Retired person with too much time on his hands?

[walt]

Way off topic for sailboats LOL.. but its near mid winter so posting about goofball stuff might be ok..

We use propane fire pits which radiate heat from the flames to people sitting around the pit but a lot of heat just goes straight up with convection. So.. for not really a good reason, Ive been playing around with a couple "contraptions" of pots I bought at thrift shops and placed above the fire pit. The idea is that the pot above the fire pit gets very hot and then radiates some of the energy that would have just escaped back at folks sitting around the fire pit. Why the different pots.. just what I found at thrift stores.

Blackbody radiation just depends on some emissivity coefficient, temperature and surface area. So the pot above the fire pit just has air inside (not trying to store any energy, just get the pot as hot as possible) and since I really dont want radiation off the top, put in high temperature insulation under the lid. Holes are also drilled in the lid to make the dang thing doesnt explode from pressure and the pots dont get hot enough to glow so stay under melting temp and way under where metal burns. Does it work.. maybe a little, maybe its mostly just some funky experiment LOL.

Or.. maybe a retired person with too much time to to waste?

 

[Tally Ho]

It looks like you have a perfectly good patio heater in the background. Those are designed to radiate the heat downward…

Just use the fire pit for ambiance (or roasting marshmallow).


I have the same problem though…my nice fire table does not really push heat outwards. You have to hold your hands over the flame to get heat.

Let me know if stumble on a winner!

My solution was to buy a place in SW Florida and head South

Greg

 

[Ralph Johnstone]

but its near mid winter so posting about goofball stuff might be ok..

Goof ball ideas are as crucial as the air we breath at this time of year. Haven't seen the sun for so long, I've forgotten what it looks like. Rain, rain, nothing but rain. People have started growing webbing between their toes. Everybody looks like they've got a tan. It's NOT a tan, it's rust.

Ive been playing around with a couple "contraptions"

Without a doubt, the most high tech campfire I've ever seen. You might want to photograph it with a an infrared camera to see what your high temperature surfaces are like.

 

[Ralph Johnstone]

My solution was to buy a place in SW Florida and head South

Most effective, yes. Perhaps a little pricey however.

 

[Leeward Rail]

Most effective, yes. Perhaps a little pricey however.

Many places in the world are cheaper than the USA.. and warm.

 

[Leeward Rail]

Being inquisitive is the best thing in life.
Keep on with the development. You need a way to accurately measure the results.
Maybe objects of the same mass to serve as humans, equally spaced.. then measured with thermal imaging or laser thermometer with etc.

Anything else is subjective.

Looking at the photos, I would likely feel perfectly warm with the fire out.
There is no snow in those photos. Here, in the land of actual cold... we just build a bigger fire, with wood, and while staying in one spot, rotate ourselves like marshmallows.

Using wood, and rotation, solves the heating problem.

 

[walt]

I have a hand held IR thermometer that only goes to 100C and it quickly pegs the limit so the pot gets hotter than 100C. Recently I ran the fire pit hot, shut the fire pit off and turned off the lights to see if the pot was glowing, it was not. So I think pot temperature is under 500C. Aluminum melts at 660C so that isnt an issue. When the propane fire is extinguished you can still feel significant radiation from the pot..

The only test I sort of plan to do is sometime when the pot is hot and some folks are sitting around it, somewhat quickly move the pot away (only can be done with the version using the free standing stand) and see if the people around the pit notice any difference. All the heat is radiation to the results will be felt immediately but of course still subjective. Will this mean much.. Hmm.. and those testers likely will have been drinking...

Used the medieval looking pot last night (in Arizona) and someone asked what's in the pot?

Tally Ho, your guest seem to be pleased with the heat!

 

[Tally Ho]

Tally Ho, your guest seem to be pleased with the heat!

Wife, sister and mom…probably taken last September or so…. They all had blankets on their laps

 

[dlochner]

If the pot is filled with sand, it will take longer to heat, however, the sand will continue to radiate the heat if the fire is turned down a bit. Water would also work, but that might steam up the spectacles on the old folks.

 

[walt]

I have not tried this with any "thermal mass" in the pot but I think it will also just delay how long it takes before the pot starts to do its job and radiate. The other thing about a propane fire pit is that if you have any wildfire risk, when you get done with the fire and want to leave, just shut it off unlike a regular fire that takes a while to go out and must be attended to. So.. I dont think I want that thermal heat storage.

