Inline or submerged pump? Answer is here.

[Dix Dogfight]

Well, a small part of the answer anyway.
There has been alot of discussion about how much heat the pump adds to the water and does it matter if i run it inline or submerged.

The pump consumes a certain amount of energy per second, around 20-30 Watts (W).
Some of that energy is transformed into waterflow and some into heatlosses in the pump itself.
The energy transformed into flow is eventually transformed into heat because of the friction in the system. If this were not the case then the velocity of the flow would increase untill it reaches lightspeed. And it doesn't so therfore all flowenrgy is transformed into heat in the water.
(And for all you nonbelievers pleace study THE FIRST LAW OF THERMODYNAMICS before you contradict this statement)

If i place my pump inline only the "flowheat" is added to the water and if i place it submerged all consumed energy is added to the water.

The question everybody wants to know is:
How much of the total amount of consumed energy is transformed into flow and how much into heatloss in pump.
----------------------------------------
Here comes a calculation=answer of that question:
(I've used data from my Eheim 1250 as input)

E_tot=28W (total consumed power)
F_max=1200l/h=0.33l/s (maximum waterflow)
h_max=2m (maximum height)
E_flow=? power transformed to flow
E_loss=? powerlosses in pump
g=9.80665N/kg (gravityconstant)
rho=0.998kg/l (density of water in 20C)

(note that F_max and h_max don't occur simultaneusly but using them together gives the "best case senario")

E_flow=F_max*rho*g*h_max=
=0.33(l/s)*1(kg/l)*9.81(N/kg)*2(m)=6.5(Nm/s)=
=6.5W

E_loss=E_tot-E_flow=21.5W

Conclusion:
If the pump was able to pump 1200l/h to a height of 2m the powerinput into the water would be 6.5W and the powerloss in the pump would be 20.5W.
So by placing the pump under water you add 20.5W of unnecessery heat to the water.
-----------------------------------------
I hope someone can use this info and if you are of a different oppinion pleace
respond with an INTELLIGENT answer.
(i hope my english isn't to unbearable)

CU

[Kevin]

Um woah that was over my head . Looks good though. So I never really go to the answer though. you are saying that inline is better right?

[mpfos]

20.5 watts you say. Hey how much more in heat to the water is that in Celsius degrees?

[redleader]

4.183 watts will heat one gram of water 1 degree C per second (at 14.5C, but its close enough). How much water you have? How efficient is your radiator?

Edit: Spelling.

[ 09-26-2001: Message edited by: redleader ]

[Dix Dogfight]

To Kevin
The calculations show that that less than 25% of the pumps powerconsumption is converted into actual flow and the rest, 75%, is heat added to the air, if you run inline, or the water if you run it submerged.

So from this perspective, yes it's better to run it inline.

[Turbokeu]

I observed that with my inline Sicce Idra (25Watts - 1300l/h) and the fanradiator off, the pump adds 5°C to the water after a couple of hours.
I'm happy it's not submerged...

CD

[Kevin]

Originally posted by Dix Dogfight:

So from this perspective, yes it's better to run it inline.

Oh okay yah we already knew this.

[simon]

Don't know if anyone will bother to read this but your figure are wrong, totally. Well infact they are perfect but the wrong calculations. You have figured out the amount of work done getting the water up tp a height of 2m. In you model here this assumes movement straight up which would reduce the friction, also not all the water makes contact with the copper, a very small portion does. Also the water can contain energy other than heat, as it moves up all the water gains potential energy which changes back to kinetic on its way down. Some of this water will go straight back through the pump so loses no kinetic energy and so on. IN other words your 20.5 watts estimate is way, way to big. Also these system are not quite, hence sound energy needs to be considered. Sorry if this sounds rude but its good news, the large amount of money used for your pump now seems better value for money.

[GigaFrog]

Another important parameter to remember: if the water pump fails, the CPU may fry.

An inline pump may overheat. A submerged pump will stay cool, at the expense of slight temp increase (the 5°C obtained by Turbokeu was with the fanradiator off).

So I personnaly prefers the submerged setup.

[[dannzig]]

i just love this a swede that knows what hes talking about

najs mannen ! precis det jag behövde veta.

