Device and method for generating dielectric barrier discharges, method for adjusting operating parameters of a control device, computer program and computer-readable storage medium

Abstract

Device for generating a dielectric barrier discharge, comprising: - a discharge reactor comprising a thermoelectric element (1) and an electrode (2), and - a control device (13) comprising a high-voltage source (12) and a low-voltage source (11), wherein the high-voltage source (12) is configured to apply a high-voltage potential to the electrode (2) sufficient to ignite the dielectric barrier discharge, wherein a gas is enriched with reactive species by the dielectric barrier discharge, wherein the low-voltage source (11) is configured to adjust a current through the thermoelectric element (1), wherein the control device (13) is configured to suitably adjust operating parameters of the high-voltage source (12) and the low-voltage source (11) for a desired composition of the enriched gas, wherein the device is configured toto generate current pulses in the discharge reactor during dielectric barrier discharge, wherein the device is designed to measure the current pulses and to determine the generated reactive species from the frequency and / or the amplitude of the measured current pulses, wherein the control device is designed to regulate the operating parameters depending on the measured current pulses.

Description

The subject matter of the present application is an apparatus and a method for generating dielectric barrier discharges, a method for setting operating parameters of a control apparatus, a computer program and a computer-readable storage medium.WO 2022 / 058 333 A1 discloses a plasma reactor which is configured to cool a process gas by means of a Peltier element.DE 102 36 196 A1 discloses an air cleaning device for reducing pollutants in the air, comprising an ionizer which is exposed to an air flow and which can be supplied with ionization power on the part of a driver stage for ionizing the air supplied by the air flow, and a gas sensor for measuring pollutant concentrations.It is now the object of the present invention to specify an improved device for generating dielectric barrier discharges and also improved methods for operating and setting the operating parameters thereof. Further objects are the information of a computer program for executing the method and of a computer-readable storage medium for executing the computer program.These objects are achieved by the subject matters of the independent claims.An apparatus for generating a dielectric barrier discharge is proposed, which comprises a discharge reactor and a control device. The discharge reactor includes a thermoelectric device and an electrode. The control device includes a high voltage source and a low voltage source. The high-voltage source is configured to apply a high-voltage potential to the electrode, which is sufficient for igniting the dielectric barrier discharge, wherein a gas with reactive species is enriched by the dielectric barrier discharge. The low voltage source is configured to adjust a current through the thermoelectric device. The control device is configured to suitably set operating parameters of the high-voltage source and the low-voltage source for a desired composition of the enriched gas.The control device can thus be configured to always select the optimum operating point for the device. In this case, the control device can take into account the influence of the individual operating parameters on the reactive species generated and can also take into account the interactions of the individual operating parameters with one another.The operating point of the device is characterized by the setting of the operating parameters of the device. The operating parameters thereby decide which reactive species are generated in what amounts during the dielectric barrier discharge. In the device, a plurality of operating parameters can now be adjusted in a targeted manner such that a desired composition of the enriched gas with the reactive species results.The high voltage source may be an AC voltage source. Accordingly, the high voltage potential applied to the electrode may vary with the frequency of the alternating voltage generated by the high voltage source. Here, an AC voltage whose amplitude is 1 kV or more can be referred to as high voltage.The low voltage source may be a DC voltage source. Accordingly, a direct current may flow through the thermoelectric device. Depending on a direction of the direct current, the thermoelectric device may cool or heat / heat a gas in the discharge reactor.The controller may determine the operating parameters by input signals applied to the low voltage source and the high voltage source.In the discharge reactor, in a first embodiment, a thermoelectric barrier discharge can be ignited, in which the thermoelectric component acts as a counter electrode. The dielectric barrier discharge can be ignited between the electrode and the thermoelectric component acting as a counter electrode.The thermoelectric device may be disposed in the reactor such that a temperature of the gas can be changed by the thermoelectric device. The thermoelectric device may either cool or heat the gas before and / or during the dielectric barrier discharge.The thermoelectric component can be, in particular, a Peltier element or a component which has a thermoelectric ceramic material.Since the device can be designed to select the operating parameters such that the desired gas composition for the activated gas always results, errors in the use of the device, for example for disinfection, can be ruled out by the user. Additional system components for supplying chemical substances can accordingly be dispensed with and consumables can be saved. If the reactive species are semistable chemical active substances with short half-lives for which storage and external provision is not possible, the device forms a possibility of producing them in situ in order to apply them directly.The device can be configured to set each operating parameter independently of the respective other operating parameters. The setting of the operating parameters can be effected dynamically, i.e. the setting can always be adapted during operation. In this case, different processes with different active ingredients to be produced in situ can be depicted in a single device.The operating parameters of the high-voltage source can comprise at least one selected from an amplitude of the high-voltage potential, a frequency of the high-voltage potential and a pulse width modulation of the high-voltage potential, wherein a duty cycle and / or a modulation frequency are set during the pulse width modulation.The amplitude of the high-voltage potential of an AC voltage signal generated by the high-voltage source can be used to set how many reactive species are generated during the dielectric barrier discharge and the ratio of the amounts of reactive species to one another. Overall, the number of reactive species produced increases with increasing amplitude. The proportion of the individual reactive species in the gas composition of the enriched gas differs, however, depending on which amplitude of the high-voltage alternating voltage is selected.The amplitude of the high voltage can be up to 8 kV. The high-voltage alternating voltage can have a frequency between 15 kHz and 100 kHz, preferably 20 to 40 kHz.The duty cycle can be adjusted by pulse width modulation of the high voltage potential. The duty cycle indicates the ratio of a time period during which a signal is applied to the electrode and dielectric barrier discharges correspondingly occur, and a time period during which no signal is applied to the electrode