Triple Point Pressure Research Articles

Vapor Pressure and Related Thermodynamic Properties of 36Ar

The 36Ar−40Ar vapor pressure isotope effect in the liquid and solid phases has been experimentally determined at about 100 temperatures between 83 and 97 K using a high-accuracy double-differential manometric technique. Differences between the vapor pressure of a highly enriched sample of 36Ar and that of natural argon were measured simultaneously with the absolute vapor pressure of natural argon. Absolute and differential vapor pressure measurements show an estimated accuracy of 0.15% and 0.001%, respectively, with respect to the absolute vapor pressure of argon. Data were obtained in both the solid and liquid regions. The vapor pressure of 36Ar is always higher than that of 40Ar by about 0.5%. Triple-point temperatures and pressures were also measured for both isotopes. All data compare favorably with previous results reported in the literature and are nicely interpreted within the framework of Bigeleisen's theory of isotope effects. Using a large temperature extrapolation of our data, liquid−vapor isotope fractionation factors were successfully inferred from the vapor pressure measurements; the estimated values agree with the experimental ones up to close to the critical point. The isotopic difference in the molar enthalpies of vaporization and sublimation was also calculated from the vapor pressure data. Additionally, molar volume and second virial coefficient isotope effects are estimated using several different theoretical approaches.

New Equation for Vapor Pressures of Difluoromethane (HFC-32)

Critically evaluated experimental vapor-pressure data sets supplemented with calculated data for low-temperature region were used in the development of vapor-pressure equations. The optimum number of terms, coefficients, and exponents of the Wagner-type equation were derived by means of the Setzmann–Wagner program OPTIM based on the combination of the stepwise regression analysis and evolutionary optimization method. Equations were checked by the reduced enthalpy of vaporization criterion derived from the Clausius–Clapeyron equation and specific volume of ideal gas. An equation developed using 261 experimental data points and low-temperature data calculated by Luddecke and Magee gives an RMS deviation of 0.102%; a second equation based on the same experimental data and low-temperature data calculated by Tillner-Roth gives an RMS deviation of 0.101% from experimental points. The triple-point pressure extrapolated to the measured temperature Ttp = 136.34 K is discussed. Comparisons with vapor pressure equations by Outcalt and McLinden, Duarte-Garza and Magee. and Kubota et al. are also given.

A nonlinear regression analysis for estimating low-temperature vapor pressures and enthalpies of vaporization applied to refrigerants

A new method is presented to extrapolate experimental vapor pressures down to the triple Point. The method involves a nonlinear regression analysis based on the Clausius Clapeyron equation and a simple relation for the enthalpy of vaporization Triple-point pressures and vapor pressures up to 0.1 0.2 MPa are estimated for R125, R32, R143a, R134a, R152a, R123, R124, and ammonia; they generally agree with available experimental data within their uncertainty, Equations for the enthalpy of vaporization which describe this property fairly well at low temperatures are obtained as a byproduct.

Free expansion study of liquid nitrogen

The phenomenas involved in the free expansion of liquid/superc ritical hydrogen are of great importance in many space applications. In this study, liquid nitrogen was substituted for hydrogen due to practical reasons. An experimental setup was designed to study the free expansion process when liquid/supercritical nitrogen is injected into an evacuated chamber. The effects of nozzle size, upstream pressure, and downstream pressure were studied. During the experiment, three different nozzle sizes were tested. When the pressure inside the expansion chamber was below the triple point, the nitrogen injected into the chamber solidified in two different forms. For the smallest nozzle, the solid formation occurred inside the nozzle, whereas, for the larger nozzles, the fluid solidified after being sprayed into the expansion chamber. No solidification was observed at chamber pressures higher than the triple point pressure. It was also found that supercritical nitrogen acts like a liquid in the free expansion process. Nomenclature Cd = coefficient of discharge d = nozzle orifice diameter g = gravitational acceleration L = length m = mass flow rate mN2 = mass of liquid nitrogen P = pressure Pc = critical pressure R = gas constant of nitrogen T = temperature t = time U = internal energy V = volume of the expansion chamber p = density

High p, T physical property studies of Earth's interior: Thermoelectric power of solid and liquid Fe up to 6.4 GPa

