Variable Pressure Conditions Research Articles

Study of low and high temperature oxidation of n-pentane at supercritical conditions in a jet stirred reactor

The intermediate/low and high temperature oxidation of n-pentane from atmospheric pressure to supercritical pressures (1-100 atm) was studied by using Chemkin, a commercial software. A recently developed n-pentane model was used to predict the temperature evolutions of major and intermediate species, like n-pentane, O2, CO, CO2, CH2O, C2H4, CH3CHO at varied pressure and temperature conditions. It is found that as the environmental pressure increases, the difference between high temperature oxidation and low temperature oxidation becomes less obvious because the negative temperature coefficient (NTC) is decreasing (at 10 atm and 100 atm, high temperature oxidation occurs right after low temperature oxidation). At supercritical pressures, the high temperature oxidation is governed by the branching reactions of RO2, and the addition reaction of QOOH with oxygen dominates the reaction paths at both low and high temperature oxidations because the addition reaction between QOOH and oxygen is still more important than the decomposition reaction of QOOH at high temperature and 100 atm. According to the pathway analysis and sensitivity analysis, the branching reactions of RO2 are dominating at both low and intermediate to high temperatures.

Experimental determination of the dew point pressure for bulk and confined gas mixtures using an isochoric apparatus

A robust high precision experimental approach to determine the Dew Point Pressure (DPP) of the gas condensates in a nano-porous medium is presented in this study. Gas condensate reservoirs have been the center of attention for numerous numerical and experimental studies for decades. Therefore, accurate measurement of DPP is crucial in developing long-term production plans for these reservoirs. This paper presents for the first time a proof of concept for a procedure to study the effect of the pore size distribution on the degree and direction of the shift in the saturation pressure of hydrocarbon gas mixtures under confinement over a relevant range of pressures and temperatures.Isochoric method, an indirect high-precision way of phase transition point determination, is commonly used in other disciplines where a clear non-visual determination of phase transition of a fixed volume of fluid is needed. This study provides an insight into using this approach for determining DPP of gas mixtures inside and outside of the porous media. A semi-automated apparatus for measuring and monitoring equilibrium conditions along with fluid properties is designed based on the isochoric method. The apparatus provides constant volume, variable pressure (0–104 bar), and variable temperature (290–410 K) experimental conditions. Pressure and temperature measurements provide a way to detect the phase transition point along the constant-mole-constant-volume line based on the change in the slope of this line at the phase transition point. A packed bed of BaTiO3 nanoparticles, providing a homogenous porous medium with pores of 1–70 nm is used as a representative nano-scale porous medium. The synthesized porous medium is very helpful in uncoupling the effect of pore size from the effect of mineralogy on the observed deviations in behavior, providing a volume more than 1000 times larger than the typical nano channels.The result is a set of isochoric lines for bulk and confined sample, plotted on the mixture's corresponding phase envelope to demonstrate the change in the saturation pressure. Phase envelopes (P-T diagrams) of the same mixture using different equations of state are created and the accuracy of each of these equations of state in providing an estimate of the experimentally detected DPP is discussed. Many attempts in explaining the shift in saturation pressures of the reservoir fluid confined in the narrow pores of unconventional reservoirs compared to those of the bulk can be found in the literature. However, there are some contradictions between the predicted behavior using different mathematical approaches. Experimental data could be substantially helpful in both validating the models and improving the understanding of the fluid behavior in these formations. Contrary to what many published models proposed, our results show that confinement effect shifts the DPP towards higher values compared to the bulk for a fixed temperature in the retrograde region. Capillary condensation is identified as the main source of the deviations observed in the behavior of fluids inside the nanopores. We evaluated some published models, including those based on EoS modifications, by comparing those to the experimental results which provides a quantification of their accuracy in estimating saturation pressure values for the confined mixtures.

Numerical simulation of electrokinetic desalination using microporous permselective membranes

A new scheme for parallelization of microchannels for ion concentration polarization-based seawater desalination is proposed. In the proposed system, microchannels/micropores are paralleled only in ion-selective membrane region and all other parts are simply merged. A two-dimensional simulation model is developed to study performances of such a system, by calculating the salt removal ratio (SRR) and the average velocity of fluid, under varied working conditions. Our results show that SRR >98% for seawater salinity (realizing drinkable water) is achievable. It is found that a stronger cross membrane voltage strengthens electrokinetic flow of the second kind (EOF2) and increases both SRR and flow velocity. Increasing pressure promotes fluid flow but decrease SRR and EOF2 significantly when the ion depletion zone is destroyed. Volumetric energy consumption and energy per ion removal (EPIR) were also characterized under varied electric field and pressure conditions. Energy consumption as low as 12.82 kWh/m3 was realized to convert seawater (salinity ~500 mM) to the desalinated water (salinity ~10 mM) at a flow speed of 0.56 mm/s. The overall cost of water for such a process was estimated as 2.08 $/m3, which is competitive for small-scale desalination applications.

