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Re: Pumps
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Posted by Sjer (more from Sjer) on Sun, 3 Feb 2002 13:25:00 Share Post by Email
In Reply to: May be too fanatic?, Cedar White, Sat, 2 Feb 2002 22:17:37
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I spec pumps used in industrial process applications as part of my job. Higher viscosities reduce the pump flow because of higher pressure drop in the coolant passages. (If you look at a centrifugal pump curve, you will see the flowrate drops as the backpressure on the pump increases.) As you point out, not really a concern at start-up, except that it makes the engine harder to start. The components of the pump (impeller, shaft, bearings, etc.) can handle any reasonable viscosity that may be seen w/ coolant. The pump life is more influenced by overly high operating temperature.

One of the reasons for keeping the ethylene glycol down to 50% is viscosity, but not for the reason you might think. Heat transfer rate goes way down as ethylene glycol fraction is increased, because of the higher viscosity and lower thermal conductivity of ethylene glycol vs water. Also the water pump delivers higher flow when a higher percent of water is present as I mentioned earlier. So for all these reasons a 50/50 mixture provides better cooling than 70/30 mixture. Also, higher amounts of ethylene glycol make coolant mixtures more prone to leaking through seals.

Viscosity is critical in lubricants because the pumped oil provides the lubrication. Viscosities outside the desired range result in poor lubrication, especially on the high side.

Hope this is of interest, I did not mean to be overly critical.



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