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In this study, the solid–liquid equilibria of five binary systems containing refrigerants with low global warming potential, namely carbon dioxide (R744) + 1,1-difluoroethene (R1132a), R1132a + 2,3,3,3-tetrafluoropropene (R1234yf), R1132a + trans-1,3,3,3-tetrafluoropropene (R1234ze(E)), trifluoromethane (R23) + R1234yf, and R23 + R1234ze(E), was experimentally determined. Two experimental setups based on the cooling curve method were employed to measure the samples obtained from different sources. The results obtained using the two setups were in good agreement with the experimental uncertainty. In addition, the experimental data were compared with the values calculated using the Schröder equation, showing limited deviations. The accuracy of the experimental setups was tested by measuring the triple-point temperatures of the components of the studied binary systems, showing good agreement between the experimental data obtained for the pure refrigerants and the data available in the literature., International Journal of Refrigeration, 144, pp. 254-263; 2022

The triple point temperature of refrigerants is crucial because it serves as a reference for the lower limit of their use temperature in a refrigeration system. In this study, the triple point temperatures for recently proposed refrigerants with low global warming potential were experimentally determined. Ten hydro-fluoro-olefins, two hydro-chloro-fluoro-olefins, and trifluoroiodomethane were investigated. The triple point temperatures of the refrigerants were determined from the obtained cooling and heating curves. To improve measurement accuracy, measurements were conducted on samples obtained from different companies using two different measurement devices. The measured data were found to be in good agreement within the estimated measurement uncertainty., International Journal of Refrigeration, 133, pp.172-180; 2022

Ternary 0.552Pb(Ni1/3Nb2/3)O3-xPbZrO3-(0.448-x)PbTiO3 (PNN-PZ-PT) ceramics near the triple point compositions were fabricated by an improved two-step sintering method. The triple point composition 0.552PNN-0.135PZ-0.313PT ceramic has outstanding piezoelectric performance with piezoelectric coefficient d33 = 1200 pC/N. Its easy fabrication and low cost make this piezoelectric material an excellent candidate for high sensitivity sensors and ultrasonic transducers. The evolution of domain structures for ceramics with composition near the triple point provides deeper insight into the mechanism of ultrahigh piezoelectric properties of PNN-PZ-PT ceramics.

Some studies in recent years have shown the possibility of extending the application temperature of the natural refrigerant carbon dioxide (CO2) below its triple point. Thus, CO2 could be a potential alternative refrigerant for R-23 in ultralow-temperature (ULT) refrigeration systems. This paper introduces a special cascade system, whose lower stage can be switched between a CO2 sublimation cycle and a conventional R-23 cycle, so that both cycles can be compared directly under the same ambient conditions. The sublimation system features a unique sublimation heat exchanger, which allows the operation with an extra carrier fluid in order to improve the heat transfer and reduce the blockage by solid CO2. In this study, experiments were carried out using HFE-7500 as the carrier fluid (“wet sublimation”) as well as without the carrier fluid (“dry” sublimation). The system was able to be operated continuously in both operating mode. A refrigerating capacity of 600 W was achieved at a sublimation temperature of -79°C. The transient behavior and blocking issues of the system are discussed. The efficiency of the sublimation system during stable operations are compared with the result of the reference R-23 system. It shows that there is still large potential for improvement on the system performance of the CO2 sublimation system.

CO2 shipping is a viable transport alternative when pipelines are impractical. Lack of experience in large-scale CO2 shipping projects implies uncertainty in selecting optimal cargo conditions and operational safety procedures. The risk of uncontrolled release of CO2 arises in case of mechanical failure of storage or cargo vessels, and a thorough understanding of the discharge phenomena, including the propensity for solid formation, is necessary to develop safety protocols. A refrigerated experimental setup is established in this study to investigate the release phenomena of liquid CO2 under shipping conditions. The rig features a dome-ended cylindrical pressure vessel, a discharge pipe section and a liquid nitrogen refrigeration system that enables conditioning near the triple point – at ∼0.7 MPa, 223 K - and higher liquid pressures (∼2.6 MPa, 263 K). Pressure, temperature and mass monitoring were considered to enable an extensive observation of the leakage behaviour under typical operation scenarios. Three different sets of experiments were considered to inform the designer in the selection of optimal process conditions, with low-pressure (0.7 – 0.94 MPa, 223–228 K), medium-pressure (1.34–1.67 MPa, 234–245 K) and high-pressure tests (1.83–2.65 MPa, 249–259 K) demonstrating distinct behaviours relative to phase transitions, leakage duration and solidification of inventory.

Hypothesis: As a fluid approaches three phase coexistence, adsorption may take place by the successive formation of two intervening wetting films. The equilibrium thickness of these wetting layers is the result of a delicate balance of intermolecular forces, as dictated by an underlying interface potential. The van der Waals forces for the two variable adsorption layers may be formulated exactly from Dzyaloshinskii-Lifshitz-Pitaevskii theory, and analytical approximations may be derived that extent well beyond the validity of conventional Hamaker theory. Calculations: We consider the adsorption equilibrium of water vapor on Silver Iodide where both ice and a water layers can form simultaneously and compete for the vapor as the triple point is approached. We perform numerical calculations of Lifshitz theory for this complex system and work out analytical approximations which provide quantitative agreement with the numerical results. Findings: At the three phase contact line between AgI/water/air, surface forces promote growth of ice both on the AgI/air and the water/vapor interfaces, lending support to a contact nucleation mode of AgI in the atmosphere. Our approach provides a framework for the description of adsorption at three phase coexistence, and allows for the study of ice nucleation efficiency on atmospheric aerosols., Accepted Manuscript

The impact of the differing phase change characteristics on the electrocaloric effect (ECE) and thermophysical properties of Ba(ZrxTi1-x)O3 (BZT) were investigated. It is demonstrated that the ECE reduces strongly with increasing Zr concentration, from 1.25 K to 0.10 K. The strong reduction of ECE is associated with the vanishing of the latent heat as the nature of paraelectric to ferroelectric phase transition changes. Despite the second order nature of the phase transition, an enhanced electrocaloric responsivity, 0.225 × 10−6 Km V-1, occurs at the triple point composition ( x = 0.13), where the stability fields of ferroelectric phases converge. The decreasing ECE and thermophysical properties with increasing Zr concentration result in a more than one order of magnitude reduction in a caloric figure of merit, from ∼3500 J m−1s−1/2 to ∼200 J m−1s−1/2. The caloric figure of merit was used to compare the performance of other representative electrocaloric, magnetocaloric and mechanocaloric materials.

