The hybrid CO_(2) thermal technique has achieved considerable success globally in extracting residual heavy oil from reserves following a long-term steam stimulation process.Using microscopic visualization experiments...The hybrid CO_(2) thermal technique has achieved considerable success globally in extracting residual heavy oil from reserves following a long-term steam stimulation process.Using microscopic visualization experiments and molecular dynamics(MD)simulations,this study investigates the microscopic enhanced oil recovery(EOR)mechanisms underlying residual oil removal using hybrid CO_(2) thermal systems.Based on the experimental models for the occurrence of heavy oil,this study evaluates the performance of hybrid CO_(2) thermal systems under various conditions using MD simulations.The results demonstrate that introducing CO_(2) molecules into heavy oil can effectively penetrate and decompose dense aggregates that are originally formed on hydrophobic surfaces.A stable miscible hybrid CO_(2) thermal system,with a high effective distribution ratio of CO_(2),proficiently reduces the interaction energies between heavy oil and rock surfaces,as well as within heavy oil.A visualization analysis of the interactions reveals that strong van der Waals(vdW)attractions occur between CO_(2) and heavy oil molecules,effectively promoting the decomposition and swelling of heavy oil.This unlocks the residual oil on the hydrophobic surfaces.Considering the impacts of temperature and CO_(2) concentration,an optimal gas-to-steam injection ratio(here,the CO_(2):steam ratio)ranging between 1:6 and 1:9 is recommended.This study examines the microscopic mechanisms underlying the hybrid CO_(2) thermal technique at a molecular scale,providing a significant theoretical guide for its expanded application in EOR.展开更多
Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirm...Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.展开更多
Extended experiments were conducted on the oscillation characteristics of merged liquid slugs in a horizontally oriented polymer pulsating heat pipe(PHP).The PHP’s serpentine channel comprised 14 parallel channels wi...Extended experiments were conducted on the oscillation characteristics of merged liquid slugs in a horizontally oriented polymer pulsating heat pipe(PHP).The PHP’s serpentine channel comprised 14 parallel channels with a width of 1.3 mm and a height of 1.1 mm.The evaporator and condenser sections were 25 and 50 mm long,respectively,and the adiabatic section in between was 75mmlong.Using a plastic 3D printer and semi-transparent filament made from acrylonitrile butadiene styrene,the serpentine channel was printed directly onto a thin polycarbonate sheet to form the PHP.The PHP was charged with hydrofluoroether-7100.In the experiments,the evaporator section was heated,and the condenser section was cooled using high-temperature and low-temperature thermostatic baths,respectively.Flow patterns of the working fluid were obtained with temperature distributions of the PHP.A mathematical model was developed to analyze the flow patterns.Themerged liquid slugs were observed in every two channels,and their oscillation characteristics were found to be approximately the same in time and space.It was also found that the oscillations of the merged liquid slugs became slower,but the heat transfer rate of the PHP increased with a decrease in the filling ratio of the working fluid.This is because vapor condensation was enhanced in vapor plugs as the filling ratio decreased.However,the filling ratio had a lower limit,and the heat transfer rate was maximum when the filling ratio was 40.6%in the present experimental range.展开更多
The objective of this paper is to investigate the effect of water temperature on cavitation characteristics in a turbopump inducer,a series of experiments at different temperatures have been conducted in a newly devel...The objective of this paper is to investigate the effect of water temperature on cavitation characteristics in a turbopump inducer,a series of experiments at different temperatures have been conducted in a newly developed visualization test facility.It is found that higher temperature shows little influence on the non-cavitation performance and breakdown characteristic in the investigated range.The relationship between cavitation development and pressure fluctuation has been discussed in detail.Higher temperature displays a remarkable stabilization effect on the cavitation excited pressure.In particular,the inception cavitation numbers of both the super-synchronous rotating cavitation and synchronous rotating cavitation are decreased at higher temperatures,and the corresponding frequencies are not affected,while the amplitudes are distinctly reduced,and the occurrence range of synchronous rotating cavitation is significantly narrowed.A generalized RayleighPlesset equation has been employed to account for the thermal effect on the bubble development,which may provide a deep insight in understanding the experimental results.Thermal effect is found to act as a remarkable dissipation mechanism to suppress the bubble growth,smooth the collapse.In particular,the excited pressure during collapse is smaller at higher temperatures,which may lead to the stabilization effect of high temperature in this study.展开更多
