Cantenna oil
joel
question is what sort of oil is used? I would imagine transformer oil, but
what about other oil.. Cooking for example?
Joe ( AG4QC )
Alan Beagley
transmission fluid suggested -- I don't recall whether Dexron or ATF, or
if it matters at all.
Don't know for sure, but my guess is that cooking oil wouldn't work.
-=-
Alan
Bob Nielsen
> PCB-free transformer oil is usual, but I have seen automatic
> transmission fluid suggested -- I don't recall whether Dexron or ATF, or
> if it matters at all.
>
> Don't know for sure, but my guess is that cooking oil wouldn't work.
Mineral oil is also suggested. Cheaper at a feed store than your local
pharmacy.
Bob, N7XY
'Doc
Transformer oil would probably be 'best', and
your local power company probably has it by the ton.
Mineral oil works, tell your pharmanacist it's for
your elephant. Not very smart to use any type of
automotive 'fluids', besides being flamable, most of
it stinks.
'Doc
OK1SIP
Hi Joe,
use some sort of mineral oil. "Mineral oils" are (in general) a
composition of liquid carbohydrates, while "cooking oils" are esters
of glycerine and high-order organic acids. These esters often
decompose and/or oxidize with time and high temperature.
BUT: Use a cooking oil if you are going to prepare fried potato chips
during tuning your rig 8-)) .
BR from Ivan
AB Brown
I used to have a Heathkit type cantenna that used mineral oil. The outside
of the can had a graph comparing wattage versus mineral or transformer oil.
As power was increased into the dummy load, the transformer oil wouldn't
heat up as quickly as the mineral oil. However, the mineral oil worked well
enough in most cases.
AB
Bob Miller
I had a Cantenna which I filled with mineral oil. Worked fine with 100 watts. It
wasn't cheap, though, coming out of the drug store with dozens of small bottles
of mineral oil, enough to fill the damned can.
MFJ currently sells a Cantenna-style dummy load. You can buy it with or without
transformer oil. They will also sell you a gallon of transformer oil. I believe
Ameritron may have their version of the same thing.
I'd stay away from cooking oils -- they go rancid over time and smell bad,
especially if heated frequently.
Bob
k5qwg
John Passaneau
setting up the ham shack (first things first) and need oil for the Cantenna,
so we went to the store and bought 4 quarts of mineral oil, and while we
were there we also picked up some water glasses and a new flapper valve for
the toilet. We got strange looks from the clerk, so I told her we had found
a new way to turn on, and asked if she wanted to try it with us. My friend
said they looked at him strangely for months after that when he went to the
store.
--
John Passaneau
Penn State University, State College Pa.
W3JXP
w3...@arrl.net
"AB Brown" <abbrow...@mail.com> wrote in message
news:aa3d2b$p0v$1...@slb2.atl.mindspring.net...
Ken
I just went through this and decided to buy the MFJ item from Texas
Towers, which includes a gallon of transformer oil, for $59.95.
It is hard to find cheap transformer oil or mineral oil. At one
local drug chain, mineral oil was $8 a *pint*. I found it cheapest at
K-Mart (better hurry!) where it was every-day priced at around $2 per
pint. This brings it to $16 a gallon, which is not too bad.
The next best choice IMHO is low viscosity non-detergent motor oil.
If you can get 5-WT, it is probably as good as the mineral oil --
better because it will only cost around $6 for the gallon.
Ken KC2JDY
Ken
(to reply via email
remove "zz" from address)
mke...@powerup.com.au
additives.
--
******************************************************************
* Murray Kelly vk4aok mailto://mke...@powerup.com.au *
* 29 Molonga Ter. / Graceville/ QLD. 4075/ Australia *
* ph/fax Intl+ 61 7 3379 3307 *
******************************************************************
Bill Turner
wrote:
>Back in the 70's, I was helping a friend move into a new house. We were
>setting up the ham shack (first things first) and need oil for the Cantenna,
>so we went to the store and bought 4 quarts of mineral oil, and while we
>were there we also picked up some water glasses and a new flapper valve for
>the toilet. We got strange looks from the clerk, so I told her we had found
>a new way to turn on, and asked if she wanted to try it with us. My friend
>said they looked at him strangely for months after that when he went to the
>store.
_________________________________________________________
Made my day. Thanks!!
Bill, W7TI
joel
generate. Thank you all!
I narrowed it down to either transformer or mineral oil. I found a old
heathkit manual and they recommend either. After I priced the oil, I decided
to buy the MFJ 250 and get it over with. ($59.00). It's amazing, the MFJ is
constructed just like I would have built in my basement shop and the quality
is about the same too..
Joe (AG4QC)
<mke...@powerup.com.au> wrote in message
news:3CC605EB...@powerup.com.au...
Ken
>I use mineral oil because it is usp food grade. If a child or pet
>gets back there and tastes some, they may get the runs, but they won't
>drop dead.
Not to mention that with a gallon you could shit easy for 20 years.
Brian P Burke
"joel" <jo...@cyberbest.com> wrote in message
news:vZ2x8.11103$Bh.3689680965@twister2.starband.net...
Brian P Burke
> Well gang. It's unbelievable all the ideas that two days of messages will
> generate. Thank you all!
> I narrowed it down to either transformer or mineral oil. I found a old
> heathkit manual and they recommend either. After I priced the oil, I
decided
> to buy the MFJ 250 and get it over with. ($59.00). It's amazing, the MFJ
is
> constructed just like I would have built in my basement shop and the
quality
> is about the same too..
>
> Joe (AG4QC)
Some guys are always bragging about their home workshops and homebrewing
skills!
Watch out for the sharp edges.
;) Brian
captbrian
G3GVB
Brian P Burke <bpb...@prodigy.net> wrote in message
news:IJxy8.785$1M5.33...@newssvr17.news.prodigy.com...
