Part 2 of 4
===============================================================================
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.
Figure 2 shows the thermal conductivities of solutions of EG in water at
different temperatures.
Figure 2. Thermal conductivities of solutions of ethylene glycol in water
at different temperatures.
===============================================================================
Ethanediol -40C -20C 0C 20C 40C 60C 80C 100C 120C 140C
- ------------------------------------------------------------------------------
0% - - .00132 .00142 .00150 .00156 .00160 .00163 - -
10% - - .00123 .00132 .00139 .00144 .00147 .00148 - -
20% - * .00118 .00124 .00128 .00131 .00133 .00134 - -
30% - .00107 .00111 .00115 .00118 .00120 .00121 .00121 - -
40% * .00102 .00105 .00107 .00108 .00109 .00109 .00109 * -
50% * .00100 .00100 .00100 .00100 .00100 .00099 .00098 * -
60% .00094 .00094 .00093 .00093 .00092 .00090 .00089 .00087 * -
70% .00091 .00089 .00088 .00086 .00084 .00082 .00080 .00078 .00076 -
80% .00086 .00084 .00082 .00080 .00078 .00075 .00072 .00069 .00066 *
90% * .00080 .00077 .00074 .00071 .00068 .00065 .00062 .00058 .00054
100% * * .00073 .00069 .00065 .00062 .00058 .00054 .00051 .00048
- ------------------------------------------------------------------------------
- temperature is above/below boiling/freezing point, no data.
* data extends partway toward this temp, but not all the way.
===============================================================================
The thermal conductivity of a substance is the time rate of transfer of heat
by conduction (cal/sec) through a mass of unit thickness across a unit area
for unit difference in temperature. It is expressed as a
gram-calories-centimeter, per second-square centimeter-degree centigrade
(g-cal-cm/sec-cm2-C).
The heat exchange capacity of the EG/water solution is reduced with
increasing EG content. Water remains the better heat exchange fluid compared
to any mixture of EG and water. A compromise between the required freezing
protection and heat exchange efficiency has to be made.
The viscosity of the cooling fluid is also a factor in evaluating the overall
heat exchange efficiency. Lower viscosity (better fluidity) will aid heat
transport.
Figure 3 shows the viscosities of solutions of EG and water as a function of
EG concentration and temperature.
Figure 3. Viscosities of solutions of ethylene glycol in water as a
function of glycol concentration and temperature.
================================[Ethanediol by Weight]=========================
Temp 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
- ------------------------------------------------------------------------------
- -45.5C(-50F) - - - - - - 300.00 450.00 800.00 - -
- -34.4C(-30F) - - - - - 65.00 100.00 150.00 250.00 * -
- -28.8C(-20F) - - - - * 45.00 65.00 100.00 180.00 295.00 -
- -23.3C(-10F) - - - - 20.00 30.00 45.00 65.00 110.00 180.00 -
- -17.8C( 0F) - - - * 15.00 20.00 30.00 45.00 70.00 115.00 *
- -12.2C( 10F) - - - 8.00 11.00 15.00 22.00 30.00 48.00 75.00 130.0
- - 6.7C( 20F) - - 4.50 6.00 8.00 12.00 18.00 24.00 35.00 55.00 90.0
- - 3.9C( 25F) - * 3.50 5.00 6.50 9.50 15.00 20.00 30.00 45.00 70.0
10.0C( 50F) 1.50 1.80 2.40 3.00 4.00 5.50 7.50 10.00 15.00 22.00 35.00
37.8C(100F) .68 .85 1.20 1.50 1.80 2.50 3.00 4.00 5.00 7.00 12.00
66.0C(150F) .45 .55 .65 .80 1.00 1.20 1.80 2.00 2.50 3.50 5.00
93.0C(200F) .35 .38 .45 .52 .62 .78 .90 1.20 1.50 1.80 2.50
121.0C(250F) .30 .35 .40 .45 .50 .60 .70 .80 .80 .80 .70
149.0C(300F) - - - - - - - - - - -
177.0C(350F) - - - - - - - - - - -
- ------------------------------------------------------------------------------
- temperature is above/below boiling/freezing point, no data.
* data extends partway toward this temp, but not all the way.
===============================================================================
Aqueous EG solutions have higher viscosities at higher EG concentrations. A
better fluidity is thus obtained in solutions containing less freezing point
depressant.
Again, a compromise between freezing protection and fluidity has to be made.
Freezing Protection
Becasue of its low cost and good heat exchange properties, water was used
alone in the past as the coolant for internal combustion engines. However,
its relatively high freezing point is a serious disadvantage. When water
freezes, its volume expands about 9%. This change is enough to rupture a
radiator or even an engine block.
The freezing point depressing properties of aqueous EG solutions are shown in
Figure 4. At about 68% volume solution, the extrapolated eutectic point,
freezing is at its maximum at about -69C (-92F). Solutions having a
concentration either higher or lower than this concentration offer less
freezing protection. Pure EG has a freezing point of -13.3C (+8F).
Figure 4. Freezing Points of solutions of ethylene glycol
AF&C in water.
===============================================================================
0C| *
| *
- -10C| *
| *
- -20C| * *
| * *
- -30C| * *
| * *
- -40C| * *
| *
- -50C| *
| * *
- -60C| _ _ _ _ _ _ _* _ _ _ _ <-- data points below this line are
| . extrapolations. A 68% volume
- -70C| . solution gives maximum freezing
| . protection at the extrapolated
+----+----+----+----+----+----+ eutectic point.
