Degraded Aqueous Glycoil Solutions: pH Values and the Effects of Common Ions on Suppression pH Decreases.
Degraded Aqueous Glycoil Solutions: pH Values and the
Effects of Common Ions on Suppression pH Decreases.
Clifton, J. R.; Rossiter, W. J., Jr.; Brown, P. W.
Solar Energy Materials, Vol. 12, No. 1, 77-86, 1985.
glycols; ions; ethylene glycol; propylene glycol; heat
transfer liquids; solar collectors; solar system;
thermal oxidative degradation; temperature; metals;
oxidation; thermal stability; copper; equations;
Aqueous solutions of ethylene glycol and propylene
glycol are used as heat transfer liquids in
flat-plate solar collector systems. Both of the glycols
are susceptible to thermal oxidative reactions,
which produce organic acids with a resulting decrease in
pH of the solutions. The effects of
temperature, metals, common ions and oxidation
conditions (aeration/deaeration) on the thermal
stability of the glycol solutions were evaluated based
on measuring changes in pH. Aerated heated
glycol solutions produced acidic solutions within 3360 h
(140 d) of testing, when in contact with
either metallic aluminum or copper. Common ions (anions
of the acid degradation products) were
effective in suppressing decreases in pH, especially
when aluminum was present.