and no dielectric barrier discharges are ignited. In this way, the pulse width modulation makes it possible to regulate the power of the dielectric barrier discharge. The pulse width modulation of the high-voltage alternating voltage thus changes the power density in the reactor, which has a direct influence on which reactive species are generated during the dielectric barrier discharge. Furthermore, during pulse width modulation, a modulation frequency can be set by the control device.The operating parameters of the low voltage source that are adjusted by the controller may include a current of the current flowing through the thermoelectric device. By changing the current intensity, the intensity and direction of the heat conveyed via the module can be adjusted, and thus a regulation of the temperature of one side of the thermoelectric component can be carried out.The thermoelectric component can be used both for cooling and for heating the gas in the discharge reactor. In particular, when cooling the gas, the ozone concentration in the enriched gas can be increased. If, on the other hand, the gas is heated, nitrogen oxides are increasingly generated as reactive species, which degrade the ozone and thus lead to a reduced ozone concentration in the enriched gas.The operating parameters mentioned here are not considered to be isolated from one another. Rather, the control device can be configured to take into account the influence, of each of the operating parameters mentioned, on the composition of the enriched gas at all times.The control device can furthermore be configured to control a chemical composition of the reactive species generated during the dielectric barrier discharge by the control device performing pulse width modulation of the high-voltage potential and / or adjusting a current intensity of the current flowing through the thermoelectric component and / or adjusting an amplitude of the high-voltage potential and / or adjusting a frequency of the high-voltage potential. Preferably, all four of the operating parameters mentioned here are always adapted to the desired chemical composition.Furthermore, the control device can be configured to take account of environmental parameters which likewise have a substantial influence on the composition of the reactive species generated during the dielectric barrier discharge.In particular, the control device can be configured to take into account at least one or more of the following environmental parameters when setting the operating parameters: a flow rate of the gas through the discharge reactor, a composition of the gas and / or a temperature of the gas before entering the discharge reactor. Furthermore, an ambient temperature may be taken into account. Taking these environmental parameters into account may make it possible to model the mapping function of the plasma chemistry even more accurately and to adapt the composition of the enriched gas even more accurately to a desired composition.As gases, for example, air, pure oxygen, synthetic air (CDA) or compressed dry air (CDA) can be introduced into the unloader. The stated gases differ in their behavior in the dielectric barrier discharge, so that the type of gas used has an influence on the type and the amount of reactive species generated. For example, an atmospheric humidity of the gas used plays a role in the type and amount of the species generated in the dielectric barrier discharge.The device may comprise sensors which measure the environmental parameters. Alternatively, the influence of the environmental parameters can be taken into account indirectly by current pulses generated in the discharge reactor being detected and evaluated. Alternatively, the influence of the environmental parameters can be taken into account indirectly by comparing the composition of the generated species with the desired composition and adjusting the operating parameters taking into account the comparison result.A surface of the electrode facing the thermoelectric device may include protrusions. A dielectric barrier discharge can occur as a surface dielectric barrier discharge (SDBD) at the projections, while volume dielectric barrier discharge (VDBD) can be triggered in the spaces between two projections, in which the electrode is spaced apart from the thermoelectric component. Accordingly, the apparatus can enable a hybrid operation mode in which both surface and bulk discharges are present.The projections of the electrode can abut on the thermoelectric component. In this case, the projections can serve both as a discharge point for surface discharges and as spacers define a distance between the thermoelectric component and the regions of the electrode which do not have projections. In this way, a volume for the volume discharges can be defined by a length of the projections.The thermoelectric component may include a plurality of thermoelectric elements and metal bridges, each metal bridge connecting two adjacent thermoelectric elements to one another. In particular, the metal bridges can connect the thermoelectric elements to one another in a meandering manner, wherein the metal bridges are arranged alternately on an upper side of the thermoelectric component which faces the electrode and on an underside of the thermoelectric component which faces away from the electrode. The protrusions of the electrode may be arranged such that each protrusion exactly faces a metal bridge on the top side of the thermoelectric device. The projection can be arranged centrally on the metal bridge. The metal bridges may be covered by a dielectric barrier layer, for example a ceramic layer. The protrusions may abut the dielectric barrier layer.By means of the projections of the electrode, heat which arises on the surface of the electrode during the dielectric barrier discharge can be transported away. By virtue of the central arrangement of the projections with respect to the metal bridges, the heat transport can be configured particularly effectively and undesired parasitic discharges in the interior of the thermoelectric component can be prevented.The high voltage source may be autoresonant. A high-voltage source is referred to as autoresonant if it is designed to always readjust a frequency of the high-voltage signal generated by it in such a way that the discharge reactor operated by it is operated in a resonance mode. In an alternative embodiment, the discharge reactor may be operated at a frequency that does not correspond to the resonant frequency of the discharge reactor.The control device can have a computing unit which is designed to determine the suitable operating parameters for a desired composition of the enriched gas. The control device can then set the operating parameters according to the specifications of the computing unit.The computing unit can be configured to determine the operating parameters in an analytical method, in a regression method, in a numerical method, in a computer-implemented method or by means of a self-learning algorithm.The device may comprise sensors configured to determine the composition of the enriched gas, wherein the control device is configured to compare the composition determined by the sensors with the desired composition and to adjust the operating parameters depending on the result of the comparison. Accordingly, the sensors may provide feedback in which a generated signal describing the gas composition in the enriched gas is compared to the desired gas composition. Via the feedback, an adjustment of the operating parameters can be iteratively carried out, which makes it possible to achieve the desired gas composition.During the dielectric barrier discharge, current pulses are generated in the discharge reactor. The device is