Calculating pressure drop?
 

hello.
im thinking about getting into watercooling (as some already know) and ive come across a vital question.
Is there a way to calculate head loss/pressure drop in a given system (at a given flow rate)? this will aid in selecting a pump.
the system im thinking about is one with cathar's cpu block, a heater core, and either 1/2" or 5/8" tubing.
thanks.

That's the million dollar question. But, to answer your question, no there is no easy way to actually calculate flow or head.

I wish there was, as do most of the people here.

The best that can be done is to look at the individual components. But some of them do not have any good information on them. You can calculate loss and flow for the tubing that you will use, but since that is only a small part of the system it only helps.

The biggest limiting factor in selecting a pump is how much your willing to spend.

IMHO if your willing to go around $145 then a Iwaki WMD-30RLZT is the way to go. 4.6 GPM max flow, 36.1 ft max head, ~29 ft head @ 3 GPM for only ~47W = 1/16HP.

i heard that the wmd's are no good...
thats not good news...
i was hoping that i could get a pump that would give the best compromise between rad/wb performance

is it possible to calculate the head loss for each component then add them up or something?

in theory i believe this works, if you are calculating for the same flowrate?

Not sure, someone can clarify hopefully. but still, calculating for the waterblock and radiator would be difficult, i imagine.

From what I hear the Iwaki's with the japanese motors are the best

Yes.

You have to add each item as a length of a certain diameter or, in the case of some waterblocks and odd elements (heatercore), find their hydraulic equivalent.

You also have to consider surface smoothness: a rusty iron pipe can have twice the restriction of a smooth PVC pipe.

is there any site or anything that details how to do this? do you have any idea what the pressure drop is for most radiators.
thanks a lot.

here's a site for calculating single pressure drop in pipes of certain diameter, i'm not sure how much it really applies, but here it is:

http://www.processassociates.com/process/fluid/dp_1.htm

and a "general" idea of some common pressure drops for radiators might be obtained from an article by BillA at overclockers.com not sure of the name, maybe someone else can provide a link.

of course if you are using a non-conventional rad. it might not be too helpful

thanks very much, thats pretty much all i need.

The Iwaki pumps are about as good as I've found. I'm doing much the same as you are, trying to choose components for a new system. The thing is there are 2 types of Iwaki pumps.


The WMD denotes the pump has a american moter and cooling fan. These are louder, hotter and shorter service life, but at a savings.

The second type is the japanese moter: quiet, cool running, long service life, but higher cost.

If you get the japanese built type they have a differant designation of MD instead of WMD at the beginning of the model #.

The best price I've found for a MD-30RLZT is $208.00 so far.

what store is that? also how bout the 20rzt?

thanks

m3:
Try this place out. These are the best prices I have found for Iwaki pumps.
Customaquatic

Well I can't really answer your first question but I'm currently using a whitewater block with a heater core and 1/2in clearflex 60 so i suppose I can give firsthand advice on this. Im using an eheim 1046 with this setup and its giving me temps of only 9C above ambiant measured with the oh so inaccurate motherboard sensor. A beefy pump should not be required by your setup.

thanks dan_dude.
do you have a flowmeter in your system? this would allow us to consult the power/flow curve for the eheim 1046 and derive the pressure drop for your system (i think).
thats the same system im hoping for except for the pump which im trying to decide on right now.