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The ambient-pressure phase α of C4H2N5Cl transforms under 0.18 GPa to a higher-symmetry phase α′, but its high-pressure recrystallization below 0.20 GPa leads to a stochastic hydrate while above 0.20 GPa recrystallization leads to a new phase, β., Partial hydration of organic compounds can be achieved by high-pressure crystallization. This has been demonstrated for the high-nitro­gen-content compound 6-chloro-1,2,3,4-tetrazolo[1,5-b]pyridazine (C4H2N5Cl), which becomes partly hydrated by isochoric crystallizations below 0.15 GPa. This hydrate, C4H2N5Cl·xH2O, is isostructural with the ambient-pressure phase α of C4H2N5Cl, but the crystal volume is somewhat larger than that of the anhydrate. At 0.20 GPa, the α-C4H2N5Cl anhydrate phase transforms abruptly into a new higher-symmetry phase, α′; the transformation is clearly visible due to a strong contraction of the crystals. The hydrate α-C4H2N5Cl·xH2O can also be isothermally compressed up to 0.30 GPa before transforming to the α′-C4H2N5Cl·xH2O phase. The isochoric recrystallization of C4H2N5Cl above 0.18 GPa yields a new anhydrous phase β, which, on releasing pressure, transforms back to the α phase below 0.15 GPa. The structural transition from the α to the β phase is destructive for the single crystal and involves a large volume drop and significant elongation of all the shortest intermolecular distances which are the CH⋯N and CH⋯Cl hydrogen bonds, as well as the N⋯N contacts. The α-to-α′ phase transition increases the crystal symmetry in the subgroup relation; however, there are no structural nor symmetry relations between phases α and β.

The thermodynamic properties of MgCaSi and its mother phase Ca2Si are comparatively investigated from ab initio calculations and quasi-harmonic Debye-Gruneisen model. At 0 K, MgCaSi is more thermodynamically stable. Under high temperature, the advantage of higher thermodynamically stability of MgCaSi is reduced, originating from the less negative entropy contribution because the thermodynamic entropy of MgCaSi increases more slowly with temperature and the entropy values are slightly smaller. With increasing temperature, the anti-softening ability for MgCaSi is slightly smaller due to the slightly faster decrease trend of bulk modulus than that of Ca2Si, although the bulk modulus of MgCaSi is higher in the whole temperature range considered. The thermal expansion behaviors of both MgCaSi and Ca2Si exhibit similar increase trend, although thermal expansion coefficient of MgCaSi is slightly lower and the increases is slightly slower at lower temperature. The isochoric heat capacity CV and isobaric heat capacity CP of MgCaSi and Ca2Si rise nonlinearly with temperature, and both CV are close to the Dulong–Petit limit at high temperature due to the negligibly small electronic contribution. The Debye temperature of both phases decrease with increasing temperature, and the downtrend for MgCaSi is slightly faster. However, MgCaSi possess slightly higher Debye temperature, implying the stronger chemical bonds and higher thermal conductivity than the mother phase Ca2Si. The Gruneisen parameter of MgCaSi and Ca2Si increase slightly with temperature, the values of MgCaSi are slightly larger. The investigation of electronic structures shows that with substitution of partial Ca by Mg in Ca2Si, the stronger Mg Si, Mg Ca and Si Si covalent bonds are formed, and plays a very significant role for the structural stability and mechanical properties.

The absorption-cycle technology driven by low-grade thermal energy has attracted significant attention. Hydrofluoroolefins refrigerant and ionic-liquid absorbent have been currently proposed as the promising candidates to traditional NH3/H2O and H2O/LiBr working pairs. The properties of refrigerant/absorbent pairs have a vital impact on the efficiency of an absorption-refrigeration cycle, especially the solubility of the gaseous refrigerant in an absorbent. In this work, solubilities were measured for two new working pairs (R1234ze(E)/[P66614][Cl] and R1233zd(E)/[P66614][Cl]) by an isochoric saturation method at the temperature range from 283.15 to 343.15 K. Solubilities increase with the increase of pressure and decrease with increase of temperature. To assess solubility model of refrigerant/IL pairs, the Krichevsky-Ilinskays (KI) equation and Nonrandom Two-Liquid (NRTL) model were used to correlate the new data. From the results, we found that the NRTL model could provide smaller deviations than KI equation. In contrast with the existing IL, the [P66614][Cl] has the highest solubility. Furthermore, the enthalpy, entropy, and Gibbs energy of dissolution were estimated.

In this article, the response of an interfacial layer developed along a particulate–continuum interface is explored under two opposite normal confining constraints. To this end, a cohesionless gran...

High-pressure polymorphs can be obtained and stabilized at ambient pressure by utilizing dopants with more voluminous molecules, inducing internal strain in the structures. This effect has been confirmed for doped resorcinol and imidazole derivatives by nucleating and stabilizing their high-pressure phases under ambient conditions. The dopant molecular volume and concentration, as well as the bulk modulus of the polymorph in the binary system, are related to the stability region in the single-component phase diagram. High-pressure isothermal and isochoric recrystallizations yielded pure single crystals of resorcinol ε above 0.20 GPa and a new polymorph ζ above 0.70 GPa. These recrystallizations of pure resorcinol revealed within 1 GPa of the p–T phase diagram the boundaries and the stability regions of four resorcinol polymorphs α, β, ε, and ζ, contrary to the compression experiments on ambient-pressure polymorphs α and β, when the high-pressure phases were hidden behind the wide hysteresis extending to nearly 5 GPa. The hysteresis, originating from the H-bonding networks, hinders the formation of polymorphs ε and ζ when polymorphs α and β are compressed without melting or dissolving the crystals. Polymorph ζ is the only known resorcinol structure built of hydrogen-bonded layers.

