2 Jul
1999
2 Jul
'99
5:29 p.m.
<>As Richard said filtered air in the intake, board mounted vertical,
<>orientation of plug in boards in line with primary airflow.
<
<That makes sense, except for the board mounted vertical. Why that?
If the fan fails convection flow is helpful. Actually vertical with
airflow from bottom to top works well.
Allison
2 Jul
2 Jul
6:41 p.m.
allisonp(a)world.std.com (Allison J Parent) wrote:
<>As Richard said filtered air in the intake,
board mounted vertical,
<>orientation of plug in boards in line with primary airflow.
<
<That makes sense, except for the board mounted vertical. Why that?
If the fan fails convection flow is helpful. Actually vertical with
airflow from bottom to top works well.
Allison
Hi All
Actually air flow is quite complicated. Using muffin type fans
makes it worse. Here are some basic rules of thumb.
1. Fast moving air in an open space will find a surface
and run along it.
2. The only way to make uniform air flow is with restriction.
3. Rotating air will do strange things until straightened
out. ( examples, air coming from a rotary fan and also
most air going through a single small restriction ).
4. Laminar flow is best understood but turbulent
flow removes more heat.
I have seen the above problems cause all kinds of effects
that were not obvious at first.
Dwight
3:07 p.m.
Date: Fri, 2 Jul 1999 16:41:41 -0700 (PDT)
Reply-to: classiccmp(a)u.washington.edu
From: Dwight Elvey <elvey(a)hal.com>
To: "Discussion re-collecting of classic computers"
<classiccmp(a)u.washington.edu>
Subject: Re: PC form factor
Snip! Good comments...
Allison
Hi All
Actually air flow is quite complicated. Using muffin type fans
makes it worse. Here are some basic rules of thumb.
1. Fast moving air in an open space will find a surface
and run along it. 2. The only way to make uniform air flow is with
restriction.
In other words: ducts and shrounds?
3. Rotating air will do strange things until
straightened
out. ( examples, air coming from a rotary fan and also
most air going through a single small restriction ).
Tell me about this "rotating air will do strange thing till
straightened out" what it do strange thing? And how is done to
straighten it out?
4. Laminar flow is best understood but turbulent
flow removes more heat.
Correct.
I have seen the above problems cause all kinds of effects
that were not obvious at first.
Do tell your tales about this! I'm trying to design a case to do
cooling of all drives, PSU motherboard and CPU by one large quiet
fan and ducts/shrounds. Isssues: noise and reliablity from too many
fans.
Dwight
Wizard
7:46 p.m.
jpero(a)cgocable.net wrote:
Also, if you have a flat surface near this air flow, it will
swing to the side and follow that surface. The rest of the volume
may even have slight counter flow.
Here is an experiment you can try for your self. Take a rotary
muffin type fan and place a flat piece of metal across the center
such that the air flow would be split on either side.
Use an anemometer to see where the air is going. Much to
many's surprise, the air will make an angled change and go
off to the right or left along the metal surface but not
straight out as one would expect. This is why people that
are serious about cooling will usually us a squirrel cage
fan over a bunch of muffin type fans. Squirrel cage
fans output a mostly non-rotating air flow.
1. Fast moving
air in an open space will find a surface
and run along it.
I append: Air likes least resistance paths. Suppose: bunch of
short cards with space above it and space front of it. Most of air
will not go into it, it will bypass it.
> 2. The only way to make uniform air flow is with restriction.
In other words: ducts and shrounds?
No, ducts and shrouds only help to get the air to an area.
What I mean is that is you want nice uniform air flow,
you need to make something that provides a uniform resistance
to air flow across the air flow. Screens and meshes are
what I mean.
3. Rotating air will do strange things until
straightened
out. ( examples, air coming from a rotary fan and also
most air going through a single small restriction ).
Tell me about this "rotating air will do strange thing till
straightened out" what it do strange thing? And how is done to
straighten it out?
Do tell your tales about this! I'm trying to design a case to do
cooling of all drives, PSU motherboard and CPU by one large quiet
fan and ducts/shrounds. Isssues: noise and reliablity from too many
fans.
The best solution is to provide impingement cooling where
cooling is needed and an air extraction system.
Dwight
4:11 p.m.
Date: Fri, 2 Jul 1999 17:46:42 -0700 (PDT)
Reply-to: classiccmp(a)u.washington.edu
From: Dwight Elvey <elvey(a)hal.com>
To: "Discussion re-collecting of classic computers"
<classiccmp(a)u.washington.edu>
Subject: Re: PC form factor
jpero(a)cgocable.net wrote:
Also, if you have a flat surface near this air flow, it will
swing to the side and follow that surface. The rest of the volume
may even have slight counter flow.
True, sometimes I noticed that. I remembered doing a experiment
blowing into narrow end of funnel and only air races across surface
and air do DRAWS in middle. (!!).
1. Fast
moving air in an open space will find a surface
and run along it.
I append: Air likes least resistance paths. Suppose: bunch of
short cards with space above it and space front of it. Most of air
will not go into it, it will bypass it.
> 2. The only way to make uniform air flow is with restriction. In other
words: ducts and shrounds?
No, ducts and shrouds only help to get the air to an area.
What I mean is that is you want nice uniform air flow,
you need to make something that provides a uniform resistance
to air flow across the air flow. Screens and meshes are
what I mean. Tell me about
this "rotating air will do strange thing till
straightened out" what it do strange thing? And how is done to
straighten it out?
straight out as one would expect. This is why people
that
are serious about cooling will usually us a squirrel cage
fan over a bunch of muffin type fans. Squirrel cage
fans output a mostly non-rotating air flow.
Oh, I know about that because I can tell it blows rotating air in a
cone shaped flow due to "flinging" air outwards because of rotation,
but I was asking u why it's would do strange things and what is the
_method_ to straighten it out properly? My comments: Rotary fans
mounted on heatsinks have a dead spot about 20% more than the area of
the fan motor and very inefficient! Blowers is not that easy to
obtain except from electronic supplier at greater cost.
fan and
ducts/shrounds. Isssues: noise and reliablity from too many
fans.
The best solution is to provide impingement cooling where
cooling is needed and an air extraction system.
Dwight
8:18 p.m.
jpero(a)cgocable.net wrote:
but I was asking u why it's would do strange
things and what is the
_method_ to straighten it out properly?
Hi
I've seen a honey comb aluminum used on mil stuff but
I've never been able to find a good source. Similar thing
will work. For experimenting, a stack of thin strips
of corrugated cardboard will work.
Dwight, exactly, I forgot to say that I'm PULLING air from heat
producing components via shrouds around heatsinks and ducts to draw
out hot air from cards and PSU. Like vacuuming up hot air and keep
it seperated from cooler air till exhausted outside.
Only problem here is that pulling air is slightly less effective
at cooling than blowing. Still, you'll end up better than simply
dumping air from a fan into an enclosure.
Dwight
9311
days inactive
9311
days old
5 comments
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allisonp＠world.std.com -
elvey＠hal.com -
jpero＠cgocable.net