On the triple point temperature of CO2

This paper describes the measurement of the triple point (TP) of carbon dioxide using two cells. Using two different platinum resistance thermometers, the TP was measured within 1 mK.     

Vapour pressure of nitrogen below the triple point

Techniques are discussed whereby liquid helium consumption can be reduced by extension of the range of use of nitrogen. The vapour pressure-temperature relationship has been determined for commercial high-purity nitrogen from the triple point down to 45 K; this data conforms to the expression log₁₀P = 7.614676 ? 356.281/T to within a 1% pressure deviation. A value of 63.148 K has been deduced for the triple point temperature on IPTS of 1968; this corresponds to a pressure of 93.905 mm Hg. Our data is compared with some earlier data which extends down to 30 K.     

New equations for enthalpy of vaporization from the triple point to the critical point

Two new equations are proposed for the enthalpy of vaporization from the triple point to the critical point. One of these equations containing four parameters is exceptionally good for fitting the data. The other equation containing three parameters is quite adequate for fitting the data but it is exceptionally suited for interpolation when the data do not cover the entire range. These equations have been tested using the enthalpy of vaporization of water from the triple point to the critical point and are compared with other equations.Nomenclature T _c Critical temperature, K - T _t Triple point, K - T _x Any particular temperature, K - T _r Reduced temperature - P _r Reduced pressure - R Gas constant - P Vapor pressure - X (T _c–T)/T _c - Y (T _c–T)/T - X _x (T _c–T)/(T _c–T _x) - X _t (T _c–T)/(T _c–T _t) - H _vt Enthalpy of vaporization at the triple point, kJ · mol^–1 - H _vx Enthalpy of vaporization at any temperature x, kJ · mol^–1 - Z _v Compressibilty factor of the saturated vapor - Z ₁ Compressibilty factor of the saturated liquid Relative deviation = 100[H_v(obs)–H_v(cal)]/H_v(obsd) Standard deviation = { [H _v(obs)–H _v(cal)]²/(No. points — No. parameters)}^0.5     

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.     

A generalized equation for surface tension from the triple point to the critical point

A three-parameter generalized equation is proposed for surface tension from the triple point to the critical point. This equation not only fits the data well but also is good for interpolation between the normal boiling point and the critical point. This equation is also good for extrapolation to the triple point. This equation has been tested using the surface tension of water from the triple point to the critical point. The constants of this equation obtained using orthobaric surface tensions are given for a number of compounds. The isobaric surface tensions determined at a pressure of 1 atm do not differ significantly from the orthobaric surface tensions. Such data also have been used in obtaining equations from the triple to the critical point.Nomenclature T _c Critical temperature, K - T _t Triple point, K - T _m Melting point, K - T _r Reduced temperature, K - X (T _c-T)/T _c - Surface tension, dyne · cm^–1;10^–3N · m^–1 - _m Surface tension at the melting point - _f Surface tension at T _r=0.9 - _t Surface tension at the triple point - Relative deviation 100[ _obsd– _calcd]/ _obsd - Standard deviation [( _obsd– _calcd)²/(No. points—No. parameters)]^0.5     

The process of heat and mass transport at the critical point of pure fluids

The effects of fast isentropic temperature propagation, called the piston effect, or critical speeding up, and slow mass diffusion, called critical slowing down, are investigated. A temperature propagation experiment in a spherical cell filled with pure SF₆ at critical density was performed during the Second German Spacelab Mission D2 in 1993. The results evidently confirm the presence of the piston effect both in the one-phase region and in the two-phase region. The numerical simulations are in remarkable good quantitative agreement with the experimental results.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0⁷.0 m)都较缓,而进入远场(>7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0~7.0 m)都较缓,而进入远场(7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

Determination of saturated vapor pressure of organic substances from the triple to critical point

Methods are given of extrapolating the saturated vapor pressure of substances of “atmospheric range” to the entire liquid phase region from the triple to critical point. The extrapolation of the pT parameters from room temperature to the triple point is performed by simultaneous processing of vapor pressure and of differences between the heat capacities of ideal gas and liquid. The liquid-vapor equilibrium in the region from the normal boiling temperature to the critical point is predicted by the law of corresponding states of L.P. Filippov using the experimentally obtained pT data and values of density of liquids. Experimental facilities are described for determining the saturated vapor pressure by the comparison ebulliometric method and for determining the low-temperature heat capacity by the vacuum adiabatic calorimetry. The methods of extrapolating the vapor pressure are tested with standard substances for which reliable pT data are available for the entire liquid phase region.     

