Understanding Thermal Energy and Heat Transfer

Thermal Energy

Thermal energy is the energy a body has due to the movement of its particles. Temperature is a physical magnitude which measures the thermal energy, that is, the movement of a body's particles - SI: KELVIN. The CELSIUS is more generally used. Heat is the thermal energy in transit. This process is carried out naturally between two material systems which are at different temperatures - SI: JOULES-Calories. 1 cal = 4.18 J 1 J = 0.24 Cal. Two bodies A and B have thermal equilibrium when both are at the same temperature.

Physical Changes

Temperature variation: normally the temperature of a body increases when it gains heat and decreases when it loses heat. Changes of state: when a change of state occurs, the temperature of a material system remains constant. Dimension variation: when a body or material system exchanges heat with its surroundings, its dimensions change - it expands or contracts. Chemical changes: the nature of the substance changes. Example: combustion.

Heat Transfer Processes

• Conduction: heat is conducted in solids.
• Convection: heat is conducted in fluids.
• Radiation: heat is conducted in a vacuum.

Thermal Conductors and Insulators

Thermal conductor is a material through which heat flows easily. Thermal insulator is a material through which heat does not flow easily.

Thermal Machines

Thermal machines change thermal energy into a different type of energy, generally mechanical energy. Examples include internal combustion engines and steam engines. The Industrial Revolution began with the invention of the steam engine by J. Watt in 1768 in England.