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It is said it makes the cooking more efficient to surround the fuel canister and fire with rocks. How to explain it with physics?

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PS.

  • How does rocks compare with wood blocks in efficiency? Is the heat capacity of rocks relatively high as compared to most other materials found in field environment? Is it the main point that rocks can be used as a heat reservoir?
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  • $\begingroup$ First reason you use rocks is to reduce the risk of wildfires, I think. But it could also help that the rocks heat up and continue to release heat in the surroundings... $\endgroup$ – valerio Jan 1 '18 at 1:09
  • $\begingroup$ The rocks block airflow. Some airflow is necessary for combustion, of course, but beyond that minimum amount the air just carries away heat. Also, the rocks reflect heat inward. $\endgroup$ – Hot Licks Jan 1 '18 at 1:43
  • $\begingroup$ The rocks just define the outer boundary of the fire. $\endgroup$ – MaxW Jan 1 '18 at 4:28
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The rocks heat up, and radiate heat back towards the pot. This increases the over all flow of heat to the pot; if the rocks were not there, there would be nothing there that gets hot and radiates heat.

Somewhat relevant is my earlier answer about how close you can get to lava without burning - it covers how the solid angle of the hot object affects the heating.

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  • $\begingroup$ I understand these elements. The main thing I'm asking is why using rocks is efficient -- why not big wood blocks for example. Please ignore other factors such as wood blocks are harder to find and move etc. etc. Is the heat capacity of rocks relatively high? $\endgroup$ – qazwsx Jan 1 '18 at 5:12
  • $\begingroup$ I think that the rocks can get closer, and thus get hotter - and since the radiated power goes as the 4th power of temperature, that matters. If you put logs that close, they are either wet (and won't get hot) or they catch fire - in which case you are using more fuel and you can't really speak of "efficiency". $\endgroup$ – Floris Jan 1 '18 at 20:41

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