Particle generator

Abstract

A particle generator (1) for testing or calibrating particle measuring devices (5) is proposed, which has a reaction chamber (2), a drying chamber (3) downstream of the reaction chamber (2), wherein air is supplied to the reaction chamber (2) via a supply line (11) and the output of the drying chamber (3) can be connected to a particle measuring device (5) via a connecting line (12).In order to provide a particle stream or aerosol for testing or calibrating a particle measuring device (5) in a cost-effective manner, it is proposed that the reaction chamber (2) has a porous layer (21) on which a salt solution (22) is arranged, and that the supply of air into the reaction chamber (21) is made below the porous layer, so that rising bubbles are generated in the salt solution which, when they burst, release salt particles which are dried in the drying chamber (3) before the particles flow to the connecting line (12) in the form of an aerosol.

Description

The invention relates to a method for providing a particle stream or aerosol for testing and / or calibrating particle measuring devices or a particle generator for testing or calibrating particle measuring devices according to the features of the preamble of claim 6. In practice, particle measuring devices must be regularly tested and calibrated. The particle generators required for this are relatively complex, meaning the testing or calibration process is relatively time-consuming and therefore expensive. German utility model DE 94 08 604 U1 discloses an aerosol generator for producing test aerosols. The aerosol is generated using a two-fluid nozzle by atomizing liquid from a container with compressed air. Furthermore, a cyclone must be installed downstream of the two-fluid nozzle to select the particle size distribution. This process is relatively complex to implement, as the generation of compressed air is costly and requires appropriate filtration, and the generated particles must undergo post-treatment to be usable as test aerosols. DE 198 21 552 C1 also discloses an aerosol generator with a two-fluid nozzle operating on the injector principle. This nozzle also requires a pressurized gas supply to generate aerosol streams. Furthermore, this method produces relatively high particle concentrations, which must be diluted using complex and expensive processes before they can be used as test aerosols. DE 199 42 210 A1 describes a process for producing aerosols in the nanometer range, wherein a humidified carrier gas is irradiated with UV light, and substances inert and non-decomposable under UV light are added to the carrier gas in a gaseous state. This is also a relatively complex manufacturing process. The object of the present invention is to provide a method for producing particle streams and a particle generator with which testing and / or calibration of particle measuring devices is possible in a simple manner, which reliably generates a constant particle stream and is cost-effective in application and / or manufacture. This problem is solved according to the invention by a method for producing a particle stream with the features of claim 1 and by a particle generator for testing or calibrating particle measuring devices with the features of claim 6. The invention relates to a method for providing a particle stream or aerosol for testing and / or calibrating a particle measuring device, comprising the following steps: - providing a reaction chamber with a downstream drying chamber and a connection for connecting a particle measuring device to be tested, wherein the reaction chamber has a porous layer on which a salt solution is arranged, - introducing air into the reaction chamber below the porous layer, - passing the air through the porous layer and the salt solution to generate rising bubbles which, upon bursting, release salt particles which are directed into the drying chamber and dried there before the particles flow to the connection, or wherein the particles flow to the connection (12) before being directed into the drying chamber (3). Furthermore, the invention relates to a particle generator for testing or calibrating a particle measuring device, in particular for carrying out the method according to the invention, comprising a supply line for supplying air and a connection line for connecting to a particle measuring device to be tested, further comprising a reaction chamber, wherein air is supplied to the reaction chamber via the supply line and the outlet of the reaction chamber can be connected to a particle measuring device via the connection line. It is essential that the reaction chamber has a porous layer on which a salt solution is arranged, and that the supply of air to the reaction chamber is located below the porous layer, such that the air flows through the porous layer into the salt solution to generate rising bubbles which, upon bursting, release salt particles that