BASICS OF HEAT TRANSFER

Difference between heat and temperature


In describing heat transfer problems, we often make the mistake of interchangeably using
the terms heat and temperature. Actually, there is a distinct difference between the two.
Temperature is a measure of the amount of energy possessed by the molecules of a
substance. It is a relative measure of how hot or cold a substance is 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. On the
other hand, heat is energy in transit. The transfer of energy as heat occurs at the molecular
level as a result of a temperature difference. The usual symbol for heat is Q. Common units
for measuring heat are the Joule and calorie in the SI system.

What is Heat Transfer?

“Energy in transit due to temperature difference.”

Difference between thermodynamics and heat transfer


Thermodynamics tells us:
• how much heat is transferred (δQ)
• how much work is done (δW)
• final state of the system
Heat transfer tells us:
• how (with what modes) δQ is transferred
• at what rate δQ is transferred
• temperature distribution inside the body