Hair dye

Hair dryer or blow dryer is an electromechanical device designed to blow cool or hot air over damp hair, in order to accelerate the evaporation of water particles and dry the hair. Blow dryers allow to better control the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds inside each strand. These hydrogen bonds are very powerful (allowing for stronger hair shaping than the sulfur bonds formed by permanent waving products) but are temporary and extremely vulnerable to humidity. They disappear with a single washing of the hair.

History

The first model was created by Alexander F. "Beau" Godefroy in his salon in France in 1890. The handheld, household hair dryer first appeared in 1920. Early blow dryers used to be heavy, often up to 2 pounds (0.9 kg), and were difficult to use. They also had many instances of overheating and electrocution. Today's hand-held hair dryers are much lighter and safer to use.

Types

There are two types of hair dryers: the rigid-hood dryer and the flexible-hood dryer. The rigid-hood dryer is used in beauty salons and can be placed over the client's head. The flexible-hood dryer is used at home and includes a flexible hose that blows the air.

Technology

Hair dryers use three different types of energy to work: electrical energy, heat energy, and mechanical energy. Electrical energy is used to generate heat; this heat energy is then converted into mechanical energy when the electric motor turns the fan. The fan pushes the hot air out of the hair dryer.

Safety

Modern hair dryers have safety cut outs, which switch off the heater elements if they get too hot. This prevents the dryer from overheating and catching fire. Some hair dryers also have a 'cool shot' button, which turns off the heater and blows room-temperature air while the button is held down.

Environmental Impact

Hair dryers use a significant amount of electricity. This contributes to greenhouse gas emissions, particularly if the electricity is produced by coal-fired power plants.

See Also

• Hairbrush
• Hair straightening
• Hair iron
• Hair roller

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