flow to the connection line. Advantageously, the inventive method or particle generator can provide a particle stream or aerosol that can be directly connected to a particle measuring device for testing and / or calibration. A particle measuring device is understood to be a particle counter, such as those used, for example, for exhaust gas measurement in motor vehicles or for quality control in cleanrooms. A drying chamber can be provided to dry the salt particles produced in the reaction chamber. In one embodiment, the drying chamber can be arranged within the particle generator. Preferably, a drying chamber can be connected downstream of the reaction chamber, such that the salt particles formed in the reaction chamber are fed into the drying chamber and dried there before flowing to the connecting line. Alternatively, a particle measuring device with an integrated drying chamber can be used. In this case, the drying chamber of the particle measuring device can be used to dry the salt particles. This means that the particle generator does not necessarily have its own drying chamber; instead, the drying chamber of the particle measuring device being tested or calibrated can be used. This allows the salt particles to be fed directly from the reaction chamber to the connection point—that is, directly from the reaction chamber to the particle measuring device. This keeps the design of the particle generator simple and cost-effective. Prior art particle generators often produce a particle stream with a high particle density, which must first be diluted in a complex process before it can be used for testing and / or calibrating sensitive particle counters. An advantage of the inventive method or particle generator is that a particle stream or aerosol stream with a constant particle number concentration can be provided in a simple manner. In particular, the number of particles can be adjusted between 5,000 and 100,000 particles per cm³. Tests have shown that the median particle size is approximately 70 nm with a deviation of + / - 20 nm. A further advantage is that the inventive method or particle generator functions without an additional pump, compressor, or compressed air. With known particle generators on the market, an additional pump or compressor is often necessary, which is not only expensive and requires installation space, but also necessitates appropriate pretreatment of the compressed air to make it suitable for particle generation. Preferably, the inventive method or particle generator utilizes the suction of the particle measuring devices under test. Advantageously, it can be provided that only the volume flow generated by the particle measuring device under test is used to introduce the air and / or to generate the bubbles. Preferably, air flows through the porous layer into the salt solution. The porous layer divides the airflow into a multitude of small air droplets, which form a multitude of rising bubbles in the salt solution. As the bubbles transition from the liquid to the gas phase, they burst and release small salt particles. These rise with the airflow in the reaction chamber and are dried in the drying chamber. Conventional particle generators on the market have a flow rate or volumetric flow rate in the range of 1 l / min to 10 l / min. The method and particle generator according to the invention are designed such that a constant aerosol flow or particle flow can be generated within a volumetric flow rate range of 1 l / min to 20 l / min, such that the number of particles per cm³ remains constant regardless of the volumetric flow rate. In particular, a volumetric flow rate in the range of 0.5 l / min to 20 l / min, preferably in the range of 1 l / min to 5 l / min, or in the range of 5 l / min to 10 l / min, can be used for air. The preferred volumetric flow rate range can be selected by the geometry or the area of ​​the porous layer.In practice, areas of the porous layer in the range of 1 cm2 to 65 cm2, preferably in the range of 1.5 cm2 to 10 cm2, most preferably between 1.8 cm2 to 5 cm2 have proven to be advantageous. Preferably, the air can be filtered before being introduced into the reaction chamber, in particular by a HEPA filter. For example, the supply line can have an air filter, in particular a HEPA filter, or be connected to one. Filtering the air before introducing it into the reaction chamber removes airborne particles, preventing them from interfering with the generation of the particle stream. A HEPA filter is used in particular. Such filters are readily available on the market and offer a reliable way to filter the air with minimal pressure loss. The air filter is designed with a replaceable element, allowing it to be changed after a certain operating period to maintain a consistent particle stream quality. In a preferred embodiment, the particles in the drying chamber can be dried by means of a diffusion dryer, a membrane dryer, or an