tailieunhanh - Ultraviolet Light in Water and Wastewater Sanitation - Chapter 2

Ánh sáng có thể được tạo ra bằng cách kích hoạt điện tử đến một nhà nước cao hơn quỹ đạo của một phần tử, sự trở lại của rằng các loài kích hoạt để giảm trạng thái năng lượng được đi kèm với sự phát xạ của ánh sáng. Quá trình này được sơ đồ minh họa trong hình 5. Các khía cạnh định lượng được thể hiện như E1 - E0 = hn. Nói cách khác, các bước sóng thu được phụ thuộc vào sự khác biệt về năng lượng giữa trạng thái kích hoạt và nhà nước. | 2 Available Lamp or Burner Technologies 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 hv. In other words wavelengths 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 matter and is quantified by the Stefan-Boltzmann law P T sT4 where P T is the total radiant power in watts radiated into one hemisphere 2 -solid angle by unit surface at T Kelvin. The Stefan-Boltzmann constant s equals X 10-12 W cm-2. 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. MERCURY EMISSION LAMPS Activation or ionization of mercury atoms by electrons . 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 reaction underlying the electrical discharge. A vapor pressure diagram is given in Figure 6. Activation-ionization by collision with electrons and return to a lower energy state . the ground state is the principle of production of light in the system see Figure 5 . 2002 by CRC Press LLC S hv El E0 FIGURE 5 Emission of radiation by matter schematic . As .