Thermodynamic Properties Of Pure Water Research Articles

The hydrophobic effect: is water afraid, or just not that interested?

Our understanding of the hydrophobic effect has advanced greatly since 1990, with the help of experimental, theoretical, and computer simulation results. The key hydrophobic signature of positive ∆C°P and negative ∆S° at room temperature has been interpreted in light of the importance of solvent cavity creation, solvent-excluded volume, and solute–water intermolecular forces, along with some unusual thermodynamic properties of pure water. Application of the hydrophobic effect to the hydration of small nonpolar solutes, protein folding stability, and protein–ligand binding is discussed in detail in this review, with an emphasis on thermodynamic analyses and interpretations.

Evaluation of the PR, tc-PR, CPA, PC-SAFT and IAPWS-95 models in the predicting thermodynamic properties of pure water at the supercooled, compressed liquid, saturated liquid-vapor and superheat regions

This study provides a comprehensive understanding of the potential and limitations of the PR, tc-PR, CPA, PC-SAFT and IAPWS-95 equations of state in the prediction of thermodynamic properties of pure water. Using these equations of state (EoS), non-derivative properties, including entropy, enthalpy, internal energy, volume and derivative properties including heat capacity at constant pressure (∂H/∂T)P and constant volume (∂U/∂T)V, isobar expansivity (∂V/∂T)P, isothermal compressibility (∂V/∂P)T and speed of sound were calculated for water. The IAPWS-95 is a specialized formulation for water, which has great performance, but it shows limitation to the temperature and the pressure range where the parameters are fitted. At supercooled and compressed liquid region, the PR, tc-PR, CPA, and PC-SAFT models could not predict the properties well. At saturated liquid-vapor region, all of the equations of state lead to acceptable results for non-derivative properties; however, the CPA and PC-SAFT, as the associating type models, have limitations at the near-critical region. Accordingly, the parameters of these two models must be re-tuned to experimental data covering triple to the critical point. The PR, tc-PR, CPA and PC-SAFT models have a major shortcoming in predicting derivatives properties including (∂P/∂V)T, (∂P/∂T)V, (∂V/∂T)P and (∂V/∂P)T in all regions. Results showed that the tc-PR is a suitable EoS for predicting thermodynamic properties in saturated liquid-vapor and superheated regions. None of the models can predict the thermodynamic properties of pure water at the supercooled and compressed liquid region.

Properties of pure water and sodium chloride solutions at high temperatures and pressures: a simulation study

The structural and thermodynamic properties of pure water and sodium chloride solutions at high temperatures and pressures are studied by using molecular dynamics simulations and quantum molecular simulations. Properties are calculated as functions of temperature and pressure. The results show that the structure of pure water becomes looser as temperature increases from 298 to 400 K, with the collapse of the traditional tetrahedral structure. For sodium chloride solutions, the same collapse is also found with the increased concentration. Moreover, a critical point for the diffusion coefficient of and is evident when the temperature increases linearly under 100 atm. At the critical points, the ions are abnormally clustered, due to the weakly hydrogen-bonded water molecules. The cluster size of the ions is synchronous with the corresponding diffusion coefficients.

The speed of sound and derived thermodynamic properties of pure water at temperatures between (253 and 473) K and at pressures up to 400 MPa

The speed of sound in high-purity water has been measured in the temperature range (253 to 473) K at pressures up to 400 MPa. The experimental technique used was based on a double-path pulse-echo method with a single 5-MHz ultrasound transducer placed between two unequally spaced reflectors. The cell was calibrated in water at T = 298.15 K and p = 1 MPa against the speed of sound given by the 1995 equation-of-state formulation of the International Association for the Properties of Water and Steam (IAPWS-95) which, for that state point, has an uncertainty of 0.005%. Corrections for the effects of temperature and pressure on the path length difference are considered in detail. The estimated expanded relative uncertainty of the speed of sound determined in this work is shown to be between 0.03% and 0.04% at a confidence level of 95%. The density and isobaric specific heat capacity of water have been obtained in the temperature range (253.15 to 473.15) K at pressure up to 400 MPa by thermodynamic integration of the sound-speed data subject to initial values computed from IAPWS-95 on the isobar at p = 0.1 MPa. The speed of sound, density, and isobaric specific heat capacity were compared with IAPWS-95 with corresponding absolute relative deviations within 0.3%, 0.03%, and 1%, respectively at T ≥ 273.15 K and p ≤ 400 MPa; larger deviations, especially for heat capacity, were found at lower temperatures. The results imply that the uncertainties of properties computed from IAPWS-95 may be significantly reduced over the major part of the region investigated in this work.

SteamTablesGrid: An ActiveX control for thermodynamic properties of pure water

An ActiveX control, steam tables grid ( StmTblGrd) to speed up the calculation of the thermodynamic properties of pure water is developed. First, it creates a grid (matrix) for a specified range of temperature (e.g. 400–600 K with 40 segments) and pressure (e.g. 100,000–20,000,000 Pa with 40 segments). Using the ActiveX component SteamTables, the values of selected properties of water for each element (nodal point) of the 41×41 matrix are calculated. The created grid can be saved in a file for its reuse. A linear interpolation within an individual phase, vapor or liquid is implemented to calculate the properties at a given value of temperature and pressure. A demonstration program to illustrate the functionality of StmTblGrd is written in Visual Basic 6.0. Similarly, a methodology is presented to explain the use of StmTblGrd in MS-Excel 2007. In an Excel worksheet, the enthalpy of 1000 random datasets for temperature and pressure is calculated using StmTblGrd and SteamTables. The uncertainty in the enthalpy calculated with StmTblGrd is within ±0.03%. The calculations were performed on a personal computer that has a “Pentium(R) 4 CPU 3.2 GHz, RAM 1.0 GB” processor and Windows XP. The total execution time for the calculation with StmTblGrd was 0.3 s, while it was 60.0 s for SteamTables. Thus, the ActiveX control approach is reliable, accurate and efficient for the numerical simulation of complex systems that demand the thermodynamic properties of water at several values of temperature and pressure like steam flow in a geothermal pipeline network.