evaporator tube. Preferably, the drying chamber can be configured as a diffusion dryer, a membrane dryer, or an evaporator tube. For example, in the case of a diffusion dryer, the drying chamber can have a coating of a microscopic material, such as silica gel, to dry and thus stabilize the generated salt particles. Alternatively, a membrane dryer can be used, the membrane thickness of which is dimensioned such that the water particles are retained and only the salt particles are allowed to pass through. The use of an evaporator tube is also conceivable, provided that the particle measuring device under test is capable of measuring at high temperatures.In an evaporator tube, the excess water in the aerosol can be evaporated. In a preferred embodiment, the porous layer may have a porosity in the range of 40 µm to 250 µm, preferably in the range of 100 µm to 160 µm, and most preferably a porosity of 100 µm. In practice, it has been shown that a pore size in this range offers a particularly good yield of the aerosol to be collected. In particular, according to the definition in standard ISO 4793-80, the porosity may be within class 1. In particular, it may be provided that the porous layer has a layer thickness in the range of 200 µm to 10000 µm (0.2 mm to 10 mm), preferably in the range of 400 µm to 7500 µm (0.4 mm to 7.5 mm), most preferably in the range of 500 µm to 5500 µm (0.5 mm to 5.5 mm). In a preferred embodiment, the salt solution may be arranged only above the porous layer. That is, the aqueous salt solution does not penetrate the porous layer. Preferably, the porous layer is already watertight due to its small pores. This means that water or the salt solution could only move through the layer under pressure. To further improve the watertightness of the layer, in a preferred embodiment, the porous layer may have a hydrophobic surface or be designed as a hydrophobic layer. In an advantageous embodiment, the salt solution can be arranged above and below the porous layer. In particular, the salt solution can penetrate the porous layer. This has the advantage that salt crystals cannot be deposited on the porous layer, which could potentially obstruct the flow. Preferably, the porous layer can be made of a ceramic, or of sintered glass, or of a plastic. In particular, the salt solution may be an aqueous NaCl solution in the range of 0.7% to 1.2%, especially in the range of 0.8% to 1%, and especially a 0.9% NaCl solution. Such salt solutions are readily available on the market at low cost and are already standardized to a specific dilution, for example, 0.9%. It may also be possible to easily replace the salt solution in the reaction chamber, for example, to exchange it for a fresh solution after a certain operating cycle, thus ensuring that the concentration of the salt solution used remains constant. In particular, it can be provided that the salt solution on or above the porous layer has a height in the range of 0.8 cm to 15 cm, preferably in the range of 1.5 cm to 10 cm, most preferably in the range of 2 cm to 5 cm. Preferably, it can be provided that only the volume flow generated by the particle measuring device under test is used for supplying the air and / or generating the bubbles. In particular, the walls of the reaction chamber and / or the drying chamber may be made of a rigid material, especially glass, metal, ceramic, or rigid plastic. In this context, rigid material means a material that is not flexible at the volume flow rate used, so that the volume of the reaction chamber and / or the drying chamber does not change. In an advantageous embodiment, a particle measuring device can be provided which has an input for measuring particle concentrations in gaseous media. The particle measuring device can also include a particle generator according to one of the previously described embodiments, such that the input for testing or calibrating the particle measuring device can be connected to the output or port of the particle generator. This offers the advantage that the particle measuring device can be tested or calibrated, so to speak, during operation. This enables rapid testing or calibration of the particle measuring device without having to interrupt ongoing operation or send the particle measuring device to a suitable testing facility. To simplify testing and calibration of the particle measuring device, the device's input can be equipped with a valve to connect it to the output of the particle generator. Specifically, this valve can be a switchable Y-valve, allowing the particle measuring device's input to be toggled between normal measurement operation and test / calibration mode. Alternatively, the particle measuring device's input can be connected manually to the particle generator's output, for example, via a cable. A particularly compact and user-friendly design is achieved by preferably providing the particle measuring device with a housing in which