Quiet case/PSU for a Prescott setup?

[Peter Nelson]

Originally Posted by leifbk

With the glass door & blue lights all over the place, it's got a definite juvenile look about it. Any teenager bringing this rig to a LAN party, would probably be bursting with pride.

regards, Leif.

I have a blue fan in my case. Actually I also have a RGB colour scrolling fan too (both Akasa 80cm) in another machine which looks even better. Hey I've taken it to our local linux user group, but I left my teenage years behind a way back. Hmmm, I'll take it as a compliment that I'm younger-looking than I am, I think?

Call me sad, but I also have a blue usbkey led adapter stuck in the usb port on the front of my case. These give enough ambient light to walk through the dining room (yes, it got repurposed as my datacentre, complete with table) and see the keyboard to type without turning on the main lights. It also acts as a visible confirmation the machine has power (I wouldn't want it to not be switched on and missing out on primality testing).

I did get an Akasa 80mm FLASHING blue Led fan but that WAS just too much. It went back in the packaging and has hidden there since.

For your case I suggest you might add some ducting to manage your multi-fan turbulent airflow problem. For illustration of examples, check out the website of a UK supplier I know (you may have local sources/alternatives).

www.maplin.co.uk

Example Parts:
A09BB Thermaltake ducting mod (bent 80mm clear plastic)
A41BB adapter to change 80mm to 120mm
A90AN Flexible tunnel cooling kit (comes with some adapters/filters)

Just answer me a question about the A09BB ducting mod....
It claims that the "reduced pressure" reduces turbulence. ie moving the same fan a little off the processor will help because the pressure will be less?
Well, one end of the tube is 80mm, the other end is 80mm so how come there is any reduction in pressure? Hello? I don't think this is true if my memory of physics serves me right, if there is air going in one end it comes out the other.

But then I was always a bit confused by high school physics (like a car on a road. Gravity acts to pull the car down, OK I know that like apples fall out of trees, what got me was the balancing force, the upward arrow to show the road pushing the car back upwards, that was just Twilight Zone stuff!). Yes if I stand on the pavement I don't sink into it, I'm prevented from going down but I don't feel pushed up, just why is that :-) Things got worse with applied maths - mechanics later. Fortunately I don't have any pulleys in my PC.

Seriously, if you have an adapter from 80 to 120mm then the pressure might (maybe does) change from one end to the other (like constriction in pipes of a fridge that makes coolant condense/evaporate). I'm not sure I'll ever understand that stuff again, just as long as it keeps my processor cool, that's cool with me! And if it looks cool too that's way cool!

[cheesehead]

Originally Posted by Peter Nelson

Yes if I stand on the pavement I don't sink into it, I'm prevented from going down but I don't feel pushed up, just why is that :-

Because you're so accustomed to feeling the upward pressure on the bottom of your feet that your mind interprets it as feeling your body pressing down instead of as the pavement pressing up. If you were to trip and fall on your face, the force of the pavement pressing up on your face might be interpreted somewhat differently because it's coming from an unaccustomed direction relative to your body.

When I was in a car crash, I distinctly felt my shoulder belt firmly thump me in my chest while I sat still, which was a surprise to me. But an onlooker would have seen that what happened was that when the shoulder belt stopped moving forward (when my car's frame hit the other car's frame), for a split second my upper body kept moving forward until it struck the _motionless_ shoulder belt.

[Peter Nelson]

I was in a car crash once, and quite disappointed my airbag didn't go off. I just closed my eyes then stepped out unharmed. I was talking about the stationery car being pulled down/pushed up. Things get more complex if you go forward/back. Consider driving off a cliff - or jumping off a cliff. I don't feel pushed up any less - although never tried it. I think if I was an astronaut in space in a space suit I would not have the force of the ground. Would the force of the shoe sole in my suit press up on my foot like the ground does. What if it was a very loosely fitting space shoe - like 4 size too large, would the air between it and my foot be pressing up on my foot? Why up rather than down - assuming I could spin in space to any orientation. eg if I was upside down relative to the earth, would the forces of my foot and shoe be reversed? I think it's just a con trick to make the mathematical model work.
Well, at a nuclear level there are the strong and weak forces, repelling to parts of the atom/molecules in the road/shoe/seatbelt which oppose compression. But the force is there whether we compress it or not. And what happens if I drive my car into quicksand and it sinks down? I'm still confused. Enough of this.

