Internal pressure measurements of the binary 0.7393H₂O + 0.2607NH₃ mixture near the critical and maxcondetherm points

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• 作者：Nikolai G. Polikhronidi ; Rabiyat G. Batyrova ; Ilmutdin M. Abdulagatov ; Genadii V. Stepanov
• 关键词：Critical point ; Internal pressure ; Isochoric heat capacity ; Maxcondetherm point ; Thermal-pressure coefficient
• 刊名：Fluid Phase Equilibria
• 出版年：2010
• 出版时间：25 May 2010
• 年：2010
• 卷：292
• 期：1-2
• 页码：48-57
• 全文大小：794 K

文摘

The pressure, P, and their temperature derivative (∂P/∂T)_V, of binary mixture 0.7393H₂O + 0.2607NH₃ has been measured in the near- and supercritical regions. Measurements were made in the immediate vicinity of the liquid–gas coexistence curve (one- and two-phase regions) using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter. Measurements were made along 40 liquid and vapor isochores in the range from 120.03 kg m⁻³ to 671.23 kg m⁻³ and at temperatures from 403 K to 633 K and at pressures up to 28 MPa. Temperatures at the liquid–gas phase transition curve, T_S(ρ), for each measured density (isochore) were obtained using the quasi-static thermograms technique. The expanded uncertainty of the pressure, P, and temperature derivative, (∂P/∂T)_V, measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 0.05 % and 0.12–1.5 % (depending on temperature and pressure), respectively. The direct measured pressures, P, and temperature derivatives, (∂P/∂T)_V, has been used to calculate the internal pressure (or energy-volume coefficient) as (∂U/∂V)_T=T(∂P/∂T)_V−P. We also measured the temperature derivatives of the internal energy (∂U/∂T)_V=C_V (isochoric heat capacity) using the same apparatus. The measurements were made at isochoric heating of the system at quasi-equilibrium conditions. The effect of pressure, temperature, and concentration on the internal pressure was studied. The measured values of pressure (P_S), temperature derivative, (∂P/∂T)_VS, temperature (T_S) and density (ρ_S) at the saturation curve together with isochoric heat capacity measurements were used to calculate other thermodynamic properties of the mixture at the bubble- and dew-pressure points curves. Some unusual “appendix type shape” behavior of the (∂P/∂T)_V and internal pressure, P_int, near the critical and maxcondetherm points (in the retrograde region) was found.