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Winter mornings would be much more uncomfortable if hair dryers didn't exist.
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- Hair dryers utilize a motor-driven fan and a heating element to blow hot air over damp hair, speeding up the evaporation of water.
- The heating element is typically a bare, coiled wire that heats up through electrical resistance. The fan circulates air over this element, warming it before the air exits the dryer and contacts the hair.
- Since their invention in the 1920s, hair dryers have significantly advanced in terms of safety, with innovations like Ground Fault Circuit Interrupters (GFCI) designed to prevent electrocution by instantly shutting off the power when the dryer comes into contact with water.
Most people are accustomed to the daily process of washing, drying, and styling their hair. While hair will eventually dry naturally, most turn to a hair dryer to speed things up. Although research has debunked the myth that wet hair leads to colds, it's still unpleasant to be left with damp hair, particularly during the cold winter months.
Hair dryers, also referred to as blow dryers, made their debut in the 1920s. Initially, they posed significant risks, with numerous individuals being electrocuted after dropping their hair dryers into sinks and bathtubs filled with water.
Today, the risk of electrocution is significantly reduced thanks to the introduction of Ground Fault Circuit Interrupters (GFCI). Since 1991, U.S. federal law has mandated that all portable hair dryers come equipped with this safety feature to protect users from electric shocks in the event the dryer is dropped in water while plugged in [source: CSPC]. This applies regardless of whether the dryer is turned on or off. A GFCI is the larger, polarized plug found on many household appliances. It monitors the flow of current between the slots of a wall outlet, and if it detects any leakage, it trips the circuit, cutting off the power (See How does a GFCI outlet work? for more information).
What happens if a hair dryer is dropped in water when it's unplugged? While there's no risk of electrocution due to the lack of current, the hair dryer may still sustain damage if its components become wet. So, whether plugged in or not, dropping it in water is never a good idea.
Ever wondered what makes it possible for a hair dryer to blow hot air through your hair without causing burns to your scalp? Continue reading to learn why you won't end up sizzling your skin.
Understanding Hair Dryers
Inside a hair dryer: Motor-driven fan (left) and heating element (right).You can find a hair dryer like this one in nearly every drugstore or discount store. Basic models typically feature two switches: one to turn the device on and off and another to adjust the airflow rate. Some models also include an additional switch to control the temperature of the airflow.
A hair dryer accelerates the evaporation of water from your hair by increasing the temperature of the air around each strand. The warm air can hold more moisture than cooler air, causing more water to leave your hair and enter the air. This temperature rise also helps the water molecules break free from one another and transition from liquid to gas more easily.
Since their creation, countless patents have been filed for various hair dryer designs. However, most of these innovations only alter the exterior appearance of the dryer to make it more visually appealing. Aside from a few added safety features, the inner workings of hair dryers have remained relatively unchanged over the years.
A hair dryer only requires two essential components to create the hot air blast that dries your hair:
- a motor-driven fan
- a heating element
Hair dryers use the combination of a motor-driven fan and a heating element to convert electrical energy into convective heat. The entire system is quite straightforward:
- When you plug in the hair dryer and switch it on, electricity flows through the device.
- The circuit first powers the heating element. Most hair dryers have a simple coiled wire for this, though more expensive models may use advanced materials like a tourmaline-infused ceramic coating.
- Next, the current powers the small electric motor, which spins the fan.
- The fan generates airflow that moves through the barrel of the hair dryer, passing over and through the heating element.
- As the air moves over the heated element, the heat warms the air via forced convection.
- The heated air then exits from the end of the barrel.
With the heat ready, continue reading to learn how the hair dryer propels that heat through the air.
Hair Dryer Airflow
The small black fan is positioned on top of the motor. The motor drives the fan, pulling air in through the openings on the sides of the hair dryer.How does a hair dryer produce such a powerful stream of air? This design utilizes a small fan resembling a hydraulic turbine (similar to a water wheel). Unlike a water wheel that captures the potential energy of flowing water to generate power, the fan in a hair dryer uses electrical energy to create airflow. The motor is housed within the fan, which is securely attached to the motor's shaft. When the motor is powered, both the motor and fan spin. The centrifugal motion of the fan blades draws air through the round air inlets on the side of the hair dryer. These openings are protected by a safety screen to prevent foreign objects (like hair strands) from being sucked in. The air is then blown down the barrel of the dryer.
Most hair dryers (including this model) feature high and low airflow settings, which are commonly referred to in the user manual as high and low speed settings. Adjusting the airflow is done by changing the speed at which the motor spins. This is accomplished by varying the current flowing through the motor's circuit. When the current is low, the motor and fan rotate slowly, producing less airflow. With a higher current, the motor speeds up, causing the fan to spin faster, drawing in more air and increasing the airflow.
