Patent Number: 051947404
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in FIGS. 1 and 2 the irradiation device comprises an internal dielectric tube 1, for example a glass or quartz tube 1, which is provided in the interior with a metal layer 2, preferably an aluminum layer. Said layer 2 forms the internal electrode of the radiator. The internal tube 1 is surrounded concentrically by, and at a distance from, a middle dielectric tube 3 which consists of a UV-transparent material, for example quartz. The space between the two tubes 1 and 3 forms the discharge chamber 4 of the radiator. The discharge chamber 4 is bounded towards the outside by an external tube 5 made from dielectric material, for example glass or quartz. The space between the tube 3 and the tube 5 forms the treatment chamber 6 of the irradiation device. A second metal layer 7, preferably made from aluminum, is applied to the external surface of the tube 6 and forms the external electrode of the radiator. Whereas the two ends of the middle tube 3 are connected gastight to the internal tube 1, for example are fused together, the external tube 5 is held together with the coating 7 on both sides in a sealing washer 8. The latter consists of an elastomeric material or of another insulating material, for example PTFE (polytetrafluoroethylene), which separates the treatment chamber 6 gastight from the external chamber 9. Given the use of a less elastic material, gaskets (not illustrated) are then between. Two sockets 10 are provided in the external tube 5 for the supply and discharge of the medium to be treated. The supply and discharge can also be performed through the sealing washers 8 instead of via sockets 10 in the external tube 5. This results in a simplified design of the external tube 5. This variant is illustrated in FIG. 1 by sockets 10a, drawn in with dashes, in the two sealing washers 8. The design described enables the treatment chamber 6 to be separated simply from the discharge chamber 4 in order, for example, to carry out cleaning work or the like. It can be advantageous when handling highly toxic gases to limit the number of seals to the absolute minimum. This is realized in FIGS. 3 and 4, for example, in that instead of the sealing washers 8 of the embodiment in accordance with FIGS. 1 and 2 respectively the ends 11 of the external tube 5 are drawn inwards and are connected gastight to the middle tube 3, for example are fused together. In such a design of the irradiation device, only sealing problems that are easy to grasp occur. Otherwise, the design corresponds to that of FIGS. 1 and 2, as demonstrated by the same reference numerals for the same parts. In both embodiments of the irradiation device, a cooling medium can be led through the interior of the internal tube 1. By contrast, it can be advantageous for the destruction of certain gaseous components not to (force-) cool the radiator, and this is eminently possible by means of the quartz apparatus in accordance with FIG. 3. The feeding of the discharge in the discharge chamber 4 is performed by an ac source 12 of adjustable frequency and amplitude, which is connected to the two electrodes 2 and 7. The ac source 12 basically corresponds to those such as are used to feed ozone generators. Typically, it delivers an adjustable ac voltage of the order of magnitude of several 100 volts to 20,000 volts at frequencies in the range of industrial alternating current up to a few MHz--depending on the electrode geometry, pressure in the discharge chamber and composition of the filling gas. The discharge chamber 4 between the tubes 1 and 3 is filled with a filling gas which emits radiation under discharge conditions and is, for example, mercury, noble gas, a mixture of noble gas and metal vapor or a mixture of noble gas and halogen, if necessary with the use of an additional further noble gas, preferably Ar, He, Ne, Xe as buffer gas. Depending on the desired spectral composition of the radiation, a substance/mixture of substances in accordance with the following table can be used in this regard: ______________________________________ Filling gas Radiation ______________________________________ Helium 60-100 nm Neon 80-90 nm Argon 107-165 nm Argon + fluorine 180-200 nm Argon + chlorine 165-190 nm Argon + krypton + chlorine 165-190 nm, 200-240 nm Xenon 120-190 nm Nitrogen 337-415 nm Krypton 124 nm, 140-160 nm Krypton + fluorine 240-255 nm Krypton + SF.sub.6 + Ar 240 nm-255 nm Krypton + chlorine 200-240 nm Mercury 185 nm, 254 nm, 295-315nm, 365 nm, 366 nm Selenium 196, 204, 206 nm Deuterium 150-250 nm Xenon + fluorine 340-360 nm, 400-550 nm Xenon + chlorine 300-320 nm ______________________________________ In addition, a whole series of further filling gases come into