The molecular structure and phase behavior of carbon dioxide confined in an ordered mesoporous carbon (CMK-3) are investigated by total neutron scattering with in situ adsorption and cooling/heating cycles. The neutron signal from CO2 sorbed in the micropores of CMK-3 shows clearly liquid-like properties. Close to the bulk CO2 triple point (T3), the mesopore-confined CO2 is found in a liquid yet strongly densified state with a density similar to that of solid dry ice. Upon cooling the CO2 loaded carbon sample below T3, it was observed that depletion of the confined phase occurs and CO2 molecules escape from the pores to solidify externally. It was concluded that depletion occurs only in “secondary” pores having larger sizes (>50 A) than the well-defined uniform mesopores (47 A) of CMK-3. These pores exist due to imperfect ordering of the hexagonal network of the carbon rods. Surprisingly, this phenomenon does not happen in the main mesopores (47 A), implying thus that 50 A is a critical size for depletion below T3. This in turn suggests that in larger pores a pore triple point cannot be attained. The depletion process is reversible with a temperature hysteresis; when heating the sample CO2 molecules re-fill the pores.

The EU F-Gas Regulation grants exceptions from the GWP-related placing on the market prohibition for stationary refrigeration equipment for applications below -50 °C. Nonetheless, non-flammable refrigerants, which can be used for that temperature range, become increasingly expensive and rare inside the EU due to the phase down of HFCs under the regulation. Flammable alternatives based on methane, ethane and ethylene are available, but are not viable for all applications due to their flammability. Carbon dioxide cannot be used for applications below -50 °C due to CO2's triple point at -56 °C. Nitrous oxide with a triple point at -92 °C seems to be an alternative. However, possible exothermal decomposition of N2O calls for additional measures in order to be able to operate such systems safely. Two low-temperature systems have been developed, built and successfully operated at evaporation temperatures down to -80 °C with mixtures of N2O and CO2 and different lubricants at ILK and Karlsruhe University of Applied Sciences. The units achieved similar energy efficiency as the standard HFC-equipment used for freeze drying. Possible decomposition of N2O could successfully be supressed by various measures. CAUTION: Pure N2O as well as mixtures of N2O and CO2 with lubricants based on hydrocarbons can cause violent explosive decomposition reactions abruptly increasing the pressure inside a refrigeration system approximately tenfold.

Crystal structures and piezoelectric properties of PbZrO3-PbTiO3-Pb(Ni1/3Nb2/3)O3 ceramics near the triple point composition, particularly characteristics of the pseudocubic phase, were investigated. The pseudocubic phase, which formed near the triple point composition, disappeared with increase in the PbZrO3 content. The pseudocubic phase had the Pm3m cubic structure. The tetragonal-pseudocubic morphotropic phase boundary (MPB) structure was developed during the tetragonal-to-cubic phase transformation. However, the rhombohedral phase directly transformed to the cubic phase because the structure of pseudocubic phase was similar to the rhombohedral structure. The specimens with pseudocubic phase and the specimens near pseudocubic phase exhibited nano-sized domains and small coercive electric fields, revealing their low domain wall energies. These specimens exhibited second-order ferroelectric-to-paraelectric phase transition and low Curie temperatures, confirming their low domain wall energies. The enhanced dielectric and piezoelectric properties of these specimens could be attributed to their low domain wall energies.

In this work, we studied detonation in condensed-phase explosives of PETN and the oblique shock waves in the surrounding fluid. The surrounding fluid was modeled as an ideal gas equation of state using the specific heat ratio as a parameter. Depending on the specific heat ratio, four types of flow structures were observed behind the oblique shock wave in the ideal gas. We measured the detonation/shock angles and the contact angle between the detonation products and the ideal gas. When the specific heat ratio was greater than the critical value, the oblique shock wave was detached from the detonation front at the PETN/ideal gas interface. When attached, three types of waves are observed, depending on the specific heat ratio: a strong oblique shock wave, strong and weak oblique shock waves which meet at the triple point as well as a weak oblique shock wave. To understand the properties of the flow near the detonation and the oblique shock waves, they were modeled as planar Chapman–Jouguet (CJ) detonation in PETN and as oblique shock waves in ideal gas. They were theoretically estimated as (1) Prandtl–Meyer expansion of the detonation products from the CJ state, and (2) oblique shock waves around a wedge using oblique shock theory or around a cone using the Taylor–Maccoll equation. From the flow models, we obtained a solution for the pressure equilibrium and parallel flows between the detonation products and ideal gas under the assumption that the wedge and cone angles correspond to the contact angle between them. For the attached cases, the solution was consistent with the simulated observations at the PETN/ideal gas interface. From the flow models, the maximum deflection angles for the detonation products and the ideal gas were obtained, and their magnitude correlations used to classify the four types of flow.

In this paper, the solid – liquid equilibrium of the binary system containing difluoromethane (R32) and trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) was experimentally evaluated. An experimental setup was used to measure 20 different compositions of the binary system in the temperature range from 168.2 K to 132.00 K. The studied binary system showed an eutectic point which was estimated at the temperature of 132.00 K. The results for the solid – liquid equilibrium of the studied system showed a general agreement with the prediction provided by the Schroder equation, showing deviations generally within 2 – 3 K. In addition, in order to test the validity of the experimental setup, the triple point temperatures of the components of the binary system and four well described refrigerants (namely R125, R152a, R143a, and R41) were measured. The experimental results for the pure refrigerants agreed with reliable values available in the literature.

In this research, full density, single phase microstructure (in the XRD and SEM detection limits), and fine-grained SnO2 varistors with an average grain size of 0.65 μm was acquired at low temperature by the two-step sintering technique. The sintering temperature was successfully decreased from 1300 °C in the normal sintering to 1150 °C and 1100 °C of respectively the first and the second stage in the two-step sintering. The mechanism of grain growth suppression of the two-step sintered samples was discussed and it was suggested that in addition to triple point junction, solute drag and/or nano-secondary phases contribute to cease the grain growth. These SnO2 varistors exhibited ultra-high breakdown electric field of 26 kV/cm with a nonlinear coefficient of about 120 in the 1–10 mA/cm2 standard. The exact evaluation showed that this high value of the nonlinear coefficient is artificial and was the result of joule-self heating phenomenon. The true value of the nonlinear coefficient (28) is measured within the 0.1–1 mA/cm2 standard. Due to the joule self-heating phenomenon, the thermal runaway was observed for ultra-high voltage SnO2 varistors in DC-accelerated aging test conditions (0.85 E1mA/cm2 and room temperature). By changing DC-accelerated aging electric field to 0.85 E0.1 mA/cm2, TSS3-20h presented excellent stability after 10 h from room temperature to 75 ᵒC.

