Patent Application
20130313104
The present invention generally relates to air purification systems, and more particularly, to an air purification system using ultraviolet light emitting diodes (LED) and photocatalyst-coated supports.
The use of recirculated air may be common within inhabited enclosures. In some cases, airflow may be necessarily recirculated to provide breathable air where air external to the enclosure may not be viable. In other cases, it may be more economical to use recirculated air which has already been adjusted to the correct temperature and humidity. For example, pressurized cabins in aircraft may commonly recirculate a portion of the air rather than try to circulate only external air into the cabin. One result of using recirculated air is that organic contaminants may increase in concentration and may be passed to the inhabitants of the cabin.
One approach to removing contaminants from airflow is to use a photocatalytic air cleaner on airflow. It may be known to use for example, mercury vapor lamps to irradiate a photocatalyst in contact with airflow. Lamps may produce a heterogeneously distributed intensity across a photocatalyst. This may result in portions of the airflow which are less well treated, and still contain contaminants. Mercury vapor lamps may also be commonly made of glass or quartz, and, therefore not useful in environments where mechanical shock might result in their shattering. In addition, the use of lamps may result in insufficient energy absorption by the photocatalyst to provide effective catalysis. This can occur if the emission spectrum of the lamps does not overlap with the absorption spectrum of the photocatalyst.
In some purification systems, titanium dioxide based photocatalysts may be employed. The absorbance of titanium dioxide for photocatalysis drops rapidly with increasing wavelength, and is negligible above 410 nanometers. At wavelengths at which the photocatalyst does not absorb light, no reaction will occur, so use of a light source whose emittance spectrum overlaps poorly with the absorption spectrum of the photocatalyst can result in poor efficiency. It may be desirable to operate a photocatalytic device using a light source which has a wavelength higher than that normally absorbed by titanium dioxide. In some cases, the absorbance spectrum of titanium dioxide may be shifted to higher wavelengths by, for example, doping titanium dioxide with nitrogen or carbon. The effectiveness of titanium based photocatalysts may be short lived as the doped element may degrade quickly and the titanium dioxide is again ineffective at wavelengths above 410 nm.
As can be seen, there is a need for an air cleaning system that may provide efficient and evenly distributed photocatalysis in airflow.
In one aspect of the present invention, an air cleaning system comprises an ultraviolet light emitting diode (UV LED); a support disposed proximate to the UV LED; and a photocatalyst on the support disposed to contact airflow passing across or through the support, wherein: airflow is between the UV LED and the photocatalyst and, the UV LED is positioned to emit ultraviolet light onto the photocatalyst.
In another aspect of the present invention, an air cleaning system comprises a chamber; an ultraviolet light emitting diode (UV LED) positioned to emit ultraviolet light into the chamber; a plurality of support plates in the chamber spaced parallel to one another, wherein at least one of the plates is disposed proximate the UV LED; and a photocatalyst on the support plates disposed to contact airflow passing across or between the support plates, wherein the UV LED is positioned to emit ultraviolet light onto the photocatalyst.
In yet another aspect of the present invention, a method of purifying airflow comprises passing the airflow through a reactor including an ultraviolet light reactive photocatalyst; emitting ultraviolet light from an ultraviolet light emitting diode into the airflow and onto the photocatalyst; and removing organic contaminants from the airflow that makes contact with the photocatalyst while the ultraviolet light is emitted on the photocatalyst.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below.
The present invention generally provides an air cleaning system that removes organic contaminants from airflow. Exemplary embodiments of the present invention may be used, for example, in enclosed quarters where airflow may be recirculated and individuals may be subjected to breathing in air that aggregates organic contaminants.
In one aspect, exemplary embodiments of the present invention may use, for example, titanium dioxide as a photocatalyst irradiated with ultraviolet light (UV). The ultraviolet light source employed may be a light emitting diode (LED) whose emission wavelength is centered approximately near 400 nm. As may be seen in
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In one exemplary embodiment, the reactor 180 may include a plurality of the support plates 120 supported by the chamber 115. The plates 120 (shown as plates 120a, 120b, 120c, and 120d) may be spaced parallel from one another. In one aspect, spacing of the plates 120 and the air velocity there through can be adjusted to ensure adequate contact between the air and the photocatalyst 170. In an exemplary embodiment, the plates 120 may include one or more perforations 160. The perforations 160 may be arranged as a set 165. It may be appreciated that some airflow passing over surface 125 of a support plate 120 may pass through one of the perforations 160 and flow along the underside (not shown) of the plate 120 making contact with photocatalyst 170 on said underside. While the support 120 is shown as a plate, other exemplary embodiments may use supports 120 which are not flat. For example, the support 120 may be corrugated to enhance air mixing.
It may also be appreciated that there may be a tradeoff between the size and number of perforations 160 in plates 120 and the amount of surface area available for photocatalytic reaction. The reactor 180 may be configured to optimize irradiation of the photocatalyst 170 on the outermost plates (120a and 120d) and underlying plates (120b and 120c). In exemplary embodiments where a plurality of support plates 120 are used, the set of perforations 165 of two adjacent support plates 120 may not line up to one another. For example, the set of perforations 165 of plate 120b may not have centers lined up with the centers of the set of perforations 165 of plate 120a. Light entering at any angle should at some depth impinge on a catalyst-coated surface. The amount of photocatalytic exposure may be controlled by increasing or decreasing the number of perforations 160 and by increasing or decreasing the number of UV light sources 110.
UV light sources 110 may be positioned to emit ultraviolet light into the chamber 115. The wavelength range of ultraviolet light emitted by the UV light source 110 may be approximately between 200 nm to 435 nm, and depending on the type of photocatalyst 170 used, may be around 385 nm to 410 nm. In an exemplary embodiment, the UV light source 110 may be positioned to provide focused ultraviolet light onto the photocatalyst 170. The support(s) 120 may be supported by the chamber 115 proximate to the UV light source 110 so that the surface 125 holding the photocatalyst 170 is in a plane orthogonal to the UV light source 110. The distance of the photocatalyst 170 from the UV light source 110 may be set so that the beam of ultraviolet light (not shown) remains substantially uniform in coverage and intensity. The UV light source 110 may be approximately 1 inch from the photocatalyst 170 on the outermost plates 120a and 120d. It may be appreciated that the use of a UV-LED at such a close distance may provide about 4000 mW/cm2 of intensity. Thus, effective catalysis of air contaminants may be achieved within the air cleaning system 100.
In an exemplary embodiment, the UV light source 110 may be one or more UV LEDs. For example, an array 150 of UV LEDs may be employed. In one exemplary embodiment, the UV light source 110 may include an array 150a on one side 135 of the chamber 115 and an array 150b on an opposite side 145 of the chamber 115. The arrays 150a and 150b may be positioned to emit ultraviolet light orthogonal to airflow, onto the support plate(s) 120 between the two arrays (150a; 150b). For example, the array 150a may be proximate the outermost support plate 120a while the array 150b may be proximate the outermost support plate 120d. The UV light sources 110 may be arranged so that light emitted from adjacent sources may overlap or may irradiate the plates 120 at an angle, thus exposure of the inner plates 120b and 120c through the perforations 160 may be achieved.
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It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
