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How big is too big?

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gbaz

Member
Joined
Feb 23, 2003
Location
New Orleans LA.
At what point does a water pump get too big? I have seen 1000-3000gph pumps but dont recall ever seeing one in a water cooling set up. They produce too much heat? Will be looking into water cooling my hot box eventually, and just looking for more info.

Thanks
 

ZachM

Member
Joined
Oct 11, 2003
Yup, most of those big pumps produce a lot of heat, and are expensive. Unless you are doing a multi computer or huge radiator (i.e. 50' of copper pipe buried in the ground) you don't need a huge pump.
 

SureFoot

Member
Joined
Jun 6, 2004
Yeah the cooling performance increase of waterblocks / rads will be small but the heat dumped into the system by the pump will be greater: diminishing returns. And the noise, the size.. And practical difficulties such as bleeding air..
And a 300gph pump with a good head is a way better choice than a 1000gph with a poor head, because our systems offer a lot of restriction.
 
OP
gbaz

gbaz

Member
Joined
Feb 23, 2003
Location
New Orleans LA.
how bout a 1000gph pump with 14 feet of head :) they do produce alot of heat though... Mabey somewhere between 300 and 1000 will do, less noise also probably.
 

clocker2

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Dec 5, 2003
Location
Mile High
Moving the water too fast through the loop is counterproductive.
It needs to travel slowly enough through the blocks and radiator to pick up/shed the heat.
 

SureFoot

Member
Joined
Jun 6, 2004
clocker2 said:
Moving the water too fast through the loop is counterproductive.
It needs to travel slowly enough through the blocks and radiator to pick up/shed the heat.
Sorry this is totally wrong.
The total heat transfer is a positive function of the fluid velocity. Turbulence is also a positive factor. Consider that the heat transfer is a function of the total surface area between the hot body and the cold body. The greater the surface area, the greater the transfer.
So higher flow -> better heat transfer. ALWAYS. Radiator or waterblock, they function THE SAME WAY. You want a heat transfer between flowing water and a fixed metal surface. The direction has no importance - metal to water or water to metal.
Now, this is *not* a linear function, but more an inverse exponential function, i.e. gains are big at low flows, then the curve "flattens" as flow increases. Now those *small* gains at very high flows are counter-balanced by the heat dumped into the system by the more powerful pump. Heat production of the pump is a positive exponential, or at least polynomial, function of the flow. The higher the flow, the double higher the heat produced by the pump (random figure, just to make my point clear enough).
For the formulas backing this up, i'd point you to any thermics school manual.
Or for practical experience, and relative to our very topic, please read Bill Adams articles at overclockers.com and read his charts.

(edit) back to our topic, there is *definitely* a point where the gains turn to losses due to increased pump heat. It's placed quite high indeed - and serious tests show that most wateblocks gain little performance above a certain point which is reached with a 300-400gph pump (porovided the head is enough to get through the cooling loop)
 

clocker2

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Dec 5, 2003
Location
Mile High
SureFoot,
Sorry, but I must disagree.
My experience with the watercooling on racebikes showed that varying the speed of the waterflow (using restrictor plates) made all the difference in the world.
Modern GP bikes come with a selection of plates that have graduated opening sizes...the running temp is set by swapping out the plate.
You can verify the truth of this by removing the thermostat in your car.
Not only does the thermostat regulate the temp at which the water is allowed to freeflow through the entire sytem ( makes warm up faster), it is also a precisely calculated restrictor.
Removing this restriction will in most cases result in higher temps.
 

