Convection

Convection air current occurs due to the unequal Heating of the Earth‟s atmosphere by the sum. (Thus current called strong convection current).

Convection is the transfer of heat through the movement of fluids such as air or water. This means that when a fluid (like air or water) moves past a warm object—such as the human body—it takes away some of the heat, causing heat loss. A common example happens when a person is in cold water. If the person stays still, a thin layer of water next to their skin becomes warm due to body heat. This layer acts like an insulator and helps to keep the person warm by reducing heat loss. However, if the person starts moving around, this warm layer is disturbed and replaced by colder water. As a result, the body loses more heat through convection.

When a person remains in cold water for a long time, most of their skin becomes cool with low blood flow. However, certain areas remain warmer because major blood vessels are close to the skin. These areas include:

• Neck
• Armpits
• Groin

These regions are known for high heat transfer. In cold conditions, they lose heat quickly, while in hot conditions, they gain heat easily. That is why during rescue or rewarming, heat is often applied directly to these areas, especially the armpits and chest, to warm the body effectively.

Domestic hot water system

Convection is used in home hot water systems to circulate water. The system typically consists of:

1. Boiler (B) – Heats the water
2. Hot water storage tank (H) – Stores heated water
3. Cold water supply tank or cistern (C) – Supplies cold water

How it works:

1. Water at the bottom of the boiler is heated (by electricity or fire).
2. The heated water becomes less dense and rises to the top of the boiler.
3. The hot water flows through the outlet at the top of the boiler into the top part of the storage tank.
4. As hot water rises, cold water from the cistern flows into the bottom of the tank to replace it.
5. When the hot water tap (T) is opened, water is pushed out of the tank due to pressure from the cistern above.
6. The cistern has a ball cock mechanism that maintains the water level by letting in more water when needed.