Intro to Heat Transfer Flashcards
Heat transfer is…
thermal energy in transit due to a temperature difference.
Thermal Energy is…
associated with the translation,
rotation, vibration and electronic states of the atoms and molecules that comprise matter. It represents the cumulative effect of microscopic activities and is directly linked to the temperature of matter.
Total Energy in system =
Heat(Q) - Work(W)
Conduction
Heat transfer in a solid or stationary fluid due to the molecular interactions.
Convection
Heat transfer due to gas or moving fluids.
Radiation
Requires no medium. Heat is transported as electromagnetic waves, as long as it has a non-zero temperature.
Rate Equations
Fourier’s Law, Newton’s Law of Cooling, Sefan-Boltzmann Law
Fourier’s Law
Conduction: q’’=-k(dt/dx)
Newton’s Law of Cooling
Convection: q’‘=h(Ts - Tf)
Stefan-Boltzmann Law
Radiation
What is Q? What are the units?
Thermal Energy; J or Btu
What is q? What are the units?
Heat Transfer Rate: W(J/s) or Btu/hr
What is q’’? What are the units?
Heat Flux (heat rate/unit time/unit surface area); W/m^2 or BTU/ft^2*hr
Conduction Thermal Resistance
Rt = L/k*A
Convection Thermal Resistance
Rt=1/h*A
