I thought some of you would be interested in the following article on
coolant. It is interesting, but long. I will post it in 4 parts so it
will not dominate the digest. The graphs work best if you set your
margins to 80 charecters.
Part 1 of 4
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This information in this article is copyright Texaco Inc., Texaco Magazine
LUBRICATION. This article may not be reproduced, copied, or retransmitted
in any form without express written consent of Texaco Inc.
- ------------------------------------------------------------------------------
ANTIFREEZE AND COOLANT
Courtesy of Texaco Magazine LUBRICATION
Copyright Texaco Inc.
Introduction
The popular definition of antifreeze is a liquid which prevents freezing
when mixed with water in an automotive cooling system. At one time this
definition was fairly adequate.
The modern antifreeze, however, does much more. It provides year-round
protection of the cooling system: It prevents freezeup in winter and
boilover in summer (especially in cars with air conditioning). It provides
protection from rust and corrosion and does not harm rubber hoses and
plastics. In addition, ethylene glycol-based antifreeze is relatively low in
cost, is chemically stable, does not have an unpleasant odor and does not
affect automotive finishes. Thus, the modern antifreeze is aptly called
"antifreeze and coolant" (AF&C). For convenience, the term "AF&C" will be used
throughout this article.
This article reviews the requirements, properties and characteristics of
modern AF&Cs, tests used to evaluate them and trends which will influence
future AF&C development.
AF&C Requirements
The performance requirements of AF&Cs became more severe during the 1980's.
What was once a commodity product, primarily aimed at providing freezing
protection for the cooling system of internal combustion engines, became a
complex product containing a delicate balance of additives designed to meet
many stringent requirements. The increased awareness of the importance of
AF&C was prompted by the introduction of more efficient engines operating at
higher temperatures, the use of light metals and plastics in the cooling
system and a growing concern relative to the toxicological and ecological
aspects of the AF&C itself.
The reduction of the overall mass of vehicles to improve fuel economy
entailed extensive use of light materials such as aluminum and plastics for
the construction of engine and cooling system parts. The volume of AF&C used
was also drastically reduced to further reduce weight, subjecting the AF&C to
high rates of flow, high temperatures and significant metal-to-coolant heat
fluxes.
Todays smaller, efficient and powerful engines dissipate more heat, requiring
that the AF&C keep the heat exchange surfaces in clean condition. In
addition, corrosion, which in itself is of concern, can also result in the
deposition of bulky corrosion products that will impede heat transfer.
Initial-fill user requirements and specifications are changing rapidly and
contain demands for a cooling fluid that is:
- an effective heat exchange fluid,
- capable of providing freezing and boiling protection,
- capable of protecting metals against corrosion,
- compatible with plastics and elastomers,
- chemically stable at low and high temperatures,
- compatible with hard water,
- low foaming and
- ecologically and tocicologically acceptable.
These requirements are met by the development of multicomponent AF&Cs that
provide a low freezing point, high thermal conductivity and specific heat,
good fluidity, elevated boiling point, low toxicity, good chemical stability
and a proper balance of supplemental additives. A corrosion inhibitor package
is usually present at a concentration of two to five percent. Other additives,
which may be present, include stabilizing agents to improve the hard water
stability of inhibitors that form insoluble calcium salts, sequestering
agents to inhibit deposit formation, antifoamants to inhibit excessive
foaming and a dye to characterize the product.
ETHYLENE GLYCOL CHARACTERISTICS
Overview
Water-ethylene glycol (EG) formulations are today's preferred AF&Cs because
they provide year-round, cost effective freezing, boiling and corrosion
protection. In addition, they are chemically stable and are compatible with
elastomers and plastics used in the cooling system.
The physical properties of water, methyl alcohol (CH3OH), 1,2-ethanediol or
ethylene glycol (EG), and 1,2-propanediol or propylene glycol (PG), the
compounds considered as AF&C bases, are shown in Table 1. Ethylene glycol is
the preferred AF&C base because of its high boiling point and flash point
compared to methyl alcohol and its lower viscosity (better fluidity) compared
to propylene glycol.
Table 1.
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Typical Physical Properties of Cooling System Compounds
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Property Water CH3OH EG PG
- ------------------------------------------------------------------------------
Specific gravity, 20/20C 1.000 0.7924 1.1155 1.0381
Specific heat, cal/g-C 0.998 0.6000 0.5740 0.6000
Freezing point: pure 0.000 -97.7000 -13.3000 *
Freezing point: 50% H2O mix -- -44.5000 -36.6000 -33.0000
Boiling point, C 100.000 64.5000 197.3000 187.2000
Vapor pressure, 20C, mm Hg 17.500 96.1000 0.1200 0.1800
Flash point, open cup, C -- 15.6000 115.6000 107.2000
Viscosity, cP
20C 1.000 0.6000 20.9000 60.5000
40C 0.650 0.4600 9.1000 19.3000
100C 0.280 -- 1.8000 2.6000
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* - Supercools
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Many raw materials such as crude oil fractions, naphthas, and natural gases
can be used in a light olefins unit to manufacture ethylene. Ethylene can be
reacted with oxygen to manufacture ethylene oxide, which, in turn, can be
reacted with water to produce ethylene glycol. About 10 million tons of
ethylene glycol are manufactured worldwide annually for use not only as an
AF&C base, but also as an industrial solvent and an intermediate in the
manufacture of polymers.
Heat Exchange
The capability of an AF&C to transport heat away from heat producing surfaces
is expressed in terms of the specific heat and thermal conductivity of the
fluid.
The specific heat of a substance is the ratio of its thermal capacity to that
of water at 15C (59F). Thermal capacity is the quantity of heat necessary to
produce unit change of temperature per unit mass. It is expressed as calories
per gram per degree Centigrade (cal/g-C).
Figure 1 shows the specific heats of solutions of EG in water at different
temperatures.
Figure 1. Specific Heats of solutions of ethylene glycol in water
at different temperatures.
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Ethanediol -40C -20C 0C 20C 40C 60C 80C 100C 120C 140C
- ------------------------------------------------------------------------------
0% - - 1.000 1.000 1.000 1.000 1.000 1.050 - -
10% - - .968 .970 .971 .975 .980 .990 - -
20% - * .925 .930 .937 .945 .955 .965 - -
30% - .850 .870 .885 .900 .915 .925 .938 - -
40% - .790 .820 .840 .860 .875 .890 .905 * -
50% * .730 .760 .790 .815 .835 .855 .870 * -
60% .645 .680 .710 .740 .770 .790 .812 .830 * -
70% .595 .630 .660 .690 .720 .750 .770 .790 .810 -
80% .550 .585 .620 .650 .680 .700 .725 .745 .765 *
90% * .545 .575 .600 .630 .650 .680 .700 .720 .740
100% * * .540 .560 .580 .600 .630 .650 .670 .695
- ------------------------------------------------------------------------------
- temperature is above/below boiling/freezing point, no data.
* data extends partway toward this temp, but not all the way.
===============================================================================
End of Part 1 of 4
Joe Dille
Telford PA USA
(joe@dille.montgomery.pa.us)
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