Flowback fracture closure of multi-fractured horizontal wells in shale gas reservoirs

In multi-fractured horizontal wells (MFHW), fracture properties such as permeability and fracture half-length significantly deteriorate during production, which negatively affects gas production from shale reservoirs. Therefore, it is crucial to evaluate the temporal changes in fracture properties using production data. This paper presents two multiphase flowback models for gas and water phase under boundary dominated flow (BDF) condition by considering gas influx from matrix. In addition, a workflow is proposed to quantitatively evaluate hydraulic fracture closure and fracture properties using both water-phase and gas-phase flowback data. A material balance equation (MBE) is derived to obtain average pressure in the fracture by calculating gas influx from matrix under variable bottomhole pressure (BHP) condition based on Duhamel's principle. The flowback models, average pressure calculation method, and workflow are validated against numerical simulations and applied to an MFHW drilled in Marcellus Shale. The results show that the developed models are capable of predicting fracture properties, and MBE could accurately calculate average pressure in the fracture. Furthermore, the proposed workflow provides quantitative insights into the performance of stimulation jobs by accurately predicting fracture half-length, fracture permeability, and permeability modulus using flowback data. By reconciling flowback analysis with long-term production data analysis, a significant decrease in fracture properties due to fracture closure is observed in the Marcellus MFHW.

Experimental measurement on the viscosity of supercritical carbon dioxide

In this paper, a generalized and pragmatic experimental method has been established to measure the viscosity of SC-CO2 which can be used to estimate SC-CO2 tackifier in the application of CO2. A visualization apparatus and high-speed camera system were used to record the settling process and the terminal velocity of particles were measured. The terminal velocity tests in SC-CO2 are conducted to examine the effect of pressure, temperature, particle size and particle type under different conditions of various pressures (6–16 MPa), temperatures (35–70 °C) and different particles (Steel, Glass, Aluminum). A power-law relationship between the particle’s Reynolds (Reynolds number range: 1000–25000) and Archimedes numbers was found due to the experimental results. Using the power-law relationship, viscosity of SC-CO2 can be easily calculated according to the terminal of particle measured in the experiment.

Hexagonal boron nitride grown using high atomic boron emission during microwave plasma chemical vapor deposition

Boron nitride (BN) is a member of Group III nitrides and continues to spark interest among the scientific community for its mechanical properties, chemical inertness, thermal conductivity, and electrical insulating properties. In this study, microwave plasma chemical vapor deposition is used to synthesize BN on silicon substrates. Feed gas mixtures of H2, NH3, and B2H6 are used for a range of systematically varied power, pressure, and flow rate conditions. Plasma optical emission from atomic boron is shown to increase nonlinearly by nearly a factor of five with decreasing chamber pressure in the range from 100 to 10 Torr. Copious amounts of atomic boron in the plasma may be beneficial under some growth conditions for producing high hardness boron-rich nitrides, such as B13N2, B50N2, or B6N, which, to date, have only been synthesized under high pressure/high temperature conditions. Despite the higher atomic boron emission in the plasma at low pressure, BN coatings grown at 15 Torr result in hexagonal BN (B/N ratio of 1), regardless of the B2H6 flow rate used in the range of 0.6–3.0 sccm.

CFD modeling of the OSU High Temperature Test Facility inlet plenum flow distribution during normal operation

This paper investigates the fundamental physical phenomena associated with internal coolant flow distribution in the upper plenum of a prismatic Very High Temperature Reactor (VHTR) during normal operation. Previous studies have revealed the importance of complex flow distribution in the inlet plenum with the potential to generate low velocity or stagnation zones that can subsequently lead to the formation of hot spots in the reactor core and hot streaks in the lower plenum. It is therefore of interest to ensure that coolant is evenly distributed when entering multiple reactor coolant channels. Non-uniformity in the flow distribution is assessed for the reference Oregon State University High Temperature Test Facility (HTTF) case. The HTTF is a reduced scale model (1:4 in height and diameter) of the Modular High Temperature Gas-Cooled Reactor (MHTGR). The developed CFD model reflects complete and detailed geometry of the HTTF upper plenum along with upcomer and metallic core support structure (MCSS). CFD results include parametric studies performed for circulator mass flow rate variation and mesh sensitivity analysis, generated using Siemens Starccm+ software. Outcomes also include variable pressure and temperature boundary conditions impact on the flow distribution.

