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Water Condensation on Peltier‐Cooled Thermocouple Psychrometers: A Photographic Study 1
Author(s) -
Wiebe Herman H.
Publication year - 1984
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1984.00021962007600010041x
Subject(s) - thermocouple , thermoelectric effect , drop (telecommunication) , condensation , materials science , thermoelectric cooling , coalescence (physics) , mechanics , analytical chemistry (journal) , thermodynamics , chemistry , composite material , electrical engineering , physics , astrobiology , engineering , chromatography
Abstract Water condensation on Peltier‐cooled thermocouple psychrometers (used to measure water potential) was observed and photographed under a microscope. Hundreds of minute droplets condensed on the entire junction within a second. As Peltier cooling continued these grew and coalesced, and after 1 min some 50 to 20 droplets uniformly covered the junction. After 5 min these had grown and merged into one (sometimes 2) large drop(s) that adhered to only part of the junction and to a lead wire. This drop grew by coalescence of the droplets that continued to condense on the junction until the drop eventually attained a constant diameter of about 0.3 mm, 6 times that of the junction. Evaporation during the psychrometric water potential measurement stage appeared uniform from the entire junction surface after short condensation times when it was covered with many small droplets. The two‐step procedure used to measure very low water potentials requires a large amount of condensed water. Poor psychrometric cooling is a hazard, however, if a drop only partly covers the junction after prolonged condensation times.