DIELECTRIC BARRIER DISCHARGE LAMP

FIELD OF THE INVENTION

The current invention is related to a dielectric barrier discharge (DBD) lamp and a method for manufacturing a dielectric barrier discharge lamp.

BACKGROUND OF THE INVENTION

US 6,294,869 Bl discloses a high intensity light irradiation apparatus having a simpler, lighter, easy to assemble and replace support member for a dielectric barrier electrical discharge lamp. The dielectric barrier electrical discharge lamp comprises concentric outer tube and inner tube to form an inert gas filled electrical discharge space defined by the outer and inner tubes and their end walls. A metal rod is inserted into the inner tube of the electrical discharge lamp. A pair of clamp members is secured to both ends of the metal rod for clamping the both ends of the electrical discharge lamp. An AC voltage is applied between the metal rod and an outer electrode on the surface of the outer tube. Cooling water flows through the gap between the metal rod and the inner tube. Sealing gaskets are provided between the clamp members and the dielectric barrier discharge lamp preventing the outflow of the cooling water. The sealing gaskets are exposed to ultraviolet radiation emitted by the dielectric barrier discharge lamp causing accelerated aging of the gaskets reducing the reliability of the dielectric barrier discharge lamp.

SUMMARY OF THE INVENTION

It is an objective of the current invention to provide a robust DBD lamp. The objective is achieved by means of a dielectric barrier discharge lamp,

comprising a coaxially shaped discharge vessel having a principal axis, the coaxially shaped discharge vessel having a first outer radius Rl and a first inner radius R2 with respect to the principal axis, - the coaxially shaped discharge vessel enclosing a discharge volume filled with a discharge gas, at least one electrode of a first type and at least one electrode of a second type, the electrode of the first type being designed to act as a low voltage electrode and the electrode of the second type being designed to act as a high voltage electrode , at least one first coaxial elongation aligned with a the coaxially shaped discharge vessel with respect to the principal axis, the coaxial elongation having a second outer radius R3 and a second inner radius R4 with respect to the principal axis and - the second inner radius R4 of the coaxial elongation being bigger as the first inner radius R2 of the coaxially shaped discharge vessel.

The coaxially shaped discharge vessel of the DBD lamp usually consists of an inner tube and an outer tube and both tubes are welded at both ends forming the gas tight discharge volume. The material used for the coaxially shaped discharge vessel has to be at least partly transparent with respect to wavelength of the emitted (ultraviolet) radiation, e.g. Quartz glass. The quality of Quartz glass processing determines largely the mechanical quality of the sealing system. Tight tolerances at acceptable effort in order to ensure robust and cheap manufacturing, are needed to provide a stable mounting and a gastight or watertight connection with a device enabling the cooling of the DBD lamp during operation. The coaxial elongation can consist of a Quartz glass tube with a defined diameter and a defined length preventing this disadvantage because the side of the coaxial elongation used for mounting the DBD lamp is not exposed to heat treatment causing deformation of the coaxial shape.

Additionally gaskets used for sealing the connection to the cooling device can easily protected from direct exposure to ultraviolet radiation; Ultraviolet radiation causes accelerated aging of most materials used for gaskets.

Further, the stability of the mounting of the DBD lamp and the lamp system is influenced by the diameter of the coaxial elongation. Especially if the lateral extension of the DBD lamp makes the total lamp rather long (one meter or longer) as e.g. in case of municipal water treatment, big forces are introduced to the glass. A coaxial elongation with the same or even bigger outer diameter as the coaxially shaped discharge vessel results into a more stable lamp positioning, because the mechanical forces acting on the lamp - due to the flow of process media - is distributed over a larger diameter at the lamp ends, and because seals of narrow tolerance can be used.

DBD lamps in high-end municipal water treatment units are equipped with wiper systems. These wipers clean the DBD lamp mechanically and chemically. These wiper systems have elastomer seals and only minor variations in the diameter can be overcome. This condition is fulfilled best if the outer diameter of the coaxial elongation is the same as the outer diameter of the coaxially shaped discharge vessel. The coaxial elongation can be used to place the wiper system during operation of the DBD lamp at the elongation decreasing the aging of the elastomer seals due to decreased ultraviolet radiation while keeping the ultraviolet radiation output of the "active" lamp length above the coaxially shaped discharge vessel at it's maximum.

