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Fan cooling , qualitative assessment

N

N Cook

Jan 1, 1970
0
Without having to learn about pneumatics
For an existing product with a 12V fan with ducted area across fan ie minus
the central motor area, of about 6 square inches and current consumption of
..2 amps.
As it stands this fan would seem to waste a lot of power and increase in
noise, blowing through a set of 14 slots in the case of total air-vented
area 1.5 sq ins.
If most of this grill section was totally cut away , fared off, and an
external wire grill added would that allow the use of .1 amp fan for
more, or less air throughput and a bonus of less audible noise.
 
J

John Larkin

Jan 1, 1970
0
Without having to learn about pneumatics
For an existing product with a 12V fan with ducted area across fan ie minus
the central motor area, of about 6 square inches and current consumption of
.2 amps.
As it stands this fan would seem to waste a lot of power and increase in
noise, blowing through a set of 14 slots in the case of total air-vented
area 1.5 sq ins.
If most of this grill section was totally cut away , fared off, and an
external wire grill added would that allow the use of .1 amp fan for
more, or less air throughput and a bonus of less audible noise.


That all makes sense. One ROT is that the grille area should be at
least as big as the fan area, so 4:1 will seriously restrict flow.

Extech makes a nice, inexpensive air flow + temperature meter that
lets you quantify things like this. Air flow can be counter-intuitive,
and mere mortals can't afford to purchase or learn worthwhild airflow
simulation software.

John
 
J

Jim Thompson

Jan 1, 1970
0
That all makes sense. One ROT is that the grille area should be at
least as big as the fan area, so 4:1 will seriously restrict flow.

Extech makes a nice, inexpensive air flow + temperature meter that
lets you quantify things like this. Air flow can be counter-intuitive,
and mere mortals can't afford to purchase or learn worthwhild airflow
simulation software.

John

A really sharp M.E. that I worked with at GenRad from '77 to '87 had a
smoke generator that he used to examine airflow.

He would build a mock-up of the equipment with foam board, place
cardboard obstacles shaped like components, add fans and observe the
flow.

Then move things around and/or add baffles to shape the airflow.

...Jim Thompson
 
J

John Larkin

Jan 1, 1970
0
A really sharp M.E. that I worked with at GenRad from '77 to '87 had a
smoke generator that he used to examine airflow.

Incense, joss sticks, work fine.
He would build a mock-up of the equipment with foam board, place
cardboard obstacles shaped like components, add fans and observe the
flow.

Then move things around and/or add baffles to shape the airflow.

Right. A wood/plastic/cardboard/duct tape mockup can be done in an
hour or two and is enormously instructive. You can also clamp some of
those metal-case power resistors onto candidate heat sinks, crank in
some power, and see what their operating temps will really be, and get
an idea of how noisy the mess will be.

It's fun to test cardcages with fan trays, or PC enclosures. You'll
often get dead spots directly above fan trays, or air flowing
leisurely in the opposite direction to where high-velocity flow was
expected. Air is funky stuff, and there's an incredible amount of
really bad thermal designs, or rather "designs", around.

John
 
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