Heatsinks and Fans - Which Way Should The Air Move

Discussion:

(too old to reply)

Irv Finkleman VE6BP

2015-06-12 02:52:03 UTC

I have been wondering which way the fans on my TS-930 should be
blowing. Should they take the ambient air from outside and blow
it on the heatsink, or should they be evacuating the inside air
in the vicinity of the heatsink and blowing it out? I have been
restoring the unit and both fans required replacement.

I've surfed a number of sites on the subject but can never get
a definitive answer.

Thanks in advance for any assistance...

de Irv, VE6BP

Channel Jumper

2015-06-12 12:27:56 UTC

Permalink

Post by Irv Finkleman VE6BP
I have been wondering which way the fans on my TS-930 should be
blowing. Should they take the ambient air from outside and blow
it on the heat sink, or should they be evacuating the inside air
in the vicinity of the heat sink and blowing it out? I have been
restoring the unit and both fans required replacement.
I've surfed a number of sites on the subject but can never get
a definitive answer.
Thanks in advance for any assistance...
de Irv, VE6BP

If the fans are forcing the air in, it is forcing the hot air deepe
inside of the heat sink, making it hotter, not colder - unless the ai
outside of the radio is colder than the air inside of the heat sink.

We tried push pull on a set of car stereo amplifiers in a box and foun
that if the fans drew the air away from the box, the amplifiers ra
cooler than if we tried to push air into the box and then draw air bac
out of the box.

You need almost twice as much fan drawing the hot air out as what yo
use to push it in.

I would make sure that I used your radio in an open air space and no
inside of a box or cabinet. Too many people tries to hide their ha
radios, out of sight, out of mind, out of the old lady's sight and the
don't think about what it does to the transceiver - since it bot
transmits and receives.
They confuse it with a plain old radio that just receives.
A radio that just receives shouldn't get very hot.
Then they wonder why it gets so hot when they transmit and do not hav
airflow around the radio.
Dumb

--
Channel Jumper

Jerry Stuckle

2015-06-12 14:05:48 UTC

Permalink

If the fans are forcing the air in, it is forcing the hot air deeper
inside of the heat sink, making it hotter, not colder - unless the air
outside of the radio is colder than the air inside of the heat sink.

Not necessarily. For instance, many tube type rigs blow air directly on
the finals to keep them cool, with vents over the finals to let the hot
air out. Much more efficient than trying to draw air through the case.

We tried push pull on a set of car stereo amplifiers in a box and found
that if the fans drew the air away from the box, the amplifiers ran
cooler than if we tried to push air into the box and then draw air back
out of the box.
You need almost twice as much fan drawing the hot air out as what you
use to push it in.

It depends on where the heat is generated and how the fan is designed to
handle the heat. Both methods are used.

I would make sure that I used your radio in an open air space and not
inside of a box or cabinet. Too many people tries to hide their ham
radios, out of sight, out of mind, out of the old lady's sight and they
don't think about what it does to the transceiver - since it both
transmits and receives.
They confuse it with a plain old radio that just receives.
A radio that just receives shouldn't get very hot.
Then they wonder why it gets so hot when they transmit and do not have
airflow around the radio.
Dumb!

I would find someone with the same radio and ask them which way the air
is blowing.

But then this once again shows you have no inkling about ham radios. Go
back to your CB pals.

--
==================
Remove the "x" from my email address
Jerry Stuckle
***@attglobal.net
==================

j***@specsol.spam.sux.com

2015-06-12 18:41:36 UTC

Permalink

Which it obviously will be and your wording implies that the heat
sinks are closed to air flow.

In a good design, heat sinks are put on the hottest part of the equipment
and the thing that needs cooling the most. The best way to do that is
to blow outside air into the heat sink. If the design was done properly,
there will be an air path out of the heat sink back to the outside.

That result will depend on where you put the fans and the air flow
in the box. If the box was not originally designed for forced air
cooling, your results with add on fans will be entireyly random.

You need almost twice as much fan drawing the hot air out as what you
use to push it in.

Again, that would entirely depend on the equipment design.

I would make sure that I used your radio in an open air space and not
inside of a box or cabinet.

Lots of equipment routinely operates inside of a box or cabinet. If the
enclosed equipment generates much heat, then the cabinet needs its own
set of fans to ensure enough cool outside air for the enclosed equipment.

Obligatory war story: Years ago we were building racked equipment and
the controversy arose as to whether it was better to blow air into
the rack from the top or the bottom.