Mark Hall
Boys). 450° C is a big number.
Fredric J. Einstein
>> > > I'm seriously thinking about building a cantenna type dummy load. My
>> > > question is what sort of oil is used? I would imagine transformer oil,
>> but
>> > > what about other oil.. Cooking for example?
'Mineral Oil' sold at drug stores is the standard type of oil that's
used normally used in commercial dummy loads.
joel
think I would have used a more substantial can then the cheap tin MFJ used.
I have to be very careful to not tilt the can too much as the oil seeps out
of the 239 connector on top. It will work, just a piece of junk!
"Brian P Burke" <bpb...@prodigy.net> wrote in message
news:yMxy8.789$AG5.33...@newssvr17.news.prodigy.com...
Bill Turner
>I have to be very careful to not tilt the can too much as the oil seeps out
>of the 239 connector on top.
_________________________________________________________
I used a similar Heath Cantenna for years and had the same oil seepage
problem. I just set it in a pie pan to collect the drips. Works fine.
In my case, it's because the oil expands as it heats up and forces its
way out.
Bill, W7TI
Ken
wrote:
>In my case, it's because the oil expands as it heats up and forces its
>way out.
The MFJ has a closable vent on top to prevent pressure buildup. I
have one and it is entirely satisfactory. This is not an item that
spending $300 for would get you something materially better. For $59
(including transformer oil) I think MFJ has done a very good job.
BTW, half of my smaller components are MFJ or Vectronics. I have
found the company to be very responsive and supportive. My MFJ items
all do the job at half the price of the next nearest competitor.
Also, I wonder if the MFJ bashers know that MFJ gave generously to
help emergency efforts after 9/11.
Ken KC2JDY
Bill Turner
>Also, I wonder if the MFJ bashers know that MFJ gave generously to
>help emergency efforts after 9/11.
_________________________________________________________
Are you saying because of that their products are now better? Or that
we should accept inferior products?
IOW, there is no connection. I don't want to be rude, but I hate it
when a company or person makes their charitable contributions public in
a transparent effort to increase goodwill. Charity is a wonderful
thing, but don't brag on it. The Good Lord knows you've done it; that's
enough.
(soapbox mode off)
Bill, W7TI
Richard Clark
Hi Joe,
Seems the critical element of this thread is left undisclosed.
It is the "Specific Heat" (capacity) of the liquid you are interested
in comparing one to the other.
Specific Heat is the work required to raise a given weight of
substance one degree celsius.
For an opener Water stands at an impressive c = 4.183
compare to machine oil at c = 1.68
or glycerine at c = 2.43
73's
Richard Clark, KB7QHC
J. Harvey
> Seems the critical element of this thread is left undisclosed.
> It is the "Specific Heat" (capacity) of the liquid you are interested
> in comparing one to the other.
> Specific Heat is the work required to raise a given weight of
> substance one degree celsius.
> For an opener Water stands at an impressive c = 4.183
> compare to machine oil at c = 1.68
> or glycerine at c = 2.43
If this is really an issue for a 'Cantenna' in Amateur use, then use cooking
oil so that you can make french fries. :-)
.Bill :-)
>
>
> If this is really an issue for a 'Cantenna' in Amateur use, then use cooking
> oil so that you can make french fries. :-)
Toss in some flour and keep some good peppers in the can and you'll find
a nice Cajun 'roux' at the bottom.
Sometimes enjoying a good Cajun recipe on the stove might be better than
keying down for 5 minutes.
(haw!!!)
-ex
Stephen C. Robbins
pointed out, the specific heat is the primary concern with the goal being to
get the heat off the resistors and into the oil so as not to let the
resistors overheat and thus change impedance (or worse). Thermal
conductivity is the second factor with the oil being able to absorb heat and
then release it to the surface of the can. Mineral oil has a specific heat
of about .25 Cal/Gram/Centegrade at 75 Centegrade and decreases to .06
Cal/Gram/Centegrade at 150 Centegrade. My Collins 30S1 could overheat it I
suspose, but their is rarely a need to put full output power to a dummy
load. If you are really out to heat up the shack, you can use "Purple
Synthetic" which shows a 30% better performance
(http://www.royalpurple.com/pdfs/SynTran/SynTranps.pdf) A pressure relief
port is a must to deal with expansion. A 5 gallon can instead of a one
gallon paintcan has been used but is probably overkill. One advantage of
the 5 gal can is that it is roomie enough for more resistors (of smaller
values) which results in more surface area exposed to the oil and thus
better heat transfer and cooler running.
Steve
"Richard Clark" <kb7...@attbi.com> wrote in message
news:ca5pcuoh97c34otg6...@4ax.com...
.Bill :-)
>
> It is the "Specific Heat" (capacity) of the liquid you are interested
> in comparing one to the other.
>
> Specific Heat is the work required to raise a given weight of
> substance one degree celsius.
>
> For an opener Water stands at an impressive c = 4.183
> compare to machine oil at c = 1.68
> or glycerine at c = 2.43
>
> 73's
> Richard Clark, KB7QHC
Where does Texaco 'No-Lead' fall in those numbers?
-ex
Richard Clark
Hi Bill,
c = 1.80
Mark Hall
wondering.
'73 KI4Z
Richard Clark
<vze2...@bellatlantic.net> wrote:
>Anybody know what the Specific Heat of DOT-3 Brake Fluid is? Just
>wondering.
>
>'73 KI4Z
Hi Mark,
I looked hard and long for a list or table of Specific Heat of liquids
on the net that would offer a wide range of options - not easy, and
not much useful.
The method to determine is quite simple, put the same power into the
same weight samples and measure the temperature rise.
Brian P Burke
tuner cut me.
