Static Pressure Gradient Research Articles

Numerical Simulation and Analysis of the Airflow Field in the Crushing Chamber of the Hammer Mill.

The airflow dynamics within hammer mills' crushing chambers significantly affect material crushing and screening. Understanding the crushing mechanism necessitates studying the airflow distribution. Using a self-built crushing test platform and computational fluid dynamics (CFD) simulations, we investigated the impact of screen aperture size, rotor speed, hammer-screen clearance, hammer quantity, and mass flow rate on airflow distribution within the rotor region, circulation layer, and screen apertures. Results indicated generally uniform axial static pressure distribution within the rotor region, with radial gradients. Increased rotor speed improved radial static pressure gradients, while higher mass flow rates reduced them. The highest airflow velocity within the circulation layer reached approximately 83.46% of the hammer tip's tangential velocity. Greater rotor speed and hammer quantity intensified circulation airflow, whereas increased mass flow rate decreased it. Eddies formed within screen apertures with higher rotor speeds and hammer quantities but diminished with larger apertures and higher mass flow rates. Static pressure differences across screen apertures increased with mass flow rate and rotor speed but decreased significantly with larger apertures. This systematic examination provides insights into airflow distribution within hammer mill crushing chambers, offering a theoretical foundation for improving and designing hammer mills.

The synergistic effects of salinity and pressure gradients on sustainable energy conversion in nanofluidics

In recent years, osmotic energy conversion and electrokinetic energy conversion within nanochannels have received widespread attention. In this work, we propose four kinds of energy conversion models in nanochannels, including pressure-driven power generation, salinity-driven power generation, the positive combination of pressure gradient and salinity gradient and the negative combination. The changes in ion transport behavior and energy conversion characteristics are analyzed. The results show that the combination of salinity gradient and pressure gradient is not a simple superposition. Compared to the power of the single drive mode before optimization, the power under positive combination (PC) can reach 1.02 pW, and the power enhancement ratio is as high as 1.6. The negative combination has a certain optimization potential under a large concentration ratio and small pressure gradient condition. The higher the surface charge density, the greater the output power, but the optimization effect worsens. On the contrary, a larger channel length corresponds to a smaller output power, but the optimization effect becomes better. The reasonable choice of surface charge density and channel length needs to be weighed. These studies provide valuable guidance for the design of future nanofluidic energy conversion devices.

Numerical analysis of novel wavy wall based control of turbulent boundary layer separation

In this work, a comprehensive insight into the new passive flow control method, i.e. a two-dimensional streamwise waviness (recently proposed by Dróżdż et al. [1]) is provided using Large Eddy Simulations. This approach was demonstrated to be effective in postponing turbulent boundary layer separation at high Re, which is out of reach for other commonly known passive flow control strategies. Although the effectiveness of the wavy wall in delaying flow separation has been confirmed, the physical mechanisms standing behind the skin friction enhancement are not fully understood which opens a space for future work. Of particular interest is an insight into the fluid flow in the near-wall region just above the waviness and this paper is aimed at doing so. To separate the effect of the global adverse pressure gradient, the results were confronted with the ones obtained under zero pressure gradient conditions for the identical wavy wall geometry and the same Reτ=2500. Also additional simulations of the turbulent boundary layer building up on the flat wall were conducted to have an additional reference for the flow fields obtained above the wavy wall under zero and adverse pressure gradients respectively. A detailed inspection of the streamwise velocity and its fluctuation profiles indicated that the contribution of the global adverse pressure gradient to the flow statistics begins when the Rotta-Clauser pressure gradient parameter β≥3. The paper confirms an enhancement of the wall shear stress τw downstream the corrugation, which is the necessary condition to postpone the separation. Interestingly, the effect of increased τw was not observed for the case with the same waviness and without pressure gradient.

