Grades 3–5 · Machines
How does a hair dryer help water leave hair?
Wet hair carries liquid water on and between its strands. A hair dryer helps that water move into the air as invisible water vapor. Two parts inside the dryer have different jobs: a fan moves air, and a heater adds warmth.
In the diagramA fan moves air; a heater gives it energyMoving air carries evaporated water away from hairFanHeaterWet hairThe heater warms the passing airLiquid water becomes vapor; the airflow carries it away.
An electric motor turns the fan. The moving blades draw air into the dryer and push it toward the outlet. Along the way, the air passes a heating element. Electric current through the element changes electrical energy into thermal energy, which transfers to the passing air.
The airflow reaches the wet hair. Water at the surface can evaporate, changing from liquid to gas. Evaporation takes energy. Warm air can supply energy, while moving air carries vapor away and brings more air across the wet surface.
The water has changed its form and location. Some of the liquid that was on the hair is now vapor mixed with the surrounding air. Even with its heater off, the fan still moves air and carries moisture away.
About this explanation
Starting knowledge: Recognize a fan and understand that liquid water can evaporate into air.
Sources
- United States Patent and Trademark Office · Google Patents — US20050069303A1: Hair dryers
- US Geological Survey — Evaporation and the Water Cycle