typical head loss

[m3_arun]

does anyone have an estimate of the head loss (ft) in a typical w/c system (pump,HC,cpu)?

if i wanted to measure the amount of head loss, could i simply measure the flow in a given system and match the flowrate to the head (ft) in the pump's power curve?

help is appreciated (i am trying to figure out the parts for my first WC system)

[Cathar]

Problem is that head loss is proportional to the flow rate. There's no one answer for "head loss" because it depends on how fast the pump is pushing the water.

Incidentally I'm heading over to San Jose, CA in 2 week's time.

[m3_arun]

im not sure if i understand completely...

There's no one answer for "head loss" because it depends on how fast the pump is pushing the water.

doesnt the rate at which the pump pushes the water dependent on the amount of head loss in the system?

[Cathar]

Originally posted by m3_arun
im not sure if i understand completely...



doesnt the rate at which the pump pushes the water dependent on the amount of head loss in the system?

Yes.....but head loss pressure goes up quadratically as the flow rate is increased.

For example, if a system is providing say 1.0m of back-pressure head when running at 6.0lpm, then the system will then have 4.0m of back-pressure head when pushing 12.0lpm through it.

So it's not as simple as just saying "the system has a head loss of X, therefore pump Y will run at flow rate Z".

You have to look at the PQ curve for the pump, and using a known head loss/flow value for a system, determine whereabouts on the pump's PQ curve the system will sit, which involves a little bit of mathematics and trial and error of point plotting, unless of course you know the exact mechanical specifications of all elements in the system in which case there is just a single formula that you can plug into to arrive at a figure.

Usually faster to point plot and in the space of less than 5 minutes determine what the flow will be.

To answer your opening question, every system is different because each block has a different head loss characteristic, so your question has no one answer. You need to specify a block/heatercore in order to attempt to answer the question.

[m3_arun]

how bout a white-water block anda chevette heater core with 5/8id tubing (what im planning for my system).

[Cathar]

Originally posted by m3_arun
how bout a white-water block anda chevette heater core with 5/8id tubing (what im planning for my system).

I think you'd find that there's minimal difference between a 1/2" and 5/8" system for flow rates less than about 12lpm if the tubing length is less than a few meters in total.

I'm not familiar with the Chevette heater-core, but I'll assume it has roughly the same flow resistance as the heater-core I'm using.

White Water + Heatercore in a 1/2" system gives around 1.0m of head loss at 5.0lpm, and around 4.0m of head loss at 10.0lpm. I say "around" 'cos I'm just back-extrapolating from the PQ curves of the pumps that I'm using.

Here's a graph of Iwaki PQ curves (note - you want to be looking at the USA 60Hz graphs)

So with a US version of the Iwaki MD20-RZ this would translate to roughly 9.5lpm flow rate.
With an Iwaki MD20-R this would give roughly 9.0lpm.
With an Iwaki MD20-RX this would result in roughly 7.5lpm

So clearly the RZ is the better pump here.

For the MD30 series:

MD30-RZ -> ~11.5lpm
MD30-R -> ~10.5lpm
MD30-RX -> ~9.5lpm

I assumed that you were looking at Iwaki pumps from your earlier posts.

[m3_arun]

yah i was looking at the md20RZ
so, with that pump, i wouldnt see any benefit from using 5/8ID tubing?

[UnloadeD]

I think the guy is asking if he knows the flow rate of his sytem (I'm assuming he's disconnecting a hose after components and before pump and timing it) if he can use that figure with a pchart to firgure out the head on his system.

Thats how I read his question anyway. Which makes me wonder...

Does the suction of the pump create a negative head on part of the system lowering the total amount of head?

peace.
unloaded

[bigben2k]

Originally posted by m3_arun
yah i was looking at the md20RZ
so, with that pump, i wouldnt see any benefit from using 5/8ID tubing?

You want to keep the coolant speed under 5 fps, to minimize the pressure loss within the tubing.

5 gpm (300 gph) in 1/2 tubing is 8 feet-per-second.

