Heat Transfer: Convection, Conduction, and Radiation

Convection

the process in which heat is carried from one place to another by the bulk movement of a fluid.

Thermal Conductors

Materials that conduct heat well are called

Thermal Insulators

Materials that conduct heat poorly are called

Conduction

the process whereby heat is transferred directly through a material, with any bulk motion of the material playing no role in the transfer.

Perfect Blackbody

A material that absorbs completely is called a

Radiation

Radiation is the process in which energy is transferred by means of electromagnetic waves.

Insulation

Insulation is used to limit the conduction of heat from the inside to the outside (in winters) and from the outside to the inside (in summers).

Convective Loop

Air heated by the so-called gravity furnace expands and rises, forming a convective loop that transfers energy to other parts of the room.

Heat Transfer in Water

Convection plays an important role in heat transfer inside a pot of water, where hotter water expands, decreases in density, and rises.

Dead Air Spaces

Materials with dead air spaces are usually excellent thermal insulators.

Energy Transfer from Fire

Most of the heat transfer from this fire to the observers is through infrared radiation.

Sensitivity to Infrared Radiation

Skin is very sensitive to infrared radiation, so that you can sense the presence of a fire without looking at it directly.

Heating System Efficiency

A properly designed heating system using natural convection can be quite efficient in uniformly heating a home.

Energy Transfer Mechanism in Conduction

One mechanism for conduction occurs when the atoms or molecules in a hotter part of the material vibrate or move with greater energy than those in a cooler part.

Collisions in Conduction

By means of collisions, the more energetic molecules pass on some of their energy to their less energetic neighbors.

Heat Transfer from Ceiling

As the air is cooled at the ceiling and outside walls, it contracts, eventually becoming denser than room air and sinking to the floor.

Heat Transfer Methods

The construction of a thermos bottle is designed to inhibit all methods of heat transfer.

Convection in Fur

Convection is very slow in fur, because the loops are so small and the low conductivity of air makes fur a very good lightweight insulator.

Heat Transfer from Observers

Convection transfers energy away from the observers as hot air rises, while conduction is negligibly slow.

Visible Light

transfers relatively little thermal energy.