Experimental study on the influence of inlet pressure on the flow parameters at the reverse flow boundary of vortex tube and its relation with energy separation performance

The performance of the vortex tube (also known as the Ranque-Hilsch tube) is significantly influenced by the inlet pressure and the internal flow processes, which can be categorized into two distinct flows: the center and the outer flow. The reverse flow boundary, acting as the interface between the two flows, plays a crucial role in energy separation. However, the research on the location of the reverse flow boundary and the associated flow parameters and energy transfer at this boundary are still insufficient. Therefore, this research employs the measurement method of interpolation probe to analyze the distribution of the reverse flow boundary and the specific flow parameters at this boundary. These parameters include static pressure gradient, angular velocity, and static temperature gradient, which substantially impact energy separation. A qualitative analysis of the energy transfer process in the vortex tube by examining mass flow in the reverse area and tangential and axial velocities are further delved. This analysis covers momentum transfer, heat transfer, and turbulent heat transfer processes resulting from the compression and expansion processes. The findings provide a research direction for exploring the energy separation performance of vortex tubes.

Considerations on static pressure gradients in closed circulatory systems.

Siphons are devices that transport liquids uphill between two containers. It has been proposed that a siphon principle operates in closed circulatory systems, as best exemplified by the circulation of blood in mammals. This principle is supposed to ensure that no additional work is necessary to pump blood above the level of the heart, and that there is no gravitational static pressure gradient in the column of blood. The first statement is correct, while we demonstrate that, ignoring hydraulic resistance to blood flow, the static pressure gradient is equal to the hydrostatic gradient in a siphon model of blood circulation, although the details of the proof do not depend on the geometry of the circulatory system and the proof can be trivially extended to other models such as a vascular waterfall. This implies that the controversy over the siphon principle has no implications for the description of blood circulation, and that mechanisms such as the "baffle," which some authors have appealed to in order to obtain the expected gradient, are not necessary. In our discussion, we also discuss empirical data that appear to provide additional verification of our results, as well as several everyday occurrences that provide additional support.

Numerical investigation of gas migration behaviour in saturated bentonite with consideration of temperature

AbstractGas migration behaviour in saturated, compacted bentonite, especially under rigid-boundary conditions, is controversial. Gas breakthrough phenomena, observed under higher pressure gradient conditions in laboratory experiments, are described in literatures by adopting visco-capillary or dilatancy-controlled flow concept. Since, under rigid-boundary conditions, volumetric expansion is restricted and/or water dissipation is not detected, these concepts cannot be implemented satisfactorily. Instead, a diffusion and solubility-controlled (DSC) flow concept was previously found to be adequate for describing the behaviours at lower temperatures (20 °C). The DSC concept describes gas breakthrough as a function of gas solubility. Breakthrough occurs when concentration of dissolved gas reaches or surpasses the solubility limit in the entire specimen. In this work, the DSC flow concept is applied to validate gas migration and breakthrough experiments conducted at higher temperatures, e.g. 40 and 60 °C. Good agreements are observed between the experimental and predicted results, suggesting that the DSC flow concept can be applied to describe gas migration behaviour satisfactorily in rigidly confined saturated bentonites (under constant volume conditions) for various temperature regimes. Results also show that helium dissolution and diffusion processes in saturated bentonite are sensitive to test temperature and pressure conditions. The processes become more stable with increasing gas injection pressure and ambient temperature.

Consistent outer scaling and analysis of adverse pressure gradient turbulent boundary layers

