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Thermocouple psychrometry

January 1, 2002

Thermocouple psychrometry is a technique that infers the water potential of the liquid phase of a sample from measurements within the vapor phase that is in equilibrium with the sample. The theoretical relation between water potential of the liquid phase and relative humidity of the vapor phase is given by the Kelvin equation

Ψ = energy/volume = (RT/Vw) ln(p/po) [3.2.3–1]

where ψ is water potential (sum of matric and osmotic potential, MPa), R is the universal gas constant (8.314 × 10-6 MJ mol-1 K-1), T is temperature (K), Vw is molar volume of water (1.8 × 10-5 m3 mol-1), and p/po is relative humidity expressed as a fraction where p is actual vapor pressure of air in equilibrium with the liquid phase (MPa) and po is saturation vapor pressure (MPa) at T.

Publication Year 2002
Title Thermocouple psychrometry
DOI 10.2136/sssabookser5.4.c22
Authors Brian J. Andraski, Bridget R. Scanlon
Publication Type Book Chapter
Publication Subtype Book Chapter
Series Title Soil Science Society of America Book Series
Series Number 5.4
Index ID 70194882
Record Source USGS Publications Warehouse
USGS Organization Nevada Water Science Center; Toxic Substances Hydrology Program
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