Abstract:
Ultraviolet radiation is used to disinfect water ( 5 ) in a flow tube, where the flow tube ( 10 ) acts a fluid filled light guide for the ultraviolet radiation and the ultraviolet radiation propagates through the flow tube via total internal reflection.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a water purification system using intense ultraviolet irradiation to break down chemical bonds in toxic compounds and to de-activate pathogens. The method can also be applied to any mass transport, including the purification of air. These systems can be applied to purify fluids containing naturally occurring toxins or those resulting from biological and chemical agents used in warfare. 
     2. Background Art 
     The first application of an ultra violet (UV) low-pressure mercury vapor discharge lamp to disinfect water was in Marseilles, France in 1901. However, it was not until 1955 that UV disinfection became widely applied in Europe for potable water. In that year UV disinfection equipment was installed in Switzerland, Austria and Norway. Following the discovery of the formation of halogenated hydrocarbons during chlorination, UV disinfection since became popular in most European countries. 
     U.S. Pat. No. 1,196,481, issued Aug. 29, 1916 described the use of a mercury vapor lamp to generate sufficient ultraviolet light (mostly 254-nm wavelength) to purify water. This basic approach, built upon the UV efficacy of extended-arc continuous-duty mercury based lamps, has been refined over the years, such as in Ellner U.S. Pat. No. 3,182,193 issued May 4, 1965, Maarschalkerweerd U.S. Pat. No. 4,482,809 issued Nov. 13, 1984, Moyher U.S. Pat. No. 5,069,782 issued Dec. 3, 1991, Tiede U.S. Pat. No. 5,393,419 issued Feb. 28, 1995, and Anderson U.S. Pat. No. 6,099,799 issued Aug. 8, 2000. Much of the latter art improved upon aspects related to commercial viability, such as improving UV dosage uniformity through the use of baffles, UV-transparent coils, and controlled turbulence; increasing UV intensity for higher flow rates by increasing the number of lamps in a given volume; and improving maintenance through the use of Teflon coatings, wiper mechanisms, and adding turbulence. 
     Prior art UV water disinfecting systems expose the water to UV radiation such that the radiation passes through the water, strikes a reflecting surface and then passes through the water after reflection. The reflecting surfaces absorb a significant amount of radiation. There is a long-felt need to improve the efficiency of such systems. 
     SUMMARY OF THE INVENTION 
     My invention is an apparatus and method for disinfecting water, or other fluid, that channels water through one end of a tube and couples ultraviolet (UV) energy from a high intensity lamp through the tube from the other end. The water, or other fluid, acts like the core of a liquid light pipe, with an air gap surrounding the tube acting as a low index cladding. The tube itself is constructed of a non-UV-absorbing material, such as UV-grade fused silica glass. Advantageously, the use of light-pipe technology, which is based on total internal reflection (TIR), ensures that all the input UV radiation is dissipated in the water. Preferably, the tube is polygonal in cross-section, which is known in the art to maximize light flux uniformity within a light pipe. 
     Embodiments of my invention with multiple zones efficiently handle a wide range of water absorption coefficients, all at the highest practical efficiency. In accordance with an aspect of my invention one of three zones is defined by a concentric UV-grade tubing concentrically around only a portion of the tube through which the water flows and others of these zones are defined between these tubes and the enclosing outer tube. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Brief Description of the Several Views of the Drawing 
     FIG. 1 depicts an apparatus for disinfecting water using ultraviolet radiation (UV) in accordance with one illustrative embodiment of my invention. 
     FIG. 2 depicts a sectional view of the UV disinfecting apparatus of FIG.  1 . 
     FIG. 3 depicts a light pipe irradiation zone within the UV disinfecting apparatus of FIG. 1, showing how the ultraviolet radiation is contained using total internal reflection (TIR). 
    
