Heat Transfer

Three methods of Heat Transfer:         1. Conduction              2. Convection              3. Radiation

1. Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule, without any overall movement of the substance.

You are expected to be able to demonstrate how to compare rates of conduction through different solids (Junior Cert)

U-Value

U-Values are used in domestic situations to give an indication of how well a substance (roof, walls, tiles, etc) allows heat to flow (conduct) through it.

U-Values are a measure of the conductivity of a substance, i.e. a structure that is a good insulator has a low U-Value.

The U-Value of a structure is the amount of heat energy conducted per second through 1 square metre of that structure when a temperature difference of 1⁰ C is maintained between its ends.

2. Convection is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat.

Because hot water expands, it is less dense than cooler water and so rises.

This principle is used in domestic hot water and heating systems.

3. Radiation is the transfer of heat energy from one place to another in the form of electromagnetic waves.