Conduction Flashcards
How does steady state effect conduction equation?
The time derivative on right side vanishes
What is C, c bar and lambda for conducting and non-conducting solids?
Conducting: C is electron specific heat per unit volume, c bar is mean electron velocity, lambda is photon mean free path
Non-Conducting: C is photon specific heat per unit volume, c bar is mean sound velocity, lambda is photon mean free path
Why is thermal conductivity of fluids smaller than solids?
Motion of molecules is more random
What is thermal diffusivity?
measure of how quickly a material is able to change its temperature
What is thermal contact resistance?
Resistance due to unevenness of contact at microscopic level
What is thermal grease used for?
Decreasing contact resistance
What is the critical radius of insulation?
Radius after which addition of insulation increases heat transfer
What is an important assumption for fins?
No heat generation or radiation
What does fin performance depend on?
- Fin efficiency
- Fin effectiveness
- Overall surface efficiency
What is fin efficiency?
Heat transfer of fin / maximum possible heat transfer
What is fin effectiveness?
Heat transfer with fins / heat transfer without fins
What is overall surface efficiency?
characterizes and array of fins and the base surface to which they are attached
What is the biot number?
lumped capacitance can be used if it is less than 0.1
What is Fourier number?
Fo = Fourier number: Dimensionless in time: the ratio of heat transfer time
t, to a characteristic time, td
, for heat diffusion
