Well, that certainly complicates things. -- Mike "Rocket J Squirrel" Elliott 84 Westfalia: Mellow Yellow ("The Electrical Banana") 74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.) Bend, OR KG6RCR
On 12/12/2009 5:28 PM Keith Hughes wrote: >> Date: Sat, 12 Dec 2009 12:20:09 -0800 >> From: Jim Arnott <jrasite@EONI.COM> >> Subject: Re: About coolant >> >> Short answer: yes. Water transfer heat better than glycol. >> >> Longer answer: When I worked in aerospace about a century ago, one of >> my first assignments was process control for the heat treat area. We >> solution heat treated a bunch of aluminum. (Solution heat treat: >> <http://www.azom.com/Details.asp?ArticleID=2540 >> > This was done to soften the material for forming. To reduce >> residual stress, we used a quenchant of 20% polyalkalene glycol. This >> provided a slower quench than water. Quenching in water would have >> resulted in much more residual stress and distortion. Slower quench = >> slower heat transfer. >> >> Numbers here: >> http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html >> http://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html >> >> >> Water is about 14% more efficient at 220 deg F. >> >> Jim > > Uhm, well, you forgot the last half of the "longer answer"; Yes pure > *liquid* water has a higher specific heat than does glycol or > glycol/water mixtures. However, the glycol raises the boiling point > significantly, and *that* is the key parameter. When the cooling water > reaches the boiling point (i.e. when the system temperature results in a > system pressure greater than the reservoir cap bypass valve setpoint - > when water begins to dump into the overflow) then the dissolved gases > will begin to come out of solution. This causes two major problems, > both of which increase with additional temperature rise; cavitation in > the water pump, which reduces fluid flow, and a water/vapor mixture > (foam if you will) at the heat transfer interfaces (water/metal contact > point in the water jackets and radiator). Both of these result in a > dramatic reduction in cooling efficiency. So yes, as long as the > cooling water remains below boiling, pure water is better (for cooling, > not, certainly for corrosion) than water/glycol. In real life > operation, in hot climes, pure water is almost always the wrong choice > for a vehicle, like the stock Vanagon, with a pretty marginal cooling > system. > > Keith Hughes > '86 Westy Tiico (Marvin) in Phoenix > |
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