"joel" <jo...@cyberbest.com> wrote in message
news:6dLy8.12117$kz4.402...@twister1.starband.net...
joel
from MFJ.. I have a 269 that lasted a month before it stopped working and is
now back in the shop at MFJ. But then again, I have a 989B tuner that seems
to work well, and most everything else too. I guess I expected a thicker
gage of tin in the tin can. It's reminds me of the thin tin they use to make
beer cans... Yuh know, the ones you smash on your forehead.. LOL..
Joel AG4QC
"Brian P Burke" <bpb...@prodigy.net> wrote in message
news:dIlz8.3389$Sl4.12...@newssvr17.news.prodigy.com...
Robert Spooner
It's not so much the specific heat as the viscosity. The reason
transformer oil is better than mineral oil for this application is that
the lower viscosity of the transformer oil allows for better convection
of heat from the resistive element to the surface of the can so that it
can be transfered to the surroundings.
73,
Bob AD3K
Richard Clark wrote:
>
> On Sun, 28 Apr 2002 23:24:18 -0400, ".Bill :-)"
> <TheRea...@netscape.net> wrote:
>
> >Richard Clark wrote:
> >>
> >> It is the "Specific Heat" (capacity) of the liquid you are interested
> >> in comparing one to the other. ...
> >>
--
Robert L. Spooner
Registered Professional Engineer
Associate Research Engineer
Intelligent Control Systems Department
Applied Research Laboratory Phone: (814) 863-4120
The Pennsylvania State University FAX: (814) 863-7841
P. O. Box 30
State College, PA 16804-0030 rl...@psu.edu
Richard Clark
wrote:
>Richard,
>
>It's not so much the specific heat as the viscosity. The reason
>transformer oil is better than mineral oil for this application is that
>the lower viscosity of the transformer oil allows for better convection
>of heat from the resistive element to the surface of the can so that it
>can be transfered to the surroundings.
>
>73,
>Bob AD3K
Hi Bob,
Viscosity has nothing to do with heat capacity nor heat transfer, it
is a mechanical specification.
Think about the viscosity of mercury and its heat holding/transfer
characteristic - wholly unrelated.
Mark Hall
Bill Turner
wrote:
>Viscosity has nothing to do with heat capacity nor heat transfer, it
>is a mechanical specification.
_________________________________________________________
It has very much to do with heat transfer. Inside the dummy antenna,
the oil circulates in response to localized heating at the resistor.
The hot oil rises and draws up cool oil from below until the oil temp
becomes uniform throughout the can.
Take a Heathkit cantenna apart and you'll see the resistor is a large
hollow cylinder mounted vertically in order to facilitate the
convection process.
Bill, W7TI
Ken
<srobbinsN...@netacc.net> wrote:
> Thermal
>conductivity is the second factor with the oil being able to absorb heat and
>then release it to the surface of the can.
Actually, almost no heat is conducted away from the resistor because
the oil is a poor conductor. Rather, it is convected away. So a
whole different set of parameters become more important, like
viscosity.
Gary Schafer
wrote:
>On Tue, 30 Apr 2002 18:29:15 GMT, Richard Clark <kb7...@attbi.com>
Makes you wonder why the oil filled Bird loads are all horizontal?
73
Gary K4FMX
Richard Clark
wrote:
>Richard,
>
>It's not so much the specific heat as the viscosity. The reason
>transformer oil is better than mineral oil for this application is that
>the lower viscosity of the transformer oil allows for better convection
>of heat from the resistive element to the surface of the can so that it
>can be transfered to the surroundings.
>
>73,
>Bob AD3K
>
>Richard Clark wrote:
>>
>> On Sun, 28 Apr 2002 23:24:18 -0400, ".Bill :-)"
>> <TheRea...@netscape.net> wrote:
>>
>> >Richard Clark wrote:
>> >>
>> >> It is the "Specific Heat" (capacity) of the liquid you are interested
>> >> in comparing one to the other. ...
>> >>
Hi all,
Given the propagation of myth, a quote:
>VISCOSITY - measurement of a fluid’s resistance to flow.
>The common metric unit of absolute viscosity is the poise,
>which is defined as the force in dynes required to move a
>surface one square centimeter in area past a parallel surface
>at a speed of one centimeter per second, with the surfaces
>separated by a fluid film one centimeter thick.
>For convenience, the centipoise (cp) - one one-hundredth of a poise -
>is the unit customarily used. Laboratory measurements of viscosity
>normally use the force of gravity to produce flow through a capillary tube
>(viscometer) at a controlled temperature. The measurement is
>called kinematic viscosity. The unit of kinematic viscosity is the stoke,
>expressed in square centimeters per second.
>The more customary unit is the centistoke (cSt) - one one-hundredth of a stoke.
Most, if not all who hold dear to this notion of a mechanical
specification expressed in mm²/second being used as an index to heat
flow are working it from the wrong side of the equation.
Viscosity is a dependant variable of heat NOT the other way around.
Bill Turner
>Actually, almost no heat is conducted away from the resistor because
>the oil is a poor conductor. Rather, it is convected away.
_________________________________________________________
We've got some strange physics going on in this thread.
Please explain how heat can be convected away unless it is first
conducted to the oil. (In the context of a dummy load resistor
submerged in oil).
Bill, W7TI
Stephen C. Robbins
"Bill Turner" <w7...@dslextreme.com> wrote in message
news:q0qtcuctru7olah2u...@4ax.com...
> On Tue, 30 Apr 2002 18:29:15 GMT, Richard Clark <kb7...@attbi.com>
> wrote:
>
> >Viscosity has nothing to do with heat capacity nor heat transfer, it
> >is a mechanical specification.
>
Bill is correct, it is a mechanical measurement of fluid's shear. IE, how
well does it flow through an opening. Has nothing to do with heat
convection, conduction, etc. Their might be a coincidental relationship of
viscosity to conduction/heat transfer but I have never seen any tables on
it....
