WindTunnel anyone

[RnRollie]

Hiya all,

My head is spinning, i can't trust my memory anymore, i've been confused and sidetracked by so many internet searches, that i simply do not know anything for sure anymore.. (did you know that all 260million facts on the internet are wrong? and that is a fact!)

So, i'm humbly asking for some input, visions, comments, ideas here. As someone inhere is bound to have a certainty whihc can be backed up by figures.

imagine a box.

a box which so happens to be approx. 45cm long, 20 cm wide and 15 or 20 cm high... strangely enough the footprint of my current pccase Without going into too much detail: the front and rear are 'open', that is to say.. front and rear are baffled, with a nice grille to finish it and to match the look of my case. The interior is lined with sound dampening material.
Hence, thus, sofar an empty 'box' or square/rectangular 'tube' if you want.

Now, what i want to do is put two or three Rads (+fans obviously) into that 'box'.

The purpose: twofold:
-1- Cooling Air
by hooking up the box to an external (ground)loop, to cool down air and feeding the cooler air into the PC.

OR

-2- Cooling Water
by hooking the box up to my internal PC-WCloop while 'breating' the outside winter-cold air, to drop the temps of my PC-WCloop a bit and still provide some cooler air into the PC

The first is mainly in the summer of course, but also, maybe now in the winter months to drop the airtemp of the room before it gets used by the PC. reason: I like to have warm feet and my little office cozy at 24 C. But at 24 ambient, the temps inside my PC go way too up for my liking, mainly because of the GeForce card
CPU and drives are held at bay by the WCloop, but ram, mosfets, N/S-bridges become a bit too hot. So i have to up the RPM of the fans and the thing goes beyond the soothing effect of rushing water. Now, if i am playing a game, the soundtrack or explosions or the splatter of blood hitting walls and ceiling masks the extra noise of the fans.
But at idle, when browsing, it gets annoying. The seasons in between are not too bad, when it doesnt get too hot or cold, cuz, then i can run everything on idle and the lowest RPMs.
A silent case is a hot case.

Now, why not hook everything up to the external loop?
Well,... i do like to fiddle around inside the case every now and then. And moving the thing around when it does not have 6 feet of tubing dangling out of it without the need to flip 6 valves to decouple the thing is kinda a bonus.
Also the external (ground)loop is not a professional installation, but rather a work in progress, seriously hampered by the fact that i am RENTING this place (so i have to resist certain sledgehammer urges) in the UK... A country where they are willing to let a young obnoxious boy off with a slap on the wrist for stealing and setting fire to your car, but do want minute details on a 23 page form on why exactly you would want to dig a 16 feet deep hole in your backgarden...

Anyways, i know i could save myself a lot of hassle by just slapping a WC block onto the noisiest/hottest element in my PC, the GeForce card. However, since this being a GeForce 7800 GS (AGP), there are to my knowledge no simple, good blocks for it on the market. And i do trust my skills with wood, electrics and tubes a lot more then my 'milling-your-own-custom-waterblock' skills. Not to mention that i just do not have the equipment nor the inclination to do that. No, i'll wait to replace the GPU till there is a GeForce 8800 GTX with WC/block availble for a DECENT price somewhere in March 2007.


Now, after all this background information, back to the original question.....

but first some data:

Forget for a minute where the water is coming from or going to. Just remember that it could be driven by any size pump, from 60 l/h to 6000 l/h, but when part of the external (ground)loop, probably by a centralheating circulation Grundfos pump at 3000 l/h. If the box would be bolted directly to the bottom of the PC and being part of the PC-loop, then it'll be two laing dcc pumps at 600 l/h.

The Rads could be something like a Black-Ice pro, rated at 1500 BTU/h, unless i can find some ford fiesta or vw polo heatercores. But i dont have too much data on how restrictive they are as far as air or waterflow is concerned.

The fans themselves would be 120 mm either at 7/12v, 30-40CFM at 20db(A) OR 230v, 80CFM at 45db(A).
I feel inclined to go for the AC 230v fans, because then i can just plug the box into the mains and not use an extra powersupply for the fans. Also, because of the rads seriously dropping the airflow, i think i'll need some power to push the air thru the box and the baffles.

Now, i know that heatercores are more efficient in heating up air then cooling it (otherwise they would be called coolercores ) for several reasons, which have to do with flow, density, expansion, humidity,... or simply put: air being more 'willing' to be heated then cooled. So you cannot simply invert the formula/values/figures/energy needed to warm air from 10 to 20 C and apply it to cooling air from 20 downto 10 C. Unless each element involved would be 100% efficient, which is not the case in this universe.

Anyways, finally:
consider this (real 21st century ascii-art) , what i call for lack of a better word for now... a windtunnel

Design1:
Sx C -> Water-R-->--R-->--R-->---> Ex C
Sy C -> Air->-Rf->>-Rf->>-Rf->> -> Ey C
Water at Sx degrees C flows from left to right into a series of Rads, into rad1 then into rad2 then into rad3
While air at Sy degrees C flows also from LEFT TO RIGHT thru the rads.


However: consider this:

Design2:
Sx C -> Water-R-->--R-->--R-->---> Ex C
Ey C <- Air-<fR-<<-fR-<<-fR-<< <- Sy C

Water at Sx degrees C flows from left to right into a series of Rads, into rad1 then into rad2 then into rad3
While air at Sy degrees C flows from RIGHT TO LEFT thru the rads.


Now, what would be the most efficient design? The first or the second?

I really cant find a conclusive answer that just uses air and water and not exotic fluids and gasses and extreme flow rates and conditions. Maybe there is an university or engineering company somewhere that has the answers, but i just can find it. And i cant trust my own memory anymore on this. But i AM inclined to believe that the second design would be more efficient (for a certain application)

So i humbly ask the input of you smart people on this... Design1 or Design2 ?


Now, if someone would feel inclinded to solve following equations upto 15 decimal points, i wont stop you , but a wild guestimate that supports the efficiency of the design would also be appreciated, since one has to do some rough calculations to judge the efficiency of the designs anyway...

Cooling Air:
Sx = 14 C
Sy = 24 C
Ex = ?
Ey = ?

Would Ey be equal to Sx or would Ey be Sy - ((Sy-Sx) / 2)


Cooling Water:
Sx = 30 C
Sy = 10 C
Ex = ?
Ey = ?

Would Ex be Sy or would Ex be Sy + ((Sx-Sy) / 2)




Thank you for your patience, and lookign forward to reactions, thoughts, ideas,...


concise is my middle name