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Lecture-1. Governing Laws for Thermal Radiation

Lecture-1. Governing Laws for Thermal Radiation. Contents of the lecture. 1.1 Heat Transfer Mechanisms. 1.2 Electromagnetic Radiation. 1.6 Geometrical Considerations. 1.7 Governing Laws for Thermal Radiation. 1.8 Blackbody Radiation in a Wavelength Interval.

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Lecture-1. Governing Laws for Thermal Radiation

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  1. Lecture-1. Governing Laws for Thermal Radiation Contents of the lecture 1.1 Heat Transfer Mechanisms 1.2 Electromagnetic Radiation 1.6 Geometrical Considerations 1.7 Governing Laws for Thermal Radiation 1.8 Blackbody Radiation in a Wavelength Interval 1.10 Historical Note – Origin of Quantum Mechanics 1.11 Blackbody Emission into a Medium Other than Vacuum 1.12 Summary Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  2. What is heat transfer? Heat transfer (or heat) is energy in transit due to a temperature difference HEAT TRANSFER MODES Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  3. Amount of heat (energy) in J Heat transfer rate in W (J/s) Heat flux in W/m2 The convention (in this lecture series) is Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  4. Radiation which is given off by a body because of its temperature is called thermal radiation A body of a temperature larger than 0 K emits thermal radiation Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  5. A scene from “Silence of the lambs” A photograph of a car The number plate has been wiped out taken with an ordinary camera taken with an infrared camera Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  6. RELEVANCE OF THERMAL RADIATION Whenno medium is present radiation is the only mode of heat transfer Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  7. Quantum theory ELECTROMAGNETIC WAVES Classical theory Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  8. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  9. SPEED, FREQUENCY and WAVELENGTH For any wave: Determined by the source Determined by the medium For electromagnetic waves: c=3·108 m/s ( in vacuum) Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  10. SPEED, FREQUENCY and WAVELENGTH For a medium other than vacuum: The frequency stays the same so, Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  11. COMMON UNITS FOR WAVELENGTH 1 micrometer = 10-6 m 1 nanometer = 10-9 m 1 angstrom = 10-10 m Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  12. Frequency (Hz) Photon energy in J Energy in electron volts Number of photons in a joule of energy Short radio waves ν=107 4.1·10-8 1.5·1026 4.1 1.5·1018 6.63·10-27 X-rays ν=1018 6.63·10-16 4.1·103 1.5·1015 Visible light waves ν=1015 6.63·10-19 Gamma rays ν=1020 6.63·10-14 4.1·105 1.5·1013 Example 1.1 (Calculate energy of photons) Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  13. THERMAL RADIATION Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  14. 1.6 Geometrical Considerations 1.6.1 Normal to a Surface Element Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  15. 1.6.2 Solid Angle Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  16. Plane angle in radiance Example 1.2 Derive formula for calculating the length of an arc and the circumference of a circle. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  17. The solid angle in steradians Derive formula for calculating the area of a sphere How to calculate the solid angle? Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  18. How to calculate the solid angle? Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  19. How to calculate the solid angle? Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  20. Now we can complete the integration since we know how to calculate the solid angle: Solid angle for a hemisphere is Solid angle for a sphere is Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  21. 1.6.3 Area and Projected Area Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  22. indicates direction 1.6.4 Radiation Intensity and Irradiation Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  23. for isotropic incoming radiation Irradiation Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  24. For isotropic radiation An important integral in radiation Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  25. reflectivity absorptivity transmissivity 1.7 Governing Laws for Thermal Radiation 1.7.1 Black Body Radiation Real surfaces (bodies) Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  26. BLACK BODY RADIATION Definition of a black body A black body is defined as an ideal body that all incident radiationpass into it and internally absorbs all the incident radiation. This is true for radiation of all wavelengths and for all angles of incidence Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  27. BLACK BODY RADIATION Properties: Black body is a perfect emitter In a black body enclosure radiation is isotropic Black body is a perfect emitter in each direction Black body is a perfect emitter at any wavelength Total radiation of a black body into vacuum is a function of temperature only Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  28. The angular distribution of radiation intensity emitted by a black body Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  29. 1.7.2 Planck’s Radiation Law Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  30. Planck’s Radiation Law Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  31. Planck’s Radiation Law Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  32. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  33. See Example 1.4 of the lecture notes to understand the meaning of: Frequency distribution Cumulative frequency distribution Relative cumulative frequency distribution Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  34. Example 1.4 Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  35. Example 1.4 Histogram and frequency polygon of heights of 130 students Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  36. Example 1.4 Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  37. Example 1.4 Cumulative distribution (less than the upper class boundary) Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  38. Example 1.4 Students smaller than 174 cm The relative cumulative distribution Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  39. Example 1.4 Cumulative distribution Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  40. 1.7.3 Wien’s Displacement Law We are looking for a wavelength that maximizes the Planck’s function for a given temperature Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  41. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  42. Wien’s Law Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  43. 1.7.4 Stefan-Boltzmann Law Stefan-Boltzmann constant Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  44. 1.8 Blackbody Radiation in a Wavelength Interval Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  45. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  46. Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  47. 1.9 Blackbody Emission into a Medium Other than Vacuum Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  48. n- refractive index Planck’s function in vacuum Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  49. Stefan-Boltzmann Law Wien’s Displacement Law Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

  50. 1.10 Historical Note – Origin of Quantum Mechanics Advanced Heat Transfer - Prof. Dr.-Ing. R. Weber - Winter 2005/2006 - Lecture 1 (Governing Laws)

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