High p,T experiments provide indirect access to the deep interior of Earth. High p, T research at the University of Western Ontario using large volume cubic anvil presses has focused on in-situ measurements of physical properties of mantle and core related substances as they relate to Earth's interior physical processes. Thermoelectric power measurements of solid and liquid Fe, using twisted Fe/Pt–10%Rh junctions, have been made at p up to 6.4 GPa. By isolating the sign determining energy derivative of the density of states at the Fermi energy, ∂N(εF)/∂ε, in the expression for the Seebeck coefficient of Fe, these measurements show that ∂N(εF)/∂ε is positive for liquid Fe at p below approximately 4.0 GPa but ∂N(εF)/∂ε is negative for p above 4.0 GPa. The solid phase polymorphism which Fe exhibits in this p region, and its influence on the liquid state, is suggested as the explanation for the short range bcc-like and fcc-like properties of the liquid. This finding corroborates our earlier measurements on the p-dependence of the T-coefficient of electrical resistivity of liquid Fe, which showed a similar discontinuity at the δ(bcc)–γ(fcc)-liquid triple point pressure.

Dependence of the lamellar thickness of an extended-chain single crystal of polyethylene on the degree of supercooling and the pressure

The dependence of the lamellar thickness (I) of an extended-chain single crystal (ECSC) of polyethylene (PE) crystallized at various pressures below or at the triple-point pressure (Ptri= 0.5 GPa) on the degree of super-cooling (ΔT) and the pressure have been studied. The value of I increased with the decrease in ΔT[i.e. increase in the crystallization temperature (Tc)] at a fixed pressure, similar to the well known ΔT dependence of I for a folded-chain single crystal (FCC). The observed maximum value of I, obtained at the lowest ΔT(Imax) increased with increasing pressure and the crystal changed from FCC to an extended-chain crystal (ECC) at ca. 0.25 GPa. Application of the chain-sliding diffusion theory, previously proposed by one of the authors (M.H.) was found to explain well observed significant ΔT dependence of I and the pressure dependence of Imax. It was proposed that the value of I is determined by the cessation of lamellar thickening growth at the phase transition from metastable hexagonal to stable orthorhombic. The phase transition was also studied and it is suggested to be a nucleation-controlled process of the primary nucleus.

Water Flash Evaporation in Vacuum. 1st Report.

Water flash evaporation in vaccum exhibits high performance of heat exchanger and is an important means especially for spacecraft. As the first report, this paper mainly describes the verification of the relation between the heat transfer coefficient and the saturation temperature in [Ref. (1) ] which is fundamental and essential for the phenomena mentioned above. The results show that flash evaporation has better capablities of cooling under low pressures, especially below the triple-point pressure of water than the mentioned in [Ref. (1) ], and that the phenomenon below the triple point pressure is so unstable that it may cause rapid icing ; hence, flash evaporation is unsuitable for use under such a condition and finally that the maximum heat flux exists above the triple-point pressure for the target cooling temperature, so the pressure control is necessary for the flash evaporation cooling with high efficiency.

DTA determination of the high-pressure-high-temperature phase diagram of CdSe

Differential thermal analysis (DTA) was used to determine the high-temperature part of the p-T diagram of CdSe. The slope method was employed for identification of melting temperatures of wurtzite and rocksalt phases of CdSe for pressures up to 17 kbar. A novel method, based on the estimation of the enthalpy of fusion (the area method) was proposed to obtain the coordinates of the wurtzite-rocksalt-liquid triple point. The triple-point pressure of 10.90 kbar and temperature of 1221 degrees C is in agreement with earlier work of Jayaraman et al.

Effect of liquid phase on the triple point pressure of argon

We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value ofτ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔP h), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.

Equilibrium triple point pressure and pressure-temperature phase diagram of polyethylene

The equilibrium triple point and pressure and temperature phase diagram of polyethylene were obtained by in situ optical microscopic and X-ray observations of the melting temperature of hexagonal and orthorhombic isolated extended chain single crystals at high pressure. The melting temperatures of extended chain crystals still showed a ΔT dependence at high pressure, which has been neglected in previous studies. The triple point pressure and temperature were 0.5 × 10 8 − 1.5 × 10 8 Pa and 20–30°C higher than those previously obtained by the d.t.a. method. These results suggest that lamellar thickness dependence is important even in extended chain crystals to obtain equilibrium thermodynamic physical quantities of polymers.

