# ME 3304 - Ch. 1

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1. Heat Transfer (Heat)
Thermal energy in transit due to a SPATIAL temperature difference.
2. Heat Flux
The rate of heat transfer in the x direction per unit area PERPENDICULAR to the direction of transfer

q'' = q / A
3. variable: k
Conduction Heat Transfer Coefficient

PROPERTY
4. CONDUCTION

Mechanism, Who?, Equation
Diffusion of energy due to random molecular motion

• Fourier's Law
• Heat flux, q'' =
5. CONVECTION

Mechanism, Who?, Equation
Same as conduction + energy transfer due to bulk motion

Newton's Law of Cooling

q'' = h ( Tsurface - Tfluid )
6. variable: h
Convection Heat Transfer Coefficient

W/(m2 * K)

NOT A PROPERTY
energy transfer due to bulk motion
8. Convection heat transfer is_______ if transferred TO the surface
--( Tsurface < Tfluid )
NEGATIVE heat transfer TO the surface
9. Convective heat transfer is________ if heat is transferred FROM the surface
--( Tsurface > Tfluid )
POSITIVE heat transfer FROM the surface
10. Forced Convection
Flow is caused by external means, such as by a fan, pump, or atmospheric winds.
11. Free (natural) Convection
Flow is induced by buoyancy forces, which are due to density differences caused by temperature variations in the fluid.
12. Sensible energy
Internal thermal energy of the fluid
13. Latent heat exchange
associated with a phase change between the liquid and vapor states of the fluid

Mechanism, Equation

**occurs most efficiently in a vacuum**
Energy transfer by electromagnetic waves (or photons)

• qrad'' = q / A =
15. variable:
emissivity variable

PROPERTY
Blackbody: emits radiation at the maximum possible rate

= 1
17. variable: Eb
Emissive Power
18. Stefan-Boltzmann Law
= 5.67 x 10-8 W/(m2K4)

Eb =
may originate from a special source, such as the sun, or from other surfaces to which the surface of interest is exposed.
20. variable: G

=

Irradiation energy = (reflected + transmitted + absorbed) energy
21. variable:
ABSORBTIVITY
22. Gray surface condition?
23. variable: hr

24. Thermal and Mechanical Energy Equation
25. 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
26. Simplify the TME Equation for STEADY STATE conditions.
Edot stored = 0
27. Simplified STEADY-FLOW thermal energy equation
Qdot = q = mdot x Cp 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
28. Surface Energy Balance
Edot in - Edot out = 0

q''cond - q''conv - q''rad = 0

 Author: kylecaro ID: 126944 Card Set: ME 3304 - Ch. 1 Updated: 2012-01-12 20:55:14 Tags: Conduction Folders: Description: Study Material Show Answers: