Solid-liquid Interactions Research Articles

The Effect of Liquid–Solid Interactions upon Nucleate Boiling on Rough Surfaces: Insights from Molecular Dynamics

Despite the fact that engineered surface enabling remarkable phase change heat transfer have elicited increasing attention due to their ubiquitous applications in thermal management, the underlying mechanisms of intrinsic rough structures as well as the surface wettability on bubble dynamics remain to be explored. Therefore, a modified molecular dynamics simulation of nanoscale boiling was conducted in the present work to investigate bubble nucleation on rough nanostructured substrates with different liquid-solid interactions. Specifically, the initial stage of nucleate boiling was mainly investigated and the bubble dynamic behaviors were quantitively studied under different energy coefficients. Results shows that as the contact angle decreases, the nucleation rate increases, because liquid obtains more thermal energy there compared with that on less wetting surfaces. The rough profiles of the substrate can provide nanogrooves, which can enhance initial nucleate embryos, thereby improving thermal energy transfer efficiency. Moreover, atomic energies are calculated and adopted to explain how bubble nuclei are formed on various wetting substrates. The simulation results are expected to provide guidance towards surface design in state-of-the art thermal management systems, such as the surface wettability and the nanoscale surface patterns.

Modeling liquid penetration into porous materials based on substrate and liquid surface energies

HypothesisThe widely used Lucas-Washburn (LW) equation depends on the contact angle as the driving force for liquid penetration. However, the contact angle depends on both, the liquid and the substrate. It would be desirable to predict the penetration into porous materials, without the requirement to measure the solid–liquid interaction. Here, we propose a novel modeling approach for liquid penetration from mutually independent substrate- and liquid properties. For this purpose, the contact angle in the LW-equation is replaced by polar and dispersive surface energies, utilizing the theories of Owens-Wendt-Rabel-Kaelble (OWRK), Wu, or van Oss, Good, Chaudhury (vOGC). ExperimentsThe proposed modelling approach is validated exhaustively by measuring penetration speed for 96 substrate-liquid pairings and comparing the results to model predictions based on literature- and measured data. FindingsLiquid absorption is predicted very well (R2 = 0.8–0.9) with all three approaches, spanning a wide range of penetration speed, substrate- and liquid surface energy, viscosity, and pore size. The models for liquid penetration without measurement of solid–liquid interaction (contact angle) performed well. Modeling calculations are entirely relying on physical data of the solid and the liquid phase (surface energies, viscosity and pore size), which can be measured or retrieved from databases.

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan's Surface.

Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, and the extent of Titan's habitability. Previous works have shown that a pyridine:acetylene (1:1) co-crystal forms under specific temperatures and experimental conditions; however, this has not yet been demonstrated under Titan-relevant conditions. Our work here demonstrates that the pyridine:acetylene co-crystal is stable from 90 K, Titan's average surface temperature, up to 180 K under an atmosphere of N2. In particular, the co-crystal forms via liquid-solid interactions within minutes upon mixing of the constituents at 150 K, as evidenced by distinct, new Raman bands and band shifts. X-ray diffraction (XRD) results indicate moderate anisotropic thermal expansion (about 0.5-1.1%) along the three principal axes between 90-150 K. Additionally, the co-crystal is detectable after being exposed to liquid ethane, implying stability in a residual ethane "wetting" scenario on Titan. These results suggest that the pyridine:acetylene co-crystal could form in specific geologic contexts on Titan that allow for warm environments in which liquid pyridine could persist, and as such, this cryomineral may preserve the evidence of impact, cryovolcanism, or subsurface transport in surface materials.

Droplet evaporation dynamics on heterogeneous surfaces: Numerical modeling of the stick-slip motion

The interplay between the solid surface properties and transport phenomena during sessile droplet evaporation is extremely important in solid deposition processes. Engineering design requires realistic modeling of evaporation dynamics, on heterogeneous surfaces, which is very challenging. In this study, a continuum level, sharp-interface, ALE (Arbitrary Lagrangian- Eulerian) numerical model is developed. The model can efficiently deal with the problem of the moving three-phase contact line (TPL) during evaporation by incorporating the solid-liquid interactions in a Derjaguin pressure (commonly called disjoining pressure) term. It is found that, depending on the surface roughness and the material wettability, the evaporation dynamics proceeds following the Constant Contact Angle (CCA), Constant Contact Radius (CCR) or a mixed mode (stick-slip behavior). Numerical predictions concerning droplets evaporating on rough, hydrophobic substrates, are experimentally validated showing exceptional agreement. The stick-slip motion is found to appear during evaporation and is particularly affected by specific roughness features of the surface. Our findings are compared to Shanahan's theory. Interesting insights into the mechanisms of the stick-slip motion are presented for a rough hydrophobic substrate with weak pinning effects.

