High Pressure Region Research Articles

A new modelling approach for reliable prediction of solid-fluid behaviour: Application to the methane + benzene system including low-temperature and high-pressure regions

Because of their high melting temperature, aromatic compounds are amongst the heaviest components to deal with in the evaluation of the crystallization risk of methane-rich mixtures feeding main cryogenic heat exchangers widely employed in LNG production plants.In this paper, the GERG-2008 equation of state as implemented in the Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) has been coupled to the Gibbs free energy equation for phase I of solid methane and phase I of solid benzene to predict the solubility of benzene in vapour, liquid, and supercritical methane, and the global phase diagram of the binary methane + benzene mixture down to 60 K and up to 60 MPa.Predicted values are in a rather good qualitative and quantitative agreement with solid-fluid and solid-fluid-fluid data when compared to results obtained from other solid-phase and predictive models for the fluid phases. The obtained results point out the importance of an accurate representation of the density of the fluid phase for the reliable prediction of solubility of solids in fluids.

Preparation of Elastic Macroporous Graphene Aerogel Based on Pickering Emulsion Method and Combination with ETPU for High Performance Piezoresistive Sensors.

High-performance pressure sensors provide the necessary conditions for smart shoe applications. In this paper, the elastic Macroporous Graphene Aerogel (MGA) was synthesized via the modified Hummers' method, and it was further combined with Expanded-Thermoplastic polyurethane (ETPU) particles to assemble MGA-ETPU flexible sensors. The MGA-ETPU has a low apparent density (3.02 mg/cm3), high conductivity (0.024 S/cm) and fast response time (50 ms). The MGA-ETPU has a large linear sensing range (0-10 kPa) and consists of two linear regions: the low-pressure region (0 to 8 kPa) and the high-pressure region (8 to 10 kPa), with sensitivities of 0.08 kPa-1, and 0.246 kPa-1, respectively. Mechanical test results show that the MGA-ETPU sensor showed 19% reduction in maximum stress after 400 loading-unloading compression cycles at 40% strain. Electrical performance tests showed that the resistance of MGA-ETPU sensor decreased by 12.5% when subjected to sudden compression at 82% strain and returned to its original state within 0.05 s. Compared to existing flexible sensors, the MGA-ETPU sensors offer excellent performance and several distinct advantages, including ease of fabrication, high sensitivity, fast response time, and good flexibility. These remarkable features make them ideally suited as flexible pressure sensors for smart shoes.

A multifunctional hydrogel-based strain sensor and triboelectric nanogenerator for running monitoring and energy harvesting

Recently, flexible wearable electronics for human running posture monitoring and human energy harvesting have attracted widespread attention. Hence, we design a mixed type conductive hydrogel based on polyvinyl alcohol, cotton paper, graphite oxide, and MXene, named PCGM hydrogel. Furthermore, the PCGM hydrogel can act as the PCGM-based strain sensor and triboelectric nanogenerator (P-TENG) for running posture monitoring and mechanical energy harvesting. The PCGM-based strain sensor has two sensing linear regions: The pressure sensitivity is 0.0164 kPa−1 in the low pressure region (0–16 kPa), whereas it is 0.002 86 kPa−1 in the high pressure region (16–120 kPa). To achieve comprehensive health monitoring of runners, the PCGM-based strain sensors can be installed on human joints and facial skin to monitor human posture and facial expressions. The PCGM hydrogel can be combined with a polytetrafluoroethylene film to form a P-TENG device for mechanical energy harvesting. The P-TENG maximum output power can reach 135 µW with a 30 MΩ load. The short-circuit current (Isc), open-circuit voltage (Voc), and transfer charge (Qsc) of P-TENG can reach 10.36 µA, 229.85 V, and 49.24 nC, respectively. This research provides an effective approach for human-running motion monitoring by using multifunctional flexible devices.

