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Heat Transfer on Electrical Components by Radiation

Heat Transfer on Electrical Components by Radiation. R. Haller. Topics. Motivation and Introduction Physical basic relations Determination of Radiant Power Fields of Application Conclusions. Motivation. Is the radiation in the low temperature range

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Heat Transfer on Electrical Components by Radiation

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  1. Heat Transfer on Electrical Components by Radiation R. Haller

  2. Topics • Motivation and Introduction • Physical basic relations • Determination of Radiant Power • Fields of Application • Conclusions Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  3. Motivation Is the radiation in the low temperature range (< 100 … 150 °C) important for thermal calculation or not ? Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  4. Introduction Heat transfer (heating, cooling) is possible by • conduction • convection • radiation Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  5. design- tasks for electrical components (indoor) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  6. design- tasks for electrical components(outdoor) sky Influence of heat power on outdoor components caused by sun and sky radiation Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  7. Topics • Motivation and Introduction • Physical basic relations • Determination of Radiant Power • Fields of Application • Conclusions Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  8. type of electromagnetic radiation thermal radiation  0.1 … 400 µm Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  9. Physical basic relations radiation processes are different from those by conduction or convection • no transfer medium is necessary • transferred heat power is mainly determined by the object temperature Tand the interactions between the radiated areas (absorption, emissivity) what can lead to a difference of temperature T ) and can´t be described by classical thermodynamics Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  10. generation of thermal radiation (modelling) thermal radiation will be generated by changes of atomic dipol moment caused by thermal induced oscillations Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  11. classification Objects with a temperature T > 0 K emit electromagnetic radiation and, therefore, are able to give away energy to other objects • The radiation takes place from the surface of solid and fluid objects and/ or from the volume of gases • area radiator (radiators are described by their radiation area) • volume radiator (physical basic processes) the heating by radiation will be generated by inner atomic processes into the radiated object (near the surface, absorption) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  12. intensity of radiation infrared range Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  13. intensity of thermal radiation [Wien] [Planck] Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  14. Physical basic relations area of radiation [Stefan- Boltzmann´s law] emissivity Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  15. thermal radiation balance Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  16. Physical basic relations The ratio of emission is equivalent to the ratio of absorption (thermal balance  Kirchhoff´s law Ratio of emission for real radiators: radiation of real object with T1 radiation of „black radiator“ with T1 ε = Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  17. Physical basic relations classification of radiators: • black: all radiations will be absorbed (ά = ε = 1) • white: all radiations will be reflected (ρ = 1) • gray: all radiations will be absorbed/ emitted in the same ratio about all wave lengthes (ε < 1) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  18. radiation characteristic for planes [Lambert´s law] Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  19. Topics • Motivation and Introduction • Physical basic relations • Determination of Radiant Power • Fields of Application • Conclusions Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  20. Determination of Radiant Parameters •  determination of emissivity ε • ε ≠ f (T) • ε = f (surface material, ..)  determination of surfaces O • determination of power P and/ or temperature T • exact calculation • numerical calculation (thermal- grid, … .) • measurement (thermografy, ..) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  21. exact calculation = geometrical faktor Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  22. radiation characteristic for two planes Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  23. emitted radiation between two planes with significant area difference Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  24. emitted radiation between two planes with significant area difference Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  25. emissivity  usually determined by measurement Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  26. numerical calculation [Stefan- Boltzmann] Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  27. numerical calculation analogous to the thermodynamic relation [Newton] Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  28. determination of heat power (radiation + convection) [Newton] with = k + S1,2 Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  29. determination of heat power  heatpower parts must be determined separately Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  30. heat transfer by convection • exact calculation of Navier- Stokes- Equations • numerical calculation (FEM, CFD, …) • theory of similarity Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  31. simulation by FEM- program (ANSYS) α = αkonv + αrad boundary conditions results Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  32. theory of similarity free convection: forced convection: Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  33. theory of similarity free convection forced convection Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  34. theory of similarity Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  35. theory of similarity Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  36. thermal grid method Gth· θ + Cth· (dθ/ dt) = P with θ  temperature P heat power Gth , Cth  thermal admittance, capacity ordinary differential equation system coefficients are dependent from variable Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  37. thermal grid method DQ=Rth * P (steady state) with DQ  difference of temperatures P  heat power Rth  thermal resistances procedure:  separation of interesting areas/ volumes into n- parts  determination of heat power sources  calculation of thermal resistances  appropriate network calculation method (nonlinear, iterative calculations) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  38. thermal grid method Rth = RL + RKo + RS Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  39. thermal grid method Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  40. thermal grid method Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  41. radiation influence on outdoor components Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  42. influence of sky radiation Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  43. comparison with convective transferred heat power vertical plate with temperature T > T0 T T0 I bus- bar of switching equipments Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  44. comparison of heat transfer PKo PS vertical plate (OS1 = 1m2), T1 = 70 °C, T2 = 30 °C 1 = 0,25/ 0,9; 2 = 0,9; OS1 << OS2 free convection S= 1,92 W/m2K S= 6,9 W/m2K Ko= 5,83 W/m2K PKo = 233,2 W/m2 PS= 76,8W/m2 PS= 276 W/m2  Ps > Pk ! Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  45. comparison of heat transfer Parameter: I = 2000 A, bus- bar (10 x 100) mm2, Al = Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  46. comparison of heat transfer Prad --- (ε = 0,25; 0,9) Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  47. measurement of radiant power measurement principle Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  48. measurement of radiant power transmission ability of measuring distance working range of IR- measurement systems Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  49. application in electrical power engineering Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

  50. heating up process of an electronic circuit Department of Electrical Power and Environmental Engineering Prof. Dr.- Ing. habil. Rainer Haller, Dr.sc.techn.

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