Equilibrium Vapor Research Articles

Experimental investigation on the phase behaviour for gas hydrates in CO2 rich gas mixtures & multiphase system

Almost 40% of undiscovered hydrocarbon reserves have high CO2 and H2S concentrations around the globe. So it is crucial to understand these hydrocarbon systems’ thermophysical properties for the excellent design of production facilities. An experimental investigation is conducted in this study to understand and evaluate the thermodynamic conditions of gas hydrate formation in natural gas systems with high CO2 levels gas and dominant multiphase (high CO2 level gases, deionized water, and crude oil). Three gas mixtures were chosen in this study to simulate natural gas with high CO2 content. The experiments are conducted within the critical pressure of the selected gas to avoid any phase change due to pressure. The impact of high CO2 levels in gas systems on the thermodynamic conditions of the gas hydrates was first explored. Then, the effect of a multiphase system was investigated after the addition of the oil phase into the system. The thermodynamic equilibrium conditions obtained from experiments were used to construct the Hydrate liquid–vapour Equilibrium (HLVE) curves, and the phase behaviour was studied. The details about the temperature variance and enthalpy are also clearly discussed. It has been discovered that gas mixtures with a higher CO2 content tend to promote compared to the pure methane gas system but inhibit compared the pure CO2 system. But in the multiphase system, all the gases show an inhibition effect compared to their respective pure gas system results.

Phase equilibria molecular simulations of hydrogen hydrates via the direct phase coexistence approach.

We report the three-phase (hydrate-liquid water-vapor) equilibrium conditions of the hydrogen-water binary system calculated with molecular dynamics simulations via the direct phase coexistence approach. A significant improvement of ∼10.5K is obtained in the current study, over earlier simulation attempts, by using a combination of modifications related to the hydrogen model that include (i) hydrogen Lennard-Jones parameters that are a function of temperature and (ii) the water-guest energy interaction parameters optimized further by using the Lorentz-Berthelot combining rules, based on an improved description of the solubility of hydrogen in water.

Water Retention Curve of Biocemented Sands Using MIP Results

Biocementation is a soil treatment technique wherein bacteria living in soil pores promote the precipitation of calcium carbonate. One of the most recent applications of this treatment is to provide resistance against the erosion of slopes by creating a resistant cover but still allowing infiltration to avoid water runoff. For modeling infiltration, it is fundamental to know the water retention curve of the treated material. This may not be an easy task because the soils most suitable for biocementation treatment are sands, due to their large pore sizes and consequent high permeability. The water retention curves (WRCs) of such types of soil are characterized for having a very small air entry value, followed by an almost-horizontal zone, which cannot be measured by using the vapor equilibrium, most of the existing sensors, or a water dewpoint potentiometer. Data from mercury intrusion porosimetry (MIP) tests can be used as an alternative to find the WRC, and this is explored in this paper. The model for the water retention curve presented considers the deformability of the soil during the MIP test, assuming an isotropic elastic behavior. The WRC derived from the MIP tests is well-fitted to the points measured by using a water dewpoint psychrometer (only for suctions above 1 MPa) and vapor equilibrium.

Printability and microstructure of directed energy deposited SS316l-IN718 multi-material: numerical modeling and experimental analysis

In the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10−3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final.

Connecting the Phase State and Volatility of Dicarboxylic Acids at Elevated Temperatures

The partitioning of semivolatile organic molecules between condensed phases and the vapor phase has broad application across a range of scientific disciplines, with significant impacts in atmospheric chemistry for regulating the evolving composition of aerosol particles. Vapor partitioning depends on the molecular interactions and phase state of the condensed material and shows a well-established dependence on temperature. The phase state of solid organic material is not always well-defined, and many examples can be found for the formation of amorphous subcooled liquid states rather than crystalline solids. This can lead to significant changes to vapor equilibrium processes by modifying the thermodynamics and kinetics of evaporation. Here, we explore the influence of phase state on the evaporation dynamics of a series of straight-chain dicarboxylic acids across a range of above-ambient temperatures. These molecules show an odd/even alteration in some of their properties based on the number of carbon atoms that may be connected to their phase state under dry conditions. Using a newly developed linear-quadrupole electrodynamic balance, we levitate single particles containing the sample and expose them to dry conditions across a range of temperatures (ambient to ∼350 K). Using the rate of evaporation measured from the change in the size or relative mass, we derive the vapor pressure and enthalpy of vaporization. Light scattering data allows for unambiguous identification of the phase of the particles (crystal vs amorphous) allowing the vapor equilibrium properties to be attributed to a particular state. This work highlights a new experimental method for characterizing vapor pressures of low volatility substances and extends the temperature range of available data for the vapor pressure of terminal dicarboxylic acids. These measurements show that crystalline and subcooled liquid states persist at elevated temperatures and provide a direct comparison between subcooled and crystal phases under the same experimental conditions.