During the displacement of water plugging with binary flooding in internally heterogeneous reservoirs,it is essential to understand the distributions of remaining oil as well as the oil displacement mechanisms at diff...During the displacement of water plugging with binary flooding in internally heterogeneous reservoirs,it is essential to understand the distributions of remaining oil as well as the oil displacement mechanisms at different stages.In this study,two types of internally heterogeneous systems,i.e.,vertical and horizontal wells are investigated experimentally through a microscopic approach.The results show that plugging agent types have a greater impact on oil recovery than well types,and foam injection can enhance oil recovery more effectively than gel injection.Additionally,the injection sequence of plugging agents significantly affects oil displacement efficiency.Injecting gel after foam is more beneficial.According to the present results,the main formation mechanisms of remaining oil in each displacement stage are influenced by:capillary force,viscous force,inertial force,shear force,microscopic fingering&channeling.展开更多
Computational fluid dynamics was used and a numerical simulation analysis of boiling heat transfer in microchannels with three depths and three cross-sectional profiles was conducted.The heat transfer coefficient and ...Computational fluid dynamics was used and a numerical simulation analysis of boiling heat transfer in microchannels with three depths and three cross-sectional profiles was conducted.The heat transfer coefficient and bubble generation process of three microchannel structures with a width of 80μm and a depth of 40,60,and 80μm were compared during the boiling process,and the factors influencing bubble generation were studied.A visual test bench was built,and test substrates of different sizes were prepared using a micro-nano laser.During the test,the behavior characteristics of the bubbles on the boiling surface and the temperature change of the heated wall were collected with a high-speed camera and a temperature sensor.It was found that the microchannel with a depth of 80μm had the largest heat transfer coefficient and shortest bubble growth period,the rectangular channel had a larger peak heat transfer coefficient and a lower frequency of bubble occurrence,while the V-shaped channel had the shortest growth period,i.e.,the highest frequency of bubble occurrence,but its heat transfer coefficient was smaller than that of the rectangular channel.展开更多
Due to its long lifespan and high sand-removal efficiency,gravel packing is one of the most applied sand control methods during the recovery of reservoirs with sanding problems.The blockage and retention of injected s...Due to its long lifespan and high sand-removal efficiency,gravel packing is one of the most applied sand control methods during the recovery of reservoirs with sanding problems.The blockage and retention of injected sand in a gravel pack is a complex process affected by multiple mechanisms.The majority of existing studies based on the phenomenological deep bed filtration(DBF)theory focused on the gravel pack’s overall permeability damage and failed to obtain the inner-pore particle distribution pattern.In this work,experiments and simulations were carried out to reveal the particle distribution in a gravel pack during flooding.In particular,through real-time monitoring of particle migration,the penetration depth and distribution pattern of invaded particles with different gravel-sand particle ratios,fluid viscosities and injection rates could be determined.By simplifying each unit bed element(UBE)into a pore-throat structure with four tunnels(two horizontals for discharge and two verticals for sedimentation),a new network simulation method,which combines deep bed filtration with a particle trajectory model,was implemented.Cross comparison of experimental and numerical results demonstrates the validity and accuracy of the model.展开更多
The lunar surface is a typical vacuum environment,and its harsh heat rejection conditions bring great challenges to the thermal control technology of the exploration mission.In addition to the radiator,the sublimator ...The lunar surface is a typical vacuum environment,and its harsh heat rejection conditions bring great challenges to the thermal control technology of the exploration mission.In addition to the radiator,the sublimator is recommended as one of the promising options for heat rejection.The sublimator makes use of water to freeze and sublimate in a porous medium,rejecting heat to the vacuum environment.The complex heat and mass transfer process involves many physical phenomena such as the freezing and sublimation phase change of water in the porous medium and the movement of the phase-change interface.In this paper,the visualized ground-based experimental approaches of space sublimation cooling were presented to reveal the moving law of threephase point and the growth phenomenon of ice-peak and icicle in microchannels under vacuum conditions.The visualized experiments and results prove that the freezing ice is divided into the porous ice-peak and the transparent icicle.As the sublimation progresses,the phase-change interface moves downward steadily,the length of the ice-peak increases,but the icicle decreases.The visualized experiments of space sublimation cooling in the capillary have guiding significance to reveal the sublimation cooling mechanism of water in the sublimator for lunar exploration missions.展开更多
