Gas Pressure Research Articles

Quantum physisorption behavior of methane in nanoporous shales: Model and new mechanism

Methane adsorption in nanoporous shales plays a significant role in the storage and flow of shale gas. Although previously numerous theoretical models have been proposed to describe the gas adsorption behavior, how the potential energy distribution in nanopores impacts gas adsorption remains unclear. The mechanism of methane adsorption in extremely complicated nanopores is still no satisfactory explanation. In this study, a total of 28 shale samples located in the Paleozoic-Mesozoic strata from different sedimentary environments were utilized to investigate the nature and process of quantum physisorption of methane in nanoporous shales. It was suggested that methane confined within nanoscale space shows a quantum effect, and the physisorption behavior of methane may be the result of molecular energy level transition. Further, the quantum physisorption model was developed by considering the quantum potential energy distribution, maximum adsorption amount, gas temperature and gas pressure, which matches the isothermal adsorption data well for a various of shales under widely varied temperature and gas pressure condition. The adsorption amounts of methane with different energy levels can also be obtained by the model. Finally, a new mechanism of the methane quantum physisorption in nanoporous shales was proposed. Uneven spatial distribution of gas molecules and elementary space of gas adsorption are the intrinsic factors of controlling the quantum physisorption behavior. The former is mainly influenced by minimum potential unit (E0) and gas temperature, while the latter is represented by the parameter of maximum adsorption amount (nL) which impacted by specific surface area and gas temperature. Gas pressure only affects the molecule concentration with different energy levels, but does not affect the spatial distribution of molecule. E0 and nL vary in shales from different sedimentary environments, due to the difference in organic matter properties (TOC content and kerogen type), which indirectly impacts the methane physisorption behavior. These results are helpful to deeply understand the storage of methane in shales and improve the efficient development of shale gas. In addition, this study is expected to open a new research direction about the quantum physisorption of gas in nanoporous media.

Modeling and experimental testing of a UAV liquid hydrogen propulsion set

In this paper, an analytical model of an Unmanned Aerial Vehicle (UAV) propulsion system using liquid hydrogen to supply a fuel cell is presented. The article also describes experimental tests of the performance of a liquid hydrogen (LH2) tank at different ambient temperatures and ground tests of the UAV propulsion system using LH2. These tests were used to validate and calibrate the analytical model. The model is of reduced order and is based on the literature. Despite the simplicity of the model, the tank Boil-Off Gas (BOG) rate and pressure drop, the time for complete evaporation of LH2, the fuel cell performance, and the coolest temperature that the hydrogen can reach, were predicted with deviations not exceeding 0.3%, 0.5%, 2.2%, 0.6%, and 0.5% respectively. The final proposed model allows the incorporation of different conditions, materials, and geometries to suit each mission, all at low operational cost.

Validation of prediction capability of operating space for plasma initiation in MAST-U

Abstract DYON is a plasma initiation modelling code that solves the differential equation system of the full circuit equations (plasma current, active coil currents and eddy currents in full passive structures) and 0D global energy and particle balance equations[1]. In order to test the capability of the full electromagnetic plasma initiation model to predict individual discharges in experiments and thus the operating space in the device, a dedicated experimental database was built in MAST-U by scanning the prefilled gas pressure p0 and the induced loop voltage Vloop . In the experimental operating space of p0 and Vloop the lower and the upper limits of p0 are determined by the plasma breakdown failure and the plasma burn-through failure, respectively. The lower limit of Vloop is determined by the plasma burn-through failure. By directly reading the control room data used in each discharge (i.e. currents in the solenoid, poloidal field coils, and toroidal field coils, p0 , and gas puffing rate), the full electromagnetic DYON consistently predicted the failed breakdown, failed burn-through, and successful plasma initiation discharges in the experimental database, demonstrating its capability to predict the operating space for inductive plasma initiation. The Paschen curve calculated with the effective connection length in MAST-U indicates a much higher p0 required for plasma breakdown than the experimental data, indicating that individual field line evaluation is necessary to calculate the quantitative requirements for Townsend breakdown. The demonstration in this paper shows that the full electromagnetic DYON could be a useful simulation tool to assess the feasibility of inductive plasma initiation and to optimise operating scenarios in future devices. [1] Hyun-Tae Kim 2022 Nuclear Fusion 62 126012

Thermodynamic modeling of coal-gas interactions and desorption temperature analysis

