Abstract:
Controlled generation of ozone is provided by flowing air around an electrodeless low pressure discharge lamp having high ultraviolet transmission properties. Power to the lamp is controlled by a circuit that is driven by a photocell for detecting visible light emissions from a phosphor triggered by ultraviolet radiation from the lamp upon the phosphor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to systems for generating ozone, and in particular to controlled use of ultraviolet radiation for generating ozone. 
     Ultraviolet radiation has long been known to be an effective generator of ozone. Prior art ozone generation systems rely solely on the use of electroded linear low pressure discharge lamps that use mercury. These linear systems are very similar to standard fluorescent lamps in terms of operation, except that there are no phosphor coatings and the glass used (a hard glass, not quartz) usually transmits a substantial amount of the 254 nm radiation emitted from the mercury atom. These electroded systems have two typical modes of failure: 1) electrode failure and 2) solarization of the glass due to the UV flux. 
     It would be a desirable advance upon the prior art to have a UV ozone generation device having a longer-lived lamp and ballast. It is furthermore desirable that such a device be made out of high quality quartz which does not degrade as rapidly as treated hard glass. It is also desirable to provide such a device with a compact design which operates at higher power and provides higher UV output. 
     BRIEF SUMMARY OF THE INVENTION 
     A low-pressure electrodeless lamp having high ultraviolet transmission properties is used for controlled generation of ozone. The lamp envelope is preferably comprised of a glass/quartz composite. The ultraviolet output (primarily 254 nm radiation) is directed from the low pressure (e.g., mercury) discharge into a cylindrical enclosure around the lamp, through which air is channeled. The cylindrical enclosure is constructed with a fan at one end that forces air from outside the enclosure over the lamp body such that air mixed with ozone flows out the other end of the cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective drawing of one embodiment of a lamp used to generate ultraviolet radiation in accordance with the invention. 
     FIG. 2 is an overhead view of the lamp of FIG. 1 showing the flow of air around the lamp. 
     FIG. 3 is a drawing showing a phosphor coating on a portion of the lamp, together with a photocell for detecting visible light and a circuit for controlling power to the lamp. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an embodiment of an electrodeless fluorescent lamp  10  according to the present invention. Such an electrodeless fluorescent lamp may be manufactured using technology of a type employed to manufacture lamps such as those sold under the trademark GENURA of General Electric Company. Lamp  10  has an envelope  9  containing an ionizable, gaseous full. Envelope  9  is preferably made of quartz. 
     A suitable fill for the electrodeless fluorescent lamp of FIG. 1 comprises a mixture of a rare gas (e.g., krypton and/or argon) and mercury vapor and/or cadmium vapor. A re-entrant cavity  16  within the envelope  9  has an excitation coil  19  associated therewith, e.g., contained within the re-entrant cavity. Envelope  9  fits into one end of a lamp base assembly (not shown), such as an Edison type base, for example, for coupling to a radio frequency power supply. 
     In operation, current flows in excitation coil  19  as a result of excitation by the radio frequency power supply. As a result, a radio frequency magnetic field is established within envelope  9 , in turn creating an electric field which ionizes and excites the gaseous fill contained therein, resulting in a UV discharge  11 . A useful UV discharge is in the range up to about 400 nm, particularly at 254 nm. For the illustrated embodiment, the discharge body  11  is toroidal in shape. 
     By way of illustration, an exemplary compact design of electrodeless fluorescent lamp  10  of FIG. 1 has a 20 W discharge, and the cross section of the toroidal discharge can be represented by an ellipse with a major axis  12  of about 23 mm and a minor axis  13  of approximately 13 mm. For this example, the major radius (measured from the center of the discharge  11  to the axis  15  running through the center of re-entrant cavity  16 ) of the discharge is at 18.75 mm. An exemplary outside diameter (OD) may be as large as 80 mm. A larger OD enables operation of the device without saturating UV output, but may increase the difficulty of manufacturing the lamp body. There is also shown in FIG. 1 an exhaust tube  14  used for filling the lamp during the manufacture thereof. In alternative embodiments, the exhaust tube may be situated at other positions in the lamp without effecting operation of the lamp as described herein. 
     For the example set forth hereinabove, simulations indicate that the main portion of the UV flux exits the lamp  10  from the discharge body  11  within a width (in the direction of the major axis  12 ) of 23 mm centered on the discharge body  11 . For a lamp having an OD of 50 mm, for example, the total circumferential surface area is π×50 mm×23 mm=36 cm 2 ; and for a discharge of 20 W, simulations show that the amount of 254 nm radiation directly impinging on this region is about 6 W. This means that the UV flux, Γ, through this band is Γ=6 W/36 cm 2 =0.17 W/cm 2 . 
     The lamp system is configured to have the air flow  22  over the circumference of the lamp  10 , as shown in FIG. 2, by using a fan  25  connected to a cylindrical container  27  that houses the lamp  10 . UV radiation  28  (e.g., primarily at a wavelength of 254 nanometers) from the lamp  10  penetrates into container  27 , producing Ozone (O 3 ) through a chemical reaction between the UV photons  28  and the oxygen in the air  22 . 
     Output  23  of ozone (mixed with air) is a function of the dimensional constraints of the particular application. Since the technology is scalable, it is feasible to construct larger lamps which support proportionally larger devices. To achieve compact design with high power, a lamp with an OD in the range of 70 mm to 90 mm may be used, for example; and for that range the corresponding major and minor axes of the discharge toroid would be in the range of 20 mm to 25 mm and in the range of 10 mm to 15 mm, respectively. 
     FIG. 3 shows a phosphor  31  applied to a part of the lamp  10  which is exposed to low amounts of UV radiation  38 . The phosphor generates visible light when exposed to UV. This visible light  39  is detected by photocell  32 , whose output  35  will be directly proportional to the UV radiation  38  applied to the phosphor  31 . Alternatively, a photocell  32  may be used for directly detecting UV radiation  38 . A photocell output signal  35  is used in a control circuit  33  to provide a signal  37  to turn off the power connected to the lamp  10 , for example, when the visible light  39  emitted by the phosphor  31  drops below a certain threshold value. Control circuitry used in this fashion would also avoid destruction of the lamp should ignition fail to occur during startup. 
     Lamps constructed according to preferred embodiments of the present invention have quartz envelopes (rather than glass which is usually used for lamps having electrodes), such as, for example, quartz known commercially as GE 214 quartz of General Electric Company, thereby enabling operation at higher power without damaging the envelopes. 
     While preferred embodiments of the invention have been described herein, those skilled in the art will recognize that such embodiments have been provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the are without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.