The effects of pressure treatment on the flamelet modeling of supersonic combustion

The flamelet method has been used extensively as an affordable turbulence-combustion interaction model that obviates the need to solve the evolution equations for the species mass fractions during a large-eddy or Reynolds-averaged Navier–Stokes calculation of a reactive flow field, leading to substantial savings in the simulation time and enabling modeling with relatively complex kinetic mechanisms. The canonical problem analyzed and stored in a look-up array in the flamelet procedure usually assumes some baseline fields; in particular, the pressure is often specified at a fixed value that is characteristic of the examined configuration. However, pressure in supersonic combustion has significant dynamical roles, unlike in low-Mach number or incompressible flows, and a constant pressure field will not be adequate for the former. To remedy this problem, reaction rate in the combustor is often assumed to scale squarely with pressure. This approach, which is probably acceptable for low-speed, high pressure combustors, is not suitable for dealing with the variable pressure conditions in supersonic combustion. This paper focuses on the assessment of the aforementioned scaling, in absolute sense, and also relative to an approach where pressure is added as a control parameter in the flamelet library. To achieve this, three classes of reactive systems with different levels of modeling complexities are investigated to show that representative chemical variables do not scale squarely with pressure. For the case of supersonic combustion, the scaling treatment in general leads to over-prediction of pressure and combustion and also tends to stabilize the flame. To the knowledge of the authors, no previous studies have reported on the issues addressed in the present paper.

Peculiarities of hydrogen interaction with alloys of ZrFe2[sbnd]ZrMo2 system

The quasi-binary ZrFe2ZrMo2 system is an example of a fairly complex metal system with the structure of the Laves phases. Both ZrFe2 and ZrMo2 intermetallic compounds crystallize in the cubic type λ2-MgCu2, for intermediate compositions ZrFe2-xMox an extended region with a hexagonal type of structure λ1-MgZn2 is detected, and also two-phase regions (λ1 + λ2). The formation of hydrides in this system under conditions of various pressures and temperatures was investigated in a number of works. In this paper, an attempt was made to summarize all previously obtained results.

Effect of tool coatings on the interfacial heat transfer coefficient in hot stamping of aluminium alloys under variable contact pressure conditions

The interfacial heat transfer coefficient (IHTC) is an essential parameter in hot stamping for determining the optimal process parameters necessary to achieve the critical cooling rate and thus the desired post-form strength in a formed component. Aluminium chromium nitride, chromium nitride and titanium nitride are currently being widely studied in the hot stamping industry as tool coatings due to their excellent wear performance, although their effects on the IHTC have yet to be determined. In practical hot stamping processes, the contact pressure may also change over extremely short periods of time, leading to abrupt changes in the IHTC and consequently the temperature evolutions of the workpiece. These abrupt changes in contact pressure and their effects on the IHTC have yet to be studied either. In this paper, to address those challenges, the IHTCs between an AA7075 aluminium alloy and different coated tools with a 3-stage evolutionary variable contact pressure were quantitatively determined, and a mechanism-based model developed to accurately predict their values.

Dynamic Temperature Analysis Under Variable Rate and Pressure Conditions for Transient and Boundary Dominated Flow

Current analytical approaches for temperature transient analysis heavily rely on the assumption of the constant rate production, which is often invalid for the extended period of oil production. This work addresses this issue by introducing novel analytical approaches to model the temperature signal under dynamic rate and pressure conditions. The introduced methods share underlying theories of superposition principle and production rate normalization from pressure transient analysis and include a newly derived analytical solution when these theories are not applicable. With adapting these methods, cases with complex production history are modeled using analog cases producing with a constant rate. The dynamic temperature analysis developed herein is validated using synthetic temperature data both graphically and by quantitative estimation of reservoir properties. The estimation outputs of these methods include permeability, drainage area, and damaged zone properties. Other features of existing temperature transient analysis, such as fluid property correction and monitoring well surveillance, are also extended to variable rate and pressure conditions in this paper. Two cases documented in the literature are addressed by dynamic temperature analysis for which decent reservoir characterization results are obtained. The dynamic temperature analysis proposed in this paper extends the scope of temperature transient analysis to complex production constraints and demonstrates convincing results for practical purposes.