On the explosion characteristics of natural gas with hydrogen and inert gas additions

In this work, the explosion limits of three different natural gas mixtures (with various proportions of methane (CH4), ethane (C2H6), and propane (C3H8)) have been investigated numerically based on detailed chemical kinetics. Furthermore, a comprehensive investigation of the effects of hydrogen (H2) and inert gas (N2, CO2) addition on the explosive properties of natural gas has been carried out. The results indicate that the C3H8 components have a dominant effect on the explosion limits of natural gas. The addition of high-hydrocarbons in natural gas can significantly reduce the auto-ignition temperature, shorten the ignition delay time, and enhance the explosion risk of the mixture. Furthermore, the negative temperature coefficient (NTC) response of natural gas in the second explosion limit gradually disappears, and changes to the Z-curve response with the addition of H2. However, the explosion tendency of the mixture is reduced with the addition of H2 under normal to high-pressure conditions. In addition, with the increase of inert gas (N2, CO2), the explosion limits of the mixtures shift upwards to a higher-pressure region, which significantly reduces the explosion tendency. Nevertheless, the explosion propensity of the mixture increases significantly under low-pressure conditions when the mixture contains hydrogen. To elucidate the critical control reactions and determine their synergistic effects, sensitivity analyses under different conditions are performed. Finally, the interaction of different fuels in natural gas mixtures is further summarized by analyzing the explosion limits of single-component, binary-component, and multi-component mixtures of hydrogen to propane. This paper provides an important guidance for the development of natural gas with high safety, low risk, and low pollution.

Experimental research on self-initiation process of rotating detonation wave by high-temperature ethylene-rich gas

This study investigates an experimental process of high-temperature ethylene-rich gas and air for rotating detonation. After abandoning the pre-detonator method, the high-temperature ethylene-rich gas was injected and collided with the outer wall to create a localized high temperature and pressure region that ignited the gas mixture to form the deflagration state. Whether it is a single deflagration flame or double deflagration flame, it is eventually transformed through the deflagration-to-detonation transition (DDT) process into a double detonation wave. With propagation and collision of the double waves, the injection pressure increases, which results in shortening the self-initiation delay time. The equivalence ratio, gas temperature, and mass flow rate affect the success ratio of self-initiation. Rotating detonation engine (RDE) can be successfully initiated in the equivalence ratio range of 0.82 to 1.69. Equivalence ratio and gas temperature increase the propagation velocity of rotating detonation wave (RDW), for maximum RDW velocity of 1324.61 m/s, the gas temperature is 1021.3 °C. At the double wave collision point, a new weak RDW appears that decreases the RDE operating stability and a periodic quenching and re-initiation of RDW phenomenon occurs at that point.

Large-eddy simulation of unsteady flows past a spiked body

Unsteady flows past a spiked body are investigated numerically with wall-resolved large-eddy simulation (LES). The inflow features a Mach number of Ma=2.21 and a Reynolds number of Re=1.2×105. The ratio of the spike length to the blunt body diameter is L/D=1.0. A comparative study of three meshes of different grid resolutions has been conducted by assessing their predictive accuracies and associated subgrid-scale effects. The LES results obtained based on three meshes are compared with the experimental and numerical data found in the literature. A proper orthogonal decomposition (POD) analysis has been conducted based on the pressure and axial velocity fluctuations to investigate turbulence structures. It is observed that the turbulence structures corresponding to the first four POD modes are the most energetic. Furthermore, it is seen that the dominant recirculation zone along the spike in a pulsation cycle can be reconstructed based on the first two POD modes of axial velocity fluctuations. The physical mechanisms of the collapse and inflation processes of the pulsation cycle are investigated based on a detailed transient analysis of fine-resolution LES data. The temporal evolution of vortices and shock waves are investigated. An interesting characteristic Z-shaped trajectory of the instantaneous flow pattern is observed. It is discovered that the pulsation cycle is dominated by the pressure differences between the recirculation zone and two high-pressure regions immediately in front of the cylinder face and near the spike tip.

Flow Topology of a Slanted Cylinder with Rounded-Edges Under Compressible Conditions

In this study, the slanted afterbody was modified to more closely represent cargo aircraft afterbodies through the addition of a basal edge fillet. Two slant angles ( and ) were explored over two Mach numbers ( and ) and two Reynolds numbers ( and ) using oil flow visualization and pressure-sensitive paint to identify surface flow phenomena, while the spanwise shadowgraph enabled the observation of mean wake phenomena. The rounded-edge afterbody surface measurements displayed a centerline-separated vortex state with flow features and regions of suction qualitatively similar to those of the baseline sharp-edge case, with some notable differences. For example, a separation bubble at the slant leading edge is nearly twice the size of the baseline sharp-edge model. This is accompanied by the presence of a “source point,” indicated by a region of high pressure where the flow reattaches, and a tighter counter-rotating vortex pair in comparison to the baseline. The rounded-edge prevented the previously seen compressible transition to a fully separated wake state within the Mach number range studied while showing an increase in separation bubble size with increasing Mach number. Also noteworthy was the existence of a new vortex state for the model, where the flow remains attached at the model centerline. This is in contrast to the previously observed flow topology of the centerline-separated vortex state in the sharp-edge model, which formed a separation bubble at the model centerline. The transition between the new centerline-attached vortex state and the traditional centerline-separated vortex state was shown to be dependent on both Mach number and Reynolds number, revealing the importance of boundary-layer development on the rounded afterbody flowfield. Overall, these observations indicate that the rounded afterbody produces flowfields with distinct features that vary from the previously described sharp-edge afterbody wake field under certain conditions.