[bigben2k]

Originally posted by UnloadeD
Does the suction of the pump create a negative head on part of the system lowering the total amount of head?

No.

Total head (aka total pressure) is measured as the difference between inlet pressure, and outlet pressure. The relative pressure i.e. atmosphere, is (almost) irrelevant, except for viscosity purposes (where applicable).

The pressure at the inlet can be negative, relative to the atmosphere (in other words, if you have a leak there, air will enter the rig, instead of water rushing out).

[m3_arun]

I think the guy is asking if he knows the flow rate of his sytem (I'm assuming he's disconnecting a hose after components and before pump and timing it) if he can use that figure with a pchart to firgure out the head on his system.

actually i dont have a system, im planning to get one.
but that is the questin i am asking.
now my main problem is whether to get 1/2 or 5/8 ID tube.

[m3_arun]

You want to keep the coolant speed under 5 fps, to minimize the pressure loss within the tubing.

5 gpm (300 gph) in 1/2 tubing is 8 feet-per-second.

So with a US version of the Iwaki MD20-RZ this would translate to roughly 9.5lpm flow rate.

9.5lpm=2.5gpm

5gpm flowrate sounds pretty unrealistic to me...

since im planning to get teh md20rz, would 2.5gpm be under 5fps?
what kind of performance increase would i see with 5/8 tubing?

thanks

[bigben2k]

I love math problems, so I'll calculate it for you:

if 5 gpm in 1/2 tubing is 8 fps then... (mumble)...

2.5 gpm in 1/2 tubing is 4 fps!

So you're all set


Increasing the tube size from 1/2 ID to 5/8 ID will not yield an appreciable increase in flow rate/speed, and certainly will be immeasurable in CPU temp. If you want the actual calculation, let me know.

[m3_arun]

ok well now ive changed to the md30rz... now i should move to 5/8 shouldnt i? maybe even 3/4?

[Cathar]

Originally posted by m3_arun
ok well now ive changed to the md30rz... now i should move to 5/8 shouldnt i? maybe even 3/4?

Nope. 5/8" or 3/4" tubing is HUGE in comparison to the insides of a case. I already feel that 1/2" tubing is too bulky at times. 1/2" tubing will still serve you well, even with an MD30-RZ, although you are just starting to get into the flow rate range where one may consider switching to 5/8" for some tangible benefit, but still not necessary to do so.

Have to consider practicality in all this as well.

[m3_arun]

yah i kinda just bought it cuz it was cheap on ebay... i dunno if its practical at all...
i know its not going to fit in my case

[bigben2k]

For tubing size, there's two things to remember: keep the tubing at max size for the pump inlet (at least), THEN keep the overall flow speed under 5 fps.

Since you've selected the pump, you should have an idea of what kind of flow rate you'll be getting.

Just do the math. Otherwise, try it out with cheap thin-walled vinyl tubing, available for pennies per foot at any hardware store.

[nikhsub1]

Originally posted by Cathar
So with a US version of the Iwaki MD20-RZ this would translate to roughly 9.5lpm flow rate.
With an Iwaki MD20-R this would give roughly 9.0lpm.
With an Iwaki MD20-RX this would result in roughly 7.5lpm

So from this I can assume with my MD-15R I am getting roughly 8 - 8.5lpm? Cathar what were you getting with the 1250? Was it 6.5lpm? If indeed I did gain 1.5 - 2lpm with my switch to the MD-15R, I am a happy camper, plus, it only outputs 3 more watts

[Cathar]

Originally posted by nikhsub1
So from this I can assume with my MD-15R I am getting roughly 8 - 8.5lpm? Cathar what were you getting with the 1250? Was it 6.5lpm? If indeed I did gain 1.5 - 2lpm with my switch to the MD-15R, I am a happy camper, plus, it only outputs 3 more watts

My prediction is that you'd be getting around 8-8.5lpm with the US version of the MD15-R, so yes, that agrees.

The Eheim 1250 was giving me 6.8lpm in my setup.