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post #14 of Old 05-05-2012
SlowButSteady
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Re: water flow GPM per HP of an engine?

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Originally Posted by JimsCAL View Post
More importantly, you forgot the rather significant heat in the exhaust. Basically the heat rejected is roughly split equally between the cooling water and the exhaust. So your cooling water estimate is about double what's needed.
Actually, I did think about it. But I assumed that the water and the exhaust gases would be at equilibrium by the time they got to the end of the system. That may not be true, strictly speaking. However, unlike a car, truck, or anything else with a dry exhaust, we're talking about a wet system. As such, the exhaust gases must be pretty close to thermal equilibrium with the water. If that weren't the case the hot gases would cause localized heating of the seawater. That would, in turn, cause precipitation of the calcium salts (i.e., "scale") all along the exhaust hose. While this definitely does happen at the mixing elbow, it's usually much less of a problem downstream (particularly after the water lift muffler). So, the heat of the exhaust gas may take some of the energy away from the engine, but not all that much.

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