Convection
1. What is Convection?
Convection is a mode of heat transfer that occurs in fluids (liquids and gases) due to the actual movement of the fluid particles.
Heat is transferred from a hotter region to a colder region because warmer fluid becomes less dense and moves, while cooler fluid becomes more dense and sinks.
➡️ Convection cannot occur in solids or vacuum.
2. Why Convection Happens (Core Reason)
The root cause of convection is density difference caused by temperature change.
When a fluid is heated:
Its particles gain energy
They move faster and spread out
Density decreases
Fluid rises upward
When a fluid cools:
Particles lose energy
They come closer together
Density increases
Fluid sinks downward
This continuous rise and fall creates convection currents.
3. Types of Convection
(A) Natural Convection (Free Convection)
Occurs without any external force.
✔ Caused only by temperature and density differences.
Examples:
Hot air rising from a heater
Warm air rising near a candle
Sea breeze and land breeze
Hot water rising in a pot
(B) Forced Convection
Occurs when fluid motion is caused by an external device.
✔ Requires fans, pumps, or blowers.
Examples:
Fan cooling your body
Water pumped through a radiator
Air conditioner circulation
Engine cooling systems
4. How Convection Works (Step-by-Step Mechanism)
Let’s take water in a heated container as an example:
Heat is supplied at the bottom
Bottom water gets heated
Heated water expands → density decreases
Lighter hot water rises upward
Cooler, denser water from above sinks down
This cycle repeats
Continuous circulation forms convection currents
Heat spreads throughout the fluid
This is how convection transfers heat.
7. Real-Life Applications of Convection
Daily Life
Boiling water
Room heaters
Chimneys
Cooking food
Hot air balloons
Nature
Wind formation
Thunderstorms
Ocean circulation
Mantle convection (plate tectonics)
Engineering
Cooling of engines
Heat exchangers
Air conditioning
Refrigerators
Electronics cooling