Conduction -Convection- Radiation-Heat Transfer

Heat Transfer

Heat transfer is the movement of thermal energy from one object or region to another. It occurs in three main ways: conduction, convection, and radiation.

conduction

Conduction is the transfer of heat through direct contact between two objects.

When two objects at different temperatures are in contact, thermal energy flows from the hotter object to the colder object until they reach thermal equilibrium.

Examples of Conduction

  • When you touch a hot stove, heat from the stove is transferred to your skin through conduction.
  • When you put a metal spoon in a hot cup of coffee, heat from the coffee is transferred to the spoon through conduction.

 

Convection is a method of heat transfer that involves the movement of a heated fluid, such as a liquid or a gas.

Here’s a simple explanation of how heat is transferred by convection:

Heating a Fluid:

  • When a fluid, such as air or water, is heated, its molecules gain energy and move faster.
  • The faster-moving molecules become less dense and rise.
  • The less dense, heated fluid rises due to buoyancy.
  • As it rises, it displaces the cooler, denser fluid, which sinks.
  • The rising and sinking of the fluid creates a continuous circulation pattern called a convection current.
  • This circulation pattern distributes heat throughout the fluid.

 

convection
radiation

Radiation is the transfer of heat through electromagnetic waves.

Heat radiation is the transfer of heat energy through electromagnetic waves. These waves are a form of energy that travels outward in all directions from a heat source. Unlike conduction and convection, heat radiation does not require a medium to travel through, so it can even travel through a vacuum.

The amount of heat radiation emitted by an object depends on its temperature and surface area. The hotter an object is, the more heat radiation it emits. The larger the surface area of an object, the more heat radiation it emits.

Heat radiation is absorbed by objects when the electromagnetic waves interact with the atoms and molecules in the object. The absorbed heat energy causes the atoms and molecules to vibrate, which increases the temperature of the object.

Here are some examples of heat transfer in everyday life:

  • When you turn on your oven, heat from the heating element is transferred to the food through conduction.
  • When you boil water, heat from the bottom of the pot is transferred to the water through convection.
  • When you sit in the sun, heat from the sun is transferred to your skin through radiation.
  • When you wear a sweater, heat from your body is transferred to the sweater through conduction.
  • When you open a window, heat from inside your house is transferred to the outside air through convection.