Solid contamination existing as solid particles in power fluid transmission systems may lead to transmission performance reduction,system failures,and component damage.The hydraulic reservoir will deposit the contamin...Solid contamination existing as solid particles in power fluid transmission systems may lead to transmission performance reduction,system failures,and component damage.The hydraulic reservoir will deposit the contamination and store hydraulic fluid.To investigate its purification ability for solid contamination,experiments and simulations for the motion and deposition status of the typical hydraulic system particles are carried out to reveal the interaction of particles and fluid in hydraulic water reservoirs.The results show that the CFD-DEM coupling method could predict the accurate deposition position of iron particles and sand particles when ignoring the small-scale turbulence effect in the flow field.Besides,the particle motion traces and deposition patterns in the reservoir illustrate that the flow development on the bottom surface results in the particles turning,and particles tend to settle in the low flow energy position.The motion of particles is also linked to particles Stokes number,and the same-size sand particles are easily driven by the fluid.The contribution of this paper could provide a guide for predicting the particle motion and deposition pattern in the hydraulic reservoir.展开更多
The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir r...The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir remain unclear. The flowback efficiencies of different types of surfactant micellar solutions were evaluated by core experiments, a multi-level pore-throat system micromodel characterizing pore-throat structures of low permeability reservoir was made, and flooding and flowback experiments of brine and surfactant micellar solutions of different salinities were conducted with the micromodel to show the oil flowback process in micron pores under the effect of surfactant micellar solution visually and reveal the mechanisms of enhancing displacement and flowback efficiency of surfactant micellar solution. During the displacement and flowback of brine and low salinity surfactant micellar solution, many small droplets were produced, when the small droplets passed through pore-throats, huge percolation resistance was created due to Jamin’s effect, leading to the rise of displacement and flowback pressure differences and the drop of flowback efficiency. The surfactant micellar solutions with critical salinity and optimal salinity that were miscible with crude oil to form Winsor Ⅲ micro-emulsion didnot produce mass small droplets, so they could effectively reduce percolation resistance and enhance oil displacement and flowback efficiency.展开更多
The biomimetic hydrofoils are frequently employed to enhance cavitation performance,although the underlying mechanisms remain to be fully elucidated.This study utilizes a cavitation visualization experimental system a...The biomimetic hydrofoils are frequently employed to enhance cavitation performance,although the underlying mechanisms remain to be fully elucidated.This study utilizes a cavitation visualization experimental system and mechanical characterization to experimentally investigate the transient cavitation features of a NACA0015 hydrofoil and its biomimetic counterparts with modified lending-edge.The findings demonstrate that,in comparison with the flat hydrofoil,the biomimetic hydrofoil experiences a cavitation morphology transition at a lower cavitation number,with a reduction of up to 0.38.Moreover,the maximum cavity length and the maximum cavitation area are reduced by 17.11%,17.32%,signifying a reduction in cavitation intensity.Proper orthogonal decomposition(POD)analysis revealed that the primary mechanism for the enhanced cavitation performance of the leading-edge wave structured biomimetic hydrofoil is the suppression of cloud cavitation shedding.At an attack angle of 6°,the biomimetic hydrofoil exhibited the highest lift coefficient increase of 18.56%,corresponding to a lift-to-drag ratio improvement of 9.56%.By analyzing the cavitation patterns of the two hydrofoils,it is evident that the rate of change in the maximum cavity length isolines for the biomimetic hydrofoil is lower than that of the flat hydrofoil.For an equivalent level of cavitation intensity,the biomimetic hydrofoil exhibits a lower cavitation number compared with the flat hydrofoil.These demonstrate that the wavy leading-edge design of the biomimetic hydrofoil effectively reduces the severity of cavitation,thereby confirming the efficacy of the biomimetic hydrofoil in enhancing cavitation performance.展开更多