Numerical study on the design of multi-staged, opposing pulsed-jet cleaning (M-OPJC) for pleated filter cartridges

Opposing pulsed-jet cleaning (OPJC) has recently been proposed as a method to improve the filtration media regeneration of pleated filter cartridges, specifically addressing the patchy cleaning issue typically encountered in conventional pulsed jet cleaning. In this study, we first investigate the effect of pressure ratio (PR, the ratio of pressures at the opposing nozzles) on the OPJC performance in terms of cleaning intensity, uniformity, comprehensive pressure, and cleaning efficiency for pleated filter cartridges. A new OPJC strategy, named multi-staged, opposing pulsed-jet cleaning (M-OPJC), is proposed to enable the movement of a high-pressure region (formed by the collision of the pulsed-jet airflows introduced from opposing nozzles) within the core of a filter cartridge during the cleaning. The M-OPJC divides one cleaning jet cycle into four jetting stages with different PR values. Among all the evaluated cases, the M-OPJC with PR = [1.00, 1.00, 1.33, 2.00] offers the best cleaning performance for a pleated filter cartridge. Compared to conventional pulsed-jet cleaning (i.e., M-OPJC with PR = [0, 0, 0, 0]), the M-OPJC method increased the peak pressure at the cartridge’s upper part by 325.93%, comprehensive pressure by 171.10%, and cleaning efficiency by 48.85%.

Controllable C2H2/CO2 inverse adsorption and separation in pillar-layered Zn-1,2,4-triazolate-dicarboxylate frameworks induced by the ligand aromaticity

Acetylene (C2H2) and carbon dioxide (CO2) both are linear molecules and the similarity in size and physical properties makes their separation very challenging. Compared to the C2H2-selective C2H2/CO2 separation, the inscrutable CO2-selective capture (also called inverse C2H2/CO2 separation) process is ideal as it enables one-step production of high-purity C2H2. Herein, we demonstrate the controllable C2H2/CO2 inverse adsorption and separation in a series of isomorphic Zn-1,2,4-triazolate-dicarboxylate pillar-layered frameworks (Zn-FA-TRZ, Zn-MUC-TRZ, and Zn-BDC-TRZ) based on the aromaticity modulation strategy. Compared with Zn-MUC-TRZ, the utilization of shorter FA linker only with one double bond leads to an intersection point between the isothermal adsorption curves. After the intersection points, Zn-FA-TRZ showed higher CO2 uptakes than C2H2 (thermodynamic inversion) and the intersection point moving towards the high-pressure region with the increasing temperature. When BDC involved, the enhanced ligand aromaticity enables a complete thermodynamic inversion for C2H2 and CO2 adsorption due to the much stronger interactions between the aromatic ring and CO2 molecules. The isosteric heats of adsorption for CO2 and C2H2 clearly support such inverse adsorption induced by the ligand aromaticity. Furthermore, the fixed-bed dynamic breakthrough experiments indicate that Zn-FA-TRZ and Zn-MUC-TRZ both have common C2H2-selective separation process, but Zn-BDC-TRZ adsorbent shows a prominent CO2-selective inverse C2H2/CO2 separation. Specially, with temperature increased, the inverse separation performance enhanced, and high purity C2H2 (>99.99 %) can be obtained via one-step separation from C2H2/CO2 (50/50) mixture at room temperature. Overall, inverse C2H2/CO2 separation was successfully achieved in pillar-layered metal–organic frameworks, which is helpful for the exploration of practical acetylene adsorbents.