An embedded/immersed surface-knot is a closed and connected surface embedded/immersed in R 4 , respectively. The triple point number t ( F ) of an embedded/immersed surface-knot F is the minimum number of triple points required for a diagram of F. Satoh proved that (i) there does not exist an embedded surface-knot F such that t ( F ) = 1 , and (ii) there does not exist an embedded 2-knot F such that t ( F ) = 2 or 3 . In this paper, we prove similar results for immersed surface-knots with some conditions.

Grand canonical simulations were carried out to determine the microscopic structures of the sub-monolayer of methanol on a graphite model with two hydroxyl groups attached to the basal plane. At temperatures below the triple point temperature of methanol (176 K), the adsorption isotherm exhibits four distinct transitions: (1) saturation of the OH groups, (2) formation of 2D ring clusters floating on the basal plane, (3) transition to 2D string clusters with one end attached to the OH groups, and (4) compaction of the 2D string clusters. The variation in the molecular distribution and orientation for these transitions is studied, and correlated with the changes in isosteric heat across these transitions. It is found that the ring-to-string transition occurs more readily at low temperatures, and that the hydrogen bond length (O⋯H) within a ring or a string is constant.

Carbon dioxide, a natural refrigerant, is attracting attention as a direct solution to the legal restrictions on hydrofluorocarbon (HFC) refrigerants. The use of carbon dioxide as a refrigerant is limited by the triple point temperature of −56.5 °C. However, used along with a carrier fluid, carbon dioxide can provide refrigeration to temperatures lower than the triple point. A blend composed of carbon dioxide (R744) and isobutane (R600a) is experimentally studied. An experimental setup was designed, built, and verified in order to obtain the sublimation heat transfer coefficients of R744/R600a mixtures at temperatures lower than −56.5 °C. The test section comprises a horizontal copper tube with an inner diameter of 10 mm and length of 1 m. The tube is electrically heated by a copper wire heater wrapped uniformly around the tube. The tests were conducted with a novel refrigerant blend at heat fluxes from 3630 W m−2 to 8480 W m−2. The heat transfer coefficient decreases with increasing heat flux. Furthermore, a heat transfer coefficient calculation correlation has been developed.

Most research into the formation of the lamellar eutectics has focused on the growth patterns. However, those growth patterns can be attributed to the behavior of the triple junction, at which the solute distribution determines the long-range spatial periodicity of patterns. From both theoretical validation and phase-field simulations, we characterize the solute concentration at the triple point and demonstrate the existence of abnormal solute distribution. The solute concentration at the triple point equals the eutectic concentration only when the coexisting solid phases are evenly distributed, which is essential to balance the concentration gradient and maintain the interfacial thermodynamic equilibrium.

In this study, the flow, temperature and solute concentration fields in the melt during the CZ growth process are numerically investigated. The results show that the magnitude and distribution of the solute concentration in the melt is strongly affected by the convective flow and thermal distribution. The maximum solute concentration always occurs at the crucible sidewall where the maximum temperature in the melt is found and the solute concentration at the crystal-melt interface increases from the triple point to the centerline. Heat transport from the side crucible wall towards the crystal-melt interface is enhanced by the crucible rotation. The level of the solute concentration inside the melt is reduced due to the lowering of the maximum temperature at the crucible wall. As a consequence, the distribution of the solute concentration along the crystal-melt interface becomes smaller and more uniform as the crucible rotation rate increases. However, after the crucible rotation rate becomes large enough, the maximum solute concentration and the solute concentration along the crystal-melt interface start to increase. Heat transport inside the melt is also affected by the crystal rotation. The centrifugal force induced by the crystal rotation generates a vortex below the crystal-melt interface. This vortex gets larger and stronger as the crystal rotation rate increases. In the smaller crystal rotation rate regime, this vortex is very small, suppressing the solute concentration at the crystal-melt interface. Therefore, the solute concentration along the crystal-melt interface becomes less when the crystal rotation rate is higher, although there is an increase in the maximum solute concentration in the melt due to the higher maximum temperature. In the higher crystal rotation rate regime, there is a reduction in the convexity of the crystal-melt interface due to enhancement of heat transport from the bottom wall of the crucible by vortex motion under the crystal-melt interface. Therefore, there is a switch to an increase in the transport of solute impurities into the crystal-melt interface. Hence, the solute concentration along the crystal-melt interface increases as the crystal rotation rate increases. However, with a further increase in the crystal rotation rate, as the shape of the crystal-melt interface changes becoming concave towards the melt, the solute concentration along the crystal-melt interface decreases because the maximum temperature is significantly reduced. In this study, both counter- and iso-rotations are considered. The results of a comparison of the cases of iso- and counter- crystal rotation show that the lowest and most uniform solute distribution along the crystal-melt interface is achieved when there is no crystal rotation and the crucible rotation rate is fixed at 1 rpm. In other words, the lowest and most uniform solute concentration can be achieved with the only crucible rotation.

Over the past decade, the Mie λ-6 (generalized Lennard-Jones) potential has grown in popularity due to its improved accuracy for predicting vapor-liquid coexistence densities and pressure compared to the traditional Lennard-Jones 12-6 potential. This manuscript explores the hypothesis that greater accuracy in characterizing the coexistence properties may lead to greater accuracy for viscosity predictions. Four united-atom force fields are considered in detail: the Transferable Potentials for Phase Equilibria (TraPPE-UA and the recently developed TraPPE-2) model of Siepmann and coworkers, the Transferable Anisotropic Mie (TAMie) model of Gross and coworkers, the fourth generation anisotropic-united-atom (AUA4) model of Ungerer and coworkers, and the model of Potoff and coworkers. Equilibrium molecular dynamics simulations are analyzed using the Green-Kubo method for viscosity characterization. Simulations are performed for linear alkanes with two to twenty-two carbons and branched alkanes with four to eight carbons. Simulation conditions follow the saturated liquid from reduced temperatures of 0.5–0.85 and along the 293 K isotherm in the dense liquid region. In general, the more accurate force fields for coexistence properties do indeed predict viscosity more accurately. For saturated liquids, both Mie-based potential models (Potoff and TAMie) provide roughly 10% accuracy for linear alkanes, while deviations are between 20 and 50% for TraPPE-UA. For branched alkanes, the performance is slightly diminished, but Potoff still provides roughly 15–20% accuracy, while the TAMie force field results in deviations of 20–40%, and TraPPE-UA has deviations of approximately 25–60%. The AUA4 deviations are 10–20% for ethane and 30–60% for 2,2-dimethylpropane, the only compounds tested with the AUA4 force field. The TraPPE-2 deviations for ethane are similar to those using the original TraPPE force field, namely, between 10 and 20%. The percent deviations for each compound and force field tend to increase with decreasing temperature, with the exception of the Potoff deviations for propane, which are nearly constant to the triple point temperature. For compressed liquids, the Mie-based potential models perform better once again than the Lennard-Jones-based force fields, but tend to over estimate the viscosity at very high densities. As the Potoff and TAMie models also tend to over estimate the pressure at high densities, a fortuitous cancellation of errors leads to predictions of viscosity with respect to pressure that are accurate to within about 10%. The comparison with experimental viscosity data is limited to pressures below 200 MPa for most normal and branched alkanes. However, accurate predictions are obtained for propane near 1000 MPa with the Potoff force field.

