
Heat Transfer (Heat)
Thermal energy in transit due to a SPATIAL temperature difference.

Heat Flux
The rate of heat transfer in the x direction per unit area PERPENDICULAR to the direction of transfer
q'' = q / A

variable: k
Conduction Heat Transfer Coefficient
PROPERTY

CONDUCTION
Mechanism, Who?, Equation
Diffusion of energy due to random molecular motion
 Fourier's Law
 Heat flux, q'' =

CONVECTION
Mechanism, Who?, Equation
Same as conduction + energy transfer due to bulk motion
Newton's Law of Cooling
q'' = h ( T_{surface}  T_{fluid} )

variable: h
Convection Heat Transfer Coefficient
W/(m^{2 }* K)
NOT A PROPERTY

Advection
energy transfer due to bulk motion

Convection heat transfer is_______ if transferred TO the surface
( T_{surface} < T_{fluid} )
NEGATIVE heat transfer TO the surface

Convective heat transfer is________ if heat is transferred FROM the surface
( T_{surface} > T_{fluid} )
POSITIVE heat transfer FROM the surface

Forced Convection
Flow is caused by external means, such as by a fan, pump, or atmospheric winds.

Free (natural) Convection
Flow is induced by buoyancy forces, which are due to density differences caused by temperature variations in the fluid.

Sensible energy
Internal thermal energy of the fluid

Latent heat exchange
associated with a phase change between the liquid and vapor states of the fluid

RADIATION
Mechanism, Equation
**occurs most efficiently in a vacuum**
Energy transfer by electromagnetic waves (or photons)
 q_{rad}'' = q / A =
 q_{rad}'' =

variable:
emissivity variable
PROPERTY

Ideal Radiator
Blackbody: emits radiation at the maximum possible rate
= 1

variable: E_{b}
Emissive Power

StefanBoltzmann Law
= 5.67 x 10 ^{8} W/(m ^{2}K ^{4})
E_{b} =

Incident Radiation
may originate from a special source, such as the sun, or from other surfaces to which the surface of interest is exposed.

variable: G
IRRADIATION
=
Irradiation energy = (reflected + transmitted + absorbed) energy

variable:
ABSORBTIVITY


variable: h_{r}
radiation heat transfer coefficient

Thermal and Mechanical Energy Equation

Internal energy consists of a:
1. Sensible component
2. Latent component
3. Chemical component
4. Nuclear component
 1. accounts for translational, rotational, and/or vibrational motion of the atoms composing the matter.
 2. relates intermolecular forces influencing phase change
 3. accounts for energy stored in the chemical bonds
 4. accounts for binding forces in the nucleus

Simplify the TME Equation for STEADY STATE conditions.
E_{dot stored} = 0

Simplified STEADYFLOW thermal energy equation
Q _{dot} = q = m _{dot} x C _{p} x ( Tout  Tin )
 1. ideal gas with _{ }KE, PE, W = 0
 2. incompressible liquid with _{ }KE, PE, W = 0
 OR
 ideal gas/incompressible fluid with negligible viscous dissipation

Surface Energy Balance
E_{dot in } E_{dot out} = 0
q''_{cond}  q''_{conv}  q''_{rad} = 0
_{ }

