Glycol Intro #1

Glycols are colourless, odourless liquids, whose viscosities increase with increasing molecular weights. Glycols have higher viscosities than water and they are less volatile. Ethylene and propylene glycols have little tendency towards crystallization when they are cooled. They generally freeze to form glassy solids, without sharply defined freeze points. The freeze points are taken at the point where crystallization is first observed, even though most of the material may still be in the form of a highly viscous liquid.

Mixtures of water and glycol freeze. Mixtures, like pure glycol freeze below the point of water, and have an extremely low tendency to crystallize. They solidify over a wide temperature range. Because of their good heat exchange properties, glycols have acquired considerable importance as heat transfer media and coolants. They may be used undiluted, but in most cases, it is preferable to use them mixed with water. Because glycols lower the freeze point, it is possible to produce aqueous heat transfer media for use as down as low as -20C and to provide customization frost proofing media down as low as -50C.

"SHRINKAGE" is a term associated with the known glycol affinity for water. When glycols are mixed with water, the resultant volume is less than the to starting volumes. For example, the shrinkage of a 50/50 ethylene glycol - water mix solution is 1.31%.

"BURST PROTECTION" is the term associated with the reduction of the expansion factor when a glycol and water solution freezes. Substantially less glycol is required to prevent bursting of he pipes than to prevent freezing. Major system equipment manufacturers recommend 10 to 30% glycol to provide burst protection.

Heat transfer efficiency is reduced when glycol is introduced into a system. Water is a very efficient heat transfer fluid, while glycol exhibits less efficiency than water, the final solution being dependent upon temperatures and glycol concentrations. In order to improve the scope of the application of the glycol and water mixtures, inhibitor packages are added, which reduce the corrosion attack and provide stabilization against oxygen attack.

Glycol Type	General Use Characteristics
ethylene glycol	main use as anti-freeze compounds
diethylene glycol	drying medium for gases and intermediate raw material
triethylene glycol	low toxicity bacteriocidal solvent
tetraethylene glycol	solvent and plasticizer
propylene glycol	non toxic anti-freeze and intermediate raw material
dipropylene glycol	oil solvent, hydraulic fluid, dye manufacturing
tripropylene glycol	ink solvent, lubricant, intermediate raw material