3- Modes of Heat Transfer + Inro to Thermal agents

PPT Modes of Heat Transfer and Chp 7 Intro Thermal agents

Specific heat

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

• Materials with more require more energy and hold the energy for longer

What is the specific heat of water?

4.19 joules per gram per degrees Celsius (J/g^oC)

Conduction

• Heat transfer resulting from energy exchange by direct collision between molecules of two materials at different temperatures; heat is transferred when materials are in contact with one another

• Materials have to be a different temps

• Ex. ice pack, paraffin, hot pack

Thermal conductivity

The rate at which a material transfers heat by conduction

Convection

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

• Circulation of blood in the body uses this concept to help maintain the local temperature of the body to reduce the risk of thermal injury

• Ex. whirlpool, fluidotherapy

Conversion

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

• Ex. diathermy (vibration of molecules), ultrasound (rotation, friction between molecules)

Radiation

• The transfer of energy from one material without the need for direct contact or an intervening medium

• Ex. infrared lamps

Evaporation

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

• Ex. Vapocoolant spray

Materials with high specific heat require more energy to heat up and hold more energy at a given temp (than materials with low specific heat)

True