Under adverse pressure gradient (APG) conditions, the outer regions of turbulent boundary layers (TBLs) are characterized by an increased velocity defect $U_{e}-U$ , an outwards shift of the peak value of the Reynolds shear stress $-\langle uv\rangle$ and an appearance of the outer peak value of the Reynolds normal stress $\langle uu\rangle$ . Here $U_{e}$ is the TBL edge velocity. Scaling APG TBLs is challenging due to the non-equilibrium effects caused by changes in the APG. To address this, the response distance of TBLs to non-equilibrium conditions is utilized to extend the Zagarola–Smits scaling $U_{zs} = U_{e}({\delta ^{*} }/{\delta })$ and ensure that the original properties of the Zagarola–Smits scaling are maintained as $Re \to \infty$ . Here $\delta ^{*}$ is the displacement thickness and $\delta$ is the boundary layer thickness. Based on the established correlation between $U_{e}-U$ and $-\langle uv\rangle$ , the scaling is extended to $-\langle uv\rangle$ . Furthermore, considering the coupling relationship between Reynolds stress components, the scaling is extended to encompass each Reynolds stress component. The proposed consistent scaling is verified using five non-equilibrium databases and five near-equilibrium databases, successfully collapsing the data of the TBL outer region. The pressure gradient parameter $\beta =({\delta ^{*} }/{\rho u_{\tau }^{2} }) ({\mathrm {d} P_{e} }/{\mathrm {d}\kern0.7pt x})$ of these databases spans two orders of magnitude. Here $P_{e}$ is the boundary layer edge pressure, $u_{\tau }$ is the friction velocity and $\rho$ is the density. Finally, the influence of the APG on the inner and outer regions of TBLs is analysed using the mean momentum balance equation. The analysis suggests that the shift of the $-\langle uv\rangle$ peak to the outer region under APG conditions is due to an insufficient inertia term near the inner region to balance the APG. It is observed that the APG promotes interaction between the inner and outer regions of TBLs, but the inner and outer regions still retain distinctive properties.

Solute band transport in electroosmotic-pressure-driven flow of Carreau–Yasuda fluid over micropillar arrays

In this study, we numerically investigate the transport and dispersion characteristics of a neutral solute band in a fluid following generalized Carreau–Yasuda constitutive equations. The combined action of electroosmotic forcing and pressure gradient drives the flow through a microchannel embedded with micropillars. We analyze the band transport process by altering the flow-controlling parameters and fluid rheology. We observe an enhancement in band dispersion with increasing solute diffusivity. An augmentation in band dispersion is achieved using bluff micropillar designs compared to the streamlined micropillars. We also observe that the dispersion of solute band is less in shear-thickening fluids than in shear-thinning fluids. In a mixed electroosmotic-pressure-driven flow, the favorable pressure gradient conditions enhance the band dispersion phenomenon. Our results may prove valuable in understanding solute transport dynamics in non-Newtonian fluids, which has implications for lab-on-a-chip diagnostics and precise drug delivery.

An ex vivo method to evaluate vasoactivity induced by hemoglobin-based oxygen carriers in resistance vessels.

Red blood cell substitutes offer a solution to the problem of blood shortage and side effects of blood transfusion. Hemoglobin-based oxygen carriers (HBOCs) are one of the promising substitutes for red blood cells. Vasoactivity, which refers to the side effect of HBOCs that causes vasoconstriction and subsequent hypertension, limits the clinical application of HBOCs. In this study, an ex vivo method for the evaluation of vasoactivity induced by HBOCs was established based on isolated rat mesenteric artery vessels and the DMT120CP system. The DMT120CP system, equipped with a flowmeter, permits the control of intravascular pressure, pressure gradient, and flow conditions with high accuracy, simulating the physiological conditions for isolated vessels. The concentration of noradrenaline was optimized to 1 × 10-6∼3 × 10-6M. PEGylated bovine hemoglobin (PEG-bHb) was synthesized and perfused into the vessel for vasoactivity evaluation, with bHb as the positive control and PSS buffer solution as the negative control. PEG-bHb showed a hydration diameter of 15.5 ± 1.4nm and a P50 value of 6.99mmHg. PEG-bHb exhibited a colloid osmotic pressure of 64.1mmHg and a viscosity of 1.73 cp at 40mg/mL. The established vasoactivity evaluation method showed significant differences in samples (bHb or PEG-bHb) with different vasoactivity properties. The vasoconstriction percentage induced by PEG-bHb samples synthesized in different batches showed coefficients of variation less than 5%, indicating good applicability and repeatability. The established evaluation method can be applied to study the vasoactivity induction and elimination strategies, promoting the clinical application of HBOCs.