In this study, with the aim of deriving a temperature-based energy equation and evaluating the fractal dynamic SGS (FDSGS) combustion model under an isochoric condition, modelling of the filtered e...

R1234ze(E) and R1234yf, as green refrigerants, have received more and more attention in recent years. To better understand the performance of the evaporator working with a refrigerant/lubricating oil mixture, the solubilities of R1234ze(E)/POE85 and R1234yf/POE85 were measured using the isochoric saturation method in the temperature range from 278.15 K to 348.15 K. The NRTL model was used to correlate the new data. Using the new data, the pressure-enthalpy-vapor quality diagram and superheat-non-evaporation diagram were presented. The results show that the enthalpies of refrigerant/lubricating oil are always lower than those of pure refrigerant. The critical vapor quality is related to the refrigerant/oil solubility and oil circulation mass ratio. The enthalpy change ratio is directly proportional to the superheat and inversely proportional to the oil circulation mass fraction. The non-evaporation quality decreases as the superheat increases and increases as the mass fraction of oil circulation increases.

Methane adsorption on a recuperated activated carbon, AR-V, was studied over the temperature range of 213–393 K and at pressures up to 10 MPa from the perspective of its potential application for adsorption-based storage and separation technologies. The porous structure, phase and chemical compositions of AR-V were examined by nitrogen adsorption at 77 K, x-ray diffraction, and scanning electron microscopy. The amount of adsorbed methane increased with pressure up to 6.3 mmol/g at 243 K and fell dramatically to ~ 1 mmol/g with a temperature rise to 393 K. The molar differential isosteric heat of methane adsorption on AR-V was evaluated from the linear isosteres within the studied P,T-range; the effects from the non-ideality of a gaseous phase and the AR-V non-inertness were considered. The maximal summarized contribution from the AR-V thermal expansion and directly measured adsorption-induced deformation to the molar differential isosteric heat of methane adsorption turned out to be less than that from the gas compressibility. The initial drastic changes in the thermodynamic state functions of the adsorption system were attributed to the binding methane molecules with non-uniformly distributed high-energy adsorption sites. When methane molecules occupied all high-energy adsorption sites, the subsequent variations in the thermodynamic functions were governed by the intensifying attractive forces between methane molecules upon methane adsorption resulting in the formation of adsorption clusters. The temperature dependence of the isosteric heat capacity of the methane/AR-V system varied during adsorption; its value exceeded 2–3 times the isochoric heat capacity of the equilibrium methane gaseous phase.

An empirical partition function, f, for polyethylene (PE) was determined based on a pressure (PV)-volume (V)-temperature (TV)-entropy (SV) isochoric equation of state where the variables of PV, TV ...

This paper is a theoretical study of a protocol for transport of high concentrations of cryoprotectants into biological matter, using isochoric freezing. Unlike isobaric freezing, where the entire system freezes at temperatures lower than the freezing temperature, in isochoric freezing a substantial portion of the system remains unfrozen at temperatures below freezing. In isochoric freezing cryopreservation, the system is designed in such a way that the biological matter remains unfrozen and surrounded by an unfrozen solution. The protocol in this study involves the freezing of an isochoric systems along the "liquidus line" at which water and ice are in thermodynamic equilibrium. Rejection of solutes by ice increases the concentration of the solutes in the unfrozen solution surrounding the unfrozen biological matter, leading, thereby, to transport of increasingly higher concentrations of cryoprotectants into the biological matter, as the temperature of the system is lowered and the toxicity of the cryoprotectants is reduced.

Traditionally, it is commonly assumed that a single gas hydrate (or clathrate hydrate) structure/phase is formed in natural gas systems—e.g., “s-II natural gas (NG) hydrates” or “s-I methane hydrates”—based on that which is understood to be the most thermodynamically stable at incipient phase boundary conditions. This applies with respect to both studies of hydrates in natural sediments, and in the case of hydrocarbon production operations, including the testing of low-dosage hydrate inhibitors (LDHIs). Here, we present the results of experimental studies of simple propane (C₃), binary methane–propane (C₁–C₃), and ternary methane–ethane–propane (C₁–C₂–C₃) hydrate systems, aimed at investigating phase behavior at higher subcoolings where significant water conversions to clathrates—and associated gas fractionation—might be expected to result in the formation of more than one hydrate structure. Measurements were made by means of established, reliable, isochoric equilibrium step-heating/cooling approaches. In the single guest propane system, pressure–temperature (PT) conditions follow the gas hydrate phase boundary, in agreement with the univariant hydrate + gas + water (H + G + W) equilibrium. By contrast, binary and ternary mixes clearly show PT behavior consistent with the growth of at least two and four hydrate phases, respectively, with these forming sequentially on cooling, and dissociating in the corresponding reverse order upon heating. In-house hydrate model (HydraFLASH) predictions support experimental observations, pointing to processes being gas fractionation driven; the mixed C₃–C₁ or C₃–C₂–C₁ s-II type hydrates formed first close to the phase boundary preferentially incorporating the most strongly clathrate cage (5¹²6⁴) stabilizing propane, making the remaining gas leaner. Once C₃ is largely consumed, trends agree with less stable C₂–C₁ structures (s-II followed by s-I) then growing (where ethane is present), with this, like C₃ uptake, making remaining free gas increasingly of almost pure C₁. This ultimately drives systems toward the final simple, single guest C₁ s-I clathrate formation as the well-established univariant phase boundary for this structure is reached. As observed phase behavior arises because of gas fractionation, it can be expected to occur during hydrate formation in all mixed gas systems of relatively fixed composition (at constant volume or pressure). The findings highlight that care should be taken in the application of isochoric methods to multicomponent gas systems, given the potential for numerous (rather than just one) clear changes in heating curve slopes as different hydrate structures form/dissociate. In addition, results show that extending equilibrium steps well into the hydrate region can reveal important information on clathrate phase behavior with potentially significant implications for issues such as gas production from hydrates in sediments, hydrate technologies for gas capture/separation/storage in the energy industry, and flow assurance in hydrocarbon production operations.

