Water Disinfection - Crystal IS experience: ( reference: Crystal IS application notes)
Engineers can leverage highly UV reflective materials to maximize the efficiency of UVC reactors in Water and Air Ducts, to decrease the amount of UV intensity required throughout.
The amount of UVC radiation applied to a given volume over a specific time period needed for disinfection in a particular system is commonly referred to as the required UV Dose. UV Dose is comprised of two factors—the irradiance of the UVC light and the length of exposure to radiation. The reactor designers consider reactor size and shape, flow rate and the UV power of the system. In systems where there is less flexibility around flow rate, residence time and effectiveness of the UV light becomes a crucial factor. One way is to maximize internal reflection to take full advantage of the UV energy or photons emitted from the light source and increase efficiency. Table 1 shows the UV reflectivity of standard materials used in disinfection reactors.
Commercial UV disinfection systems use stainless steel, highly resistive to microbial growth. SS has only 20 - 28% reflectance of UV light. Flow cells that contain e-PTFE (expanded PolyTetraFluoroEthylene) provide more than 95% reflectance making the UVC more than three times effective than traditional reactors.
EXAMPLE 1: WATER DISINFECTION REACTOR
UV reactors are a mainstay for water treatment facilities and residential appliances designed to
disinfect water flowing through a system for safe public consumption.
To illustrate the impact of material reflectivity, Crystal IS examined two reactors with the same
dimensions (Figure 1), flow rate and UVC LED arrangement. The total power in the reactor is 200 mW. Reactor 1 was composed of stainless steel while reactor 2 used e-PTFE.
At the center of the reactor 7.5 cm from the end caps, the average irradiance in reactor 1 was 4.5 mW/cm2 whereas in reactor 2 the average was 17 mW/cm2. The radiation patterns in the reactors at the mid-point can be seen in Figure 2.
EXAMPLE 2: AIR DISINFECTION REACTOR
HVAC systems rely on UV disinfection to inhibit mold growth and reduce energy consumption. Filtration coupled with UV light is commonly integrated into ducts for complete disinfection. These ducts come in various sizes—the models in this example are based on a duct that is 380 cm wide by 250 cm long. The 35 LEDs in the system were arranged in a grid pattern to ensure the entire duct was covered with UVC light.
The irradiance was modeled within the duct based on two different materials: duct 1 comprised of a surface having no reflective properties and duct 2 is lined with Alzak Sheet aluminum which has more than 80% reflectance. The increase in reflectance between duct 1 and 2 increased the peak irradiance from 0.2 mW/cm2 to ~0.3 mW/cm2 . In addition, the UV dispersion was more uniform within duct 2, as can be seen in Figure 4a and 4b.
Addendum1:
One candidate UV reflector material is an aluminized polymer film having a front surface protective coating without appreciable UV absorption, suitable for indoor applications. Its also most cost effective. Another candidate is electropolished aluminum having an anodized protective coating (Al03). The "semi-specular" material has comparable cost, while "highly specular" material could cost double. Both have questionable outdoor durability. Typically, thin (2-3 pm) oxide layers are used to provide some measure ofabrasion resistance but no protection against moisture or pollutants. Thicker oxide layers (10-50 pm) are usually specified when anodized aluminum is intended for engineering/marine applications, but such layers can affect specular reflectance. Another approach is to apply multilayer dielectric (MLD) protective coats over the oxide layer. Considerable added expense can be incurred by the coating process.
Addendum2:
Diffuse-Reflectance (DR) UV-visible spectra of as received aluminum foil and TiO 2 -electrosprayed aluminum foil
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