This research developes an innovative thermodynamic coupling model for gas-bearing coal, improving temperature change simulations during coalbed methane desorption. The model distinctively integrates adsorption/desorption heat effects, free gas expansion, dynamic diffusion, the Klinkenberg effect, and moisture influence, offering a more comprehensive perspective of thermodynamic behavior. Comparisons with empirical data and previous models demonstrate that the predicted temperature changes closely match experimental results, indicating superior accuracy. The investigation finds a 23.51 % increase in desorption temperature as gas pressure rises from 0.4 MPa to 1.2 MPa, with temperature changes following the sequence CO2 > CH4 > N2, in the ratio ΔT(CO2): ΔT(CH4): ΔT(N2) = 1.76: 1.35: 1. Adsorbed gas desorption and free gas expansion are recognized as the primary drivers, especially near 0.5 MPa, where adsorbed gas contributes nearly 70 %. Sensitivity to variables such as gas pressure, adsorption heat, and permeability diminishes over time, with moisture exerting minimal impact. The study highlights a close thermodynamic connection between temperature changes and gas outbursts, proposing temperature variation as an reliable indicator for predicting and evaluating outburst risks. These findings enhance understanding of coalbed methane desorption and provide new theoretical foundations for efficient resource development and disaster prevention.

Analysis of dynamic characteristics and influencing factors of CO2 low-permeability coal reservoir sequestration

ABSTRACT Abandoned coal seams can be an important carrier for CO2 geological storage. Considering the gas seepage-diffusion and physical adsorption coupling characteristics in the process of CO2 adsorption and storage in coal and rock, a two-dimensional model of coupled flow-solidity for geological storage of CO2 in low-permeability reservoir with double voids was established by introducing the Zhang Hongbin model algorithm and adding the Klinkenberg effect and the compression effect of the rock skeleton in coal reservoirs in the controlling equation for rock deformation. The coupled flow-solid model was solved by using the PDE equation of COMSOL Multiphics program, and the simulation results difference between the new model and the traditional model in terms of sequestration dynamics were compared. The dynamic characteristic of reservoir gas pressure, formation stress, permeability and sequestration density in the process of CO2 geologic sequestration and injection were analyzed, and the influences of injection pressure and injection well diameter on the amount of CO2 sequestration were explored. The results show that the new model is more reasonable for calculating reservoir gas pressure and permeability compared with the Palmer-Mansoori model (PM model), and can simulate the free-state seepage movement of CO2 in the fracture system as well as its physical adsorption process compared with the single-heavy pore medium model. With continuous CO2 injection, the maximum sequestration density was raised to a limit value of about 1000 kg/m3 after 1 year. The date of reaching the limit of the sequestration volume was advanced by about 45 d when the positive pressure of the injected gas was increased from 10 kPa to 50 kPa. This model can reproduce the main parameters including, when affecting the effect, and realize the calculation of parameters such as CO2 density reaching the limit value, sealing limit day, sealing limit amount, which can provide a theoretical basis for further deep understanding of CO2 geological sealing law and scientific development of gas injection scheme.

Optimizing Cold Spray Parameters for High Entropy Alloy Coatings Using Taguchi and Box–Behnken Design Approaches for Mechanically Alloyed Powder

The present study focused on optimizing the cold spray (CS) process parameters for depositing Fe20Cr20Mn20Ni20Co20 (Cantor alloy) coatings using mechanically alloyed (MA) powder. A two-step design of experiments approach was employed, beginning with the initial screening of input variables using the L8 Taguchi method, followed by the refinement of process parameters through the Box–Behnken design of experiments. Key performance indicators included deposition efficiency (DE), coating thickness per pass, and microstructural parameters including porosity, cracks, and interfacial defects/delamination. The study identified process gas temperature as the primary factor influencing both DE and thickness per pass. Higher gas temperature and pressure, combined with increased scanning speed, resulted in higher DE. The DE of the MA Cantor alloy powder peaked at around 14-15%, with a deposit density greater than 99% achieved at the highest process gas temperature and pressure (1000 °C and 60 bar, respectively). The average hardness of the optimal CS coating deposited using MA powder was found to be 679 ± 17 HV0.1, which is approximately 90% greater than the average hardness reported for CS coatings deposited using atomized powder.

