On Fri, 2 Jan 2009 01:35:16 -0500, "NoSPAM"
wrote:

However, the Cantenna relies on natural
convection of the oil for cooling and the higher viscosity of commonly
available silicone oils will limit the power handling capability of the
Cantenna.

So, a low density fluid would be the better choice? If that were the
prime criteria, I would think that water or antifreeze would be the
best. If having convection currents agitate the fluid is important,
it would be easy enough to install a paddle stirrer and thermometer.
Oh wait. This is ham radio. Forget the thermometer.

I'm also wondering if the electrical characteristics of water are an
issue for an HF dummy load. Even if someone dumps salt water into the
paint can, the conduction losses to ground from the resistor to the
can ground can't be all that much below 30MHz.

Thermal Conductivity Viscosity
W/mK cSt @20c
Water 0.6 0.9
AF (glycol) 0.24 2.0
Water+AF 0.8(?) 1.5 50%/50%
Silicon Oil 0.1 varies radically
Mineral Oil 0.138 34.5
Fluorinert FC-77 0.063 0.75

Ok, I see why. Water has 1/5th of the thermal conductivity of mineral
oil. 50/50 water and antifreeze won't work. That raises the boiling
point but ruins the thermal conductivity. Pure ethylene glycol looks
tolerable. Other than the health and ecology issues, any reason that
100% antifreeze won't work?

Incidentally my theory is that the Heath engineers of the 1960's used
mineral oil because that's what's inside a Lava Lamp. They were
probably designing Heathkit Lava Lamps but when that failed, they had
to do something useful with the mineral oil.

Remember that the Cantenna must be de-rated when used for long
duty cycles, and a high viscosity oil will lower the power rating still
more. Also remember that silicone oils are not cheap (and my buddy at Dow
would only send me small samples).

Well, if you want expensive and near perfect, there's 3M Fluoinert.
http://en.wikipedia.org/wiki/Fluorinert
http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtnxTE5X46EVuQEcuZgVs 6EVs6E666666--
About $400/liter for recycled FC-77 and $2,200/liter for the new
FC-770 stuff from various 3M dealers. A 1 gallon cantenna required
3.78 liters or about $1,500 in recycled FC-77. For those hams that
want the very best. Gold plated paint can is optional.

I would suggest using modern RF terminations made by Bourns and other
companies. These are designed to be bolted to a large heatsink. The
CHF9838CNF series is rated for 50 ohms, 250 watts, VSWR below 1.1 from DC
to 2.2 GHz. It only costs $27.50 in single lot quantities. I think this
is higher than the continuous rating of the Cantenna. I don't know for
sure as I disposed of my Cantenna years ago. Digi-Key sells these Bourns
terminations if you want one.

Nice. Thanks.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CHF9838CNF500L-ND
http://www.mouser.com/Search/Refine.aspx?Msid=65210000&Keyword=CHF9838CNF500L
http://www.bourns.com/data/global/PDFs/CHF9838CNF.pdf
I kinda prefer to use 4ea 200 ohm loads in parallel. In a previous
power amp design, I had to dump 200 watts into a load if the antenna
failed. The thermal resistance of the flange mount was too high for
one device to handle the load at the rated temperatures. However, 4
devices did the trick.

Barry L. Ornitz, PhD WA4VZQ
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article ,
Jeff Liebermann wrote:

I'm also wondering if the electrical characteristics of water are an
issue for an HF dummy load. Even if someone dumps salt water into the
paint can, the conduction losses to ground from the resistor to the
can ground can't be all that much below 30MHz.

It's probably not worth much, but here's some anecdotal evidence. About 50
years ago several of us at W8LT (The Ohio State University amateur radio
club) needed a low-power dummy load to be used at moderate frequencies (e.g.
20 meters). I came up with the idea of immersing a 2 watt, 51 ohm carbon
resistor in a large glass of Columbus, Ohio tap water. We found that at 14
MHz putting the resistor under water made negligible change in observed SWR,
which surprised me because Columbus water (unlike the stuff we're blessed
with here in the Vancouver, BC area which comes right from the mountain
snow-pack) was fairly hard. This also indicated that the water didn't put
too much capacitance in parallel with the resistance. Water-cooling did
allow the 2 watt resistor to absorb a fair bit more power than 2 watts, at
least for a while until the water heated up too much.

