Have you ever sat around a campfire in the evening and thought, other than it being a huge fire warming you, have you considered the scientific research on how a campfire warms you?
Sitting around an open campfire, most of the heat you’re getting from the flame from the campfire is not directly from the hot air. It’s actually due to thermal radiation!
In general, there are three ways in which heat can move:
- Radiation conduction
Thermal radiation comprises electromagnetic waves (mostly visible and infrared light) released by objects because of their temperature. The radiation is carried by the energy that can be converted into heat when it strikes another object and absorbs.
Conduction, on the other hand, is the direct flow of energy through an object. Since air is superior to thermal insulation, conduction is the most efficient method of heat to move through the air.
Additionally, convection involves the majority movement of pockets that contain heated water. In convection, a small pocket of fluid, like water or air, is heated and is then moved other by the flow of fluid.
The heat radiation generated by thermal radiation generally spreads throughout the entire. In the same way, heat that is transferred through conduction is likely to be able to travel in all directions and primarily flows through object components with higher thermal conductivity.
Convection-generated heat may also flow in any direction if a current moves in the same direction (e.g., an air stream produced by the fan). However, heated liquid tends to condense upwards in normal conditions on earth. This is because heated fluids tend to be lighter than the colder fluid around them, which is why they are pulled up and out of the way when gravity pulls more on the denser, colder pocket of liquid.
With these fundamentals set, let’s head towards the fire at camp. The campfire releases warmth through all three of them. Because air isn’t a good thermal conductor, it is unlikely that you be able to absorb lots of heat from the campfire through conduction unless you place your hand into the flame. Thus, if you’re just a few feet from the fire, we can ignore conductive heat transfer. The radiation of the fire radiates across all directions and can be absorbed by you. This radiation comes comprised of visible light and infrared radiation.
Contrary to this the heat from the campfire that is generated by convection is sucked towards the sky but doesn’t reach you (i.e., hot air billows upwards). So, near a campfire, nearly 100% of the warmth you absorb from the fire is transferred via thermal radiation.
This is why the part of your body facing the flame gets hot, and the other side away from the fire remains cold. Thermal radiation is a kind of light that can travel through straight lines. The body part facing away from the flame is in shadow and cannot receive the heat radiation.