Heat Transfer - Chapter 1 Summary Notes
Alejandro Villanueva
1.1 Introduction to Heat Transfer
Definition: Heat transfer is thermal energy in transit due to a temperature difference.
Distinctions:
• Thermal Energy (U): Microscopic energy from molecular activity [J]
• Temperature (T): Measure of average molecular energy [K or °C]
• Heat (Q): Energy transferred due to temperature difference [J]
Units and Variables:
• Q̇: Heat rate [W = J/s]
• q ′′ : Heat flux (rate per unit area) [W/m2 ]
• q ′ : Linear heat rate [W/m]
• u: Specific thermal energy [J/kg]
Assumptions:
• Steady-state unless otherwise noted
• Uniform material properties
Intuition: Temperature is like pressure for energy: it drives flow from high to low.
1.2 Modes of Heat Transfer
A. Conduction
Mechanism: Direct transfer via molecular collisions or electron movement in solids.
Fourier’s Law:
dT ∆T
q ′′ = −k , Q̇ = −kA
dx L
Assumptions:
1
Alejandro Villanueva
1.1 Introduction to Heat Transfer
Definition: Heat transfer is thermal energy in transit due to a temperature difference.
Distinctions:
• Thermal Energy (U): Microscopic energy from molecular activity [J]
• Temperature (T): Measure of average molecular energy [K or °C]
• Heat (Q): Energy transferred due to temperature difference [J]
Units and Variables:
• Q̇: Heat rate [W = J/s]
• q ′′ : Heat flux (rate per unit area) [W/m2 ]
• q ′ : Linear heat rate [W/m]
• u: Specific thermal energy [J/kg]
Assumptions:
• Steady-state unless otherwise noted
• Uniform material properties
Intuition: Temperature is like pressure for energy: it drives flow from high to low.
1.2 Modes of Heat Transfer
A. Conduction
Mechanism: Direct transfer via molecular collisions or electron movement in solids.
Fourier’s Law:
dT ∆T
q ′′ = −k , Q̇ = −kA
dx L
Assumptions:
1