consideration: a noble gas (Ar, He, Kr, Ne, Xe) or Hg with a gas or vapor of F.sub.2, I.sub.2, Br.sub.2, Cl.sub.2 or a compound which splits off one or more atoms of F, I, Br or Cl in the discharge; PA1 a noble gas (Ar, He, Kr, Nr, Xe) or Hg with O.sub.2 or a compound which splits off one or more O atoms in the discharge; PA1 a noble gas (Ar, He, Kr, Ne, Xe) with Hg. When a voltage is applied between electrodes 2 and 7, a multiplicity of discharges 13 (illustrated only in FIGS. 2 and 4) is formed in the discharge chamber 4. The electron energy distribution in said discharge zone can be optimally adjusted by the thickness of the dielectric tube 1 or 3, the spacing of the tubes, pressure and/or temperature. The discharges radiate the UV light, which then penetrates through the UV-transparent tube 3 into the immediately adjoining treatment chamber 6. The substance to be irradiated is led through the treatment chamber 6. Said substance can be gaseous or liquid. It is important in the case of liquid substances that they have a sufficiently high dielectric constant to be able to couple the energy from the external electrode 7 through the treatment chamber 6 into the discharge chamber 4. Since the invention is preferably provided for irradiating watery substances, said condition is fulfilled in any case: as a consequence of its high dielectric constant only low electric field strengths prevail in water (or watery substances), so that the greatest part of the voltage applied between electrodes 2 and 7 occurs at the discharge chamber 4, that is to say between the dielectric tubes 1 and 3, and drives the discharge. The two electrodes 2 and 7 serve at the same time as a reflector for the UV radiation, because, as is known, aluminum layers reflect UV radiation effectively. Instead of water or watery substances, it is also possible, of course, for any other liquid, emulsion or even a gas which fulfills the abovementioned preconditions to be irradiated. If a gas is used, it must merely be ensured that the ignition voltage in the discharge chamber 5 is smaller than that in the gas of the treatment chamber. This can always be achieved by appropriate selection of pressure and gap width, in particular in the discharge chamber: In the non-ignited state, the described arrangement behaves like a capacitive voltage divider. The individual component voltages at the dielectrics and the gas gaps can be calculated using the capacitance formulae for cylindrical capacitors. It is to be borne in mind in this regard that quartz has a dielectric constant of .epsilon.=3.7, while .epsilon.=1 can be assumed with adequate accuracy for all gases. The preponderant component of the voltage is located at the gas sections, approximately equal electric field strengths being produced for the discharge chamber and the treatment chamber. Assuming, for example, air at a pressure of 1 bar in the treatment chamber of width 2 mm, an ignition field strength of just 40 kV/cm is produced in accordance with the known breakdown curves for air. If a xenon-excimer radiator is selected as UV source having a filling pressure below 0.3 bar and a discharge gap of width 5 mm, an ignition field strength of approximately 9 kV/cm is produced in the xenon. It is thus easy to find voltage ranges in which the gas discharge burns in the xenon without ignition of the air gap to be irradiated. On the other hand, in the irradiation of gases or gas mixtures quiet electric discharges can be forced in the treatment chamber 6 by increasing the ac voltage applied at the electrodes 2 and 7. Thus, the gas to be treated is additionally subjected to the action of high-energy electrons, ions and excited atoms or molecules. This combined effect of hard UV radiation and an electric discharge is suitable, in particular, for decomposing relatively poorly fissionable substances. A range of modifications are possible without leaving the framework fixed by the invention: Instead of tubes 1 or 5 made from dielectric material and coated with metal layers 2, 7, it is also possible to use metal tubes which are provided with a dielectric layer--outside in the case of the internal tube 1 and inside in the case of the external tube 5. In the case of the external tube 5 this layer must extend completely over the entire surface facing the treatment chamber 6, in order to ensure the "freedom from metal" of the treatment chamber 6. The above discussions are related essentially exclusively to radiators having cylindrical geometries. The invention is not, of course, limited to such radiators. The teaching on which the invention is based can also be applied without any problem to configurations having plane dielectrics, preferably quartz plates. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.