29 Apr 2005 12:59
Angående Redline Waterwetter
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Does it work? I cannot give a conclusive answer to that question. But I like "Water Wetter" and have been using it in all of my cars for many years now.
What I can say with conviction is that the person who wrote Redline's Technical Information brochure on "Water Wetter" knew what he or she was talking about. I have a Ph.D. in Heat Transfer and have taken a graduate course in Boiling and Condensation. Based on my training I can say that Redline's explanation of their product makes good scientific sense.
First we must dispel a common misconception: "Water Wetter" is not designed to lower your car's bulk coolant temperature. So if you put it in your E30 M3 hoping to see lower operational coolant temp's, then you will probably be disappointed.
"Water Wetter" is designed to reduce hot spots in your cylinder head. It does this by reducing the build-up of water vapor in any superheated areas. The bad thing about having hot spots in your cylinder head (read combustion chamber) is that they can promote pre-ignition - definitely a bad thing. This harks back to Smokey Yunick's theory of "soft combustion chambers". Any sharp edges in your combustion chamber (around valve seats for example) may tend to get very hot (even red hot) during operation. These areas of the combustion chamber can then form local hot spots in the cooling passages. Thus, even though your bulk coolant temperature is well below its boiling point (i.e. your gauge reads just fine), there may be localized boiling in some regions of the coolant tract.
This localized boiling can cause a layer of water vapor to form over the hot spot. This vapor forms an insulative blanket and prevents heat from leaving this area, thus making the hot spot even worse. But reducing the surface tension of the water makes it easier for vapor bubbles to leave the surface of the cylinder head and allows the bubbles to convect heat away from the area. Something that changes the surface tension of a liquid is called a "surfactant". It does not take very much surfactant to significantly change the surface tension of water. Hence, you do not need to add very much "Water Wetter" in order for it to do its job.
An additional benefit of using "Water Wetter" (in conjunction with 100% water) in you cooling system is that water has an extremely high heat capacity. Thus a gallon of 100% water can carry more heat away from you engine than an equivalent gallon of 50/50 water and coolant. Water also has a high thermal conductivity which increases the convection of heat away from the coolant passage walls and into the free stream of the liquid flowing through the passages.
"Water Wetter" does not increase the boiling point of water. Standard automotive coolant does increase the boiling point of the mixture above that of 100% water. But remember that if your cooling system is operating properly, it should never get hot enough to boil (I mean BOIL, not just localized boiling). Raising the boiling point of the coolant in passenger cars is primarily a safety measure, so that if the cooling system is over stressed (climbing a hill on a hot day with AC on), it will not boil over. on performance cars the primary duty of the cooling system is to keep the engine in its optimum temperature range. This is best accomplished with 100% water, because its high heat capacity makes it very efficient at transferring heat.
Performance cars often run relatively high cooling system pressures. This also raises the boiling point of the coolant. But the high system pressure is not used to avoid boiling so much as to allow the engine to operate at a higher temperature for reasons of efficiency. A higher cooling system bulk temperature also allows the use of a smaller radiator (there is a greater driving force to transfer heat from the coolant to the free stream air). Take a look at the E30 M3's "tiny" radiator and you will see what I mean.
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/ Niklas Sandström
BMW CS/SC
Understeer is when you hit the wall with the front of the car and oversteer is when you hit it with the back
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