Convection- Blow Dryer

Objective

To understand the process of heat transfer through convection.

Outcome

Students will learn to observe convection that occurs commonly in everyday life.

Requirements

A blow dryer, two handkerchiefs, a water bottle containing water, timer.

Prerequisites

None

Note: Convective heat transfer is the transfer of heat between two bodies by currents of moving gas or fluid. In free convection, air or water moves away from the heated body as the warm air or water rises and is replaced by a cooler parcel of air or water.

Procedure

Step 1: Bring blow dryer to the classroom
Step 2: Take a small amount of water from the water bottle and wet both handkerchiefs.
Step 3: Hold one handkerchief in the air to dry.
Step 4: Turn on the blow dryer and hold the other handkerchief in front of it to dry.
Step 5: Note down the time taken for drying the handkerchief in both the cases and compare it.

Table

Time taken by the surrounding air to dry the handkerchief (min)	Time taken by the blow dryer to dry the handkerchief (min)

Step 6: Discuss the movement of different energies. 

• Inside the dryer, electrical energy causes an electric fan to rotate and it blows air across a heating element. 
• As the air passes through the heating element, the air is warmed and heated up. Here, heat transfer occurs due to both conduction and convection. 
• The hot air exits the dryer through a nozzle, to concentrate the air flow. 
• When it reaches the wet handkerchief, heat travels from the hotter air to the cooler cloth thereby drying it. 

Greater the difference in temperature between a hot and a cold body greater the heat transfer. 

Step 7: Where can we observe the principle of convection around us?

Reference Image