the particle generator is integrated. This makes it possible to provide a particle measuring device with integrated testing and calibration capabilities. Due to the simple and cost-effective design of the particle generator, this is also economically feasible, so that the expected additional cost for the particle measuring device should be recouped within a very short time through the anticipated savings in testing and calibration. The advantages and features described herein for the method of providing a particle stream also apply to the particle generator for testing or calibrating a particle measuring device and vice versa. Further embodiments and examples of the invention are described in the figures. These show: Fig. 1: a schematic view of the particle measuring device or the method according to the invention; Fig. 2: measurement results of an experimental setup of the particle generator according to the invention regarding volume flow; Fig. 3: measurement results of an experimental setup of the particle generator according to the invention regarding repeatability; Fig. 4: measurement results of an experimental setup of the particle generator according to the invention regarding volume flow; Fig. 5: measurement results of an experimental setup of the particle generator according to the invention regarding volume flow; Fig. 6: measurement results of an experimental setup of the particle generator according to the invention regarding salt concentration; Fig. 7: measurement results of an experimental setup of the particle generator according to the invention regarding salt concentration; Fig. 8: measurement results of an experimental setup of the particle generator according to the invention regarding area dependence; Fig.9 : Measurement results of an experimental setup of the particle generator according to the invention regarding the filling level. The embodiment shown in the figures is for illustrative purposes only and is not intended to be restrictive. It is clear to a person skilled in the art that they can modify the features shown in the figures within the scope of the claims without thereby exceeding the scope of the patent. Fig. 1 shows a schematic view of the particle generator 1 according to the invention. The particle generator 1 has a reaction chamber 2 to which a drying chamber 3 is connected via a connecting line 13. The supply line 11 to the reaction chamber 2 has an air filter 4, which is designed as a HEPA filter. The air filter element of the air filter 4 can be replaced. Inside the reaction chamber, a porous layer 21 is arranged, on which an aqueous NaCl solution with 0.9 vol.% is placed. The outlet of drying chamber 3 is connected via connection 12 to a particle generator 5 under test. The particle generator 5 under test produces a constant volume flow, which is used to convey the air. The air is filtered through the air filter 4 and introduced into the reaction chamber 2 below the porous layer 21 via the supply line 11. The introduced air expands below the porous layer and flows upwards through the porous layer 21 and the aqueous NaCl solution on it, generating numerous small bubbles. These small bubbles burst upon transitioning from the liquid to the gaseous phase, carrying salt particles with them. This particle stream is directed from the reaction chamber 2 to the drying chamber 3 via the connecting line 13, as indicated by the angled arrow. The drying chamber 3 is designed as a diffusion dryer and serves to reduce the moisture content of the particle stream. The dried particle stream 14 is then directed to the particle counter 5 under test via the connecting line 12. Figure 2 shows test results for the sketched experimental setup. In Figure 2, the number of particles per cm³ was measured as a function of the volume flow rate. The graph clearly shows that within the varied volume flow rate between 1.2 l / min and 4.5 l / min, the aerosol flow rate, or particle flow rate, exhibits constant values ​​between 11,000 and 12,000 particles per cm³. Only when the volume flow rate increases above 4.5 l / min does the number of particles per cm³ increase. This means that the experimental setup can be used up to a volume flow rate of 4.5 l / min, regardless of the volume flow rate. The downward-pointing peaks shown in the diagram, where the volume flow drops to 0, result from repeatedly connecting and disconnecting the particle counter 5 to the experimental setup. This was done to demonstrate the repeatability of the measurements. Figure 3 shows a graph in which repeated measurements were performed on the same experimental setup using different flow rates. The setup was optimized for a flow rate between 5 l / min and 10 l / min. A stabilization period of 30 seconds was observed between each measurement, and then the mean values ​​of the measured number concentrations were determined. The flow rate range was varied from 1 to 10 l / min. A total of three