Modes of Heat transfer (week 1)

Specific heat

is the amount of energy required to raise the temperature of a given weight of a material by a given number of degrees

Materials with a high specific heat require more energy to heat up and hold more energy at a given temperature than materials with a low specific heat.

Conduction

Heat transfer resulting from energy exchange by direct collision between molecules of two material at different temperatures. Heat is transferred when materials are in contact with each other.

Ex: Ice pack, paraffin, hot pack

Thermal conductivity is the rate at which a material transfers heat by conduction

As metal has a high thermal conductivity (heats up fast), it should be removed before the application of a heating or cooling agent.

Remove the bling first!

Convection

Heat transfer through direct contact of a circulating medium with a material of a different temperature

Ex: Whirlpool, fluidotherapy

Circulating blood helps to keep local body temperature at baseline which reduces the risk of thermal injury. Poor circulation would increase the chance of thermal injury.

Conversion

Heat transfer by conversion of a non-thermal form of energy, such as mechanical, electrical or chemical energy into heat.

Ex: Diathermy – vibration of molecules

Ultrasound – rotation, friction between molecules

These modalities also have non-thermal effects

Radiation

Transfer of energy from one material without the need for direct contact or an intervening medium

Evaporation

A material absorbs energy and changes from a liquid to a gas or vapor

Ex: Vapocoolant spray