I want to understand turbulance and air pressure in my case not the feet of astronauts.

So, if I put a long 80mm tube (constant diameter) on my fan will it (a) run at the same rpm (b) provide the same cfm throughput (c) give the same amount of cooling? (d) have any less turbulence?

I suspect the answers are yes/yes/yes/yes

Any other observations are welcome.

[Peter Nelson]

1)

leifbk wrote "I turned the 120 mm CPU fan around so that it now is blowing air towards the CPU."

That should be better. Why - because many heatsink assemblies have fins curved to facilitate airflow in the direction the fan spins.
Turning the fan upside down is not like reversing the polarity (which if it worked would fight against the directionality of the heatsink) but the are generally designed to have air blown down onto them which vents out the sides rather than sucked from around then up. The aforementioned pressure changes will come into effect at the heatsink point. You should be able to monitor temperature at the cpu for comparison and see a lower value to support the downward airflow hypothesis.

2)

Originally Posted by cheesehead

Because you're so accustomed to feeling the upward pressure on the bottom of your feet that your mind interprets it as feeling your body pressing down instead of as the pavement pressing up. If you were to trip and fall on your face, the force of the pavement pressing up on your face might be interpreted somewhat differently because it's coming from an unaccustomed direction relative to your body.

When I was in a car crash, I distinctly felt my shoulder belt firmly thump me in my chest while I sat still, which was a surprise to me. But an onlooker would have seen that what happened was that when the shoulder belt stopped moving forward (when my car's frame hit the other car's frame), for a split second my upper body kept moving forward until it struck the _motionless_ shoulder belt.

Well, thinking about it I go down, the earth goes up. But my mass is the vastly smaller of the two bodies so the accelleration effect is greater on me toward the earth than vice versa? Thus if I step off a cliff I don't feel the beach rushing up to meet me. (it's psychological too, I know).

However, aside from gravity there is another force at play.

That is the centrifugal force (or centripetal) which acts in a sling. eg put a pebble at the end of a string and swing it around. While there is something connecting it to your hand it will stay. Similarly, gravity connects me in proximity to the earth. However there is the other force because of the spin of the earth. If it wasn't for gravity we would all fly off the planet rather rapidly. So, gravity is just a (roughly) balancing force.

Going back to the car, yes gravity pulls it onto the road, and the upward arrow in the diagram could make sense for me if it is this tendency for the car to fly off the planet because of rotation. In fact these forces do not exactly balance, the gravity is stronger.

For me to overcome the DIFFERENCE I have to apply force.

Since I can't lift my car with my little finger (I need a strongman or a big jack which equates to quite a bit of extra force) I conclude that rather than the forces being equal (drawn by same length force arrows as in text books) the downward force EXCEEDS the upward.

As the rotation of the planet slows down (very slightly) will we actually weigh more over time (provided we retained constant body mass) because the gravity would have less other force to oppose it.

Still not sure how this helps with fan placement :-)

[leifbk]

So, I got my two new 92 mm fans and did some modding.

As the CPU fan was blowing hot air all over the motherboard, I turned it around again and made an air guide. It's amazing what can be done with some cardboard, a sharp knife, and a glue gun in a few minutes. Now, the air is blowing out from the top of the CPU fan, then it is directed towards the outlet fan in the back. I finally was able to block the side hole without risking a meltdown event. The CPU temp is stable at 60-62 C with mprime running full blast, and the sound level is way down in the general background noise. The HDD is a very quiet Seagate Barracuda, and does probably not contribute much to the overall sound compared to the other 8 HDDs, some of which are getting rather aged.

