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A few words about pumps and flow rate. - Page 4

post #31 of 74
Thread Starter 
Quote:
Originally Posted by Martinm210 View Post

I understand the "nearly"incompressible fluid part, and not arguing that the tubing in our loops probably store much of this energy, but the energy is there and produced by the pump. A block can not produce energy, it can only consume energy through friction. The pump is the only item creating hydraulic energy in a loop.

Well now you're just reiterating what i've said xD
Quote:

Understanding pressure head and head loss is the basis for designing any pump or hydraulic system so saying a pump doesn't create pressure will only cause more confusion than help.. Friction is an energy loss and head loss is the tool we use to measure friction and pump head is the tool we used to understand how well a pump can overcome that friction. Without Head, we are lost.

I appeciate the technical discussion and information very much.
Cheers!
Martin

Now what you are saying is right for the most part.
Friction is a force, fluid shear stress creates an impedance to flow, head/pressure loss. it takes a certain amount of pressure to sustain that flow and the pump is the thing exerting that pressure. It may be the driving force but it is not "trying" to create pressure. It is trying to create flow. It is pumping fluid, and in a theoretical loop with no resistance, it will have no pressure. The blocks resisting the flow essentially cause a back up, until the pump is exerting pressure to overcome fluid shear stress. System pressure is consequential, not inherent to the operation of the pump. And the pressure is not an energy, it is merely the consequence of force propagation. If there were no fluid shear there would be no pressure, as there is, the pressure acts as a mechanical couple allowing the pump to do work further down the loop. This is the correct way to think of it.
 
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post #32 of 74
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And yes, technical discussion is always a treat XD
 
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post #33 of 74
Quote:
in a theoretical loop with no resistance, it will have no pressure
This is the main difference between your perspectives. There is no such thing as no resistance; even if you could find some way of using the meissner effect on fluids, the water would still have to push against itself, creating pressure; no inertia to positive inertia means it resisted. Thus, a pump will always produce both flow and pressure.

Fluids don't compress much (negligible), but do compress a little. Since they compress enough to be measured, some (not much) of the kinetic energy provided from the pump changes into potential energy in the form of compressed liquid. In the grand scheme of things, that really doesn't mean squat.

Quote:
System pressure is consequential, not inherent to the operation of the pump.
I'd have to disagree here. Since the pump is designed to move water, the water itself is part of its inherent operation. If you want to get technical about the water not being part of the actual pump, here's the definition of inherent: "1.naturally a part or consequence of something.".


Here's a proof of concept: voltage without amperage is nothing, just as flow without pressure is nothing.
Quote:
If there were no fluid shear there would be no pressure, as there is, the pressure acts as a mechanical couple allowing the pump to do work further down the loop.
As I stated above, even without any external friction, water moving water causes restriction (from rest).

Quote:
This is the correct way to think of it.
I can't agree here. You're asking for people to think about the flow, but not pressure? I'd have to say the real world works in reverse to that: you think about the pressure and use that to determine flow. Just like how an electronic circuit is calculated by voltage drop, a fluid circuit is calculated by pressure drop.
post #34 of 74
Quote:
Originally Posted by YowZ View Post

Friction is a force, fluid shear stress creates an impedance to flow, head/pressure loss. it takes a certain amount of pressure to sustain that flow and the pump is the thing exerting that pressure. It may be the driving force but it is not "trying" to create pressure. It is trying to create flow. It is pumping fluid, and in a theoretical loop with no resistance, it will have no pressure.

This might be only semantics but I think of it the opposite way.
A pump is only creating pressure, it is merely trying to create pressure and nothing else. If that pressure is countered by equal opposite force (a.k.a. a plug in tbe hose) that pressure remains only as pressure. If you lessen the opposite force by taking out the plug, or getting a less restrictive block, that pressure is turned into flow. So the less restrictive your loop is, the larger amount of that pressure from the pump gets turned into flow.

But my bet is you will likely snear at this and reply something like "I'm not wrong on this, I'm an engineer"
Edited by PepeLapiu - 2/4/13 at 11:14am
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post #35 of 74
Thread Starter 
Electrocutor, we are talking in idealized terms, obviously in reality there is resistance to flow within the pump itself. The impeller does not try and squash the fluid, but displace it. Flow, not pressure. But these are minor details, I'm trying to convey the principle. You can argue specifics all you like. Martin is the right person for this as he has an extensive knowledge of the various pump available and their performance characteristics.

Fluids do compress alot, air is fluid, any gas is a fluid. The laws are the same for both liquids and gases.

There is no potential energy stored in a fluid, and compressing it does not store mechanical energy. It raises its temperature. As the molecules collide with the compressing body, there are billions of approximately elastic collisions. These collisions like a ball off a tennis racket add kinetic energy to the molecules and raise the temperature of the fluid. This is the work done during compression. As water is not readily compressible, there is little rise in temperature and it takes very little energy to raise its pressure.

