Generating 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 fan in 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 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 strands of your hair) from being sucked in as well. The air is then blown down the barrel of the hair dryer.

The small black fan sits atop the motor. The motor spins the fan. Air is drawn in through the openings on the side 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 thus 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.

Two switches regulate whether and how much current flows through the hair dryer circuitry. One (left) regulates the speed of the motor (and thus the airflow) and the other (right) turns the hair dryer on and off.