Mechanisms of Heat Transfer

The five main mechanisms

1. Conduction

2. Convection

3. Radiation

4. Evaporation

5. Condensation

Conduction, convection, radiation and evaporation are the most significant contributors to animal thermoregulation. Condensation plays a minor role in heat gain.

Sensible vs. Insensible

1. Conduction: no movement of material. Energy is transferred by the vibrational kinetic energy of particles. Metal conduction is distinct in that free electrons carry the energy rather than the limited vibrations of atoms in non-metals.

--> butter in the metal spoon is melted because metal is a good conductor, and wood is a good insulator (poor conductor)

2. Convection: Movement of material substance in circulation transfers heat through liquids and gases. This may be natural (e.g. a light breeze) or forced (e.g. airflow created by a fan)

3. Radiation: electromagnetic waves spread from a single point source. This may be an object such as the sun OR an animal, and the heat is able to travel through a vacuum. This is the only mechanism affected by the color of the surface.(DIFFERENT THAN RADIOACTIVITY)

4. Evaporation: water molecules on a surface are vaporized, taking heat with them and resulting in a cool sensation.

5. Condensation: Gaseous molecules in the atmosphere convert to liquid droplets. When these droplets precipitate on a surface, they bring energy with them and effectively heat the surface.

TEMPERATURE =

measure of average kinetic energy of all the particles in a substance

Heat transfers do not always result in a detectable temperature change

(+) provides heat, (-) causes heat loss

SENSIBLE heat transfer mechanisms are those that cause a change in temperature that can be read using a thermometer. It just makes sense!

- conduction

- convection (flow)

- radiation

INSENSIBLE mechanisms still cause heat transfer, but a temperature change cannot be detected at the time.

- evaporation

- condensation

Insensible a.k.a. LATENT