Thermal Conductivity Viscosity
W/mK cSt @20c
Water 0.6 0.9
AF (glycol) 0.24 2.0
Water+AF 0.8(?) 1.5 50%/50%
Silicon Oil 0.1 varies radically
Mineral Oil 0.138 34.5
Fluorinert FC-77 0.063 0.75

Ok, I see why. Water has 1/5th of the thermal conductivity of mineral
oil.

It's still a heck of a lot better than air.

As I recall, we were in a hurry, we had the resistor, and we didn't have any
suitable oil on hand.

David. ex-W8EZE

--
David Ryeburn

To send e-mail, use "ca" instead of "caz".

On Sat, 03 Jan 2009 18:53:59 -0800, Jeff Liebermann
wrote:

Thermal Conductivity Viscosity
W/mK cSt @20c
Water 0.6 0.9
AF (glycol) 0.24 2.0
Water+AF 0.8(?) 1.5 50%/50%
Silicon Oil 0.1 varies radically
Mineral Oil 0.138 34.5
Fluorinert FC-77 0.063 0.75

Air 0.025
Copper 370.
Diamond 1000.

Ok, I see why. Water has 1/5th of the thermal conductivity of mineral
oil. 50/50 water and antifreeze won't work. That raises the boiling
point but ruins the thermal conductivity. Pure ethylene glycol looks
tolerable. Other than the health and ecology issues, any reason that
100% antifreeze won't work?

Sorry, I goofed. Vicodin etc. It should be the higher the W/mK, the
better the thermal conductivity.

So why is Fluorinert favored for cooling when it has such a lousy
thermal conductivity?
http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtnxTE5X46EVuQEcuZgVs 6EVs6E666666--
Since it's usually circulated with a pump and involves direct
immersion, is it because of it's low viscosity and superior electrical
characteristics?

It would also appear that water has 5 times the thermal conductivity
than mineral oil. So, why use mineral oil?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Sat, 03 Jan 2009 18:53:59 -0800, Jeff Liebermann
wrote:

Thermal Conductivity Viscosity
W/mK cSt @20c
Water 0.6 0.9
AF (glycol) 0.24 2.0
Water+AF 0.8(?) 1.5 50%/50%
Silicon Oil 0.1 varies radically
Mineral Oil 0.138 34.5
Fluorinert FC-77 0.063 0.75

Air 0.025
Copper 370.
Diamond 1000.

Ok, I see why. Water has 1/5th of the thermal conductivity of mineral
oil. 50/50 water and antifreeze won't work. That raises the boiling
point but ruins the thermal conductivity. Pure ethylene glycol looks
tolerable. Other than the health and ecology issues, any reason that
100% antifreeze won't work?

Sorry, I goofed. Vicodin etc. It should be the higher the W/mK, the
better the thermal conductivity.

So why is Fluorinert favored for cooling when it has such a lousy
thermal conductivity?
http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtnxTE5X46EVuQEcuZgVs 6EVs6E666666--
Since it's usually circulated with a pump and involves direct
immersion, is it because of it's low viscosity and superior electrical
characteristics?

It would also appear that water has 5 times the thermal conductivity
than mineral oil. So, why use mineral oil?


It doesn't turn to steam or otherwise evaporate.

Dave WD9BDZ

In article ,
Jeff Liebermann wrote:

On Sat, 03 Jan 2009 18:53:59 -0800, Jeff Liebermann
wrote:

Thermal Conductivity Viscosity
W/mK cSt @20c
Water 0.6 0.9
AF (glycol) 0.24 2.0
Water+AF 0.8(?) 1.5 50%/50%
Silicon Oil 0.1 varies radically
Mineral Oil 0.138 34.5
Fluorinert FC-77 0.063 0.75

Air 0.025
Copper 370.
Diamond 1000.

Ok, I see why. Water has 1/5th of the thermal conductivity of mineral
oil. 50/50 water and antifreeze won't work. That raises the boiling
point but ruins the thermal conductivity. Pure ethylene glycol looks
tolerable. Other than the health and ecology issues, any reason that
100% antifreeze won't work?

Sorry, I goofed. Vicodin etc. It should be the higher the W/mK, the
better the thermal conductivity.

So why is Fluorinert favored for cooling when it has such a lousy
thermal conductivity?

High resistivity
High dielectric strength
Low maintenance
Low corrosion = very compatible with most materials
Leaks don't cause more damage
low viscosity
Wide useful temperature range

http://multimedia.3m.com/mws/mediawe...E5X46EVuQEcuZg
Vs6EVs6E666666--
Since it's usually circulated with a pump and involves direct
immersion, is it because of it's low viscosity and superior electrical
characteristics?