Установка для ультразвуковых измерений на образцах геоматериалов в условиях термобарических воздействий

Установка для ультразвуковых измерений на образцах геоматериалов в условиях термобарических воздействий

АНАЛІЗ АКУСТИЧНИХ ВЛАСТИВОСТЕЙ ПОРІД-КОЛЕКТОРІВ РУНОВЩИНСЬКОЇ ПЛОЩІ НА ОСНОВІ ПЕТРОФІЗИЧНИХ ДОСЛІДЖЕНЬ У РІЗНИХ БАРИЧНИХ УМОВАХ

The results of rock physics study of 68 core samples from well No. 110 of the Runovshchynska field of the Dnipro-Donets depression in Ukraine are presented. Investigation of the P-waves on samples under different pressure conditions with the use of 'Kern-4' and high pressure VSC-1000 was performed. Analysis of the obtained data and calculated reservoir values of P-waves was performed. The character of the change in velocity of P- and S-waves for atmospheric conditions is considered. It is shown that the predominant amount of water saturated samples has a velocity of P-waves 3200–3500 m/s (dry samples 2100–2550 m/s), and the S-wave velocity for saturated samples is 2100–2550 m/s (dry specimens 1400–1500 m/s). For a collection of samples, which were measured in atmospheric conditions, the correlation dependence between velocities of P-waves and their density with a close correlation was established. Correlation dependences between elastic wave velocities and the connected porosity of saturated samples were investigated. The dependences of type Vð = f (Kð) with high correlation coefficient for three separate picks of the homotypic sandstones were established. During the analysis of the acoustic studies results under conditions of variable pressure for the majority of samples from the studied intervals, the authors obtained the following common factors. The values of the P-wave velocity, measured in atmospheric conditions, are always smaller than the values obtained after the removal of the pressure; however, there are sometimes quite noticeable fluctuations in their difference, which can be explained by a sharp (possibly hopping) closure of microcracks in the rock with increasing pressure and their delayed opening or non-disclosure when it is reduced. The most contrasting changes in the behavior of the P-wave velocities are haracteristic for several samples (Nos. 27, 48, 50, 53/1), which is most likely due to the void space structure in the rocks, possibly with an increased number of microcracks compared with other samples. On the basis of a priori data and the results of researches of samples at variable pressures, the authors calculated the P-wave velocities in reservoir conditions, conducted their comparative analysis with velocities that are characteristic for samples in atmospheric conditions, built a tight (R² = 0,85) correlation dependence of the investigated parameters.

Ambient-pressure atomic force microscope with variable pressure from ultra-high vacuum up to one bar.

We present the design and performance of an ambient-pressure atomic force microscope (AP-AFM) that allows AFM measurements using the laser deflection technique in a highly controlled environment from ultra-high vacuum (UHV) up to 1 bar with various gases. While the UHV of the AP-AFM system is obtained by a combination of turbo-molecular and ion pumps, for the higher-pressure studies, the ambient-pressure chamber is isolated from the pumps and high-purity gases are dosed via a leak valve from a gas manifold. The AP-AFM system, therefore, provides versatile AFM techniques, including the measurement of topography, friction and local conductance mapping, and force spectroscopy in a highly controlled environment with pressures ranging from UHV up to atmospheric pressure. Atomically resolved stick-slip images and force spectroscopy of highly ordered pyrolytic graphite (HOPG) at variable pressure conditions are presented to demonstrate the performance of the AP-AFM system. Force spectroscopy results of vacuum-cleaved HOPG, followed by exposure to lab air, oxygen, and methane show that adhesion between the AFM tip and the HOPG depends significantly on the exposed gas and pressure. Our results show that the deposition of airborne hydrocarbon impurities at ambient conditions leads to a significant change in adhesion force, implying that the wettability of the HOPG surface depends on the environment and the pressure.