SteamTables: An approach of multiple variable sets

Using the IAPWS-95 formulation, an ActiveX component SteamTablesIIE in Visual Basic 6.0 is developed to calculate thermodynamic properties of pure water as a function of two independent intensive variables: (1) temperature ( T) or pressure ( P) and (2) T, P, volume ( V), internal energy ( U), enthalpy ( H), entropy ( S) or Gibbs free energy ( G). The second variable cannot be the same as variable 1. Additionally, it calculates the properties along the separation boundaries (i.e., sublimation, saturation, critical isochor, ice I melting, ice III to ice IIV melting and minimum volume curves) considering the input parameter as T or P for the variable 1. SteamTablesIIE is an extension of the ActiveX component SteamTables implemented earlier considering T (190 to 2000 K) and P (3.23×10 −8 to 10000 MPa) as independent variables. It takes into account the following 27 intensive properties: temperature ( T), pressure ( P), fraction, state, volume ( V), density ( Den), compressibility factor ( Z 0), internal energy ( U), enthalpy ( H), Gibbs free energy ( G), Helmholtz free energy ( A), entropy ( S), heat capacity at constant pressure ( C p ), heat capacity at constant volume ( C v ), coefficient of thermal expansion ( CTE), isothermal compressibility ( Z iso ), speed of sound ( VelS), partial derivative of P with T at constant V ( dPdT), partial derivative of T with V at constant P ( dTdV), partial derivative of V with P at constant T ( dVdP), Joule-Thomson coefficient ( JTC), isothermal throttling coefficient ( IJTC), viscosity ( Vis), thermal conductivity ( ThrmCond), surface tension ( SurfTen), Prandtl number ( PrdNum) and dielectric constant ( DielCons).

Equation of state taking into account dipolar interactions and association by hydrogen bonding: II—Modelling liquid–vapour equilibria in the H 2O–H 2S, H 2O–CH 4 AND H 2O–CO 2 systems

The CPAMSA equation of state proposed in Perfetti et al. [Perfetti, E., Thiery, R., Dubessy, J., 2008-this issue. Modelling liquid–vapour equilibria with an equation of state taking into account dipolar interactions and association by hydrogen bonding. I—Application to water and hydrogen sulphide. Chem. Geol.](2008-this issue) results in a better reproduction of the thermodynamic properties of pure water and pure hydrogen sulphide than obtained using the classical CPA or SRK equations of state along the vapour–liquid equilibrium. It considers three contributions. The first contribution represents the reference Van der Waals fluid which is modelled by the SRK cubic EOS. The second contribution accounts for association through hydrogen bonding and is modelled by a term derived from Cubic Plus Association (CPA) theory. The third contribution corresponds to the dipolar interactions and is modelled by the Mean Spherical Approximation (MSA) theory. This present paper extends the CPAMSA equation of state for multi components systems, thus simple mixing rules between dipolar molecules are proposed to model the H 2O–H 2S binary system using a symmetrical approach. Binary interaction parameters which steps in the cubic terms (i.e. the Van der Waals mixing rule) are optimized on experimental solubility data of gas in aqueous solutions. Calculated phase equilibria in the H 2O–H 2S, H 2O–CO 2, H 2O–CH 4 systems reproduced the experimental data within 7% of average accuracy. Except for the H 2O–CH 4 system, binary interactions parameters estimated by fitting experimental data are closed to zero.

Steam tables for pure water as an ActiveX component in Visual Basic 6.0

The IAPWS-95 formulation for the thermodynamic properties of pure water was implemented as an ActiveX component ( SteamTables) in Visual Basic 6.0. For input parameters as temperature ( T=190–2000 K) and pressure ( P=3.23×10 −8–10,000 MPa) the program SteamTables calculates the following properties: volume ( V), density ( D), compressibility factor ( Z 0), internal energy ( U), enthalpy ( H), Gibbs free energy ( G), Helmholtz free energy ( A), entropy ( S), heat capacity at constant pressure ( C p ), heat capacity at constant volume ( C v ), coefficient of thermal expansion ( CTE), isothermal compressibility ( Z iso ), velocity of sound ( VelS), partial derivative of P with T at constant V (d Pd T), partial derivative of T with V at constant P (d Td V), partial derivative of V with P at constant T (d Vd P), Joule–Thomson coefficient ( JTC), isothermal throttling coefficient ( IJTC), viscosity ( Vis), thermal conductivity ( ThrmCond), surface tension ( SurfTen), Prandtl number ( PrdNum) and dielectric constant ( DielCons) for the liquid and vapor phases of pure water. It also calculates T as a function of P (or P as a function of T) along the sublimation, saturation and critical isochor curves, depending on the values of P (or T). The SteamTables can be incorporated in a program in any computer language, which supports object link embedding (OLE) in the Windows environment. An application of SteamTables is illustrated in a program in Visual Basic 6.0 to tabulate the values of the thermodynamic properties of water and vapor. Similarly, four functions, Temperature(Press), Pressure(Temp), State(Temp, Press) and WtrStmTbls(Temp, Press, Nphs, Nprop), where Temp, Press, Nphs and Nprop are temperature, pressure, phase number and property number, respectively, are written in Visual Basic for Applications (VBA) to use the SteamTables in a workbook in MS-Excel.