Document xYONDaYNBz9vY0Lwq9gY4JqQ

376 CHAPTER 21 1965-Guide AmJ Data Boole Secondary Coolants (Brines): 377. Rg. '11 ..Boiling Point and Condensation of Aqueous Solutions of Ethylene Glycol Rg. 12 .... Boiling : Point and Condensation of Aqueous ;' Solutions of Propylene Glycol two facts, namely, the proximity of. the values-for'propylene glycol to water (when compared with ethylene glycol) and-the' (act that propylene glycol values show a. maximum around the 70-75 percent concentration leveL This combination of factors makes it somewhat difficult to ascertain the propylene glycol content of solutions.by specific gravity measurements. Control by refractive index measurement or Kari Fischer analyms for water are the.perferred laboratory methods for determining the composition of propylene glycol .solutions.' ' ' .The conversion of specific gravity to density is'affected by multiplying the appropriate value from Fig. 13 or 14 t>y the .density of water at. the 60 F reference temperature -(62.37 Ibpercu ft). ... '' . ..Figs. 15 and 16 show the viscosity, in centipoises, as a func tion. p cp'mpoatioh at different temperature levels for ethylene and propylene glycol-water systems. The most notable consid eration in .these plots is the significantly higher viscosity for the propylene glyool solutions, particularly at low tempera: turesi : '.j ' .iFigs. 17.and 18 -give the specific heat values versus, tem: peraftire at. various concentrations for aqueous solutions of ethylene glycol 'and'propylene glycol These figures show that, oh:an equivalent percent by. weight hagin, propylene glycol solutions generally have,slightly higher values of specific bait than ethylene glycol, though solutions of either glycol are hot as efficient as water'alone for heat transfer applications. Figs.. 19.and 20;give the thermal conductivity 'rallies,as a functaon of tempe'raturefor various aqueous 'ethylene glycol and'propylene glycol solutions. These plots indicate .that]the thermal conductivity of'the glycols 'decrease with increase in temperature, but that dilution with water, offsets this effect to some degree. -Additional.physical property data can be obtained-upon request-from the various suppliers of ethylene glycol-and propylene glycoL . .: Approach to Corrosion Inhibition Commercial ethylene or propylene glycol, when pure, is generally less corrosive to the common metals of construction than water itself. Aqueous solutions of these glycols, however, assume the corrosivity of the water from which they are pre pared and may become increasingly corrosive with use, if not properly inhibited. -This is because glycols, like most other organic compounds,.are subject to oxidation by air to acidic end products- The amount of oxidation is influenced by such factors as temperature, the'degree of aeration, and, to'some extent, even the particular combination of metal components to which the glyool solution is exposed. . " As pointed'out in the reference literature,*'' the concept'of corrosion inhibition is, perhaps,. most easily understood in fundamental terms by classifying additives either as: (a) corrosion inhibitors or (b) environmental stabilisers and ad justers. Corrosion inhibitors are considered to function by forming a surface barrier which protects the metal from attack. These barriers are usually formed by mechanisms such as adsorption of the inhibitor by the metal, dr by reac tion of the'inhibitor with the metal or perhaps the incipient reaction product. In most cases, the metal surfaces are covered by films of their oxides, and the inhibitor serves to reinforce tfiifl film Rg.' 14 .... Specific Gravity ' of Aqueous. Solutions . of ' Propylene Glycol Environmental stabilisers or adjusters, while not corrosion inhibitors in the strict sense of the word, function to decrease corrosion by stabilising or favorably altering the1' overall environment. An alkaline buffer, such- as borax, is a .simple PTrampb*, since its prime, purpose is to maintain an .alkaline condition,(pH.above 7).-Some chelating agents may. function asstabilisers by removing from the solution certain deletenpua ions that might otherwise act to accelerate the corrosion; process or mechanism; however caution must-be exercised.in, their use.- - Rg^'lS ;.. .-Vbcosity<-of'<Aqueous^-Solutior(s of Ethylene' Glycol-^ ` Rg. 16;... Absolute Viscosity of Aqueoui Solutions of Propylene Glycol