An empirical pressure (P)-volume (V)-temperature (T)-entropy (S) equation of state (P-V-T-S Eos) of polyethylene (PE) has been determined based on the experimental data of P-V-T and isobaric heat c...

A unified fundamental equation of state has been developed for 2,3,3,3-tetrafluoropropene (R1234yf), a fourth-generation ozone-safe refrigerant, and a method for constructing the equation has been proposed. In the gas region, this equation transforms into an equation of state of the virial form, and in the vicinity of the critical point it satisfies the requirements of the modern scale theory of critical phenomena and transforms into the Widom scale equation. Based on a single fundamental equation of state in accordance with GOST R 8.614-2018, “GSI. State Service of Standard Reference Data. Basic Provisions,” we developed standard reference data GSSSD 380-2020 on density, enthalpy, isobaric heat capacity, isochoric heat capacity, entropy and speed of sound in R1234yf in the temperature ranges 230–420 K and pressures 0.1–20 MPa. We compared the calculated values of equilibrium properties with the most reliable experimental data obtained in well-known global laboratories and tabular data obtained from the known fundamental equations of state R1234yf. Uncertainties of tabulated data for saturated vapor pressure, density, enthalpy, isobaric heat capacity, isochoric heat capacity, entropy and speed of sound of 2,3,3,3-tetrafluoropropene are estimated – standard relative uncertainties for types A, B, total standard relative and expanded uncertainties. The results obtained in this work show that the proposed unified fundamental equation of state adequately describes the equilibrium properties of R1234yf in the above stated range of state parameters.

The determination of the soil-water characteristic curve (SWCC) of compacted bentonites in the isochoric condition is a prerequisite for unsaturated flow simulations in several geoenvironmental applications. The SWCC data are, however, not readily available for many compacted bentonites over a wide suction range due to difficulties associated with the testing. In this work, wetting SWCCs of four Indian bentonites of different plasticity were established experimentally at compaction dry densities of 1.4, 1.6, and 1.8 Mg/m3 in isochoric conditions using two independent laboratory techniques in different suction ranges. The modified Kovács (MK) model was extended to simulate the SWCC data of the Indian bentonites. Empirical relationships between MK model parameters and compaction dry density for these bentonites were established. A theoretical procedure for the estimation of SWCCs of the compacted bentonites based on the basic bentonite properties and proposed correlations was proposed and validated on the available wetting SWCC data of compacted GaoMiaoZi (GMZ), MX80, and FEBEX bentonites from the literature studies. The proposed method predicts the wetting SWCCs of compacted powder bentonites, in volume-restrained condition, from the basic properties satisfactorily. The proposed model is an approximate method for predicting the SWCCs of bentonites in the absence of measured data and in understanding the influence of dry density and plasticity.

Knowledge of the solubility of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) in lubricant oil is an indispensable factor for designing refrigeration system and choosing suitable lubricant oil. In this work, the solubilities of R1234yf in polyol ester (POE) base oil, polyvinylether (PVE) base oil, and polyalkylene glycol (PAG) base oil were measured in the temperatures range from 273 K to 353 K based on the isochoric method. The experimental solubility data were correlated using the Peng-Robinson (PR) equation of state and Wilson activity coefficient model. The absolute average relative deviations of the experimental data and calculated values for the R1234yf + POE base oil system, R1234yf + PVE base oil system, and the R1234yf + PAG base oil system are 2.47%, 1.66%, and 1.29%, respectively.

We report the effect of isochoric confinement on the characteristic length of the glass transition (ξα) for polystyrene (PS) and poly(4-methylstyrene) (P4MS). Utilizing silica-capped PS and P4MS nanoparticles as model systems, ξα values are determined from the thermal fluctuation model and calorimetric data. With decreasing nanoparticle diameter, ξα decreases, suggesting a reduction in the number of segmental units required for cooperative motion at the glass transition under confinement. Furthermore, a direct correlation is observed between ξα and the isochoric fragility (mv) in confined polymers. Due to a nearly constant ratio of the isochoric to isobaric fragility in confined polymer nanoparticles, a correlation between ξα and mv also implies a correlation between ξα and the volume contribution to the temperature dependence of structural relaxation. Lastly, we observe that when the fragility and characteristic length are varied in the same system the relationship between the two properties appears to b...