Synthesis and thermal properties of two novel cobalt (II) Schiff's base complexes as precursors for coating cobalt oxide (Co3O4) thin film by a Plasma Enhanced Metallo-Organic Chemical Vapour Deposition

Two Schiff's base complexes namely, Co(3,5-di-tertbutyl-salicylaldehydatoethylimine)2 (1) and Co(3,5-di-tertbutyl-salicylaldehydatobutylimine)2 (2) were synthesized by template method and characterized by elemental (C, H & N), FT-IR, DART-MS, TG/DTA and single crystal XRD analysis. Both 1 and 2 were found to crystallize in Orthorhombic crystal system. The complexes 1 and 2 undergoes single step volatilization in an inert N2 atmosphere giving a negligible percentage of residues at 331 °C (1) and 362 °C (2) as observed from thermogravimetry (TG) analysis. The molecular mass (M) of Co-bearing species were found to be 580 and 636 Da for 1 and 2 respectively. The equilibrium vapour pressures (pe) measurement by a TG - based transpiration technique over the temperature range of 489–550 K for 1 and 459–561 K for 2 yielded values of 107.0 (±1.8) and 105.2 (±2.1) kJ mol−1 for 1 and 2 respectively for their standard enthalpies of vapourisation (ΔHovap). Complex 2 was used as precursor for demonstrating the formation of Co3O4 thin film at a substrate temperature of 350 °C in an Ar plasma by using a home-built plasma assisted Chemical Vapour Deposition (CVD) method with a deposition pressure of 0.6–1.0 mbar. The phase identification by XRD showed the preferential growth of cubic Co3O4 in (311) plane. The morphology by SEM confirmed densely agglomerated cauliflower like structure. The particle size (D = 15.6 nm) was calculated using Debye-Scherrer's equation. A band gap value of 2.23 eV was obtained using Kubelka-Munk function.

The Separation Behavior of Impurities in the Purification of High-Purity Magnesium via Vacuum Distillation

Magnesium-based materials with exceptional properties are being widely used in the automotive and aerospace industries, as well as in electronic equipment and Mg-based implants. The development of many advanced engineering structures and precision devices prompts the demand for high-purity Mg with better performance and service. However, the current purification methods meet challenges such as the complex equipment, potential dangers due to the powdery condensed products, and the lack of systematic analysis of the impurity behavior. Here, we report the purification of commercial raw materials into 99.9958% (± 0.0034%) pure magnesium products through one-step vacuum distillation. The process adopts a vertical distillation device, which has the advantages of high recovery efficiency, lumpy condensation products, easy cleaning, and reusability. Experimental results confirm that vacuum evaporation is more effective than vacuum sublimation for the purification of magnesium. Then, the behavior of eight impurities is analyzed theoretically and experimentally. The results significantly verify the difficulty sequence of impurity separation from the Mg base, which is Zn > Ca > Pb > Al > Cu > Ni. The similar equilibrium vapor pressure of Zn and Mg and the separation coefficient close to unity are the reasons that cause zinc to be the most difficult one to be separated.Graphical

Numerical simulation of a drying colloidal suspension on a wettable substrate using the lattice Boltzmann method

A computational method based on the lattice Boltzmann method (LBM) is developed to simulate a drying colloidal suspension on a wettable substrate. In this method, solid particles moving in the fluid are treated with an improved smoothed-profile LBM, and the liquid–vapor system is described by the free-energy LBM. To represent solvent evaporation dominated by density gradients, the density at the boundary of the simulation domain is specified to be lower than the equilibrium vapor density. We simulated the drying of a colloidal suspension on a wettable substrate and found that particles with higher wettability aggregated more slowly, but the aggregation proceeded more significantly. This result can be explained based on capillary interactions (i.e., capillary flotation force and capillary immersion force) between the particles. The proposed method can effectively simulate the particle arrangement process induced by the evaporation of the solvent from a colloidal suspension on a wettable substrate.

