ME 309 Test 1 Notes
Terms & Definitions
•
Temperature - indicator of thermal energy of a system ( K or Celsius )
•
Thermal Energy – measure of kinetic energy of atoms. Measure of energy like potential, chemical,
electrical, etc. ( J )
Heat – Thermal energy in motion. Transfer of thermal energy over a period of time ( J )
Heat Transfer Rate – transfer of thermal energy per unit time ( J/S → W )
Heat Flux – heat transfer rate per unit area ( W/m^2 )
Heat Generation Rate – rate at which heat energy conversion is taking place, thermal energy must be
involved ( W )
Volumetric Heat Generation – heat generation per unit volume ( W/m^3 )
•
•
•
•
•
•
3 Modes of Heat Transfer
• Conduction – direct contact between two objects or heat transfer within an object due to the
random motion of energy carriers within the object
• Convection – bulk motion that causes heat transfer
• Radiation – electromagnetic waves carry heat, think the sun
•
Thermal Resistance - heat property and a temperature difference measurement by which an object
or material resists a heat flow.
Emissivity – the measure of how strongly an object or surface interacts with thermal radiation in
terms of emission and absorption. High emissivity implies high absorption.
•
Isotropic - heat transfers evenly in all directions
Anisotropic - heat transfer varies depending on direction (different in x, y, & z directions)
ME 309 Test 1 Notes
ME 309 Heat Transfer
Quiz 1
1. Heat transfer within a solid medium happens
via
a. Conduction
b. Convection
c. Radiation
d. All of the above
2. In the absence of bulk movement, heat
transfer between solid and fluid as well as
within a fluid
happens via
a. Conduction
b. Advection
c. Convection
d. Radiation
3. Heat transfer via convection is governed by
a. Fourier’s law
b. Newton’s law of cooling
c. Stefan-Boltzmann law
d. None of the above
4. If two bodies (not in direct contact) are at
different temperatures, and there is vacuum in
the space
between them, heat transfer between them
can occur by
a. Conduction
b. Radiation
c. Convection
d. Advection
5. In general, it is appropriate to use heat
generation and thermal energy
interchangeably
a. True
b. False
ME 309 Heat Transfer
Quiz 2
1. As per Fourier’s law, heat transfer in a rod via
conduction is proportional to
a. Thermal conductivity of the material
b. Cross sectional area
c. Length of the rod
d. All of the above
2. Heat flux is a scalar
a. True
b. False
3. The inner surface of a wall is cooled by the air
circulated by the air conditioning system. What
would be the appropriate boundary condition to
use at the inner surface of the wall:
a. First kind – Constant surface
temperature
b. Second kind – Constant surface heat flux
c. Third kind – Convective heat flux
d. None of the above
4. A wall is made up of multiple layers of different
thicknesses and thermal conductivities. Heat
must past through all these layers to conduct
through the wall. The thermal resistors
representing
the layers are connected in
a. Parallel
b. Series
c. Combination of series and parallel
d. Cannot be determined
5. If the convective heat transfer coefficient is
extremely large on a surface, first kind boundary
condition is appropriate to use instead of third
kind.
a. True
b. False
ME 309 Test 1 Notes
Equations & Symbols
Fourier’s Law
• q : heat transfer rate ( W )
• q”: heat flux ( W/m^2 )
• q_(dot) : volumetric heat
generation rate ( W/m^3 )
Newton’s Law of Cooling
𝑞 = ℎ ∗ 𝐴 ∗ 𝑇1 − 𝑇∞
•
•
•
•
•
q : rate of heat transfer
• (W)
h : heat transfer coefficient
• ( W/m^2*K )
A : heat transfer surface area
• ( m^2 )
T_1 : temp of object
• (K)
T_(inf) : temp of environment
• (K)
Fourier’s Law – Thermal Resistance
through a wall
Stefan-Boltzmann Law
ME 309 Test 1 Notes
Thermal Resistance
𝑅
𝑅
𝐿
𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑜𝑛= 𝐾∗𝐴
1
𝑐𝑜𝑛𝑣𝑒𝑐𝑡𝑖𝑜𝑛/𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛= ℎ∗𝐴
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes
ME 309 Test 1 Notes