Quote:
Here's a proof of concept: voltage without amperage is nothing, just as flow without pressure is nothing.
If you wish to use an electricity analogy, then you have voltage and amperage the wrong way round. voltage without amperage being akin to pressure without flow.
Quote:
I can't agree here. You're asking for people to think about the flow, but not pressure? I'd have to say the real world works in reverse to that: you think about the pressure and use that to determine flow. Just like how an electronic circuit is calculated by voltage drop, a fluid circuit is calculated by pressure drop.
Again, voltage is merely a driving potential, amperage is the actual movement of electrons. And you require both voltage and amperage to calculate energy. Voltage is not energy in the same way pressure in not energy.

PepeLapiu, other way around mate.
 
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post #36 of 74
Thread Starter 
Sorry if the energy thing was irrelevant in that part of the conversation. Got a bit hung up on what I was saying with Martin earlier xD
 
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post #37 of 74
Quote:
Originally Posted by YowZ View Post

There is no potential energy stored in a fluid, and compressing it does not store mechanical energy.

headscratch.gif

Explain compressed air.

Mechanical energy used in the compressor to increase the pressure in a storage tank.

Lots of potential energy stored in a can or tank of compressed air that can be released to power anything from tools to air horns.

Pressure can be considered a potential energy in this case.



To complicate matters in non-compressiblefluid flow there are two pressures; static and dynamic.

Static pressure is what you would read on a pressure gauge.

Dynamic pressure is the pressure contained in the kinetic energy in the flow. It is the pressure that you would see if you brought the fluid to a stop.

q = 1/2 * rho * v²

That looks a lot like the kinetic energy formula, Ek = 1/2 * m * v², the only difference being that q is per unit volume whereas Ek is for a discrete object.
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post #38 of 74
Quote:
air is fluid, any gas is a fluid. There is no potential energy stored in a fluid.
http://en.wikipedia.org/wiki/Compressed_air_energy_storage

Quote:
we are talking in idealized terms
Quote:
If you wish to use an electricity analogy, then you have voltage and amperage the wrong way round.
You missed the point. I know that voltage is to pressure as current is to flow, but the point does not change: flow without pressure is nothing and pressure without flow is nothing. There is no work without displacement. There can be no displacement without pressure even in an ideal scenario (the absence of all friction) because the water itself is initially not moving. The only way to remove the necessity of pressure is to remove the water itself.


If the entire world designs electronic circuits via voltage drop, and designs hydraulic circuits via pressure drop, why would you tell people to only be concerned with flow?

Quote:
Pumps do NOT create pressure. They create flow.
This is just silly. A pump creates both: the motor speed determines flow and the motor torque determines pressure.
post #39 of 74
Quote:
Originally Posted by YowZ View Post

Coolant and water, coolants are normally 97-99% water with additives, they're not gonna perform significantly better or worse than water.

Depends on what you mean "significantly".

I've been running my current build on pure distilled water for a week or so now and when doing Folding@Home (and Intel Burn Test), I noticed one set of temperatures. Yesterday I switched over to a Mayhem's Pastel dye, and while the ratio was 75% distilled water (and I can only assume that the vast majority of the remaining part, the pastel dye, was also "water"), my temperatures went up about 4-5C.

Exact same loop (RX360 radiator, Monsta 360 radiator, 2 GTX 580 Hydro Copper 2 video cards, Koolance i380 CPU block, and an XSPC Twin Dual D5 bay res with 2 D5 pumps set at 3), and two what I would consider pretty significantly different temperatures. And it's not like either of the radiators or the i380 CPU block are "highly restrictive".
post #40 of 74
Thread Starter 
GingerJohn, compressed air doesn't store energy the way a spring does, if you read back I already explain that the work done compressing a gas is converted to heat. Even if the gas is cooled and some of that energy is lost it is still under pressure and as it expands it cools, that energy is converted to mechanical energy by the turbine is passes through, air tool etc. either way it dissipates some of its heat during expansion, but does not store potential energy strictly speaking. Its ability to do work is no less significant of course.

Yeah, dynamic pressure was great fun when I was doing a module of jets and turbofans at uni. Creeping in my equations and causing all kinds of trouble xD.

Electrocutor, yes that is entirely accurate about pressure being needed for flow. But the pump itself is attempting to displace fluid not compress it or create a high pressure condition.
Once the fluid is moving, if it were in a vacuum it would continue to move without pressure, so excluding the conditions that occur within the pump itself (fluid momentum and internal resistance which both create an opposition to flow and therefore pressure), pressure is not necessary for flow. If it pleases you to think such a fair, and impeller attempts to move fluid, the fluid resists and then you have a newtons third law pair of forces and then the argument becomes which came first the chicken or the egg.

At no point did I say that pressure was irrelevant, merely that it is not what their pump is trying to achieve. I was also trying to create a short few paragraphs that would give people the right idea, this enormous discussion is going to be boring to alot of people and they aren't going to want to read all this.

47 Knucklehead, that's interesting to here. I didn't notice any difference in temps when I was running my loop on distilled water for a few days (use EK Blood Red and was waiting for it too ship). Perhaps an atmospheric condition or some kind of freak case. I couldn't say without more information. Either that or it makes more of a difference than I've had experience with. Either that or the pastel is significantly different in composition and thermal properties to most coolants? IDK
 
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