Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater Hannes Schmidt Henning Wolf Egon Hassel.
Veröffentlicht von:Alma BöhmeGeändert vor über 2 Jahren
Präsentation zum Thema: "Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater Hannes Schmidt Henning Wolf Egon Hassel."— Präsentation transkript:
1 Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater Hannes SchmidtHenning WolfEgon Hassel
2 Content Introduction Motivation Approach Technical realisation Results Importance of thermo physical properties of seawaterSimplifications in calculation of thermo physical properties of seawaterMotivationPractical salinity and conductivityPossible inconsistencyApproachTraceability of salinity to densitySubstitution methodTechnical realisationDemands on equipmentDensity at atmospheric pressureDensity at high pressureResultsMeasurement resultsSummary
3 Importance of thermo physical properties of seawater /2000-years-of-global-temperatures-small.gif/climate_files/ClimateSimulation_ _IPCC2007.JPGMeasurement data is used for understanding and predictionof climate on long term scales.
4 Importance of thermo physical properties of seawater Thermohaline circulationConveyor beltDeviations in density – meaning salinity and temperature – are driving forces of subsurface currents (below 400 m).Surface currents are mainly driven by wind.
5 Simplification in calculation of thermo physical properties of seawater SourceTheoreticalMeasurandPressure,Temperature,ConductivityN-1 amounts of substancesResulting relation e.g. heat capacityConductivity replaces information on amounts of substances in calculations.
6 Possible inconsistency SourcesSimplification by using conductivityPractical salinity determinationsalt composition is changingsalt composition is changing (!)not all dissociated salts are contributing to conductivity (silicates,..)reference substance not certified (purity,..)Especially a change in salt composition can cause inconsistency.
7 Substitution MethodProcedureSea water density (Sample)Ultrapure water density (Reference)Seawater densityUltrapure water density…10 times…Ultrapure water1 bottle (200 ml) = 1 temperature = 8 hSeawaterSubstitution method decreases measurement uncertainty about factor 10.
8 Density at atmospheric pressure MeasurandSpecification rangeTemperature0..40 °CVAISALA1,013250,1 MPaREARMMS-BUSUSB0,1 MPaFRONTS-BUSVGA998,205FANRS232ETHAIR INAIR INCANA. Paar DMA 5000MSECONH2OSSWSSW Standard Sea WaterH2O Ultrapure WaterMeasurandMeasurement uncertainty (k = 2)Reproducibility (Std. deviation)Temperature5 mK1 mKPressure0.007 kPa0.002 kPaDensity0.002 kg/m3kg/m3
9 Density at high pressure (2) Teledyne ISCO 100DM Syringe pumpand controllerDHI RPM4 Pressure measuring unitDMA HP DensitometerDMA 5000M master device
10 Density (Seawater) in kg/m3 Density (Water) in kg/m3 Measurement results1.2 ppmUltrapure waterSeawaterSubstitution resultDensity (Seawater) in kg/m3Density (Water) in kg/m30.4 ppmTime in sSeawater measurement values were corrected by appr kg/m3.
11 SummaryCalibration and measurement routines for seawater have a risk of data inconsistency when data is collected over decades.The solution is tracing back salinity to density directly by high precision density measurements and electrolytic conductivity measurements.A fully automated density measurement device was built and measurement uncertainties of 2 ppm at 1 bar (20 ppm at > 1 bar) were reached.Atmospheric density measurements are finished and high pressure density measurements will start soon.