Experimental investigation and modelling of synergistic thermodynamic inhibition of Diethylene Glycol and glycine mixture on CO2 gas hydrates

In this experimental and modelling study, Diethylene glycol (DEG) and Glycine (Gly) mixtures are introduced to hinder carbon dioxide hydrate formation by pushing the phase boundaries on the lower temperature side. The mixture of DEG and Gly with the ratio of 1:1 is experimented at 15, 10, and 5 wt% concentrations and the pressure vary from 2.5 to 4.0 MPa. The T-cycle method is employed to assess the effect of the studied blends on the CO2 hydrate by evaluating the hydrate dissociation temperature. Varied compositions of pure DEG and Gly as well as their mixtures are used to compute the synergistic effect. The studied system's thermodynamic hydrate inhibition (THI) influence is a concentration-driven phenomenon. Higher concentration can shift the hydrate liquid vapor equilibrium (HLVE) curve to lower temperatures and high-pressure regions. The outcomes depict that mixture of DEG and Gly at 15 wt%. Shows comparatively better results than the mixtures at 5 and 10 wt%, respectively. The obtained 10 wt% mixture results have also been compared with the conventional hydrate inhibitors and other THIs systems and provide a significant hydrate average suppression (ΔT) of 2.4 K. Furthermore, the freezing point-based Dickens and Quint Hunt model was also applied to predict the HLVE data of CO2 hydrates and satisfactory agreement found with maximum mean absolute error (MAE) of 0.498 K. A better inhibitory performance was seen when diethylene glycol and glycine were combined, demonstrating the potential of amino acids as synergistic inhibitors in the exploitation of hydrates, transportation of oil and gas, and flow assurance.

Deformation of unsaturated collapsible soils under suction control

Abstract Collapsible soils present significant geotechnical and structural engineering challenges worldwide. They can be found in arid or semi-arid regions and are directly affected by the multi-step wetting procedure due to the reduction of soil suction. The main objectives of this paper are to investigate the volume change behaviour, collapse mechanism and deformation characteristics under the control of suction and net vertical stress. In this study, three types of collapsible soils were investigated such as natural soils of sandy gypseous, silty loess, and artificial soil of gypsum–sand mixture. A series of constant net stress-suction control (wetting and drying) tests using a combination of axis-translation and vapor equilibrium techniques were deployed to cover a wide range of applied suction. The test results show that large volume change and collapse deformation occur upon a stepwise suction decrease. On the other hand, shrinkage behaviour resulting from increases in imposed suction is observed during the drying path. The collapse deformation depends on the stress path and is a function of net normal stress, suction, dry density, and degree of saturation. The water content and the degree of saturation dramatically increase as the applied suction decreases from the initial high to zero values at the drying path.

Multiphase simulation and parametric study of direct vapor generation for a solar organic Rankine Cycle

Parabolic trough collectors coupled with Organic Rankine Cycles are an attractive option for decentralized power generation. This work is dedicated to the parametric study of a parabolic trough collector system filled with benzene under solar irradiation for use in an Organic Rankine Cycle; the Computational Fluid Dynamics software ANSYS FLUENT was used in the study. Different inlet temperatures (465, 475 and 485 K), mass fluxes (168, 336 and 504 kg/m2s), and solar-concentrated heat fluxes (15.1, 18.5 and 22.2 kW/m2) are used in the simulations. The numerical model is validated with experimental data to a good concordance (maximum measured error for outlet equilibrium vapor quality and temperature is about 6 % and 0.01 %, respectively). The results indicate that (1) the inlet temperature does not have an effect in the fluid boiling behavior, (2) increasing the mass flow rate decreases the fluid evaporation rate, (3) the fluid evaporation rate is directly affected by the solar heat flux and (4) the mass flux affects the point where evaporation begins occurring (tube lengths of 10, 15 and 25 m for mass fluxes of 168, 336 and 504 kg/m2s, to 15.1 kW/m2, respectively.) Results also show that an excessive heat flux can result in large thermal gradients inside the collector (hence, overheating), and an excessive mass flow will delay the net vapor generation point.

