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After almost twenty (I think) years on this group, I know that it's
not a chemical or metallurgy forum, however with all the talented
people here I was hoping that someone could possibly offer a
suggestion for my problem, or perhaps refer me elsewhere.
For the past 35 years I have heated my home with a wood stove.
We are now on the third incarnation of wood stoves which we have
had. As they burn out we replace them. They have all been made
out of heavy gauge 55 gallon barrels, and I have been very satisfied
with all of them. There is a door for loading the wood in and an
output for smoke. It is a very simple, inexpensive and yet completely
passive but effective scenario.
Standing behind the stove for the last 30 or so years and again, in
keeping with the idea of simple and passive has been a 42 gallon
galvanized water tank. My first two tanks have sported a dull grey
finish.
The first tank was replaced about twenty years ago, and last Fall it
was necessary the replace the second tank. This will now be the third
tank since we've lived here. The new tank I purchased was equivalent
to the last two we've had, and it was installed directly in place of
the old one.This one however has a shiny metal finish.
Cold water runs into this tank and is heated by the stove. As the
electric hot water heater calls for water it is supplied by this tank.
Since the water is preheated, this has saved us thousands of
dollars over the years.
From the very beginning of the season I started to notice that the
new tank failed to get as hot as the older tanks did. In fact on the
coldest days even with the wood stove cranking, the new galvanized
tank barely would get hot at all. The best I ever noticed when putting
my hand on it was tepid, but never hot, as the old tanks would get.
I have wracked my brain trying to figure out what could possibly be
going on here, and the only thing I could come up with is the fact
that the first two old tanks had a dull grey finish to them, while the
new tank has a grey shiny metal finish.
It has been suggested that while a dull finish absorbs heat, a shiny
surface would reflect it, and so to make it perform as the last two did
I have to find a way to dull the surface of this tank.
I have thought about possibly painting this new tank with a flat paint.
Because it's indoors, this must be done with a brush, and during the
warm weather months so as to air out the house. I am however finding
out that flat high temperature paint, especially paint that that can
be used on galvanized surfaces is very difficult to find. Rutland
makes what would seem like an ideal high temperature flat black product
for wood stoves, however they do not recommend it's use on galvanized
surfaces. And truthfully I don't even know if painting the surface
with flat paint would even accomplish what I need to have happen.
My other thought, and a preferable one would be to find some way to
dull the existing finish to make this new tank comparable to the old
ones. I wonder if this could be done with some type of acid, like
muriatic perhaps?
I've really run into a wall here and I would sincerely appreciate any
thoughts on this matter and how it might be remedied. Thanks to all very
much for any information which you may be able to offer.
Lenny
I found this Web page on the galvanization process, but it doesn't
really help me:
http://www.google.com/url?q=http%3A%2F%2Fwww.galvanizeit.org%2Finspection-course%2Ftypes-of-inspection%2Ffinish-and-appearance%2Fdifferent-appearances&sa=D&sntz=1&usg=AFQjCNFzvuxoxyDJr81E9wnLxfLobTS_Qg
On Wednesday, May 20, 2015 at 9:47:35 AM UTC-4, captainvi...@gmail.com wrote:
My tank stands right behind the stove and touches it as this one appears to.
Ah ha!
I really believe (as I have all along) that radiation transfer is a tiny part of the total. Therefore black paint will do little good.
Most of your heat transfer has always occurred through conduction from the contact.
For some reason your new stove and new tank are not making the same contact as before.
There are two things you can do: improve the area of metal to metal contact, and enclose the area between that is not in contact to allow the air to heat up and give you some convection transfer. I think the most bang for your buck is to improve the contact. Add a brace or two, or even wedge a curved piece of metal between.
You might as well paint it first. You fixated on a solution too soon, before the root cause was known, and you aren't going to give it up until you've tried and failed, at least if you're like most people.
Hi Tim, The radiation can be a lot more than you expect.
If there was a square meter of radiating area, and the stove was ~300F
150 C = 420 K. And the emissivity was one then I calculate a heat transfer of
about 1 kW. Radiation goes as the fourth power of the temperature. And radiation from 300 K to 0K is about 500W/ m^2.
George H.
I'd agree that contact is best.On Wednesday, May 20, 2015 at 9:47:35 AM UTC-4, captainvi...@gmail.com wrote:
My tank stands right behind the stove and touches it as this one appears to.
Ah ha!
I really believe (as I have all along) that radiation transfer is a tiny part of the total. Therefore black paint will do little good.
Most of your heat transfer has always occurred through conduction from the contact.
For some reason your new stove and new tank are not making the same contact as before.
There are two things you can do: improve the area of metal to metal contact, and enclose the area between that is not in contact to allow the air to heat up and give you some convection transfer. I think the most bang for your buck is to improve the contact. Add a brace or two, or even wedge a curved piece of metal between.
You might as well paint it first. You fixated on a solution too soon, before the root cause was known, and you aren't going to give it up until you've tried and failed, at least if you're like most people.
