Abstract:
The light system has a plurality of bulbs configured to emit light when energised by microwaves, an outer conductive element which is at least partially transmissive to UV light; and an inner conductor situated within the outer conductive element. The inner conductor of the light system coupled directly to a microwave source. Additionally, the inner conductor is provided with a plurality of projections, each projection contacts one of the bulbs to promote even distribution of the microwave energy.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an improved UV light system having electrodeless UV bulbs that are energised by microwave energy. The UV light system may be used submerged in fluids or gases for the purpose of, for example, water or air purification, disinfection, sanitization or other treatment. 
       BACKGROUND OF THE INVENTION 
       [0002]    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 if UVC efficiency is to be maintained above the desired minimum of 20-30%. 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. 
         [0003]    U.S. Pat. No. 4,266,162 describes a known UV light system where an electrodeless bulb is powered by two inputs which are connected to a high frequency power source. However, the presence of a single bulb limits the power output of the light system which can be obtained efficiently. 
         [0004]    In accordance with the invention, there is provided apparatus including a plurality of bulbs configured to emit light when energised by microwaves, an outer conductive element which is at least partially transmissive to UV light and an inner conductor situated within the outer conductive element, the inner conductor including a plurality of projections each projection contacting one of the bulbs and being directly coupled to a microwave source or microwave transmission line. Thus, it can be seen that a coaxial system exists where the bulbs become central conductors within an inner conductor. 
         [0005]    A co-axial system such as the one of the present invention is preferable to a system where bulbs are separate in a non-coaxial waveguide because it can be constructed with smaller dimensions (including those that would render a non-co-axial waveguide beyond cut-off and thus prevent transmission). Additionally, in the present invention, radio frequency/microwave energy is directly split and coupled to the plurality of bulbs in an even and controlled manner which considerably aids bulb striking. 
         [0006]    Optionally, the inner conductor extends substantially the length of the apparatus. Optionally, the inner conductor may be provided with a further plurality of projections, each projection contacting one of the bulbs at a second point. 
         [0007]    Advantageously, the plurality of projections contact the bulbs at one end of the bulbs. The further plurality of projections may contact the bulbs at another end of the bulbs. One of the plurality of projections may contact a bulb at an intermediate point between two ends. 
         [0008]    Optionally, the apparatus may be provided with a structural element situated within the outer conductive element, the structural element including at least one cavity in which the bulb is situated. The structural element may also be provided with at least one gap through which the plurality of projections pass and may be made from one of the following: an electrical conductor, PTFE or dichroic coated quartz. 
         [0009]    Preferably, the structural element is provided with a bore and the inner conductive element extends through the bore. 
         [0010]    Preferably, the light emitted by the bulbs is UV light. The apparatus may also include a UV transmissive fluid-tight envelope arranged around the outer conductor which allows the apparatus to operate whilst immersed in a fluid such as water. The envelope may be formed from quartz. 
         [0011]    Optionally, the apparatus may include a spark generator arranged to generate a spark through, or adjacent, to one or more of the plurality of bulbs in order to encourage ignition of the bulb. 
         [0012]    Alternatively, the apparatus may include a wire having a high melting point in or adjacent to at least one bulb. The wire being arranged to generate a spark through or adjacent to the at least one bulb in order to encourage ignition of the bulb. The wire may be made from tungsten. 
         [0013]    Alternatively, the apparatus may include a UV lamp in proximity to the bulb in the apparatus the UV lamp acting as an igniter bulb. 
         [0014]    The apparatus may be provided with one or more reflectors positioned to reflect light emitted by the bulbs out of the apparatus. The reflectors may be made from one of the group comprising: polished metal, PTFE and dichroic coated quartz. 
         [0015]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  illustrates a cross-section through the light system of the first embodiment of the present invention; 
           [0017]      FIG. 2  is a section view along the line I-I of  FIG. 1 ; 
           [0018]      FIG. 3  illustrates section view of the second embodiment of the present invention; 
           [0019]      FIGS. 4 and 5  illustrate section views of the third embodiment of the present invention; 
           [0020]      FIG. 6  illustrates a cross-section through the light system of the fourth embodiment of the present invention including a structural element; and 
           [0021]      FIG. 7  is a section view along the line II-II of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    With reference to  FIGS. 1 and 2 , the UV light system  10  includes plurality of electrodeless bulbs  12  situated radially within an outer conductor  14 . The outer conductor  14  is preferably formed from a reticulated material, such as electrically conductive mesh or from a perforated conductive material. The outer conductor  14  is electrically conductive in order to contain an electromagnetic field and allows transmission of light in the UV spectrum. 