History of water on Mars: A biological perspective

We divide the history of water on the Martian surface into four epochs based upon the atmospheric temperature and pressure. In Epoch I, during which a primordial CO 2 atmosphere was actively maintained by impact and volcanic recycling, we presume the mean annual temperature to have been above freezing, the pressure to have exceeded one atmosphere, and liquid water to have been widespread. Under such conditions, similar to early Earth, life could have arisen and become abundant. After this initial period of recycling, atmospheric CO 2 was irreversibly lost due to carbonate formation and the pressure and temperature declined. In Epoch II, the mean annual temperature fell below freezing but peak temperatures would have exceeded freezing. Ice covered lakes, similar to those in the McMurdo Dry Valleys of Antarctica could have provided a habitat for life. In Epoch III, the mean and peak temperatures were below freezing and there would have been only transient liquid water. Microbial ecosystems living in endolithic rock “greenhouses” could have continued to survive. Finally, in Epoch IV, the pressure dropped to near the triple point pressure of water and liquid water could no longer have existed on the surface and life on the surface would have become extinct.

Thermal acoustic oscillations in triple point liquid hydrogen systems

Thermal acoustic oscillations are often observed in tubes which penetrate a cryogenic system and are closed at the warm end and open at the cold end. Such tubes are genrally used for filling or vetning the tank, providing relief pressure or inserting instruments taps. Large amounts of heat (of the order of ten to a thousand times more than by normal heat conduction) can be transferred into a cryogenic system when such thermaloscillations occur. A number of studies examining thermal acoustic oscillations in liquid helium systems have been performed by Rott et al. However, only minimal consideration has been given to such oscillationsin liquid and sluch hydrogen systems. This study extends Rott's theory to the stability aspects of thermal acoustic oscillations for a straight tube closed at the warm end and inserted into a Dewar flask filled with triple point liquid hydrogen when the cold open end is located above the liquid surface. These results can also be applied to a slush hydrogen when the pressure in the Dewar flask is reduced to the triple point pressure of hydrogen. Numerical results have been obtained in this study for developing stability curves, establishing oscillation frequency characteristics and identifying critical configurations for initiating such oscillation. The mechanisms associated with the two branches of the stability curves for thermal acoustic oscillations have also been investigated.

Triple point corresponding states in long-chain n-alkanes

Evidence for triple point corresponding states in temperature and pressure are presented for long-chain n-alkanes. As the carbon chain length exceeds n=9, variation in triple point pressures, Pm, due to odd-even carbon number effects rapidly converge to a single line. Similar behavior is observed for the reduced value, Prm=Pm/Pc. Likewise, odd-even variations in the reduced triple point temperature, Trm=Tm/Tc, rapidly approach 0.4 Trm deviates less than 1 per cent from 0.4 between n=12 and n=100 when Tc is based on a regression of experimental data to the Kreglewski—Zwolinski equation form. The rapid convergences in Trm and in Prm allow determination of Tc and Pc of thermally unstable n-alkanes based on triple point measurements. Triple point correlations for n-alkanes can be used to constrain vapor pressure correlations for conformal fluids at low pressures.

A Unified Fundamental Equation for the Thermodynamic Properties of H2O

A new unified equation of state for H2O is presented, which includes the revised and extended scaling equation of Levelt Sengers, Kamgar–Parsi, Balfour and Sengers, is continuous over all single phase states of H2O from triple point pressure and temperature to 1000 MPa (or the melting line) and 1000 °C and provides accurate representation of existing thermodynamic data in that range. In addition it provides a smooth transition from singular critical region functions to the nonsingular far-field functions. This is demonstrated by the variations of isochoric specific heat, isothermal compressibility, speed of sound, specific heat ratio and coexistence line properties in the critical region.

Measurement of the radiance temperature (at 655 nm) of melting graphite near its triple point by a pulse-heating technique

Measurements of the radiance temperature of graphite at 655 nm have been performed in the vicinity of its triple point by means of a rapid pulse-heating technique. The method is based on resistively heating the specimen in a pressurized gas environment from room temperature to its melting point in less than 20 ms by passing an electrical current pulse through it and simultaneously measuring the radiance temperature of the specimen surface every 120 μs by means of a high-speed pyrometer. Results of experiments performed on two different grades of POCO graphite (AXM-5Q1 and DFP-1) at gas pressures of 14 and 20 MPa are in good agreement and yield a value of 4330±50 K for the radiance (or brightness) temperature (at 655 nm) of melting graphite near its triple point (triple-point pressure, ∼ 10 MPa). An estimate of the true (blackbody) temperature at the triple point is made on the basis of this result and literature data on the normal spectral emittance of graphite.

