8.1 Efficiency of a Counterflow Heat Exchanger. IT-50 9.0 Radiation Heat Transfer(Heat transfer by thermal radiation) HT-52 9.1 Ideal radiators 9.2 Kirchhoff's Law and Real bodies HT-55 9.3 Radiation Heat Transfer Between Planar Surfaces 9. 4 Radiation Heat Transfer Between Black Surfaces of Arbitrary Geometry8.1 Efficiency of a Counterflow Heat Exchanger.................................................................HT-50 9.0 Radiation Heat Transfer (Heat transfer by thermal radiation).............................................HT-52 9.1 Ideal Radiators ..............................................................................................................HT-53 9.2 Kirchhoff's Law and "Real Bodies" ...............................................................................HT-55 9.3 Radiation Heat Transfer Between Planar Surfaces.........................................................HT-55 9.4 Radiation Heat Transfer Between Black Surfaces of Arbitrary Geometry ......................HT-60