Structural and morphological features of magnetron nanofilms of TaN with different thicknesses

Purpose of research. Study of morphological and phase changes in the structure of tantalum nitride nanofilms formed by magnetron reactive sputtering on a silicon substrate.Methods. Magnetron sputtering on a silicon substrate was performed using the MVU TM-Magna T setup with the sputtering time parameter changing from 300 to 900 sec, and also with constant power parameters of 500 W and working gas pressure of Ar 0,5 Pa. The morphological and phase changes in the structure of tantalum nitride nanofilms were studied using atomic force microscopy and X-ray phase analysis. The fractal dimension was determined using the cube counting method. X-ray diffractometric analysis in the in situ measurement mode with discrete heating (in 100 °C increments) in air up to 1000 °C using the PAAR HTK-16 high-temperature attachment.Results. Using atomic force microscopy methods, it was found that the granulometric distribution of nanoclusters in the studied TaN nanofilms was Gaussian and an increase in the lateral size of particles was observed with an increase in the deposition time. The nanofilm with a deposition time of 300 s had minimal roughness. The statistical fractal dimension was calculated, the value of which corresponded to their three-dimensionality. According to the X-ray phase analysis data, the sizes of the coherence region, texturing, microdeformations and interplanar deformation distortions were determined, and a mixed Stranski-Krastanov mechanism of nanofilm formation was established.Conclusion. The surface roughness of nitride nanofilms formed at a constant power (500 W) depends significantly on the magnetron sputtering time and N2 concentration. In all studied nanofilm structures, the dominant growth mechanism was the mixed Stranski–Krastanov mechanism.

A risk assessment of a gas pressure reduction station system with confidence for dealing with imprecisions and unknowns

Process systems are sensitive and vital industrial facilities. Disturbances in their performance may cause harm to the environment,humans,or significant economic damage. In risk assessment of chemical process industries, the available data, information, and knowledge are typically rare, limited, and often unrealistic. This issue poses a challenge to conducting a credible quantitative risk assessment and effects the robustness of the results. To address these challenges, this work proposes a methodology based on the Dempster-Shafer theory of evidence as the reasoning framework. It incorporates risk identification, analysis, and mitigation phases to ensure a thorough analysis of risks and the integration of proactive risk reduction strategies. The approach aims to model the worst-case hazard scenario and assess associated risks using various methods such as FMECA, Bow-Tie, Credal Network, and Dempster-Shafer theory. The proposed approach models imprecision and data ambiguity using intervals and associated belief mass. This extension provides a basis for addressing the fundamental problem of prior ignorance about the distribution of the observed data, which is prevalent in data mining applications. A new approach is proposed that utilizes Belief and Plausibility curves, similar to a Cumulative Distribution Function, to propagate uncertainty, enhance criticality discrimination, and determine cumulated belief measures. This approach is applied in analyzing the failure modes identified in FMECA and is further extended through the credal network for comprehensive risk assessment. Results show how to express irrelevant and independent judgments, and how to work out with inferences in credal networks. This issue is often overlooked, but if properly addressed it represents the key to ultimately drawing reliable conclusions and fully utilizing the system's available data. A case study of the City Gate Station system was used to verify the application potential of the proposed approach.

Synergistic effects of carbon nanotubes on α-MnO2 electrocatalysts for improved oxygen reduction in alkaline fuel cells

The Alkaline Membrane Fuel Cell (AMFC), is a device crucial for electrochemical energy production through the oxygen reduction reaction (ORR), conventionally relies on platinum catalysts. However, the challenges of excessive cost and inadequate stability in alkaline environments have hindered its widespread commercialization. Alpha manganese dioxide (αMnO2), with diverse applications in energy and environmental domains, has potential as an alternative catalyst due to its lower metal costs and comparable catalytic activity. This study focuses on the synthesis of αMnO2 nanotubes through controlled environment temperature, and integration with carbon nanotubes (CNTs). Optimizing the gas pressure and temperature during synthesis resulted in structural changes in αMnO2 nanotubes, with a notable increase in catalytic behavior at elevated temperatures. The sample treated at 450 °C and mixed with CNTs (CNT-MO450) demonstrated outstanding ORR performance and prolonged stability in an alkaline medium. Furthermore, the CNT-MO450 exhibited the highest current density of −5.2 mA/cm2 at a potential of 0.65 V vs RHE, a peak power density of 73 mW/cm2 (comparable to Pt/C at 95 mW/cm2), and a charge transfer resistance of 310 Ω. The temperature treatment affected the αMnO2 nanotubes, which resulted in increased length at an optimal temperature, leading to a larger surface area. This enhancement in surface area is crucial to improved catalytic activity, electrical conductivity, and extended stability during operation in alkaline media. The findings suggest that CNT-MO450 catalysts hold promise as a cost-effective and stable alternative catalyst for AMFCs.