    
     List of Reference Numbers for the Major Elements in the Drawing 
     The following is a list of the major elements in the drawings in numerical order. 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 5 
                 fluid (to be disinfected) 
               
               
                 10 
                 fluid inlet tube 
               
               
                 11 
                 entrance end (fluid inlet tube) 
               
               
                 12 
                 exit end (fluid inlet tube) 
               
               
                 13 
                 internal surface (fluid inlet tube) 
               
               
                 14 
                 external surface (fluid inlet tube) 
               
               
                 15 
                 concentric gap (between inlet tube and optical cladding tube) 
               
               
                 20 
                 optical cladding tube 
               
               
                 30 
                 fluid containment vessel 
               
               
                 31 
                 ultraviolet mirror (fluid containment vessel internal surface) 
               
               
                 32 
                 air gap (fluid containment vessel) 
               
               
                 33 
                 inner tube (of fluid containment vessel) 
               
               
                 35 
                 ultraviolet inlet aperture 
               
               
                 36 
                 lower ultraviolet window surface 
               
               
                 37 
                 upper ultraviolet window surface 
               
               
                 40 
                 high intensity ultraviolet lamp 
               
               
                 50 
                 fluid outlet tube 
               
               
                 71 
                 first UV light ray (exiting lower ultraviolet window surface) 
               
               
                 72 
                 second UV light ray (exiting fluid) 
               
               
                 73 
                 third UV light ray (entering fluid inlet tube internal surface) 
               
               
                 74 
                 fourth UV light ray (exiting fluid inlet tube internal surface) 
               
               
                 75 
                 fifth UV light ray (entering fluid) 
               
               
                 100 
                 light pipe (formed from fluid, fluid inlet tube, and concentric gap) 
               
               
                 1 
                 incidence angle (refraction at fluid inlet tube internal surface) 
               
               
                 2 
                 internal reflection angle (reflection at fluid inlet tube external 
               
               
                   
                 surface) 
               
               
                   
               
             
          
         
       
     
     DESCRIPTION OF THE INVENTION 
     Mode(s) for Carrying Out the Invention 
     Referring first to FIG. 1, the basic construction of an ultraviolet (UV) water disinfecting device in accordance with my invention is shown, including a fluid inlet tube  10  that acts as a central light pipe, an optical cladding tube  20  around the lower portion of fluid inlet tube  10  and defining therewith a concentric gap  15 , a fluid containment vessel  30 , a fluid outlet tube  50 , and a high intensity UV lamp  40 , such as a flashlamp. 
     Referring next to FIG. 2, the fluid containment vessel  30  includes an internal surface configured as an ultraviolet mirror  31 ; for example, the fluid containment vessel may be constructed from aluminum and the internal surface may be polished aluminum. A fluid  5  to be disinfected, such as water, enters the fluid inlet tube  10  through an entrance end  11 . The fluid inlet tube  10  may be manufactured, for example from UV-grade fused silica. 
     The fluid  5  travels through the fluid inlet tube  10  towards the high intensity UV lamp  40  and exits the fluid inlet tube  10  at the exit end  12 . The fluid  5  flow then strikes an ultraviolet (UV) window lower surface  36 , which forms a portion of the lower end of fluid containment vessel  30 . Next, the fluid  5  flow is redirected to the fluid outlet tube  50 , which is located in the upper end of the fluid containment vessel  30 . 
     The fluid  5  is contained within the fluid containment vessel  30 . The fluid containment vessel  30  includes an inner tube  33 , which may be constructed from UV-grade fused silica, contained within an outer aluminum shell with a reflective interior surface defining a UV mirror  31 , with an air gap  32  between the outer shell and the inner tube  33 . Then ends of the outer tube  30  are closed off with the lower ultraviolet window surface  36  and an ultraviolet window upper surface  37 . 
     The preferred orientation of the ultraviolet (UV) water disinfecting device is vertical, so that the fluid  5  flow approximates plug-flow, and the position of the fluid outlet tube  50  is at or near the highest point, allowing for quick and efficient removal of undesirable air bubbles. Air bubbles present in the fluid  5  can form scattering sites for the UV radiation thereby degrading system efficiency. These UV scattering sites result in UV radiation being directed at less than optimum angles causing reflections from the fluid containment vessel internal surface, the ultraviolet mirror  31  that is approximately 86% reflective when composed of aluminum tube. Without these UV scattering sites, the ultraviolet radiation is dissipated mostly within the fluid  5 , because all reflections are near loss-less because of the total internal reflection (TIR) operation of a light pipe. 
     Referring next to FIG. 3, a light pipe  100  region is formed from the fluid  5 , such as water, the fluid inlet tube  10 , such as a UV-grade fused silica tube, and the concentric gap  15 , such as an air gap or a vacuum gap. The concentric gap  15  is hydraulically isolated from the fluid  5 , in order to allow the light pipe  100  to operate. Light pipe operation is based on the refractive index of the concentric gap being less than the refractive index of the fluid  5 . The refractive indices of fused silica and water in the UV region of the light spectrum are shown in Table 1 below. 
     