This work proposed a simple corresponding state equation depending on reduced temperature to predict compressed liquid isochoric heat capacity (cv) for HCs, HCFCs, HFCs and HFOs pure and mixtures at 0.3 2ρc). With known critical parameters, acentric factor and ideal gas isochoric heat capacity, the developed equation can represent the compressed liquid cv well with the average absolute relative deviation (AARD) of 1.82%. Compared with the generalized equation of Zhong et al. (2019a) and the special multiproperty equations in REFPROP 10.0 software, the proposed equation is slightly poor in accuracy, but simpler in form and requires fewer parameters. In addition, liquid cv data of 13 pure and 9 mixtures were used to verify the prediction performance of the developed equation and the applicability to the mixtures. The equation in this work is in good agreement with the experiment cv data of 9 pure and 9 mixtures including HCs, HFCs, HCFCs and HFOs, but the large deviation for 4 substances (N2, CO2, H2O and CH3OH).

This paper analyzes the pressure response to an unsteady heat release source in an unconfined one-dimensional domain. An analytical model based on the acoustic wave equation with an unsteady heat source is derived, and then compared against results from highly-resolved numerical simulations. Two different heat release profiles, a Gaussian spatial distribution with either a step or a Gaussian temporal distribution, are used to model the heat source. The analytical solutions predict two regimes in the pressure response depending on the Helmholtz number, which is defined as the ratio of the acoustic time over the duration of the heat release pulse. A critical Helmholtz number is found to dictate the pressure response regime. For compact cases, in the subcritical regime, the amplitude of the pressure pulse remains constant in space. For noncompact cases, above the critical Helmholtz number, the pressure pulse reaches a maximum at the center of the heat source, and then decays in space converging to a lower far field amplitude. At the limits of very small and very large Helmholtz numbers, the heat release response tends to be a constant pressure process and a constant volume process, respectively. The parameters of the study are chosen to be representative of the extreme conditions in a rocket combustor. The analytical models for both heat source profiles closely match the simulations with a slight overprediction. The differences observed in the analytical solutions are due to neglecting mean flow property variations and the absence of loss mechanisms. The numerical simulations also reveal the presence of nonlinear effects such as weak shocks that cannot be captured by the linear acoustic wave equation.

Propane (R290) is considered as a promising substitute for R22 or R410A used in room air conditioners. In this work, the solubility of R290 in two mineral oils (3GS and 4GS) was measured at the temperatures from 253.15 K to 343.15 K using isochoric saturation method. The non-random two liquid activity coefficients model was used to correlate the experimental solubility data. The absolute average relative deviation of equilibrium pressure between experimental data and calculated values from the model was 1.93% and 1.79% for R290/3GS and R290/4GS system, respectively. In addition, the enthalpy of the refrigerant and lubricating oil mixtures was calculated, and the relationship of the pressure-enthalpy-quality (p-h-X diagrams) of the mixtures was given and analyzed at the oil circulating mass fraction of 2% and 4%, respectively.

The preservation of foods at low temperatures is a well-established concept. While conventional methods of food freezing rely on the isobaric (constant pressure) approach, they often result in a series of irreversible changes that can significantly hamper the quality of frozen foods. In recent years, taking its roots from the biomedical industry, isochoric (constant volume) freezing is gaining both research and commercial interest as an effective method of food preservation. The focus of this review is to present the state of the art of isochoric freezing of foods, highlighting the underlying mechanisms that make it unique, and understanding its impact on food quality, considering reports published in the past decade. An exclusive section is dedicated to its non-food applications, and this work also provides insights into the costs and economics of the process. Importantly, as this is an emerging area, the review concludes by highlighting the challenges and provides perspectives on the directions for future research.

A new experimental method, i.e., isochoric cooling/heating cycle measurement using differential scanning calorimetry (DSC), is applied to investigate the hysteretic phenomenon of pure components an...

An experimental study has been made of the density and the velocity of sound for liquid decalin and cyclohexane in the range of temperatures 298.15–433.15 K and pressures 0.1–100.1 MPa. Parameters of equations have been obtained that describe the dependences of the specific volume of liquid decalin and cyclohexane on their temperature and pressure and of the isobaric heat of these substances on their temperature at atmospheric pressure. The density, the velocity of sound, the isobaric and isochoric heats, the isobaric expansion coefficient, and the coefficients of isentropic and isothermal compressibilities of liquid decalin and cyclohexane have been determined in the range of temperatures 298.15–433.15 K at pressures to 100 MPa.

Some physicochemical properties of water fluids (WFs) that underlie their applications and criteria for determining the parameter domains with qualitative differences in their physical state were considered. The qualitative relationship between the type and intensity of intermolecular interactions in various substances and their macroscopic characteristics (normal boiling temperatures and critical points) was analyzed. Special attention was paid to the density as a macroscopic parameter that reflects the influence of intermolecular interactions in the WF. Despite the technological importance of isobaric dependences, for understanding the mechanisms of various effects on the properties of fluids, it is necessary to consider isochoric and isothermal dependences, especially when analyzing the dielectric properties of water and its dissociation into counterions.