Investigation of bubble nucleation on inhomogeneous wettability surfaces

ABSTRACT Surface wettability plays an essential role in bubble nucleation. This paper investigates the phase transition behaviour of argon films placed on inhomogeneous wettability substrates using molecular dynamics simulations. The location of bubble nucleation and initial nucleation time is investigated to reflect the effect of hydrophobic area fraction of inhomogeneous wettability surfaces on bubble nucleation. The results show that the bubbles appear first on the hydrophobic part of the inhomogeneous wettability surface. The relationship between hydrophobic area fraction and initial nucleation time is nonlinear. The initial nucleation time first decreases and then increases as the area of the hydrophobic region increases. In addition, the bubble nucleation process is restricted when the hydrophobic occupation is relatively large on inhomogeneous wettability surfaces. At last, the mechanism of bubble nucleation on inhomogeneous wettability surfaces is discussed in combination with the restrictive relationship between heat absorption and solid–liquid interaction energy. The amount of heat absorption does not directly determine the bubble nucleation. Bubble nucleation can arise in the location with a lower surface energy barrier once the heat absorption can overcome the solid–liquid interaction energy.

Phononic Crystal Made of Silicon Ridges on a Membrane for Liquid Sensing.

We propose the design of a phononic crystal to sense the acoustic properties of a liquid that is constituted by an array of silicon ridges on a membrane. In contrast to other concepts, the ridges are immersed in the liquid. The introduction of a suitable cavity in the periodic array gives rise to a confined defect mode with high localization in the cavity region and strong solid-liquid interaction, which make it sensitive to the acoustic properties of the liquid. By using a finite element method simulation, we theoretically study the transmission and cavity excitation of an incident flexural wave of the membrane. The observation of the vibrations of this mode can be achieved either outside the area of the phononic crystal or just above the cavity. We discuss the existence of the resonant modes, as well as its quality factor and sensitivity to liquid properties as a function of the geometrical parameters. The performance of the proposed sensor has then been tested to detect the variation in NaI concentration in a NaI-water mixture.

Molecular dynamics study of the wettability effect on the evaporation of thin liquid sodium film

The nanoscale liquid sodium film exists in the porous wick of the sodium heat pipe. Understanding its evaporation is essential for further exploring the heat transfer inside the heat pipe. Due to the solid–liquid interaction, surface wettability has significant effects on evaporation. In this work, molecular dynamics is adopted to study these effects. A cuboid evaporation system is constructed. It consists of the bottom solid surface and thin liquid sodium film. By changing the potential well depth between solid and liquid atoms, four surfaces with different wettability are built. The 400 K equilibrium evaporation is achieved. The self-diffusion coefficients of liquid atoms on four surfaces are acquired. The non-equilibrium is introduced by increasing the heat source wall’s temperature to 600 K. The main phase of evaporation is in 0–8 ns. The variation of gas atoms number is observed. The evaporation rate, average heat flux, and heat transfer coefficient are acquired. The results indicate that evaporation could be improved with surface wettability. For the 0°, 58° hydrophilic surface, the heat transfer efficiency could reach 96.9 %, 96.3 % respectively. The surface wettability effects are achieved by two paths: it enhances the heat transfer in the solid–liquid contact region and intensifies the atoms’ collision heat transfer inside the liquid film.

Effect of Wettability and Adhesion Property of Solid Margins on Water Drainage

Liquid flows at the solid surface and drains at the margin under gravity are ubiquitous in our daily lives. Previous research mainly focuses on the effect of substantial margin's wettability on liquid pinning and has proved that hydrophobicity inhibits liquids from overflowing margins while hydrophilicity plays the opposite role. However, the effect of solid margins' adhesion properties and their synergy with wettability on the overflowing behavior of water and resultant drainage behaviors are rarely studied, especially for large-volume water accumulation on the solid surface. Here, we report the solid surfaces with high-adhesion hydrophilic margin and hydrophobic margin stably pin the air-water-solid triple contact lines at the solid bottom and solid margin, respectively, and then drain water faster through stable water channels termed water channel-based drainage over a wide range of water flow rates. The hydrophilic margin promotes the overflowing of water from top to bottom. It constructs a stable "top + margin + bottom" water channel, and a high-adhesion hydrophobic margin inhibits the overflowing from margin to bottom and constructs a stable "top + margin" water channel. The constructed water channels essentially decrease marginal capillary resistances, guide top water onto the bottom or margin, and assist in draining water faster, under which gravity readily overcomes the surface tension resistance. Consequently, the water channel-based drainage mode achieves 5-8 times faster drainage behavior than the no-water channel drainage mode. The theoretical force analysis also predicts the experimental drainage volumes for different drainage modes. Overall, this article reveals marginal adhesion and wettability-dependent drainage modes and provides motivations for drainage plane design and relevant dynamic liquid-solid interaction for various applications.

