability limit. Various criterion numbers are calculated to quantify the aero-/thermo/flame- dynamic stability. It is found that excellent flame-dynamic/thermo-acoustic stability plays a crucial role in achieving steady combustion of pure ammonia, which can be measured by Ra(x) and the “Gain” of the flame transfer function. The degree of synergy between flame disturbance and fluid disturbance, as well as the response of flame disturbance to fluid disturbance in SVRF, is identified as the primary factor influencing different levels of combustion stability performance. Furthermore, a relationship between aero-/thermo-dynamic stability and flame stability has also been discovered. Favorable aero-/thermo-dynamic stability promotes excellent flame-dynamic behavior by suppressing normal direction fluid fluctuation and resulting in more stable intensity and spatial location fluctuations of the flame. Additionally, momentum flux decreases within the interior region, enhancing good flame-dynamic stability when using pure ammonia as fuel.

Investigation of multi-field coupling mechanisms during well cement through gas hydrate layer in horizontal well

Exploitation of natural gas hydrates from horizontal wells can significantly improve the production rate and final recovery. However, the long interaction surfaces of horizontal wells may easily disturb the hydrate reservoir. Cement hydration in wellbore is an exothermic reaction, which may lead to the premature dissociation of hydrate, thereby threatening the wellbore integrity. In the present study, experimental and numerical investigations are carried out to analyze the cement hydration in a wide range of temperatures. Then, a coupled model is established considering the multi-field coupling mechanisms between horizontal wells and the hydrate reservoir during well cementing. In the proposed model, the cement hydration, phase change of hydrate, and the multiphase flow in porous hydrate layer are considered. The cement hydration process, transient temperature and pressure distributions, and the hydrate phase change are analyzed by numerical simulations. Results show that the temperature of wellbore and hydrate increases rapidly. The saturation of the hydrate layer within the region 3 times of wellbore diameter decreases significantly. The pressure at the wellbore-hydrate layer interface increases significantly, which may lead to gas penetration into the wellbore. Moreover, threats imposed by the premature dissociation of hydrate last even for a long period after well cementing.

Experimental study on CO2 flooding characteristics in low-permeability fractured reservoirs

ABSTRACT CO2 flooding in oil reservoir is a complex process, which includes fluid flow in fractured sandstone and interaction of CO2 and displaced oil. In order to thoroughly understand the CO2 flooding characteristics in low-permeability fractured reservoirs, a series of CO2 flooding experiments were conducted based on the multi-field coupling experimental system. Considering the difference of the fractured cores, pore cores and pore-fracture model, the effect of fracture, injection pressure, CO2 phase, and heterogeneity of horizontal composite on the CO2 flooding were analyzed. The results show that the oil recovery of fractured core was 46.96%, 7.13% higher than that of pore core, and there was no relatively stable gas-oil ratio (GOR) stage. For the pore-fracture model, the final recovery of two models increased from 49.45% to 45.86% at 2 MPa to 78.83% and 77.35% at 8 MPa, and the pore core was the main contributor to enhance oil recovery. The supercritical CO2 (sc-CO2) enhanced the oil recovery in post-gas breakthrough state, which accounted for final recovery 65.02%. Compared with the vertical layered heterogeneity, the horizontal composite heterogeneity had less influence on the final oil recovery, with differences of below 2%, and the highest CO2 utilization rate was occurred at the permeability model of Low-High-Low. The work provides insight on oil recovery improvement of CO2 flooding in low-permeability fractured reservoirs.

A system-level multi-field coupling algorithm for regenerative cooling thrust chamber of a LOX/methane rocket engine

A systematic and hierarchical multi-physics coupling simulation method is proposed to model the combustion, combustion-gas transonic flow, coolant transcritical flow, and transient heat transfer phenomena inside the regenerative cooling thrust chamber subsystem of a LOX/methane rocket engine. By combining this algorithm with a self-developed platform, two distributed parameter modules are developed. Based on the ground test conditions of a LOX/methane engine, a verification case is established, and transient simulation studies are conducted. Comparisons with steady-state test data show that the calculated errors for coolant temperature rise and pressure drop are not higher than 4%. The simulation results reveal the locations where the transition from liquid to supercritical state occurs within the cooling jacket and provide three peril points of wall temperature on the thrust chamber. This study comprehensively reveals the occurrence of transcritical transient processes inside the cooling channels during the regenerative cooling process, laying the foundation for future entire system simulation.