The process of formation of an equilibrium liquid-gas interface, beginning with a sharp stepwise interfacial surface between phases with equal pressures, temperatures and chemical potentials, has been reproduced in molecular dynamics (MD) simulation of one- and two-component Lennard-Jones systems. In binary mixtures, the second component was a volatile impurity that is adsorbed in the interfacial layer. The tasks of this study are quantitative estimations of the establishment time of mechanical equilibrium between phases, the magnitude of the non-equilibrium surface tension and the time of its relaxation, the characteristic times of achieving equilibrium values of the composition, the shape and the thickness of the interface, as well as the effect of the volatile component on the relaxation processes in liquid-gas interfaces and nucleation in a superheated solution. Time dependences of the surface tension, the thickness of the interfacial layer and the relative adsorption of the volatile component have been obtained, and the times of their relaxation have been determined for a temperature close to the temperature of the solvent triple point, at the concentration range of the volatile component in the liquid phase cl from 0 to 0.25 mol fraction. It is shown that the maximum value of the non-equilibrium surface tension exceeds the equilibrium value 1.2 to 1.6 times. The relaxation time of the surface tension to equilibrium increases from 10 to 100 ps with an increase in cl. In a two-component system with a limited volume of the gas phase an equilibrium interfacial layer forms in two stages. At the first stage the volatile component is transferred into the interfacial layer from the near-surface regions of the gas phase and liquid phase. While achieving the equilibrium partial density of the volatile component in the gas phase, a transition to the second stage takes place, when particles are mainly transferred from the liquid phase, which leads to a considerable increase in the relaxation time of the relative adsorption and surface tension. Comparison of the data obtained with the results of an MD study of nucleation in solution shows that the time for establishment of adsorption equilibrium in a liquid-gas interfacial layer exceeds by an order of magnitude the time in which the equilibrium composition and the size of a vapor-gas bubble are established. This can lead to the fact that when the top of the activation barrier of nucleation is passed, the surface tension at the bubble-solution interface can exceed its equilibrium value.

A two-dimensional (2D) numerical simulation is conducted to clarify the propagation behavior of gaseous detonation in a water spray and its structure. The computational target refers to the experiment conducted by G. Jarsale et al., and C2H4–air gaseous detonation propagates where the water droplets (WDs) are sprayed. The parameters used are the C2H4–air equivalence ratio and WD mass fraction. The flow field, Favre-averaged one-dimensional profile, and cellular structure are revealed in 2D simulations. Stable propagation of gaseous detonation is observed in the water spray, and the decrease in velocity relative to the Chapman–Jouguet velocity without WDs is as much as 3.2%. Adding WDs changes the cellular pattern, especially for leaner mixtures. The weak triple point decays, and the cell width increases because of the longer induction length due to decreased velocity. The WD presence changes the detonation flow field substantially, and evaporation occurs primarily at 10 mm behind the shock wave. The high-evaporation region propagates at the detonation speed, and the compression wave formed when the detonation reflects from the two-phase medium propagates backward. Furthermore, WD evaporation suppresses the velocity, vorticity, and temperature fluctuations. Rapid evaporation with WDs leads to lower hydrodynamic thickness than that without WDs or in the Zel'dovich–von Neumann–Doring model.

Solidification of a liquid drop on a vertical wall is a typical phase change heat transfer problem that exists widely in natural and engineering situations. In this study, we present the fully resolved two-dimensional simulations of such a problem by a front-tracking/finite difference method. Because of gravity, the liquid drop assumed stick to the cold wall shifts to the bottom during solidification. Numerical results show that the conical tip at the solidified drop top is still available with the presence of volume expansion, but the tip location is shifted downward, resulting in an asymmetric drop after complete solidification. The tip shift, height and shape of the solidified drop are investigated under the influences of various parameters such as the Prandtl number Pr, the Stefan number St, the Bond number, the Ohnesorge number Oh, and the density ratio of the solid to liquid phases ρsl. We also consider the effects of the growth angle ϕgr (at the triple point) and the initial drop shape (in terms of the contact angle ϕ0) on the solidification process. The most influent parameter is Bo whose increase in the range of 0.1–3.16 makes the drop more deformed with the tip shift linearly increasing with Bo. The tip shift also increases with an increase in ϕ0. However, increasing Oh (from 0.001 to 0.316), St (from 0.01 to 1.0) or ρsl (from 0.8 to 1.2) leads to a decrease in the tip shift. Concerning time for completing solidification, an increase in Bo, ϕgr or ϕ0, or a decrease in St, or ρsl results in an increase in the solidification time. The effects of these parameters on the drop height are also investigated.

The objectives of this paper are to (1) validate the present numerical modeling framework for liquid hydrogen cavitating flow, (2) investigate the dynamic evolution of liquid hydrogen cavitating flows in a wide range of free-stream conditions and (3) propose a thermal parameter to evaluate and predict the transition process of two typical cavitation dynamics in thermo-fluids. The dynamic evolutions of liquid hydrogen cavitating flows in a wide range of free-stream conditions (T∞ = 14–33 K, U∞ = 63.9 m/s, 90 m/s, σ∞ = 0.38, 0.8, 1.2) are numerically investigated. General agreements are obtained between the numerical results and the experimental measurements, including the pressure distribution, temperature drop as well as the cavity structures. The results show that the cavitation behaviors near the triple point are similar to cavitating flows without thermodynamic effects. Two typical cavitation dynamics named the quasi-isothermal mode and the thermo-sensitive mode in liquid hydrogen are observed under the same cavitation number and flow velocity. When the free-stream T∞ is below 30 K (TN ≤ 0.85), as the temperature increases, the cavity area increases to the maximum around the thermal transition temperature and then decreases when the cavitation dynamics transits from the quasi-isothermal mode to the thermo-sensitive mode. Further analysis indicates that the thermal transition temperature for liquid hydrogen is approximately at T∞ = 17 K and the transition temperature slightly increases with the increasing free-stream velocity and cavitation number. When the free-stream T∞ is above 30 K (TN > 0.85), the thermodynamic effects significantly decrease due to the suddenly changed physical properties. And then, the cavitation dynamics turns from the thermo-sensitive mode to the quasi-isothermal mode with the increasing temperature. The modified C-factor including both the thermodynamic effects and the effects of turbulent pressure fluctuations proposed in this paper could quantitatively evaluate and predict dynamics transition from the quasi-isothermal mode to the thermo-sensitive mode in thermos-fluids cavitating flows. It could be utilized as a parameter to design the operating conditions for thermos-fluids apparatus or system to avoid the maximum cavitation aggressiveness around the thermal transition temperature.