The bottom blower group maintained that since heat rises, you would
get better airflow from blowing in from the bottom.

A quick calculation showed that the fans overpowered the convection
flow by many orders of magnitude, so it should be irrelevant.

So an empirical test was done with two cabinets side by side.

The long term result was ths bottom blower cabinet got hotter because
the fans at the bottom picked up more dust and crap from the environment
clogging things up while the top blowers remained much cleaner.

--
Jim Pennino

Irv Finkleman VE6BP

2015-06-12 20:46:44 UTC

Permalink

Good info -- thanks!

Irv

Post by j***@specsol.spam.sux.com

Which it obviously will be and your wording implies that the heat
sinks are closed to air flow.
In a good design, heat sinks are put on the hottest part of the equipment
and the thing that needs cooling the most. The best way to do that is
to blow outside air into the heat sink. If the design was done properly,
there will be an air path out of the heat sink back to the outside.

That result will depend on where you put the fans and the air flow
in the box. If the box was not originally designed for forced air
cooling, your results with add on fans will be entireyly random.

You need almost twice as much fan drawing the hot air out as what you
use to push it in.

Again, that would entirely depend on the equipment design.

I would make sure that I used your radio in an open air space and not
inside of a box or cabinet.

Lots of equipment routinely operates inside of a box or cabinet. If the
enclosed equipment generates much heat, then the cabinet needs its own
set of fans to ensure enough cool outside air for the enclosed equipment.
Obligatory war story: Years ago we were building racked equipment and
the controversy arose as to whether it was better to blow air into
the rack from the top or the bottom.
The bottom blower group maintained that since heat rises, you would
get better airflow from blowing in from the bottom.
A quick calculation showed that the fans overpowered the convection
flow by many orders of magnitude, so it should be irrelevant.
So an empirical test was done with two cabinets side by side.
The long term result was ths bottom blower cabinet got hotter because
the fans at the bottom picked up more dust and crap from the environment
clogging things up while the top blowers remained much cleaner.

Ian Jackson

2015-06-26 22:30:28 UTC

Permalink

In message <0olr4c-***@mail.specsol.com>, ***@specsol.spam.sux.com
writes

Post by j***@specsol.spam.sux.com

Which it obviously will be and your wording implies that the heat
sinks are closed to air flow.
In a good design, heat sinks are put on the hottest part of the equipment
and the thing that needs cooling the most. The best way to do that is
to blow outside air into the heat sink. If the design was done properly,
there will be an air path out of the heat sink back to the outside.

That result will depend on where you put the fans and the air flow
in the box. If the box was not originally designed for forced air
cooling, your results with add on fans will be entireyly random.

You need almost twice as much fan drawing the hot air out as what you
use to push it in.

Again, that would entirely depend on the equipment design.

I would make sure that I used your radio in an open air space and not
inside of a box or cabinet.

Lots of equipment routinely operates inside of a box or cabinet. If the
enclosed equipment generates much heat, then the cabinet needs its own
set of fans to ensure enough cool outside air for the enclosed equipment.
Obligatory war story: Years ago we were building racked equipment and
the controversy arose as to whether it was better to blow air into
the rack from the top or the bottom.
The bottom blower group maintained that since heat rises, you would
get better airflow from blowing in from the bottom.
A quick calculation showed that the fans overpowered the convection
flow by many orders of magnitude, so it should be irrelevant.
So an empirical test was done with two cabinets side by side.
The long term result was ths bottom blower cabinet got hotter because
the fans at the bottom picked up more dust and crap from the environment
clogging things up while the top blowers remained much cleaner.

Can I make a late contribution, and suggest that maybe the best position
for the fans could be about half way up? Unless a rack can be made a
virtually airtight tube, if they're mounted at the top, the amount of
suck they have on the air at the bottom is virtually nil. All they do is
create a noise.

--
Ian

Irv Finkleman VE6BP

2015-06-27 00:52:12 UTC

Permalink

Thanks Ian,

There were existing fans and holes in the rear panel, and I was
just curious before replacing the fans. Both had become noisy and
I removed them without checking air flow direction.

The new fans blow air in and onto the heatsink, and there is a good
outflow for the heated air. I've run the unit into a dummy load for
some time and everything is working well now.

My only regret is that the original fans are no longer available
and consequently the restoration of the unit is not 'perfect', but
the TS-930S is a lovely unit and is now running well again.