The equation for black body radiation (Stefans law I believe) has the radiation power as a function of temperature to the 4th power . This would seem like radiation would go up very quickly with temperature but its on the kelvin scale so not so dramatic. So when heat is applied to the pot, it heats up until an equilibrium of heat energy in from the flame equals radiation heat energy out at which point the temperature stabilizes. The radiation power is only dependent on surface area, not thermal mass. A lower thermal mass should however heat up faster.

 

[Tally Ho]

Same reason I put a ceramic flower pot on my boat stove when I need to use it as a heater…

Greg

 

[Leeward Rail]

The only test I sort of plan to do is sometime when the pot is hot and some folks are sitting around it, somewhat quickly move the pot away (only can be done with the version using the free standing stand) and see if the people around the pit notice any difference.

That's what I meant when I said to measure..

Objects spaced away from fire/pot at consistant distances.
Unbiased, identical stand-ins for humans. Something similar in mass to humans.

Use your thermometer to measure them, not the pot over the flames.

If you want to be really fun, get some sensors on sticks in the ground at chair height. and log the data.

Worst case the thermometer would work by just testing the surface of the humans, but that would lower accuracy. Likely more accurate than subjective opinions though.

That tarp is a huge help in trapping the heat. If you had a bigger one in a dome shape, it would trap the heat more. Propane avoids the smoke issue that we have to adjust for when having a wood fire under a tarp roof in the cold.

 

[Leeward Rail]

Same reason I put a ceramic flower pot on my boat stove when I need to use it as a heater…

What's the point when it's heating the cabin air regardless ?

Outside with a fire, the heated air rises into the atmosphere unimpeded.

The point of the top cones on outside patio heaters it to try keep the heated air in the area longer by forcing it outwards before it rises above the cones.
A tarp/roof above a bonfire has the same effect.

Inside a boat, the heated air is trapped in the cabin. I can't see the pot helping much when the heat is already prevented from quickly rising out of the boat.(Unless the stove is directly below an open hatch).
I tried the pot idea on our previous boat and it didn't seem to make a difference in spreading the heat sideways.

A better option in a boat on the stove would be one those thermally driven wood stove fans sitting on a metal pan over the flames. (I used a battery.powered fan instead)

 

[Project_Mayhem]

A few thoughts, some which others have touched on...

• As we all know, 90% of the heat will go upwards
• Radiant heat is good at warming stationary objects while forced air is good at warming the air
• Cutting down on wind will help a lot
• Will the insulation get too hot? Some will release toxic fumes if subjected to high heat
• Rocks or sand work well if you want to retain heat
• I'd consider heating up some bricks and then placing them under peoples chairs to keep them warm
• If you really want to get sophisticated, I'd look into heat pipes or pumping heated liquid to the right places
• Heated outdoor mats for melting snow might work if placed under people's chairs

 

[walt]

The word retired was used in the title.. Some of this is sounding like a having a job!!

The comment about the high temp insulation is good and something Im a little concerned about. I have used both pots in the pictures a fair amount with some type of "high temperature wool" insulation rated to 1200F (650C) and so far, there doesnt seem to be any strange outgassing or burning issue. The medieval looking pot is getting used now and I will open it later and inspect the insulation.

Neither pots get hot enough to glow so I think they are staying under the 1200F temp. There likely is a better choice for the high temperature insulation which is ceramic fiber blanket rated to 2400 F.

And of course.... I would need to do a lot of work to prove that insulating the top does anything so this likely wont happen. Haven't checked the medieval looking pot yet but the red pot lid actually only gets warm to the touch in use so actually does have much reduced upwards radiation also (likely) meaning the lower pot face which radiates towards people sitting around the fire runs slightly hotter.

 

[Project_Mayhem]

How about a bunch of small DC fans on the perimeter of the fire pit blowing towards people? I wouldn't do AC fans, just in case something melts, shorts, etc

 

[Tally Ho]

I saw this version of a fire pit on the web today…actually in my hometown on-line newspaper…

More of a reflector/defector like the commercial propane patio heaters.

I think the article had to do with saunas and stuff in the winter…

Greg

 

[shemandr]

or you could go inside.

 

[Leeward Rail]

The word retired was used in the title.. Some of this is sounding like a having a job!!

Don't you know that retirement often means more projects ?

 

[JBP-PA]

Being retired has enabled me to do so many more fun projects!