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  #21 (permalink)  
Old 16th February, 2002, 01:43 PM
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Quote:
Maybe once the nasty chemicals have left the brain
Nasty chemicals have left the brain now From the thread you linked to, I'd guess that everybody there has immense thermo knowledge, and yet no experience at all with fluid dynamics.

The issue with having multiple separate waterblocks coming off one pump, with precisely controlled flows to each is trivial to design - it's the principle of a multi-pass heat exchanger. It becomes a matter of workmanship as the manifolds necessary will need to be built within close tolerances. The same set of codes also account for gravity within the system. (They're all derivatives of Bernoulli's equation - that's a good starting point).

wrt the thermal aspect of it - your measurements have been very useful to me insofar as I can now see what design shortcuts I can take ... please, keep posting them

Isolating your unit from extraneous heat loss: wouldn't it be simpler just to calculate the heat lost based on surface temperature? (Natural convection method) You might consider doing this anyway as it might help reconcile your experimental data with the theory. I'll dig out the equation next w/e if you wish (half my books are archived, atm)

Just a final question - your simulated heat source: can I have a circuit diagram?
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  #22 (permalink)  
Old 16th February, 2002, 03:05 PM
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  #23 (permalink)  
Old 16th February, 2002, 05:19 PM
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Quote:
Originally posted by dimmreaper
The delta is constant so long as the load is not changed.

I have used a thermistor in the waterblock inlet to calculate the C/W of my own waterblocks as well as various industry leading waterblocks.
thats what I thought!

Now, this is only a simple project right.

So what if I set up a CPU with a waterblock and pump going through it but NO radaitor.

Put the CPU at 100% load. And measure the cpu temps and water temps efore it hits the block temps at say 30 second intervals. and HOPEFULLY the delta T will stay the same? thus proving my initial theory?

I mean, if this is as complicated as you thought, it will go straight over my teachers head anyway, and the write up should get the marks.

What do you reckon?
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  #24 (permalink)  
Old 16th February, 2002, 05:55 PM
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Random Nonsense
ahh, head as in loo ?

Kaitain
several of the posters have post-graduate degrees, yes
no experience ? well, this is the old theory vs. practice thing - slightly

not all participated in the dual wb discussion, I was just trying to get Colin to swap the hoses and had followed him there from OC AU
- the reduction in flow rate/turbulence with parallel blocks is not benificial
(and this I KNOW from testing)

if you PM me your e-mail, I'll send you a more complete (but un-corrected) dataset
I doubt I'll post another
- but the "essence" of much of this will appear in a wb test methodology article in the works for Joe C

my leaving the wb exposed was kind of in line with the way they are used, and my original intention was not ever to try and make a comprehensive heat-balance calculation
though it seems now as if I've sort of backed into it

interesting that you should inquire about the heat source diagram:

the simple answer is that it is a (resistive, 35 ohm nominal) heater cartridge being driven with a regulated DC power supply; having an ammeter in series and a voltmeter in parallel with the load

of course the real answer is much more complex:
the ammeter has a "burden voltage" which needs to be corrected for
and the voltmeter's "loading error" needs to be addressed as well
- in the interest of accuracy if one is to attempt to balance the input and output

I am, as I write, now comparing the Data Precision 1350 which I was using as the ammeter; and the Fluke 8010A which I will henceforth use
- the results are depressing, the gd 1350 measurements are "all over the map", the Fluke vary by 1 or 2 mA
(using the same source, same setting, 10 min. soak)

hi ho
be cool

EDIT: spelling
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  #25 (permalink)  
Old 16th February, 2002, 08:19 PM
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am I a hopeless cause bill?

ah well.

I'll choose something simplar then, like hookes law
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  #26 (permalink)  
Old 16th February, 2002, 09:53 PM
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Spode
I did not see your post 'till the other went up
and not hopeless, just doing a different thing a different way

there are many ways to skin a cat, much depends on the purpose intended

it's difficult for me to contribute much, for our "language" is not the same
for eg; when you say "use 24c water and get 27c temps, thats a 3c delta"
my eyes roll back in my head because I know that that's simply not correct
and without a BUNCH of additional info I can't even really say how or why
(the goop alone with even 15W will have a 3^C temp rise)

don't mean to be cruel here, but
I don't ever deal with thermisters because I know just how hard they are to get good data from
I don't ever deal with CPUs as a heat source because they are of even less "accuracy" than thermistors

perhaps dimmreaper can give you some useful tips as he seems to have experience using this type of setup

be cool
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  #27 (permalink)  
Old 16th February, 2002, 10:36 PM
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I'm 17, this is just a peice of coursework. The degrees of accuracy your talking about are just far too much for this project!

I'm gonna try my way, cos I think it will probably work. I just don't fancy runny my 1.4 athlon at 80c. But I know my duron will :P

Hell, as long as I get SOME results and show what I've done, it's fine.
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  #28 (permalink)  
Old 17th February, 2002, 03:29 AM
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Quote:
Originally posted by Spode
I'm 17, this is just a peice of coursework. The degrees of accuracy your talking about are just far too much for this project!

I'm gonna try my way, cos I think it will probably work. I just don't fancy runny my 1.4 athlon at 80c. But I know my duron will :P

Hell, as long as I get SOME results and show what I've done, it's fine.
Billa is taking this a your trying to find out something usefull about watercooling.
Your taking this as a fun way to get your coursework done.

These two dont have to be opposites but in this case (having done A level physics myself) they are.

I think that a high wattage resistor bolted to some copper will be better than a CPU as you can use a lab PSU to find its approximate wattage.
Lagg the thing up as best you can to reduce heat loss to the surroundings

You will need some way of measuring the blocks temperature....if you can embed a thermistor into the copper block...if you cant jam the thermistor between the resistor and the block. (sorry Billa) that should give a reasonable temperature measure.
You might also want to measure the water temperatures in and out.