         [0023]    The UV light system is also provided with an inner conductor  16 . The inner conductor  16  is directly coupled using a coupler  18  to a microwave source such as a magnetron. In the case of a magnetron, the antenna of the magnetron is coupled to the inner conductor  16  using an impedance transformer or any other suitable means. 
         [0024]    The inner conductor  16  is provided with projections  20 . Each of the projections  20  of the inner conductor  16  is in contact with one of the bulbs  12  in the light system  10 , as can be seen in  FIG. 2 . The projections  20  may contact the bulb in any suitable manner. These projections  20  act to direct the microwave energy received from the microwave source to the electrodeless bulbs  12  increasing the UV light output of the bulbs  20 . 
         [0025]    A second embodiment of the invention is illustrated in  FIG. 3 . In  FIG. 3 , the UV light system is provided with a second inner conductor  17 . The second inner conductor is also provided with a plurality of projections  19 , each of the projections  19  being in contact with on e of the bulbs in the light system. The second inner conductor  17  is coupled using a second coupler  21  to microwave source such as a magnetron. The microwave source may be connected to both the inner conductors  16  and  17  or, alternatively, separate microwave sources may be connected to each of the inner conductors  16 ,  17 . 
         [0026]    A third embodiment of the invention is illustrated in  FIGS. 4 and 5 . In  FIG. 4 , the inner conductor  16  extends through the length of the UV light system. The extended inner conductor  12  promotes microwave energy transmission through the length of the UV light system. Optionally, the end of the inner conductor  16  furthest from the microwave source may be provided with further projections  22  as illustrated in  FIG. 5 . This enables the energy to be split evenly between the electrodeless bulbs  12 . Additionally, because the electrodeless bulbs  12  are receiving microwave energy at both ends the amount of UV light generated by them is increased. 
         [0027]    A fourth embodiment of the invention is illustrated in  FIGS. 6 and 7 . In  FIG. 6 , the plurality of electrodeless bulbs  12  are arranged around a structural element  24 . The structural element  24  has a plurality of concave surfaces  26  which form longitudinal cavities each cavity being arranged to receive one bulb  12 . The surfaces 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 . 
         [0028]    The structural element  24  is further provided with a hollow bore (‘core’)  28  forming a path that runs through the centre of the structural element  24 . The inner conductor  16  passes through this bore  28 . 
         [0029]    Optionally, the inner conductor  16  is provided with projections  20  at either end (not shown). This means that the electrodeless UV light bulbs  12  can be energised at both ends, thereby enabling a more even distribution of UV emissions from each of the UV bulbs  12  in the light system. 
         [0030]    The structural element may be 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. Alternatively, the structural element may be made from a non-conductive material that is reflective to UV light. For example, PTFE or dichroic coated quartz. 
         [0031]    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. Additionally, 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. 
         [0032]    It is preferable that the structural element is a continuous 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. 
         [0033]    As will be understood by the skilled man any of the following features may be incorporated into any of the features described above as desired. 
         [0034]    The electrodeless bulbs  12  may be supported in their arrangement using one or more supports. Holes (not shown) may be provided within the support to enable the passage of cooling fluids etc through the light system. 
         [0035]    Optionally, cooling air or any other fluid can be moved such that it circulates through the UV light system. Preferably, the air circulates through the centre of the system and then flows back over the UV light bulbs  12  thereby promoting cooling of the system. 
         [0036]    If desired, further projections (not shown) may be provided at intermediate positions along the inner conductor  16 . This will result in an even more even distribution of UV emissions from each of the UV bulbs  12  in the light system. Additionally, the projections from the inner conductor may be spaced in any suitable way and need not be from one or more ends of the inner conductor. 
         [0037]    The inner conductor  12  may be reflective to UV light and shaped to optimise reflection of UV radiation to prevent shadowing by other bulbs in the light system. Additionally, the light systems described above may also be provided with additional non-conductive reflectors (not shown) to optimise reflection. The non-conductive reflectors may be made, for example, from PTFE or dichroic coated quartz. 
         [0038]    The UV light 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.