SureFoot

Member
Joined
Jun 6, 2004
clocker2 said:
SureFoot,
Sorry, but I must disagree.
Then you disagree with basic laws of thermodynamics, and with Physics. Please back up your point with relevant scientific proof. In the meantime, i highly suggest you read a book on thermodynamics (even a basic one will cover more than that), or the stickies of this forum, or maybe you take a peek at Bill Adams very thourough graphs at overclockers.com, which *all* contradict your case. Of course if you got real evidence, F1 / Indy race teams will be highly interested in your discoveries. Oh and NASA too.

clocker2 said:
My experience with the watercooling on racebikes showed that varying the speed of the waterflow (using restrictor plates) made all the difference in the world.
Waterflow where ? Restrictor plates placed where ? By pure speculation, aren't you confusing *velocity* and *flow* ?


clocker2 said:
Modern GP bikes come with a selection of plates that have graduated opening sizes...the running temp is set by swapping out the plate.
You can verify the truth of this by removing the thermostat in your car.
If i remove the thermostat, which is an *electrical* device, i will create an high impedance, which certainly will produce interesting results with the ECU, mostly throwing an error code..
But believe me: if i pinch a water hose somewhere, to restrict flow, i'm 100% sure that my car will overheat. Oh 110% sure, it happened to a friend for that very reason (hose clogged with gunk, low flow... overheated at the track)

clocker2 said:
Not only does the thermostat regulate the temp at which the water is allowed to freeflow through the entire sytem ( makes warm up faster), it is also a precisely calculated restrictor.
Removing this restriction will in most cases result in higher temps.
??? thermostat is a restriction ? if it's like in "it controls a vane that restricts flow so the car can warm up faster, then open up the vane when the car is hot" it means that higher flow cools better.

Another easy experience. Put two identical frying pans each on an electrical plate at full burn. Wait 5mn. Put the first frying pan under a *thin* stream of water, almost dripping. Place the second pan under a full flowing stream of water. Wait 5 seconds. On which pan do you want to put your hand ?
 
OP
gbaz

gbaz

Member
Joined
Feb 23, 2003
Location
New Orleans LA.
well one reason for a thermostat in any engine is that efficiency is related to the heat of the engine. The higher the heat the more efficent it is. So keeping the engine too cool is actually bad for it, but that would have nothing to do with heat transfer in a computer. Im not at home so dont have my old text books to pull the formulas out of to prove my self :(
 

eXCeSS

Member
Joined
Aug 25, 2003
Location
New York
SureFoot said:
Then you disagree with basic laws of thermodynamics, and with Physics. Please back up your point with relevant scientific proof. In the meantime, i highly suggest you read a book on thermodynamics (even a basic one will cover more than that), or the stickies of this forum, or maybe you take a peek at Bill Adams very thourough graphs at overclockers.com, which *all* contradict your case. Of course if you got real evidence, F1 / Indy race teams will be highly interested in your discoveries. Oh and NASA too.


Waterflow where ? Restrictor plates placed where ? By pure speculation, aren't you confusing *velocity* and *flow* ?



If i remove the thermostat, which is an *electrical* device, i will create an high impedance, which certainly will produce interesting results with the ECU, mostly throwing an error code..
But believe me: if i pinch a water hose somewhere, to restrict flow, i'm 100% sure that my car will overheat. Oh 110% sure, it happened to a friend for that very reason (hose clogged with gunk, low flow... overheated at the track)


??? thermostat is a restriction ? if it's like in "it controls a vane that restricts flow so the car can warm up faster, then open up the vane when the car is hot" it means that higher flow cools better.

Another easy experience. Put two identical frying pans each on an electrical plate at full burn. Wait 5mn. Put the first frying pan under a *thin* stream of water, almost dripping. Place the second pan under a full flowing stream of water. Wait 5 seconds. On which pan do you want to put your hand ?

Youre completely right, if anyone disagrees with him read the "how heatercored work" and im sure if you search around youll find more people making the same mistake and getting corrected. Its better to learn from your mistakes now then to be spreading wrong info for a while.

And if we wanted water to flow slower, I wouldnt be running a mag3 with ~3 feet of tubing.
 

clocker2

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Joined
Dec 5, 2003
Location
Mile High
SureFoot,
Clearly you have no idea of what a thermostat is.
It is not an electrical device at all.
It is a purely mechanical flow restrictor in the water line of an engine which depends on a bimetalic spring to open and close a restrictor plate thus changing the flow through the system.

