Quote:
Originally posted by Alchemy
Remember that there will also be a change in kinetic energy of the fluid if the suction and discharge lines are different sizes.
I assume you're quite familiar with the Bernoulli equation?
|
Many folks run closed systems with the same size tubing on both the suction and discharge. Depending on where you "cut the lines" to examine the system, the average fluid velocity may be the same. I'd agree that it is not uncommon to see port sizes vary with the discharge often a little smaller than the suction. And yeah, the Bernoulli equation is about as familiar as F=ma.
Quote:
Where else can energy enter the system if there is no CPU heat load?
Alchemy
|
In the literal sense, anywhere. There's no such thing as a perfect energy barrier. In a more practical sense, the CPU and pump are responsible for virtually all energy that you have to get out of the fluid eventually. What's comical is seeing some folks use pumps that are rated as high or higher than the energy used by a CPU. At some point people need to realize that the closer you get a fluid to ambient, the more it takes to close the gap further still. It's also possible to go over the top where a pump adds so much energy that your final CPU temperatures begin to climb. Yeah, we're talking tenths of a degree here, but when the differences are that small, what is the point of using an ever larger pump?
I got a good chuckle over your "work" comments above. People outside engineering aren't held to the definitions that we construct. Work is, after all, simply another measure of energy and it is only because someone decided to call the integral of F*d "work" that we use that definition as engineers. If Ben was an engineer, I would have expected him to say "energy" rather than "work". Us engineering geeks are the only ones really concerned about the distinctions between potential energy, kinetic energy, work, etc., etc.
I am a little confused by your final comments about friction/turbulence in water. I guess I want to separate your comment from what happens within a pump. In a pump there is a lot of wasted energy because of secondary flows that don't contribute to system flow. The best of centrifugal pumps max out well less than 100% efficient with many "pond pumps" running under 50% efficient. The excess energy put into the impeller that doesn't generate flow generates heat. This heat isn't heat transfer but rather due to non-useful "churning of the water". So in this respect, it really is the internal friction of the water. It is not, however, quite the same as the turbulence in as established flow stream. I think this is what you were getting at in your post.