Вторичные течения Прандтля 2-го рода в пространственно-неравновесном турбулентном течении

In this work, a numerical study of turbulent flow and heat transfer in a plane channel was carried out. The features of secondary flows of Prandtl's 2nd kind, which arise in the vicinity of longitudinal ribs on the channel walls, are studied under conditions of spatial inhomogeneity of the flow. Simulations of four turbulent flows were carried out: flows in a smooth channel uniform in length, a uniform ribbed channel, as well as flows in a smooth and ribbed channel with an average velocity varying along the length. It is found that the presence of a rib in a homogeneous channel in the considered case significantly changes the distribution of turbulent flow characteristics over the channel section. These changes are due to the action of the emerging secondary flow with a maximum velocity of 5.2% of the average flow rate. In this case, changes in the velocity and thermal characteristics are similar. Both friction and heat transfer increase by about 10% due to the increased wetted surface area. The inhomogeneity of the flow, which is provided by the organization of blowing and suction through the upper wall of the channel, leads to more noticeable changes. In areas where the flow slows down, the fluid moves under conditions of an unfavorable pressure gradient. The intensity of turbulent pulsations in these places increases noticeably. In the presence of ribs, this leads to a significant increase in secondary flows. Both in the smooth and in the ribbed channel, an increase in the Reynolds analogy coefficient to a value of 1.07 was recorded, which is 6% higher than the uniform flow index. In general, based on the results of this work, we can conclude that the longitudinal ribbing is hardly capable of significantly changing the thermal-hydraulic properties of a flat surface in a turbulent flow, at least without taking special optimization measures. The spatial inhomogeneity of the flow, on the contrary, due to the different effects on the velocity and temperature profiles, has a certain potential for designing heat exchange devices with more suitable thermal-hydraulic properties.

Experimental test of a compressor cascade with non-axisymmetric end-wall contouring at off-design conditions

End-wall losses in axial flow turbomachinery, particularly in compressors, constitute a significant challenge due to their adverse impact on overall efficiency. Pioneering works in this field have demonstrated the potential for end-wall loss reduction by improving end-wall profiles. However, many previous efforts have concentrated solely on design conditions, largely disregarding the behavior of these contoured end-walls under off-design conditions—where compressors often operate. This study investigates the adaptability of a non-axisymmetric end-wall contour, performing well under design conditions, to off-design scenarios, focusing particularly on the influence of Mach numbers on its ability to control corner separation effects. Experimental research was conducted using a combination of surface static pressure taps and aerodynamic probes to quantitatively and qualitatively analyze the effect of the non-axisymmetric end-wall contour on reducing losses. Quantitative outcomes demonstrate a notable decrease in overall losses in the blade cascade due to this end-wall contour. For all tested Mach numbers, the average loss reduces by 4% at 0 degrees of incidence, with a 0.9° decrease in deviation angle, and an 8% average loss reduction at 5 degrees of incidence, accompanied by a 1.5° decrease in deviation angle. Qualitative findings suggest that the mechanism by which the non-axisymmetric end-wall contour reduces blade cascade losses involves the enhancement of pitchwise pressure gradients. This enhancement redirects low-momentum fluid toward the blade's suction surface, diminishing its reach in the pitchwise direction. However, it also intensifies loss in the low-momentum fluid core. Additionally, the presence of a convex feature in the rear section of the blade passage mitigates pitchwise static-pressure gradients, effectively ameliorating secondary flows and preventing their further decline. Moreover, it was observed that the control effectiveness of the end-wall contour on corner separation increases with higher Mach numbers.