Comment on “DPM-LES investigation on flow field dynamic and acoustic characteristics of a twin-fluid nozzle by multi-field coupling method”

This paper presents some comments on “Chen, Bo, et al. "DPM-LES investigation on flow field dynamic and acoustic characteristics of a twin-fluid nozzle by multi-field coupling method." International Journal of Heat and Mass Transfer 192 (2022): 122927. “We thank the authors for conducting this valuable research. However, some points should be noted to improve their paper. In general, there are some serious concerns about the accuracy and validity of experimental and simulation results. In addition, some less important things such as the lack of definition of some symbols in their paper should be corrected. Details are mentioned below in comments 1-8.

Thermal-fluid-solid coupling analysis of vacuum brazing process for a titanium alloy plate-fin structure

Vacuum brazing is the most significant step in the production of titanium alloy plate-fin heat exchangers, and its quality regularly determines the mechanical properties and service life. In response to the demand, the thermal-fluid-solid coupling method was established, which focuses on the temperature uniformity, fluidity of brazing filler metal, residual stress distribution characteristics, and deformation distribution characteristics of titanium alloy plate-fin structure (PFS). The multi-field coupling mechanisms involved the vacuum brazing processes were investigated. The formation mechanism during the brazing process was parametrically analyzed using the developed model. The temperature distribution on PFS during vacuum brazing was non-uniform with a maximum temperature difference of less than 70 K. The velocity of fluid flow varied considerably across various regions of the brazing layer during vacuum brazing. The temperature gradient acted as the main driving force for fluid flow. Stress concentration was present at the upper surface of fins and in the middle of the backside. The PFS experienced significant deformation in the Z-axis, reaching a peak value of around 1.1 mm. By verifying experimental measurement results of deformation, the analysis approached based on the multi-field coupling was feasible and highly accurate.

A photo-mechanical coupling theory for photoisomerization hydrogel considering the distribution state of molecular chains

Owing to the possibility of controlling its specific mechanical behaviors uptaken by irradiated by light at particular wavelengths, the photoisomerization hydrogels have a broad range of potential applications. A theory connecting the optical excitation to mechanical behavior is essential to precisely control the photo-mechanical behaviors of the hydrogel. In this work, a photo-mechanical coupling theory is developed to describe the photo-mechanical responses of photoisomerization hydrogels within the framework of finite deformation continuum thermodynamics. In the model, the deformation gradient is decomposed into two parts to effectively model the light-induced deformation and the elastic one. To consider the effect of the optical excitation on mechanical behaviors, we first investigate the transporting mechanism of light in hydrogel, as well as the photochemical reaction process; and we then explore the disturbance of light irradiation on the equilibrium of the thermodynamic system of hydrogel, as well as the relationship of conformational entropy of hydrogel network with the photochemical reaction; finally, based on the entropy elasticity theory, we propose a new free energy function of the photosensitive hydrogel to consider the effect of molecular chain distribution evolution on the stiffness of the hydrogel network. With the implementation of the proposed model, we study the photo-mechanical behaviors and mechanical properties of photoisomerization hydrogels. The present research is helpful for understanding the multi-field coupling behaviors of the photosensitive hydrogel, and then providing guidelines for the application of photoisomerization hydrogel.

Microwave Regenerable Nickel, Zinc Co-doped Nitrogen-Coordinated Porous Carbon Catalyst for Nitrogen Fixation.

More than 90% of the global NH3 synthesis is dominated by the Haber-Bosch process, which consumes 2% of the worldwide energy and generates 1.44% of the global carbon emission. The electrochemical N2 reduction reaction (NRR) is regarded as an attractive alternative route to produce NH3 under mild reaction conditions, but the electrocatalysts suffer from the difficulty of N≡N cleavage. In this work, we report a leaf-like MOF-derived Ni/Zn bimetallic co-doped nitrogen-coordinated porous carbon (Ni/Zn-NPC) as a cost-effective NH3 synthesis electrocatalyst. The resultant electrocatalyst achieved a high NH3 production rate of 22.68 μg h-1 mgcat-1 at -1.0 V vs a reversible hydrogen electrode (RHE) in a 0.1 M Na2SO4 electrolyte. The Ni/Zn-NPC material can be called a microwave regenerable catalyst because microwave treatment has proven to be a crucial part of the multi-field coupling to detoxify and make the catalyst reactive, further improving its stability. Density functional theory (DFT) was chosen to explore the mechanism of Ni/Zn-NPC for NRR, providing a profound prediction of the structure of the active site and related reaction pathways and revealing that trace Ni doping optimizes the local coordination environment and N2 adsorption of Zn atoms.