The most dificult bit will be getting the water to a constant temperature to pump it through the block.

The simplest method will be to allow the water to heat up on its own using a single resevoire (the heat from the resistor heats the water). Then measure the block temperature and the water temperature at the same time. Then plot water temperature over block temperature and you will get a nice straight line (I hope)

You could...if you where feeling ambitious(sp?) use the specific heat capacity of the water (4200j/Kg/K i think) and the wattage x time on the PSU to find the efficency of your experiment. If you intend to do that you should lagg everything to prevent heat loss. This value might be quite crappy so you can write in your conclusion about how heat was lost to the stmosphere..the PSU wasnt accurate ect..ect

EDIT--I was going to correct my mistakes but there are so many Im not going to bother..its late and im tired.
If you dont get what im saying spode post up your questions.
If you do get what im saying ill give you a job as my full time translator.
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Last edited by Holst; 17th February, 2002 at 03:33 AM.
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  #29 (permalink)  
Old 17th February, 2002, 02:15 PM
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I get EXACTLY what your saying holst! you read my mind.

My only worry is, I'm not allowed back to school for a week, and the coursework is DONE during that week. So infact I won' even have access to school equipment :S

So I may have to resort to home equipment.

But hell, if I'm doing it from home..... a couple of photos, who says my voltage WASN'T stable

I'll get this done. I have a 25W resistor here, do you think that will be enough, or do you tihnk I'll need more?

And perhaps If I sink the thing in expanding foam?
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  #30 (permalink)  
Old 17th February, 2002, 04:05 PM
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Spode
I'll try and be helpful

re your 25W resistor:

E = I * R
P = I * E

you can use AC or DC to power the resistor, though a DC regulated source is better

set the voltage (E) for that amount of current (I) whose product will equal the power rating of the resistor
(you did not indicate the resistance)

if you have a large power input, say 75W or 100W, the effects will be MUCH easier to "see"

go to it
be cool
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  #31 (permalink)  
Old 18th February, 2002, 10:21 AM
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Quote:
you can use AC or DC to power the resistor, though a DC regulated source is better
If you use AC, then you get complications with phase - it's been a long time since I've done any physics, but I believe that the actual power you get out of an AC system of given voltage and current is less than the equivalent DC system:

P = I * E * pf

where pf is a performance factor. (This for single phase)

When exactly is your coursework due in?

Expanding foam should be adequate as an insulator for this - just give it another 24 hours after it's set for all the solvent to dissipate before you use it... it can get a little combustible, with all that trapped butane

I've dug out my thermo notes, and the shc's of water at 1 bar absolute pressure at various temperatures are:

0ºC -> 4.1923 kJ/(kg.k) (all of them are in this unit)
10ºC -> 4.1812
20ºC -> 4.1774
30ºC -> 4.1775
40ºC -> 4.1799
50ºC -> 4.1840
60ºC -> 4.1896
70ºC -> 4.1967
80ºC -> 4.2056
90ºC -> 4.2164
100ºC -> 4.2296

Mean for liquid water: 4.1937

This should let you do some background theory, first.
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  #32 (permalink)  
Old 18th February, 2002, 12:51 PM
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Well, this week is supposed to be the PRACTICAL side of things, not sure when the hand-in is. So I'm awaiting a phone call from my physics teacher to find out when things are happeneing. I still gotta get this ICT coursework done!
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Old 24th February, 2002, 08:41 PM
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Good luck
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  #34 (permalink)  
Old 24th March, 2002, 10:52 AM
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Hey guys!

Well I have to hand this coursework in TOMORROW and I ahven't started the write up yet. Much as the way things go for me!

I'm actually very happy with the way things went.

I used a large bucket for a reservoir, that way the water temperature stays quite constant (well as long as it stays constant for 30 seconds I'm happy).

I tried a 25W resistor and the watercooling was SO good there was no raise in temperature! LOL.

So I bought an 150W resistor (2.2 ohm) and it was HUGE!!!

Running through the power supply at school at 20V with 6.75A.

Using P = I^2 * R, thats 100W of power!

This showed the difference a lot better. I strapped it to my Danger Den Maze 2, with some thermal paste inbetween (lapped the resistor first). and covered the thing in moist toilet tissue, then when it dried it gave a REALLY good insulation layer.

Put some 10c water in (23c room temp) and within seconds the resistor went down to 10c, so the insulation works well.

The probe was embedded in enough that air temperatuer wasn't affecting things either.

I turned on the resistor and found a nice 8c above water temperature after a short time (waited for it to stablist).

If I left it on too much, the current being drawn slowly rose (due to what we were talking about with resistors heating up, right) So I tried to have it switched on as little as possible.

I then just used a kettle and a stirring rod to slowly increase the water temperature and take new readings.

Got 6 or 7 results from 10c to 50c. I'll make up the rest of them. LOL, it's only a coursework.

Overall, I'm pleased with the outcome of the practial side of things, and cheers for your help!! And BillA for putting up with me!

Well I'm off to write up. If I get problems.... You'll be hearing from me :P
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  #35 (permalink)  
Old 24th March, 2002, 03:15 PM
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Hey Spode,

Perseverance is the key, glad it worked out

if you are still interested in more on the subject, try this thread

and how the Big Boys do it:

http://www.intersil.com/data/tb/tb3/tb379/tb379.pdf
http://www.micred.com/prodserv/produ...dies/ttmc.html
http://www.delphiauto.com/products/m...onics/testdie/

be cool
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