[Dave_C]

Hi,

A strange circumstance happened at work and I can't figure it out. We have a 50/50 mix of ethylene glycol and water in a 200 gallon tank which was set at 35 degrees F and was used for circulating through condensors.

It had a 1 1/2" closed cell insulation lid which had lifted as the water rose, exposing it to the muddy water pouring in the building. Two days later when the basement drained, my workers and I were amazed to find that the exposed tank was completely in tact, not a speck of muddy water in it.

It stayed just the way it was before the flooding.

Can anyone explain that?

Thanks,
Dave Christofferse

Edit: I will add that the fact that we shouldn't edit to cover our mistakes, I regret it.

[pgk]

This results from combination of many factors and it is a nice example of how chemistry works in nature.
1). The density of a fluid depends on the temperature. Thus, fluid amounts of different temperatures form two layers; an upper and a lower layer according lower/higher density). Among others, the latter explains the temperature inversion in big cities during intense air pollution.
Therefore, the solution of ethylene glycol /water 50/50 w/w and muddy water cannot initially be mixed.
2). A solution of ethylene glycol /water 50/50 w/w (cooling liquid) has density > 1.1 gr/cm3 at 35oF ≈ 1.67oC which is quite higher the density of muddy water. Therefore, the solution of ethylene glycol /water 50/50 w/w forms the lower layer and muddy water forms the upper layer. Otherwise, muddy water would penetrate into the tank by pouring the cooling liquid out of the tank.
3). After thermal equilibrium by contact heat transfer, the two layers are mixed up. But this is not instant. If you slowly add warm water into a half-filled glass with cold water and then, touch the top and the bottom of the glass, you will observe that thermal equilibration takes time.
In the given case and assuming that the tank is thermally insulated, the lid of Φ = 1 1/2" represents a small contact surface area that does not permit a quick thermal equilibration of such amounts of liquids.
4). Due to irregularity of water thermal expansion, water density at 0-4oC is higher than above 4oC. Among others, the latter explains how underwater sea life is kept under ice, in frozen seas.
Therefore, even if the temperature of the tank would start to rise, mixing muddy water and cooling liquid would be more difficult.
5). When a concentrated aqueous solution of a water soluble organic material is mixed with a saturated aqueous solution or dispersion of minerals, solid sedimentation and separation of liquids immediately starts. Among others and according this principle, glycerol is removed from soaps, by addition of NaCl after saponification.
Therefore, even if an amount of muddy water would penetrate into the tank, mud particles would immediately precipitate in the bottom of the tank that wouldn’t easily be observed, together with formation  of clear solution and a thin layer of ethylene glycol.

[Dave_C]

Hi pgk,

Thanks for the answer.

Dave