       
         
               
             
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Refractive Indices of Fused Silica and Water 
               
             
          
           
               
                   
                 Wavelength (nm) 
                 Refractive Index 
               
               
                   
                   
               
             
          
           
               
                 Fused Silica UV Grade (SiO2) 
               
             
          
           
               
                   
                 170 
                 1.615 
               
               
                   
                 185 
                 1.575 
               
               
                   
                 200 
                 1.550 
               
               
                   
                 214 
                 1.534 
               
               
                   
                 280 
                 1.494 
               
               
                   
                 302 
                 1.487 
               
               
                   
                 436 
                 1.467 
               
               
                   
                 546 
                 1.460 
               
               
                   
                 656 
                 1.456 
               
             
          
           
               
                 Water 
               
             
          
           
               
                   
                 172 
                 1.568 
               
               
                   
                 185 
                 1.549 
               
               
                   
                 200 
                 1.543 
               
               
                   
                 215 
                 1.513 
               
               
                   
                 280 
                 1.492 
               
               
                   
                 305 
                 1.475 
               
               
                   
                 450 
                 1.344 
               
               
                   
                 550 
                 1.336 
               
               
                   
                 650 
                 1.331 
               
               
                   
                   
               
             
          
         
       
     
     As shown in Table 1, water has about the same refractive index as UV grade Silica glass in the ultraviolet (UV) portion of the light spectrum. 
     Ultraviolet (UV) radiation is transmitted from the high intensity ultraviolet lamp  40 , passes through the ultraviolet inlet aperture  35 , and enters the lower ultraviolet window surface  36  as shown in FIG. 2. A first UV light ray  71  exits lower ultraviolet window surface, is bent by refraction, and enters the fluid  5 , defining a second UV light ray  72 . The second UV light ray  72  impinges upon the internal surface  13  of the fluid inlet tube  10 , which is in contact with the fluid  5 , at an incidence angle  1 , where incidence angle  1  is measured with reference to the surface normal of internal surface  13 . As the second UV light ray  72  enters a sidewall of the fluid inlet tube  10 , it is bent by refraction and redirected at a new internal reflection angle  2 , defining a third UV light ray  73 . 
     The value of angle  2  is a function of incident angle  1  and the refractive indices of the fluid  5  and the material, such as UV-grade silica, from which the fluid inlet tube  10  is constructed. The third UV light ray  73  continues through the fluid inlet tube  10  material and impinges upon the external surface  14  of the fluid inlet tube that is in contact with the concentric gap  15 . The third UV light ray  73  is reflected back into the sidewall of the fluid inlet tube  10 , defining a fourth UV light ray  74  when the refractive indices of the fluid inlet tube  10  material and the concentric gap  15  meet certain conditions as defined by Snell&#39;s Law. The refractive index of the concentric gap  15  is defined by the material contained in the concentric gap such as glass, plexiglas, or acrylic, or by the refractive index of a vacuum if no material is contained within the concentric gap  15 . 
     It is a feature of my invention that a light pipe  100  region exists for at least part of the length of the fluid inlet tube  10 . Therefore, it is required that the incidence angle  2  be limited to a predetermined range in accordance with the refractive indices of the fluid  5 , the material from which the fluid inlet tube  10  is constructed, and the concentric gap  15 . In a preferred embodiment of my invention, the fluid inlet tube  10  is constructed from UV-grade silica glass, the fluid  5  to be disinfected is water, and the concentric gap  15  contains a vacuum. 
     Alternate Embodiments 
     Alternate embodiments may be devised without departing from the spirit or the scope of the invention. For example, the methods described herein can be applied not only to water flow, but also to other fluids that require purification such as breathable air.