Here's a full overview of the internals. The air guide decoration is from a six-pack of one of my favourite beverages.

[leifbk]

Here's a close-up on the air guide. The air is led towards the outlet fan, and escapes from the box.

[moo]

nj is that a radon vid card in there sorry just had to ask *radon 9000;)* jw what are the benchmarks for that thing

[leifbk]

Originally Posted by moo

nj is that a radon vid card in there sorry just had to ask *radon 9000;)* jw what are the benchmarks for that thing

According to the order confirmation, it's a "PowerColor Radeon 9800SE 128MB, 256bit AGP, ATI 9800SE, DVI-I, TV-Out". It's not particularly expensive, I paid the equivalence of c. 120 USD for it last August.

Like all ATI cards it's got lousy performance under Linux, but I don't do much gaming anyway. I set the machine up with a separate Win2k partition that I planned to use mainly for playing Civilization III, but haven't actually booted the machine into that OS more than once since I installed it. Linux is much more fun.

regards, Leif.

[moo]

;) dang ... radon 9000 is about 3 years old agp tho and 128 megs plays decent on most games 800x600 in hl2 and 640x 480 in doom 3 demo ;)
i dont play high end games very much pets ut u2 and tribes 2 ;)

[cheesehead]

[Pretty soon this is going to look like it needs to be a separate thread. :)]

Originally Posted by Peter Nelson

Well, thinking about it I go down, the earth goes up. But my mass is the vastly smaller of the two bodies so the accelleration effect is greater on me toward the earth than vice versa?

No. The formula is: gravitational force = G * M1 * M2 / R^2, where G is a constant, M1 and M2 are the masses, and R is the distance between their centers of mass. It doesn't matter whether M1 > M2 or M2 > M1 -- force is the same either way.

Thus if I step off a cliff I don't feel the beach rushing up to meet me. (it's psychological too, I know).

If the fall were unexpected instead of deliberate, or you were looking toward the ground instead of away from it, it might feel the other way.

Last week I slipped on ice. Since I fell mostly on my back, I wasn't watching the pavement as I fell, so didn't see it suddenly rush at me in my vision. (I saw the trees suddenly tilt.) I didn't have much of a feeling that the ground moved up to hit me until the moment I actually made contact.

[cheesehead]

Originally Posted by Peter Nelson

However, aside from gravity there is another force at play.

That is the centrifugal force (or centripetal) which acts in a sling. eg put a pebble at the end of a string and swing it around. While there is something connecting it to your hand it will stay. Similarly, gravity connects me in proximity to the earth. However there is the other force because of the spin of the earth. If it wasn't for gravity we would all fly off the planet rather rapidly. So, gravity is just a (roughly) balancing force.

Your wording suggests that gravity and centripetal force are roughly equal, but in "everyday" situations, they're not. For someone/thing just standing on the surface and thus revolving around the earth's axis at 24 hours per revolution (~ 1000 miles per hour at the equator, ~ 700 MPH at latitude 45 degrees N or S, 0 MPH at either pole), centripetal force is much less than gravity.

To have centripetal force roughly equal to gravity, you'd have to be revolving at the speed that orbiting satellites move: about 18,000 MPH near the surface. Near-Earth orbit takes about 90 minutes per revolution.

Going back to the car, yes gravity pulls it onto the road, and the upward arrow in the diagram could make sense for me if it is this tendency for the car to fly off the planet because of rotation. In fact these forces do not exactly balance, the gravity is stronger.

MUCH stronger, if the car is moving at ordinary car-driving speeds. The forces are far from balanced. Centripetal force at 1000 MPH relative to the earth's center (e.g., standing "still" on the equator, or driving east at 300 MPH, relative to the ground, at 45 degrees latitude) is less than 1% of gravitational force.