Along with the anti-cavitation performance,the high speed and the high power density,are the main trends in the development of centrifugal pumps.At present,the most effective method is to install an inducer in front o...Along with the anti-cavitation performance,the high speed and the high power density,are the main trends in the development of centrifugal pumps.At present,the most effective method is to install an inducer in front of the impeller.However,the tip leakage of the inducer results in the vortex cavitation at the blade leading edge of the inducer,and the cavitating flow inside the inducer seriously interferes with the hydraulic behavior of the inducer as well as the impeller with the development of the cavitation,thus to badly affect the operational reliability of the high-speed centrifugal pump.In the present paper,the cavitating flow in a high-speed centrifugal pump with an inducer is investigated by numerical simulations and visual experiments for different cavitation numbers.A typical evolution process of the cavitation is shown,including the inception,the development and the deterioration.A general description of the pump head-drop phenomenon is made through the study of the local and global flow fields,and the relationship between the vapor distribution and the static pressure distribution along the inducer is determined to describe the evolution of the cavitation.This paper intends to provide the foundation for studying the overall cavitation state of a high-speed centrifugal pump,and designing the inducer with a better cavitation resistance.展开更多
Latent heat thermal energy storage systems can effectively fill the gap between energy storage and application, and phase-change materials(PCMs) are crucial media for storing thermal energy. Therefore, how to maximize...Latent heat thermal energy storage systems can effectively fill the gap between energy storage and application, and phase-change materials(PCMs) are crucial media for storing thermal energy. Therefore, how to maximize the utilization efficiency of PCMs has attracted widespread attention. In this study, the thermal behavior of two thermal storage units employing a spiral tube and straight tube as heat transfer tubes was experimentally researched and comprehensively compared. Stefan numbers were used to investigate the impact of the heat transfer fluid temperature on the PCM melting process. The temperature distribution of PCMs,temporal evolution of the melting front, and temperature variations of measurement points in both tanks were compared. The average temperature and energy storage of PCMs were calculated to evaluate the thermal performance of different configurations. The results indicate that compared to cylinder B(with a straight tube), the energy storage in cylinder A(with a spiral tube)increased by 78.8%, 38.5%, and 19.6% at Stefan numbers of 1.08, 1.28, and 1.48, respectively. Moreover, the increase in the Stefan number simultaneously ascended the average temperature and energy storage of PCMs in containers A and B, causing the shortening of the melting time. When the Stefan number was increased from 1.28 to 1.48, the storage capacity was raised from3233.18 to 3463.8 k J, and the total melting time was decreased by 34.2% from 547.5 to 360 min after the PCM was loaded in cylinder A. The research results lay a certain foundation for a deeper study of enhanced heat transfer in spiral tubes.展开更多
The primary wind of a low-NO_x coaxial swirling burner was visualized byusing glycol as smog tracer. The information of the visual flow field was input into a computerthrough image-capturing card with CCD camera as th...The primary wind of a low-NO_x coaxial swirling burner was visualized byusing glycol as smog tracer. The information of the visual flow field was input into a computerthrough image-capturing card with CCD camera as the image-capturing element. The boundary of thevisual zone, i. e. , the interface of the primary wind and secondary wind was obtained by imageprocessing. The fractal dimension (FD) of the boundary was examined and found to vary from 1. 10 to1. 40 with S_1, S_2 and ζ_1 . It is concluded that when FD is small, the complex level of theinterface is low, and mixture between the primary and secondary wind is weak near the exit of theburner at the initial phase of combustion resulting in stratified flow; when FD is big, mixturebecomes strong near the exit of the burner. It is showed that the flow with FD ranging from 1.10 to1. 20 is stratified flow, which is benefical to reduce NO_x yield and the flow with FD from 1. 25 to1. 40 is mixed flow, producing much NO_x. The mechanism of the forming of stratified flow and mixedflow was theoretically analyzed. The corresponding S_1 , S_2 and ζ_1 of these flows were given.展开更多
The oil-gas two-phase hybrid transportation technology is one of the innovative technology directions for the exploitation and transportation of marginal and deep ocean oilfields.The helical-axial multiphase pump is a...The oil-gas two-phase hybrid transportation technology is one of the innovative technology directions for the exploitation and transportation of marginal and deep ocean oilfields.The helical-axial multiphase pump is a key equipment for oil and gas extraction.At this stage,most of the research on this kind of pump focuses on the improvement of the structure and conveying performance.However,because of insufficient understanding of the flow behavior and mechanism of bubbles,it is easy to cause the gas-liquid separation.In this paper,the numerical simulation and test are combined to explore the changes in the bubble trajectory and flow structure of the helical-axial multiphase pump.The results shown that when the speed is lower than 1200 r/min,the bubble reaches the maximum volume at 1/2 of the midline of the impeller blade and it contact with the pressure surface,broken to the suction surface.When the rotation speed is higher than 1450 r/min,the number of bubbles in the impeller increases and the size decreases.The backflow occurs in the tip clearance and strength increases continuously.The research results have important significance for the theoretical design and engineering application of the helical-axial multiphase pump.展开更多