Chemical dissolution of minerals in anthracite after supercritical carbon dioxide immersion: Considering mechanical damage and enhanced porosity

Carbon dioxide injection into in-situ coal seams can effectively enhance coalbed methane recovery and promote carbon sequestration, increasing energy production while reducing greenhouse gas emissions. CO2 is prone to exist in a supercritical state in deep coal seams, so it is of great significance to quantitatively describe the mechanical properties damage of coal caused by supercritical carbon dioxide (SC–CO2). Based on the non-equilibrium thermodynamic framework, a nonlinear model of SC–CO2–coal interaction is developed using the special forms of Helmholtz free energy and energy dissipation. Two damage variables are employed to quantify the irreversible degradation induced by chemical reactions and mechanical loads, respectively. The results indicate that the long-term effect of SC-CO2 can increase the porosity of anthracite by approximately 5.49%, but reduce the elastic modulus and strength by about 58% and 56% respectively. The experimental data confirms that the damage model facilitates an analysis of the interplay among SC-CO2 absorption, porosity, elastic modulus and tensile strength of anthracite. The degradation of anthracite mechanical properties is time-dependent, which means that the risk of coal-rock dynamic disasters increases with the passage of CO2 injection time. This work is expected to study the complex multi-field coupling mechanism of SC-CO2 on in-situ coal seams, providing a theoretical basis for guiding CO2 geological sequestration and CO2 enhanced coalbed methane recovery.

Correlation between meso-structures and magnetoelectric properties in 0-3 magnetoelectric composites

The quantitative characterization of macroscopic properties of 0-3 polymer-based magnetoelectric (ME) composites is the basis of their application, and the meso-structure is the source that affects their macroscopic properties. In this study, theoretical models consistent with the meso-structures of the composites are developed to address scenarios involving random, chain, and agglomeration particle distributions. The focus is on investigating the nonlinear mechanical behavior of multi-field coupling. The validity and rationality of the theoretical model are confirmed by comparing the theoretical results with existing experimental data. Based on this, the distribution characteristics of elastic field, electric field and magnetic field of 0-3 polymer-based ME composites with different particle arrangements are analyzed. Additionally, the influence of several factors on the ME properties, such as magnetic field strength and direction, particle proportion and frequency, is discussed. The results indicate that the ME performance is optimized when the direction of the densest chain row of particles aligns with the direction of the applied magnetic field. Furthermore, the phenomenon of current leakage is examined when the direction of the chain row of ferromagnetic particles coincides with the direction of polarization. To mitigate this leakage effect, a solution is proposed by adding thin layers of piezoelectric polymer to the surface of the composite, resulting in a 62.6% increase in ME performance. The research findings reveal the response mechanisms and essence of 0-3 polymer-based ME composites under applied magnetic fields, establishing a connection between meso-structures and macro properties. This provides guidance for the design and optimization of mesomorphic structures and performance, and serves as a foundation for the design, fabrication, and development of a new generation of ME devices.

Flow Velocity Deviation of Spinning Solution Under Multi-field Coupling

Flow Velocity Deviation of Spinning Solution Under Multi-field Coupling

Research on Downhole Throttling Characteristics of Gas Wells Based on Multi-Field and Multi-Phase

The formation of natural gas hydrates seriously affects the production efficiency of gas wells. Obtaining the correct temperature and pressure profile along the wellbore of gas wells is a prerequisite for accurately predicting the location of hydrate formation and using downhole throttling technology. According to the numerical iterative transfer law of wellbore microelement state parameters, a multi-field and multi-phase coupling method is proposed. Based on the analysis of typical temperature and pressure models, considering the gas well velocity field and density field, a gas well multi-phase correction coefficient is introduced. Based on the judgment method of multi-phase flow pattern, the friction gradient equation of multi-phase flow is obtained, and the respective theoretical prediction equations are created for the temperature field, pressure field, density field, and velocity field. Thereby, a wellbore temperature and pressure field model with multi-field and multi-phase coupling is established. The model was applied to K1 and K2 gas wells, and the calculation results of the research model were compared with the PIPESIM simulation results and measured values. At the same time, the mean μ, variance σ, and the coefficient of variation Cm were evaluated, and the results show that the coefficient of variation of the calculation results of this research model is less than 15%, which indicates greater accuracy than the PIPESIM simulation results. These findings provide a theoretical basis for the design of wellbore structures and the use of downhole tools.

