Unburnable paper! The impressive effects of high thermal conductivity materials
Safety: Please take all necessary safety precautions
Thermal Conductivity plays a role in a wide variety of aspects of everyday life ranging from electronics to cooking and coffee making. In fact, without this fundamental concept energy, (in the form of heat) would have a hard time moving from place to place. This concept will be explored by exposing a piece of paper, tightly wrapped around a good thermal conductor, to a fire or source of heat above 250°C. Surprisingly, the paper does not burn when in contact with the good thermal conductor, however; the paper will burn if simply exposed to the fire. These findings indicate that good thermal conductors can transfer the heat generated from the fire away from the paper effectively preventing the paper from reaching its auto ignition temperature.
The goal to be achieved in this experiment is a quantitative visualization of the powerful ability inherent to good thermal conductors in transferring heat across a gradient. In doing so, a greater understanding of thermal conductivity will be achieved and what roles it may play in everyday life.
The fundamental concept which will be employed in the experiment is thermal conductivity. Thermal conductivity is a measure of a materials ability to conduct heat across a gradient (source of high temperature to low temperature) and is measured in Watts/Meter-Kelvin. For this experiment to be SUCCESSFUL and SAFE it is recommended to only use materials with thermal conductivities above 200 W/m-K.
Temperature of an average candle flame: 1100-1400 ⋅C (ideal circumstances)
Auto Ignition temperature of wood: 200-250 ⋅C
- If using a candle, place the candle on a stable flat surface as to not require being held
- Obtain the desired piece of paper and cut out a 1-inch-wide strip along the length of the paper
- Obtain the desired cylindrical rod
- Wrap the piece of paper (tightly) around the rod and hold both extremities above the rod. Example below
- Hold only the paper, place the portion of the paper, in direct contact with the metal, up to the flame for at most 5 seconds
- Record your observations
The piece of paper wrapped around a metal cylinder should not ignite as compared to a freely held piece of paper. The black spot which will appear on the paper is not burnt paper. In fact, it is an impurity (soot) produced by incomplete combustion of the candle wick. This impurity should be able to be removed via wiping or eraser. If both potential situations are compared, the piece of paper with the cylinder is in contact with the metal cylinder and air, whereas; a freely held piece of paper is only in contact with air. Due to the contact with the metal, the paper can transfer the heat of the fire to the bar.
This effectively prevents the paper from reaching an auto-ignition temperature between 200-250 °C. The freely held piece of paper cannot transfer the heat from the fire to only the air due to the poor thermal conductivity of the air. Therefore, the freely held piece of paper will burn.
Taking it further
In this section put: Grab a paper cup or snow cone and fill it with water. Place it over a candle. The cup will not burn, but the water will eventually boil. This is due to water’s high heat capacity; it can absorb a lot of heat when it rises in temperature. Once all, or enough, of the water has boiled away, the paper will burn.
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