Review of heat transfer Fundamentals Convection- heat transfer via flowing flu uIds Conduction- heat transfer within materials other than flowing fluids Radiation heat transfer via electromagnetic waves
6 Review of Heat Transfer Fundamentals • Convection – heat transfer via flowing fluids • Conduction – heat transfer within materials other than flowing fluids • Radiation – heat transfer via electromagnetic waves
Convection g=h*A*AT h= heat transfer coefficient Important to spacecraft during launch after fairing separation Convective heat transfer is used in some pumped-liquid thermal control systems especially in manned spacecraft
7 Convection • h = heat transfer coefficient • Important to spacecraft during launch after fairing separation • Convective heat transfer is used in some pumped-liquid thermal control systems, especially in manned spacecraft q = h ∗ A∗ ∆T
Conduction q=(71-72 Rectangular 2kmL(71-T2) q Cylindrical ln(D。/D) 4mkRR(71-72) q (R。-R) k is the thermal conductivity
8 Conduction • Rectangular • Cylindrical • Spherical • k is the thermal conductivity ( ) 4 ( ) ln( / ) 2 ( ) ( ) 1 2 1 2 1 2 o i i o o i R R kR R T T q D D k L T T q T T x kA q − − = − = − ∆ = π π
Radiation g=EoT g=emissivity at the wavelength mix corresponding to temperature t o=Stefan-Bolzmann's constant =5670x108W/m2-K4 T is temperature in Kelvin Primary energy transfer mechanism for spacecraft Most spacecraft have large radiators to rid themselves of heat q is the heat transfer per unit area and T is the surface temperature
9 Radiation ε=emissivity at the wavelength mix corresponding to temperature T σ=Stefan-Bolzmann’s constant = 5.670 x 10-8 W/m2-K4 T is temperature in Kelvin 4 q = εσT Primary energy transfer mechanism for spacecraft. Most spacecraft have large radiators to rid themselves of heat. q is the heat transfer per unit area and T is the surface temperature
Planck's equation 2k ch/kT 入= wavelength h=Planck's constant c=speed of light kBolzmann's constant At any temperature above absolute zero, all materials emit thermal(blackbody) radiation For a perfect blackbody, the rate of total energy emission and the energy distribution across all wavelengths is strictly a function of the absolute temperature T For spacecraft and atmosphere covered planets these distributions are modified, but we usually use the perfect blackbody energy distribution at least as an initial estimate perfect blackbody. Eb is the energy per unit wavelength of a blackba on of a Plancks equation gives us the spectral energy distributio h=66260755e-34Ws2k=1380658e-23Ws/K
10 Planck’s Equation λ=wavelength h=Planck’s constant c=speed of light k=Bolzmann’s constant 1 2 1 5 / 2 − = ∗ b ch k T e hc E λ λ λ π At any temperature above absolute zero, all materials emit thermal (blackbody) radiation. For a perfect blackbody, the rate of total energy emission and the energy distribution across all wavelengths is strictly a function of the absolute temperature T. For spacecraft and atmosphere covered planets these distributions are modified, but we usually use the perfect blackbody energy distribution at least as an initial estimate. Planck’s equation gives us the spectral energy distribution of a perfect blackbody. Eb is the energy per unit wavelength of a blackbody. h=6.6260755e-34 Ws2 k=1.380658e-23 Ws/K