Preface "An historical perspective on the development of the Thermodynamic Equation of Seawater – 2010" (original) (raw)
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An historical perspective on the development of the Thermodynamic Equation of Seawater – 2010
Ocean Science, 2012
Oceanography is concerned with understanding the mechanisms controlling the movement of seawater and its contents. A fundamental tool in this process is the characterization of the thermophysical properties of seawater as functions of measured temperature and electrical conductivity, the latter used as a proxy for the concentration of dissolved matter in seawater. For many years a collection of algorithms denoted the Equation of State 1980 (EOS-80) has been the internationally accepted standard for calculating such properties. However, modern measurement technology now allows routine observations of temperature and electrical conductivity to be made to at least one order of magnitude more accurately than the uncertainty in this standard.
Thermophysical properties of seawater: a review of existing correlations and data
Desalination and Water Treatment, 2010
Correlations and data for the thermophysical properties of seawater are reviewed. Properties examined include density, specific heat capacity, thermal conductivity, dynamic viscosity, surface tension, vapor pressure, boiling point elevation, latent heat of vaporization, specific enthalpy, specific entropy, and osmotic coefficient. These properties include those needed for design of thermal and membrane desalination processes. Results are presented in terms of regression equations as functions of temperature and salinity. The available correlations for each property are summarized with their range of validity and accuracy. Best-fitted new correlations are obtained from available data for density, dynamic viscosity, surface tension, boiling point elevation, specific enthalpy, specific entropy and osmotic coefficient after appropriate conversion of temperature and salinity scales to the most recent standards. In addition, a model for latent heat of vaporization is suggested. Comparisons are carried out among these correlations, and recommendations are provided for each property, particularly over the ranges of temperature and salinity common in thermal and/or reverse osmosis seawater desalination applications.
Thermodynamic properties of standard seawater
2009
(p, ρ, T) data of standard seawater with practical salinity S≈35 (corresponding to an absolute salinity S A ≈35.16504 g/kg) measured at T =(273.14 to 468.06) K and pressures up to p=140 MPa are reported with an estimated experimental relative combined standard uncertainty of 0.006% in density. The measurements were made with a newly constructed vibration-tube densimeter. The system was calibrated using doubledistilled water, methanol and aqueous NaCl solutions. An empirical correlation for the density of standard seawater has been developed as a function of pressure and temperature. This equation of state was used to calculate other volumetric properties such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, internal pressure and secant bulk modulus. The results can be used to extend the present equation of state of seawater to higher temperature as a function of pressure.
Desalination, 2016
In a previous paper, the authors have given correlations for seawater thermophysical properties as functions of temperature and salinity, but only for near atmospheric pressures. Seawater reverse osmosis (SWRO) systems operate routinely at pressures of 6 MPa or more; however, experimental data for seawater properties at elevated pressures (P = 0.1–12 MPa) are limited to a salinity of 56 g/kg. To accurately model and design SWRO and thermal desalination systems, a reliable method of estimating the effect of pressure on seawater properties is required. In this work, we present this method and new correlations for seawater thermophysical properties that are valid within the range: t = 0–120 °C, S = 0–120 g/kg, and P = 0–12 MPa. Seawater isothermal compressibility data, available until a salinity of 56 g/kg, were used to develop a correlation for compressibility that is extrapolated to 160 g/kg. Thermodynamic identities were then used to develop accurate pressure dependent correlations for seawater: density, isobaric expansivity, specific heat capacity, enthalpy, entropy and Gibbs energy. New correlations were proposed for seawater: vapor pressure, thermal conductivity and activity of water. Recent work on seawater surface tension and osmotic coefficient were reviewed. Uncertainty bounds were calculated for each correlation.
The relative conductivity and density of standard seawaters
Deep Sea Research, 1977
Dear Editors, AT THE last meeting of the UNESCO (United Nations Educational, Scientific and Cultural Organization) Joint Panel of Experts for Oceanographic Tables and Standards, POISSON (197S) reported on his comparison measurements of different batches of standard seawater relative to KCl. He found a maximum deviation of the conductivities equivalent to an apparent salinity deviation of almost O.otroo at 25°C. These differences are in reasonable agreement withthe earlier conduetivity measurements of PARK (1964). The panelconsidered that these findings are serious and recommended that theseresults need to bereconfirmed by other laboratories.
Improved seawater thermodynamics: How should the proposed change in salinity be implemented?
The SCOR/IAPSO Working Group 127 on the “Equation of State and Thermodynamics of Seawater” is charged with providing improved algorithms and descriptions of the thermodynamic properties of seawater. The working group has made significant progress on many of its goals, and it is now time to seek the advice of the oceanographic community regarding the best practical ways of adopting these developments into oceanographic practice. The Working Group has met twice to date, once in Warnemünde in 2006, then in Reggio Calabria in 2007. Our next meeting is in Berlin in September 2008. The working group will soon provide the most accurate algorithms to date for the thermodynamic properties of seawater (such as density, entropy, enthalpy, specific heat capacity, etc). In order to achieve such accuracy it became evident that a salinity variable is required that more accurately represents absolute salinity than does the conductivity-based Practical Salinity. Spatial variations in the composition...
Ocean Science Discussions, 2008
A new seawater standard has been developed for oceanographic and engineering applications that consists of three independent thermodynamic potential functions, derived from extended distinct sets of very accurate experimental data. The results have been formulated as Releases of the International Association for the Properties of Wa-5 ter and Steam, IAPWS (1996IAPWS ( , 2006IAPWS ( , 2008 and are to be adopted internationally by other organizations in subsequent years. In order to successfully perform computations such as phase equilibria from combinations of these potential functions, mutual compatibility and consistency of these independent mathematical functions must be ensured. In this article, a brief review of their separate development and ranges of 10 validity is given. We analyse background details on the conditions specified at their reference states, the triple point and the standard ocean state, to ensure the mutual consistency of the different formulations, and we consider the necessity and possibility of numerically evaluating metastable states of liquid water. Computed from this formulation in quadruple precision (128 bit floating point numbers), tables of numerical 15 reference values are provided as anchor points for the consistent incorporation of additional potential functions in the future, and as unambiguous benchmarks to be used in the determination of numerical uncertainty estimates of double-precision implementations on different platforms that may be customized for special purposes.
Extended equation of state for seawater at elevated temperature and salinity
Desalination, 2010
To the Gibbs function for seawater endorsed in 2008 by the International Association for the Properties of Water and Steam (IAPWS), an extension to higher temperature and salinity has been developed, based on density measurements at atmospheric pressure, temperatures up to 90°C and absolute salinities up to 70 g/kg, as recently published by . In the range considered, the standard uncertainty in density of those data is less than 7 ppm. The new extension improves the applicability of the current standard formulation to hot seawater concentrates as encountered in desiccating seas or desalination plants, and maintains numerical consistency with most of the data used for the original formulation within their experimental uncertainties. Absolute salinity is expressed in the Reference-Composition Salinity Scale of 2008, temperature in the International Temperature Scale of 1990, ITS-90.