Radiative heat transfer on the peristaltic flow of an electrically conducting nanofluid through wavy walls of a tapered channel

Present analysis deals with the characteristics of radiative heat on the peristaltic flow of nanofluid through wavy walls of a tapered channel. Peristaltic flows within the pumping process arise in the region having lower to higher pressure region. Assumption of velocity slip along with the convective boundary condition energizes the thermal system as well as the flow phenomena. However, the combined effect of Brownian motion and thermophorsis due to the cross-diffusion effect affects the flow properties. One of the significant applications of the flow is that the blood pumping in the human body. It acts as a vehicle through the liquid that past through the wavy channels walls contacting liquids expands in its length due to the dynamical rush. However, solution of the transformed governing flow phenomena is obtained by employing approximate analytical technique known as Variation Parameter Method (VPM). The characteristics of the parameters involved in the system are presented via graphs. Present outcome warrants that, the significance of magnetic strength and flow through the permeable medium may favours to enhance the pumping procedure as the pressure gradient lower down in the non-Darcy medium found to be one of the important observations. Further, significant enhancement in the fluid temperature and concentration profile is exhibited due to the consideration of the convective conditions i.e. the augmentation in the thermal and solutalBiot numbers respectively.

Experimental Comparison of Hydrogen Refueling with Directly Pressurized vs. Cascade Method

This paper presents a comparative analysis of two hydrogen station configurations during the refueling process: the conventional “directly pressurized refueling process” and the innovative “cascade refueling process.” The objective of the cascade process is to refuel vehicles without the need for booster compressors. The experiments were conducted at the Hydrogen Research and Fueling Facility located at California State University, Los Angeles. In the cascade refueling process, the facility buffer tanks were utilized as high-pressure storage, enabling the refueling operation. Three different scenarios were tested: one involving the cascade refueling process and two involving compressor-driven refueling processes. On average, each refueling event delivered 1.6 kg of hydrogen. Although the cascade refueling process using the high-pressure buffer tanks did not achieve the pressure target, it resulted in a notable improvement in the nozzle outlet temperature trend, reducing it by approximately 8 °C. Moreover, the overall hydrogen chiller load for the two directly pressurized refuelings was 66 Wh/kg and 62 Wh/kg, respectively, whereas the cascading process only required 55 Wh/kg. This represents a 20% and 12% reduction in energy consumption compared to the scenarios involving booster compressors during fueling. The observed refueling range of 150–350 bar showed that the cascade process consistently required 12–20% less energy for hydrogen chilling. Additionally, the nozzle outlet temperature demonstrated an approximate 8 °C improvement within this pressure range. These findings indicate that further improvements can be expected in the high-pressure region, specifically above 350 bar. This research suggests the potential for significant improvements in the high-pressure range, emphasizing the viability of the cascade refueling process as a promising alternative to the direct compression approach.

Effects of wake interaction on energy extraction performance of tandem semi-active flapping foils

A numerical investigation was carried out to analyze the interactions between semi-active tandem flapping foils at various tandem distances with a chord-based Reynolds number of 1100. Results indicate that with a tandem distance of less than 1.5 chord lengths and released in-phase, both foils exhibited terminal periodic motions with a nonzero mean stagger distance. In contrast, under the other conditions, the two foils ended up with periodic flapping motions without stagger. Due to the high-pressure region near the leading edge of the aft foil, the heaving motion of the fore foil resulted in lower energy extraction performance than that of single foil, when the tandem distance was less than 5 chord lengths. However, as the tandem distance increased, the fore foil acted like a single foil. The aft foil demonstrated significant fluctuations in performance parameters when subjected to the wake of the fore foil. The favorable interaction between the wake and aft foil resulted in lower power consumption for pitching and enabled the aft foil to extract an additional 15.2% power compared to a single foil. Conversely, during the unfavorable wake–foil interaction, the pitching motion of the aft foil consumed more energy than energy extraction from the heaving motion, leading to net energy consumption. The initial inter-foil pitching phase difference also significantly influenced the performance of the aft foil. Two models, the global phase and the wake phase model, affect these tandem configurations, both proving effective in capturing these effects with the wake phase model displaying notable efficacy.

