Heating the Air

The heating element is composed of coiled nichrome wire on an insulating board.

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:

• Nichrome wire is 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.
• Nichrome does not 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 coil and transferred to the air. The latest models on the market use up to 1875 watts! This concerns some haircare professionals, who worry that the high heat generated by these dryers can damage the hair and the scalp.

  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 coils.

• 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.