Re: CFD - software

Oh, boy. I really should know better...

"Steven M. Schweda" wrote:

From: "David J. Dachtera" <djesys.no@xxxxxxxxxxxxxxxx>

I know from (bitter) experience how pointless physics discussions
tend to be in this forum, but sometimes I just have a Popeye moment.

After all the studies and engineers and drawings and ..., two
fundamental facts will remain: warm air is less dense, cool air is more
dense.

Depending on the humidity. (Perhaps counterintuitively, adding water
vapor to air decreases its density.)

For any given moisture content, the principle still holds, even when the
air is cooled below the point of condensation. The relative humidity
changes, thus the "density altitude", as pilots might call it, will
vary.

It's said that, "Nature abhors a vaccuum", and perhaps truer words are
hard to come by.

Actually, it's quite easy to find truer words than those. For
example: "Nature doesn't give a rat's hindquarters about a vacuum." For
some clues, try a Google search for "Nature abhors a vacuum". ("Hey,
Torricelli, what's that at the top of your barometer? Looks abhorrent
to me!") Get yourself 35 feet of transparent garden hose, a cap for
each end of it, and a bucket of water. (As I recall, I ran that
experiment about 42 years ago. It helps to have a partner at the other
end of the hose who's not bored out of his mind. Otherwise, it was
great fun, not to mention educational (for me, at least).)

Quite. The sealed-column type of barometer wouldn't work at all if
indeed, nature did not "abhor a vacuum".

Question: Why can you not "suck" mercury all the way up a 35 inch column
at sea level under standard conditions? (Vacuum pump at one end, other
end open.)

If your air handling systems are effective at removing
warm air, the "void" left will naturally be filled by the cooler air
from the chillers. If cooled air is delivered uniformly throughout the
space below your gear, an effective system of removing the warmed air
above it will cause that cooled air to be lifted by the laws of physics
rather than the quantity of electrical wattage exerted against it.

I'll just skip the part about things exerting electrical wattage.

You appear to assume here that there's an unlimited supply of cooled
air available. There's not. If you remove (warm) air at an enormous
rate, it will not be replaced by cold air a similarly enormous rate,
because the refrigerator can't make cold air at an enormous rate.

It is frequently the case that an "air conditioning system" is a
"closed" system. Typically, this is mostly true in homes (though some do
provide for air replacement using the outside air), especially in the
case of a window ("room") air conditioner which may provide for a little
bit of venting to the outside.

In datacenters, however, it is more common to find that chillers take
ambient air in and discharge it (cooled) into the plenum floor, or the
reverse: take air in from an overhead plenum and simply discharge it
(cooled) back into the room. In this case, the supply of cooled air is
usually approximately the same as the supply of warmed air. Local codes
may require some air replacement if the conditioned space is considered
"occupied".

--
David J Dachtera
dba DJE Systems
http://www.djesys.com/

Unofficial OpenVMS Marketing Home Page
http://www.djesys.com/vms/market/

Unofficial Affordable OpenVMS Home Page:
http://www.djesys.com/vms/soho/

Unofficial OpenVMS-IA32 Home Page:
http://www.djesys.com/vms/ia32/

Unofficial OpenVMS Hobbyist Support Page:
http://www.djesys.com/vms/support/
.

Relevant Pages

  • Re: Air Conditioning on the increase
    ... THE DELUDED WORLD OF AIR CONDITIONING. ... The percentage of single-family homes built with central air ... Countries once cooled by outdoor air now cool ...
    (rec.travel.europe)
  • Re: Plug-In Hybrid Vehicles - The Next Step In Hybrid Evolution
    ... Graham, evidently the buyers in the US don't agree with you. ... drive in air conditioned comfort at a fraction of their list prices. ... While its air conditioning ...
    (sci.energy.hydrogen)
  • Re: 139 deaths later, heat wave appears over
    ... found the constant switches from air conditioning to outside conditions ... sealed buildings are really bad - you're basically recirculating the ... same germy air that everyone else is breathing, ...
    (rec.pets.cats.anecdotes)
  • Re: www.hp.com/go/openvms is still toast
    ... off the air for most of Sunday too. ... please make the necessary phone calls. ... Unofficial Affordable OpenVMS Home Page: ... Unofficial OpenVMS Hobbyist Support Page: ...
    (comp.os.vms)
  • Re: How much more fuel does air con use?
    ... effective heating and ventilation system can do many things very well; ... high ambient air temperatures*, it's plain uncomfortable. ... ventilation systems don't appear optimised for air conditioning in that they ... the climate control's fan speed / temperature bias. ...
    (uk.rec.cars.misc)