Numerical simulation of lateral jet interaction with rarefied hypersonic flow over a two-dimensional blunt body

Reaction Control System (RCS) is a direct force control system that successfully adjusts a craft's attitude or orbit using the reaction force created by jet flow. RCS is frequently employed in the management of near-space vehicles due to its properties of fast response time and effective control efficiency. When the near-space vehicle is navigating at high altitude in a low density atmosphere, the Navier–Stokes equation is no longer applicable. The numerical approach utilized in this study is known as the Conserved Discrete Unified Gas Kinetic Scheme, and the governing equation is the Boltzmann equation, which is not constrained by the continuum hypothesis. In velocity space, an unstructured mesh is utilized, which minimizes the amount of discrete velocity points and considerably increases computation efficiency. The numerical results are in good agreement with the direct simulation Monte Carlo code DS2V when modeling large Knudsen number lateral jet flow. The interaction flow field between hypersonic free stream and lateral jet is then simulated at altitudes of 60–90 km using argon as the working gas and a two-dimensional blunt cone with lateral jet as the study object. Under a fixed jet pressure ratio, preliminary research was conducted on the variation of the lateral jet interference flow field characteristics with the freestream Knudsen number and angle of attack. The differences in surface pressure and heat flux caused by jet opening and shutting are compared. Under rarefied atmospheric conditions, the variation of the force/moment amplification coefficient is given. The numerical results show that when the angle of attack is 0°, the separation area in front of the nozzle and a pair of opposite vortices, which are common in the jet interference flow field, gradually disappear with increasing altitude, but the separation vortex reappears when the angle of attack of the freestream is increased. The high-pressure region generated upstream of the nozzle is the primary cause of the extra force/moment. The density of the main flow decreases as altitude increases, various shock wave patterns of the interference flow field gradually dissipate and the force/moment amplification factor changes considerably. The rarefied gas effect has a significant effect on the lateral jet interference flow.

Effect of the arrangement of cavitation generation unit on the performance of an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the “simplified flow field” strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c, N, γ, and r, performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the “simplified flow field” strategy which may induce the unfavorable “sidewall effect” and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs.

Coalescence-induced droplet jumping on superhydrophobic surfaces with non-uniformly distributed micropillars

The phenomenon of droplet jumping induced by coalescence holds significant potential for application in diverse areas such as water collection, self-cleaning, and thermal management of electronic devices. In comparison to a flat surface, a superhydrophobic surface with structure can affect the interaction between the droplet and the surface, thereby affecting parameters such as the droplet jumping velocity. In this study, numerical simulation was used to examine the similarities and differences of coalescence-induced droplet jumping on superhydrophobic surfaces with uniform and non-uniform micropillars, as well as the effect of micropillar non-uniformity on droplet jumping. The results indicated that the non-uniform distribution of micropillars could lead to asymmetries in the shrinkage of the liquid bridge, the morphology of the droplet when it jumps off the surface, and the distribution of the high-pressure region at the bottom of the droplet. Additionally, it decreased the droplet’s vertical velocity while substantially increasing the horizontal velocity. When the droplet radius was constant, decreasing the micropillar width or increasing the micropillar spacing on the sparse side was advantageous for the droplet jumping on a superhydrophobic surface with non-uniform micropillars. By defining the solid fraction on the micropillar surface with non-uniform distribution, the coupling effect of the width and spacing of the micropillars on the droplet jumping was thoroughly analyzed, and the optimal solid fraction for the best directional transport effect of droplets was determined. This study revealed the mechanism underlying the effect of surface micropillar structure on coalescence-induced droplet jumping, and the findings could guide the design of superhydrophobic surface microstructures, which was of great significance for the advancement of droplet jumping applications.

Numerical investigation of the cavitation bubble near the solid wall with a gas-entrapping hole based on a fully compressible three-phase model

The solid surface with several cavities containing gas strongly influences the bubble’s dynamical behaviors. To reveal the underlying physical mechanism of the cavitation bubble near a rigid boundary with a gas-entrapping hole, a fully compressible three-phase model, accounting for the three-phase volume transport equation, was implemented in OpenFOAM. The predicted bubble shape was validated with the corresponding experimental photos, and good agreement was achieved. The bubble’s primary physical features (e.g., the expanding shock wave, upward and downward liquid jet, and high-pressure region) are well reproduced, which helps understand the underlying mechanisms. The numerical results show that the solid wall with a gas-entrapping hole could affect the morphology of both the bubble and liquid jet, as well as shortens the bubble's first oscillation period in comparison to an intact rigid wall. The relationship among the prolongation factor, the standoff distance, and the relative size ratio is analyzed. It is found the prolongation factor increases as the relative size ratio decrease. As the standoff distance decreases, the gas entrapping hole plays a significant role in the oscillation period of the bubble. The current model can be further extended to reveal the microscopic mechanism of aeration avoiding cavitation damage and investigate the interaction between air bubbles and cavitation bubbles, which is of great interest to practical applications.