Numerical study on flow characteristics and heat transfer enhancement of oscillatory flow in a spirally corrugated tube

The flow and heat transfer characteristics of oscillatory flow in a smooth tube and two-start spirally corrugated tube were investigated by using a three-dimensional unsteady numerical simulation. The simulation was performed under variable properties, pressure and velocity conditions, with helium (He) as the working medium. The results indicated that longitudinal swirl vortexes were generated with the guidance of a spirally corrugated channel in a two-start spirally corrugated tube in which the fluid flowed spirally forward. The heat absorption (Q) of a two-start spirally corrugated tube exceeded that of a smooth tube (Q0). The difference in the average heat absorption was 561 W and the average of Q/Q0 was 1.36. At the same inlet and wall temperatures of 575 K and 1000 K, the outlet temperature of the smooth and spirally corrugated tube increased by 205 K and 365 K, respectively. Therefore, the spirally corrugated tube presented a superior heat transfer performance when compared to that of the smooth tube. Two types of performance evaluation criterion (PEC) calculation methods in a cycle were used to evaluate the heat transfer enhancement of a spirally corrugated tube. The average value of transient PEC in a cycle was 1.69, and the PEC calculated by average parameters in a cycle was 1.38. When compared with the change of pressure in a MPa level in a heating tube, the pressure drop of hundreds of Pa was negligible. However, the outlet temperature of the heating tube could be subject to an additional temperature increase of hundreds of K with the negligible pressure drop of hundreds of Pa. Thus, the benefits were apparent for the heat transfer enhancement by using spirally corrugated tubes in the heater.

Quantification of dissolved metals in high-pressure CO2-water solutions by underwater laser-induced breakdown spectroscopy

Underwater laser-induced breakdown spectroscopy has been employed for the measurement of dissolved metals (Mg, Ca, Sr, Ba and Mn) in high-pressure CO2-water solutions. The CO2 pressure was varied over the range from 10 to 400 bars and the concentrations of Mg, Ca, Sr, Ba and Mn were determined by spectral analysis and establishing the calibration curves. Limit of detection (LOD) for Mg, Ca, Sr, Ba, and Mn at 10 bars were found to be 31.7 ppm, 2.5 ppm, 3.3 ppm, 4.4 ppm, and 10.5 ppm, respectively. The LOD for Mg, Ca, Sr, and Ba were unaffected by the pressure however, a 2-fold decrease in LOD of Mn was observed with an increasing pressure from 10 to 400 bars. The results demonstrate that low-ppm range concentrations of Mg, Ca, Sr, Ba and Mn can be precisely measured in CO2-charged water at varied pressure conditions by using underwater LIBS. The study has implications in monitoring of CO2 leak in carbon sequestration.

Temporary and Permanent Viscosity Loss Correlated to Hydraulic System Performance

ABSTRACTStraight- and multigrade fluids were evaluated in a hydraulic dynamometer that incorporated a pressure-compensated axial piston pump and a fixed displacement axial piston motor. Pump, motor, pressure compensator, and directional control valve internal flow losses were determined under various conditions of pressure, speed, and temperature. Fluid samples were collected before and at various times during the dynamometer experiments, and viscosity measurements were performed to probe for correlations between viscosity, operating time, and system leakage flow losses. The low shear rate viscosities of the multigrade fluids decreased linearly throughout the duration of testing due to polymer degradation. However, system flow losses did not exhibit a statistically significant increase as the multigrade fluids sheared down. The fluids were also characterized by their permanent viscosity loss produced in sonic shear and tapered bearing tests and by their temporary shear thinning measured in an ultra-high-shear viscometer at several temperatures. The effects of these viscous properties were analyzed using an empirical model to identify which measures of viscosity were most correlated with flow loss. The results suggested that the relative contributions of temporary and permanent viscosity loss change as the fluid is used. Further, analysis of torque loss and input power revealed that input power and losses are more useful indicators of the effect of fluids on hydraulic system performance than pump efficiency.