Physics of droplet impact on various substrates and its current advancements in interfacial science: A review

Droplet impact dynamics is an interfacial phenomenon that is shown everywhere in nature and is the underlying of numerous technological applications including bio-printing, tissue engineering, pharmaceuticals, fight against COVID-19 pandemic, smart biomaterials, and flexible electronics. Over the last decade, expeditious advancement of novel functional interfacial surfaces, high-speed visualization, nanoscience, nanotechnology, machine learning, and computational power, as well as the connection of flow physics with interfacial science, have contributed to enhancing the understanding of relevant complex physical phenomena. Droplet, upon impacting onto substrates, can deposit, spread, bounce, and splash. Features of droplet impact physics and surface wettability necessitate elaborate solid–liquid interactions. Given the significance of droplet impact physics for healthcare and electronics, it is recommended for the scientific community to direct research studies to profound the understanding of such complex physics. Therefore, this Review initially focuses on liquid–solid interfacial science. Second, droplet impact physics on numerous solid surfaces was discussed. Substrates with various wettability and physical features were considered: hydrophilic, hydrophobic, superhydrophobic, smooth, rough, and flexible elastic surfaces. Furthermore, numerous advancements of droplet impact on solid surfaces related to advanced technologies and challenges including printed electronics, smart biomaterials, tissue engineering, machine learning, and COVID-19 pandemic were reviewed. Finally, this Review outlines future perspectives and research directions in complex droplet impact physics.

Effective decontamination of methylene blue from aqueous solutions using novel nano-magnetic biochar from green pea peels

The conversion of agricultural waste into high-value carbon products has been an attractive area in waste management strategy. This study highlighted the synthesis and effectiveness of green pea peels (GPP), green pea biochar (GPBC), and nano-ferromagnetic green pea biochar (NFGPBC) by the ferrous/ferric co-precipitation synthesis method for eliminating cationic dyes molecules from solutions. The morphological, physicochemical, and structural properties of GPP, GPBC, and NFGPBC were approved by Scanning Electron Microscopy (SEM), Transmission Emission Microscopy (TEM), Energy Dispersive X-ray (EDX), Bruneau Emmett Teller (BET), Fourier Transform Infrared spectroscopy (FTIR), and X-ray Diffraction (XRD) techniques. Vibrating Sample Magnetometry (VSM) analysis confirmed the NFGPBC magnetization performance. The capacity of each adsorbent for methylene blue removal was evaluated at various parameters of material dosage (50–250 mg/150 mL), pH (2–12), initial concentration (50–250 mg/L), contact time (0–90 min) and temperature (20–60 °C). The three developed adsorbent materials GPP, GPBC, and NFGPBC, possessed reasonable BET surface areas of 0.6836, 372.54, and 147.88 m2g-1, and the corresponding monolayer adsorption capacities of 163.93, 217.40, and 175.44 mg/g, respectively. The superior performances of GPBC and NFGPBC were due to their increased surface area compared with the parent green pea peels (GPP). The results from adsorption kinetics studies of all prepared materials were pseudo-second-order and Elovich kinetics models. The thermodynamic parameters exhibited MB sorption's favorability, spontaneity, and endothermic nature. The NFGPBC material experienced Vander Waal forces, electrostatic interaction, hydrogen bonding, and hydrophobic interactions as predominant modes of the solid-liquid interaction. The regeneration, recycling, and reusability of the synthesized GPP, GPBC, and NFGPBC performed at five adsorption cycles revealed that NFGPBC demonstrated excellent cyclical performances attaining a minimum 8.9% loss in capacity due to paramagnetic properties. Thus, NFGPBC is a green, efficient, and eco-friendly material recommended for large-scale production and application in wastewater.

Electrically Manipulated Vapor Condensation on the Dimpled Surface: Insights from Molecular Dynamics Simulations.