In the continuous casting of steel, solidification begins at a triple point where solid steel, molten steel and molten flux meet; the motion of this point determines how surface defects known as oscillation marks (OSMs) are formed. Here, under a number of simplifying assumptions, we derive an asymptotic model in 15 dimensionless parameters that describes the relevant momentum and heat transfer for the process, and involves both surface tension at the meniscus between molten flux and molten steel and solidification; further development couples an earlier lubrication-theory model for the region below the triple point to a reduced model for the region above that is based around a regular perturbation treatment of the Navier Stokes equations in terms of the capillary number. The resulting problem is then broken up into a hierarchy of four sub-problems; the first one – for the velocity field in the molten flux – is considered in depth. A numerical algorithm is developed for an isothermal situation in which the triple point moves only perpendicular to the casting direction; this involves the solution of a novel “moving point” problem to determine motion of the triple point. Comparison of model and experimental results indicates that this reduced model could produce OSMs having the observed depth if the triple point were not too far below the top of the meniscus; otherwise, the computed marks would be too deep. The analysis also tentatively relates the location of the triple point to the fold- and overflow-type OSMs that generally form in practice.

This paper reports about recent melting probe experiments under a pressure that is within the pressure regime at the surface of Mars. As compared to the results given in Komle et al. (2018), the experiments were extended in several aspects: (i) A deeper ice sample was used in order to study the performance of the probe in the subsurface, (ii) dust layers were embedded inside the samples in order to study their influence on probe penetration, (iii) a surface cover of granular CO2-ice was added, in order to study the performance of the probe in the presence of dry ice, and (iv) the performance of the melting probe in a highly porous ice layer (fresh bonded snow) was studied. In addition, the case of several heating cycles, interrupted by cooling periods, was considered. The experiments demonstrated that the melting probe concept remains successful also in the presence of embedded sand and dust layers, as long as such non-volatile layers are thin, say in the order of centimetres. Under Mars pressure there is always liquid water present in the melt hole, except for the fresh bonded snow case, where the melt water is absorbed by the surrounding snow. However, because the Mars surface pressure is typically just slightly above the water triple point pressure, this water is permanently boiling and there are strong convective motions which whirl up dust particles and remove them at least partially from the hot nose region. The presence of a porous CO2-ice cover on the surface does not seriously hamper melting probe penetration, because CO2-ice is much more volatile than water ice and the probe passes such a layer very fast when heated with the same power. In fresh bonded snow, which has very high porosity, the probe penetrates correspondingly faster than in compact ice. Finally, in the last experiment, it was demonstrated explicitly that the melting probe concept works also, when heating is applied in several cycles, interrupted by periods of no active heating.

A two-dimensional Lattice Boltzmann model was established to study the dynamic physical process of frost growth on a cold flat surface. It is verified that the theoretical results are in good agreement with the experiment data with better accuracy. The frost morphology is explored by showing two-dimension density distribution with different cold surface temperatures. The results also include dynamic characteristics of frost properties such as thickness, deposition weight, volume fraction, density, temperature. According to the results, it is found that the nearer it is from the cold flat plate, the larger of frost crystal volume fraction and density are. The frost surface temperature increases rapidly at the early period of frosting and then increases gradually towards the triple point temperature of the water. The frost internal temperatures rise in a linear tendency with the frost thickness and decrease at the same frost layer location with frost growth. Super-saturation degree of moist air has non-negligible effect on frost growth parameters such as frost thickness, frost crystal deposition mass, frost deposition rate and frost crystal volume fraction.

Electromigration (EM) has aroused substantial attention with the shrinkage of modern devices. EM is an interaction between electron carriers and atoms, meaning that it arises from atomic behaviour. Both the number of twin boundaries (TBs) and the direction of electron flow are crucial factors affecting EM behaviour. In this study, EM phenomena with perpendicular and parallel electron flow were investigated by high resolution transmission electron microscopy (HRTEM). Twin planes could limit the growth direction of voids in the parallel case. The evolution of smooth surfaces into step-like surfaces resulting from the triple point retarding EM has been demonstrated. With the measurement of the resistance, it could be concluded that the specimen with electron flow perpendicular to the TBs had better EM restriction. Columnar grains can confine the position of the voids. This study demonstrates the dynamic evolution of the surface structure, providing insight into the fabrication of interconnections in the integrated circuits industry.

The paper aims at filling a gap in accurate data on the triple point temperature of iodine, I2, whose experimental determination is found remarkably absent in the literature, by reporting accurate calorimetric results obtained in 1978 by a reliable Laboratory and so far unpublished, providing the ITS-90 value T90 = 386.464 ± 0.005 K (t90 = 113.314 ± 0.005 °C).

Molecular dynamics (MD) simulations were used to study the coexistence of solids and vapors of Lennard–Jones methane condensed within cylindrical carbon nanopores. The simulated unit cell includes both the inside and outside of the pores. This allowed us to observe the solid-vapor coexistence within the pores while simulating the pressure depression of the bulk vapor outside the pores. The condensates in the pores were cooled in stages, and the equilibrium vapor pressures were determined at each temperature. The obtained vapor–solid coexistence curves showed significantly lower shifts in pressure than those in the bulk phase. The results of the MD simulations were compared with the Clausius–Clapeyron equation starting from the triple point in the nanopores. The thermodynamic model successfully predicted the simulation results without introducing tunable parameters, demonstrating this concept’s validity. Thus, a whole Lennard-Jones phase diagram in cylindrical nanopores can now be predicted.

Gravimetric measurements are often used to generate excess adsorption isotherms. However, adsorbed density and volume should be known to transform excess isotherms into absolute ones by considering buoyance effects. Depending on the strategy used, the results may present artifacts, especially at high pressures. A Density Functional Theory (DFT) augmented with the PCP-SAFT equation of state is applied to describe the experimental data of excess and absolute adsorption isotherms of CH4 and CO2 fluids on activated carbon slit pores. The representative pore size distribution (PSD) adequately predicted the excess adsorption isotherms at different temperatures. The absolute adsorption isotherms obtained using our approach are compared with the classic approaches as the triple point density of the liquid and the Ozawa expression (and extrapolated to the high-pressure regions). The classical methodologies underestimate the amount adsorbed while the proposed methodology provides thermodynamically consistent results even when condensation of CO2 occurs in the bulk phase.

