Introduction to Heat Trasnfer

Chapter One: Introduction to Heat Transfer

Heat transfer is the science that seeks to predict the energy transfer that may take place between material bodies as a result of a temperature difference.

Difference between heat and temperature
Temperature is a measure of the amount of energy possessed by the molecules of a substance. It manifests itself as a degree of hotness, and can be used to predict the direction of heat transfer. The usual symbol for temperature is T. The scales for measuring temperature in SI units are the Celsius and Kelvin temperature scales.
Heat, on the other hand, is energy in transit. Spontaneously, heat flows from a hotter body to a colder one. The usual symbol for heat is Q. In the SI system, common units for measuring heat are the Joule and calorie.

Difference between thermodynamics and heat transfer
Thermodynamics tells us:
• how much heat is transferred (?Q)
• how much work is done (?W)
• final state of the system

Heat transfer tells us:
• how (with what modes) ?Q is transferred
• at what rate ?Q is transferred
• temperature distribution inside the body

Modes of Heat Transfer
Conduction
Convection
Radiation

Conduction Heat Transfer: An energy transfer across a system boundary due to a temperature difference by the mechanism of inter-molecular interactions. Conduction needs matter and does not require any bulk motion of matter.

Convection Heat Transfer: An energy transfer across a system boundary due to a temperature difference by the combined mechanisms of inter-molecular interactions and bulk transport. Convection needs fluid matter.

Radiation Heat Transfer: Radiation heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of the body. Radiation does not need matter.