Snake oil product or not ?

[waterworks178]

Recently a product has come on the market that consists of a cage to hold coal inside a solid fuel burning stove in a vertical stack instead of laying piled up on the great, the inventor claims this increases radiant heat, buyers are reporting they are saving significant amounts of fuel using this product, many stories are too good to be true and my own test of it found nothing . I'm interested if there is any scientific principles that could explain why this product would work,

why would an increase in radiated heat inside a cast iron stove lined with fire brick make it more efficient at heating a room? ( This is not for use on open fires )

The door to most stoves this product is being used on have a glass window, could this transmit more radiated heat if the fuel was placed in a stack behind it ?

Is it possible to get more energy from coal by burning it in a different arrangement or is all the energy released however you burn it( without forced air )?

https://www.coalcage.com

 

[Latexman]

Not snake oil, but . . .

Two different shaped piles of coal of the same mass when oxidized completely, yield the same energy.

Maybe the vertical support allows more mass, or a faster rate of oxidation than a flatter pile on a grate.

Good Luck,
Latexman

 

[Compositepro]

It looks like a good way to support the coal so that it has access to combustion air and the combustion products can flow out of the coal bed freely. This will tend to make the coal burn faster and hotter, which probably will result in some improvement to overall efficiency. But the effect will be small and depend on the design of the entire stove and flue system.

The heat content of the coal is a constant. All that can change is what percentage of the heat goes into the room vs up the flue. Excess air flow is the is the main factor that will reduce heating efficiency. The cage may help reduce the need for excess air to keep the coal burning.

 

[cranky108]

Yes, air mixing technology can make a difference. Also the flame temp. can make a difference in how much NOx is produced, and that can eat up a few BTUs.

But I like my coal pulverized, and blown into the boiler in a cyclone pattern.

Excess air also reduces the amount of heat left in the burn chamber.

 

[LittleInch]

There's a few things here.

Less air going past the coals will reduce the amount lost up the chimney and higher radiant heat should heat up the outer metal skin and give more heat to the outer side of the fire. There may be a small increase in radiant heat through the glass door for sure, but only fairly minor.

Concentrating it all in the middle will help with grates which only have air inlet in a circle in the middle like mine does then the coals will burn better and not just glow less on the outside of the firegrate.

Coals apparently burn better with "bottom air" rather than top air like wood.

Can see it being more efficient in making sure the coals burn better and faster, but with less of them.

but "significant amounts better"??Hmmm - would need a more controlled test than many people can give it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waterworks178]

Why would increasing the radiant heat transfer from the fuel to the stove body be better than the other methods of heat transfer to the stove body?

 

[IRstuff]

Because radiant heat is roughly proportional to the 4th power of absolute temperature, while convection and conduction is only linearly proportional.

TTFN (ta ta for now)
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[chicopee]

Keeping combustion air flow, coal mass and the external size of the stove the same, the cage design may provide more radiant heat generated from the cage as there is more surface area from the cage configuration generating thermal radiation than from a flat grate.

 

[Compositepro]

I believe the main benefit of the cage is that it creates a chimney effect inside the coal bed. Cool combustion air is heavy and will enter the cage near the bottom then rise through the bed rapidly due to the chimney effect causing the very hot combustion products to rise through the coal bed. By the time the gases exit the bed at the top all of the oxygen will have been consumed, thus no excess oxygen (or, more importantly, the associated excess nitrogen) that causes heat losses up the flue.

The cage has less radiant surface area than a flat bed of coal. The purpose of firebrick in a stove is to trap radiant energy in the stove to keep the fuel hot enough to burn. Caged coal traps radiant energy inside the coal bed so it burns very efficiently and most of the the heat goes into the gasses leaving the top. Airflow is controlled by dampers in the flue and in the air inlet.