Random vapor nucleation leads to flooding condensation with degraded heat-transfer efficiency. Since an external electric field has a significant effect on manipulating droplets' motion, it is possible to be one of the effective methods to hinder flooding phenomena and improve the heat-transfer rate by applying the external electric field during condensation. However, the motion of nanodroplets is more sensitive to the electric field owing to the scale effect on the nanoscale. The effect of the electric field on growth has not explicitly been comprehended. This work studied the condensation processes on a nanodimpled surface under an electric field with various strengths and directions. The results showed that condensed droplets' growth under the electric field depends on the competition between the electric field force and solid-liquid interactions. Increased vertical electric field strength, the higher torsion by the electric field hindered the motion of vapor, decreased the collision frequency for water molecules with the cooled surface, and elongated the cluster when the electric field force dominates, thus deteriorating the condensation performance. While applying the horizontal electric field, the greater electric field strength leads to better condensation performance by the larger contacting area for heat exchange. A wetting transition induced by the electric field was observed when the electric field strength increased to a certain extent (E > 5.2 × 108 V/m in this study). When the V-shaped surface replaced the dimpled surface as the condensed substrate, the same wetting transition phenomena occurred under a more significant horizontal electric field strength, showing that this method is universal. Besides, different electric field frequencies influenced both the growth and the nucleation, thus exhibiting various condensation performances.

A study of how solid-liquid interactions affect flow resistance and heat transfer at different temperatures based on molecular dynamics simulations.

Non-equilibrium molecular dynamics simulations of liquid flow through the surface were performed to investigate the flow resistance and thermal resistance under conditions of different solid-liquid interactions and surface temperatures. A novel phenomenon was observed in the simulation, namely the rise of surface temperature increases the flow resistance when solid-liquid interaction is weak, but decreases the flow resistance when solid-liquid interaction is strong. A higher density of the boundary layer brings a larger friction force to increase the flow resistance. For heat transfer, it is innovative to calculate the heat conduction and convection of the boundary region discretely. The results showed that the heat transfer performance of the interface is not positively correlated with the boundary liquid density, and the structure of the boundary liquid is also crucial. We believe that this research can improve the existing theory of flow heat transfer and provide a more effective method for analyzing the flow heat transfer of the solid-liquid interface.

How droplets move on laser-structured surfaces: Determination of droplet adhesion forces on nano- and microstructured surfaces.

Lateral adhesion forces are a fundamental property of liquid-solid interactions and a key aspect of dynamic droplet mobility. But, commonly applied conventional wetting analysis is limited to static and quasi-static methods and cannot resolve dynamic and spatial liquid-solid interactions. However, droplet mobility is assumed to be affected by chemical and topographic surface inhomogeneities introduced by femtosecond laser treatment. In this study, we used a customized droplet adhesion force instrument to determine lateral adhesion forces on various femtosecond laser-structured surface designs to obtain a deeper understanding of the dynamic droplet motion with regard to chemical and topographic surface features. We show that the droplet motion was highly affected by the chemical and topographical surface design and local inhomogeneities. The droplet mobility on femtosecond laser-structured surfaces could be classified into a static, a transfer, and a kinetic regime, which is essential for designing surfaces with extreme wetting characteristics and a wide range of scientific and industrial processes. Furthermore, with proper tailoring of surface structures and chemical modification, we were able to provoke adhesion forces on self-organized laser microstructures similar to those found on the natural lotus leaves.

Microscopic liquid-gas interface effect on liquid wetting.

Young contact angle is widely applied to evaluate liquid wetting phenomena on solid surfaces. For example, it gives a truncated-spherical shape prediction of a droplet profile through the Young-Laplace equation. However, recent measurements have shown deviations between microscopic droplet profiles and the spherical shape, indicating that the conventional Young contact angle is insufficient to describe microscopic wetting phenomena. In this work, we hypothesize that a liquid-gas interface nano-bending, which is caused by the nonlinear coupling between the effects of the microscopic interface geometry and solid-liquid interactions, is responsible for this deviation. Using molecular dynamics simulations and mathematical modeling, we reveal the structure of the nano-bending and the mechanism of the nonlinear-coupled effect. We further apply our findings to illustrate a liquid microlayer with the saddle-shaped profile in nucleate boiling. The nonlinear-coupled effect is responsible for the deviation of a nano-droplet profile and also the very thin microlayer captured by different experiments. The saddle-shaped interface significantly highlights the nonlinear-coupled effect. The interface nano-bending, rather than the Young contact angle, acts as the boundary condition and dictates the liquid wetting system, especially for the case with high interface curvature. These findings provide insight into recent nano-scale droplet- and bubble-related wetting phenomena.