Studies on autoignition and combustion wave propagation in a spatial reactivity gradient environment constructed using the shock-converging method were conducted to obtain a new understanding of combustion modes and their mutual transition mechanism. Autoignition induced by the converging cylindrical shock wave and weak detonation can be observed by experiment and numerical simulation. Research indicates that for an appropriate spatial reactivity gradient, the velocity of the weak detonation wave can decrease and adjust to the local sound speed. This leads to the transformation of the weak detonation into the self-propagating Chapman-Jouguet (CJ) detonation. The speed of the spontaneous reaction wave characterizing the end of the chemical reaction is never less than the local sound speed; hence, there is no overdriven phenomenon throughout the weak-to-CJ detonation transition. This conforms to the fact that the overdriven phenomenon is not a necessary condition to initiate the detonation, and the combustion has higher thermal efficiency compared with isochoric combustion. Further research indicates that CJ detonation propagating in the preheated reactant can also transform into weak detonation for an appropriate spatial reactivity gradient. The initial CJ detonation degrades into a shock that decays and finally disappears. The wave-eliminating effect of the CJ-to-weak detonation transition can ensure the flow field quality and thermal efficiency of the combustion. In summary, performing a controllable weak detonation between isochoric combustion and CJ detonation in an engine has significant practical importance for improving combustion thermal efficiency and knock suppression.

We designed a hydrogel with a thermoresponsive crosslinked domain (CD) structure, which expressed thermoresponsive toughening in an isochoric manner in air. The responsive behavior of conventional thermoresponsive hydrogels is usually a macroscopic volume change along with water transfer to and from the outside of the polymer network. In order to expand the scope of thermoresponsive hydrogels, a network design that requires no external water for thermoresponsive transition has been demanded. To this end, we focused on the polymerization-induced self-assembly process for the direct synthesis of gels with designed domains and performed reversible addition–fragmentation chain transfer polymerization of N-isopropylacrylamide in water at a high temperature using a bifunctional macro-chain transfer agent, yielding a transparent gel. The structural analysis of the obtained gel revealed that dispersed CDs reversibly swelled and shrunk in response to temperature change in air without aggregation. Such an internal structural change induced the increase of elastic modulus and elongation at a high temperature.

The mechanical properties of α-Na3(U0.84(2),Na0.16(2))O4 have been researched using the first-principles calculations combined with the quasi-harmonic Debye model. The obtained lattice parameters agree well with the published experimental data. The results of elastic constants indicate that α-Na3(U0.84(2),Na0.16(2))O4 is mechanically stable. The polycrystalline moduli are predicted. The results show that the α-Na3(U0.84(2),Na0.16(2))O4 exhibits brittleness and possesses obvious elastic anisotropy. The hardness shows that it can be considered a “soft material”. Furthermore, the Debye temperature θD and the minimum thermal conductivity kmin are also discussed, respectively. Finally, the thermal expansion coefficient α , isobaric heat capacity C P and isochoric heat capacity C V are evaluated through the quasi-harmonic Debye model.

The ignition of methane/air and ethylene/air mixtures by nanosecond pulsed discharges (NSPD) is investigated numerically using a zero-dimensional isochoric adiabatic reactor. A combustion kinetics model is coupled with a non-equilibrium plasma mechanism, which features vibrational and electronic excitation, dissociation, and ionization of neutral particles (O2 and N2) via electron impact. A time to ignition metric τ is defined, and ignition simulations encompassing a wide range of pressures (0.5–30 atm) and pulsing conditions for each fuel are executed. For each fuel, it is found that τ depends primarily on initial pressure and energy deposition rate, and scaling laws are derived. In order to quantify the benefit gained from plasma-assisted ignition (PAI), τ is compared with a thermal ignition time. It is found that for both fuels, PAI leads to a faster ignition at low pressures, while at higher pressures (p0 ≥ 5 atm), methane/air ignition becomes inefficient (meaning a longer ignition time for the same input energy compared to thermal ignition). Ethylene/air PAI shows only a modest deterioration. The drop in performance with pressure is found to be due to the mean electron energy achieved during the pulse, which shows an inverse relationship with pressure, leading to fewer excited species and combustion radicals. The poor performance of methane/air mixture ignition at high pressure is explained by an analysis of the reaction pathways. At high pressures (p0 ∼ 30 atm), H is consumed mostly to form hydroperoxyl (HO2), leading to a bottleneck in the formation of formyl (HCO) from formaldehyde (CH2O). Instead, for ethylene/air ignition, at both low and high pressures there exist several bypass pathways that facilitate the formation of HCO and CO directly from various intermediates, explaining the more robust performance of PAI for ethylene at pressure.

Purpose A general first-invariant constitutive model has been derived in literature for incompressible, isotropic hyperelastic materials, known as Marlow model, which reproduces test data exactly without the need of curve-fitting procedures. This paper aims to describe how to extend Marlow’s constitutive model to the more general case of compressible hyperelastic materials. Design/methodology/approach The isotropic constitutive model is based on a strain energy function, whose isochoric part is solely dependent on the first modified strain invariant. Based on Marlow’s idea, a principle of energetically equivalent deformation states is derived for the compressible case, which is used to determine the underlying strain energy function directly from measured test data. No particular functional of the strain energy function is assumed. It is shown how to calibrate the volumetric and isochoric strain energy functions uniquely with uniaxial or biaxial test data only. The constitutive model is implemented into a finite element program to demonstrate its applicability. Findings The model is well suited for use in finite element analysis. Only one set of test data is required for calibration without any need for curve-fitting procedures. These test data are reproduced exactly, and the model prediction is reasonable for other deformation modes. Originality/value Marlow’s basic concept is extended to the compressible case and applied to both the volumetric and isochoric part of the compressible strain energy function. Moreover, a novel approach is described on how both compressive and tensile test data can be used simultaneously to calibrate the model.