Effects of the plasma-facing materials on the negative ion H− density in an ECR (2.45 GHz) plasma

Within the framework of fundamental research, the present work focuses on the role of surface material in the production of H− negative ion, with a potential application of designing cesium-free H− negative ion sources oriented to fusion application. It is widely accepted that the main reaction leading to H− production, in the plasma volume, is the dissociative attachment of low-energy electrons (Te ≤ 1 eV) on highly ro-vibrationally excited hydrogen molecules. In parallel with other mechanisms, the density of these excited molecules may be enhanced by means of the recombinative desorption, i.e. the interaction between surface absorbed atoms with other atoms (surface adsorbed or not) through the path . Accordingly, a systematic study on the role played by the surface in this reaction, with respect to the production of H− ion in the plasma volume, is here performed. Thus, tantalum and tungsten (already known as H− enhancers) and quartz (inert surface) materials are employed as inner surfaces of a test bench chamber. The plasma inside the chamber is produced by electron cyclotron resonance (ECR) driving and it is characterized with conventional electrostatic probes, laser photodetachment, and emission and absorption spectroscopy. Two different positions (close to and away from the ECR driving zone) are investigated under various conditions of pressure and power. The experimental results are supported by numerical data generated by a 1D model. The latter couples continuity and electron energy balance equations in the presence of magnetic field, and incorporates vibrational kinetics, H2 molecular reactions, H electronically excited states and ground-state species kinetics. In the light of this study, recombinative desorption has been evidenced as the most probable mechanism, among others, responsible for an enhancement by a factor of about 3.4, at 1.6 Pa and 175 W of microwave power, in the case of tantalum.

Effect of hydrophilic silica nanoparticles on hydrate formation: Insight from the experimental study

Abstract Invasion of drilling fluid into natural gas hydrate deposits during drilling might damage the reservoir, induce hydrate dissociation and then cause wellbore instability and distortion of the data from well logging. Adding nanoparticles into drilling fluid is an effective method in reducing the invasion of drilling fluid and enhancing borehole stability. However, the addition of nanoparticles might also introduce hydrate formation risk in borehole because they can act as the “seeds” for hydrate nucleation. This paper presents an experimental study of the effect of hydrophilic silica nanoparticle on gas hydrate formation in a dynamic methane/liquid-water system. In the experiment, the ultrapure water with and without 1.0 wt%–6.0 wt% concentrations of silica nanoparticles, grain sizes of 20 and 50 nm, were pressurized by methane gas under varied conditions of temperature and pressure. The induction time, the gas consumption, and the average rate of gas consumption in the system were measured and compared to those in ultrapure water. The results show that a concentration of 4.0 wt% hydrophilic SiO2 particles with a grain size of 50 nm has a relatively strong inhibition effect on hydrate formation when the initial experimental condition is 5.0 °C and 5.0 MPa. Compared to ultrapure water, the hydrophilic nano-SiO2 fluid increases the induction time for hydrate formation by 194% and decreases the amount and average rate of hydrate formation by 10% and 17%, respectively. This inhibition effect may be attributed to the hydrophilicity, amount and aggregation of silica nanoparticle according to the results of water activity and zeta potential measurements. Our work also elucidates hydrophilic, instead of hydrophobic, nanoparticles can be added to the drilling fluid to maintain wellbore stability and to protect the hydrate reservoir from drilling mud damage, because they exhibit certain degree of hydrate inhibition which can reduce the risk of hydrate reformation and aggregation during gas hydrate or deep water drilling if their concentration can be controlled properly.

Numerical and experimental study of La–Ni hydriding kinetics based on the varying-size model

Particle size often varies during gas–solid heterogeneous reactions. For example, metal hydrides (MH) can reversibly absorb and desorb H2, accompanied by the expansion and shrinkage of the alloy particles, respectively. Although the traditional shrinking-core model (SCM) can be used to describe the H2 absorption/desorption process, the calculation results from SCM show relatively large deviations from the experimental data without considering the factor of particle expansion/shrinkage. Therefore, we proposed a shrinking-core–varying-size model (SC-VSM, henceforth VSM) for MH particles that accurately determines the kinetics equation with particle deformation. Three types of control mechanism including H2 dissociative chemisorption, H internal diffusion, and surface reaction were studied extensively, and the rate-controlling step for both VSM and SCM was determined to be the internal diffusion of H. Hydriding experiments on the systems of LaNi5 and LaNi4.5Al0.5 were performed under quasi-isothermal and variable-pressure conditions. The simulation results indicated that the new VSM was highly consistent with the experimental data for both alloys, evidently providing higher precision than the traditional SCM. The simplified forms of the VSM diffusion equations for LaNi5 and LaNi4.5Al0.5 were also developed to facilitate their practicability during the hydriding process: LaNi5:1.426-1.419(1-X)23-0.046(1-X)53-0.95X+0.038(1-X)2=tτdiff′LaNi4.5Al0.5:1.362-1.35(1-X)23-0.069(1-X)53-0.90X+0.057(1-X)2=tτdiff′