It would also appear that water has 5 times the thermal conductivity
than mineral oil. So, why use mineral oil?

DI water is very corrosive and requires stainless steel heat transfer
radiators among other components. It is difficult to keep uncontaminated
and you have to keep changing filters for example. Get a leak and it
usually causes additional damage.

Mineral oil makes a mess and is old technology.

I know of one ATE manufacture that used DI water for cooling in the
mainframe and test head. What a mistake that was. Every time they had a
leak in the test head expensive boards got damaged.

--
Telamon
Ventura, California

On Jan 4, 3:21*am, Telamon
wrote:
In article ,
*Jeff Liebermann wrote:





On Sat, 03 Jan 2009 18:53:59 -0800, Jeff Liebermann
wrote:

* * * * *Thermal Conductivity * * Viscosity
* * * * * * * * *W/mK * * * * * * * * cSt @20c
Water * * * * * * 0.6 * * * * * * * * *0..9
AF (glycol) * * * 0.24 * * * * * * * * 2.0
Water+AF * * * * *0.8(?) * * * * * * * 1.5 * 50%/50%
Silicon Oil * * * 0.1 * * * * * * * * *varies radically
Mineral Oil * * * 0.138 * * * * * * * *34.5
Fluorinert FC-77 *0.063 * * * * * * * *0.75

*Air * * * * * * * 0.025
*Copper * * * * *370.
*Diamond * * * *1000.

Ok, I see why. *Water has 1/5th of the thermal conductivity of mineral
oil. *50/50 water and antifreeze won't work. *That raises the boiling
point but ruins the thermal conductivity. *Pure ethylene glycol looks
tolerable. *Other than the health and ecology issues, any reason that
100% antifreeze won't work?

Sorry, I goofed. *Vicodin etc. *It should be the higher the W/mK, the
better the thermal conductivity. *

So why is Fluorinert favored for cooling when it has such a lousy
thermal conductivity?

High resistivity
High dielectric strength
Low maintenance
Low corrosion = very compatible with most materials
Leaks don't cause more damage
low viscosity
Wide useful temperature range

http://multimedia.3m.com/mws/mediawe...SLXTtnxTE5X46E....
Vs6EVs6E666666--
Since it's usually circulated with a pump and involves direct
immersion, is it because of it's low viscosity and superior electrical
characteristics?

It would also appear that water has 5 times the thermal conductivity
than mineral oil. *So, why use mineral oil?

DI water is very corrosive and requires stainless steel heat transfer
radiators among other components. It is difficult to keep uncontaminated
and you have to keep changing filters for example. Get a leak and it
usually causes additional damage.

Mineral oil makes a mess and is old technology.

I know of one ATE manufacture that used DI water for cooling in the
mainframe and test head. What a mistake that was. Every time they had a
leak in the test head expensive boards got damaged.

--
Telamon
Ventura, California- Hide quoted text -

- Show quoted text -


No kidding on how messy mineral oil can be. I had a leak in a
recirculating pump and it put about 20 gal of oil on the carpeted
floor of the radar site. We had to take up the carpet and the asphalt
tile. The floor is now bare concrete because carpet is forbidden
around oil and the concrete will not take adhesive to put down new
tile.

Jimmie

Jeff Liebermann wrote:

...
... The thermal resistance of the flange mount was too high for
one device to handle the load at the rated temperatures. However, 4
devices did the trick.

Barry L. Ornitz, PhD WA4VZQ

Yeah, all that, and then try to sink 5KW+ into a paint can ... 20 X 1000
ohm resistors is very minimum, in a tubular aluminum heat-sink-no less,
in my humble opinion ... as when you are in key-down, and your attention
is diverted, things can get warm, quickly, or so it seems!

Regards,
JS

"John Smith" wrote in message
...
Jeff Liebermann wrote:

...
... The thermal resistance of the flange mount was too high for
one device to handle the load at the rated temperatures. However, 4
devices did the trick.

Barry L. Ornitz, PhD WA4VZQ

Yeah, all that, and then try to sink 5KW+ into a paint can ... 20 X 1000
ohm resistors is very minimum, in a tubular aluminum heat-sink-no less, in
my humble opinion ... as when you are in key-down, and your attention is
diverted, things can get warm, quickly, or so it seems!


That's where the crisco comes in handy!



Regards,
JS

http://groups.google.com/group/alt.p...hl%3Den%26q%3D