Steve
Richard Clark
wrote:
>Richard,
>
>It's not so much the specific heat as the viscosity. The reason
>transformer oil is better than mineral oil for this application is that
>the lower viscosity of the transformer oil allows for better convection
>of heat from the resistive element to the surface of the can so that it
>can be transfered to the surroundings.
>
>73,
>Bob AD3K
>
>Richard Clark wrote:
>>
>> On Sun, 28 Apr 2002 23:24:18 -0400, ".Bill :-)"
>> <TheRea...@netscape.net> wrote:
>>
>> >Richard Clark wrote:
>> >>
>> >> It is the "Specific Heat" (capacity) of the liquid you are interested
>> >> in comparing one to the other. ...
>> >>
Hi All,
Yet another quote quite specific to all points raised and answered
(and notably consistent with physics):
>High Specific Heat - Specific Heat is a measure of a liquid's ability
>to remove heat. Water, being the perfect heat remover,
>has a specific heat value of 1.
>Mineral transfomer oils typically have a specific heat value of 0.43.
>This means that mineral oils are only 43% efficient as water in removing heat.
This quote then goes on to show how the manufacturer has improved over
mineral oil:
>Royal Purple Synthetic Transformer Oil typically has a
>specific heat value of 0.56 which is 56% as efficient as water,
>and 30% more efficient than mineral transformer oils in removing heat.
The fact remains, you want to focus on the "Specific Heat" (capacity)
of the liquid you choose. Face it, you are unlikely to do better than
water and these other machinations between brake fluid, mineral oil,
transformer oil, olive oil, or the rest are simply shaving numbers out
in the rather insignificant digits in comparison to water. They are
meaningful one to the other (as indicated in the comparison between
the synthetic and natural product) and this again returns us to the
caution to compare on the basis of "Specific Heat" NOT viscosity.
It takes very little math to come to the same conclusion without this
ad piece above. When you drive 100W of heat into water, its
temperature rises far less than the same 100W of heat driven into an
equal weight of an alternative liquid.
If you want hot french fries, use oil, if you want a cool load, use
water. However, water has its own problems when it comes to this
application, but heat capacity is not counted amongst them.
Bill Turner
wrote:
>this again returns us to the
>caution to compare on the basis of "Specific Heat" NOT viscosity.
_________________________________________________________
I'm almost ready to give up on this, but I'll try one more time.
In the "Cantenna" type dummy load we're talking about,
VISCOSITY IS IMPORTANT. Why? Because heat dissipation inside the can
depends on circulation of the oil due to convection heating.
High viscosity = low circulation.
Imagine an oil with high specific heat but as viscous as molasses in
January. The oil in direct contact with the resistor will absorb heat
wonderfully, but can not carry the heat away because the viscosity is so
high as to impede circulation. Heat in the resistor will quickly build
up to the point of damage.
I hope the picture is clear now. Otherwise, I quit.
Bill, W7TI
Richard Clark
wrote:
>On Wed, 01 May 2002 02:32:36 GMT, Richard Clark <kb7...@attbi.com>
>wrote:
>
>>this again returns us to the
>>caution to compare on the basis of "Specific Heat" NOT viscosity.
>
>_________________________________________________________
>
>I'm almost ready to give up on this, but I'll try one more time.
>
>In the "Cantenna" type dummy load we're talking about,
>VISCOSITY IS IMPORTANT. Why? Because heat dissipation inside the can
>depends on circulation of the oil due to convection heating.
>High viscosity = low circulation.
The circulation you appeal to is mechanical movement of the oil - by
definition.
>
>Imagine an oil with high specific heat but as viscous as molasses in
>January.
This is obviously a contradiction on the face of it Bill, offer an
example of a highly viscous oil at high temperature (or simply except
mine that follows below).
The viscosity of Royal Purple: at 40°C cSt = 9.4
The viscosity of Gulf Mineral Oil: at 40°C cSt = 5.0
The mineral oil is superior in viscosity and inferior in application.
If you wish, try Gulf Degreasing Fluid: at 20°C cSt = 1.9
(clearly a killer according to the logic of viscosity)
Then there is Gulf's Gulftherm Oil specifically designed for closed
unpressurized heat transfer systems and described as:
>>Gulftherm oils have high specific heat and thermal conductivity at all temperatures
and spec out: at 40°C cSt = 22 to 68 (depending on grade)
which clearly contradicts the correlation you draw. That or Gulf is
clearly lying. More than 10 times as viscous as their Mineral Oil,
and they prefer it for its heat capacity. You are free to select a
highly viscous oil for comparison (and we both know it will fail
miserably - unless, of course, it offers a high specific heat).
>The oil in direct contact with the resistor will absorb heat
>wonderfully, but can not carry the heat away because the viscosity is so
>high as to impede circulation. Heat in the resistor will quickly build
>up to the point of damage.
Again this counter to the physics of heat. Bird Shit (AKA thermal
compound) is extremely viscous (a grease in fact) and the most common
form of heat conductor interface used in electronics. Anyone who has
handled this substance can easily attest to the fact of its viscous
nature.
What you describe as the build up of heat is called "Thermal
Resistance" which is expressed in °C/Watt. By definition, higher
"Specific Heat" (capacity) does not allow the heat to build in the
FIRST PLACE for water which is much better than any oil (as admitted
to by a manufacturer and supplier of that same oil you hold so
dearly).
>
>I hope the picture is clear now. Otherwise, I quit.
>
>Bill, W7TI
Again, the simple math shows that "Specific Heat" (capacity) will
faithfully predict a cooler dummy load for the highest factor. I have
reviewed dozens of transformer (and other) oil vendors and have
offered at least two examples that would be exemplars of your premise.
To this point for this topic I've yet to observe any factual data
beyond what I have reported.
I have cited at least two sources and four examples (five if we
include water, but I will remove that joker from the deck) from both
sides of the argument. Who here is to challenge them with an actual
application, comparison and report? I will note that along the way I
have also observed only ONE report of that same observation of
convection and viscosity from those same several dozen manufacturers.