基金financially supported by the National Natural Science Foundation of China(No.U20B6003)the China Scholarship Council(No.202306440015)a project of the China Petroleum&Chemical Corporation(No.P22174)。
文摘The hybrid CO_(2) thermal technique has achieved considerable success globally in extracting residual heavy oil from reserves following a long-term steam stimulation process.Using microscopic visualization experiments and molecular dynamics(MD)simulations,this study investigates the microscopic enhanced oil recovery(EOR)mechanisms underlying residual oil removal using hybrid CO_(2) thermal systems.Based on the experimental models for the occurrence of heavy oil,this study evaluates the performance of hybrid CO_(2) thermal systems under various conditions using MD simulations.The results demonstrate that introducing CO_(2) molecules into heavy oil can effectively penetrate and decompose dense aggregates that are originally formed on hydrophobic surfaces.A stable miscible hybrid CO_(2) thermal system,with a high effective distribution ratio of CO_(2),proficiently reduces the interaction energies between heavy oil and rock surfaces,as well as within heavy oil.A visualization analysis of the interactions reveals that strong van der Waals(vdW)attractions occur between CO_(2) and heavy oil molecules,effectively promoting the decomposition and swelling of heavy oil.This unlocks the residual oil on the hydrophobic surfaces.Considering the impacts of temperature and CO_(2) concentration,an optimal gas-to-steam injection ratio(here,the CO_(2):steam ratio)ranging between 1:6 and 1:9 is recommended.This study examines the microscopic mechanisms underlying the hybrid CO_(2) thermal technique at a molecular scale,providing a significant theoretical guide for its expanded application in EOR.
基金supported by the National Key R&D Program of China(2021YFB3301100)Beijing University of Chemical Technology Interdisciplinary Program(XK2023-07).
文摘Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.
基金supported by JSPS KAKENHI Grant Number 22K03947.
文摘Extended experiments were conducted on the oscillation characteristics of merged liquid slugs in a horizontally oriented polymer pulsating heat pipe(PHP).The PHP’s serpentine channel comprised 14 parallel channels with a width of 1.3 mm and a height of 1.1 mm.The evaporator and condenser sections were 25 and 50 mm long,respectively,and the adiabatic section in between was 75mmlong.Using a plastic 3D printer and semi-transparent filament made from acrylonitrile butadiene styrene,the serpentine channel was printed directly onto a thin polycarbonate sheet to form the PHP.The PHP was charged with hydrofluoroether-7100.In the experiments,the evaporator section was heated,and the condenser section was cooled using high-temperature and low-temperature thermostatic baths,respectively.Flow patterns of the working fluid were obtained with temperature distributions of the PHP.A mathematical model was developed to analyze the flow patterns.Themerged liquid slugs were observed in every two channels,and their oscillation characteristics were found to be approximately the same in time and space.It was also found that the oscillations of the merged liquid slugs became slower,but the heat transfer rate of the PHP increased with a decrease in the filling ratio of the working fluid.This is because vapor condensation was enhanced in vapor plugs as the filling ratio decreased.However,the filling ratio had a lower limit,and the heat transfer rate was maximum when the filling ratio was 40.6%in the present experimental range.
文摘The objective of this paper is to investigate the effect of water temperature on cavitation characteristics in a turbopump inducer,a series of experiments at different temperatures have been conducted in a newly developed visualization test facility.It is found that higher temperature shows little influence on the non-cavitation performance and breakdown characteristic in the investigated range.The relationship between cavitation development and pressure fluctuation has been discussed in detail.Higher temperature displays a remarkable stabilization effect on the cavitation excited pressure.In particular,the inception cavitation numbers of both the super-synchronous rotating cavitation and synchronous rotating cavitation are decreased at higher temperatures,and the corresponding frequencies are not affected,while the amplitudes are distinctly reduced,and the occurrence range of synchronous rotating cavitation is significantly narrowed.A generalized RayleighPlesset equation has been employed to account for the thermal effect on the bubble development,which may provide a deep insight in understanding the experimental results.Thermal effect is found to act as a remarkable dissipation mechanism to suppress the bubble growth,smooth the collapse.In particular,the excited pressure during collapse is smaller at higher temperatures,which may lead to the stabilization effect of high temperature in this study.