Analysis of the thermo-pneumatic properties of copper oxide-based nanofluids for pressure generation during membrane filtration

• The method used in the synthesis of nanoparticles, influences their shapes. • The stability of nanoparticles in nanofluids greatly affects their thermal conductivity enhancement. • The enthalpy of vaporization of volatile liquids is lowered when nanoparticles are dispersed in the fluid. • Nanofluids generally have improved thermal properties than their pure base fluids. The development of nanofluids and their application in heat transfer systems has been improved in recent years. These nanofluids enable heat engines to work at lower temperatures and utilize low-grade energy sources more efficiently especially in membrane filtration systems. In this study, CuO and Cu 2 O nanoparticles were synthesized, characterized, and used in preparing nanofluids. These nanofluids were then tested for vapour pressure generation enhancement in a diaphragm pump. Optimization of the thermo-pneumatic properties of the nanofluids was done through altering the nature, shape, size, and weight concentrations of the copper oxide nanoparticles in different base fluids. The equilibrium vapour pressure generated by a 0.1 wt% CuO nanofluid at 30 °C was found to be 100% higher than that of the pure working liquid. The 0.1 wt% CuO nanofluid also attained equilibrium pressures at a rate that was 37% faster on average than for the pure working liquid in the temperature range of 35 °C to 60 °C. he latent heat of vaporization of the pure volatile liquid was decreased by 15,7% and its thermal conductivity was enhanced by 26,2% by the 0.1 wt% CuO working liquid which showed the best stability at a pH of 6.

Molecular models for O2 and N2 from the second virial coefficient

• O 2 and N 2 models were generated in gas phase and by rescaling the energy the interfacial properties were obtained. • The convenience to reproduce the N 2 and O 2 properties using the 2cLJQ and 2cANCQ fluids were analyzed. • We implement algorithms with HyperOpt and MPI4Py libraries to optimize the search in the parameter domain. In this work we take up the molecular models generation for O 2 and N 2 . This aim is achieved with the two center Lennard-Jones and two center ANC potentials, plus quadrupole interactions. We analyze the convenience to perform the fitting of potential functions to the experimental data of the second virial coefficient and then rescaling the energy well depth to simulate properties in the liquid phase: surface tension, liquid vapor equilibrium and vapour pressure. The main objective is to study the following: 1) To analyze if due to the fact that the ANC interaction sites have a greater number of parameters their results enhance these one obtained from the LJ interaction sites in the gas phase, and 2) to establish whether the effect of the interaction of three bodies, included through rescaling the energy well depth, is enough to get that the results of the ANC interaction sites enhance the results obtained with the LJ interaction sites in the liquid phase. Although the first objective was fulfilled satisfactorily, that is, the results with the ANC interaction sites reproduce better the experimental second virial coefficient, for the second objective, both types of pairwise interaction lead to similar results of properties in the liquid phase. As a consequence of this similarity, it is deduced that the objective function used to optimize the two center ANC leads to optimal parameters in accordance with the N 2 and O 2 models of the two center Lennard-Jones. Therefore, rescaling the depth of the energy well is not enough to overcome the results found with the two center Lennard-Jones in the liquid phase. It is worth mentioning that for reduce the computational cost, to obtain the best fitting curves in the gas phase, bayessian optimization were performed using the Python Hyperopt library. In addition, the O 2 and N 2 molecular models were also evaluated by transferring the parameters to the cross second virial coefficient for O 2 + N 2 and N 2 + NO binary gas mixtures, the second virial coefficient for NO pure gas, and the third virial coefficient of O 2 and N 2 pure gases.