I will also add another source (low viscosity too), Dow Corning 200
centipoise Silicone Oil that is explicitly called for by HP for their
Caloric Power Meter. I offer this from my days at the RF Metrology
bench knowing it was designed to this fluid (a power meter flat from
DC to 1GHz). It is ancient by today's standards, but none here could
equal its performance for less than a grand out of pocket. You can
buy the instrument for less, but filling it will take some bucks.
You fellows wanted a low viscosity oil? Look above and cite one
lower! Dime store mineral oil certainly doesn't enter into the
picture. But in the end it hardly matters, this is all shaving points
out in the statistical noise for what we can afford and that warm
fuzzy feeling of having optimized the problem.
Bill Turner
wrote:
>But in the end it hardly matters, this is all shaving points
>out in the statistical noise for what we can afford and that warm
>fuzzy feeling of having optimized the problem.
_________________________________________________________
Agreed. My post was intended only to dispute the statement "viscosity
doesn't matter" which was made several times. It is not the ONLY
characteristic of importance, but it DOES matter.
Now, I'm giving it a rest.
Bill, W7TI
Robert Spooner
In a wet dummy load, viscosity has _everything_ to do with heat
transfer. Convection currents are the primary means of transporting
heat from the resistive element to the can. That's why a liquid is
used, so it can move and transfer heat. The oil is heated by the
surface of the resistive element, moves up to the top surface and then
flows down the inside surface of the can, cooling as it transfers heat
to the can. The heat is then transferred from the can to the
surrounding air by radiation and convection.
73,
Bob AD3K
Richard Clark wrote:
>
>
> Viscosity has nothing to do with heat capacity nor heat transfer, it
> is a mechanical specification.
>
--
Robert Spooner
>
>
> Then there is Gulf's Gulftherm Oil specifically designed for closed
> unpressurized heat transfer systems and described as:
> >>Gulftherm oils have high specific heat and thermal conductivity at all temperatures
> and spec out: at 40°C cSt = 22 to 68 (depending on grade)
> which clearly contradicts the correlation you draw. That or Gulf is
> clearly lying. More than 10 times as viscous as their Mineral Oil,
> and they prefer it for its heat capacity. You are free to select a
> highly viscous oil for comparison (and we both know it will fail
> miserably - unless, of course, it offers a high specific heat).
>
designed to use convection for cooling. A high specific heat capacity
will influence how long it takes the dummy load to get to steady state
at a given power dissipation, but viscosity will be the larger influence
on how much power can be dissipated in a steady state condition. That's
why power companies cool transformers with transformer oil rather than
something else as well, the transformers are designed to use convection
cooling.
73,
Bob AD3K
Richard Clark
wrote:
>Richard Clark wrote:
>>
>>
>> Then there is Gulf's Gulftherm Oil specifically designed for closed
>> unpressurized heat transfer systems and described as:
>> >>Gulftherm oils have high specific heat and thermal conductivity at all temperatures
>> and spec out: at 40°C cSt = 22 to 68 (depending on grade)
>> which clearly contradicts the correlation you draw. That or Gulf is
>> clearly lying. More than 10 times as viscous as their Mineral Oil,
>> and they prefer it for its heat capacity. You are free to select a
>> highly viscous oil for comparison (and we both know it will fail
>> miserably - unless, of course, it offers a high specific heat).
>>
>What you don't seem to recognise is that the Cantenna type dummy load is
>designed to use convection for cooling.
What I do seem to recognize is no more detail nor argument beyond
"'tis so!" A truly less than useful answer to the matter of the
subject.
>A high specific heat capacity
>will influence how long it takes the dummy load to get to steady state
>at a given power dissipation, but viscosity will be the larger influence
>on how much power can be dissipated in a steady state condition.
There is absolutely nothing in the specification of "Specific Heat"
(capacity) that attends created issues of steady state and mocks the
manufacturer's admission of water being a far better performer (or
their product for that matter); much less their direct comparison to
other fluids specified for like use on that basis of "Specific Heat"
(capacity) AND viscosity.
This is the long way of saying "show your work for credit."
>That's
>why power companies cool transformers with transformer oil rather than
>something else as well, the transformers are designed to use convection
>cooling.
>
>73,
>Bob AD3K
>--
> Robert L. Spooner
> Registered Professional Engineer
> Associate Research Engineer
> Intelligent Control Systems Department
>
> Applied Research Laboratory Phone: (814) 863-4120
> The Pennsylvania State University FAX: (814) 863-7841
> P. O. Box 30
> State College, PA 16804-0030 rl...@psu.edu
Hi Bob,
Still, to this point I have provided detail and data for BOTH sides of
the argument and find correspondence with nothing more to add than the
repetition of weak and unsubstantiated statements that are clearly
refuted by industry to the matter of the application that is specific
to this thread.
I am surprised by how much the obvious is so avoided. This argument
of "convection" so closely tied to viscosity: a truly moving target
that when shown is in contradiction with itself then mutates into
another myth. It would be obvious to a 7th grade science student that
the lowest viscosity liquid is water, and yet none pounding away with
this message of the viscous seems to realize, acknowledge, or face it;
much less use it to rebut me.
I even have to supply my own counter arguments and yet the criticism I
garner appears to be wholly ignorant of the implications nor do they
take the leads offered. I have allowed holes in the statements I've
made to give you fellows some opportunity to offer some guide to
others over what constitutes a better fluid for Cantenna use (the
explicit point of this thread) and apparently there is no motivation
to follow through except to repeat the same homilies.
There is nothing held so dear as the faith of the miracles and brake
fluid.