configured to measure the current pulses and to determine the generated reactive species from the frequency and / or the height of the measured current pulses. The control device is configured to regulate the operating parameters as a function of the measured current pulses.By using sensors or evaluating current pulses generated in the discharge reactor, it can be made possible to take into account the influence of environmental parameters on the composition of the enriched gas without having to measure each environmental parameter.A further aspect relates to a method for generating a dielectric barrier discharge. In this method, in particular the above-described device can be used.The method uses an apparatus comprising a discharge reactor and a high voltage source, wherein the discharge reactor comprises a thermoelectric component and an electrode, and wherein the control apparatus comprises a high voltage source and a low voltage source. The high voltage source is configured to generate a high voltage potential between the electrode. The method comprises the steps of:adjusting a current through the thermoelectric device, wherein the current is adjusted by the low voltage source,applying a high voltage potential to the electrode so as to ignite a dielectric barrier discharge, wherein a gas with reactive species is enriched by the dielectric barrier discharge, wherein the high voltage potential is applied by the high voltage source, andadjusting operating parameters of the high voltage source and the low voltage source to produce a desired composition of the enriched gas, wherein the control device adjusts the operating parameters.The operating parameters of the high-voltage source can comprise at least one selected from an amplitude of the high-voltage potential, a frequency of the high-voltage potential and a pulse width modulation of the high-voltage potential, wherein a duty cycle and / or a modulation frequency are set during the pulse width modulation, and wherein the operating parameters of the low-voltage source comprise a current intensity of the current flowing through the thermoelectric component.The adjustment of the operating parameters performed by the controller to generate the desired composition of the enriched gas may be determined using a modelling function which determines from inputs describing a gas entering the discharge reactor and from the operating parameters outputs describing the gas exiting the discharge reactor.The input variables may comprise at least one selected from the chemical composition of the gas entering the discharge reactor, the temperature of the gas entering the discharge reactor and the flow rate of the gas entering the discharge reactor.The input variables can comprise at least one selected from an ambient temperature and current pulses generated in the discharge reactor.The outputs may comprise at least one selected from a temperature of the gas exiting the discharge reactor, a flow rate of the gas exiting the discharge reactor, and a composition of the gas exiting the discharge reactor.A further aspect relates to a method for setting operating parameters of a control device which actuates a discharge reactor. It may be the above-described control device including a high voltage source and a low voltage source, and the above-described discharge reactor including an electrode and a thermoelectric element. The method for setting operating parameters of the control device can be part of the method described above for generating a dielectric barrier discharge.The method for setting operating parameters of the control device has the following steps:determining operating parameters of the high-voltage source and of the low-voltage source such that a dielectric barrier discharge is generated at the electrode, in which a desired composition of the enriched gas is generated,controlling the operating parameters to the values determined in the preceding step.The operating parameters of the high-voltage source can comprise at least one selected from an amplitude of the high-voltage potential, a frequency of the high-voltage potential and a pulse width modulation of the high-voltage potential, wherein a duty cycle and / or a modulation frequency are set during the pulse width modulation, and wherein the operating parameters of the low-voltage source comprise a current intensity of the current flowing through the thermoelectric component.The adjustment of the operating parameters performed by the controller to generate the desired composition of the enriched gas may be determined using a modelling function which determines from inputs describing a gas entering the discharge reactor and from the operating parameters outputs describing the gas exiting the discharge reactor.The input variables may comprise at least one selected from the chemical composition of the gas entering the discharge reactor, the temperature of the gas entering the discharge reactor and the flow rate of the gas entering the discharge reactor.The input variables can comprise at least one selected from an ambient temperature and current pulses generated in the discharge reactor.The outputs may comprise at least one selected from a temperature of the gas exiting the discharge reactor, a flow rate of the gas exiting the discharge reactor, and a composition of the gas exiting the discharge reactor.A further aspect relates to a computer program which carries out the method described above for determining the operating parameters. The computer program comprises a first step in which the desired composition of the enriched gas is input and a second step in which the method is executed. The input of the desired gas composition can be effected by a user or by a higher-order system to which the device is connected. The first step may alternatively be performed by a fixedly programmed input of a desired gas composition.The determination of the operating parameters can be carried out by means of an analytical method, a regression method, a numerical method, a computer-implemented method or a self-learning algorithm.A further aspect relates to a computer-readable storage medium which has the computer program described above, wherein the computer program has.Preferred embodiments are described below with reference to the figures. Fig. 1 shows a discharge reactor. Fig. 2 shows the discharge reactor and a control device. FIG. 3 shows schematic diagrams showing the influence of operating parameters on the generated reactive species. FIG. 4 schematically shows a method for generating a dielectric barrier discharge. FIG. 5 schematically shows which variables are influenced by the operating parameters that can be set by the control device. FIG. 6 shows a discharge reactor according to an alternative embodiment.FIG. 1 shows a discharge reactor of a device for generating a dielectric barrier discharge, which has a thermoelectric component 1 and an electrode 2. The thermoelectric component 1 is a Peltier element.The thermoelectric device 1 is an electrothermal transducer. It is configured to change a temperature of a gas that is introduced into the discharge reactor as process gas and exits the discharge reactor as enriched gas. When a DC voltage is applied to the thermoelectric device 1 and a DC current flows across the thermoelectric device 1, a temperature difference is generated based on the Peltier effect or the Seebeck effect or the Thomson effect. The Peltier element 1 can be used both for cooling and--in the case of current direction reversal--for heating the process gas.The thermoelectric component 1 has thermoelectric elements 3 which are connected to one another by metal bridges 4 to form a meandering structure.If the thermoelectric component 1 is a Peltier element, semiconductor