Determination of stoichiometry deviation in wide-band II-VI semiconductors on the basis of equilibrium vapor phase composition

A method of determining stoichiometry deviation in cadmium and zinc chalcogenides that is based on the temperature dependence of the ratio of components partial pressures during evaporation of solid compounds in a limited volume has been suggested. The new method differs from methods implying the collection of excessive component during evaporation in large volumes. The method includes measuring vapor phase components partial pressures during material heating to above 800 K, solving a set of material balance equations and the electric neutrality equation, and calculating the stoichiometry deviation in the initial compound at room temperature. Intrinsic point defect concentrations are calculated using the method of quasichemical reactions. The independent variables in the set of equations are the sought stoichiometry deviation, the partial pressure of the metal and the concentration of free electrons. We show that the parameter of the material balance equation which determines the method’s sensitivity to stoichiometry deviation, i.e., the volume ratio of vapor and solid phases, can be considered constant during heating and evaporation unless this parameter exceeds 50. If the partial pressure is measured based on the optical density of the vapors, then the sensitivity of the method can be increased to not worse than 10-6 at.%.

Phase equilibria of hydrates from ternary mixtures of methane + ethane + propane and methane + propane + carbon dioxide

AbstractHydrate–liquid–vapour (HLV) equilibrium of aqueous clathrates formed from gas mixtures can be complex compared to hydrates formed with single guests. Typically, pressure and temperature are controlled to obtain these data, but for multicomponent systems, it is necessary to control/report more intensive variables, namely, composition. Metastability, manifested as impractically long experimental times, has been reported to be a challenge with some multicomponent systems. We present HLV equilibrium conditions of two ternary gas mixtures: methane + ethane + propane (90:7:3 molar ratio) and methane + propane + carbon dioxide (55:5:40 molar ratio). Conditions varied in the temperature range of 275–285 K and the pressure range of 1.24–4.75 MPa. Experimental standard uncertainties were on average 0.10 K and 0.005 MPa for methane + ethane + propane and 0.19 K and 0.005 MPa for methane + propane + carbon dioxide. Our technique allowed us to bypass the limitations reported in the literature and provided fast, reproducible HLV equilibria for gas‐dominated systems.

Determination of stoichiometry deviation in wide-band II–VI semiconductors on the basis of equilibrium vapor phase composition

A method has been suggested for determining stoichiometry deviation in cadmium and zinc chalcogenides based on the temperature dependence of the ratio of components partial pressures during evaporation of solid compounds in a limited volume. The new method differs from methods implying the collection of excessive component during evaporation in large volumes. The method includes measuring the partial pressures of vapor phase components during material heating to above 800 K, solving a set of material balance equations and the electric neutrality equation, and calculating the stoichiometry deviation in the initial compound at room temperature. Intrinsic point defect concentrations are calculated using the method of quasichemical reactions. The independent variables in the set of material balance equations are the sought stoichiometry deviation, the partial pressure of the metal and the concentration of free electrons. We show that the parameter of the material balance equation which determines the method’s sensitivity to stoichiometry deviation, i.e., the volume ratio of vapor and solid phases, can be considered constant during heating and evaporation if this parameter does not exceed 50. If the partial pressure is measured based on the optical density of the vapors, then the sensitivity of the method can be increased to not worse than 10–6 at.%.

Hard-core attractive Yukawa fluid global isomorphism with the lattice gas model.

In this work, we study the global isomorphism between the liquid-vapor equilibrium of the hardcore attractive Yukawa fluid (HCAYF) and that of the Lattice Gas (LG) model of the Ising-like type. The applicability of the global isomorphism transformation and the dependence of its parameters on the screening length of the Yukawa potential are discussed. These parameters determine both the slope of the rectilinear diameter of the liquid-vapor binodal and the Zeno-element, which are the core ingredients of the fluid-LG isomorphism. We compare the Zeno-element parameters with the virial Zeno-line parameters, which are commonly used in the literature for the formulation of generalized law of the correspondent states. It is demonstrated that the Zeno-element parameters appear to be sensitive to the liquid state instability when the interaction potential becomes too short-ranged, while the virial ones do not show any peculiarities connected with this specific of the HCAYF.

