August 4, 2020

Principle of UVC sterilization

Ultraviolet germicidal lamps are mainly in the UVC band, of which the strongest germicidal power is in the range of 250-270nm. The UVC ultraviolet radiation intensity of the corresponding band needs to use a UVC light meter.
   1. The principle of UVC sterilization
Because the resonance spectrum of mercury is 253.7nm, this kind of germicidal lamp can produce 253.7nm-based ultraviolet rays, which denature bacterial and viral DNA and RNAV, and cells cannot reproduce. Ultraviolet disinfection lamps are effective against any bacteria or viruses, and concentrated high-intensity UVC ultraviolet rays can kill bacteria in a short time. It is widely used for disinfection and sterilization of air, various material surfaces, water or other liquids. The effect of UVC ultraviolet sterilization is not only related to the wavelength, but also to the radiation dose. The increase in the radiation dose increases the sterilization amount, but it is not linear, that is, the sterilization rate (percentage) is not proportional to the radiation dose (the ultraviolet radiation dose is equal to the ultraviolet irradiance value multiplied by the time).
  2, UVC generation
The best disinfection and sterilization effect is c-band ultraviolet rays with a wavelength of 254 ~ 257nm. How to obtain economical sterilization ultraviolet? Low-pressure mercury lamp is an efficient 254nm ultraviolet light source. There are many types of ultraviolet low-pressure mercury lamps, which are divided into: arc discharge low-pressure mercury lamps and glow discharge low-pressure mercury lamps; according to cathode types: hot cathode low-pressure mercury lamps and cold cathode low-pressure mercury lamps; classified according to the amount of ozone produced : There are ozone lamps and ozone-free lamps. At present, the most commonly used sterilization is the hot cathode low pressure mercury lamp. Ozone-free lamps are used for sterilization in human areas, and ozone lamps can be used for sterilization in unmanned areas. Ozone itself also has a sterilization effect. The disadvantage of the low-pressure mercury lamp is that it is not easy to make a high-power lamp, generally not more than 100W. After the power is greater than 40W, the 254nm ultraviolet conversion will decrease. This limits its scope of application. When a high-power sterilization ultraviolet source is required, a long arc high-pressure mercury lamp or a metal halide lamp (antimony neon lamp) can be used.
  3. The influence of UVC ultraviolet radiation intensity, distance and time on sterilization
When using a straight tube-shaped linear light source low-pressure mercury lamp for sterilization, when the irradiation distance is less than 1/2L (L: the length of the low-pressure mercury lamp), the ultraviolet radiation intensity is approximately inversely proportional to the distance; when the irradiation distance is more than 1/2L, The intensity of ultraviolet radiation is approximately inversely proportional to the square of the irradiation distance; when the ruler> 4L, the irradiance calculation error is less than 5%. Ultraviolet radiation dose = ultraviolet radiation intensity (E) x exposure time (t). Therefore, the ultraviolet radiation dose is directly proportional to the exposure time. When a low-pressure mercury lamp is used for sterilization indoors, the total power of the lamp is fixed after the lamp is installed, the lamp position (that is, the distance) is fixed, and the ultraviolet radiation dose is only related to the exposure time. Controlling the irradiation time controls the irradiation dose, that is, the sterilization rate.
  4, UVC ultraviolet ray sterilization of the surface of the object
Sterilize the surface of the object in a dust-free environment, and perform the sterilization according to the following conditions.
Ultraviolet radiation power: 2W/m2;
The distance between the lamp tube and the illuminated surface: 1.25~1.50m;
Irradiation time: 30rain;
Effective irradiation area (below the tube vertically): 1.5~2.0m2.