Numerical study on natural gas hydrate production by hot water injection combined with depressurization

The low efficiency and unstable gas production of hydrate exploitation have become the difficulties restricting the commercial development of combustible ice. In this work, based on the existing geological conditions, this paper establishes a low-permeability hydrate heterogeneous reservoir model to analyze the effects of hot water injection on well and reservoir. The results show that the greater the wasted heat from the produced water and some injected water migrating to the gaseous hydrocarbon layer and the underlying at the middle and late stage of hydrate production as the hot water injection rate. Moreover, the gas and water production will suddenly appear surge phenomenon during the hydrate production due to the disappearance of the water lock effect affected by thermal-hydraulic-chemical multi-field coupling, which depends on the hot fluid properties. Therefore, the new technology of slow hot water injection after depressurization or different injection rates at different stages in the injection well is proposed in this paper. And it is also necessary to optimize the vertical position of the injection well or add a thin layer with low permeability at the bottom of the gaseous hydrocarbon layer. Finally, the hot water injection temperature should be controlled above 50 °C.

Calculation of Wellbore Fracture Pressure Under Multi Field Coupling Based on M-Integral of Configuration Mechanics

Calculation of Wellbore Fracture Pressure Under Multi Field Coupling Based on M-Integral of Configuration Mechanics

Discussion on the static-thermal test technology of aircraft

During the high-speed flight of the aircraft, the cabin body will bear aerodynamic loads, engine thrust loads, structural and equipment component mass inertial loads. At the same time, aerodynamic thermal loads will be generated due to high speed flight. With the development of hypersonic aircraft technology, the demand for multi-field coupling test is more and more common. Therefore, it is necessary to carry out the technical verification of the mechanics and thermal composite test on the ground to obtain the structural characteristics. In this paper, a certain type of aircraft cabin as the research object, carried out the research on the combined mechanical and thermal test technology. The results of this paper show that the displacement response of the cabin under the combined action of force and thermal load is consistent with the change trend of the force loading curve, and the force load has obvious influence on the displacement response of the cabin. The strain response is consistent with the trend of temperature curve, and thermal load has obvious influence on cabin deformation. Through this study, we can obtain the static-thermal test technology method, and provide the technical basis for the development of similar test technology.

CO2 corrosion prediction on 20# steel under the influence of corrosion product film

Based on corrosion thermodynamics and kinetics, considering the multi-field coupling effects of fluid flow, electrochemical reaction and mass transfer process, a new corrosion prediction mechanistic model was proposed by introducing the influence factor of corrosion product film on diffusion coefficient of ion mass transfer, which is based on the CO 2 corrosion prediction model proposed by Nesic et al. The influence of temperature, flow rate and pH value on CO 2 corrosion behavior on 20# steel was studied by orthogonal tests. Scanning electron microscopy (SEM) and energy spectrum analysis (EDS) was used to analyze the surface and cross section morphology of the corrosion product film, and the thickness of the corrosion product film was measured. The results show that the introduced influence factor can simplify the ion mass transfer calculation in the presence of corrosion product film, and the relative error between the predicted value of the modified model and the experimental results is satisfactorily controlled less than 10%. Compared with the prediction model without considering the influence of corrosion product film, the influence factor can effectively correct the high prediction value of the mechanistic model under the influence of corrosion product film, improve the accuracy and applicability of corrosion prediction, and provide important theoretical guidance for the design, manufacturing, operation and maintenance of oil and gas production pipelines and related facilities.