This review presents the results of a detailed analysis of the role of isochoric heat capacity as a key thermodynamic property of matter in the investigation of critical and supercritical phenomena. A brief historical background is given on the role and contribution of Russian scientific schools to the experimental investigation of the isochoric heat capacity in the critical region in the development of the nonclassical (scaling) theory of critical phenomena, which drastically changed the understanding of the physical nature of critical and supercritical phenomena. The experimental behavior of the isochoric heat capacity and other thermodynamic properties of fluids in the critical and supercritical regions related to it is investigated in detail. The role of new experimental studies of two-phase isochoric heat capacity near the critical point in the development of a “complete” scaling theory is discussed. This theory allows us to understand the physical nature of the asymmetry of the liquid–gas coexistence curve near the critical point and to estimate the contribution of the chemical potential to the divergence of the two-phase isochoric heat capacity at the critical point. The review also focuses on supercritical phase transitions and the role of isochoric heat capacity in determining the Widom line, which separates the liquid-like and gas-like regions in supercritical states; i.e., it defines the boundaries of the coexistence of liquid-like and gas-like phases in supercritical fluids.

A method for calculating the specific surface energy σ, the isochoric and isobaric derivatives of the function σ with respect to the temperature, and the isothermal derivative of the function σ with respect to the pressure is developed proceeding from the parameters of the Mie–Lennard-Jones pairwise interatomic interaction potential. It is shown that this method is applicable for both macrocrystals and nanocrystals with specified numbers of atoms and with definite surface shapes. To implement this method, the parameters of the pair interatomic potential are determined using a self-consistent method based on the thermoelastic properties of a crystal. This method is tested using Fe, Au, Nb, Ta, Mo, and W macrocrystals at different temperatures and shows good agreement with experimental data. As the nanocrystal size is decreased along the isotherms T = 10, 300, and 2500 K, changes in the surface properties are studied using body-centered cubic (bcc) Ta as an example. It is shown that, at high pressures and low temperatures, the function σ can increase in the case of an isomorphic-isothermal-isobaric decrease in the nanocrystal size.

The (p, ρ, T) behavior of trifluoroethene (R1123) was investigated with the isochoric method. A total of 87 (p, ρ, T) data were measured along nine isochores (42, 98, 151, 197, 296, 493, 691, 790, and 888 kg · m − 3 ) at temperatures from 300 K to 430 K and pressures up to 6.9 MPa. The uncertainties in temperature are estimated to be within 10 mK below 380 K and 20 mK at higher temperatures, and the uncertainties in pressure are estimated to be within 1 kPa below 380 K and 2 kPa at higher temperatures. The estimated relative uncertainties in the density measurements are 0.15 % or less. A new Helmholtz energy equation of state was formulated based on the (p, ρ, T) data and recently published experimental data for the vapor pressure, liquid and vapor densities including those at saturation, vapor-phase sound speed, and ideal-gas isobaric heat capacity. The equation is applicable at temperatures from the triple-point temperature (195.15 K) to 480 K and pressures up to 20 MPa. Typical uncertainties in calculated properties are 0.1 % for vapor pressures, 0.1 % for liquid densities, and 0.2 % for vapor densities, except in the critical region where larger deviations up to about 1.5 % are sometimes observed in densities. The uncertainties in calculated vapor-phase sound speeds and ideal-gas isobaric heat capacities are 0.03 % and 1 %, respectively. The equation shows reasonable extrapolation behavior at extremely low and high temperatures, and at high pressures.

Modeling the pVT properties of hydrogen mixtures at high temperatures is significant for the development of relevant production and utility systems. In this work, pVT measurements are reported for ...

In the present work, dihydric alcohols (including 1,4-butanediol, 2,3-butanediol, and 1,3-propanediol) were paired with choline chloride (ChCl) to form deep eutectic solvents (DESs) with the molar ratio of ChCl to dihydric alcohol fixed at 1:3 and 1:4. The solubility of NH3 in these DESs was systematically determined at 303.15, 313.15, 323.15, and 333.15 K under pressures up to 420.0 kPa using the isochoric saturation method and was correlated using the Krichevsky–Kasarnovsky (K–K) equation. The dissolution Gibbs free energy, enthalpy, and entropy changes of NH3 solvation were further calculated according to the temperature dependence of Henry’s constants. Based on the reported CO2 solubility data, the selectivities of NH3/CO2 in DESs used herein were calculated. The density and viscosity data of the DESs were also measured and fitted at a temperature range of 303.15–343.15 K. Overall, the dihydric alcohol-based DESs present quite promising NH3 absorption and separation performance, with a value of 3.0 mol NH3 per kg DES and an NH3/CO2 selectivity of 98 at 303.15 K and 100.0 kPa.

A novel, particularly robust method for the calculation of critical curves of fluid mixtures is proposed that makes use of differential equations representing the critical conditions (isochoric the...