I will repeat in encapsulated form what I challenged previously:
>The viscosity of Royal Purple: at 40°C cSt = 9.4
>The viscosity of Gulf Mineral Oil: at 40°C cSt = 5.0
>The mineral oil is superior in viscosity and inferior in application.
>If you wish, try Gulf Degreasing Fluid: at 20°C cSt = 1.9
>(clearly a killer according to the logic of viscosity)
>
>Then there is Gulf's Gulftherm Oil specifically designed for closed
>unpressurized heat transfer systems and described as:
>>>Gulftherm oils have high specific heat and thermal conductivity at all temperatures
>and spec out: at 40°C cSt = 22 to 68 (depending on grade)
> Bird Shit (AKA thermal compound) is extremely viscous (a grease in fact)
>and the most common form of heat conductor interface used in electronics.
>Dow Corning 200 centipoise Silicone Oil that is explicitly called for by HP for their
>Caloric Power Meter.
There are six (6) examples of fluids employed in heat transfer that
bracket the discussion on all counts for all points argued (again,
removing the joker of water from the deck). No critic to this point
has seen fit to answer the contradictions of their statements to the
evidence and no critic to this point has even offered one example to
support their mantra. Again, "show your work."
There are many other readers of this thread looking for alternatives
to the staple of myth and want intelligent guides beyond the simple
repetition of totems and taboos. I will even allow some may want a
new faith, amulet, charm, or simply some inspiration. Beyond that,
they are hungry for explicit samples that can test, prove or refute
the claims of testimonials. From my effort they have much more to
examine than a laxative.
Richard Harrison
"I would imagine transformer oil, but what about other oil?"
Dielectric Systems, Inc. makes a synthetic insulating oil with excellent
heat transfer, flow at low temperature, compatible with insulation and
other transformer oils (mixes with your PCB`s), and is biodegradable. It
is fire resistant, cools better than other fluids (unamed), and is the
industry standard for retrofitting mineral oil transformers.
Who says so? Why the makers of Alpha-1 Fluid, that`s who!
You can find them on the web if you need a sample.
Best regards, Richard Harrison, KB5WZI
Richard Harrison
"It would be obvious to a 7th grade science student that the lowest
The student is aware of water`s use in radiators and other heat
exchangers. He probably doesn`t know that distilled water is an
excellent insulator used to cool radio transmitters where it must
withstand well in excess of 10 000 volts. Problem is in keeping the
water free of salt and pH neutral so the water doesn`t conduct. A couple
of the stations I worked in never worried with checking the water and
just let it leak power from the high-power supply. The other stations
checked the water regularly and and corrected the pH or changed out the
distilled water when it got leaky.
For the "cantenna", I would favor oil (it doesn`t mix with water).
Richard Clark
Hi Richard,
Thanx for the commentary on water, and the joker it presents.
Hope this doesn't lead to the discussion of the convection of oil and
vinegar. ;-)
Stephen C. Robbins
"Robert Spooner" <rl...@psu.edu> wrote in message
news:3CCFFBAE...@psu.edu...
> In a wet dummy load, viscosity has _everything_ to do with heat
> transfer. Convection currents are the primary means of transporting
> heat from the resistive element to the can.
Hmm, looking at equations for heat transfer in large oil bath transfomers
and the convection component is looking like about a 3% factor in the
equation with conduction dominating the formula. In a small volume
container like a Cantenna, this would be even more so. I think that
someone's assumptions are biting them in the butt. If I were to build a
dummy load that relied on some convection type flow, I would strive to
create a substantial temperature gradiant. I would NOT put a paper wrapper
on the can. I WOULD increase the surface area of the can by putting fins on
it and I WOULD make it tall and narrow. Lets face it, a Cantenna is a low
tech glob of substance with enough volume to hold X amount of heat,
generated in normal transmitter testing and tuning. If one dug around, he
might find a transformer that uses convection as it's primary mode of
cooling but usually these use forced flow type heat exchangers.
Suggest the professor take a Cantenna over to the mechanical engineering
department and let the undergrad heat transfer students model it as a
project.
K7JEB
>> Bob Spooner, AD3K, wrote:
>> What you don't seem to recognise is that the Cantenna
> Richard Clark, KB7QHC, wrote:
> What I do seem to recognize is no more detail nor argument beyond
> "'tis so!" A truly less than useful answer to the matter of the
> subject.
It seems to me that both of these properties (viscosity and
specific heat) play important roles and are intertwined with
themselves and other factors.
For example, since convection is driven by buoyancy, the
thermal coefficient of expansion of the fluid will have an
effect on the mechanical force created that moves the
fluid past the resistor.
And the thermal resistance of the fluid determines how fast
heat can propagate through the laminar flow region close to
the resistor.
And just to add a final complication, I'm not at all sure
the surface of the can itself will efficiently transfer a
kilowatt of heat to the surrounding air without the oil
inside getting hot enough to vaporize and flash ignite
under steady-state conditions.
It's problems like this that make me wonder how they ever
got heat engines to work in the first place.
--
Jim Bromley, K7JEB k7jeb @ arrl.net
Glendale, Arizona
Ken
wrote:
>It is the "Specific Heat" (capacity) of the liquid you are interested
>in comparing one to the other.
In India, viscosity "determines the rate of cooling."
http://www.indiaelectricmarket.com/iemhome2/products/Transformer/Transformer_Oil.htm
Jim Weir
down tight. That way you won't be tempted to measure viscosity, specific heat,
or the price of beans in China.
Jim
Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup
Wayne and Louise
I've been watching the thread now for a couple days and thought I would
chime in my 2 cents worth. I have had a couple "Cantennas" (Yep, genuine
Heathkit.) for many years. I was about to use transformer oil because I had
a "source" for the stuff. One fellow, said, "Don't use that stuff, it could
be made with PCB's." This was back in the 70s.
