Heat transfer

what is heat transfer?

thermal energy in transit due to a spatial temperature difference

Conduction definition

the diffusion of heat inside a continuous medium

Convection definition

heat transfer between a solid and a moving fluid

Radiation definition

Energy emitted by matter that is at a nonzero temperature

What are the three modes of heat transfer?

conduction, convection, radiation

contact resistance definition

A resistance that appears when you have two solid materials touching due to imperfect contact and roughness

what is the purpose of fins

increase surface area with little change in volume

what is the heat transfer along a fin? 

conduction

what is the heat transfer across a fin?

convection 

assumptions when calculating total rate of heat transfer with fins?

straight fin, constant cross section, steady state, no internal generation or radiation, h and k are uniform and known, L>t

thermal resistance analogy

temperature is voltage, heat flux is current

thermal diffusivity definition

a measure of a material’s ability to respond to changes in its thermal environment

What is transient heat transfer?

Time process for which temperature varies with time

When does transient heat transfer occur?

When a thermal system experiences a change in conditions

What is the biot number?

The ratio of resistance to conduction inside the body to the resistance to convection at the surface

What is the Fourier number?

The ratio of rate of conduction to rate of heat storage

what is the criteria for lumped capacitance to be valid?

Bi<0.1