Heat Transfer Fundamentals

Modes of Heat Transfer

• Conduction: transfer of heat between objects in physical contact
  • Occurs due to vibration of particles
  • More efficient in solids than liquids or gases
• Convection: transfer of heat through movement of fluids
  • Occurs due to difference in density between hot and cold fluids
  • Can be natural (e.g. hot air rising) or forced (e.g. using fans)
• Radiation: transfer of heat through electromagnetic waves
  • Occurs in all directions, not requiring a medium
  • Can travel through vacuum

Heat Transfer Mechanisms

• Heat Capacity: amount of heat energy required to change the temperature of an object
  • Measured in joules per kilogram per degree Celsius (J/kg°C)
• Specific Heat Capacity: heat capacity of a substance per unit mass
  • Measured in joules per kilogram per degree Celsius (J/kg°C)
• Latent Heat: energy required to change the state of a substance (e.g. melting or boiling)
  • Measured in joules per kilogram (J/kg)

Heat Transfer Equations

• Fourier's Law of Heat Conduction: rate of heat transfer through conduction
  • Q = -k * A * (dT/dx)
  • Q: heat transfer rate, k: thermal conductivity, A: cross-sectional area, dT/dx: temperature gradient
• Newton's Law of Cooling: rate of heat transfer through convection and radiation
  • Q = h * A * (T_s - T_e)
  • Q: heat transfer rate, h: heat transfer coefficient, A: surface area, T_s: surface temperature, T_e: environment temperature

Applications of Heat Transfer

• Heat Exchangers: devices that facilitate heat transfer between fluids
  • Examples: radiators, heat sinks, and boilers
• Thermal Insulation: materials that reduce heat transfer
  • Examples: fiberglass, foam, and reflective insulation
• Refrigeration and Air Conditioning: systems that use heat transfer to cool or heat spaces
  • Examples: refrigerators, air conditioners, and heat pumps