After almost twenty (I think) years on this group, I know that it's
not a chemical or metallurgy forum, however with all the talented
people here I was hoping that someone could possibly offer a
suggestion for my problem, or perhaps refer me elsewhere.
For the past 35 years I have heated my home with a wood stove.
We are now on the third incarnation of wood stoves which we have
had. As they burn out we replace them. They have all been made
out of heavy gauge 55 gallon barrels, and I have been very satisfied
with all of them. There is a door for loading the wood in and an
output for smoke. It is a very simple, inexpensive and yet completely
passive but effective scenario.
Standing behind the stove for the last 30 or so years and again, in
keeping with the idea of simple and passive has been a 42 gallon
galvanized water tank. My first two tanks have sported a dull grey
finish.
The first tank was replaced about twenty years ago, and last Fall it
was necessary the replace the second tank. This will now be the third
tank since we've lived here. The new tank I purchased was equivalent
to the last two we've had, and it was installed directly in place of
the old one.This one however has a shiny metal finish.
Cold water runs into this tank and is heated by the stove. As the
electric hot water heater calls for water it is supplied by this tank.
Since the water is preheated, this has saved us thousands of
dollars over the years.
From the very beginning of the season I started to notice that the
new tank failed to get as hot as the older tanks did. In fact on the
coldest days even with the wood stove cranking, the new galvanized
tank barely would get hot at all. The best I ever noticed when putting
my hand on it was tepid, but never hot, as the old tanks would get.
I have wracked my brain trying to figure out what could possibly be
going on here, and the only thing I could come up with is the fact
that the first two old tanks had a dull grey finish to them, while the
new tank has a grey shiny metal finish.
It has been suggested that while a dull finish absorbs heat, a shiny
surface would reflect it, and so to make it perform as the last two did
I have to find a way to dull the surface of this tank.
I have thought about possibly painting this new tank with a flat paint.
Because it's indoors, this must be done with a brush, and during the
warm weather months so as to air out the house. I am however finding
out that flat high temperature paint, especially paint that that can
be used on galvanized surfaces is very difficult to find. Rutland
makes what would seem like an ideal high temperature flat black product
for wood stoves, however they do not recommend it's use on galvanized
surfaces. And truthfully I don't even know if painting the surface
with flat paint would even accomplish what I need to have happen.
My other thought, and a preferable one would be to find some way to
dull the existing finish to make this new tank comparable to the old
ones. I wonder if this could be done with some type of acid, like
muriatic perhaps?
I've really run into a wall here and I would sincerely appreciate any
thoughts on this matter and how it might be remedied. Thanks to all very
much for any information which you may be able to offer.
Lenny
I found this Web page on the galvanization process, but it doesn't
really help me:
http://www.google.com/url?q=http%3A%2F%2Fwww.galvanizeit.org%2Finspection-course%2Ftypes-of-inspection%2Ffinish-and-appearance%2Fdifferent-appearances&sa=D&sntz=1&usg=AFQjCNFzvuxoxyDJr81E9wnLxfLobTS_Qg
I can probably come up with a method of physically "coupling" the back of the stove to the water tank, to achieve better heat transfer, perhaps with some metal in between. I do like that idea however I don't know if that would still be OK using non high temp paint on the tank though. Lenny
On Wednesday, May 20, 2015 at 3:48:23 PM UTC-4, gghe...@gmail.com wrote:
Hi Tim, The radiation can be a lot more than you expect.
If there was a square meter of radiating area, and the stove was ~300F
150 C = 420 K. And the emissivity was one then I calculate a heat transfer of
about 1 kW. Radiation goes as the fourth power of the temperature. And radiation from 300 K to 0K is about 500W/ m^2.
George H.
I agree on the 4th power, but I doubt the 300 K delta. I think the stove might be 200 F and the tank 100. I base this on water I've put on wood burning stoves, it evaporates quickly but doesn't boil. But even if i give you 300 F, you can't tell me the tank is 0 K, that would be -473 F.
Here's a test of contact versus radiation: preheat your oven to 400F and cook a pizza. Put your hand into the air space and let it absorb heat radiated from the oven sides and grill surfaces plus heat transfer from the air. Now touch the oven sides or grill surfaces. I think you will find the second case more efficient and painful.
You have to put in your own numbers for conduction in the stove case.
(Mind you I'm not saying you are wrong. It could be that most of the heat
is via conduction... you just have to run the numbers.)
George H.
On Thursday, May 21, 2015 at 9:26:20 AM UTC-4, gghe...@gmail.com wrote:
You have to put in your own numbers for conduction in the stove case.
(Mind you I'm not saying you are wrong. It could be that most of the heat
is via conduction... you just have to run the numbers.)
George H.
I remember running the numbers for a wall back in engineering school. Heat transfer through a wall is of course a function of the temperature differential (T1-T2) times Area times a coefficient divided by the R value in appropriate units.
It turned out that one nail extending through the wall could transmit a huge amount of heat, even considering the tiny area, because the resistance is so low.
Same with the stove tank problem - one metal connection between them will transmit 100s or 1000s of times the heat of radiation or convection.
Hi Tim, you can think whatever you want.
If you're an engineer, then do the numbers!