??? thermostat is a restriction ? if it's like in "it controls a vane that restricts flow so the car can warm up faster, then open up the vane when the car is hot" it means that higher flow cools better.
Go to PepBoys and look a thermostat.
Although it's outer diameter may be 2" or so, the opening that it controls is less than half that.
Using your theory, removing the thermostat entirely ( removing 100% of the flow restriction in the waterline) should cause the engine temp to drop proportionately.
This is not true.
In fact, temps will rise.

I have no desire to get into a ****ing match here..we seem to have reached the inevitable friction point between theory and real world results.
You asked for proof of my statements and I offered it...go out to your car and try it for yourself.

BTW,
Of course if you got real evidence, F1 / Indy race teams will be highly interested in your discoveries. Oh and NASA too.
I know for a fact that race cars use the restrictor plates in their waterloops having worked as a mechanic in a race prep shop.
Can't speak for NASA though...
 

SureFoot

Member
Joined
Jun 6, 2004
eXCeSS said:
Its better to learn from your mistakes now then to be spreading wrong info for a while.
Absolutely :)
I had to educate my brother on this (he has only basic education, so thermodynamics is way over is head) and the frying pan example worked wonders ;) Now he's got a full 1/2" and even 3/4" parrallel setup w. splitters, with a 1400lph pump :D I think i won't have to give him more evidence that higher flow is better...
 

SureFoot

Member
Joined
Jun 6, 2004
clocker2 said:
SureFoot,
Clearly you have no idea of what a thermostat is.
Okay we stop here. I'm a full time engineer. I've worked on plasma generators for space research. I *think* i know what a thermostat is. Coincidentally the one in my car is an electrical device, called "thermistor", ie a resistor which impedances varies with temperature.
clocker2 said:
It is not an electrical device at all.
Oh crap. I was misled by the 2 wires sticking out of it.
clocker2 said:
It is a purely mechanical flow restrictor in the water line of an engine
This is called.. a vane. Which may be controlled by the thermistor..
clocker2 said:
which depends on a bimetalic spring to open and close a restrictor plate thus changing the flow through the system.
The bimetallic spring is a very crude way of making a thermostat vane control device. But right, on some cars and indeed motorbikes it's enough.
clocker2 said:
Using your theory,
It's not theory. A theory is unproven. I talked about the LAWS of Physics. Laws are proven by scientific experience.
clocker2 said:
removing the thermostat entirely ( removing 100% of the flow restriction in the waterline) should cause the engine temp to drop proportionately.
Actually on MY car it the engine will stop running and the ECU will throw a Check Engine Light code.
clocker2 said:
This is not true.
In fact, temps will rise.
Depends on how the vane is controlled.. If it's naturally open, temps will drop. A naturally closed vane will make temps rise.

clocker2 said:
I have no desire to get into a ****ing match here..we seem to have reached the inevitable friction point between theory and real world results.
I only speak about real world, where the *laws* of Physics all work very well, more than that, we're able to send people on the moon (or soon to Mars) thanks to those laws...
clocker2 said:
You asked for proof of my statements and I offered it...go out to your car and try it for yourself.
Thanx, but i know my car well enough, as i modify it for the racetrack...

clocker2 said:
BTW,

I know for a fact that race cars use the restrictor plates in their waterloops having worked as a mechanic in a race prep shop.
Of course (read the post aboe yours) race cars need to get up to temps very fast. A cold engine can mean mechanical damage. But once it's at running temps, and racing, believe me the vane is full open.