文摘During the displacement of water plugging with binary flooding in internally heterogeneous reservoirs,it is essential to understand the distributions of remaining oil as well as the oil displacement mechanisms at different stages.In this study,two types of internally heterogeneous systems,i.e.,vertical and horizontal wells are investigated experimentally through a microscopic approach.The results show that plugging agent types have a greater impact on oil recovery than well types,and foam injection can enhance oil recovery more effectively than gel injection.Additionally,the injection sequence of plugging agents significantly affects oil displacement efficiency.Injecting gel after foam is more beneficial.According to the present results,the main formation mechanisms of remaining oil in each displacement stage are influenced by:capillary force,viscous force,inertial force,shear force,microscopic fingering&channeling.
基金supported by the National Natural Science Foundation of China Youth Program(Grant No.51905328).
文摘Computational fluid dynamics was used and a numerical simulation analysis of boiling heat transfer in microchannels with three depths and three cross-sectional profiles was conducted.The heat transfer coefficient and bubble generation process of three microchannel structures with a width of 80μm and a depth of 40,60,and 80μm were compared during the boiling process,and the factors influencing bubble generation were studied.A visual test bench was built,and test substrates of different sizes were prepared using a micro-nano laser.During the test,the behavior characteristics of the bubbles on the boiling surface and the temperature change of the heated wall were collected with a high-speed camera and a temperature sensor.It was found that the microchannel with a depth of 80μm had the largest heat transfer coefficient and shortest bubble growth period,the rectangular channel had a larger peak heat transfer coefficient and a lower frequency of bubble occurrence,while the V-shaped channel had the shortest growth period,i.e.,the highest frequency of bubble occurrence,but its heat transfer coefficient was smaller than that of the rectangular channel.
基金supported by Outstanding Youth Fund of Shandong Province(ZR2020YQ36).
文摘Due to its long lifespan and high sand-removal efficiency,gravel packing is one of the most applied sand control methods during the recovery of reservoirs with sanding problems.The blockage and retention of injected sand in a gravel pack is a complex process affected by multiple mechanisms.The majority of existing studies based on the phenomenological deep bed filtration(DBF)theory focused on the gravel pack’s overall permeability damage and failed to obtain the inner-pore particle distribution pattern.In this work,experiments and simulations were carried out to reveal the particle distribution in a gravel pack during flooding.In particular,through real-time monitoring of particle migration,the penetration depth and distribution pattern of invaded particles with different gravel-sand particle ratios,fluid viscosities and injection rates could be determined.By simplifying each unit bed element(UBE)into a pore-throat structure with four tunnels(two horizontals for discharge and two verticals for sedimentation),a new network simulation method,which combines deep bed filtration with a particle trajectory model,was implemented.Cross comparison of experimental and numerical results demonstrates the validity and accuracy of the model.
基金primarily funded by the cooperative project offered by Beijing Key Laboratory of Space Thermal Control Technologyfunded by China Postdoctoral Science Foundation(No.2020 M671618)。
文摘The lunar surface is a typical vacuum environment,and its harsh heat rejection conditions bring great challenges to the thermal control technology of the exploration mission.In addition to the radiator,the sublimator is recommended as one of the promising options for heat rejection.The sublimator makes use of water to freeze and sublimate in a porous medium,rejecting heat to the vacuum environment.The complex heat and mass transfer process involves many physical phenomena such as the freezing and sublimation phase change of water in the porous medium and the movement of the phase-change interface.In this paper,the visualized ground-based experimental approaches of space sublimation cooling were presented to reveal the moving law of threephase point and the growth phenomenon of ice-peak and icicle in microchannels under vacuum conditions.The visualized experiments and results prove that the freezing ice is divided into the porous ice-peak and the transparent icicle.As the sublimation progresses,the phase-change interface moves downward steadily,the length of the ice-peak increases,but the icicle decreases.The visualized experiments of space sublimation cooling in the capillary have guiding significance to reveal the sublimation cooling mechanism of water in the sublimator for lunar exploration missions.
基金National Key Research and Development Program of China(Grant No.2018YFB2000703)National Natural Science Foundation of China(Grant No.51975507).
