I'm baffled by this whole Crisco/shortening candle-in-contraptions meme circulating around. You've got folks shoving these things in everything from copper pots to elaborate sand enclosures, claiming superior heat output and somehow making a case for off-grid energy.
Let's unpack the physics, because frankly, it doesn't add up:
Combustion 101: A candle (or our Crisco-fied iteration) works by burning the fuel source (fat in this case), releasing heat and light through a chemical reaction with oxygen. The material surrounding it doesn't inherently influence this combustion process. Copper, terracotta, or sand won't magically accelerate the burning rate or somehow trap more heat.
Radiation & Conduction: Sure, these materials might hold and radiate a BIT more heat absorbed from the flame compared to open air. But the difference is negligible. Convection (hot air rising) is the primary heat transfer mechanism, and the enclosure doesn't significantly enhance it.
Scaling Up Fallacy: If this contraption truly held the key to efficient off-grid heating, wouldn't we be ditching fuel oil and natural gas entirely? Imagine a skyscraper-sized Crisco candle in a cosmic copper pot - it wouldn't magically solve our energy needs. The heat output wouldn't scale proportionally due to limitations in combustion itself.
In short -- why are people so fascinated with this? A simple test will show that it is not more effective than a simple candle, yet people seem to be continually fascinated by it.
You are misunderstanding the purpose of the different things you are describing. People aren't using the Crisco candles contained in sand to generate heat. Those are extended use light sources. The use of the terracotta pots placed over a candle or other flame heat source is to capture and re-radiate the heat using the terracotta pot as a larger surface for heat to radiate off of. Larger surface area = more USEFUL heat being radiated towards the people in the room. You are mixing up the ideas here. Which could work if you actually had a useful arrangement for the pot over the Crisco candle.
This isn't my picture, which is the whole point. People are making these bizarre contraptions without even a theory of what they would do.