McMullan - Heat Transfer Flashcards
What does the second law of thermodynamics tell us?
That energy has quality as well as quantity
What is conduction?
Conduction is the transfer of energy from more energetic particles of a substance to the adjacent less energetic particles
What is the equation for the steady-state heat transfer, governed by Fourier’s Law?
Q: = -kAdT/dx
Where k is the thermal conductivity
If the value of k is low, what does this imply?
That the material is a poor conductor
If the value of k is high, what does this imply?
That the material is a good conductor
What is convection?
Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion
What is natural convection?
Fluid motion is caused by buoyancy effects that are induced by temperature
What is forced convection?
Fluid is forced to flow over the solid surface by external forces
What is equation for convection, governed by Newton’s law of cooling?
Q: = hA(Too - Ts) Too = T infinity, Ts = surface temp
What is radiation?
Radiation is the energy emitted by matter in the form of electromagnetic waves
What is the equation for radiation, governed by the Stefan-Boltzman law?
Q: = 0AsTs^4 0 = Stefan Boltzman constant
Therman resistance concept. What is the equation for conduction?
Q; = T1 - T2/ R
Where R = L/kA
Thermal resistance concept. What is the equation for convection?
Q; = Too - Ts/ R
Where R = 1/hA
What is the equation for conduction, for a cylindrical system?
Qcond,cyl = T1 - T2/ Rcyl Rcyl = ln(r2/r1)/ 2piLk
What is equation for conduction, for a spherical system?
Qcond,sph = T1 - T2/ Rsph Rsph = r2 - r1/ 4pir1r2k
