Radiation heat transfer Definition and 23 Threads

Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
Infrared radiation emitted by animals (detectable with an infrared camera) and cosmic microwave background radiation are examples of thermal radiation.
If a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium, the radiation is called blackbody radiation. Planck's law describes the spectrum of blackbody radiation, which depends solely on the object's temperature. Wien's displacement law determines the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the radiant intensity.Thermal radiation is also one of the fundamental mechanisms of heat transfer.

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  1. E

    A Blackbody Radiation and Complex Refractive Index

    Hi. If the refractive index of a medium equals one, the total emitted blackbody intensity inside a medium is sigma*T^4. In general, if the refractive index of a is a real number, the total emitted blackbody intensity inside a medium is n^2*sigma*T^4. Now, when the refractive index of the medium...
  2. E

    A Interpretation of a complex angle of refraction

    Hi, Refractive index can be complex. When Snell's law is taken into account refraction angle can also be complex. What is the meaning of the imaginary part and the real part of the refraction angle? Which angle should I take into account when I want to follow the direction of a thermal...
  3. R

    Power Radiated From a Copper Cube

    ##e## is emissivity ##\sigma## is the Stefan-Boltzmann constant, ##5.67*10^{-8} W m^{-2} K^{-4}## A is the surface area T is the temperature ##\frac{dQ}{dt}## is the rate of heat transfer or radiated power At first glance this appeared to be an easy problem, just plug in the values and go, so...
  4. FEAnalyst

    Triangular cavity thermal radiation simulation

    Hi, I'm trying to solve a problem involving radiation in a triangular cavity: As you can see, lengths and emissivities of all surfaces are given. For two of them, the heat flux is known and the temperature has to be found while for the remaining surface it's the other way around. I have the...
  5. A

    Application Of Kirchoff Law (Desert)

    Homework Statement:: Sand is rough and black so it is a good absorber and radiator of heat depending on temperature. During the day, sand's radiation of the sun's energy superheats the air and causes temperatures to soar. But, at night most of the heat in the sand quickly radiates into the air...
  6. FEAnalyst

    Radiation heat transfer between parallel plates

    Hi, the approximate (not accounting for plate size and separation distance) formula for heat flux exchanged via radiation between two parallel plates is: $$q=\frac{\sigma (T_{1}^{4}-T_{2}^{4})}{\frac{1}{\varepsilon_{1}}+\frac{1}{\varepsilon_{2}}-1}$$ where: ##\sigma## - Stefan-Boltzmann...
  7. V

    Radiation heat transfer in channel flow

    Hi guys, I am confused about the heat transfer mode of between two contacting material, especially in a channel flow. Obviously, conduction or convection dominate the heat transfer process in the process with low object temperature . But I am not sure if I have a fluid of 500 Kelvin, flowing...
  8. imselva

    Radiation heat transfer using 12 heat sources

    The intensity is proportional to the square of the distance between the source and the body and also depends on the angle of incident. I = The intensity at 0° (Assuming I = some constant) then I0 = I cos(Theta) Theta = the angle of incidence. I want to solve this using trignomentry. Is it...
  9. imselva

    What is the Equilibrium State in Radiation Heat Transfer?

    I have two bodies, one at a higher temperature say 1000°C (Body A) and the other is at 22°C (Body B). Body A emits Radiation (Surface to Surface interaction). The temperature of Body A is maintained by a constant supply of Energy. The Body B will absorb the Radiation Energy from Body A, and its...
  10. B

    Radiant heat transfer and specific heat

    Homework Statement I'm a little bit stuck with this exercise.A small body with temperature T and emissivity ε is placed in a large evacuated cavity with interior walls kept at temperature Tw. When Tw-T is small, show that the rate of heat transfer by radiation is $$...
  11. R

    Heat transfer through AL shield by radiation & convection

    Hi all, I am new here, and want to thank you for help in advance! I am working on a project and need some help - I need to figure out surface temp on an object at some distance from the heat source: I need some help getting started. Is it going to be: Heat transfer (radiation) + Heat...
  12. A

    Please help me with this doubt about radiant heat transfer

    My textbook says that net rate of heat transfer due to radiation is εσA(T^4-To^4) but i couldn't understand it. Rate of emission is εσAT^4 and rate of absorption is aσATo^4 so net rate of heat transfer must be εσAT^4-aσATo^4(where T is the temperature of body and To is the temperature of...
  13. G

    Stability of radiative heat transfer

    Hi everyone. I have here a problem understanding the stability of heat transfer through radiation. I'll give you some background, and later on I'll describe the physical problem. Background I am simulating the unsteady radiative heat transfer between mutually visible surfaces of objects through...
  14. Dong Aleta

    Radiation to a small object from surroundings

    In the energy balance of a system where a small object at T1 enclosed in a body at T2 given by the Stefan-Boltzmann equation q = A1ε1σT14 - A1α12σT24 shouldn't it be a differential equation since the small body could be absorbing/releasing sufficient net energy from the enclosing body that...
  15. I

    Urban heat effect: high solar reflectance and emittance

    Homework Statement "The urban heat island (UHI) effect refers to the phenomenon of a metropolitan or built up area which is significantly warmer than its surrounding areas." Using white paint in roofs increases the solar reflectance and decrease the thermal intake into a building. Question:-...
  16. L

    Finding Temperature Distribution Across Rad Shields in a Vacuum Furnace

    Hi, We are doing radiation analysis using solidworks simulation..And as a part of this project i need to validate it theretically..Hope i will get some help here.. Its cylindrical vacuum furnace,where inside strip type heating elements are placed which are connected to transformer of 60kW.After...
  17. P

    Radiation heat transfer - mistake in attached solution?

    I attached the problem of interest (probably the only part you guys need to see is the equations at the bottom). My answers are off by a magnitude of 10 compared to the solutions. (copy and pasted it below since the pic is a little hard to see at the bottom) q = σε f*A(T^4 − Ts^4 ) = 5.67...
  18. E

    Two questions about thermal radiation heat transfer

    Hi guys, could you concretely explain me (also with a simple example) the difference between blackbody emissive power (sometimes found as e'λb) and blackbody radiation intensity (i^{'}_{λb})? and which the difference between a diffuse surface and a surface that follows the Lambert law? Thank...
  19. Z

    Radiation heat transfer between air or wall

    Lets say a hot object is at 500K and placed in a chamber with wall temperature of 300K. The surrounding air in the chamber is 320K. So what is the mode of heat transfer for the hot objection? There is convection and radiation. so the heat transfer rate, q = q(conv) + q(rad), right...
  20. D

    View Factor in radiation heat transfer

    Hi can anyone temme how to calculate view factor between two spheres.
  21. D

    Radiation heat transfer (V-shaped and rect cavity)

    Hello, I need help with this problem, Find radiosity B as a function of coordinates (x,y) over a V-shape or rectangular cavity. Consider the two walls and the surroundings to constitute an enclosure. Without any loss of generality, the cavity can have a unit depth. The temperature and...
  22. W

    Radiation heat transfer with FEMLAB

    I want to simulate radiation heat transfer between two surfaces which are in the vacuum using FemLab3.1. However, the heat transfer module only consider conduction and convection. Some additional examples I found incorporate radiation (with surace-to-surface option) but they need a conduction...
  23. Q_Goest

    Superconducting field inhibits radiation heat transfer?

    I'm reviewing a letter regarding the sheilding of an object using a superconducting magnet as is commonly found in MRI machines. The claim is that the magnetic field created by superconducting windings (wire which is carrying a current and thus creating a magnetic field) and wrapped around an...
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