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