elements are used as thermoelectric elements. The semiconductor elements are connected to one another in series by the metal bridges 4, wherein p-doped semiconductor elements and n-doped semiconductor elements alternate. The semiconductor elements may comprise bismuth telluride or silicon germanium, for example.If a direct current is conducted through the thermoelectric component 1, a temperature difference and thus a warm and a cold side of the component are produced at the metal bridges 4 on account of the thermoelectric effect, for example the Peltier effect.The thermoelectric component 1 has a first ceramic plate 5 aand a second ceramic plate 5 b. The first ceramic plate 5 ais disposed on an upper surface facing the electrode. The second ceramic plate 5 bis disposed on a lower side facing away from the electrode.The ceramic plates 5 a, 5 bmay comprise aluminum oxide or consist of aluminum oxide. Alternatively or additionally, the ceramic plates 5 a, 5 bmay comprise aluminum nitride or consist of aluminum nitride.The ceramic plates 5 a, 5 bcover the metal bridges 4. The metal bridges 4 form a thermal contact surface via which heat or cold is transferred to the ceramic plates 5 a, 5 b. The ceramic plates 5 a, 5 bfunction as heat-conducting plates. The ceramic plates 5 a, 5 bdeduct heat from the process gas or emit the heat to the process gas.The electrode 2 is disposed in parallel with one of the first ceramic plates 5a. The electrode 2 lies opposite the thermoelectric component 1 and is spatially separated from the thermoelectric component 1 in the embodiment shown in FIG. 1. A gap 6 is between the electrode 2 and the thermoelectric component 1. the gap 6 between the thermoelectric component 1 and the electrode 2 can have a width between 0.01 mm and 1.0 mm, preferably between 0.05 mm and 0.5 mm.The device is configured to trigger a dielectric barrier discharge between the electrode 2 and the thermoelectric component 1. The dielectric barrier discharge is an ignition of a non-thermal atmospheric pressure plasma. In the dielectric barrier discharge, the process gas is enriched with reactive species.An AC potential having a high amplitude is applied to the electrode 2 with respect to an electric potential of the thermoelectric device 1. A high-voltage alternating voltage is thus produced between the thermoelectric component 1 and the electrode 2. A dielectric barrier discharge DBD is ignited between the thermoelectric component 1 and the electrode 2, wherein the ceramic plate 5 afacing the electrode 1 acts as a dielectric barrier.Alternatively or additionally, a layer acting as a dielectric barrier can be attached to the side of the electrode 2 which faces the thermoelectric component 1.A DC current flows through the thermoelectric component 1. A DC voltage potential difference due to the low-ohmic thermoelectric elements 3 of the thermoelectric component 1 is negligible in relation to the high voltage required for the dielectric barrier discharge. Conversely, the current density typically occurring during the dielectric barrier discharge is small in relation to the direct current flowing through the thermoelectric elements 3. The cooling function of the thermoelectric component 1 and the discharge function of the device do not accordingly adversely affect each other.In an alternative embodiment, the thermoelectric component is not arranged opposite the electrode. In the alternative embodiment, the device can be configured to ignite the dielectric barrier discharge between the electrode and a surface at which a ground potential is present.The thermoelectric element 1 is used in the device both in its function as a cooling or heating element, which adjusts a temperature of the process gas, and as a counter electrode, which together with the electrode 2 triggers the dielectric barrier discharge. By combining the thermoelectric element 1 with the dielectric barrier discharge, the dielectric barrier discharge can be operated at a precisely set temperature and humidity, and the concentration and composition of active species generated in the dielectric barrier discharge can be adjusted and maintained stable.The thermoelectric element 1 makes it possible to regulate a temperature of the process gas located in the gap 6 between the electrode 2 and the thermoelectric element 1. When a thermoelectric element 1 is used for dielectric barrier discharge, it is possible to precisely adjust the temperature of the process gas during discharge. The gas composition of the gases generated within the scope of the dielectric barrier discharge depends, inter alia, strongly on the temperature of the process gas. In particular, the proportions of ozone (O 3) produced and nitrous gases (NO, NO 2, NO x) produced are determined by the temperature. As the temperature rises, the generation of nitrous gases is promoted and the degradation mechanisms of ozone in favor of nitrous gases are accelerated.The device further includes a heat sink 9 attached to the ceramic plate 5 bof the thermoelectric element 1 facing away from the electrode 2. The cooling body 9 contributes to cooling of the process gas in addition to the thermoelectric element 1.The discharge reactor has a gas inlet 7 and a gas outlet 8. The process gas is introduced into the discharge reactor via the gas inlet 7. In the discharge reactor, the process gas is enriched with reactive species. Via the gas outlet 8, the gas enriched in the discharge reactor is discharged from the discharge reactor.Furthermore, the device can alternatively or additionally have a fan 10 which is designed to conduct heat away from the cooling body and which thereby contributes to the cooling.FIG. 2 shows the discharge reactor shown in FIG. 1 and a control device 13 connected to the discharge reactor. The control device 13 includes a low-voltage source 11 and a high-voltage source 12. The low-voltage source 11 applies a DC voltage in the low-voltage range to the thermoelectric component 1. A DC current therefore flows via the thermoelectric component 1. The thermoelectric component 1 is at a low-voltage electric potential. The high voltage source 12 applies a high AC potential to the electrode 2. Accordingly, a high potential difference is generated between the thermoelectric device 1 and the electrode 2, and a dielectric barrier discharge occurs in the gap 6 between the electrode 2 and the thermoelectric device 1. The dielectric barrier discharge is a volume discharge.The control device 13 is configured to control operating parameters of the low-voltage source 11 and operating parameters of the high-voltage source 12. For this purpose, the control device 13 can have a computing unit 14, for example a microcontroller, which is designed to transmit control commands to the high-voltage source 12 and the low-voltage source 11.The control device 13 is configured to set the operating parameters such that a desired composition of the enriched gas results. In this case, the control device 13 can take account of the fact that both the type and the quantity of reactive species generated are influenced by the temperature of the thermoelectric component 1 and by an amplitude and a pulse width modulation of the high-voltage alternating potential applied to the electrode 2 by the high-voltage source 12.The control device 13 accordingly makes it possible to specifically generate the active substances or active substance combinations generated in the gas in desired concentrations and ratios by correspondingly adjusting the operating parameters. For the respectively desired product gas compilation, the control device 13 selects an optimally efficient operating point as the operating point of the device. The operating or working point of the device is characterized