[sloppycoder]

yeah but honestly, how likly is it that a good quality pump operating within its volatage, current and flow parameters will blow? im thinking not at all.

the calculations are nothing like detailed enough as skippy says. the akward collisions between water particles and the walls of the piping/ rad/ pump make this one of the nightmare mathematical questions that is still better left alone! to be honest its only worth considering reliability/ performance.

slop

[mrcandy224]

not sure if you wanna read this WHOLE thing but here is something that will take you a while to read and is very useful.
http://www.hardforums.com/showthread...hlight=Pumping

[WebMasta33]

If you're REALLY worried about it....

You take your pump, run it inline with your waterblocks, radiator ect....

Then place your pump in a massive copper watertank, with lots of water in it (duh). Then you take about 50 peltiers, and place them on top, add heatsinks to each one. And then get one of those 7 foot industrial fans, and have it blow across the sucker..

If that doesn't stop that inline temp increase, nothing will!!!

(btw, that was a joke... )

[ 12-19-2001: Message edited by: WebMasta33 ]

[Butcher]

Glue a heatsink to your pump with thermal epoxy

[bateslabel]

Actually I think its really irelevant. The reason is because the small amount of heat added to the water is easily handled by almost all of the radiators. The lowest you can get with plain water is ambient. The amount of heat added by a submerged pump makes no difference at all simply because tha radiator properly setup can dissapate the heat just as easy. Inline or subemerged is all up your preference IMO.

[Dix Dogfight]

Well if you can choose between adding an extra 20W of heat or not to your system.
Then not doing it sounds smarter to me.
But thats just my oppinion of course.

Merry Cristmas an a happy new year to you all

[gmat]

Just my €0.02, i've got a quite powerful -inline- pump. While it's doing its work i barely can touch it, it's *really* hot !
I couldn't imagine putting it into water... And i'm glad water doesnt come into contact with those hot parts
(edit: not a Eheim but another german product...)

[ 12-24-2001: Message edited by: SureFoot ]

[GigaFrog]

You can't barely touch it ???
You may somedy regret not having it submerged ... when it will have fried, and the CPU with it!

An advise: put a thermal switch on this pump, or on your water block.
A thermal switch should be a standard equipment to all watercooled systems.

Just as a reminder: a CPU as no moving part, and can last forever (well, more than 20 years). A water pump has moving parts, and WILL fail soon or later. Buy a $10 or a $200 pump, both will fail, the $10 probably before the $200. If your pump heats up, it will fail sooner, maybe much sooner.

It doesn't make much sense to me to say that I am smart because I did not add 20W in my water cooling system, if by doing so I reduce by half the MTBF of my system.

The water pump is the Achille heel of watercooled systems. Buy good quality, and make sure it does not overheat. It does not have to be submerged, but it does have to be cooled.
Also, check the spec on the max temp of water it is supposed to pump. Some pumps are not guaranteed with water temp above 35°C ...

Joyeux Noel.

[ 12-24-2001: Message edited by: GigaFrog ]

[gmat]

No, it's hot by design. It produces 35W of heat. It has fins on the side of engine to better get rid of heat. I've put a fan to move that air out.
Remember, Eheim's or the like ($90 or more...) are designed to withstand high pressure drops and 24/24+7/7 fail safe *inline* operation, during years. And they can withstand gravel or any kind of underwater clutter without blowing up...

[sunblade]

I've been pondering which pump to get. I like the maxi-jets for their low cost/high reliability, but they're powerheads, so they're res only (you can hack into inline, but the lifespan might be reduced). The Eheims are everybody's favorite it seems, except that they're just so large and expensive. I know that most of the volume is probably from sheilding, tho.

When looking at the maxi-jets, the MP1200 pumps 295GPH and consumes 20W. Looking at the model right below it, the MP900 pumps 230GPH (still good) and only consumes _8.5W_. Compared to other pumps, I think the MP900 would be a great pump to run in a res since it still pumps a reasonable amount of water at a low-lower power consumption. The only thing to concider is that my MP1200 that I'm playing around with doesn't recomend use in water above 35C, so maxi-jets probably aren't the best choice in a pelt setup.

If only I could fit an Eheim 1250 in my case: damn my desire for an uncluttered chasis

maxi-jet wattages:
http://www.aquariumsystems.com/pumps.htm

[ 12-25-2001: Message edited by: sunBLADE ]

[ 12-25-2001: Message edited by: sunBLADE ]