The key to efficient operation of a diesel engine is the smooth combustion of the fuel and controlled detonation. In diesel engine detonation depends on ignition delay (ID) period. An isochoric cylindrical combustion box (CCB) is fabricated for the assessment of ID tendency for simple diesel and vegetable oils-diesel fuel blend (VODFB). The combustion box consist of air heating coils, hot surface plate, fuel injector, pressure gauge, temperature indictor, temperature controller and photo sensor. A two stage compressor with intercooler is used for charging the air in the combustion box. The ignition lag was measured for injection pressures (IP) (100-bar, 200-bar and 300-bar), hot surface temperatures (400°C and 450°C), cylinder pressures (10, 15, 20 and 25-bar) for simple diesel and VODFB by using photo sensor and scope-meter. The results show that ID was decreased with increase in IP, at a specific cylinder pressure and HST for both simple diesel and VODFB. At high IP (300-bar), ID is lower for the blended fuel because at high IP, the fuel covers more physical land and more fuel is vaporized within a given time period and hence ID time decrease.

The compaction of carbon dioxide in the pores of nanoporous silicon aerogel at near-critical temperatures has been studied by coherent anti-Stokes light scattering (CARS) spectroscopy. The density was determined by the shift of the vibrational line at 1388 cm $${}^{-1}$$ under isochoric heating from the subcritical temperature of 25.2 $${}^{\circ}$$ C to the supercritical one of 31.95 $${}^{\circ}$$ C. It was found that the density of carbon dioxide in nanopores near the critical temperature increases, exceeding the average value in the cuvette by about $${\sim}20\%$$ .

The class of Double-Double Radio Galaxies (DDRGs) relates to episodic jet outbursts. How various regions and components add to the total intensity in radio images is less well known. In this paper we synthesize synchrotron images for DDRGs based on special relativistic hydrodynamic simulations, making advanced approximations for the magnetic fields. We study the synchrotron images for: Three different radial jet profiles; Ordered, entangled or mixed magnetic fields; Spectral ageing from synchrotron cooling; The contribution from different jet components; The viewing angle and Doppler (de-)boosting; The various epochs of the evolution of the DDRG. To link our results to observational data, we adopt to J1835+6204 as a reference source. In all cases the synthesized synchrotron images show two clear pairs of hotspots, in the inner and outer lobes. The best resemblance is obtained for the piecewise isochoric jet model, for a viewing angle of approximately $\vartheta \sim -71^{\circ}$, i.e. inclined with the lower jet towards the observer, with predominantly entangled ($\gtrsim 70$ per cent of the magnetic pressure) in turbulent, rather than ordered fields. The effects of spectral ageing become significant when the ratio of observation frequencies and cut-off frequency $\nu_{\rm obs}/\nu_{\infty,0} \gtrsim 10^{-3}$, corresponding to $\sim 3 \cdot 10^2$ MHz. For viewing angles $\vartheta \lesssim -30^{\circ}$, a DDRG morphology can no longer be recognized. The second jets must be injected within $\lesssim$ 4 per cent of the lifetime of the first jets for a DDRG structure to emerge, which is relevant for Active Galactic Nuclei feedback constraints., Comment: 24 pages, 8 figures

The enhanced interest in greater convenience foods has recently led to the expansion of minimally processed potato products. This study investigated the effects of isochoric freezing on pre-peeled potato cubes, including quality attributes (microstructure, texture, and color), nutritional value (ascorbic acid (AA) content, total phenolic content, and antioxidant capacity), and polyphenol oxidase activity. Isochoric freezing (-3 °C/30 MPa) was compared with isobaric freezing (-3 °C/0.1 MPa) and individual quick freezing followed by frozen storage at -20 °C for 4 weeks. The isochoric sample had lower drip loss and volume shrinkage as well as better preserved texture and microstructure than the other samples. All freezing methods caused an increase in total phenolic content and antioxidant capacity, but a decrease in AA content. Also, all freezing methods caused browning of the thawed potatoes, but isochoric freezing delayed its onset for more than 1 week. PRACTICAL APPLICATION: Results showed that isochoric freezing of pre-peeled and cut potatoes caused less freeze damage than isobaric and individual quick freezing, which might find application in the commercial preservation of minimally processed food products.

High-intensity short-pulse lasers have made possible the generation of energetic proton beams, unlocking numerous applications in high energy density science. One such application is uniform and isochoric heating of materials to the warm dense matter (WDM) state. We have developed a new experimental platform to simultaneously create and probe WDM at the matter in extreme conditions (MEC) end station at the Linac Coherent Light Source (LCLS). The short pulse optical laser (delivering up to 1 J in 45 fs) and the ultrabright LCLS X-ray laser with tunable frequency, respectively, deliver high power required to heat materials to WDM and precision-timed high-resolution X-rays to probe them. The laser-accelerated proton beam driven from a flat 1.5- $\mu \text{m}$ Cu foil was first measured then directed to a secondary sample of Al or polypropylene (PP), typically 300– $400~\mu \text{m}$ away. The time evolution of the sample electron temperature was measured using streaked optical pyrometry, where we observed a peak temperature of 0.9 ± 0.15 eV on the rear surface of an Al sample heated by the proton beam. Simulations using the hybrid-PIC code LSP and the rad-hydro code HELIOS show that a measured proton beam can heat Al to approximately 4 eV and PP to 1 eV if instead focused by a hemispherical Cu target. Through additional LSP simulations, we anticipate creating hotter WDM states (~20 eV) by increasing the laser energy to 10 J and keeping the other laser parameters fixed.