measurements were performed. Figure 3 shows that a plateau forms with increasing flow rate, at which the concentration is independent of the flow rate. Figure 4 shows the concentration profile for the same experimental setup as in Figure 3 when the flow rate is further increased. At flow rates higher than the intended 10 l / min, the concentration rises again, and the measurement results are less stable. To further visualize this effect, an experimental setup was chosen for the diagram in Fig. 5, in which a measurement was recorded over a longer period at higher flow rates. The flow rate was increased from 8 l / min to 20 l / min. A greater temporal deviation can be observed at higher flow rates. The increase and abruptness of the concentration curve at excessively high flow rates is primarily due to the formation of foam on the surface at high flow rates. The number of particles per cm³ can be adjusted by varying, for example, the concentration of the salt solution and / or the porosity of the porous layer 21. Increasing the concentration of the salt solution also increases the number of particles in the particle stream. The diagram in Fig. 6 illustrates this. The same experimental setup as shown in Fig. 3 was used, and measurements were taken with different concentrations of NaCl solution. It is evident that increasing the NaCl concentration leads to an increase in the generated particle number concentration. A desired particle number concentration can therefore be set via the NaCl concentration. The relationship between salt concentration and particle number concentration is clearly illustrated in the diagram in Fig. 7. The same experimental setup as shown in the diagram in Fig. 3 was used. Here, the particle number concentration was measured as a function of an NaCl concentration in the range between 0.5% and 5% at a constant flow rate of 9.5 l / min. It can be seen that there is a linear relationship between the NaCl concentration and the particle number concentration. The influence of geometry on particle number concentration is illustrated in the diagram in Fig. 8 for two different-sized areas of the porous layer. The experimental setup was again designed for a flow rate between 5 l / min and 10 l / min. A smaller area of ​​1.8 cm² was measured in comparison to a larger area of ​​3.3 cm² at different flow rates. It is clear that above a flow rate of 5 l / min, the influence of the porous layer area is minimal. Although the measured porous layer area is almost twice as large, the flow rate profile across the concentration is nearly identical, and the concentrations are also very similar. Figure 9 illustrates the influence of the salt solution level on the porous layer as a function of the flow rate. The experimental setup was again designed for a flow rate between 5 l / min and 10 l / min. It becomes clear that in the desired flow rate range of 5 l / min and a salt solution level of 1.5 cm, the influence of the level is negligible. At the very low fill level of 0.8 cm above the porous surface, the concentration is initially higher, presumably because larger droplets are repeatedly flung upwards. At higher flow rates, a portion of the surface remains dry at this low fill level, and therefore the concentration decreases again. Above a fill level of approximately 1.5 cm, the usual behavior resumes, with a plateau in the concentration curve visible from 5 l / min. In any case, the experiments impressively demonstrate that the inventive method and particle generator make it possible to generate a constant particle flow or volume flow in a simple manner, simply by utilizing the suction generated by the particle counter. This makes it possible to provide a simple, cost-effective particle generator that can be used for testing and calibrating particle measuring devices. Reference symbol list 1 Particle generator 11 Supply line 12 Connection line 13 Connecting line 14 Particle flow 2 Reaction vessel 21 Porous layer 22 NaCl solution 3 Drying chamber 4 Air filter 5 Particle counter QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 94 08 604 U1

[0003] DE 198 21 552 C1

[0004] DE 199 42 210 A1

[0005]

Claims

Method for providing a particle stream (14) or aerosol for testing and / or calibrating a particle measuring device (5) comprising the following steps: - providing a reaction chamber (2) with a downstream drying chamber (3) and a connection (12) for connecting a particle measuring device (5) to be tested, wherein the reaction chamber (2) has a porous layer (21) on which a salt solution (22) is arranged, - introducing air into the reaction chamber (2) below the porous layer (21), - passing the air through the porous layer (21) and the salt solution (22) to generate rising bubbles which, upon bursting, release salt particles which are directed into the drying chamber (3) and dried there before the particles flow to the connection (12), or wherein the particles flow to the