Introduction
?Definition
?Heat transfer is energy transfer due to a temperature difference in a medium or between two or more media
?Modes of heat transfer
?Conduction heat transfer is due to a temperature gradient in a stationary medium or media
?Convection heat transfer occurs between a surface and a moving fluid at different temperatures
?Radiation heat transfer occurs due to emission of energy in the form of electromagnetic waves by all bodies above absolute zero temperature
?Net radiation heat transfer occurs when there exists a temperature difference between two or more surfaces emitting radiation energy
?Relationship of Heat Transfer to Thermodynamics
?Thermodynamics taught that energy can be transferred by interactions between a system and its surroundings
?Heat and work are the only form of interactions between a system and its surroundings
?Thermodynamics is concerned with equilibrium end states and processes But does not provide information on the nature of the process or the rate at which energy is transferred
?Energy transfer rates are important in engineering process design and development
?Examples of Heat Transfer
• Power Stations -
- furnace - radiation, convection and conduction
- condensers, cooling towers
- nuclear reactors - cooling fluid may be gas or liquid
• Engines
- car radiator (convector)
- water jacket around head
- oil flow through bearings
- fins for air-cooled engines
- gas turbines - blade cooling