Vapor pressures for new low-GWP refrigerants of R1233zd(E) (trans-1-chloro-3,3,3-trifluoropropene) and R1336mzz(Z) (cis-1,1,1,4,4,4-hexafluoro-2-butene) were measured by the isochoric method. Twelv...

The aim of this work was to evaluate the effects of isochoric freezing on the quality of tilapia fillet. Isochoric freezing was compared to chilling, super-chilling, and freezing. Isochoric freezin...

In this contribution, the phase change of unvulcanized to vulcanized rubber is described by a thermo-mechanical material model within the finite element method (FEM) framework. Before the vulcanization process (curing), rubber exhibits an elasto-visco-plastic behaviour with significant irreversible deformations without a distinct yield surface. After exposing rubber to high temperature, the molecular chains build-up crosslinks among each other and its mechanical behaviour changes to stiffer viscoelastic material. The proposed model assumes, that both phases are present during the vulcanization process. The ratio changes from the uncured phase at the beginning to the cured phase according to the current state of cure. A constitutive curing formulation is introduced into the model, to capture the shape change during the vulcanization and to ensure, that the second law of thermodynamics is fulfilled. A multiplicative split of the deformation gradient is assumed to describe incompressible material. Thermal expansion due to the change of temperature is taken into account in the volumetric part, as well as shrinkage during the vulcanization process. In the isochoric part, the phase change from elasto-visco-plastic to viscoelastic material is described by micro-macro transition based on the micro-sphere model. The consistent formulation of the material model and its tangent are important for a successful implementation into a three-dimensional finite strain FEM framework. The capabilities of the model are shown by the simulation of an axisymmetric tire production process starting at the green tire inserted into the heating press up to a post-cure inflation step.

An original method of calculating isochoric and isobaric heat capacity based on the fundamental relationships of thermodynamics is presented. The theoretical development of the methodology for calculating isochoric and isobaric heat capacity can be used to obtain high metrological data on the thermophysical properties of new low-boiling working substances of power plants operating on the Rankine organic cycle and to replenish existing databases. The technique allows the use of heterogeneous experimental results of acoustic and thermal measurements to calculate the basic thermodynamic functions without information about the values of ideal gas functions, and also to evaluate the consistency of experimental data. Formulas are derived for calculating isobaric and isochoric heat capacities, which are based on reliable equations describing experimental data on the speed of sound and density depending on state parameters. The method was tested using both the characteristics of the reference substances (H2O and CO2), and own new experimental data on the thermal and acoustic properties of octafluorocyclobutane (c-C4F8) in the liquid phase for temperatures of 320 and 340 K and pressures from 4 to 10 MPa. The isochoric heat capacity was calculated from measurements of the density of octafluorocyclobutane and the speed of sound in it. According to the latest series of density measurements in a limited region of the states of the liquid phase of octafluorocyclobutane obtained by the constant volume piezometer method, the isochoric heat capacity was calculated using the equation proposed in this work. The uncertainty of the experimental data used for the test calculation of the density did not exceed 0.25%, and the speed of sound did not exceed 0.05%. The standard deviation in the description of the dependence of thermal quantities was 0.23%, and acoustic—0.15%.

Elastic tubes can experience surface instabilities when compressed beyond a critical strain, referred to as Wilkes instability herein. Soft materials may undergo the Rayleigh–plateau instability which is driven by surface tension. However, the surface instability of soft elastic tubes can be impeded by the coexistence of axial compression and surface tension. In this paper, we adopted an analytical framework for predicting the surface instability of an incompressible tube accounting for both axial loading and surface tension. A general solution in a mixed cylindrical coordinate is derived for determining isochoric transformations based on energy variational method. A linear perturbation analysis was performed to find out the critical elasto-capillary number and axial stretch for the onset of the instability. Cylindrical tubes with different thickness, i.e., the ratio of outer to inner radii, are investigated. We find that thinner tubes are more likely to experience surface instability than thicker ones, as validated by finite element simulations. We conclude that a compressive strain could prevent the Rayleigh–plateau instability induced by surface tension, while stretching will favor it. Similarly, the surface tension behaves as a barrier to the formation of compression-induced Wilkes instability.

In the production and storage processes of metal hydride material of TiH2, there are at least three kinds of explosion hazards, for example, TiH2 dust explosion, H2 explosion and hybrid H2/TiH2 dust explosion. In this study, combustion behaviors of TiH2 dust cloud under isobaric and isochoric conditions were studied using a visual dust combustion facility and a standard 20-L spherical explosion vessel bomb, respectively, and Ti dust and hybrid H2/Ti dust were used as the reference materials. Experimental results showed that at equal dust concentrations, the flame propagation speed Sf, burning velocity SL, maximum pressure rise Pex and maximum rate of pressure rise (dP/dt)ex of TiH2 dust were all higher than those of Ti dust, while much smaller than those of hybrid H2/Ti dust except the maximum pressure rise Pex. The hydrogen state and content were the primary factors for the combustion differences of dust explosions. The values of explosion index Kst showed that the explosion risks of these samples increased as follows: Ti ˂ TiH2 ˂ hybrid H2/Ti dust.