0% 20% 40% 60% 80% 100%
[ ethanediol, % by volume ]
===============================================================================
A formulated EG AF&C concentrate (before dilution with water for use) has a
freezing point of approximately -18C (0F), depending on its EG content. Apart
from the EG base, it will contain corrosion inhibitors, defoamers,
stabilizing agents, dye, and some water.
EG solutions do not solidify when exposed to temperatures several degrees
below their freezing point. After the appearance of the first ice crystals,
the liquid portion becomes more concentrated and its freezing point is thus
lowered. A further decrease in temperature will cause more crystallization
until a thick ice slush is formed. The slushing phenomenon permits the AF&C
to still flow as it expands. Although this behavior almost eliminates the
danger of freeze-cracking of the engine block, other cooling problems may
result. For example, overheating, boiling and engine damage may occur if a
thick slush forms that cannot circulate through the radiator. Consequently,
the lowest temperature at which an aqueous EG solutions provides freezing
protection and properly functions as an AF&C is the temperature when
crystallization initiates and the AF&C is still a thin ice slush.
Figure 5 shows experimentally determined freezing point curves for an EG AF&C.
Curves are shown indicating the temperatures at which the first ice crystals
are formed, at which the AF&C is a thin ice slush and at which the AF&C will
not flow (at its pour point).
Figure 5. Frost Protection by ethylene glycol AF&C solutions;
temperature at which the solution is still a thin
fluid ice slurry.
===============================================================================
Frost Protection
===============================================================================
CCV First Ice Crystals Fluid Ice Slurry Pour Point
- ------------------------------------------------------------------------------
0% 0C 0C 0C
10% -3C -4C -5C
20% -8C -10C -12C
30% -15C -18C -20C*
40% -25C -28C -31C
50% -35C -40C -46C
===============================================================================
CCV = Coolant Concentration % Volume
* = Freezing protection up to -20C ca. 33% vol. engine coolant
===============================================================================
In practice, depending upon the climate, freezing protection ranging from -20
to -40C (-4 to -40F) will be required. EG AF&C is therefore generally used in
concentrations ranging from 33 to 50 volume %.
Boiling Protection
As engine efficiency is increased, partly by increasing engine temperature,
more heat must be rejected through the cooling system. Additional cooling
can be provided by increasing the cooling system pressure and by allowing the
AF&C to circulate at a higher maximum temperature. The elevated boiling point
of EG AF&C relative to water is important because it reduces evaporation
losses, water pump cavitation caused by flash boiling on the suction side of
the pump and after-boil caused by residual heat from a shut-off engine.
Table 2 shows the boiling points of various concentrations of EG at
atmospheric pressure and at 103kPA (15psig). Figure 6 shows the boiling points
of EG at different concentrations in water at different temperatures.
Table 2.
===============================================================================
Boiling Points of Various Concentrations of Ethylene Glycol
===============================================================================
EG Concentration (Vol. %) Atmospheric Pressure System Pressure (103kPa)
- ------------------------------------------------------------------------------
33 104C (219F) 125C (257F)
44 107C (224F) 128C (262F)
50 108C (227F) 129C (265F)
60 111C (232F) 132C (270F)
70 114C (238F) 136C (276F)
===============================================================================
Concentrations higher than 70 percent are not recommended; 68% provides
maximum freezing protection, about -69C (-92F).
===============================================================================
Figure 6. Boiling points of ethylene glycol solutions in water at
different pressures.
===============================================================================
Boiling Points of Aqueous Ethanediol Solutions
===============================================================================
Ethanediol 0psig 4psig 8psig 12psig 16psig 20psig 24psig
- ------------------------------------------------------------------------------
Water 212F 225F 233F 242F 252F 260F 265F
33% 220F 230F 240F 253F 260F 268F 273F
44% 224F 234F 245F 257F 265F 272F 279F
50% 226F 236F 248F 259F 267F 275F 280F
60% 231F 241F 253F 264F 273F 280F 285F
===============================================================================
ADDITIVE TECHNOLOGY
Overview
Uninhibited solutions of EG and water are corrosive to the metals contained
in engine cooling systems, requiring the addition of an effective corrosion
inhibitor package. These additives have to be compatible with the plastics
and elastomers used as engine or cooling system components, but will also
produce insoluble corrosion products that will tend to block radiator
passageways, thermostat valves, etc. and impede heat transfer by deposition
on heat exchange surfaces.
The metals that need to be protected are of four main classes:
1) iron, steel and grey cast iron
2) aluminum alloys in cast and wrought forms
3) copper and brass
4) lead based solders
Grey cast iron has been the traditional meterial for cylinder blocks, heads
and liners, but is being replaced by lighter aluminum alloys that have better
thermal conductivity. Traditional copper or brass radiators are also being
replaced by aluminum radiators with crossflow plastic tanks. However,
heavy-duty diesel engine systems continue to use the more traditional
materials. Steel, cast iron and copper alloys are also used in more
progressive designs of component parts such as cooling pump impellers and
thermostats. This means that several inhibitors are required in a balanced
formulation to protect the aluminum, steel, cast iron, copper, solder and
brass cooling system components it might encounter in service.
In modern engine cooling systems, a variety of corrosion problems are of
concern, such as:
- pitting in radiator tubes,
- crevice corrosion in cylinder head packings,
- deposition of corrosion products,
- cavitation in coolant pumps and cylinder liners, and
- high temperature corrosion in cylinder heads.
Many standard industry tests and modern electrochemical techniques are used
to help identify corrosion inhibitors to solve these problems and optimize
the selection of inhibitor combinations.
End of Part 2 of 4
Joe Dille
Telford PA USA
(joe@dille.montgomery.pa.us)
Joe Dille
Telford PA USA
(joe@dille.montgomery.pa.us)
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:08:48 EDT