Enthalpy Increment Measurements Research Articles

Enthalpy increment measurements on nitrogen between the temperatures 160 K and 260 K, at the pressures ≈(0.3, 3.0, 5.0, and 15.0) MPa

Isobaric enthalpy increment measurements on nitrogen in the gas phase are presented over the temperature range 160 K to 260 K, at the pressures (0.3, 3, 5, and 15) MPa. The measurements were performed in an electrically heated flow calorimeter. Comparisons have been made with the best available measurements from the literature. A comparison with the SRK and Jacobsen equations of state is also given.

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.

Enthalpy increment measurements on liquid ethane between the temperatures 146.0 K and 256.2 K, at pressures (≈1.6, 3.20, and 5.07) MPa

Isobaric enthalpy increment measurements have been made on liquid ethane. The temperature and pressure ranges covered by the measurements are (146.0 to 256.2) K and (1.16 to 5.07) MPa. The measurements have an average standard uncertainty of ±0.07 kJ·kg −1or 0.21 per cent of the enthalpy increment. A new flow calorimeter test loop that avoids the two-phase region is described. The flow calorimeter used is of the electrically heated type.

Heat capacities and enthalpy increments of the metazirconates of calcium, strontium and barium

The enthalpy increments of CaZrO 3(s) and SrZrO 3(s) have been measured by drop calorimetry from 475.6 to 845.6 K, and from 474.4 to 906.5 K, respectively. Some additional enthalpy increment measurements on BaZrO 3(s) have been performed from 804.3 to 899.30 K. The results are compared with other measurements on CaZrO 3(s), SrZrO 3(s) and BaZrO 3(s), and these are discussed critically. The heat capacity functions up to 2000 K for the three zirconates are presented.

Enthalpy increment measurements of PbI 2: evidence for a reversible polytypic transition

The enthalpy increment of solid and liquid PbI 2 have been measured by drop calorimetry from 528 to 763 K and the X-ray diffraction pattern has been recorded from 300 to 633 K. The calorimetric data show evidence for a reversible transition at ∼ 580 K, the enthalpy difference between the two phases being small, 339 J mol −1. The X-ray diffraction results show a transition of the 2H to the 4H polytype at ∼ 440 K, for which the reverse reaction is not observed. The melting point of PbI 2 has been found at (679 ± 1) K by DSC, the enthalpy of fusion was obtained as Δ fusH° = 23471 J mol −1 from the enthalpy increments of the solid and liquid phase.

Enthalpy Increment Measurements from 4.5 to 350 K and the Thermodynamic Properties of Titanium Disilicide(cr) to 1700 K

Enthalpy increments for titanium disilicide were measured from 4.5 to 350 K with an adiabatic calorimeter. The enthalpy increments were combined with previous differential scanning calorimetry values to 500 K, Kopp's rule estimates for 500-800 K, and previous enthalpy increment measurements for temperatures to 1700 K in order to give the thermodynamic properties of titanium disilicide to 1700 K. Values of the Debye temperature, θ D , and the coefficient for the heat capacity of the conduction electrons, γ el , were determined from the model. Thermodynamic properties for formation from the elements at 298.15 K were also given.

Enthalpy Increment Measurements from 4.5 to 318 K for Bismuth(cr). Thermodynamic Properties from 0 K to the Melting Point

Enthalpy increments for bismuth(cr) were measured from 4.5 to 318 K with an adiabatic calorimeter. The calorimeter`s performance was demonstrated through comparison of measured enthalpy increments for copper and aluminum oxide to literature values. The effect that different temperature scales had on these comparisons for copper at low temperatures was discussed. The new enthalpy increments for bismuth(cr) were combined with previously measured thermodynamic properties for temperatures below 4 K and above 300 K in order to generate the thermodynamic properties of bismuth(cr) from 0 K to the melting point.

Accuracy analysis in flow calorimetry

The accuracy claimed for calorimetric measurements should be given at a certain confidence level. This paper describes how the standard uncertainty of isobaric enthalpy increment measurements from a new cryogenic flow calorimeter is derived. The new calorimeter has several features that reduce the heat leakage better than previous designs. The temperature and pressure ranges covered by the calorimeter are 133–335 K and 0.17–14 MPa. The enthalpy increment measurements have an average standard uncertainty of 0.10 kJ kg −1 or 0.25% of the enthalpy increment.