connection (12) before being directed into the drying chamber (3). Method according to claim 1, characterized in that the air is filtered before being introduced into the reaction chamber (2), in particular filtered by a HEPA filter (4). Method according to claim 1 or 2, characterized in that the particles in the drying chamber (3) are dried by means of a diffusion dryer, or by means of a membrane dryer, or by means of an evaporator tube. Method according to one of claims 1 to 3, characterized in that the volume flow generated by the particle measuring device (5) to be tested is used exclusively for introducing the air and / or for generating the bubbles. Method according to one of the preceding claims, characterized in that a volume flow rate in the range of 0.5 l / min to 20 l / min, preferably in the range of 1 l / min to 5 l / min, or in the range of 5 l / min to 10 l / min, is used for the air. Particle generator (1) for testing or calibrating a particle measuring device (5), in particular for carrying out the method according to one of claims 1 to 5, comprising a supply line (11) for supplying air and a connection line (12) for connecting to a particle measuring device (5) to be tested, further comprising a reaction chamber (2), wherein air is supplied to the reaction chamber (2) via the supply line (11) and the outlet of the reaction chamber (2) can be connected to a particle measuring device (5) via the connection line (12), characterized in that the reaction chamber (2) has a porous layer (21) on which a salt solution (21) is arranged, and that the supply of air to the reaction chamber (2) is located below the porous layer (21), such that the air flows through the porous layer (21) into the salt solution (22) to generate rising bubbles which, upon bursting, release salt particles which flow to the connection line (12). flow. Particle generator according to claim 6, characterized in that a drying chamber (3) is connected downstream of the reaction chamber (2), such that the salt particles formed in the reaction chamber (2) are directed into the drying chamber (3) and dried there before the particles flow to the connecting line (12). Particle generator according to claim 6 or 7, characterized in that the supply line (11) has an air filter (4), in particular a HEPA filter, or is connected to an air filter (4), in particular a HEPA filter. Particle generator according to one of claims 6 to 8, characterized in that the drying chamber (3) is designed as a diffusion dryer, or as a membrane dryer, or as an evaporator tube. Particle generator according to one of claims 6 to 9, characterized in that the porous layer (21) has a porosity in the range of 40 µm to 250 µm, preferably in the range of 100 µm to 160 µm, most preferably a porosity of 100 µm. Particle generator according to one of claims 6 to 10, characterized in that the porous layer (21) has a layer thickness in the range of 200 µm to 10000 µm, preferably in the range of 400 µm to 7500 µm, most preferably in the range of 500 µm to 5500 µm. Particle generator according to one of claims 6 to 11, characterized in that the porous layer (21) has a hydrophobic surface or is designed as a hydrophobic layer. Particle generator according to one of claims 6 to 12, characterized in that the porous layer (21) is made of a ceramic, or of a sintered glass, or of a plastic. Particle generator according to one of claims 6 to 13, characterized in that the salt solution (22) is an aqueous NaCl solution in the range of 0.7% to 1.2%, in particular in the range of 0.8% to 1%, and in particular a 0.9% NaCl solution. Particle generator according to one of claims 6 to 14, characterized in that the volume flow generated by the particle measuring device (5) to be tested is used exclusively for supplying the air and / or generating the bubbles. Particle generator according to one of claims 6 to 15, characterized in that the walls of the reaction chamber (2) and / or the drying chamber (3) are made of a rigid material, in particular of glass, or of metal, or of ceramic, or of a rigid plastic. Particle measuring device (5) with an input for measuring particle loads in gaseous media, characterized in that the particle measuring device (5) has a particle generator (1) according to one of claims 6 to 16, such that the input for testing or calibrating the particle measuring device (5) can be connected to the output (12) or connection (12) of the particle generator (1). Particle measuring device according to claim 17, characterized in that the inlet of the particle measuring device (5) has a valve to connect the inlet of the particle measuring device (5) to the outlet (12) of the particle generator (1). Particle measuring device according to claim 17 or 18, characterized in that the particle measuring device (5) has a housing and that the particle generator (1) is integrated into the housing.

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