Complex coupling between surface charge and thermo-osmotic phenomena.

Thermo-osmotic flows, generated at liquid-solid interfaces by thermal gradients, can be used to produce electric currents from waste heat on charged surfaces. The two key parameters controlling the thermo-osmotic current are the surface charge and the interfacial enthalpy excess due to liquid-solid interactions. While it has been shown that the contribution from water to the enthalpy excess can be crucial, how this contribution is affected by surface charge remained to be understood. Here, we start by discussing how thermo-osmotic flows and induced electric currents are related to the interfacial enthalpy excess. We then use molecular dynamics simulations to investigate the impact of surface charge on the interfacial enthalpy excess, for different distributions of the surface charge, and two different wetting conditions. We observe that surface charge has a strong impact on enthalpy excess, and that the dependence of enthalpy excess on surface charge depends largely on its spatial distribution. In contrast, wetting has a very small impact on the charge-enthalpy coupling. We rationalize the results with simple analytical models, and explore their consequences for thermo-osmotic phenomena. Overall, this work provides guidelines to search for systems providing optimal waste heat recovery performance.

Investigation of surface structure-wettability coupling on heat transfer and flow characteristics in nanochannels

• The effect of surface wettability and roughness coupling is investigated by MD. • The progressively subdivided rough nanostructures are established. • The effect of wettability becomes slight when the scaling parameter exceeds 1.0. • The enhanced solid-fluid interaction energy reveals the microcosmic mechanism. The high integration of electronic devices has become an irresistible trend, what bottlenecks its development is the heat dissipation in micro/nanoscale. Surface roughness and wettability are the two main factors affecting convective heat transfer in nanochannels. However, the combined effects of wettability and roughness are still unclear. Consequently, by molecular dynamics simulation, the combined impact of wettability and roughness on heat transfer and flow characteristics are investigated in rectangular nanochannels with various wettability and progressively subdivided roughness. The results show, when the surface becomes more hydrophilic and subdivided, the temperature and Nu increase, whereas the temperature slip decreases, leading to an efficient improvement of the heat transfer process. Moreover, the velocity slip decreases, and the flow resistance increases, so the fluid flow process is relatively inhibited. Particularly, the effects of wettability and roughness are inconsonant. For the cases in this research, when the wettability scaling parameter exceeds 1.0, the hindrance of wettability to velocity development becomes slight. However, the improvement of wettability to temperature development is still significant. Microscopically, it’s found more atoms accumulate at the solid-liquid interface, and solid-liquid interaction energy enhances. This investigation provides theoretical guidance for the efficient cooling of micro/nano electronic devices.

Study on wetting and spreading behaviors of compound droplets on wedge by lattice Boltzmann method

The wetting and spreading of droplets on solid walls are commonly seen in nature. The study of such a phenomenon can deepen our understanding of solid-liquid interaction and promote the development of relevant cutting-edge technological applications. In this work, the lattice Boltzmann method based on phase field theory is used to investigate the wetting and spreading of a compound droplet on a wedge. This method combines the finite-difference solution of the Cahn-Hilliard equations for ternary fluids to capture the interface dynamics and the lattice Boltzmann method for the hydrodynamics of the flow. Symmetric compound droplets with equal interfacial tensions on a wedge are considered first. Through theoretical analysis and numerical simulation, it is found that the wetted area on the wedge increases with the decrease of the contact angle of the wedge surface and the wedge apex angle. Depending on these two factors, the droplet may or may not split on the wedge. We also find that the droplet near the critical state predicted not to split by static equilibrium analysis could split during the spreading along the wall of the wedge under certain density and viscosity ratios. Based on the simulation results, a phase diagram of the droplet splitting state is generated with the density ratio and viscosity ratio as the coordinates. As the density ratio and kinematic viscosity ratio increase, the inertia effect becomes more prominent in the wetting and spreading process and the droplet is more likely to split. By comparing the phase diagrams in different initial conditions, it is found that under the same conditions, the compound droplet with an equilibrium initial state is less likely to split than that with an unequilibrium initial state, which is possibly because the initial total energy of the former is relatively small. Our study also shows that the kinematic viscosity ratio between the left half and the right half droplet may affect the results of droplet splitting. The increase of such a viscosity difference is conducive to the splitting of the compound droplet. Besides, asymmetric compound droplets with unequal interfacial tensions are also simulated, and it is found that the greater the wrapping degree between the left half and right half, the more difficult it is to separate the compound droplet.