by the respective settings of the operating parameters of the high-voltage source 12 and of the low-voltage source 11.Since the reactive species generated in the process gas also depend on ambient conditions, for example on the type of the process gas, on the temperature of the process gas when entering the discharge reactor and on the flow rate of the process gas through the discharge reactor, these ambient conditions can be taken into account by the control device 13 in the setting of the operating parameters.The control device is configured to generate the desired composition of the activated gas by a targeted combination of the operating parameters taking into account their mutual dependencies and taking into account the ambient conditions.FIG. 3 schematically shows the influence of the operating parameters on the generation of reactive species, wherein the device shown in FIG. 2 is used with the process gas air.In the curves plotted in the first row, the amplitude of the high-voltage potential applied to the electrode is varied in each case, the temperature of the thermoelectric component being kept constant and no pulse width modulation of the high-voltage signal being carried out.In the four figures shown, the concentration of ozone, of nitrogen oxides, of peroxides and of acids in the activated gas is plotted from left to right for different amplitudes of the high-voltage signal.The first curve, which shows the ozone concentration, reveals that, with increasing amplitude, the ozone concentration first rises until a maximum is reached. If the amplitude is further increased beyond this maximum, the ozone concentration in the excited gas decreases. The reason for decreasing the ozone concentration in the enriched gas at high amplitudes is that mechanisms for degrading ozone are excited when the high voltage signal has sufficiently high energy. In particular, nitrogen oxides are then generated during the dielectric barrier discharge, which cause the ozone degradation.The second curve shows a concentration of the nitrogen oxides in the enriched gas for different amplitudes of the high voltage signal. It can be seen from the curve that at comparatively low amplitudes, virtually no nitrogen oxides are generated. Only when the amplitude is sufficiently large does the concentration of the nitrogen oxides in the enriched gas increase steadily with increasing amplitude.The third curve shows the concentration of peroxides in the enriched gas for different amplitudes of the high voltage signal. This concentration has a maximum for average amplitudes.The fourth curve shows the concentration of acids in the enriched gas for different amplitudes of the high voltage signal.In the second row, it is assumed that a pulse width modulation of the high-voltage signal is carried out. The power of the high-voltage signal can be regulated by pulse width modulation by setting a duty cycle of times in which a signal is applied and times in which no signal is applied. The horizontal axis of the curves shown in the second row in each case plots the power which is directly proportional to the duty cycle of the pulse width modulation. On the vertical axis, the respective concentrations of the reactive species are plotted in arbitrary units. The temperature during the gas discharge and the amplitude of the high-voltage signal remain constant in each case.The curves in the second row show that as the power increases, the concentration of all reactive species increases. It should be noted, however, that the curves shown here are purely schematic and any units are also used. With increasing power, the ratio of the proportions of the reactive species to one another changes in particular.The third row shows four curves in which the temperature of the thermoelectric component is varied and the power and the amplitude of the high-voltage signal remain constant. The first curve, seen from the left, shows the ozone concentration. It can be seen that as the temperature increases, the ozone concentration decreases. In order to achieve a high ozone concentration, the thermoelectric component should therefore cool the process gas. The second curve shows that the concentration of the nitrogen oxides increases as the temperature increases. The third curve shows that with increasing temperature a concentration of peroxides decreases. The fourth curve shows that as the temperature increases, a concentration of acids increases.The curves shown in FIG. 3 are purely schematic and, in addition, do not take into account the interaction of the operating parameters with one another with respect to the reactive species generated. To select the optimum operating point, i.e. to set the operating parameters optimally, an exactly modeled mapping function of the plasma chemistry is required.FIG. 4 schematically shows a method for generating a dielectric barrier discharge using the device shown in FIG. 2.A gas flowing into the discharge reactor is described here by input variables which are combined in an input vector U. These input variables comprise an ambient temperature T U of the device, a temperature T in, which the gas has on entry to the gas inlet 7 and which can possibly deviate from the ambient temperature T U a flow rate of the gas, which is referred to here as mass flow of all gaseous components, and the concentrations c i1, c i2... c im of the individual chemical components, of which the gas flowing into the discharge reactor consists.A gas emerging from the discharge reactor is described by output variables which are combined in an output vector W. The output variables comprise a temperature T out of the gas emerging from the discharge reactor, a flow rate of the gas emerging from the discharge reactor and the concentrations c a1, c a2... c an of the individual chemical components of which the gas emerging into the discharge reactor consists. The gas exiting the discharge reactor contains all chemical components of the gas that has entered the discharge reactor, and may further include other chemical components generated in the dielectric barrier discharge. These can include, for example, ozone, nitrogen oxides or peroxides. Therefore, the number n of chemical components of the exiting gas is equal to or higher than the number m of chemical components of the gas entering the discharge reactor.The control unit is now designed to influence the dielectric barrier discharge and the reactive species generated thereby. For this purpose, the control unit can regulate the operating parameters of the high-voltage source 12 and of the low-voltage source 11. The operating parameters are combined in FIG. 4 as manipulated variables in the vector V. The manipulated variables comprise an amplitude U D of the high-voltage potential applied to the electrode 2 by the high-voltage source 12, a frequency f of the high-voltage potential applied to the electrode 2 by the high-voltage source 12, a pulse width modulation PWM of the high-voltage potential at which the duty cycle and a modulation frequency f can be adjusted, and a current intensity I tec of a current which is adjusted by the thermoelectric component 1 from the low-voltage source 11 and via which the temperature of the thermoelectric component 1 is controlled.During the dielectric barrier discharge, short current pulses are produced in the discharge reactor, the frequency of which pulses may be between 10 MHz and 50 MHz or the frequency of which pulses may be greater than 50 MHz. The current pulses are generated by an electric current which flows between the electrode 2 and the respective counter electrode, wherein the thermoelectric component 1 forms the counter electrode in the exemplary embodiment shown in FIG. 2. The magnitude of the current pulses