Heat rises is a MYTH!

IsaacKuo · Post by **IsaacKuo** » Mon Apr 11, 2005 8:18 am

flyingsherpa wrote:your 4" pipe has very little area and 3' is fairly short. i think all the suggestions of insulating the pipe are a good idea, but i think your pipe is just sized wrong.

I chose the pipe size based on how big I was willing to make the chimney, not based on any calculations on how big it would have to be to make sufficient airflow. I figured if the biggest chimney I was willing to put up with wouldn't provide sufficient airflow, then I wouldn't do it at all.

As it is, the generated airflow is barely even noticeable, so I've abandoned the idea in favor of my usual single fan compact designs. I like compact and stylish computers (but I'm too cheap to buy a Shuttle Zen).

I'd be quite intrigued if someone else takes this concept and makes a workable design out of it (pure air-cooled). With a pure air-cooled design, there's possibly some inherent issues with airflow constriction--if the airflow isn't bottlenecked through the CPU heatsink and PSU, then the airflow isn't doing much good at all. Possibly, the airflow could be restricted less using the CPU and PSU in parallel rather than in series.

andyb: The relevant components of my silent workstation are a random PSU (Sparkle?) and a 550mhz Pentium III. The PIII has a Zalman ZM80A heatpipe VGA cooler on it, but this doesn't really have any bearing on the total amount of heat it generates. I don't know how much total heat those two components create, but it's not much, compared to modern systems. There's also a fanless Radeon 7000 and a 6gig notebook drive in a silencing enclosure. Neither of these would have directly contributed much heat to the air coming into the chimney. I had planned from the start that the entire back side of the case would have been open. As such, the air entering the chimney would have been mostly fresh air bottlenecked through the CPU heatsink and PSU.

andyb · Post by **andyb** » Tue Apr 12, 2005 3:20 pm

Nice concept, the whole system cant generate much heat at all, have you considered multiple chimneys, one for each component, with an amount of space for fresh air each, but all combining into one chimney, this should draw air from the cooler components as well therefore keeping fresh air entering the bottom of the chimney.

Another idea, 1 x Fan at the top of the chimney (or half way). This may also allow you to run the fan at a lower rate than in the case.

Andy

wompey · Post by **wompey** » Thu Apr 14, 2005 12:37 pm

While not computer cooling related, this is along the same lines.

http://www.wired.com/news/technology/0, ... 94,00.html

They made this huge chimney for a solar powered, wind generated power plant! So the idea should work for you too

ronrem · Post by **ronrem** » Wed Jul 20, 2005 1:22 pm

an interesting if doomed experiment. Have you considered some combination of heatpipe and peltier?

Reachable · Post by **Reachable** » Wed Jul 20, 2005 4:18 pm

I gave this quite a bit of thought back in April, coming to the conclusion that the light bulb in this situation is unneeded and counterproductive. Having a heat source in a chimney will create a low pressure zone and cause more air intake at the bottom and then upwards. In a computer the heat source is the CPU and other components, so you don't need a bulb.

The solar generator tower in Australia seems to bear that out (the solar panels are just above the air intake).

A big enough chimney by itself is certainly dramatic. Open the door to an empty elevator shaft on the first floor of a skyscraper and there is a very unsubtle updraft.

IsaacKuo · Post by **IsaacKuo** » Wed Jul 20, 2005 9:45 pm

Reachable wrote:I gave this quite a bit of thought back in April, coming to the conclusion that the light bulb in this situation is unneeded and counterproductive. Having a heat source in a chimney will create a low pressure zone and cause more air intake at the bottom and then upwards. In a computer the heat source is the CPU and other components, so you don't need a bulb.

As you note, having a heat source in the chimney will create a low pressure zone and cause more air intake at the bottom and then upwards. This is a GOOD thing--you want all the airflow you can get, if it doesn't come at the cost of unwanted noise!

I still feel that for a relatively compact design, the amount of heat generated by the CPU and other components, AND a light bulb or two, will still not generate sufficient airflow.

OTOH, if you're going to have the bulk of a large chimney, an undervolted fan in the middle of a foam lined tube will produce more airflow and still be completely silent.

bobo5195 · Post by **bobo5195** » Wed Jul 20, 2005 10:52 pm

This thread makes my head hurt

The light bulb emits most of its heat as radiation so as you have seen when you put Ally foil around it to capture radiation it begins working. For a proper device a longer chimney is going to allow you to have better flow. I think that for a 60w lightbulb your chimney is far to large so you are not going to get suffiecnt volumetric flow rate of air. An electric heater and thinner diameter chimney might be better.

If you plan on trying to build a computer case on this i would suggest to go and find someone at your local university and try and get hold of the latest copy of solidworks professional edition for students. It costs £99 for a student here in the UK. In it there is a fluid modeling program called floworks which can model this kind of experiment with ease (though it would take about half a days worth of computer time depending on the boundary conditions). This is going to be far more productive than building chimneys as modeling the computer case with solidworks should be fairly easy.

Mar. · Post by **Mar.** » Thu Jul 21, 2005 4:48 pm

flyingsherpa wrote:have you played around with http://chuck-wright.com/calculators/stack_effect.html ?

If this is accurate for smaller sizes, a 3-foot chimney with an area of 1 square foot, assuming an internal temp of 115F and an external temp of 75F, will have more airflow than most fans.... and be virtually silent.

I see no reason why something like this would need to be expensive, either.... you could build one out of particle board and foam.

StarfishChris · Post by **StarfishChris** » Thu Jul 21, 2005 5:08 pm

Even a 1 foot cube would provide more airflow than most quiet computers, according to that. I just don't see how that can be right.

Mar. · Post by **Mar.** » Thu Jul 21, 2005 5:40 pm

I'm thinking that that formula is really only true for larger chimneys, and ignores a few things, like heat loss through the sides of the chimney.

The most damning thing about this is, the case itself would act as a chimney, and provide a lot of airflow. Obviously, this isn't true.

Post by **MikeC** » Thu Jul 21, 2005 5:52 pm

Wow, that Aussie Solar Tower is such an exciting prospect!

Only a couple of donwsides AFAI can see...

-- Huge space usage. Even "barren" desert is an ecological zone for life there.
-- Obvious high cost -- but still lower than nuclear and less risk

I wonder if there are hidden gotchas?

Mar. · Post by **Mar.** » Thu Jul 21, 2005 6:00 pm

Once the first is built and the technology proven to work on a large scale, I see a lot of potential in this. With some modification, for example, it may be possible to adapt the technology to be incorporated into other types of (smaller) structures, such as office buildings. The solar collector would have to be rethought, of course....