Radiation
Black body radiation
-Black body means it has emissivity=1 (1=e+R+T)
-Emissivity = Absorption
Assume b=3000um, ex) 6000K->0.5um, 300K->10um
Stefan-Boltzmann law (Energy)
Radiative energy = f(emissivity, T, Ta, surface area)
Polymer’s emissivity
Beer’s law
Science 2016
Diffuse scattering
Relative method to measure optics
-by comparing the optics with high reflection materials (BaSO4/UV-NIS-NIR, Au/IR)
900W/m2
1000W/m2
1366W/m2
Vis
390nm-700nm
UV (-390nm) | 46W/m2 5% |
VIS (390nm-700nm) | 435W/m2 44% |
IR (700nm-2500nm) | 510W/m2 51% |
Sum | 991W/m2 |
Black body radiation map for human body
Temperature of sun >> Temperature of human body
Air
Human body gets radiation from the sun and environment and emits radiation to environment.
Temperature of human body > ambient temperature
Energy absorption in human body
Energy emission from human body
Stefan-Boltzman Law
θ
Human body (surface 1.8m2) was assumed as a rectangular.
Projected area : 0.1cosθ + 0.4sinθ (m2)
Irradiated sunlight : (0.1cosθ +0.4sinθ) (m2) x 1000 (W/m2) = 100cosθ + 400sinθ (W)
0.4m2
0.1m2
Radiation energy from the sun
Simulation of solar energy radiated on human body according to solar position. Human body was assumed as a rectangular which has a 1.8m2 surface area (average value for adult).
1kcal/hr = 1.16W
Thermal comfort?
Temp. is the perfect indicator?
D. P. Wyon et al., J. Hyg.. Camb.. 1972, 70, 203.
Skin temps are various.
J. Hardy, PNAS 1937
Steady state thermal transfer model
-incoming eneryg = outcoming energy
-To simplyfy the equation, resistance of thermal transfers are utilized in terms of thermal-delaying parameters.
(moisture transfer resistance,
thermal conductive resistance,�covective resistance,�radiative resistance)
R=1/h (h = thermal coefficient)
h : W/m2K
Q=deltaT/h
Steadman, R. G. J. Appl. Meteor. 1979, 18, 861.
ex) Can you predict the temperature of graphite ball (or graphene, CNT ball) under the sunlight?
Degree C
Solar energy (W/m2)
Ta = 23 degree C
Do we need heat capacity to estimate the thermal balance?
Degree C
Solar energy (W/m2)
Can increase more temperature by sunlight absorption?
Degree C
Solar energy (W/m2)
e=0.01
e=0.5
e=1
Concentrated solar power
Sunlight (photon) -> electron -> energy
Efficiency ~20%
Sunlight -> heat -> turbin
Efficiency ~ 40%
How we can achieve wavelength-selective emissivity?
From wikipedia
Versatility of infrared properties of Mxene, Han et al, Materials Today, 64, p31-39, 2023
Convective thermal coefficient
Moisture thermal coefficient
Latent thermal transfer
Q=delta(mositure)/mositure resistance
Absolute humidity
Apparent temperature
Humiture
Do you think that high thermal conductivity leads to cooling?
By steady state model, it doesn’t matter for thermal conductivity of TIM.
IR image VS high thermal conductivity
IR image is measuring radiative thermal mapping supposing the surface has the high emissivity.
High thermal conductivity can cope with thermal shock.
Thermal conductivity is measured with a thermal wave source.
-Emissivity of composite (polymer + low emissivity medium)
-Emissivity control of polymer materials