文摘Solid contamination existing as solid particles in power fluid transmission systems may lead to transmission performance reduction,system failures,and component damage.The hydraulic reservoir will deposit the contamination and store hydraulic fluid.To investigate its purification ability for solid contamination,experiments and simulations for the motion and deposition status of the typical hydraulic system particles are carried out to reveal the interaction of particles and fluid in hydraulic water reservoirs.The results show that the CFD-DEM coupling method could predict the accurate deposition position of iron particles and sand particles when ignoring the small-scale turbulence effect in the flow field.Besides,the particle motion traces and deposition patterns in the reservoir illustrate that the flow development on the bottom surface results in the particles turning,and particles tend to settle in the low flow energy position.The motion of particles is also linked to particles Stokes number,and the same-size sand particles are easily driven by the fluid.The contribution of this paper could provide a guide for predicting the particle motion and deposition pattern in the hydraulic reservoir.
基金Supported by the China National Science and Technology Major Project (2017ZX05009-005-003)Research Fund of China University of Petroleum (Beijing)(2462019QNXZ04)。
文摘The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir remain unclear. The flowback efficiencies of different types of surfactant micellar solutions were evaluated by core experiments, a multi-level pore-throat system micromodel characterizing pore-throat structures of low permeability reservoir was made, and flooding and flowback experiments of brine and surfactant micellar solutions of different salinities were conducted with the micromodel to show the oil flowback process in micron pores under the effect of surfactant micellar solution visually and reveal the mechanisms of enhancing displacement and flowback efficiency of surfactant micellar solution. During the displacement and flowback of brine and low salinity surfactant micellar solution, many small droplets were produced, when the small droplets passed through pore-throats, huge percolation resistance was created due to Jamin’s effect, leading to the rise of displacement and flowback pressure differences and the drop of flowback efficiency. The surfactant micellar solutions with critical salinity and optimal salinity that were miscible with crude oil to form Winsor Ⅲ micro-emulsion didnot produce mass small droplets, so they could effectively reduce percolation resistance and enhance oil displacement and flowback efficiency.
基金Project supported by the National Natural Science Foundation of China(Grant No.U24A20139)supported by the Key Research and Development Project of Zhejiang Province(Grant No.22024C01117)the KeyResearch and Development Project of Hangzhou(Grant No.2023SZD0041).
文摘The biomimetic hydrofoils are frequently employed to enhance cavitation performance,although the underlying mechanisms remain to be fully elucidated.This study utilizes a cavitation visualization experimental system and mechanical characterization to experimentally investigate the transient cavitation features of a NACA0015 hydrofoil and its biomimetic counterparts with modified lending-edge.The findings demonstrate that,in comparison with the flat hydrofoil,the biomimetic hydrofoil experiences a cavitation morphology transition at a lower cavitation number,with a reduction of up to 0.38.Moreover,the maximum cavity length and the maximum cavitation area are reduced by 17.11%,17.32%,signifying a reduction in cavitation intensity.Proper orthogonal decomposition(POD)analysis revealed that the primary mechanism for the enhanced cavitation performance of the leading-edge wave structured biomimetic hydrofoil is the suppression of cloud cavitation shedding.At an attack angle of 6°,the biomimetic hydrofoil exhibited the highest lift coefficient increase of 18.56%,corresponding to a lift-to-drag ratio improvement of 9.56%.By analyzing the cavitation patterns of the two hydrofoils,it is evident that the rate of change in the maximum cavity length isolines for the biomimetic hydrofoil is lower than that of the flat hydrofoil.For an equivalent level of cavitation intensity,the biomimetic hydrofoil exhibits a lower cavitation number compared with the flat hydrofoil.These demonstrate that the wavy leading-edge design of the biomimetic hydrofoil effectively reduces the severity of cavitation,thereby confirming the efficacy of the biomimetic hydrofoil in enhancing cavitation performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.51776189,52076196)the Natural Science Foundation of Zhejiang Province(Grant No.LR20E090001)the Key Research and Development Program of Zhejiang Province(Grant No.2021C05006).
文摘Along with the anti-cavitation performance,the high speed and the high power density,are the main trends in the development of centrifugal pumps.At present,the most effective method is to install an inducer in front of the impeller.However,the tip leakage of the inducer results in the vortex cavitation at the blade leading edge of the inducer,and the cavitating flow inside the inducer seriously interferes with the hydraulic behavior of the inducer as well as the impeller with the development of the cavitation,thus to badly affect the operational reliability of the high-speed centrifugal pump.In the present paper,the cavitating flow in a high-speed centrifugal pump with an inducer is investigated by numerical simulations and visual experiments for different cavitation numbers.A typical evolution process of the cavitation is shown,including the inception,the development and the deterioration.A general description of the pump head-drop phenomenon is made through the study of the local and global flow fields,and the relationship between the vapor distribution and the static pressure distribution along the inducer is determined to describe the evolution of the cavitation.This paper intends to provide the foundation for studying the overall cavitation state of a high-speed centrifugal pump,and designing the inducer with a better cavitation resistance.