Resolving studies of Balmer alpha lines relevant to the LIBS analysis of hydrogen isotope retention

Utilizing Laser-Induced Breakdown Spectroscopy (LIBS) for detecting deuterium and tritium retention in fusion devices poses a significant challenge due to the experimental limitations in resolving hydrogen isotope Balmer alpha lines (Hα, Dα, and Tα). This study utilizes the Rayleigh criterion to distinguish Tα and Dα lines by determining the maximum line widths and corresponding plasma parameters. Experimental validation was performed through LIBS analysis of heavy water-doped graphite/silica gel targets in both argon and helium atmospheres to assess the predicted plasma parameters and line profile shapes. The optimization of laser pulse energy, gas pressure, delay, and gate times aimed at achieving fully resolved lines based on the intensity, width, and the dip between deuterium and hydrogen Balmer alpha lines. By fine-tuning these experimental parameters, the study successfully achieved a dip of less than 10 % between the Hα and Dα lines with a satisfactory signal-to-noise ratio, demonstrating the feasibility of fully resolving the Tα and Dα lines. These findings underscore the potential of LIBS in enhancing the detection of deuterium and tritium retention in fusion devices.

Analysis of SF6 and CF4 consumption for refueling high-voltage switching equipment

The article describes to eliminate possible errors in the supply of cylinders with sulfur hexafluoride and cylinders with carbon tetrafluoride to high-voltage substations for refueling switching devices such as high-voltage switches, voltage transformers, etc. Conduct an analysis of possible erroneous supplies of the two above-mentioned gases at the substation. Make an analysis of possible residuals (or shortfalls) of gas cylinders after refilling. Make an assumption about the reasons for the appearance of possible residues. Give recommendations for overcoming possible problems. Make the appropriate calculations. Propose a formula (table) for recalculating the consumption of both types of gases. Make a table for calculating the actual values of the number of supplied cylinders, related to the discreteness of the volumes of the cylinders and the switching devices themselves. Draw appropriate conclusions and make recommendations. To achieve this goal, a method was used to calculate the state of an ideal gas using software for working with spreadsheets. The article reflects the relevance of the topic and discusses the features of refueling high-voltage SF6 equipment in various climatic conditions (below minus 40-49°F). An analysis of typical ratings of high-voltage switches used at highvoltage substations was carried out. A graph is presented for converting the molar fraction (contributing to pressure) of gases into the mass fraction. A sample calculation of the number of cylinders is presented for two commonly encountered volumes of switching devices and fortyliter gas cylinders for several standard cylinder filling ratios. Presumptive conclusions are presented regarding the assessment of real errors when sending gas cylinders for refilling switching devices. The article offers an understanding of the sequence of problems associated with incorrect calculations and a complete methodology for calculating the correct volumes (mass) of gas depending on the actual types of devices used, depending on the volume of supplies pieces of equipment.

Modeling of high-pressure transient gas-liquid flow in M-shaped jumpers of subsea gas production systems

Two-phase flow with low liquid loads is common in high-pressure natural gas offshore gathering and transmission pipelines. During gas production slowdowns or shutdowns, an accumulation of liquid in the lower sections of subsea pipelines may occur. This phenomenon is observed in jumpers that connect different units in deep-water subsea gas production facilities. The displacement of the accumulated liquid during production ramp-up induces temporal variations in pressure drop across the jumper and forces on its elbows, resulting in flow-induced vibrations (FIV) that pose potential risks to the structural integrity of the jumper. To bridge the gap between laboratory experiments and field conditions, transient 3D numerical simulations were conducted using the OpenFOAM software. These simulations facilitated the development of a mechanistic model to elucidate the factors contributing to increased pressure and forces during the liquid purging process. The study examined the influence of gas pressure level, pipe diameter, initially accumulated liquid amount, liquid properties, and gas mass flow rate on the transient pressure drop and the forces acting on the jumper's elbows. The critical gas production rate required for complete liquid removal of the accumulated liquid was determined, and scaling rules were proposed to predict the effects of gas pressure and pipe diameter on this critical value. The dominant frequencies of pressure and force fluctuations were identified, with low-pressure systems exhibiting frequencies associated with two-phase flow phenomena and high-pressure systems showing frequencies attributed to acoustic waves.