Thanks also to all those who replied to my queries.

Irv VE6BP

Ian Jackson

2015-06-27 09:35:34 UTC

Permalink

Post by Irv Finkleman VE6BP
Thanks Ian,
There were existing fans and holes in the rear panel, and I was
just curious before replacing the fans. Both had become noisy and
I removed them without checking air flow direction.

Ah....
I was thinking more of a 19" rack horizontal fan tray (holding maybe a
couple of 6" diameter fans - which can sound like a hovercraft on full
power!).

--
Ian

Jerry Stuckle

2015-06-27 15:00:21 UTC

Permalink

Post by Ian Jackson

Ah....
I was thinking more of a 19" rack horizontal fan tray (holding maybe a
couple of 6" diameter fans - which can sound like a hovercraft on full
power!).

Ian, we do a couple of dozen racks a year. The best cooling (even
recommended by the rack manufacturers) is fans with filters at the
bottom, blowing air directly into the rack. If you need additional
cooling, you can put fans at the top pulling the air out.

You don't want fans just pulling air through, as you would have if the
fans were at the middle or top; you have no control of how or where the
air enters the rack; air can be pulled in through spaces between units,
or even through holes in equipment, for instance. But you can place
fans at the top if you have fans at the bottom; the bottom fans will
still supply the air and the top fans will increase airflow.

The biggest problem with cooling a cabinet is equipment placement. You
generally want the heaviest items near the bottom for stability, but
these also generally generate the most heat. Additionally, deeper items
will block more of the airflow. You don't, for instance, want a
full-depth item immediately above one that generates significant heat.
But most items that run hot generate the heat near the rear of the
chassis, so you can place a low depth item above it, if convenient. If
not, you may have to place a 2 or 3 RU blank panel above it to allow for
sufficient airflow.

You also need to consider things like too many full-depth items you have
in the cabinet. Each one of them adds air resistance, lowering air
flow. You may, for instance, want to go to a 28" deep rack, even if
everything will fit into a 23" deep one, to allow for more airflow. Or
you may go for two 28RU racks instead of one 44RU rack to split the heat up.

There is a certain art to good rack design; you don't just slap
everything together and hope it works. When you're done, you should
power up everything in the cabinet and monitor temperature for a few
hours. And if you generate significant heat (or even moderate heat in
unconditioned space), it's a good idea to have a thermometer with remote
alert capabilities in case of a problem like a fan failure.

--
==================
Remove the "x" from my email address
Jerry, AI0K
***@attglobal.net
==================

Ian Jackson

2015-06-30 08:21:17 UTC

Permalink

Post by Jerry Stuckle

Post by Ian Jackson

Ah....
I was thinking more of a 19" rack horizontal fan tray (holding maybe a
couple of 6" diameter fans - which can sound like a hovercraft on full
power!).

Ian, we do a couple of dozen racks a year. The best cooling (even
recommended by the rack manufacturers) is fans with filters at the
bottom, blowing air directly into the rack. If you need additional
cooling, you can put fans at the top pulling the air out.
You don't want fans just pulling air through, as you would have if the
fans were at the middle or top; you have no control of how or where the
air enters the rack; air can be pulled in through spaces between units,
or even through holes in equipment, for instance. But you can place
fans at the top if you have fans at the bottom; the bottom fans will
still supply the air and the top fans will increase airflow.
The biggest problem with cooling a cabinet is equipment placement. You
generally want the heaviest items near the bottom for stability, but
these also generally generate the most heat. Additionally, deeper items
will block more of the airflow. You don't, for instance, want a
full-depth item immediately above one that generates significant heat.
But most items that run hot generate the heat near the rear of the
chassis, so you can place a low depth item above it, if convenient. If
not, you may have to place a 2 or 3 RU blank panel above it to allow for
sufficient airflow.
You also need to consider things like too many full-depth items you have
in the cabinet. Each one of them adds air resistance, lowering air
flow. You may, for instance, want to go to a 28" deep rack, even if
everything will fit into a 23" deep one, to allow for more airflow. Or
you may go for two 28RU racks instead of one 44RU rack to split the heat up.
There is a certain art to good rack design; you don't just slap
everything together and hope it works. When you're done, you should
power up everything in the cabinet and monitor temperature for a few
hours. And if you generate significant heat (or even moderate heat in
unconditioned space), it's a good idea to have a thermometer with remote
alert capabilities in case of a problem like a fan failure.