Vapor-liquid equilibrium (VLE) measurements of the (CO2 + CH4) system are reported along seven isotherms at temperatures varying from just above the triple point to just below the critical point of CO2 at pressures from the vapor pressure of pure CO2 to approximately 9 MPa, including near-critical states. From these data, the critical locus has been determined and correlated over its entire length. The VLE data are correlated with the Peng-Robinson equation of state (PR-EoS), using a temperature-dependent binary interaction parameter, and also compared with the predictions of the GERG-2008 equation of state. The former represents the phase compositions across all isotherms with a root-mean-square mole-fraction deviation of S = 0.0075 while, for the latter, S = 0.0126. Measurements of the three-phase solid-vapor-liquid equilibrium (SVLE) line are reported at temperatures from approximately (204 to 216) K and a new correlation is developed which is valid from 145 K to the triple point of CO2. Additionally, we report the partitioning of trace levels of H2S between coexisting liquid and vapor phases of the (CO2 + CH4) system and compare the results with the predictions of the PR-EoS.

Melting probes as vehicles to explore terrestrial ice sheets have been designed and applied successfully since the early 1960’s. Later on, in the 1990’s, various proposals were made to apply such probes also as a means to explore ice sheets on other bodies of the solar system, e.g. Jupiter’s icy satellite Europa or the ice caps of Mars. For this type of subsurface probes the name cryobot has become common. We review both early developments and more recent efforts to develop probes for application in planetary environments, i.e. under low pressures and low temperatures. The current state of art as well as the pros and cons of the different concepts hitherto considered are described. While many tests with various probes have been done in terrestrial environments, experiments under low surface pressure conditions are rare. Therefore, we report here on lab tests with a simple melting probe under the range of pressure and temperature conditions that would be encountered on the surface of Mars and compare them with corresponding tests under a much lower gas pressure, possibly representative for icy satellites. The contribution of evaporation during the melting and its variation with surface pressure is also considered. All surface pressure measurements that have been performed on Mars up to now indicate a surface pressure above the water triple point pressure (612 Pa). This means that water ice always transforms into the liquid phase when warmed up to 0°C, before it evaporates into the ambient atmosphere. The temporary existence of the liquid phase around the heated tip of the cryobot allows good thermal conductance between probe and surrounding ice, which is an important pre-requisite for efficient melt penetration. Our experiments indicate that under all possible Mars surface pressures the liquid phase is present when the probe is heated up. This finding confirms experimentally that a probe as it was proposed by Paige (1992) for in situ exploration of the Mars north polar layers would work in the expected way, although the penetration velocity must be expected be lower than under Earth pressure conditions. A test with the same probe, but under an almost two orders of magnitude lower gas pressure than on Mars, still indicates the temporary existence of the liquid phase in the contact region between the probe and the surrounding ice.

Cylindrical detonations propagating in free space characterized by different activation energies were computationally studied. It is found that unstable detonations with the 2-D cellular structure have more velocity deficit than those without the cellular structure computed with the 1-D simulation. The weakening is due to lengthening of the detonation structure and the unreacted pocket behind the cylindrical front, while propagation sustenance depends strongly on the re-amplification and regeneration of transverse shocks and triple points. For low activation energies, cellular detonation can be initiated in free space through the subcritical initiation path due to absence of unreacted pockets, and the propagation is not very sensitive to the attenuation of transverse waves and triple points. However, for high activation energy the unreacted pocket aggravates initiation such that even a cellular detonation first established is prone to quench due to the lack of re-amplification of the transverse wave and the triple point. When considering confinement, it is demonstrated that a detonation that quenches in free space can be reinitiated in confined space.

Hysteresis phenomenon of the oblique detonation wave (ODW) is numerically studied. Two-dimensional unsteady reactive Euler equations are numerically solved as governing equations with a two-step reduced reaction mechanism. Wedge angle variation is realized by modifying inflow direction. It is found that hysteresis phenomenon does exist in ODW problem, i.e., the final state of the ODW is closely relevant to initial condition. Two types of hysteresis are discovered in this study: the hysteresis of upstream-downstream triple point and the hysteresis of smooth-abrupt transition pattern. Detonation/Shock polar analysis on primary triple point structure of abrupt ODW demonstrates that the precursor shock of the ODW near primary triple point is actually a strong shock solution and therefore characterized by local detachment behavior which is responsible for primary triple point's upstream moving. Similar to hysteresis of shock reflection, irreversibility is the mechanism for ODW's hysteresis. It is found that hysteresis will disappear when the wedge angle is smaller than a certain value, which means that it may be impossible to obtain a standing Chapman–Jouguet (CJ) ODW without ignition delay or with short ignition delay at a CJ wedge angle via hysteresis.

The effect of shock passage in commercially pure titanium (cp-Ti) with minimal macroscopic plastic strain was investigated in the present study. For the first time, ex-situ residual strain relaxation in a shocked material was recorded post-shock exposure. Femtosecond laser was used to produce a shock in cp-Ti. Post-shock investigation was carried using EBSD, TEM imaging, and TEM OIM. Uniform but low misorientations were observed inside the grains. Lamella like structures and nano grain pockets were present in the material. Observed misorientations of the remnant nanograins correspond to the multiple twinned region of twins with low twinning shear. However, a large fraction of misorientation pertains to the double twinned structure. Lattice misorientation build-up was absent in the microstructure, in spite of a large number of defects observed. This is confirmed by the GND component analysis, indicating that the macroscopic plastic strain is minimal. The lattice displays alternating curvature which cancels out over long distances, which indicates the presence of SSDs. Ex-situ strain relaxation was observed in the TEM sample resulting in bending of the TEM lamella about the triple point junction of grain. This resulted in the reverting back of defects to the parent grain, which is similar to defect annihilation on shock unloading as reported in previous MD simulations. A schematic spanning the microstructural changes before and after shock passage, and showing the effect of further strain relaxation on the microstructure is shown. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

For a slowly cooled series of NiMn1-xCrxGe half-Heusler alloys (x = 0.04, 0.11, 0.18 and 0.25) the magnetostructural (P,T) phase diagrams, under hydrostatic pressure up to 13.5 kbar, were determined. At ambient pressure a magnetic (second order) transition and a structural (first order, martensitic) phase transition are observed. The temperature of the magnetic phase transition increases while the one of the structural phase transition decreases with increasing pressure. The lines of these dependences intersect at so-called triple point (PTRI, TTRI) and a magneto-structural (first order) phase transition develops with further pressure increase. The magneto-structural transition temperature decreases with increasing pressure. The value of the triple point pressure PTRI decreases with increasing Cr content, from about 8 kbar (for x = 0.04) to about 1 kbar (for x = 0.25) on heating.