is proportional to the discharge intensity in a first approximation and is also proportional to the concentration of the newly generated chemical species within wide ranges. If pure oxygen is used as the process gas, the height of the current pulses is proportional to the amount of ozone generated. From the frequency of the current pulses, conclusions can be drawn about the reactive species generated.The current pulses generated in the discharge reactor can be detected and evaluated by the control device 13. In this way, the controller 13 can measure the type and amount of the generated reactive species.In FIG. 4, the current pulses are denoted as S. The current pulses are coupled out of the discharge reactor and are detected in the input vector U. The input vector U thus contains the input variables which describe the ambient conditions and the gas on entry into the discharge reactor, and information obtained from the current pulses.In the control device, the output quantities are now precomputed using a modelling function f(U,V), wherein the input vector U and the vector V, in which the manipulated variables are combined, are taken into account as parameters in the modelling function f(U,V). The modeling function f(U,V) is a multi-dimensional function having a plurality of variables. The modeling function f(U,V) may be a purely analytical function calculated by an analytical method. The modeling function f(U,V) can be calculated in a regression method. The modelling function f(U,V) can be calculated in a numerical method. The modeling function f(U,V) can be a computer-implemented method, wherein the modeling function f(U,V) is carried out, for example, by a self-learning algorithm. The modelling function f(U,V) can be a combination of the method types mentioned here.In the modeling function f(U,V), the output quantities are calculated in the form of an output vector W r. The calculated output vector W r comprises a calculated temperature T rout of the gas as it exits the discharge reactor, a calculated flow rate and calculated concentrations c r1, c r2... c rn of the chemical components of the gas as it exits the discharge reactor. The quantities combined in the calculated output vector W r represent approximate values of the actual output quantities. The more accurately the plasma chemistry in the dielectric barrier discharge is mapped by the modelling function f(U,V), the smaller the deviation between the calculated output quantities and the actual output quantities.A user or a higher-order system connected to the device transmits a desired chemical composition of the enriched gas to the control device. The arithmetic unit 14 now determines the optimum operating point of the discharge reactor for producing the desired chemical composition. For this purpose, the arithmetic unit 14 determines, based on the modelling function f(U,V), to which values the operating parameters of the low-voltage source 11 and of the high-voltage source 12 are to be set. In this case, the arithmetic unit 14 can carry out the determination of the operating parameters by means of an analytical method, a regression method, a numerical method, a computer-implemented method or a self-learning algorithm.The arithmetic unit 14 then transmits the operating parameters to the high-voltage source 12 and to the low-voltage source 11, which can be arranged in a common driver module.The control unit 13 is further configured to transmit the input vector U, the vector V describing the manipulated variables and the calculated output vector W r to the higher-level system. These variables can then be displayed on a screen by the superordinate system.FIG. 5 shows how the operating parameters that can be changed by the control device 13 influence the reactive species generated.On the left-hand side of FIG. 5, the operating parameters which can be changed by the control device 13 and further parameters which describe the gas flowing into the discharge reactor are plotted. On the right-hand side, process parameters describing the dielectric barrier discharge are plotted. Arrows show which operating parameters or parameters describing the gas respectively influence which process parameter.The operating parameters that can be changed by the control device 13 comprise the amplitude of the high-voltage potential applied to the electrode 2, a pulse width modulation of the high-voltage potential applied to the electrode 2 and a current intensity through the thermoelectric component 1.The type of gas used essentially determines which molecules are available as reaction partners in the dielectric barrier discharge.The amplitude of the high voltage potential applied to the electrode 2 influences the energy and the power density of the dielectric barrier discharge. Furthermore, the amplitude of the high voltage potential applied to the electrode 2 also influences the process temperature. In this case, a higher amplitude compared to a low amplitude leads to higher energies and a higher power density being present in the dielectric barrier discharge. This also generates more heat, which increases the process temperature.The pulse width modulation duty cycle influences the dielectric barrier discharge power density and the process temperature. If the proportion of the time periods in which no high-voltage potential is present at the electrode 2 is increased at the duty cycle, the power density decreases and less heat is generated.The current intensity through the thermoelectric component 1 influences the process temperature. In this case, the thermoelectric component 1 can cool or heat the gas in the discharge reactor.The flow rate of the gas through the discharge reactor influences the dielectric barrier discharge power density and the process temperature.Both the ozone concentration and the ozone production rate increase with increasing amplitude of the high-voltage signal, wherein saturation results with a sufficiently large amplitude and the ozone concentration and the ozone production rate do not increase any further with an amplitude of the high-voltage signal which increases beyond this.As the flow rate of the gas is increased, the generated reactive species, for example ozone, are transported more quickly away from the discharge reactor. Accordingly, the concentration of the reactive species in the exiting gas decreases with increasing flow rate. At the same time, new process gas is supplied more quickly to the discharge reactor, so that the production rate of the reactive species increases as the flow rate increases. As the flow rate increases, a thermal separation layer between the electrode 2 and the dielectric barrier of the discharge reactor becomes smaller, so that the heat dissipation is improved and the temperature of the process gas is reduced. A reduced temperature results in an increased production rate of certain reactive species, for example ozone. Further, the reduction in the thickness of the thermal separation layer with increasing flow rate results in better diffusion of reaction products of the dielectric barrier discharge, thus also increasing the production rate of the reactive species.The ozone concentration in the emerging gas increases with increasing duty cycle, the duty cycle being controlled by pulse width modulation of the high-voltage signal. As the duty cycle increases, the ozone concentration initially increases approximately linearly until a plateau in the ozone concentration occurs. Both increasing amplitude and increasing duty cycle may trigger ozone depletion mechanisms that explain plateaus in ozone concentration as duty cycle increases. The higher the amplitude of the high-voltage signal, the lower the duty cycles, the corresponding plateau is reached. In the event of a