Apparatus for realizing the ITS-90 in the temperature range from the triple point of argon to the melting point of gallium

Systems for realizing the fixed points of the ITS-90 for calibrating column and capsule standard platinum thermometers, namely, the triple points of argon and mercury and the melting point of gallium, are constructed and investigated. The errors of the values of the metrological characteristics of the systems obtained enable one, using platinum resistance thermometers, to reproduce and transfer the temperature scale in the 83.8–302.9 K range. The extended uncertainty in reproducing the temperatures of the fixed points does not exceed 0.4 mK. This paper has been prepared from the contributions presented at the 3rd All-Russia Conference “Temperature 2007”; see the selection of papers in Measurement Techniques, Nos. 8 and 9, 2007. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 26–31, November, 2007.     

The effect of natural variations in the isotopic composition on the reproducibility of the temperature of the triple point of water

The effect of long-term natural variations in the isotopic composition on the temperature of the reproduction of the triple point of water – the main reference point of the ITS-90 International Temperature Scale – is investigated. Translated from Izmeritel’naya Tekhnika, No. 12, pp. 31–33, December, 2008.     

Pressure anomaly near the triple point on the magnetic phase diagram of bcc solid3He

The nuclear magnetic phase diagram of bcc solid ³ He has been determined by pressure measurements. We have observed a pressure jump at the transition from the high field phase to the paramagnetic phase (HP) near the triple point. This jump indicates that HP is first order.     

Determination of flash point in air and pure oxygen using an equilibrium closed bomb apparatus

The standard closed testers for flash point measurements may not be feasible for measuring flash point in special atmospheres like oxygen because the test atmosphere cannot be maintained due to leakage and the laboratory safety can be compromised. To address these limitations we developed a new "equilibrium closed bomb" (ECB). The ECB generally gives lower flash point values than standard closed cup testers as shown by the results of six flammable liquids. The present results are generally in good agreement with the values calculated from the reported lower flammability limits and the vapor pressures. Our measurements show that increased oxygen concentration had little effect on the flash points of the tested flammable liquids. While generally regarded as non-flammable because of the lack of observed flash point in standard closed cup flash point testers, dichloromethane is known to form flammable mixtures. The flash point of dichloromethane in oxygen measured in the ECB is -7.1 degrees C. The flash point of dichloromethane in air is dependent on the type and energy of the ignition source. Further research is being carried out to establish the relationship between the flash point of dichloromethane and the energy of the ignition source.     

Experimental determination of the volume change of pure salts and salt mixtures at their melting point

Measurements of the melting temperature as a function of pressure for some pure salts (NaNO₃, LiOH) and salt mixtures (Na₂SO₄-NaCl, NaNO₂-NaNO₃- KNO₃, Li₂SO₄-NaCl, NaCl-MgCl₂) are reported. The experiments were performed up to 250 MPa. From the melting curves, the slopes (dP/dT) _m ⁰ at atmospheric pressure were determined. Finally, using the Clapeyron equation, with the enthalpy of melting taken from the literature, the volume change on melting at atmospheric pressure was determined for each compound.     

The measurement of dew point

A sensor of the dew point of the flue gases of boilers and other installations is described, based on the occurrence of an emf between unlike metals when moisture from the flue gases is deposited.Translated from Izmeritelnaya Tekhnika, No. 12, pp. 51–53, December, 2004.This revised version was published online in April 2005 with a corrected cover date.