Entire-curve Wagner analytics are treated as “true” or “best” values, and Antoine analytic values are used as surrogate experimental data. Limited-data Wagner constants are estimated from Antoine analytics for the fully-determined case for fifty-five species, from which reduced vapor pressures below and above the interval are predicted and compared with the entire-curve Wagner analytics to estimate the ability of limited VLE data to be used to accurately represent the entire two-phase curve. The Antoine intervals have a pressure range of 0.02–2 bars for most species, an average reduced temperature interval width of 0.20, and an average lower bound reduced temperature of 0.53. The Wagner constants estimated from Antoine analytics have an average entire-curve error of 4.8%, with the majority of the error occurring when extending down towards the triple point (9.55%), compared to 1.36% average error when extending up to the critical point. Such limited-data Wagner constants produce less predictive error for alcohols, while the semi-theoretical Riedel equation has the advantage for organic acids, and the empirical Ambrose-Walton equation produces less error for the remaining species. A comparison of Wagner and Antoine analytic values strictly over the Antoine interval indicates that disagreement of VLE data in the literature averages around 2% but varies considerably between species. Data disagreement is not found to be a strong indicator of predictive power of the limited-data Wagner constants; however, it is found to be a discriminator of performance relative to that of Riedel and Ambrose-Walton for some polar species.

Storage and transportation in carbon capture and sequestration (CCS) technology involve dealing with CO2 at high pressures, which can lead to accidental releases. To assess and control risks and to calculate the minimum safe distance from tanks and pipelines to populated areas, the source term model of the leakage is extremely important, as it serves as input to model the dispersion of CO2 into the atmosphere. The modelling of high pressurised CO2 releases is relatively complex due to its thermofluidynamics particularities. Its triple point pressure is higher than the atmospheric pressure and it has a relatively high Joule–Thomson coefficient depending on the temperature and pressure conditions. Hence, it might lead to a two-phase flow and to solid formation when the depressurisation to atmospheric pressure occurs. Also, the molecular vibration of CO2 might be important in some leakage scenarios. There are several approaches in the literature which address differently the aspects of the flow, specially regarding thermal and mechanical equilibrium or non-equilibrium. The present work provides an innovative approach for the discharge calculation in accidental high pressure releases. The Homogeneous Non-Equilibrium Model (HNM) is proposed, which accounts for non-equilibrium effects regarding not only metastability but also vibrational relaxation of the molecule. It considers the possible phase transitions and dry ice formation and it is applicable to steady-flow conditions. The model was tested with experimental data from CO2PIPETRANS project, HSE experiments and Cooltrans research programme. It was found that the model works well leading to results which agree with available experimental data. The proposed source model is relatively simple to implement and it does not demand numerical effort. The discussed discharge approach for CO2 releases emerges as a good alternative to existing models.

At high temperatures and high pressures, iron reacts with hydrogen to form hydrides. Three hydride phases are present at moderate temperature and pressure ranges below 2000 K and 20 GPa: α, γ, and e′ phases, respectively, with bcc, fcc, and double-hcp (dhcp) structures. Recent reports have described studies of phase transitions at temperatures and pressures that differ greatly from those predicted from the conventional phase diagram for the Fe–H system established in the early 2000s. We conducted in-situ X-ray diffraction experiments to investigate α/e′–γ phase boundaries at temperatures up to 900 K and pressures up to 9.1 GPa. Phase transition temperatures were determined by averaging those observed upon heating and cooling under constant pressure. The α/e′–γ phase boundaries were found at temperatures 150–300 K higher than the conventional phase boundaries. The α–γ–e′ triple point was expected to relocate accordingly.

The electric field distribution is a very important factor in the performance of polymeric insulators. This distribution varies under different operating conditions. Therefore, there are different approaches to reduce the electric field strength at the critical zones to acceptable values. One of these approaches is the use of corona rings. However, the design of corona rings is not standardized, and the geometric parameters affect the electric field distribution. This work analyzed the relationship between corona ring design parameters and the electric field strength near energized-end fitting in a real 230 kV polymeric insulator with a corona ring. First, it was used the Finite Element Method to evaluate the influence of three corona ring design parameters on the electric field strength: corona ring diameter, ring tube diameter, and corona ring position. Then, the PSO algorithm was used to optimize the original corona ring and reduce the electric field strength at three critical zones: triple point, the surface of the energized-end fitting, and the surface of the corona ring. The optimization process reduced the maximum electric field strength by 50.5% relative to the insulator with the original corona ring (82.4% without a corona ring).

Triple points of a Lennard-Jones (LJ) fluid in cylindrical nanopores were examined using molecular dynamics simulations. At higher temperatures, the LJ fluid was capillary-condensed and was in equilibrium with the vapour phase in the pore space. The freezing of capillary condensates in cylindrical nanopores upon cooling represented phase transitions from vapour–liquid coexistence to vapour–solid coexistence, which occurred at the triple point in the cylindrical nanopores. The triple-point pressures in the cylindrical nanopores were approximately one order of magnitude lower than those in the bulk. The triple-point temperatures in the cylindrical nanopores were not inversely proportional to the pore size. The intersection of the thermodynamic models of vapour–liquid and solid–liquid coexistence previously derived by the authors can represent the state of vapour–liquid–solid coexistence. The thermodynamic triple-point model in cylindrical nanopores was successfully used to predict the molecular dynamics in nanopores.

Electromigration (EM) has aroused substantial attention with the shrinkage of modern devices. EM is an interaction between electron carriers and atoms, meaning that it arises from atomic behaviour. Both the number of twin boundaries (TBs) and the direction of electron flow are crucial factors affecting EM behaviour. In this study, EM phenomena with perpendicular and parallel electron flow were investigated by high resolution transmission electron microscopy (HRTEM). Twin planes could limit the growth direction of voids in the parallel case. The evolution of smooth surfaces into step-like surfaces resulting from the triple point retarding EM has been demonstrated. With the measurement of the resistance, it could be concluded that the specimen with electron flow perpendicular to the TBs had better EM restriction. Columnar grains can confine the position of the voids. This study demonstrates the dynamic evolution of the surface structure, providing insight into the fabrication of interconnections in the integrated circuits industry.

Freeze drying is a drying technology that removes water from a target by sublimation of ice to vapor. Drying at low temperature and pressure (below the triple point) results in fewer physical and chemical changes to the dried products compared with the changes observed when using other drying technologies, leading to producing a high quality product. However, the weak point of freeze-drying technology is its large energy consumption. It is therefore necessary to reduce the energy required for the freeze-drying process and the energy costs of production so that this technology can be extended to the drying of other products. In this paper, a new energy-saving freeze-drying process based on the concept of self-heat recuperation technology was proposed. The energy required for the proposed process was compared with a conventional technique using a commercial process simulator. From the simulation results, more than 80% of the energy required for drying can be saved by using the proposed process.

