Fluid streams, such as water or air, often include contaminants like dissolved halogenated or organic compounds, volatile organic compounds, nitrogen oxides, inorganic gases like hydrogen cyanide, and microorganisms such as bacteria, viruses, molds, and fungi. Photocatalysts can be used to purify the fluid stream by converting these contaminants into less harmful substances or materials which may be more easily removed from the fluid stream.
The conversion of contaminants occurs when the fluid stream is brought in contact with a photocatalyst illuminated by a nearby light source. The photocatalyst is typically deposited on the surface of a support structure of some type to provide a stable photocatalytic surface and to ensure that the photocatalyst is not carried away by the fluid stream. Reactors employing these basic concepts have been developed.
To be effective, the contaminants must be brought into contact with the photocatalyst. The effectiveness of this process is measured by the mass transfer coefficient of the reactor which is the rate at which the contaminant is transported from the fluid stream to the photocatalytic surface. If the mass transfer system of the reactor is inadequate then conversion of contaminants will be diminished. Thus, an effective reactor design should provide for adequate mass transfer from the bulk fluid to the photocatalyst.
U.S. Pat. No. 6,558,639 ('639) discloses a purifier for purifying a fluid by eliminating contaminants from the fluid. The purifier includes a fluid passage, through which the fluid flows, formed by an ultraviolet ray transmitting material. A plurality of photocatalytic pipes are arranged in the fluid passage. Each of the photocatalytic pipes has an inner surface and an outer surface on which a thin film of a photocatalyst is applied. The photocatalytic thin film is excited by ultraviolet rays irradiated from a source located near the fluid passage. This oxidizes and decomposes the contaminants and purifies the fluid.
The elongate members 9 of '639 are packed into the outer pipe creating a problem of flow resistance. Additionally, the UV radiation achieves internal catalytic TiO2 coating 9a through a number of outer TiO2 coatings having sufficiently high reflective coefficient (0.5-0.9). Radiation intensity passed through at least to coatings 3a and 9b and striking upon the coating 9a is 0.25-0.01 of intensity that is incident on the surface 3. Thus, there is a unmet and long-felt need to provide a photo-catalytic decompounding device characterized by low flow resistance and high radiation efficiency.