HOW THERMAL ENGINEERING MAKES HOLIDAYS AWESOME
The fourth of July is quickly approaching and soon we will look to the sky in awe at the beautiful eruption of color. But do you know how fireworks are able to make such magnificent displays in the night sky?
Fireworks are a series of chemical reactions that begin with an application of heat or thermal energy. The applied heat delivers enough activation energy for the chemicals, packed in a perfectly planned structure within the firework enclosure, to react with the oxygen in the air and fuel. This process (known as combustion) converts the chemicals and stored energy to other compounds and four different forms of energy: heat, light, sound, and kinetic or movement energy.
What we are seeing in the firework display is a direct result of the chemical and energy conversion process. We observe the kinetic energy as the firework expands from its point of origin, and certainly hear the sound as it rumbles through the atmosphere, but the most amazing aspect of the firework display is the color or light energy.
There are two types of light that we observe as we view the colorful display: incandescent and luminescence. Incandescent light is produced from heat and is what makes some fireworks brighter than others. Elements that burn hot, such as aluminum and magnesium, produce a brighter incandescent light. The color is a form of luminescent light. This light is produced from the energy absorbed by an electron of an atom. (In the case of a firework, it is produced from the thermal energy absorbed.) The absorbed energy excites the electron and causes it to be unstable. As is returns to a lower, more stable state, energy is released. Each element has a unique amount of energy that is released as its electron returns to a stable state. The energy is released in the form of a photon. So, the colorful, bright lights we see are determined by the chemical compound within the package and the heat applied to that compound. For example; a Lithium Carbonate compound will emit a photon with an energy that corresponds to a deep red color. A Copper Chloride compound will emit a photon that is blue. Barium, a hot burning element combined with chloride, will create a bright green light.
Now, there is one more element to designing a breathtaking show: timing. The timing of the show is a result of proper thermal management. Although firework engineers are not applying any two-phase heat transfer devices to ignite the display, they do need to calculate the burn rates of the multiple fuses to identify the exact time each reaction will occur. So, as you gaze upon the open sky this Thursday, think about thermal energy and the chemicals required to cause the beautiful display and just how awesome heat transfer really is!