Heat Transfer Exam 2

Biot number

Bi = hL_c/k (k solid)

Fourier number

Fo = αt/(L_c²) (α = thermal diffusivity, t = time)

Nusselt number

Bi = hL_c/k (k fluid)

Reynolds number

Re = ρvL/μ (μ = viscosity, ρ. =density, v = velocity, L = characteristic length)

Prandlt number

Pr = ν/α=μ/(ρα) (v = momentum diffusivity (μ/ρ), α=thermal diffusivity. all properties of fluid)

Thermal diffusivity

α=k/(ρC_p) (all properties of the solid for Fo, fluid for Pr)

L_c

generally volume/surface area

Assumptions for lumped capacitance

7: no gen, no radiation, uniform properties, nearly uniform temperature, no phase change, constant uniform h, continuum.

T_f

T_film = (T_surface+T_infinity)/2 (average)

Step 1 finding h

type of convection: internal vs external, forced vs free

Step 2 finding h

match geometry of flow and object

Step 3 finding h

want local or average h?

Step 4 finding h

laminar or turbulent

Step 5-7

choose correlation, RTFI, sanity check