Your experimental experience is noted. I have to admit that I haven't
personally experimented with trying to optimise cooling in racks.

My suggestion of 'halfway up' is essentially a gut feeling - based on my
experiences where the equipment doesn't extend all the way to the back
to the rear door/wall of the rack - ie there is a gap, say, of least 6",
where the air can get from bottom to top without having to pass
completely through the intervening hot equipment.

By the very nature of things, and with the best will in the world, racks
can rarely be made into air-tight tubes, and as a result, there is
usually quite a fair bit of leakage. If the fan tray is located at the
very top of the rack, a lot of the lower equipment doesn't really feel
their benefit. This may not matter much to the very lowest equipment, as
it probably doesn't really need the fans. It will be the equipment in
the centre of the rack that will suffer, because it will get the hot air
from the equipment beneath, but the fans won't have enough 'reach' to
extract it. That's why I feel that locating the fan tray about halfway
up might be the best compromise.

--
Ian

Jerry Stuckle

2015-06-30 13:01:32 UTC

Permalink

Post by Ian Jackson

Post by Jerry Stuckle

Post by Ian Jackson

Ah....
I was thinking more of a 19" rack horizontal fan tray (holding maybe a
couple of 6" diameter fans - which can sound like a hovercraft on full
power!).

Ian, we do a couple of dozen racks a year. The best cooling (even
recommended by the rack manufacturers) is fans with filters at the
bottom, blowing air directly into the rack. If you need additional
cooling, you can put fans at the top pulling the air out.
You don't want fans just pulling air through, as you would have if the
fans were at the middle or top; you have no control of how or where the
air enters the rack; air can be pulled in through spaces between units,
or even through holes in equipment, for instance. But you can place
fans at the top if you have fans at the bottom; the bottom fans will
still supply the air and the top fans will increase airflow.
The biggest problem with cooling a cabinet is equipment placement. You
generally want the heaviest items near the bottom for stability, but
these also generally generate the most heat. Additionally, deeper items
will block more of the airflow. You don't, for instance, want a
full-depth item immediately above one that generates significant heat.
But most items that run hot generate the heat near the rear of the
chassis, so you can place a low depth item above it, if convenient. If
not, you may have to place a 2 or 3 RU blank panel above it to allow for
sufficient airflow.
You also need to consider things like too many full-depth items you have
in the cabinet. Each one of them adds air resistance, lowering air
flow. You may, for instance, want to go to a 28" deep rack, even if
everything will fit into a 23" deep one, to allow for more airflow. Or
you may go for two 28RU racks instead of one 44RU rack to split the heat up.
There is a certain art to good rack design; you don't just slap
everything together and hope it works. When you're done, you should
power up everything in the cabinet and monitor temperature for a few
hours. And if you generate significant heat (or even moderate heat in
unconditioned space), it's a good idea to have a thermometer with remote
alert capabilities in case of a problem like a fan failure.

Your experimental experience is noted. I have to admit that I haven't
personally experimented with trying to optimise cooling in racks.

Actually, it's not experimental experience. It's recommendations from
rack manufacturers and the knowledge of the guy who designs the rack.

Post by Ian Jackson
My suggestion of 'halfway up' is essentially a gut feeling - based on my
experiences where the equipment doesn't extend all the way to the back
to the rear door/wall of the rack - ie there is a gap, say, of least 6",
where the air can get from bottom to top without having to pass
completely through the intervening hot equipment.

Yes, that's typically the case. But we occasionally have a piece of
equipment which is 25" inches deep. That requires additional space for
airflow around it.

Post by Ian Jackson
By the very nature of things, and with the best will in the world, racks
can rarely be made into air-tight tubes, and as a result, there is
usually quite a fair bit of leakage. If the fan tray is located at the
very top of the rack, a lot of the lower equipment doesn't really feel
their benefit. This may not matter much to the very lowest equipment, as
it probably doesn't really need the fans. It will be the equipment in
the centre of the rack that will suffer, because it will get the hot air
from the equipment beneath, but the fans won't have enough 'reach' to
extract it. That's why I feel that locating the fan tray about halfway
up might be the best compromise.

Locating 1/2 way up does not control the inflow of the air. If there
are vents at the top and bottom, air can enter and exit those and the
input vents can be filtered. But if there are no bottom vents or the
filters become clogged due to lack of cleaning, air will try to come in
through cracks in the front between pieces of equipment, around the rear
door, and potentially even through the equipment if the front panel is
not air tight (very little is). This airflow also allows all kinds of
contamination into the rack in the form of dirt, dust and similar. Fans
at the bottom of the rack can be filtered to limit contamination.