In a further embodiment of the current invention the coaxial elongation and the coaxially shaped discharge vessel consist of the same material. The outer tube, consisting of e.g. Quartz glass used for the coaxially shaped discharge vessel, can also be used for the coaxial elongation by having a larger length than the tube used for the inner tube. The diameter of the coaxial elongation can be obtained from suppliers at tight tolerances, reducing the effort needed to design a reliable sealing system.

In another embodiment of the current invention at least one layer absorbing ultraviolet radiation is provided on at least parts of the at least one coaxial elongation. The layer absorbing ultraviolet radiation can be a coating comprising e.g. CeC>2 provided on the inner or outer surface of the coaxial elongation and/or a coaxial sleeve made of e.g. metal or ceramic slided in the coaxial elongation. The absorbing layer can further decrease the load of gaskets of the sealing systems or elastomer seals of a wiper system due to ultraviolet radiation of the DBD lamp.

In a further embodiment of the current invention the at least one coaxial

elongation consists of a material absorbing ultraviolet radiation. The material can e.g. be doped Quartz glass with sufficient absorption at the relevant range of wavelength.

It is further an objective of the current invention to provide a method for manufacturing a robust DBD lamp. The objective is achieved by means of a method of manufacturing a dielectric barrier discharge lamp, the method comprising the steps of: providing a coaxially shaped discharge vessel having a principal axis and the coaxially shaped discharge vessel having a first outer radius Rl and a first inner radius R2 with respect to the principal axis, - enclosing a discharge volume in the discharge vessel, providing at least one electrode of a first type and at least one electrode of a second type, the electrode of the first type being designed to act as a low voltage electrode and the electrode of the second type being designed to act as high voltage electrode - providing at least one coaxial elongation being aligned with the coaxially shaped discharge vessel with respect to the principal axis , the coaxial elongation having a second outer radius R3 and a second inner radius R4 with respect to the principal axis and the second inner radius R4 of the coaxial elongation being bigger as the first inner radius R2 of the coaxially shaped discharge vessel , - filling the discharge volume with a discharge gas.

There are different approaches in order to produce a dielectric barrier discharge lamp with a coaxial elongation. In one approach the coaxially shaped discharge vessel is manufactured first and at least one coaxial elongation is aligned and fused with the coaxially shaped discharge vessel. Another approach is to start with an outer e.g. quartz tube which is longer than an inner e.g. quartz tube and the inner tube is slided in the outer tube and aligned with the outer tube with respect to the principal axis. In a further processing step the tubes are melted together by using quartz processing tools which are inserted into the outer tube to heat up and deform the inner tube towards the outer tube. Depending on the positioning of the inner tube in the outer tube either one or two coaxial elongations are formed, whereby the second outer radius R3 of the coaxial elongation or coaxial elongations is equal to first outer radius Rl of the coaxially shaped

discharge vessel.

The method of manufacturing has the advantage that standard quartz glass processing causing no extra costs can be used to process the coaxially shaped discharge vessel and the coaxial elongation. Additionally, using e.g. tubes of adapted length and defined diameter for the coaxial elongation can easily compensate the tolerances with respect to the diameter of the DBD lamps and the length of the DBD lamps.

The DBD-lamp according to the invention can be used in a wide area of applications. Preferably the lamp is used in a system being used in one or more of the following applications: fluid and/or surface treatment of hard and/or soft surfaces, preferably cleaning, disinfection and/or purification; liquid disinfection and/or purification, beverage disinfection and/or purification, water disinfection and/or purification, wastewater disinfection and/or purification, drinking water disinfection and/or purification, tap water disinfection and/or purification, production of ultra pure water, gas disinfection and/or purification, air disinfection and/or purification, exhaust gases disinfection and/or purification, cracking and/or removing of components, preferably inorganic and/or organic compounds cleaning of semiconductor surfaces, cracking and/or removing of components from semiconductor surfaces, cleaning and/or disinfection of food, cleaning and/or disinfection of food supplements, cleaning and/or disinfection of Pharmaceuticals and/or photochemical synthesis. One advantageously application is the purification or in general cleaning. Destroying unwanted microorganisms and/or cracking unwanted compounds and the like by means of ultraviolet (UV) radiation do this. By this essential function of that DBD-lamp the applications mentioned above can be easily realized. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in greater detail with reference to the figures, in which the same reference signs indicate similar parts, and in which:

Fig. 1 shows a sketch of a cross section of a first embodiment of a coaxial

DBD lamp according to the current invention comprising the principal axis of the

coaxial DBD lamp.

