Heat transfer combines conversation of energy, fluid mechanics, physics of the material.
Important because rate of ht setes the thermal limits to many applications. Maintain a certain
T, and a heat flux.
heat flux or thermal flux is the amount of heat energy passing through a certain surface.
microscale heat transfer can be referred to as heat transfer occurring
on both the micro-length and micro-time scales.
Heat transfer requires deltaT. No deltaT no q.
Heat is transferred to and from objects through three processes: conduction, radiation,
and convection.
Conduction: Purely a molecular interaction. Transfer of molecular KE, temperature measure of
KE.
The heat diffuses because of the gradients in molecular energy.
It requires a median: Solid, fluid.
Convection: combination of conduction and advection-> transfer of heat through flow of fluid.
2 step process. Fluid motion
Radiation: Electromagnetic waves, depends on surface temp, properties like color roughness
material. No median req.
Ideal radiation source called black body. Absorbs all radiation. Reflects no radiation.
Blackbody emission =stress *Tsurf^4
Radiation q_ irradiation g
If k is not constant, heat transfer analysis increase.
fins are surfaces that extend from an object to increase the rate of heat transfer to or from the
environment by increasing convection.
4 tip condition
No heat flux, infinite length, convection loss at end, Precenbed T at tip
When is bi>.1 when small k like wood, large Lc like thick walls, high h fast fluid motion.
H for convection depends on fluid flow, thermal properties, geometry.