Enhanced hydrogen degradation of two pipeline steels by increasing inert gas pressure in hydrogen-containing mixtures: experimental and theoretical insights

This study highlights the significant role of total gas pressure in enhancing hydrogen degradation in hydrogen/inert gas mixtures. Tests were performed to measure the fatigue crack growth rate (FCGR) of X80 and GB20# pipeline steels in pure hydrogen and hydrogen/nitrogen blends. Findings showed that FCGR increased in the blend with elevated total gas pressure relative to pure hydrogen, despite an equivalent hydrogen partial pressure between the two environments. First-principles molecular dynamics (FPMD) calculations revealed that the increased number of nitrogen molecules within the Fe-H2-N2 systems promoted the movement velocity of hydrogen and premature dissociation of hydrogen.

Dynamic performance analysis of proton exchange membrane fuel cell in marine applications

To investigate the dynamic characteristics of proton exchange membrane fuel cells (PEMFCs) on maritime vessels, a lumped-parameter model for the PEMFC systems was developed based on a hybrid vessel propulsion systems model. Simulations and analyses of the dynamic characteristics of PEMFCs were conducted under typical sailing conditions. The results reveal a noticeable hysteresis in the operating temperature of PEMFC stacks during vessel voyages, with a delay of about 25 s, leading to significant overvoltage in activation, ohmic, and concentration differences. Significant variations in vessel loads can cause large fluctuations in the component gas pressures in the cathode and anode flow paths within 16.6–19.8 kPa and 78.57–93.06 kPa, respectively. A comparison of different humidification levels for cathode and anode gases demonstrates that, at the same moment, as the humidification of cathode and anode gases increases from 20 % to 100 %, the water content in the proton membrane increases from 2.29 to 13.47, the ohmic impedance decreases from 1.35 mΩ/cm2 to 0.174 mΩ/cm2, and the overshoot of the fuel cell voltage decreases. The output delay decreases from 25 s to 8 s, enhancing overall fuel cell performance. These findings are significant for optimizing the design, performance, and real-time control of marine PEMFC systems.

High sensitivity gas pressure and temperature optical sensors based on tapered no-core fiber coated with polydimethylsiloxane (PDMS)

This article introduces a novel high-sensitivity pressure and temperature sensor utilizing a tapered no-core fiber (NCF) structure created by splicing the NCF with a single-mode fiber (SMF) to form a “SMF-NCF-SMF” structure, tapering the NCF, and applying a polydimethylsiloxane (PDMS) film on the tapered NCF surface. The experimental results show that the device with a diameter of 10 μm has a pressure sensitivity of 86.63 nm/MPa within one to two atmospheres. Furthermore, the temperature sensitivity is −1.97 nm/°C from 30 °C to 60 °C. The sensor exhibits excellent stability and repeatability, and the PDMS film enhances the mechanical strength of the device, indicating promising potential for high-sensitivity pressure and temperature applications.

An innovative approach to direct recovery and storage of natural gas depressurization wasted energy by using a hybrid pumped-hydro and compressed gas system

A novel mechanism is proposed to simultaneous recovery and storage of energy for use in the natural gas depressurization process. The main idea of this proposal is to use a compressor and a pump coupled with the turbo-expander to directly store the mechanical power produced by the expansion turbine in the energy storage system based on the pumped hydro combined with compressed gas. The compressor is used to create preset pressure in the vessel of the energy storage system, and the pump is used to inject water into the vessel. In this way, the density of energy storage in the system increases. In the discharge stage, electricity is produced by passing water through the turbo-generator during peak consumption hours or when energy prices are higher. The capability of the presented new method has been tested in a natural gas pressure reducing station with a nominal capacity of 50,000 Nm3/h, and the effect of different factors within the energy storage system on its performance, including the preset pressure and the volumetric ratio of water to gas in the pressurized tank, has been studied. By using the proposed plan, due to the elimination of unnecessary energy conversions the efficiency of recovery, storage and release of energy enhances. The results showed that by employing the proposed system, about 1.3 (GWh) of energy can be harvested annually; while this amount of energy is currently wasted. Also, the overall energy conversion efficiency of 48.64 %.