transition from a pulse-width-modulated signal to a continuous signal, charge accumulated at the dielectric barrier can lead to an increase in the voltage in the microdischarges. Accordingly, the ozone concentration is greatly increased when the duty ratio is over 90% and the signal is almost continuous.Cooling of the thermoelectric component influences the ozone concentration, wherein the ozone concentration falls with increasing temperature. There is a virtually linear relationship between the temperature in the discharge reactor and the ozone concentration in the emerging process gas.Overall, each of the operating parameters, temperature of the thermoelectric device, amplitude of the applied high voltage and pulse width modulation of the applied high voltage influences the generation of reactive species in the discharge reactor. In this case, there are considerable interactions under the influences of the operating parameters and the ambient conditions, in particular temperature, composition and flow rate of the inflowing gas, must be taken into account. If all these parameters are taken into account, a well modeled mapping function of the plasma chemistry in the dielectric barrier discharge results, which is taken into account by the control device 13 of the present device.Fig. 6 shows another embodiment of the discharge reactor. The electrode 6 has protrusions 15. The protrusions 15 are disposed on an upper surface of the electrode 2 facing the thermoelectric device 1. The projections 15 are arranged such that in each case one projection 15 lies centrally opposite a metal bridge 4, which is arranged on the upper side of the thermoelectric component and connects two adjacent thermoelectric elements 3 to one another. The protrusions 15 abut on the ceramic layer 15 aof the thermoelectric device 1.The protrusions 15 perform various functions in the device. Surface discharges occur in the area of the projections. Accordingly, dielectric barrier discharges in the form of volume discharges and surface discharges occur in the discharge reactor. The ignition voltage is lower for the surface discharges than for the volume discharges.The projections 15 also act as spacers between the electrode 2 and the thermoelectric component 1 and thus determine a volume of the volume discharges. Furthermore, the protrusions 15 can dissipate heat generated at the electrode 2 to the thermoelectric device 1 via the direct contact, thus reducing the temperature in the discharge space. This effect is particularly enhanced in that one projection each lies centrally opposite a metal bridge 4, since the metal bridges 4 have particularly high thermal conductivity.In addition, the projections 15 impede a gas flow through the discharge reactor and thereby enable better mixing of the process gas, which leads to improved cooling and thus to an increased ozone production rate in the discharge reactor.List of reference characters1 Thermoelectric component 2 Electrode 3 Thermoelectric element 4 Metal bridge 5 aFirst ceramic plate 5 bSecond ceramic plate 6 Gap 7 Gas inlet 8 Gas outlet 9 Heat sink 10 Fan 11 Low voltage source 12 High voltage source 13 Control device 14 Computing unit 15 Protrusion

Claims

Device for generating a dielectric barrier discharge, comprising: - a discharge reactor comprising a thermoelectric component (1) and an electrode (2), and - a control device (13) comprising a high-voltage source (12) and a low-voltage source (11), wherein the high-voltage source (12) is configured to apply to the electrode (2) a high-voltage potential sufficient for igniting the dielectric barrier discharge, wherein a gas with reactive species is enriched by the dielectric barrier discharge, wherein the low-voltage source (11) is configured to set a current through the thermoelectric component (1), wherein the control device (13) is configured to set operating parameters of the high-voltage source (12) and of the low-voltage source (11) in a suitable manner for a desired composition of the enriched gas, wherein the device is configured to generate current pulses in the discharge reactor during the dielectric barrier discharge, wherein the device is configured to measure the current pulses and to determine the generated reactive species from the frequency and / or the height of the measured current pulses, wherein the control device is configured to control the operating parameters as a function of the measured current pulses.The device according to claim 1, wherein the operating parameters of the high voltage source (12) comprise at least one selected from an amplitude of the high voltage potential, a frequency of the high voltage potential and a pulse width modulation of the high voltage potential, wherein a duty cycle and / or a modulation frequency are adjusted during the pulse width modulation.Device according to one of the preceding claims, wherein the operating parameters of the low-voltage source (11) comprise a current intensity of a current flowing through the thermoelectric component (1).Device according to one of the preceding claims, wherein the control device (13) is configured to control a chemical composition of the reactive species generated during the dielectric barrier discharge by the control device (13) performing pulse width modulation of the high-voltage potential and / or setting a current intensity through the thermoelectric component (1) and / or setting an amplitude of the high-voltage potential and / or setting a frequency of the high-voltage potential.The apparatus according to any of the preceding claims, wherein the control device (13) is configured to take into account a flow rate of the gas through the discharge reactor when adjusting the operating parameters.The device according to any one of the preceding claims, wherein the control device (13) is configured to take into account a composition and / or a temperature of the gas at the entry into the discharge reactor and / or an ambient temperature when setting the operating parameters.Device according to one of the preceding claims, wherein the thermoelectric component (1) is a Peltier element.The device according to any one of the preceding claims, wherein a surface of the electrode (2) has protrusions (15).Device according to Claim 8, wherein the electrode (2) is opposite the thermoelectric component (1), and wherein the projections (15) bear against the thermoelectric component (1).Device according to claim 9, wherein the thermoelectric component (1) comprises a plurality of thermoelectric elements (3), wherein the thermoelectric component (1) comprises metal bridges (4), wherein each metal bridge (4) connects two thermoelectric elements (3) adjacent to one another to one another, wherein the projections (15) are arranged such that each projection (15) exactly faces a metal bridge (4) on the upper side of the thermoelectric component (1), wherein the upper side of the thermoelectric component (1) faces the electrode (2).The apparatus of any preceding claim, wherein the high voltage source (12) is configured to be autoresonantly operated.Device according to one of the preceding claims, wherein the control device (13) has a computing unit (14) which is designed to determine the suitable operating parameters for a desired composition of the enriched gas.Device according to the preceding claim, wherein the computing unit (14) is configured to determine the operating parameters in an analytical method, in a regression method, in a numerical method, in a computer-implemented method or by means of a self-learning algorithm.Device according to any one of the preceding claims, wherein the device comprises sensors configured to determine the composition of the enriched gas, wherein the control device (13) is configured