Well I took his advice and used mineral oil instead. I'm glad I did
because, sure enough, next thing you know the whole country is going nuts
over PCBs and their link to cancer. I don't know if you're likely to find
transformer oil made with PCBs today. Perhaps not, bit if it were me
looking for a cooling liquid, I would be tempted to check on the source just
to make sure it doesn't contain any PCB. Some well meaning ham might just
have some sitting in a corner and be willing to give it away, not knowing of
its potential for causing health problems.
Maybe this will get us off the French fries in the shack idea, but the
culinary aspect of cooking oil as a coolant was worth a laugh. Perhaps
someone here is better equipped (smarter) to expand on this issue than me.
If so, perhaps a post from a more knowledgeable individual would be in
order.
73,
Wayne, W1KI
"Richard Clark" <kb7...@attbi.com> wrote in message
news:ca5pcuoh97c34otg6...@4ax.com...
> On Tue, 23 Apr 2002 01:41:25 GMT, "joel" <jo...@cyberbest.com> wrote:
>
> >I'm seriously thinking about building a cantenna type dummy load. My
> >question is what sort of oil is used? I would imagine transformer oil,
but
> >what about other oil.. Cooking for example?
> >
> >Joe ( AG4QC )
> >
>
> Hi Joe,
>
> Seems the critical element of this thread is left undisclosed.
>
> It is the "Specific Heat" (capacity) of the liquid you are interested
> in comparing one to the other.
>
> Specific Heat is the work required to raise a given weight of
> substance one degree celsius.
>
> For an opener Water stands at an impressive c = 4.183
> compare to machine oil at c = 1.68
> or glycerine at c = 2.43
Ralph Mowery
poison. Just do not subsitute it for meneral oil if you are
constipated. The stuff won't bother you unless you plan on drinking
it.
Roy Lewallen
Ralph Mowery
can read similar wording in almost any medical refferance on almost any
perscription drug.
Remember the sacrin (may have misspelled it) , the sugar subistute scare
? Seems that rats developed cancer from it but they were fed the dosage
as to where a human would have to take a double handful several times a
day every day.
Sylvan Butler
> Hope this doesn't lead to the discussion of the convection of oil and
> vinegar. ;-)
I don't think oil and vinegar convection is near the problem as is
the homogeneity (or not) of the solution.
;)
sdb
--
| Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
| Watch out for my e-mail address. Thank UCE. #### change ^ to @ #### |
They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety. --Benjamin Franklin, 1759
Fight terrorism, arm the population!
David G. Nagel
Bill Nelson
> In the "Cantenna" type dummy load we're talking about,
> VISCOSITY IS IMPORTANT. Why? Because heat dissipation inside the can
> depends on circulation of the oil due to convection heating.
> High viscosity = low circulation.
> Imagine an oil with high specific heat but as viscous as molasses in
> January. The oil in direct contact with the resistor will absorb heat
> wonderfully, but can not carry the heat away because the viscosity is so
> high as to impede circulation. Heat in the resistor will quickly build
> up to the point of damage.
> I hope the picture is clear now. Otherwise, I quit.
You need to think about this a bit more.
Let's consider the extreme in high viscosity - a solid metal like
aluminum. Now, when the aluminum absorbs heat from the resistor, are
you saying that the aluminum "can not carry the heat away because the
viscosity is so high as to impede circulation"?
As the others have stated, viscosity is only necessary when fluid flow
is required. It is easily possible to have heat conduction in a fluid with
little or no fluid circulation.
The Cantenna was not designed to use radiation from the can to radiate
the heat generated in testing. The oil is meant to absorb the heat, so
the two important parameters are heat capacity and heat conductivity.
--
Bill Nelson (bi...@peak.org)
Bill Nelson
>>
> What you don't seem to recognise is that the Cantenna type dummy load is
> designed to use convection for cooling. A high specific heat capacity
> will influence how long it takes the dummy load to get to steady state
> at a given power dissipation, but viscosity will be the larger influence
> on how much power can be dissipated in a steady state condition. That's
> why power companies cool transformers with transformer oil rather than
> something else as well, the transformers are designed to use convection
> cooling.
Think about this a bit more Robert. In steady state, what determines
how much power can be dissipated is the efficiency of the outer radiating
surface of the Cantenna.
As I noted in a different response - convention is not necessary. All
you need is heat conductivity in the fluid/solid. Solids would be more
efficient, but there is the problem of electrical conductivity. There
are many fluids with good heat conductivity that are poor electrical
conductors.
If I recall correctly, all the transformer oils are of rather high
viscosity. If viscosity is so important - why don't they use mineral
oil, which is very inexpensive?
--
Bill Nelson (bi...@peak.org)
Bill Nelson
>>
> What you don't seem to recognise is that the Cantenna type dummy load is
> designed to use convection for cooling. A high specific heat capacity
> will influence how long it takes the dummy load to get to steady state
> at a given power dissipation, but viscosity will be the larger influence
> on how much power can be dissipated in a steady state condition. That's
> why power companies cool transformers with transformer oil rather than
> something else as well, the transformers are designed to use convection
> cooling.
Think about this a bit more Robert. In steady state, what determines
how much power can be dissipated is the efficiency of the outer radiating
surface of the Cantenna.
As I noted in a different response - convention is not necessary. All
you need is heat conductivity in the fluid/solid. Solids would be more
efficient, but there is the problem of electrical conductivity. There
are many fluids with good heat conductivity that are poor electrical
conductors.
If I recall correctly, all the transformer oils are of rather high
viscosity. If viscosity is so important - why don't they use plain
old low viscosity household mineral oil, which is very inexpensive?
--
Bill Nelson (bi...@peak.org)
Richard Harrison
"If viscosity is so important - why don`t they use plain old low
viscosity household mineral oil, which is very inexpensive?"
Circulation of a coolant is helpful but not always needed. We see
oil-filled transformers with and without external oil circulation pipes.
