Abstract:
An apparatus having one or more UV bulbs arranged around a structural element and within an outer conductive element. The apparatus also contains an inner conductive element which extends the length of the apparatus. The inner and outer conductive elements are coupled to a microwave source to enable the UV bulbs to be powered.

Description:
FIELD OF THE INVENTION 
     This invention relates to a UV light irradiation system which is particularly, though not exclusively, suitable for submerged use in fluids or gases for the purpose of, for example, water or air purification, disinfection, sanitisation or other treatment. The irradiation being energised by microwave energy. 
     BACKGROUND OF THE INVENTION 
     UV light is used for many different purposes including, for example, the use of UVC irradiation for the purification or other treatment of fluids such as air or water. U.S. Pat. No. 6,693,382 entitled “Control system for microwave powered light sources” discloses that there is a maximum desirable power density for UVC emitting electrodeless light sources. There is also a maximum desirable bulb diameter to prevent reabsorbtion of UVC generated by a plasma core which will make the system inefficient at outputting UVC light. It is, therefore, often advantageous to maximise the amount of energisable plasma per unit of irradiator length by the use a plurality of UV bulbs in parallel. 
     In existing systems, such as that described in GB 2 399 216, when a plurality of bulbs are used in a single irradiator light source, light from each bulb is emitted evenly over it&#39;s circumference and, thus, part of each bulb&#39;s emission will be transmitted onto, and absorbed by, other adjacent bulbs and, thus, not all the light outputted from the bulb can be used to irradiate the fluid. Additionally, the power density of the neighbouring bulbs is also disturbed. Hence, the power per bulb length output is limited as some of the power is reabsorbed by neighbouring bulbs. 
     GB 2 413 005 describes an improved radiator where the centre conductor may be reflective and therefore may redirect some of the light that would otherwise be absorbed by adjacent bulbs out of the irradiator. However, the necessary shape of the centre conductor limits its ability to reflect all the light incident upon it. Additionally, if the structure is powered by microwaves from one end only it is difficult to evenly energise the bulbs within the irradiator along their entire length. 
     The present invention provides apparatus including an inner conductive element, a structural element, an outer conductive element and at least one bulb configured to emit light in response to microwaves. The outer conductive element is substantially transmissive to light. The structural element forms conductive cavities that are preferably longitudinal. The bulb is positioned within one of the cavities within the outer conductive element. The inner and outer conductive elements are coupled to a microwave source in such a way that the inner conductive element acts as the centre conductor of a coaxial transmission system and the outer conductive element acts as the outer conductor of the coaxial transmission system. 
     The structural element is preferably also conductive; thereby acting in conjunction with the outer conductive element to form an outer conductor of subsidiary coaxial systems that are formed within the cavities of the irradiator. 
     It is preferable that the structural element includes a bore that extends through it and through which the inner conductive element can pass from one end of the irradiator to the other. 
     The apparatus may be further provided with at least one chamber, but preferably two or more. The one or more chambers may be defined either by an end plate of the irradiator and the end of a section of the structural element. Alternatively, the one or more chambers may be defined by a space between two sections of inner structural element. The inner conductor extends through the chambers, and hence, a microwave cavity is created in each cavity between the outer conductive element which extends over the outside of the chamber and the inner conductive element. The elements being connected to and energised by a suitable microwave source. 
     Preferably, the apparatus is provided with a plurality of bulbs and the structural element is configured to provide an equal number of cavities to the number of bulbs. The bulbs extend through the cavities and at least partially into the chamber or chambers present in the apparatus. 
     Typically, the UV bulbs are electrodeless. Preferably, the UV bulbs have a diameter of less than 22 mm and are constructed of UVC transmissive quartz. Preferably, they contain a mixture of Argon and Mercury such that, when exposed to microwave radiation at approximately 2.45 GHz they illuminate and irradiate at the Mercury based UV spectra. 
     As described above, the chambers will energise the plasma in the parts of the bulb that extend into the chambers. As microwave induced plasmas such as those described above act as lossy conductors, the energisation of the plasma will extend along the longitudinal cavity with the UV bulb acting as the central conductor within the cavity. Thus, the cavities encompassed as they are by the outer conductive element and structural element form subsidiary coaxial transmission systems. 
     Hence, this structure enables a plurality of bulbs in cavities around a structural element can be more evenly energised by microwave energy present in the chambers. 
     Preferably, the surface of the cavities is reflective and optimised the maximise the UV emissions from the bulbs through the outer conductive element. 
     The microwave source may be introduced directly to a chamber at one end of the irradiator. Alternatively, it may be connected via a waveguide or co-axial line where the central conductor of the coaxial line is connected to the inner conductive element of the irradiator and the outer conductor of the coaxial line is connected to the outer conductive element. 
     Preferably, the structural is a solid electrical conductor. Preferably, the structural element is constructed from aluminium extrusion with a reflective polished outer surface extending up to the junction between an edge of the structural element and outer conductive element. This reduces the amount of light emitted by a bulb being intercepted by any other bulbs in the system. 