Heat Transfer Optimization Studies of Semi-Spherical Protrusions on a Concave Surface during Jet Impingement

Much of the literature available on heat transfer enhancement from rough surfaces concerns flat plates or channels. Studies on protruding concave surfaces are surprisingly rare though they have the potential to enhance heat transfer. Therefore, three-dimensional steady-state simulations and corresponding experimental validation is carried out for an air jet impinging on a concave surface projected with semi-spherical protrusions. By providing multiple protrusions, various geometrical configurations are studied by considering the dimensions, angular positions, and pitch between the protrusions. Each individual configuration has its own unique flow pattern which makes prediction of heat transfer complex. This motivates present study to consider entire geometrical parameters affecting heat transfer characteristics with the help of networking tool. Past investigations on protruded flat surfaces concerns random allocation of protrusions. Hence artificial neural network is employed in this study to easily predict the corresponding heat transfer value with set of few input data. Simulation results give detailed flow physics which helps in understanding the heat transfer behavior. It is observed that each protrusion is marked with high-pressure region around its uphill and negative pressure around the downhill. As the flow moves downstream, the protrusions obstruct the flow path and flow separates away as soon as it reaches center of the protrusion. A maximum heat transfer enhancement of 11% is obtained over a corresponding smooth surface.

Hydrogenation behavior of a C14 Laves phase under ultra-high hydrogen pressure

For high pressure metal hydride (MH) compressor applications, it is important to have a thorough understanding of the hydrogenation properties of MH forming compounds under high pressure and temperature conditions, which are still little studied. Here, a Ti0.90V0.30Mn1.00Ni0.80 compound with MgZn2-type AB2 structure has been investigated by Sieverts’ method over a wide pressure and temperature range (up to 100 MPa and between −80 and 120 °C). This provided clear experimental evidence of the downward curvature of the van’t Hoff plot in the high-pressure region, which arises from the non-ideal behavior of hydrogen. In this paper, we also show that the high-sorption pressures can be well estimated by the van’t Hoff equation using low-pressure data. Ultimately, this study was combined with synchrotron radiation X-ray diffraction (SR-XRD) performed in an effort to monitor the structural evolution of the compound in situ under ultra-high hydrogen pressure. We found that even under extreme conditions of 2 GPa and 200 °C, both the main AB2 phase and the secondary CsCl-type AB phase were fully hydrogenated and their structures were conserved. The existence of a critical temperature for the AB2-H2 system was demonstrated from the evolution of the SR-XRD patterns recorded for several temperatures during the desorption process.

Solvent effects of water on the decarboxylation of o-phthalic acid in supercritical water

Water's effect on o-phthalic acid decarboxylation was studied by varying the pressure from (20 to 40) MPa at (380, 400, and 420) °C. The rate constants decreased with increasing pressure at (400 and 420) °C, but remained nearly constant at 380 °C. The trends at (400 and 420) °C were explained using Kirkwood theory, which proposed preferential solvation of the reactant over the transition state. The 380 °C trend was thought to be explained by solvent inhomogeneities and water's peculiar behavior near the critical point. Solvent inhomogeneities were most likely responsible when rates remained low despite low dielectric constant values. These inhomogeneities could have caused a higher local dielectric constant around the solute, suppressing the rate in a manner similar to the higher-pressure region. Water, according to these findings, has the greatest influence on the reaction via solvation.

Adsorption behaviour and thermodynamics of water on deep reservoir and its influence on CO2 sequestration

In this study, the adsorption experiments of water vapour on deep reservoir were conducted. The thermodynamics for water vapour adsorption were analysed. Results illustrate that primary binding centres have stronger affinity than secondary binding centres. Water molecule will be preferentially trapped at primary binding centres in low-pressure region. In high-pressure region, secondary adsorption predominates. Primary adsorption spontaneity increases with pressure. At secondary binding centres and total binding centres, the spontaneity degree quickly improves and then slowly decreases as pressure increases. The transfer of water molecules from the more energetic binding centres to the less binding centres leads to the initial reduction in entropy loss (ΔS) and isosteric heat of adsorption (Q st). The late enhancement in ΔS and Q st is caused by the growing water clusters. Water vapour adsorption can promote CH4 desorption. By occupying adsorption sites and reducing pore connectivity, water vapour adsorption causes an unfavourable effect on CO2 sequestration.