If the water/coolant pump in your car broke, the engine might quickly
overheat. Consider the effect of the engine thermostat. When it is
closed on a cold morning, it doesn`t take long for the engine heat to
open the thermostat so that coolant circulation begins and your car
heater can go to work.
Mineral oils were flammable. Transformers were often put in expensive
fire vaults to confine damage when transformers erupted in flames.
That`s why GE`s Pyranol and other PCB oils replaced mineral oils.
Pyranol is fire resistant and saves the cost of a vault.
Bill Turner
<bi...@spock.peak.org> wrote:
>You need to think about this a bit more.
_________________________________________________________
No, I don't. Like I said before, if it's not clear by now, I quit.
Bill, W7TI
Robert Spooner
I'll have to look at my instruction book to be sure, but as I recall,
the power rating for the Cantenna is higher for transformer oil than for
mineral oil because transformer oil has a lower viscosity than mineral
oil, allowing more heat to be tramsported by convection. The data
sheets I have seen for transformer oil list viscosity but not thermal
conductivity, which seems to indicate that at least in typical
applications, viscosity is the more important characteristic.
While industrial mineral oil is available in a range of viscosities
(I've seen up to 200 cSt,) I don't know what the viscosity of ordinary
household mineral oil is. My recollection is that it is "thicker" than
transformer oil. Chevron transformer oil is listed as 8.93 cSt at 40
degrees C.
The outside of the can is the same no matter what coolant is used and is
therefore a constant in looking at the relative merits of different
coolants no matter which physical mechanism dominates the heat transfer.
Bob
Bill Nelson wrote:
>
> Think about this a bit more Robert. In steady state, what determines
> how much power can be dissipated is the efficiency of the outer radiating
> surface of the Cantenna.
>
> As I noted in a different response - convention is not necessary. All
> you need is heat conductivity in the fluid/solid. Solids would be more
> efficient, but there is the problem of electrical conductivity. There
> are many fluids with good heat conductivity that are poor electrical
> conductors.
>
> If I recall correctly, all the transformer oils are of rather high
> viscosity. If viscosity is so important - why don't they use plain
> old low viscosity household mineral oil, which is very inexpensive?
>
> --
> Bill Nelson (bi...@peak.org)
--
Richard Harrison
"The data sheets I have seen for transformer oil list viscosity but not
thermal conductivity, which seems to indicate that at least in typical
applications, viscosity is the more important characteristic."
Why not just use air cooling. Air is a very low viscosity fluid!
Could be there is much more variation in oil viscosity than oil thermal
conductivity.
Robert Spooner
Richard Harrison wrote:
>
> Could be there is much more variation in oil viscosity than oil thermal
> conductivity.
Right. And that means that given the choice between two working fluids
with the same conductivity, the one with the lower viscosity will be the
better choice because there will be more convection. You get the added
benefit of a counter-current mechanism to improve heat transfer out of
the can. The oil on the inside flows down the side of the can, and the
air on the outside flows up, maximizing the transport of heat through
the can.
Bob
Dick Carroll
> This web page sounds like all the other government gobbley gook. You
> can read similar wording in almost any medical refferance on almost any
> perscription drug.
> Remember the sacrin (may have misspelled it) , the sugar subistute scare
> ? Seems that rats developed cancer from it but they were fed the dosage
> as to where a human would have to take a double handful several times a
> day every day.
Anyone remember Times Beach, Missouri? It *was* a small town on the banks of
the Merrimac River some 30 miles west of Saint Louis, where back in the 80's
some character sprayed PCB-laden oil on nearly every street in the town of
some 3,000 population, instead of disposing of it properly as he had been paid
to do. When the EPA got wind of what had happened, they evacuated the entire
town, then bought the entire town, then proceeded to raze every house, tear up
every street and dig up prodigious amounts of soil therefrom. Then they moved
a huge incinerator into the nearby area, and hauled all that street material
and soil to it and burned it all. Took nearly a year, and untold $$$$millions
from the Super Fund. Made the headlines around the world.
Today, it is wide open space on the riverbank
Fast forward nearly 20 years, and on the back pages of the news what should
appear but a small few column-inches noting that the scientist who was largely
responsible for all that activity had recently said that if he had know then
what he knows now, all that would not have been done, as it turned out to be
unnecessary. Seems that PCB's have later been determined to be seriously
dangerous only if they have been overheated, charred etc, which none of that
was..
So what did they do with all the PCB's they took out of Times BeacH? BURNED
them, of course!
Dick Carroll
> viscosity is only necessary when fluid flow
> is required. It is easily possible to have heat conduction in a fluid with
> little or no fluid circulation.
I can attest that mineral oil in a Cantenna does indeed circulate. I proved
this one day at work when we needed to tune up a 3KW transmitter on a dummy
load, and my Cantenna was the closest possibility within many miles. We were
able to do so, but we did watch the Cantenna and limit the tuning time to
quite short duty cycles. But it will boil and circulate the oil quite nicely
at that power level if left on for very long, more than 15 seconds or so..
Dick
.Bill :-)
bit of perspective on the PCB thing.
After all, we're talking about a gallon in a sealed can...IF you were
even able to find a PCB-laced product to use.
Fact: The sky will not fall if you use a Cantenna.
-Bill
Dick Carroll wrote:
>
> Ralph Mowery wrote:
>
> > This web page sounds like all the other government gobbley gook.
> Anyone remember Times Beach, Missouri? It *was* a small town on the banks of
> the Merrimac River some 30 miles west of Saint Louis, where back in the 80's
> some character sprayed PCB-laden oil on nearly every street in the town of
> some 3,000 population, instead of disposing of it properly as he had been paid
> to do.
Roy Lewallen
dioxin, not PCB. Anyone interested can find numerous references to it on
the web.
Roy Lewallen, W7EL
Dick Carroll wrote:
>
> Ralph Mowery wrote:
>