Study of driving force characteristics in the formation of dominant unstable flow events in water jet propulsion pumps

Unstable flow events are pivotal in influencing water jet propulsion pumps' safe and stable operation. However, a notable research gap exists in systematically investigating the underlying driving force characteristics responsible for the formation of predominant unstable flow events in the impeller. To address this gap, we conducted experimental and numerical simulation studies, yielding the following results. As the flow rate decreases, a significant rise in the peak-to-peak value of pressure fluctuations and rigid vorticity occurs on both the blade outlet hub and inlet shroud sides. Two distinct unstable flow events emerge at these locations: the leading-edge separation vortex on the blade inlet shroud side and the horn-like vortex on the blade outlet hub side. To elucidate these phenomena, we conducted an analysis of the driving force characteristics employing the momentum equation of relative motion. Our analysis revealed that, as the flow rate decreases, there is a notable increase in the potential rothalpy gradient (PRG, or the reduced static pressure gradient) at these positions, surpassing the influence of the Coriolis force. Based on these findings, we have constructed the fundamental topological structures of these unstable flow events.

Case Analysis of Heavy Air Pollution Process in Xi'an Using Multi-source Data

Air pollution continues to be a serious problem in Xi'an. A heavy pollution process and formation mechanism were investigated in Xi'an in January 2019 using multi-source methods (such as material balance and sulfur/nitrogen oxidation rate (SOR/NOR)). The multi-source data included the concentrations of PM2.5, PM10, SO2, NO2, CO, and O3; the chemical components of PM2.5; the meteorological records of ground and vertical observations; the atmospheric reanalysis data. Three phases were obtained including the accumulation phase (P1), maintenance phase (P2), and dispersion phase (P3) during the pollution period. The pollution event was primarily attributed to the superposition of adverse weather conditions and feedback effects. During the periods of P1 and P2, the area of Xi'an was affected by blocking and zonal westerly airflow at 500 hPa (with flat westerly airflow) and uniform-distribution pressure at sea level with a limited pressure gradient and stable weather conditions, and the easterly wind was dominant at 925 hPa; not all of these factors were conducive to the pollutant diffusion. An interaction feedback mechanism between meteorological conditions and heavy pollution could be studied using the ground-based microwave radiometer. The correlations between PM2.5 and inversions of water vapor density, relative humidity, air temperature, and temperature inversion were significant with coefficients of 0.86, 0.62, 0.53, and 0.38, respectively. The feedback mechanism was primarily manifested as follows:with the pollutant accumulation, the radiative cooling effect could lead to or strengthen the occurrence and intensity of temperature inversion, decrease the mixed layer height, and cause moisture accumulation. High humidity could further maintain the pollution by accelerating the secondary formation and promoting the hygroscopic growth of aerosol particles. Therefore, the dominant chemical components to PM2.5were secondary inorganic ions (SO42-+NO3-+NH4+, SNA) and "other" components during the period of P2, with contributions of 43.2% and 23.1%, respectively. In addition, the peak values of PM2.5, SOR, NOR, and the light extinction coefficients all occurred on the same days (January 3 and 6), indicating that the effect of secondary formation was important for both heavy pollution events and visibility. The total contribution of NH4NO3, organic matter (OM), (NH4)2SO4, and EC to the light extinction coefficient was more than 85%. Limited variations in the proportion for components were observed in three phases. During the period of P3, the strong cold air in the mid-lower atmosphere was conducive to the dry and clean air sinking and the pressure gradient at sea level increasing. These were beneficial to the diffusion of air pollutants and water vapor.