Fig. 2 shows a sketch of a cross section of a second embodiment of a coaxial DBD lamp according to the current invention comprising the principal axis of the coaxial DBD lamp. Fig. 3 shows a sketch of a cross section of a third embodiment of a coaxial DBD lamp according to the current invention comprising the principal axis of the coaxial DBD lamp.

Fig. 4 shows a sketch of a cross section of a fourth embodiment of a coaxial DBD lamp according to the current invention comprising the principal axis of the coaxial DBD lamp.

Fig. 5 shows a sketch of a cross section comprising the principal axis of an embodiment of a coaxial DBD lamp according to the current invention comprising a wiper system.

Figs. 6-7 shows sketches of cross sections comprising the principal axis of embodiments of coaxial DBD lamps according to the current invention in combination with sealing systems.

DETAILED DESCRIPTION OF EMBODIMENTS In Fig. 1 a dielectric barrier discharge lamp is shown with a coaxially shaped discharge vessel 1 enclosing a discharge volume 2 filled with a discharge gas. The coaxially shaped discharge vessel 1 is formed by means of two tubes consisting of Quartz glass, whereby the outer tube has an outer radius Rl and the inner tube has an inner radius R2 with respect to the principal axis being the axis of symmetry of coaxially shaped discharge vessel 1. The inner tube is slided in the outer tube and both tubes are welded together at both ends forming the coaxially shaped discharge vessel 1. An electrode of a first type 3 is provided on the inner surface of the inner tube being part of the coaxially shaped discharge vessel 1 and an electrode of a second type 4 is provided on the outer surface of the outer tube being part of the coaxially shaped discharge vessel 1. The configuration of the electrodes is exemplary only. Depending on the application, the electrical current supplied to the discharge vessel can also be carried by a process

fluid and/or cooling agent, provided they offer sufficient electrical conductivity. In such a case, no electrode attachment to the lamp would be required. A coaxial elongation 7 consisting of quartz glass is welded to the coaxially shaped discharge vessel 1 at one side of the coaxially shaped discharge vessel 1 and being aligned with the coaxially shaped discharge vessel 1 with respect to the principal axis 6. As an alternative, the outer tube used for the production of the lamp can be longer than the inner tube, thus providing a coaxial elongation 7 of the discharge vessel. The coaxial elongation 7 has an outer radius R3 and an inner radius R4 with respect to the principal axis 6, whereby in this special embodiment the outer radius R3 of the coaxial elongation is equal to the outer radius Rl of the coaxially shaped discharge vessel 1. Further details as the connection of the electrodes to a power supply, the exhaust tube or pile to evacuate and refill the discharge volume 2 with the discharge gas (e.g. Xe) and the like are well known for those experienced in the art and not explicitly shown. Fig. 2 shows a second embodiment according to the current invention where at both sides of the coaxially shaped discharge vessel 1 coaxial elongations 7 are provided enabling a stable mounting of the DBD lamp at both sides of the coaxially shaped discharge vessel 1, whereby the elongations provide a simple possibility to seal the lamp at its end towards the cooling agent and / or process medium. The other features of the embodiment are discussed in connection with Fig. 1. The third embodiment according to the current invention depicted in Fig. 3 shows a DBD lamp with a coaxially shaped discharge vessel 1 with a coaxial elongation 7 at one side of the coaxially shaped discharge vessel 1 comparable to the first embodiment discussed in connection with Fig. 1. At the other side of the coaxially shaped discharge vessel 1 an elongation 8 of cylindrical shape is provided being aligned with the principal axis 6 of the coaxially shaped discharge vessel 1. The inner radius of the elongation 8 is the same as the inner radius R2 of the coaxially shaped discharge vessel 1. A variation of the third embodiment according to the current invention is shown in Fig. 4. The coaxial elongation 7 provided at one side of the coaxially shaped discharge vessel 1 has a bigger outer radius R3 as the outer radius Rl of the coaxially shaped discharge vessel 1 and the elongation 8 provided at the other side of the coaxially shaped discharge vessel 1 has a smaller inner radius as the inner radius R2 of the coaxially shaped discharge vessel 1. In Fig. 5 a simplified sketch of a DBD lamp according to the current

