The heating element in most hair dryers is a bare, coiled nichrome wire that's wrapped around insulating mica boards.
Nichrome wire is an alloy of two metals, nickel and chromium. This alloy is used in heating elements in a number of household products, from curling irons to toasters. Nichrome wire has two features that make it a good producer of heat:
- It's a poor conductor of electricity compared to something like copper wire. This gives the alloy enough resistance to get hot from all of the current flowing into it.
- It doesn't oxidize when heated. Other metals like iron rust pretty quickly at the temperatures used in toasters and hair dryers.
The airflow generated by the fan is forced through the heating element by the shape of the hair dryer casing. When the air initially enters the barrel, it is much cooler than the nichrome wire, so heat flows from the wire to the air. As the air is pushed along by the fan and convection, it is replaced by cooler air and the cycle is repeated.
How hot the air coming out of the dryer can get depends on:
- The power supplied to the heating element. The higher the wattage, the more heat is generated by the heating element and transferred to the air. Early hair dryers put out only about 100 watts of heat, but nowadays hair dryers can produce up to about 2,000 watts, drying hair considerably faster [source: Schueller].Hair dryers that offer high heat and low heat settings vary the power supplied in order to modulate the temperature of the airflow. These models are wired so that you can flip a switch and cut off part of the circuit that feeds the heating element.
- The time the air spends in the barrel of the dryer being heated by the nichrome wire. Most hair dryers limit this to approximately one-half second to prevent the air temperature from getting too high.
Something seen more often these days are hair dryers with a ceramic coating on the heating element. Coming in a variety of different configurations, ceramic-coated heating elements are said to heat more evenly and effectively. It's also popular to infuse the ceramic with materials such as crushed tourmaline, which is said to support the creation of ions and ideal heat flow.
Continue to the next page to learn about all the safety features that are built into hair dryers and how they function to prevent dangerous mishaps like overheating and fires.