a measurement of flow rate?
 

There is MUCH qualitative talk about flow rate, but I have not yet found 1 post where that number is actually measured in a closed loop.

Given that magnetic pumps will vary the flow depending on back pressure, it's impossible to calculate the flow rate without first measuring the resistance of a loop (to do that, the loop has to be open anyways)

One way to measure flow rate would be to calculate it from the temperature difference of the water before and after it passes over the cpu. sincethe heat output of the cpu is known and the heat transferred to the water is measurable, the flow rate could be calculated. One could use one of those laser thingees that measure temp. Shoot the tygon before and after the cpu and presto. Trouble is, i dont have one of those thingees.

A more elegant method might be by light scatterring. Without going into the physics of it, the analogy would be the same way an optical mouse measures velocity.

Come to think of it, has anyone used an optical mouse to measure water velocity in their loop? Since the cross sectional area of the tube is known, flow can be calculated.

I really would like to know what is the actual number - how many gpm will a d4 pump through a tdx and a bonne with 6 feet of 1/2 inch tygon?

Many years ago I saw a product anouncement for a flow meter that used optical sensors. I don't remember the name of the company and I have no idea if they are still around. I've thought about this many times since I got into water cooling since I don't like most of the intrusive methods used to measure flow rate. Using optical mouse sensors is an interesting idea. Getting the needed data out of the optical sensor may not be easy since it would require reverse engineering the communications prototcol and outputed "mouse movement" information so it could be turned into flow rate information.

I use the Swissflow SF800 flowsensor since 3 years now.
It is an optical (Infrared) flowsensor for flowrates from 0.5 to 20LPM and has an accuracy of 1% and a K-value of 6000 (pulses/liter/minute). Connexions are 3/8" BSP and its ID is about 10mm.

http://www.turbokeu.com/mycomputer/sf800/pict0114.jpg

See more on my webpage.
The output signal is an open collector square wave signal from 50 to 2000Hz (for 0.50 to 20.00LPM flow), so display of the flow is just a matter of measuring the frequency and putting the decimal point on the right place.

I also developped a frequencymeter with display for it:
http://www.turbokeu.com/myprojects/f...r/pict0053.jpg
The in the schematic used 74C925 counter chip is now obsolete and quit difficult to obtain, but I redesigned it with a (cheaper) 4553 counter and 4543 decoder/driver.

Mounted in my Lian Li PC-70 (it's the one displaying 4.35LPM):
http://www.turbokeu.com/mycomputer/pc-70/pict0190.jpg

My latest contact with Swissflow was a couple of months ago, price for the SF800 is 50 Euro/piece without taxes (25 Euro/piece for 5000 pieces :)).

Nice setup!!

I am using a PVC cross at inlet and outlet of wbs and placing RTDs and tubing for dP measurements on opposite ends. These should have a very small effect on flow rates, and if you measure dP vs flow for the wb prior to testing it in the cooling loop then you can calculate "real world" flow rates of kits. Seems to work well enough

I thought about that too as the SF800 has a not negligible flow restriction itself (can't give numbers, still have to test flowrates with and without the SF800 in the loop).

How did you "calibrate" it?

CD :)

You calibrate it with a larger pump and one or more valves and your flowmeter :)

What do you do to protect the RDTs from water?