Or, worse yet, if there are no easy ingress/egress paths, these fans
will just circulate hot air in the cabinet.

Additionally, the heaviest equipment (i.e. high power audio amplifiers)
goes at or near the bottom for stability; this equipment also generally
creates the most heat. It would be much nicer if this could go at the
top of the cabinet, but unless the rack is bolted down, you have a
tipping danger.

Depending on the equipment in the rack, fans at the bottom may or may
not be enough. When they aren't, you add exhaust fans at the top to
increase airflow.

--
==================
Remove the "x" from my email address
Jerry, AI0K
***@attglobal.net
==================

bilou

2015-08-12 00:08:45 UTC

Permalink

I have been wondering which way the fans on my TS-930 should be blowing.
Should they take the ambient air from outside and blow
it on the heatsink, or should they be evacuating the inside air
in the vicinity of the heatsink and blowing it out? I have been
restoring the unit and both fans required replacement.
I've surfed a number of sites on the subject but can never get
a definitive answer.
Thanks in advance for any assistance...
de Irv, VE6BP

Hi
My opinion is quite simple:
Pulling air out of an enclosure will ,at the limit, create a vacum inside
In such case radiators are totaly useless only ,by inertia,delaying
complete failure.
Pushing air in allows filtering it from dust and is clearly the way to go.

Michael A. Terrell

2015-10-22 03:27:03 UTC

Permalink

Post by bilou

I have been wondering which way the fans on my TS-930 should be blowing.
Should they take the ambient air from outside and blow
it on the heatsink, or should they be evacuating the inside air
in the vicinity of the heatsink and blowing it out? I have been
restoring the unit and both fans required replacement.
I've surfed a number of sites on the subject but can never get
a definitive answer.
Thanks in advance for any assistance...
de Irv, VE6BP

Hi
Pulling air out of an enclosure will ,at the limit, create a vacum inside
In such case radiators are totaly useless only ,by inertia,delaying
complete failure.
Pushing air in allows filtering it from dust and is clearly the way to go.

As a retired broadcast and CATV engineer, I find all of this amusing.
The worst install that I've run into was at a TV station. Six or seven
full sized racks for the control room for the video gear, and three 1"
Sony VTRs. They were framed into a closet, with sliding doors on the
outside, in the hallway. They had a separate 15 ton A/C for that
closet, yet equipment had a high failure rate. The HVAC contractor had
installed the supply and return vents in the ceiling. They had been
screwing around for several years, and losing about $500 a month in
failed capacitors. I took one look, felt around in the racks and told
them that the supply line should come in at the floor. Since they racks
were sitting on a poured concrete floor, there was no way to feed the
air into the bottom of the racks. They called me a fool, and told me
that engineers from the equipment OEM had been to the site. I got them
mad enough to prove me wrong by removing the ceiling vents and using a
piece of flex duct on each, that dropped to the floor. In under five
minutes, there were no hot spots in any of the racks, and after a month,
the capacitor failure rate dropped to an acceptable level. BTW, one of
the racks had a 5 kW linear 5V power supply in the bottom. Even that ran
cool.

Another site used open racks for microwave equipment at a CATV
headend. They had a large A/C mounted through the wall. MOving one rack
just four inches to the side eliminated the problems. it was deflecting
the air flow away from the other equipment racks, and the return air was
being pulled behind it, back to the A/C.

You are never going to create a vacuum with the fans used to cool
relay racks, they just aren't designed to be that tight. Instead, they
are designed to run quietly, and for a long operating life. Decent
vacuum motors are two or more stages, and the individual fans are in
enclosed areas. AMETEK/Lamb made most of the vacuum cleaner motors in
the US at one time. They were reliable, and easy to repair. Their
website has some good information about blower/vacuum motors. I
repaired some of the motors for a local steel mill, where they were used
for air quality sampling. I also rebuilt a few truckloads of them for a
guy who rebuilt and sold used vacuum cleaners. He would give me a
truckload of motors that he considered scrap. I would repair them, and
sell them back to him. He always wanted to see my armature lathe. He
freaked out when I showed him how to clean and true an armature with a
variable voltage DC power supply, and a hard gray in eraser. ;-)