Two-stage ORC (Organic Rankine Cycle) is a very competitive configuration. However, most of the works have narrowed the studies within a single or just several fluids in spite of the great effect of working fluids on system performance. In this paper, 400 combinations of working fluids are investigated. The evaporation and condensation pressures of both the high and low temperature ORCs are optimized by PSO (Particle Swarm Optimization) with the objective function of maximum exergy efficiency. The results show that the effect of fluid1 on the system exergy efficiency is much greater than that of fluid2. Critical temperature is a key indicator for fluid1 selection and triple point temperature is a crucial indicator for fluid2 selection. The largest exergy destruction occurs in the condenser of cycle II. The proper solution to reduce this exergy destruction is raising the inlet temperature of LNG, rather than lowering the condensation temperature of cycle II.

The separation of para -cresol (4-methylphenol) and meta -cresol (3-methylphenol) from their mixture have been an interesting challenge because of their close boiling points, where the boiling point difference of isomers is merely 0.29 °C. Stripping Crystallization is an intensified technique, used for separation of close boiling mixtures. This technique is based on the triple point condition, where the liquid mixture is simultaneously vaporized and crystallized, owing to three-phase equilibrium. In the current work, a detailed experimental study has been carried out to establish the feasibility of stripping crystallization process for separating out para - and meta - cresols from their mixture. Gas Chromatography has been used to determine the purity of the distinct cresols obtained from the experiments. Feasibility revealed the dependence of the process on different operating and design parameters. Hence, additional experiments were done to study the effect of these parameters. Cooling rate, seeding, availability of surface area and application of vacuum are found to be effecting the quality of the separated product. Obtained results are found to be in coherence with the available data reported in the literature.

The piezoelectric properties of (1-x-y)PbZrO3-xPbTiO3-yPb(Ni1/3Nb2/3)O3 ceramics were investigated. Specimens with a large Pb(Ni1/3Nb2/3)O3 content, which have compositions close to the triple point, show small g33 and d33 × g33 values because of their large eT33/e0. These values increased with a decrease in y (amount of Pb(Ni1/3Nb2/3)O3) and the specimen with x = 0.39 and y = 0.29 showed the largest g33 of 43 × 10−3 V·m/N and d33 × g33 of 25.2 × 10−12 m2/N. Cantilever-type energy harvesters were fabricated using specimens with 0.38 ≤ x ≤ 0.41 and y = 0.29. The output power densities of the energy harvesters were related to the d31 × g31 × k312 value of the piezoelectric ceramics. The energy harvester fabricated using a specimen with x = 0.39 and y = 0.29, which has a maximum d31 × g31 × k312 value, showed the maximum output power density of 1.01 mW/cm3.

The use of carbon dioxide (R744) in refrigeration systems is usually limited by its triple point temperature of −56.5 °C; an objective of this study was to extend the range of this natural refrigerant to include low-temperature applications. A novel wet sublimation cascade refrigeration system was developed using low-GWP mixtures of R744 with hydrocarbons (HCs) and hydrofluorocarbons (HFCs) as low-temperature refrigerants. With propane (HC-290) and difluoromethane (HFC-32) serving as solvents for solid carbon dioxide, temperatures as low as −72 °C were obtained in a closed cycle system with mixtures containing 67% CO2 by mass. Visualisation experiments were performed to illustrate the crystallisation of a supersaturated carbon dioxide solution. The excess solute was visible as clouding or crystals, depending on the saturation level of the solution. High heat transfer rates, up to 3465 W m–2K−1, were obtained in the sublimator/evaporator section, resulting in low wall superheat values, indicating potential industrial applicability of the carbon dioxide-based slurry-like fluid. The pressure–mole fraction and temperature–mole fraction diagrams were constructed to study the system parameters working with binary mixtures. Moreover, vapour pressures of the binary mixtures of R744/R290 and R744/R32 at the temperature of –72.5 °C were experimentally obtained.

Despite being a very common compound in the industry as well as in the nature, the thermodynamic description of oxalic acid is far from being complete and reliable. The literature is contradictory considering both preparation of the two known polymorphs and the triple point temperature above which β-form should be more stable. The published vapour pressure data for α-phase show also a considerable disagreement. In this work, the polymorphs of anhydrous oxalic acid are subjected to a combined thermodynamic and X-ray diffraction study since a single technique cannot give an exhaustive answer on the phase behaviour of the compound. The simultaneous correlation procedure that combines vapour pressure data, calorimetric phase-transition properties, and heat capacities of the crystalline and ideal-gas phase is used to develop a consistent thermodynamic description. Finally, the triple point temperature and transition enthalpy are derived.

Using Density Functional Theory (DFT) and Boltzmann’s transport theory, we determined the band structure and thermoelectric properties in Lithium-Aluminium-Silicide compound. The band-structure calculations showed a triple point degeneracy at Γ point due to the energy difference between the Lithium-Aluminium ligand formation. With the valence band maximum at Γ and the conduction band minimum at X , we observed an indirect bandgap along the Γ → X transition. Observation of the transport properties of LiAlSi at temperatures below 500K, showed several shoulders or minor pre-peaks which are more pronounced in the low energy range and might be due to intrinsic magnetization of the constituent elements. The Seebeck coefficient has the highest value of 325 μVK−1 in the p-type region, while the n-type doping has a maximum value of 297 μVK−1. In detail, the calculated results of Seebeck coefficient, thermal and electrical conductivity, power factor and electronic fitness function are in this work.

Molecular Dynamic simulations and experiments have been performed to investigate the evaporative behavior of a liquid droplet in the presence of nanoparticles on a smooth, heated flat plate. Nanofluids of different volume fractions with CuO and Al2O3 nanoparticles were prepared to obtain liquid droplets. Experiments were conducted for droplets of both nanofluids and base fluid (DI water). The results showed that in the pinned region of evaporation, droplets of nanofluids with higher volume fractions of dense nanoparticles evaporated by keeping their base pinned at the triple point contact line. It is also observed that the evaporation rate of nanofluid droplets with nanoparticles having higher density is slower and promoted a typical pattern formation. Molecular Dynamic simulations were further performed to analyse the influence of various nanoparticle-liquid interaction strengths ( e np − l ) on evaporative behavior. The simulation results suggest that in the pinned evaporation stage, for higher values of e np − l , the droplet undergoes a delay on evaporation while subjected to higher heat flux on the substrate.