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S herwood– R ayleigh parameterization for evaporation in the presence of surfactant monolayers
Author(s) -
Bower S. M.,
Saylor J. R.
Publication year - 2013
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.13792
Subject(s) - monolayer , oleyl alcohol , evaporation , stearic acid , pulmonary surfactant , chemistry , alcohol , chemical engineering , molecule , analytical chemistry (journal) , chromatography , organic chemistry , thermodynamics , biochemistry , physics , engineering
Presented here is an experimental investigation of the effects of several surfactant monolayers on evaporation driven by natural convection in the air above a water surface. Experiments were performed in a controlled laboratory setting with tanks of heated water for the following cases: (1) a clean water surface, and for surfaces covered with monolayers of (2) oleyl alcohol, (3) stearic acid, and (4) stearyl alcohol. Evaporation rates were measured using a laser‐based method, and the S herwood and R ayleigh numbers, Sh and Ra , were computed from the data. Power law scalings of the form Sh = B·Ra m were developed for each case which yielded, essentially, m = 1/3 for all four surface conditions. The oleyl alcohol and stearic acid conditions give essentially the same value for B as for the clean surface case. For stearyl alcohol, B is smaller than for all other surface conditions; this result is attributed to the ability of the stearyl alcohol monolayer to inhibit evaporation by blocking the passage of water molecules through the monolayer: the barrier effect. The surface temperature is measured in this work enabling a separation of the effect of surfactants on evaporation due to a reduction in surface temperature from their effect on evaporation due to a true barrier effect. This has not been accomplished heretofore. © 2012 American Institute of Chemical Engineers AIChE J, 59: 303–315, 2013