(edit) ha and think about our air cooled friends. With air cooling, is lower flow better ? Explain.
 

clocker2

Member
Joined
Dec 5, 2003
Location
Mile High
thermostat.jpg

This is a thermostat.
Every car that I have ever seen, from my '71 Z car to my '99 Lexus, uses a device almost identical to this.
Crude, maybe, but hardly outdated technology.
edit
Clearly, even in it's fully open state it presents a significant ( and intentional) restriction to the coolant flow. Removing this restriction will slow down the speed with which your car will warm up, but once past this point temps will rise above the norm when the restriction was still present.
According to you, this should not happen.
I apparently haven't the education to explain this.
But then again, I'm not an engineer.

What kind of racing do you participate in?
 
Last edited:

SureFoot

Member
Joined
Jun 6, 2004
Amateur. Racing is only a hobby. I bring my car to the track mostly to drive fast, and enjoy the full power of my car. But trust me, my "thermostat" is a small plug with 2 wires. It's screwed on the side of the engine. What you show looks terribly like a vane.
Anyway. I highly doubt that the vane you show is closed / restricted when the engine is hot and running at full power. Ask a knowledgeable mechanic.

Did you try the frying pan experiment ?
 

clocker2

Member
Joined
Dec 5, 2003
Location
Mile High
Ask a knowledgeable mechanic.
With 30 some years in the field, I consider myself to be a knowledgable mechanic.

I believe that the device you keep referring to is the water temp sensor NOT the thermostat.
 

anvil82

Member
Joined
Apr 21, 2003
Location
New Jersey
Yeah, as said before:

More flow is always better, but the added heat output by the pump offsets this.

Your waterblock also has an impact on this.
 

LV38_Eagle

Registered
Joined
Jun 26, 2004
Location
Westcountry, UK
I will add my 2 pence to the argument, just from a logical point of view, I think you really need different flow rates for the radiator and the waterblock. The waterblock is trying to move a large amount of heat from a small surface area, hence high flow rates, and high velocity nozzles will give an advantage.

With the radiator, the temperature difference between the coolant and the ambient air is quite low, (in a PC at least), and as the radiator has a high surface area, you will dissipate more heat from the coolant with a lower flow rate, (The coolant simply has more time in contact with the radiator). We need a 2 stage system for optimum results. A high flow, high pressure pump for your waterblock circuit, and then a low velocity pump, but still good pressure, for the radiator circuit, with a reservoir in between the two.
 

clocker2

Member
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Dec 5, 2003
Location
Mile High
LV38,
I suspect that your idea has a great deal of merit, although such a system would be fairly complex, no?
Furthermore, a (properly) restricted system ( whether mechanically with a restrictor, or just by choosing a different flow pump) is probably doing just as you describe...perhaps the flow isn't ideal for either the block or the radiator, but it's hit a sweet-spot comprimise that will basically satisfy both.
 

eXCeSS

Member
Joined
Aug 25, 2003
Location
New York
RhoXS said:
There is an elementary equation from basic thermodynamics that states that the rate of heat transfer (Q) equals the mass flow rate (M) times a constant (the specific heat of water) times the delta T (fluid temp out minus fluid temp in).

Q=M x c x Delta T

In other words, the rate of heat transfer is directly proportional to mass flow rate. You increase the flow rate, you will then increase the rate of heat transfer. Since you cannot mess with mother nature it is very naive to think it works any other way.

Assume the CPU inserts a constant rate of energy (Q) into the cooling system. Then, from the relationship above, increasing the mass flow rate must result in a smaller delta T because Q remains constant. This smaller Delta T (fluid out - fluid in) also means that the average fluid temperature in the water block is somewhat lower even though the rate of heat transfer has not changed.

Now lets look at the heat transfer from the CPU to the water. The rate of heat transfer between two points is proportional to the temperature difference between those points. In our case this Delta T (not to be confused with the one above) is the temperature of the CPU minus the average water temperature in the water block. Lowering the average water temperature, as we did above by increasing the flow rate, means we have a little better heat transfer from the CPU to the now somewhat cooler water. The result is that the CPU runs a little cooler.