Enthalpy increments of { xCH 3(CH 2) 3CH 3+ (1 − x)CH 3OH} and of {0.3334CH 3(CH 2) 3CH 3+ 0.3333CH 3OH + 0.3333(CH 3) 2CO} between the temperatures 291 K and 610 K at pressures to 10 MPa

Enthalpy-increment measurements were made on { xCH 3(CH 2) 3CH 3+ (1 − x)CH 3OH} and {0.3334CH 3(CH 2) 3CH 3+ 0.3333CH 3OH + 0.3333(CH 3) 2CO} along isobars from p= 500 kPa to p= 10 MPa, in the temperature range 291 K to 610 K, using a reference-fluid boil-off calorimeter. For { xCH 3(CH 2) 3CH 3+ (1 − x)CH 3OH}, measurements were made at x= 0.25 and x= 0.75. In addition to the direct calorimetric results, the equation for the enthalpy increments of the liquid and vapor, as well as enthalpy-increment behavior in the supercritical region, are reported.

New enthalpy increment flow calorimeter and measurements on a mixture of 68% methane and 32% propane

A new flow calorimeter for measuring isobaric enthalphy increment and Joule-Thomson effect was built and tested during the period 1987–1993. The calorimeter has several features that reduce the heat leakage better than previous designs; this includes thermal shields cooled by propane. a heat sink, and superinsulation on all piping. The temperature and pressure range covered by the calorimeter is 133 to 343 K and 0.17 to 14 MPa. Measurements on a mixture of 68.32% methane and 31.68% propane are presented. The enthalpy increment measurements have an average standard uncertainty of 0.08 kJ · kg−1, or 0.22% of the enthalpy increment.

Enthalpy increments of {xCH3(CH2)3CH3 + (1-x)(CH3)2CO} between the temperatures 291 K and 610 K at pressures to 10 MPa

Enthalpy-increment measurements were made on {xCH3(CH2)3CH3 + (1-x)(CH3)2CO} along isobars from p = 500 kPa to p = 10 MPa, in the temperature range 291.5 K to 610 K, using a reference-fluid boil-off calorimeter. For {xCH3(CH2)3CH3 + (1-x)(CH3)2CO}, measurements were made at x = 0.25, 0.50, and 0.75. In addition to the direct calorimetric results, the equations, the equations for the enthalpy increments of the liquid and of the vapor, as well as enthalpy-increment behavior in the supercritical region are reported.

Enthalpy-increment measurements from flow calorimetry of CO 2 and of { xCO 2+(1- x)C 2H 6} from pressures of 15 MPa to 18 MPa between the temperatures 230 K and 350 K

Enthalpy increments measured with a flow calorimeter are reported for CO 2 at temperatures from 233.169 K to 358.140 K at pressures near 15 MPa. The reported values agree with literature values within the estimated uncertainties. Results for { xCO 2+(1- x)C 2H 6} are reported for x = 0.10, 0.25, 0.50, 0.74, and 0.90 at temperatures from 230 K to 350 K and at nominal pressures of 15 MPa and 18 MPa.

Enthalpy increments of {xCH3OH + (1-x)(CH3)2CO} between the temperatures 291 K and 610 K at pressures to 10 MPa

Enthalpy-increment measurements were made on {xCH3OH + (1-x)(CH3)2CO} along isobars from p = 500 kPa to p = 10000 kPa, in the temperature range 291.5 K to 600 K, using a reference-fluid boil-off calorimeter. For {xCH3OH + (1-x)(CH3)2CO}, measurements were made at x = 0.25, 0.50, and 0.75. In addition to the direct calorimetric results, the equation for the enthalpy increment of the liquid and of the vapor, as well as enthalpy-increment behavior in the supercritical region, are reported.