A review on the solid–liquid–vapor phase equilibria of acid gases in methane

AbstractIn spite of the increasing levels of greenhouse gases in the atmosphere, and their impact on the environment, the demand for natural/biogas will increase significantly in the coming few decades. To cover this demand, the global energy industry is continuously exploiting sour gas reserves located around the world. Nonetheless, sour gas has to be sweetened before the practical utilization of natural or biogas. The cryogenic separation technologies have emerged as a new technology to separate carbon dioxide (CO2) and hydrogen sulfide (H2S gases) from natural/biogas. The cryogenic separation produces less harmful gases, and can be less expensive to operate and maintain in comparison to the conventional technologies. To design cryogenic separation equipment, vapor–liquid equilibrium (VLE), solid–liquid equilibrium (SLE), solid–vapor equilibrium (SVE), and solid–liquid–vapor equilibrium (SLVE) data for the corresponding binary systems (of CH4‐CO2, CH4‐H2S, and H2S‐CO2) and ternary system (of CH4‐H2S‐CO2) are required. The main target of this article is to review the SLVE data for the acid gases (CO2 and H2S) in methane (CH4) as the main constituent of natural/biogas. It will address SLVE data for the binary systems of CH4‐CO2, CH4‐H2S and H2S‐CO2 as well as the ternary system of CH4‐H2S‐CO2. It will not only address the available laboratory data, but it will also discuss, compare and evaluate the different models used to correlate/predict these data. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Enhanced transport in a porous medium due to dissolved salt

An experiment is presented showing enhanced water transport across a porous layer compared to pure water vapor diffusion. The enhanced transport is explained by the presence of brine in the layer and the dependence of the equilibrium vapor pressure with the dissolved salt concentration. The impact of the salt presence is further demonstrated by a comparison with the case of pure water. A significantly longer period of sustained evaporation is obtained in the presence of salt. The transport enhancement effect can last over long periods of time when the conditions are such that the porous layer reaches a dynamic equilibrium between condensation and evaporation. Also, the porous layer can adapt to changes in the boundary conditions via changes in the brine saturation and associated modifications in the salt concentration and the equilibrium vapor pressure. The transport enhancement effect is also illustrated in relation with the dynamics of salt crusts.8 MoreReceived 18 February 2022Accepted 24 May 2022DOI:https://doi.org/10.1103/PhysRevFluids.7.064304©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDisplacement of immiscible fluidsEvaporationFlows in porous mediaSurface tension effectsFluid Dynamics

Temperature effects on water retention behaviour and structural evolution of GMZ bentonite pellet mixtures

Mixtures of high-density, multi-sized bentonite pellets are considered as a promising buffer/backfill material for deep geological disposal of high-level radioactive waste (HLW). During the operation of a HLW repository, the pellet mixtures will be subjected to ground water infiltrated from surrounding rock and elevated temperatures induced by nuclide decay heat, leading to a complex hydro-mechanical behaviour. In this paper, water retention tests with suction controlled by vapour equilibrium and osmotic techniques, as well as structural observations by mercury intrusion porosimetry (MIP) were performed on three kinds of specimens of Gaomiaozi (GMZ) bentonite at different temperatures (20, 40, 60 and 80 °C), including constant-volume pellet mixtures (PM) and compacted blocks (CB) with an identical dry density (1.45 Mg/m3) and free-swelling single pellets with the same initial dry density (1.95 Mg/m3) as those involved in the PM specimen. For the three kinds of specimens, the water retention capacity decreased with increasing temperature. From a perspective of thermal dynamics theory, it is concluded that in high suction range (> 10 MPa), increasing temperature inhibited the water adsorption and promoted the water desorption process consequently leading to a decreasing water retention capacity. According to the capillary law (Young – Laplace equation), in the low suction range (< 10 MPa), increasing temperature reduces the capillary water content in terms of decreasing the surface tension, contact angle and density of the capillary water, as well as expanding the entrapped pore air. Meanwhile, the MIP test results illustrate that during hydration, most of the large pores (2000–360,000 nm) were gradually converted into medium pores (100–2000 nm) while the change of small pores (6.4–100 nm) and inaccessible pores (< 6.4 nm and > 360,000 nm) were limited. Compared to the effect of suction, the temperature influence on this structural evolution process was relatively slight. Therefore, the temperature-dependent water retention behaviour was mainly caused by temperature-induced changes of water-clay interactions as well as physical properties of adsorbed and capillary water during hydration, rather than the limited changes of pore structure of the specimen.