Exploring the link between coffee matrix microstructure and flow properties using combined X-ray microtomography and smoothed particle hydrodynamics simulations

Coffee extraction involves many complex physical and transport processes extremely difficult to model. Among the many factors that will affect the final quality of coffee, the microstructure of the coffee matrix is one of the most critical ones. In this article, we use X-ray micro-computed (microCT) technique to capture the microscopic details of coffee matrices at particle-level and perform fluid dynamics simulation based on the smoothed particle hydrodynamics method (SPH) with the 3D reconstructured data. Information like flow permeability and tortuosity of the matrices can be therefore obtained from our simulation. We found that inertial effects can be quite significant at the normal pressure gradient conditions typical for espresso brewing, and can provide an explanation for the inconsistency of permeability measurements seen in the literature. Several types of coffee powder are further examined, revealing their distinct microscopic details and resulting flow features. By comparing the microCT images of pre- and post-extraction coffee matrices, it is found that a decreasing porosity profile (from the bottom-outlet to the top-inlet) always develops after extraction. This counterintuitive phenomenon can be explained using a pressure-dependent erosion model proposed in our prior work. Our results reveal not only some important hydrodynamic mechanisms of coffee extraction, but also show that microCT scan can provide useful microscopic details for coffee extraction modelling. MicroCT scan establishes the basis for a data-driven numerical framework to explore the link between coffee powder microstructure and extraction dynamics, which is the prerequisite to study the time evolution of both volatile and non-volatile organic compounds and then the flavour profile of coffee brews.

Micro-structured fluid within a channel under static and oscillatory pressure gradients: A novel Darcy-Forchheimer flow investigation

The pertinence and importance of Darcy-Forchheimer flows can be found in large spectrum of engineering, biological and technological mechanisms like solar absorption and filtration, drainage problems, solar cells, ground stream hydrology, solar panels, irrigation and so forth. The major concern of this study is to interpret that how much a Darcy-Forchheimer flow of a micro-structured fluid (e.g., micropolar fluid) within a channel is influenced by the combined effects of static and oscillatory pressure gradients. Numerical treatment is carried out via three steps explicit Runge-Kutta method. Impacts of the preeminent parameters on the flow, mass and heat transport features of the problem are over looked by means of graphical and tabular representations. The numerical consequences evidently point out that the influence of oscillatory component is to elevate the fluid velocity whereas static component of pressure gradient tends to decelerate the velocity inside the channel. It is also determined here that Darcy parameter sufficiently reduces the angular velocity in the flow regime.

Modeling the Surface Pressure Spectrum on Rough Walls in Pressure Gradients

Abstract Models for surface pressure spectra beneath rough wall boundary layers are assessed, with particular emphasis on prediction from steady, Reynolds-averaged Navier–Stokes (RANS) data. RANS roughness boundary conditions are shown to have qualitatively good trends between roughness function and roughness Reynolds number, but model-to-model discrepancies remain and the universality of an equivalent sandgrain roughness height for turbulence models is doubtful. Existing empirical models for the surface pressure spectrum show good agreement in some spectral regions and a newly proposed model shows good matching across the spectrum in a variety of pressure gradient conditions. Adjustments are made to existing TNO analytical models to incorporate rough wall effects, including changes to the velocity spectrum model and the inclusion of a wall-shift, shown to be independent of local Reynolds number, pressure gradient, or turbulence model. The mathematical character of the rough wall spectrum has been revealed, but challenges remain to implement both flow and spectral modeling without a priori knowledge of the flow.

Explorative Gradient Method-Based Research on the Optimization of Nozzle Flow-guiding Devices

Low-frequency buffeting is a common problem in automobile wind tunnels, it induces pulsations of pressure and velocity in the test section. A 1:15 3/4 open-jet return-type scaled wind tunnel was used for this research, and numerical simulations and tests were implemented to study the flow characteristics of the jet shear layer in a model wind tunnel. The results show that guide devices on the inner wall of the nozzle can effectively reduce the low-frequency buffeting, but the presence of the devices deteriorated the axial static pressure gradient of the flow in the test section. The shape of the guide devices was optimized through the Explorative Gradient Method, and numerical simulations were carried out. An optimal shape can effectively reduce the low-frequency buffeting and ensure flow field uniformity in the test section. Finally, the reliability of the numerical simulation and the practicability of the optimal case were verified through a hot wire test and a microphone test.