基金supported by the National Natural Science Foundation of China (Grant No. 51876147)。
文摘Latent heat thermal energy storage systems can effectively fill the gap between energy storage and application, and phase-change materials(PCMs) are crucial media for storing thermal energy. Therefore, how to maximize the utilization efficiency of PCMs has attracted widespread attention. In this study, the thermal behavior of two thermal storage units employing a spiral tube and straight tube as heat transfer tubes was experimentally researched and comprehensively compared. Stefan numbers were used to investigate the impact of the heat transfer fluid temperature on the PCM melting process. The temperature distribution of PCMs,temporal evolution of the melting front, and temperature variations of measurement points in both tanks were compared. The average temperature and energy storage of PCMs were calculated to evaluate the thermal performance of different configurations. The results indicate that compared to cylinder B(with a straight tube), the energy storage in cylinder A(with a spiral tube)increased by 78.8%, 38.5%, and 19.6% at Stefan numbers of 1.08, 1.28, and 1.48, respectively. Moreover, the increase in the Stefan number simultaneously ascended the average temperature and energy storage of PCMs in containers A and B, causing the shortening of the melting time. When the Stefan number was increased from 1.28 to 1.48, the storage capacity was raised from3233.18 to 3463.8 k J, and the total melting time was decreased by 34.2% from 547.5 to 360 min after the PCM was loaded in cylinder A. The research results lay a certain foundation for a deeper study of enhanced heat transfer in spiral tubes.
文摘The primary wind of a low-NO_x coaxial swirling burner was visualized byusing glycol as smog tracer. The information of the visual flow field was input into a computerthrough image-capturing card with CCD camera as the image-capturing element. The boundary of thevisual zone, i. e. , the interface of the primary wind and secondary wind was obtained by imageprocessing. The fractal dimension (FD) of the boundary was examined and found to vary from 1. 10 to1. 40 with S_1, S_2 and ζ_1 . It is concluded that when FD is small, the complex level of theinterface is low, and mixture between the primary and secondary wind is weak near the exit of theburner at the initial phase of combustion resulting in stratified flow; when FD is big, mixturebecomes strong near the exit of the burner. It is showed that the flow with FD ranging from 1.10 to1. 20 is stratified flow, which is benefical to reduce NO_x yield and the flow with FD from 1. 25 to1. 40 is mixed flow, producing much NO_x. The mechanism of the forming of stratified flow and mixedflow was theoretically analyzed. The corresponding S_1 , S_2 and ζ_1 of these flows were given.
基金supported by the National Natural Science Foundation of China(Grant Nos.51969014,51609113)supported by the China Postdoctoral Science Foundation(Grant No.2018M633651XB)+2 种基金the Natural Science Foundation of Gansu(Grant No.20JR5RA456)the Outstanding Young Talents Funding Scheme of Gansu province(Grant No.20JR10RA204)the Hong liu Outstanding Young Talents Funding Schemeof Lanzhou University of Technology.
文摘The oil-gas two-phase hybrid transportation technology is one of the innovative technology directions for the exploitation and transportation of marginal and deep ocean oilfields.The helical-axial multiphase pump is a key equipment for oil and gas extraction.At this stage,most of the research on this kind of pump focuses on the improvement of the structure and conveying performance.However,because of insufficient understanding of the flow behavior and mechanism of bubbles,it is easy to cause the gas-liquid separation.In this paper,the numerical simulation and test are combined to explore the changes in the bubble trajectory and flow structure of the helical-axial multiphase pump.The results shown that when the speed is lower than 1200 r/min,the bubble reaches the maximum volume at 1/2 of the midline of the impeller blade and it contact with the pressure surface,broken to the suction surface.When the rotation speed is higher than 1450 r/min,the number of bubbles in the impeller increases and the size decreases.The backflow occurs in the tip clearance and strength increases continuously.The research results have important significance for the theoretical design and engineering application of the helical-axial multiphase pump.