     The inner conductive element is preferably a metallic rod. The inner conductive element preferably passes through the bore of the structural element and, thus, this acts as a coaxial transmission line transmitting microwave energy from the source input to the chambers in the irradiator. This allows the bulbs within the irradiator to be energised at multiple points along their length. 
     Preferably, pressurised air can be passed through the space between the inner conductive element and the bore of the structural element. The air can return through the longitudinal cavities thereby cooling the bulbs or allowing the creation of ozone. 
     The apparatus may include a UV transmissive fluid-tight envelope arranged around the outer conductor which allows the generator to operate whilst immersed in a fluid such as water. Preferably, the envelope may be formed from quartz. 
     Preferably, the apparatus includes a spark generator arranged to generate a spark through or adjacent the bulb or bulbs in order to encourage ignition of the bulb or bulbs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
         FIG. 1  illustrates a cross-section through the light system of the present invention; and 
         FIG. 2  is a sectional view along the line I-I of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the present application, irradiator is used to denote any light system which produces a light emission in response to microwave energisation. 
     With reference to  FIG. 1 , the irradiator  10  includes a plurality of UV light bulbs  12  arranged around a structural element  14 . The structural element  14  has a plurality of concave surfaces  16  which form longitudinal cavities each cavity  17  being arranged to receive one UV bulb  12 . The surfaces  16  of the longitudinal cavities act to reflect light emitted from the UV light bulbs  12  and to prevent light emitted by a bulb  12  being transmitted onto, and absorbed by, adjacent bulbs  12 . 
     The structural element  14  is further provided with a hollow bore (‘core’)  18  forming a path that runs through the centre of the structural element  14 . 
     An inner conductive element  20  passes through the bore  18 . The inner conductive element  20  acts as the central conductor for a primary coaxial structure. 
     Additionally, cooling air or any other fluid can be moved through the central bore  18  such that it can circulate through the irradiator  10 . Preferably, the air circulates through the bore  18  of the structural element  14  and then back over the UV light bulbs  12  thereby promoting cooling of the system. 
     With reference to  FIG. 2 , end plates  22  are positioned at either end of the light system. The structural element  14  terminates a distance away from the end plates  22  thereby forming an end chamber  24  at each end of the UV light bulbs  12 . The end of the structural element is provided with a support to support the UV bulbs  12  in place above the structural element  14 . Additional holes (not shown) in the support can be present to enable the passage of cooling fluids, etc., through the light system. 
     A microwave source is coupled to one of the end chambers  24 , for example, at  25 . The microwave source supplies microwaves into the light system. The microwaves then travel down the bore  18  of the inner structural element  14  until they reach the second end chamber. In this way, the microwaves can reach both end chambers. Hence, the electrodeless UV light bulbs can be energised at both ends, thereby enabling a more even distribution of UV emissions from each of the UV bulbs in the light system. 
     A coaxial outer  26  is formed around the outer circumference of the light system  10  by virtue of an outer conductive element. The coaxial outer  26  is made from an electrically conductive material such that it can contain an electromagnetic field and allow transmission of light in the UV spectrum. The outer conductive element  26  is preferably made from a reticulated material such as electrically conductive mesh or from a perforated conductive material. 
     In use, microwaves are introduced into an end chamber  24 . The UV light bulbs are electrodeless bulbs that emit UV light upon exposure to microwaves. 
     Optionally, the structural element may be provided with slots in its outer surface between the two end chambers. These slots allow microwaves to be transmitted from the central core to the radial coaxial cavities so that the bulbs can be further energised at intermediate points along their length. Hence, more even energisation of the bulbs can be achieved. Hence, the length of the system, the evenness of the microwave power absorption and irradiator UV emission can be increased as the points at which UV light bulbs are increased. 
     The system may be encased in a fluid-tight envelope (not shown) which allows the arrangement to be submerged in water, for example. Preferably, the envelope is UV transmissive (quartz being a typically good material for its construction). This may permit water-cooling of the magnetron and bulbs at the same time as allowing sterilisation of the surrounding water. The magnetron attached to the end chamber may be immersed directly in water, enclosed in a separate enclosure which may, for example, be oil filled to aid heat transmission, or it may be in the fluid-tight envelope with the bulb. As a further alternative, the magnetron may remain out of the water and be air or water cooled in the normal way. 
     The structural element is preferably made from a polished conductor that promotes reflection of the UV light and thus maximises UV emissions from the irradiator. For example, it may be made from polished aluminium. The structural element may, for example, be shaped as described above. Alternatively, it may take any other suitable shape, for example, be round, triangular or square in cross-section. 
     The bore through the inner structural element may also be of any suitable shape cross section and take any suitable path through the inner conductor. 
     It is preferable that the structural element is a continuous metal/conductive structure made by, for example, extrusion of a metal or any other known method. This enables the outer conductive element acting as a coaxial outer to be formed of a weaker material, for example, the holes in reticulated material may be enlarged to improve UV transmission through the outer conductive element. 
     The supports present at either end of the structural element may be made from any suitable material, for example, PTFE.