Double-Tongue Worm Shell Structure on Plastic Centrifugal Pump Performance Study

Aiming at the problem of high vibration and high wear of centrifugal pump tongue, this paper proposes a double-tongue volute structure. Under the condition of ensuring the reliability of CFD results, the influence of various combinations of tongue and volute base circle on the turbulent kinetic energy of centrifugal pump and the radial force of impeller is explored. The traditional single-tongue volute centrifugal pump is compared with various characteristic indexes, and the unsteady numerical calculation is carried out based on different working conditions. It is concluded that the double-tongue volute structure can improve the pressure fluctuation at the monitoring points near the tongue. The results show that the double-tongue volute structure can improve the static pressure gradient and velocity gradient of the middle section of the centrifugal pump and reduce the maximum turbulent kinetic energy value at the tongue under small flow conditions. When the working condition is 1.0 Q, the radial force of the impeller of the C-type double-tongue volute reaches the minimum value of 3.03 N, which can effectively balance part of the radial force.

Small lateral air pressure gradients generated by a large chamber system have a strong effect onCO2transport in soil

AbstractGas transport in soils is usually assumed to be purely diffusive, although several studies have shown that non‐diffusive processes can significantly enhance soil gas transport. These processes include barometric air pressure changes, wind‐induced pressure pumping and static air pressure fields generated by wind interacting with obstacles. The associated pressure gradients in the soil can cause advective gas fluxes that are much larger than diffusive fluxes. However, the contributions of the respective transport processes are difficult to separate. We developed a large chamber system to simulate pressure fields and investigate their influence on soil gas transport. The chamber consists of four subspaces in which pressure is regulated by fans that blow air in or out of the chamber. With this setup, we conducted experiments with oscillating and static pressure fields. CO2concentrations were measured along two soil profiles beneath the chamber. We found a significant relationship between static lateral pressure gradients and the change in the CO2profiles (R2 = 0.53;p‐value <2e‐16). Even small pressure gradients between −1 and 1 Pa relative to ambient pressure resulted in an increase or decrease in CO2concentrations of 8% on average in the upper soil, indicating advective flow of air in the pore space. Positive pressure gradients resulted in decreasing, negative pressure gradients in increasing CO2concentrations. The concentration changes were probably caused by an advective flow field in the soil beneath the chamber generated by the pressure gradients. No effect of oscillating pressure fields was observed in this study. The results indicate that static lateral pressure gradients have a substantial impact on soil gas transport and therefore are an important driver of gas exchange between soil and atmosphere. Lateral pressure gradients in a comparable range can be induced under windy conditions when wind interacts with terrain features. They can also be caused by chambers used for flux measurements at high wind speed or by fans used for head‐space mixing within the chambers, which yields biased flux estimates.

Rough Surface Effect on CO2 Displacement at the Nanoscale

CO2 injection has great potential for enhancing shale oil recovery. Understanding the CO2 displacement in nanometer pores of shale is critical for developing effective CO2 injection techniques. In this work, we applied direct numerical simulation to study the effect of the rough surface on CO2 displacement in nanometer pores of shale. By quantifying CO2 displacement in rough nanochannels, we aimed to understand how surface roughness and morphology affect displacement progress. We found that the rough surface results in shrinkage of the CO2 displacement path, slowing overall displacement rate. Additionally, the pinch-point effect in a rough nanochannel impedes the smooth progression of the interface contact line, causing periodic velocity fluctuation that further hinders CO2 displacement. We also simulated the CO2 displacement in rough nanoporous media, finding that the rough surface leads to a substantial decrease in CO2 displacement efficiency, especially under low pressure gradient conditions. Our simulation results indicate that the rough surface of a shale nanometer pore has a nonnegligible effect on CO2 displacement.