Research on Performance Test of the Optic-Electric Sensors for Reservoir Landslide Temperature Field Monitoring

In recent years, with the superposition of extreme climate, earthquakes, engineering disturbance and other effects, global landslide disasters occur frequently. Due to reservoir landslides being mostly in a multi-field coupling environment, the temperature field will impact the deformation and seepage fields, thereby affecting the stability of the reservoir landslide. The variation in the landslide’s surface temperature also directly affects the stress and deformation of deep rock masses. If hidden dangers are not detected in time, and corresponding measures are implemented, it is easy to cause landslide instability. In order to clarify the temperature measurement performance of different optic-electric sensors and the application characteristics of layout techniques, laboratory calibration tests of temperature sensors under different adhesives and attachment materials are carried out in this paper. It was found that the test data of the iron bar had the best effect among the four attachment materials overall. Therefore, the bar with a high-stiffness material should be preferred when selecting a pipe fitting as the fiber Bragg grating (FBG) temperature attachment in the borehole. However, considering the high requirements for the durability of sensors and layout techniques in on-site monitoring, the long-term stability of the adhesives used in actual monitoring needs to be improved. At the same time, it was found that the platinum 100 (PT100) temperature sensor has relatively higher testing accuracy (A: 0.15 + 0.002 × |t|; B: 0.30 + 0.005 × |t|), a larger temperature measurement range (−200~+850 °C) and better temperature measurement stability when compared to conventional sensors. Moreover, its resistance value has a good linear relationship with temperature. Finally, the Xinpu landslide in the Three Gorges Reservoir area was selected as the research object for on-site monitoring. There was a high correlation between the on-site monitoring results with the laboratory calibration test results. Therefore, through the performance test of optic-electric sensors in reservoir landslide temperature fields, more accurate solutions can be provided for selecting sensors and designing layout techniques to monitor the underground temperature field of landslides under different geological conditions. Thereby, grasping the real-time state information of the reservoir landslide temperature field is achieved accurately, providing an important reference for early warning, prediction, prevention and the control of reservoir landslide disasters.

Meso-scale simulation of thermal fracture in concrete based on the coupled thermal–mechanical phase-field model

Temperature-induced concrete fracture is a multi-field coupled process and the propagation of crack is complex because of the nonhomogeneity of materials. In this paper, the mesoscale concrete containing aggregate, interfacial transition zone (ITZ), and mortar is established using the random generation algorithm. The governing equations of the coupled thermal–mechanical phase-field model are established, and the finite element method is implemented to solve these equations. Several representative numerical samples are solved by the proposed coupled model, such as concrete under tension after high temperature, concrete spalling caused by high temperature, concrete cracking caused by the temperature rise of a circular hole, and cracking of confined concrete. Numerical results have shown that concrete cracks first appear at the ITZs and eventually develop into one or more major cracks. Most numerical results indicate that the influence of the length scale in the proposed phase-field model on crack propagation is little. It has shown that the application of the phase-field model to simulate mesoscale concrete fracture problems under multi-field coupling is feasible.

Complexity Study on Multi-Field Coupling Systems for Underground Coal Fires

Underground coal fires are a major disaster that needs to be urgently addressed in the coal mining industry, as they can cause waste of resources, environmental pollution, threaten the life and health of species, and cause serious damage to society and the economy. Currently, the research on the prevention and control of underground coal fires focuses more on the technical level and lacks scientific guidance at the methodological level. Based on this research gap, this paper uses CiteSpace 6.1.R6 to analyze the research hotspots and subjects in the field of underground coal fires and gives a comprehensive research overview of its microscopic chemical reaction substance and macroscopic multi-field coupling characteristics. Then, from the methodological level, it summarizes the complex system characteristics of underground coal fires and puts forward the elements and principles for the prevention and control of underground coal fire disasters under the paradigm of complex system research. This study proposes a new way of thinking for the prevention and control of underground coal fires and helps to build a whole-process prevention and control system.

Piezoelectric and magneto-optical effect of lanthanum-doped bismuth ferrite films on silicon substrate

Rhombohedral La:BiFeO3 films were successfully prepared on Si substrates by using Radio frequency magnetron sputtering method. The LaNiO3 as buffer layer is beneficial for improving the quality of the film, reducing surface roughness, and getting rid of the impure phase. The Bi0.9La0.1FeO3/LaNiO3/Si film has the largest piezoelectric coefficient with d33 reaching 4.76 pm/V, which is about 2.5 times larger than that of BiFeO3/LaNiO3/Si. The saturation magnetization and the MCD signal of BiFeO3 films are significantly enhanced by doping La3+. The MCD ellipticity of La:BiFeO3 film at 555 nm increase with the increase of La3+ concentration. Bi0.7La0.3FeO3/LaNiO3/Si film show strong magneto-optical effect with the high MCD ellipticity of 850 deg./cm, which is more than about 1.7 times larger than that of BiFeO3 film. This film is expected to be developed into a new multifunctional material with multi-field coupling of electro-opt-magnetism.