This all says that if you increase the flow rate, and everything else remains constant, you will decrease the CPU temperature. However, everything else will not remain constant if you increase the flow rate by using a larger pump. The pump uses some amount of electrical energy. This energy must end up somewhere. A relatively small amount of it is dissapated as heat from the motor. The overwhelming majority of it is converted from electrical energy to mechanical energy in the form of a rotating shaft that does real work on the water. This energy ends up in the water by increasing its temperature. It is called "pump heat" and can be very significant. An Eheim 1048 is rated at 10 watts, almost all of which ends up in the water. I understand a very overclocked CPU is good for upwards of 75 watts. As you can see a smaller pump like the 1048 contributes about 13% to the total heat load on a system with an energy hungry CPU. With other more common CPUs running at 25 to 50 watts, this percentage is much higher and is therfore much more significant.

As an interesting aside for those non-believers, this is also why excessive use of a blender to mix up frozen orange juice results in the juice not being as cold as expected. Also, nuclear power plants use primarily pump heat (from three or four 6,000 HP pumps) to heat up almost 75,000 gallons of water from 200 degrees F to about 550 degrees in about six hours or less.

The point here is that there is a trade off in how big a pump to use to increase the flow rate. More flow is beneficial. It is best to achieve the desired flow with a small a pump as possible and flow paths with minimum flow resistance. The bigger the pump, the more heat is added to the system. Eheim makes a 50 watts unit that I see talked about every now and then. This guy is probably a bigger heat load on the cooling system than the CPU itself.

Bottom Line: If you increase flow rate with the same pump your temperatures will trend in the direction of goodness. If you increase flow rate by going to a bigger pump you will reach a trade off somewhwere where the pump starts putting too much energy into the system and temperatures will start increasing.

I did not intend this to be so long but I do hope this helps remove some of the confusion from this issue.

http://www.ocforums.com/showthread.php?t=78055

And your guys' argument: "longer in the rad = better cooling"

jimmytp said:
You do NOT want the water in the radiator very long. The longer the water is in the radiator, the cooler it gets. That's good, right? Wrong. It decrease delta T between the water and the cooling air. Decreases in delta T mean efficiency will decrease. If you want your radiator to dissipate the maximum amount of heat, let the water get real hot. That's good, right? Wrong. That will decrease the delta T between your CPU and the water, decreasing efficiency there. If you want to dissipate the most amount of heat at your CPU, get the water as cold as possible. You want to do this again? Cause it goes in circles. The "sweet spot" is a natural equilibrium that will occur based on CPU temp, ambient temp, and water and intake air flow rate. RhoXS is 100% correct, more flow is better, hands down, no argument. Physics does not lie. For both water and air.

He is also right on with the heat from the pump, cruel world, isn't it? More flow, more better, more flow, more heat. Find the balance. The beautiful thing is that it takes a lot of energy to heat up water. As the water flows past the CPU, it does not pick up that much energy, so temp does not increase that much per pass. This means that small flow rates are fine on the CPU side, and increasing rates will decrease returns quickly. Radiators are different though. There is a lot of surface and tube to flow through in a rad, so temp will drop significantly in a rad per pass. So high flow is more important for rads.

One thing also that I should mention, intake air is the same concept. More flow, the better. And since the air is exhausted and not recycled(I'm not gonna get into your room as a system, in which it is recycled, so we can assume constant ambient temp) "pump heat" for air is negligible. More air es bueno. Hands down, no argument. If you can increase air flow or rad surface area to the point that it will drop rad temps to near ambient, that is very good, but very hard. As rad temps decrease, delta T decreases, decreasing efficiency. Thermodynamics sucks, huh?

The lesson from this? Increasing flow rate is good, for both air and water. Air is better since it has less consequence for increases in flow, no "pump heat". But both increase rad efficiency. Hope this helps, RhoXS did a pretty good job, but I was bored and felt like kicking in support for him.