Dynamic gas emission during coal seam drilling under the thermo-hydro-mechanical coupling effect: A theoretical model and numerical simulations

The potential risk of coal and gas outbursts has increased with the depth of coal mining, posing the threat of heavy casualties, vast economic losses, and harm to the ecological environment. Considering the limitations of existing coal and gas outburst prediction methods, novel indicators or methods are needed. In this study, a fully coupled dynamic drilling gas emission THM model of gas diffusion, seepage, and flow is established, and the reliability of the model was verified by the measured data. The validated model was applied to single-factor and multi-factor impact analysis of dynamic drilling gas emission. The simulation results showed that (1) During the drilling process, the increase in permeability is mainly attributed to the coal seam damage and disturbance caused by the borehole and the coupling effects of the THM model, which increase the porosity around the borehole. Driven by the pressure gradient and temperature gradient, the gas pressure and temperature of the coal seam around the borehole show a conical distribution. (2) In the single-factor analysis, increasing the values of coal seam parameters (initial gas pressure, initial permeability, and initial coal temperature) and drilling parameters (borehole radius) will promote gas emissions in the drilling process to different degrees. The most significant promoting effect is the initial permeability, and the weakest is the initial coal temperature. (3) The response surface analysis results of the four factors show that the interaction between initial coal temperature C and borehole radius D is the least significant, and the interaction between initial gas pressure A and initial permeability B is the most significant. Meanwhile, the established multiple regression model characterizes the relationship between borehole gas emissions and initial coal seam gas pressure, and the idea of using drilling gas emission volume to predict coal and gas outbursts was proposed.

Performance analysis, statistical modeling, and multiple response optimization of a novel fixed-bed quartz reactor packed with Ba-Pt@γ-AL2O3 using response surface methodology

In the present study, a novel fixed-bed continuous reactor with a preheating chamber was designed to be utilized for the practical application of removal studies of dangerous pollutants, especially NOX removal by NOX Storage Reduction (NSR) catalysts on a laboratory scale. The reactor's design and operational parameters, including outer wall temperature (50–600 °C), volumetric flow rate (0.3–3 L/min), wall temperature time (0.16–10 min), and granule surface area inside the preheating chamber (0–270 cm2), were statistically modeled and optimized using Response Surface Methodology (RSM). For more logical and effective parameter optimization, the ratio of gas and catalyst temperatures and pressure drop to the reactor outer wall temperature (GT/ROWT, CT/ROWT, and PD/ROWT) were also included in the optimization process. Experimental results showed that gas temperature, catalyst temperature, and pressure drop ranged from 31 to 177 °C, 51–585 °C, and 7–153 Pa, respectively. Optimal conditions were determined to be an outer wall temperature of 230 °C, a volumetric flow rate of 3 L/min, a wall temperature time of 0.16 min, and a granule surface area of 67.3 cm2. The results demonstrated that outer wall temperature, flow rate, time, and surface area of granules have significant and interaction effects on the responses and should be considered when researchers assess the removal efficiency of thermal catalysts.

Effects of the chirp rate on single-shot coherent Rayleigh-Brillouin scattering

Single-shot coherent Rayleigh-Brillouin scattering (CRBS) is modeled using direct simulation Monte Carlo (DSMC). In CRBS, an optical lattice generated by the interference of two pump lasers traps the neutral particles via the dipole force. The gradient of refractive index due to the trapped particles of the gaseous media leads to coherent scattering of a probe beam, resulting in the CRBS signal. Additionally, using a chirped laser beam, CRBS signals can be obtained in a single laser shot, shortening the measurement time of the gas flow (on the order of 100 ns). The DSMC results of single-shot CRBS assuming Maxwellian velocity distribution functions (VDFs) show good agreement with experimental data, including argon, carbon dioxide, and xenon, for different gas pressures. One of the key observations obtained from the present simulations is that the CRBS signals become asymmetric when using a fast chirp rate due to finite time for collisionless trapping and collisional thermalization. Published by the American Physical Society 2024

Collision of liquid drops: bounce or merge?

Whether colliding drops will merge with or bounce off each other is critical to numerous processes, and the physics involved is notoriously complex. In particular, experiments show that both sufficiently slow and fast head-on drop collisions lead to merging, but that there is often an intermediate regime in which bouncing is observed; these transitions in behaviour were recently discovered to be surprisingly sensitive to the radius of the drops and the ambient gas pressure. We show here that these transitions between bouncing and merging are governed by nanoscale phenomena; namely, gas-kinetic and disjoining pressure effects. To capture these crucial effects, a novel, open-source computational model is developed for the simulation of colliding drops. The model uses a hybrid approach, based on solving the Navier–Stokes equations in the drop with a lubrication approach for the unconventional physics of the gas film. Our simulations show remarkably good agreement with experiments of head-on collisions and also provide new experimentally verifiable predictions.