Thermocouple psychrometry

Soil Science Society of America Book Series 5.4-3.2.3
By:  and 
Edited by: Jacob H. Dane and G. Clarke Topp



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 type Book chapter
Publication Subtype Book Chapter
Title Thermocouple psychrometry
Series title Soil Science Society of America Book Series
Series number 5.4
Chapter 3.2.3
ISBN 978-0-89118-893-3
DOI 10.2136/sssabookser5.4.c22
Year Published 2002
Language English
Publisher Soil Science Society of America
Publisher location Madison, WI
Contributing office(s) Nevada Water Science Center, Toxic Substances Hydrology Program
Description 34 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title Methods of Soil Analysis: Part 4 Physical Methods
First page 609
Last page 642
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