to compare the composition determined by the sensors with the desired composition and to adjust the operating parameters depending on the result of the comparison.Device according to one of the preceding claims, wherein the thermoelectric component (1) is opposite the electrode (2) and is configured to act as a counter electrode to the electrode (2) during the dielectric barrier discharge, or wherein the electrode (2) is configured and arranged to ignite the dielectric barrier charge against a surface at a ground potential.Method for generating a dielectric barrier discharge with a device comprising a discharge reactor comprising a thermoelectric component (1) and an electrode (2), and a control device (13) comprising a high voltage source (12) and a low voltage source (11), comprising the steps of: - applying a current to the thermoelectric component, wherein the current is adjusted by the low voltage source (11), - applying a high voltage potential to the electrode (2) such that a dielectric barrier discharge is ignited, wherein a gas with reactive species is enriched by the dielectric barrier discharge, wherein the high voltage potential is applied by the high voltage source (12), and - adjusting operating parameters of the high voltage source (12) and the low voltage source (11) to generate a desired composition of the enriched gas, wherein the control device (12) adjusts the operating parameters, wherein current pulses are generated in the discharge reactor during the dielectric barrier discharge, wherein the device measures the current pulses and determines the generated reactive species from the frequency and / or the height of the measured current pulses, wherein the control device controls the operating parameters as a function of the measured current pulses.Method according to Claim 16, wherein the operating parameters of the high-voltage source (12) comprise at least one selected from an amplitude of the high-voltage potential, a frequency of the high-voltage potential and a pulse width modulation of the high-voltage potential, wherein a duty cycle and / or a modulation frequency are set in the pulse width modulation, and wherein the operating parameters of the low-voltage source (11) comprise a current intensity of the current flowing through the thermoelectric component (1).Method according to claim 16 or claim 17, wherein the adjustment of the operating parameters carried out by the control device (13) for generating the desired composition of the enriched gas is determined using a modelling function (f(U,V)) which determines output quantities (W r) which describe the gas emerging from the discharge reactor from input quantities (U) which describe a gas entering the discharge reactor and from the operating parameters (V).The method according to claim 18, wherein the input quantities (U) comprise at least one selected from the chemical composition of the gas entering the discharge reactor, the temperature of the gas entering the discharge reactor and the flow rate of the gas entering the discharge reactor.Method according to Claim 18 or Claim 19, wherein the input variables (U) comprise at least one selected from an ambient temperature and current pulses generated in the discharge reactor.The method according to any one of claims 18 to 20, wherein the outputs (W r) comprise at least one selected from a temperature of the gas exiting from the discharge reactor, a flow rate of the gas exiting from the discharge reactor, and a composition of the gas exiting from the discharge reactor.Method for setting operating parameters of a control device (13) which controls a discharge reactor, wherein the control device (13) has a high-voltage source (12) and a low-voltage source (11), wherein the discharge reactor has an electrode (2) and a thermoelectric component (1), wherein the high-voltage source (12) is designed to apply a high-voltage potential to the electrode (2) which is sufficient for igniting the dielectric barrier discharge, wherein a gas with reactive species is enriched by the dielectric barrier discharge, wherein the low-voltage source (11) is designed to set a current to the thermoelectric component (1), wherein the method has the steps of: - determining operating parameters of the high-voltage source (12) and of the low-voltage source (11), such that a dielectric barrier discharge is generated at the electrode (2), wherein a desired composition of the enriched gas is generated, - control of the operating parameters to the values determined in the previous step, wherein current pulses are generated in the discharge reactor during the dielectric barrier discharge, wherein the device measures the current pulses and determines the generated reactive species from the frequency and / or the height of the measured current pulses, wherein the control device controls the operating parameters as a function of the measured current pulses.Method according to Claim 22, wherein the operating parameters of the high-voltage source (12) comprise at least one selected from an amplitude of the high-voltage potential, a frequency of the high-voltage potential and a pulse width modulation of the high-voltage potential, wherein a duty cycle and / or a modulation frequency are set in the pulse width modulation, and wherein the operating parameters of the low-voltage source (11) comprise a current intensity of the current flowing through the thermoelectric component (1).Method according to claim 22 or claim 23, wherein the adjustment of the operating parameters carried out by the control device (13) for generating the desired composition of the enriched gas is determined using a modelling function (f(U,V)) which determines output quantities (W r) which describe the gas emerging from the discharge reactor from input quantities (U) which describe a gas entering the discharge reactor and from the operating parameters (V).The method according to claim 24, wherein the input quantities (U) comprise at least one selected from the chemical composition of the gas entering the discharge reactor, the temperature of the gas entering the discharge reactor and the flow rate of the gas entering the discharge reactor.Method according to Claim 24 or Claim 25, wherein the input variables (U) comprise at least one selected from an ambient temperature and current pulses generated in the discharge reactor.The method of any of claims 24 to 26, wherein the outputs (W r) comprise at least one selected from a temperature of the gas exiting the discharge reactor, a flow rate of the gas exiting the discharge reactor, and a composition of the gas exiting the discharge reactor.A computer program carrying out a method according to any one of claims 22 to 27, the computer program comprising: a first step of inputting the desired composition of the enriched gas; and a second step of carrying out the method according to any one of claims 22 to 27.The computer program of claim 28, wherein the determination of the operating parameters is performed by means of an analytical method, a regression method, a numerical method, a computer-implemented method or a self-learning algorithm.Computer readable storage medium comprising a computer program for performing the method according to any one of claims 22 to 27, said computer program comprising: a first step in which the desired composition of the enriched gas is input, and a second step in which the method according to any one of claims 22 to 27 is performed.The computer readable storage medium of claim 30, wherein the determination of the operating parameters is performed using an analytical method, a regression method, a numerical method, a computer implemented method, or a self-learning algorithm.

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