invention is shown comparable to the second embodiment discussed above. The coaxial extension 7 on the right side of the coaxially shaped discharge vessel 1 is longer than the coaxial elongation 7 on the left side of the coaxially shaped discharge vessel 1. The outer radius R3 of the coaxial extensions 7 is essentially the same as the outer radius Rl of the coaxially shaped discharge vessel 1. Further a wiper system is provided comprising a cleaning wiper body 20, a cleaning chamber 21 filled with cleaning liquid and elastomer wiper seals 22. The wiper system is needed to clean the DBD lamp mechanically and chemically being necessary in applications as e.g. municipal water treatment where polluted water whooshes with a speed of 1-2 m/s nearly perpendicular to the DBD lamp (indicated by the bold arrows). The wiper system cleans the DBD lamp by recurrently wiping back and forth (indicated by the thin arrow). During the resting periods the wiper system is parked on the coaxial elongation 7 in order to minimize accelerated aging of the elastomer wiper seals 22 and in order to prevent shadowing of the DBD lamp. Since the elastomer wiper seals 22 can only overcome minor diameter differences a coaxial elongation 7 with the same outer diameter as the coaxially shaped discharge vessel 1 has is preferred.

In Fig. 6 a part of a DBD lamp according to the second embodiment according to the current invention is shown with a sealing system for mounting the DBD lamp. A fitting 32 is screwed on a spout 30 in a way that a ring shaped gasket 3 Hs squeezed and pressed to the inner surface of the coaxial elongation 7 provided on one side of the coaxially shaped discharge vessel 1 forming a gas- or water-tight connection between the spout and the DBD lamp. The spout 30 consisting of e.g. stainless steel shadows the gasket 31 with respect to the ultraviolet radiation preventing accelerated aging of the gasket 31. A similar arrangement can be used on the second side of the coaxially shaped discharge vessel 1 in order to guarantee a reliable mounting of the DBD lamp.

In Fig. 7 a part of a DBD lamp similar to the second embodiment according to the current invention is shown with a sealing system for mounting the DBD lamp. The coaxial extension depicted in Fig. 7 further comprises a bead. A fitting 32 is screwed on a spout 30 in a way that two ring shaped gaskets 31 are squeezed and pressed to the surfaces of the bead forming a gas- or water-tight connection between the

spout and the DBD lamp. The fitting 32 consisting of e.g. stainless steel shadows the gasket 31 with respect to the ultraviolet radiation preventing accelerated aging of the gasket 31. A similar arrangement can be used on the second side of the coaxially shaped discharge vessel 1 in order to guarantee a reliable mounting of the DBD lamp. In Fig. 8 a part of a DBD lamp according to the second embodiment according to the current invention is shown with a sealing system for mounting the DBD lamp. A fitting 32 is screwed on a spout 30 in a way that a ring shaped gasket 31 is squeezed and pressed to the outer surface of the coaxial elongation 7 provided on one side of the coaxially shaped discharge vessel 1 forming a gas- or water-tight connection between the spout and the DBD lamp. Because the gasket 31 is pressed against the outer surface the fitting 32 cannot totally shadow the gasket 31 with respect to the ultraviolet radiation emitted by the DBD lamp. In order to protect the gasket 31 a layer 40 absorbing the ultraviolet radiation is provided at the inner surface of the coaxial elongation 40. The layer 40 can be CeC>2 coated by means of sol gel processing on the inner surface of the coaxial elongation 7.

The present invention will be described with respect to particular embodiments and with reference to certain drawings, but this is not to be construed in a limiting sense, as the invention is limited only by the appended claims. Any reference signs in the claims shall not be construed as limiting the scope thereof. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun, e.g. "a" or "an", "the", this includes a plural of that noun unless specifically stated otherwise.

Furthermore, the terms first, second, third and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, first, second and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.