The influence of fluids on the thermal history of a metamorphic terrain: New Hampshire, USA

Summary The metamorphic terrain in central New Hampshire is characterized by over 9000 km 2 of primarily sillimanite — muscovite-bearing rocks. Superimposed on this large thermal high are a series of hot spots about 20 km 2 in area. Thermal models suggest that the large-scale thermal structure of central New Hampshire can be explained by conductive heat transfer processes. However, the hot spots can neither be explained by conductive heat transfer nor by intrusion of plutons. Isotopic and petrological studies demonstrate that the hot spots were formed by the focusing of hot metamorphic fluids into zones that had relatively high fracture permeability. The infiltration of hot fluids has significantly affected the P-T paths of rocks in central New Hampshire. Within the region of abundant hot spots, the P-T history of the metamorphic rocks is different from that outside the hot spot region. The P-T paths in the central portion of New Hampshire, the area with the hot spots, are characterized by isobaric-heating paths. The rocks passed near aluminium silicate triple point pressures and temperatures and later equilibrated at similar pressures, around 4.0 kbars, and at higher temperatures, approximately 650–750°C. The absence of other mechanisms to produce the isobaric-heating paths and the evidence for intense hydrothermal activity suggest that fluids played an integral role in creating the thermal spikes along the P-T trajectory. Analytical solutions to differential equations that describe focused fluid flow are used to estimate the duration of hydrothermal activity and the amount of fluid involved. The steep thermal gradients adjacent to the hot spots and the observed temperature increase within hot spots are consistent with large fluid fluxes, > 1 × 10 −9 m 3 fluid per m 2 s −1 , over short periods of time, c. 100000 years. This indicates that P-T paths from rocks within hot spots record only small portions of the geological evolution of the metamorphic terrain.

Estimation of the bcc-fcc-liquid triple point of iron

The bcc-fcc-liquid triple point is estimated by means of the dislocation theory of melting. A simple relation between the triple point temperature and pressure is derived and applied to iron. The theoretical result is in agreement with experiment within an error of 10%.

Triple Point of Pure and Impure Deuterium

The liquidus-point behaviour of high-purity and impure D2 has been studied in both normal and equilibrium states. It was found that the liquidus point in the limit of vanishing amount of condensed phase is nearly impurity independent; D2 samples doped with as much as 1% H2 had liquidus points only about 2 mK different from the purest samples available.The temperatures (on the IPTS-68) for the triple points of equilibrium and normal D2 were found to be 18.6963 K and 18.7319 K respectively; the normal boiling point of equilibrium D2 was found to be 23.6369 K; the heat of fusion was measured as 49.53 J/g; and the density of D2 gas at the triple-point temperature and pressure for normal D2 is 4.61 g/cm3.The vapour pressure of equilibrium D2 between its normal boiling and triple points can be well described by a polynomial of the form ln (P/P0) = ∑i=−14 ai(T − T0)i

Improved predictions of equilibrium properties for spin-polarized atomic nitrogen

A reanalysis of several equilibrium properties of electron spin-polarized atomic nitrogen is presented, utilizing parameters from a new and improved theoretical calculation of the 7Σ+u state of molecular nitrogen which represents the interaction potential between two such spin-polarized atoms. The new potential well is significantly more shallow than previously assumed, resulting in substantial changes in the critical and triple point pressures and temperatures as calculated in the quantum theorem of corresponding states framework. The corresponding molar volumes are only slightly affected because the hard sphere radius is unchanged. Bulk samples are not expected to exhibit significant quantum behavior. Earlier conclusions on the relative stability of this material to single spin-flip processes remain unaltered.

Producing liquid-solid mixtures (slushes) of oxygen or hydrogen using an auger

An auger rotating inside a brass tube refrigerated with liquid helium was used to produce liquid-solid (slush) mixtures of hydrogen and of oxygen. The auger produced small particles from the cryogens so that the resulting slush mixture could be transferred and stored. The auger could produce slush continuously in an appropriate system; it could produce slush at pressures higher than the triple point pressure of the cryogen, and the energy required to produce the slush was less than the energy required to produce slush using the freeze-thaw process.