UV紫外线杀菌器在水和废水处理中的应用英文原版研究论文_C02.pdf

2 Available Lamp (or Burner) Technologies 2.1 GENERAL Light can be generated by activating electrons to a higher orbital state of an element; the return of that activated species to lower energy states is accompanied by the emission of light. The process is schematically illustrated in Figure 5. The quantitative aspects are expressed as E1 − E0 = hn. In other words, wave- lengths obtained depend on the energy difference between the activated state and the return state. Thermal activation of matter provides a means of production of light. According to the black body concept, the total radiant power depends on the temperature of the 4 matter and is quantified by the Stefan–Boltzmann law: P(T) = sT , where P(T) is the total radiant power in watts, radiated into one hemisphere (2p-solid angle) by unit −12 −2 surface at T Kelvin. The Stefan–Boltzmann constant (s) equals 5.6703 × 10 W cm . However, the emissivity obtained depends on the wavelengths of interest. Black body radiation is not a major source of technological generation of ultraviolet (UV) light, but cannot be entirely neglected in existing lamps either. 2.2 MERCURY EMISSION LAMPS Activation (or ionization) of mercury atoms by electrons (i.e., electrical discharges) at present is by far the most important technology in generating ultraviolet (UV) light as applicable to water disinfection. The reasons for the prevalence of mercury are that it is the most volatile metal element for which activation in the gas phase can be obtained at temperatures compatible with the structures of the lamps. Moreover, it has an ionization energy low enough to enable the so-called “avalanche effect,” which is a chain