More advanced and expensive hair dryers now include systems that not only blow hot air but also ionized air, filled with charged particles. Manufacturers claim this technology helps hair dry more quickly, reduces static, and leaves the hair healthier, smoother, and shinier. Reducing static is said to make hair more manageable and less likely to attract dirt and dust. Ion generators can appear in various designs and may be positioned at different points within the hair dryer.
Things are about to get really interesting on the next page as we dive deeper into how these little gust-generating devices manage to dry our hair.
Heating a Hair Dryer
The heating element is made up of coiled nichrome wire mounted on an insulating board.In most hair dryers, the heating element consists of a bare, coiled nichrome wire wrapped around insulating mica boards.
Nichrome wire is a blend of two metals, nickel and chromium. This alloy is commonly used in heating elements for various household appliances, such as curling irons and toasters. Nichrome wire has two key characteristics that make it ideal for heat production:
- It has a lower electrical conductivity compared to metals like copper. This allows the alloy to offer sufficient resistance, causing it to heat up from the electrical current flowing through it.
- It remains resistant to oxidation when heated. Metals like iron tend to rust quickly at the temperatures used in hair dryers and toasters, but nichrome does not.
The fan's generated airflow is pushed through the heating element due to the design of the hair dryer's casing. Initially, when the air enters the barrel, it is much cooler than the nichrome wire, so heat transfers from the wire to the air. As the fan pushes the air along by convection, it is replaced by cooler air, and this cycle continues.
The temperature of the air coming from the dryer depends on:
- The amount of power supplied to the heating element. The higher the wattage, the more heat the heating element generates, which is then transferred to the air. Early models of hair dryers produced about 100 watts of heat, but modern versions can reach up to 2,000 watts, allowing for much faster drying [source: Schueller]. Hair dryers with multiple heat settings adjust the power to change the temperature of the air. These models include a switch that can cut off part of the circuit that powers the heating element.
- The time the air is heated by the nichrome wire while inside the barrel. Most hair dryers keep this time to about half a second to prevent the air from becoming too hot.
Recently, many hair dryers feature a ceramic coating on the heating element. These ceramic-coated elements come in various designs and are believed to heat more evenly and efficiently. Some models even incorporate crushed tourmaline in the ceramic coating, which is said to enhance ion creation and improve heat distribution.
Turn the page to discover the various safety mechanisms built into hair dryers, and how these features work together to avoid hazardous situations like overheating or fires.
Hair Dryer Safety
The heat shield prevents the barrel of the hair dryer from reaching dangerous temperatures.While the concept of a hair dryer is relatively straightforward, designing one for the mass market requires careful thought regarding safety features. Manufacturers must anticipate how a user might improperly operate the device, and ensure that the dryer is safe under various conditions.
In addition to the ground fault circuit interrupters we covered earlier, here are some additional safety features commonly found in hair dryers:
- Safety cut-off switch - Scalp burns can occur if temperatures exceed 140 degrees Fahrenheit (about 60 degrees Celsius) [source: Hardin]. To prevent the air in the barrel from reaching this dangerously high temperature, hair dryers are equipped with heat sensors that automatically turn off the motor when the temperature gets too high. This particular model, like many others, uses a bimetallic strip as a cut-off mechanism.
- Bimetallic strip - Composed of two different metals, which expand at different rates when heated. As the temperature increases in the hair dryer, the strip bends because one metal sheet expands more than the other. When it bends sufficiently, it activates a switch that disconnects the power to the dryer. (To learn more about bimetallic strips, check out How Thermometers Work).
- Thermal fuse - For additional protection against overheating and fire hazards, many hair dryers are equipped with a thermal fuse in the heating circuit. This fuse blows if the temperature or current becomes too high, breaking the circuit to prevent further damage.
- Insulation - Without adequate insulation, the exterior of the hair dryer would become dangerously hot to touch. If you grabbed it by the barrel after use, you could burn your hand. To protect users, a heat shield made of insulating material is applied to the plastic barrel, keeping it cool.
- Protective screens - As the fan pulls air into the dryer, it also draws in other objects from the surrounding environment. That's why the air intake holes are covered with a wire screen. Over time, lint builds up on this screen, which could otherwise clog the dryer and be scorched by the heating element, potentially damaging the motor. While the screen helps prevent this, it’s important to regularly clean off lint, as a build-up could block airflow and cause overheating. Some newer models feature a removable lint screen for easier cleaning.
- Front grill - The end of the dryer barrel is covered with a grill that can withstand the heat generated by the dryer. This grill acts as a barrier, making it difficult for children or curious individuals to stick their fingers or objects into the dryer barrel, which could lead to burns from the heating element.
For more insights on household gadgets that keep things warm and toasty -- whether drying your clothes, toasting your bread, or even jumpstarting your car -- head over to the next page for some fascinating links.
