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Old 12-17-2008, 01:15 PM   #59
RickB
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
RE: Why semi-displacement (or semi-planing)?

"Geez Fred, where do you get this stuff?"

Been talking to Phil I think. FF is correct in saying pure water has better heat transfer characteristics than antifreeze but his figure is way off for the mixtures of water and glycol commonly used as engine coolant. The antifreeze mixture*transfers heat (thermal conductivity) at a rate of*around 85 to 95 percent that of water.

The thermal conductivity of pure water is .67 Watts per meter per degree K. Pure glycol is around .25 W/mK so a mixture of 50 percent glycol or less transfers heat at a rate pretty close to that of pure water. The dirt, *rust, and crud normally found in a poorly maintained cooling system will reduce heat transfer way more than glycol.
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