Reconstruction of Electric Double Layer for Long‐Life Aqueous Zinc Metal Batteries

AbstractAqueous rechargeable Zn metal batteries (AZMBs) have attracted widespread attention due to their intrinsic high volumetric capacity and low cost. However, the unstable Zn/electrolyte interface causes Zn dendrite growth and side reactions, resulting in poor Coulombic efficiency and unsatisfactory lifespan. Herein, a SiO2 reinforced‐sodium alginate (SA) hybrid film is designed to regulate solid–liquid interaction energy and spatial distribution of all species in the electric double layer (EDL) near the Zn electrode. The unique interfacial layer gives rise to a uniform distribution of Zn2+ in the Helmholtz layer through solvation sheath modulation. Moreover, theoretical calculations show that the SO42− anions and free‐water are substantially reduced in the Helmholtz layer, effectively suppressing hydrogen evolution reaction and formation of by‐products through strong charge repulsion and hydrogen bond fixing of free‐water. The reconfigured EDL not only ensures homogenous and fast Zn2+ transport kinetics for dendrite‐free Zn deposition, but also eliminates interface parasitic side reactions. The Zn@SiO2‐SA electrode enables excellent cycling stability of symmetrical cells and high‐loading full AZMBs with a lifespan over 3000 h and an areal capacity of 2.05 mAh cm−2, thus laying a solid basis for realizing practical AZMBs.

Atomistic insights into the microscope mechanism of solid–liquid interaction influencing convective heat transfer of nanochannel

Nanochannel cooling technology is widely used in the heat dissipation systems of various micro/nanoscale electronic devices or components. The consideration of resistance loss and the optimization of heat dissipation are of great significance for the widespread application of nanochannel cooling technology. A model of convective heat transfer in nanochannel with constant wall temperature is established with molecular dynamics method. The effects of solid–liquid interaction on flow and heat transfer characteristics are investigated. The microscopic mechanisms of the solid–liquid interaction influencing heat transfer performance and flow resistance of nanochannel are explored from the atomic level. The results show that the enhancement of the solid–liquid interaction leads to the increases of the coupling degree of vibration frequency between wall and liquid atoms and the orderliness of microstructure of first fluid layer, and finally facilitates heat transfer between nanochannel wall and liquid. The Nusselt number in nanochannel is not a constant and decays exponentially with the increase of temperature jump length. Meanwhile, as the solid–liquid interaction increases, the slip length decreases and the friction factor increases, which are attributed to the augment of the static structure factor, resulting in more fluid atoms in near-wall region are firmly locked by the wall. The friction factor in nanochannel not only depends on the Reynolds number, but also is closely related to the slip length. To further evaluate overall heat transfer performance of the nanochannel that considers flow resistance, the comprehensive performance coefficient is discussed. It’s found that the solid–liquid interaction is effective in improving the overall heat transfer performance of the nanochannel within a certain range.

A Minireview of the Influence of CO2 Injection on the Pore Structure of Reservoir Rocks: Advances and Outlook

The recoverable hydrocarbon reserves of conventional oil and gas resources are very limited in China. As important alternative resources, unconventional oil and gas have become a research hotspot. Though tight reservoirs have great potential to alleviate the increasing demand, issues during the development process, such as the rapid pressure depletion, fast decline in production, low productivity, and difficulties in water injection, are usually encountered due to poor physical properties like small pore throats and strong heterogeneity of the pore structure. The CO2 flooding technique could effectively replace crude oil from micro-nanopores, which is considered as a promising way to enhance the development performance of tight oil. However, precipitation and dissolution phenomena usually occur along with the CO2 injection process into reservoirs, affecting the pore structure evolution and oil displacement efficiency. In addition, artificial and natural fractures will even make this process more complicated. This paper presents the commonly used experimental approaches for CO2 injection into tight reservoirs and summarizes the main methods for investigating the influence of CO2 injection on the pore structure of reservoir rocks. Based on this, we highlighted that more attention should be paid to the influence of fractures and their dynamic changes on the evolution of pore structure during CO2 injection and the study of the solid–liquid interactions. To establish a method that could quantitatively evaluate the full-scale evolution of pore throats after CO2 injection is necessary. Meanwhile, the interaction strength of precipitation and dissolution and their effects on pore structure also remain open. Finally, a rigorous framework that could reveal the evolution mechanism and characterize the multiscale pore structure involving multiple influencing factors is urgently warranted.