hair dryers

7/31/2019 Hair Dryers

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Hair dryers, also known as blow dryers, were first sold in the 1920s.

That isn't as likely today, however, because of the advent ofGround Fault Circuit

Interrupters (GFCI). This applies whether the hair dryer is on or off. A GFCIis thelarger, polarized plug that you'll find on many consumer appliances. When they're

plugged in, GFCIs monitor the amount of current that's running from one slot of a wall

outlet through an electric circuit and back to the other slot. If they sense a leak in the

current, they trip the circuit.

What happens to a hair dryer if you drop it in water when it's not plugged in? You don't

run the risk of electrocution, since there's no source of current, but you can certainly

damage the hair dryer if all of its components get wet. So, plugged in or not, it's a bad

idea to throw it in the tub.

Have you ever wondered what those components are inside a hair dryer that lets you

blow hot air through your hair without burning your scalp? Keep reading to find out why

you won't sizzle.

Hair Dryer Basics

You can find a hair dryer like this one in almost any drug or discount store. Basic

models have two switches, one to turn them on and offand one to control therate of

airflow. Some models have an extra switch that also lets you regulate

thetemperature of the airflow.

The hair dryer dries your hair by speeding up the evaporation of water from the hair's

surface. The hot air emitted from a hair dryer increases the temperature of the air

surrounding each strand of hair. Since warm air can contain more moisture than air at

room temperature, more water can move from your hair into the air. The increase in

temperature also makes it easier for the individual molecules in a water droplet toovercome their attraction to one another and move from a liquid to a gas state.

Since they were first developed, thousands of patents have been issued for different

hair dryer designs, but most of them only tweak the outside packaging of the hairdryer

so that it looks more aesthetically appealing to you. Aside from the addition of some
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safety features, the operating system inside hair dryers hasn't changed too much over

the years.

A hair dryer needs only two parts to generate the blast of hot air that dries your hair:

a simple motor-driven fan

a heating element

Hair dryers use the motor-driven fan and the heating element to transform electric

energy into convective heat. The whole mechanism is really simple:

1. When you plug in the hair dryer and turn the switch to "on," current flows through the

hair dryer.

2. The circuit first supplies power to the heating element. In most hair dryers, this is a bare,coiled wire, but in models that are more expensive there can be fancier materials in

action, like a tourmaline-infused ceramic coating.

3. The current then makes the small electric motorspin, which turns the fan.

4. The airflow generated by the fan is directed down the barrel of the hairdryer, over and

through the heating element.

5. As the air flows over and through the heated element, the generated heat warms the air

by forced convection.

6. The hot air streams out the end of the barrel.

Now that we've got the heat, read on to find out how the hair dryer gets that heat

moving.

Hair Dryer Air Flow

How does a hair dryer generate such a strong gust of air in the first place? This model

uses a small fan that looks like a hydraulic turbine (i.e. water wheel). Unlike the water

wheel, which harnesses the potential energy of flowing water to generate power, the fanin a hair dryer uses electrical energy to generate airflow. The small motor actually sits

inside the fan, which is firmly attached to the tip of the motor. When you supply power to

the motor, the motor and the attached fan both spin. The centrifugal movement of the

fan blades draws air in through the small round air inlets in the side casing of the hair

dryer. These holes are covered by a safety screen that prevents other objects (such as
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strands of your hair) from being sucked in as well. The air is then blown down the barrel

of the hair dryer.

Most hair dryers (including this one) have high and low airflow settings. You'll see this

referred to in the manual accompanying the hair dryer as high or low speed, because

changing the airflow involves modulating the speed at which the motor is turning. This is

accomplished very simply by altering the current flowing through the part of the circuit

feeding the motor. When the power supplied is low, the motor and the fan spin slowly.

Less air is pushed through the hair dryer. With more power, the motor speeds up. The

fan rotates rapidly, drawing in more air and increasing the airflow.

Newer and more expensive hair dryers have systems which don't just deliver hot air,

they deliver hot air full of ions in the form of charged particles. The companies utilizing

this technology claim it's supposed to help hair dry more quickly, lose the static and

become healthier, smoother and shinier. Decreasing static is said to help hair be more

manageable and less prone to attracting dirt and dust. Ion generators can manifest in a

number of different design schematics and be located in a variety of points within the

hair dryer.

Things will really start to heat up on the next page when we take a closer look at how

these gusty little appliances actually dry our hair.

Heating a Hair Dryer

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.
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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 creationof 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.

Hair Dryer Safety

The basic idea behind hair dryers is pretty simple, but producing one for mass

consumption requires some hard thinking about safety features. Manufacturers have to

predict how their hair dryer might be misused. They then try to design a product that will

be safe in the widest variety of conditions.

Besides the ground fault circuit interrupters we learned about on the first page, here are

some other safety features hair dryers commonly have:
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Safety cut-off switch - Your scalp can be burned by temperatures more than 140

degrees Fahrenheit (approximately 60 degrees Celsius) [source: Hardin]. To ensure

that the air coming out of the barrel never nears this temperature, hair dryers have

some type of heat sensor that trips the circuit and shuts off the motor when the

temperature rises too much. This hair dryer and many others rely on a simple bimetallic

stripas a cut off switch.

Bimetallic strip - Made out of sheets of two metals, both expand when heated but at

different rates. When the temperature rises inside the hair dryer, the strip heats up and

bends because one metal sheet has grown larger than the other. When it reaches a

certain point, it trips a switch that cuts off power to the hair dryer. (For more information

on bimetallic strips, see How Thermometers Work).

Thermal fuse - For further protection against overheating and catching fire, there is

often a thermal fuse included in the heating element circuit. This fuse will blow and

break the circuit if the temperature and current are excessively high.

Insulation - Without proper insulation, the outside of the hair dryer would become

extremely hot to the touch. If you grabbed it by the barrel after using it, it might seriously

burn your hand. To prevent this, hair dryers have a heat shield of insulating material

that lines the plastic barrel.

Protective screens - When air is drawn into the hair dryer as the fan blades turn, other

things outside the hair dryer are also pulled toward the air intake. This is why you'll finda wire screen covering the air holes on either side of the dryer. After you've used a hair

dryer for a while, you'll find a large amount of lint building up on the outside of the

screen. If this were to build up inside the hair dryer, it would be scorched by the heating

element or might even clog the motor itself.Even with this screen in place, you'll need to

periodically pick lint off the screen. Too much lint can block the airflow into the dryer,

and the hair dryer will overheat with less air carrying away the heat generated by the

nichrome coil or other type of heating element. Newer hair dryers have incorporated

some technology from the clothes dryer: a removable lint screen that's easier to clean.

Front grill - The end of the barrel of a hair dryer is covered by a grill made out of

material that can withstand the heat coming from the dryer. This screen makes it difficult

for small children (or other especially inquisitive people) to stick their fingers or other

objects down the barrel of the dryer, where they could be burned by contact with the

heating element.
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For more information on other household appliances showing their warm, fuzzy side --

whether by drying your clothes, toasting your bread or starting your car -- get your motor

going on the next page with a bunch of interesting links.

hair dryers

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