High-temperature enthalpy-increment measurements and derived heat capacity of lithium orthosilicate (Li 4SiO 4) at temperatures from 300 K to 1000 K

The enthalpy increments of lithium orthosilicate (Li 4 SiO 4 ) have been measured by drop calorimetry at temperatures from 300 K to 1000 K. In the enthalpy-against-temperature curve, a few humps were observed above 800 K. In order to derive corresponding heat-capacity values precisely from the enthalpies, a new analytical procedure (modified-QLLR method) was used. Three heat-capacity anomalies, which correspond to the humps in the enthalpy curve, were found at temperatures of about 885 K, 930 K, and 985 K.

Enthalpy increment measurements of NaCrO 2 using a high temperature Calvet calorimeter

Enthalpy increment measurements on NaCrO 2(s) were carried out in the temperature range 323 to 839 K using a high temperature Calvet micro calorimeter. The enthalpy increment values were least-squares fitted with temperature with the constraint that (H T 0 − H 298 0) at 298.15 K equals zero and can be given by: ( H T 0 − H 298 0)( J/ mol) ± 336 = −23515 + 75.364 T( K) + 0.01256 T 2( K) (323 to 839 K). The first differential of the above equation with temperature gives the constant pressure molar beat capacity of NaCrO 2(s), which is given by: C p 0( NaCrO 2, s, T)( J/ K mol) = 75.364 + 0.02512 T( K). The thermal properties of NaCrO 2(s) were calculated using the molar heat capacities from the present study and S 0(298 K) from the literature.

Thermodynamic properties of ternary oxides of fission products from calorimetric measurements

The alkaline earth elements barium and strontium, which are produced in a mixed oxide fuel during irradiation, can combine with other major fission products such as zirconium, molybdenum and cerium under favourable conditions of temperature and oxygen potential. As a part of our programme to investigate the thermodynamic properties of these fission product compounds, we have already reported thermodynamic data on BaZrO 3, SrZrO 3, BaMoO 4 and BaCeO 3. To complete the series, enthalpy increment measurements were carried out on SrCeO 3, SrMoO 4, CaZrO 3 and CaMoO 4 using a high temperature microcalorimeter. These data along with the derived thermodynamic functions are reported in this paper. The stabilities of the whole set of fission product compounds, under conditions of oxygen potentials and temperature prevalent in the mixed oxide fuel, are examined in the light of all the data mentioned above.

Enthalpy-increment measurements for CsI(s) and Cs 2CrO 4(s) by high-temperature Calvet calorimetry

Molar thermodynamic properties of CsI(s) and Cs 2CrO 4(s) have been evaluated by measuring Δ 298.15 K T H m o using a Calvet high-temperature calorimeter by a drop technique. The enthalpy increments were treated by least-squares analyses using the constraints that Δ 298.15 K T H m o at 298.15 K and C p,m (298.15 K) are equal to the reported literature values. Enthalpy increments for CsI(s) and Cs 2CrO 4(s) are represented for CsI(s) by Δ 298.15 K TH m o/( J·mol −1 ) = 43.53(T/K)+0.01178(T/K) 2−187100(K/T)−13398, (314 to 822 K) and for Cs 2CrO 4(s) by Δ 298.15 K TH m o/( J·mol −1 ) = 114.32(T/K)+0.05789(T/K) 2+247810(K/T)−40063, (333 to 822 K) The agreement between the interpolated and the input values is within ±0.25 per cent for CsI(s) and ±0.21 per cent for Cs 2CrO 4(s). Using the values of Δ 298.15 K T H m o, C p, m (298.15 K), and Δ 0 T S m o(298.15 K), C p, m (s, T) and Δ 0 T S m o have been evaluated.

Thermodynamic functions of barium and strontium zirconates from calorimetric measurements

Enthalpy increment measurements have been carried out on BaZrO 3 and SrZrO 3 in the temperature range 1030–1700 K using a high-temperature differential calorimeter. From the measured enthalpy increment values, other thermodynamic functions, such as heat capacity, entropy and free energy functions, of these compounds have been calculated. The free energies of formation of BaZrO 3 and the equilibrium barium partial pressures for the formation reactions have been computed and compared with literature data. The equilibrium strontium pressures for the formation reactions of SrZrO 3 have also been computed.