10. Radiation Heat Transfer - cu（10。）.pdf

Part B: Heat Transfer Principals in Electronics Cooling 10. Radiation Heat Transfer 10.1Introduction Radiation heat transfer plays a major role in the cooling of electronics. As well as conduction and convection heat transfer, radiation is an equally important mode. Also the thermal radiation has many applications such as engine cooling, furnaces, boilers, piping and solar radiation. The thermal radiation transferred by electromagnetic waves, called photons, is emitted by bodies due to temperature differences. All surfaces continuously emit and absorb radiative energy by lowering or raising their molecular energy levels. The electromagnetic waves travel through any medium or in vacuum at the speed of light (c), which equals 3  108 m/s. this speed equal to the product of the wave length and frequency  c =  The metric unit for the wave length is centimeters or angstroms (1 angstrom = 10-8 centimeter). A portion of the electromagnetic spectrum is shown in Figure 10.1. Visible Blue yellow Red Green Infrared Gamma rays Microwave ultraviolet X rays Thermal radiation -5 -4 -3 -2 -1 2 3 4 10 10 10 10 10 1 10 10 10 10 λ (µm) Figure 10.1 Electromagnetic spectrum 10.2 Blackbody Radiation Materials used in electronic hard ware may be classified as black or