In my last two columns, I've investigated convection and conduction heat transfer, so now I'll look at the third member of the heat transfer triumvirate -- radiation.
Radiation is energy transfer via electromagnetic waves. The electromagnetic spectrum includes radio waves, X-rays, gamma rays and visible light, but the most useful part of the spectrum for heat transfer is infrared, which spans a range of wavelengths longer than visible light (figure 1). Infrared is further divided into three wavelength ranges: near, or short wavelength, infrared (wavelengths close to visible light); medium wavelength infrared; and far, or long wavelength, infrared. Nearly all industrial infrared heaters operate in the short or medium infrared range.