Test aerosol

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A test aerosol is an aerosol whose properties that are relevant for the intended use are known. It can be made in a number of ways, including a. for calibration of dust and particles measuring devices and to characterize and review -filtering separators such as cabin air filters and filters for air handling systems.

In some technical areas, a test aerosol is also referred to as test or test dust .

Manufacturing

The production of test aerosols is described in the VDI 3491 series of guidelines . It takes place in several steps. The first step is the constant supply of the particulate material, followed by the actual particle production. These steps are often followed by conditioning, such as diluting highly concentrated aerosols or influencing the electrical charge distribution .

Test aerosols can be mono- or polydisperse depending on the manufacturing process . Depending on the application, the particles contained in the aerosol are liquid, solid or partly liquid and partly solid.

Devices for the production of test aerosols are called aerosol generators. You can use the following u. G. Working principles work. It is particularly important that none of the particle substances used may react chemically with the materials of the respective aerosol generator.

Dispersion of solids

When dispersing solids, fine-grained materials are atomized out of a pile by means of mechanical processes . This can be done, among other things, by rotating brushes, atomization or a fluidized bed, in which the entire pile flows through and individual particles are carried away. In all of these processes, an electrically charged aerosol is created through triboelectric effects .

The common materials that are dispersed for the production of test aerosols include aluminum hydroxide , limestone , talc , titanium dioxide and club moss spores as well as synthetic dusts.

Solid dispersers are also used to determine the dustiness of nanomaterials .

Dispersion of liquids

Pure substances , solutions , emulsions or suspensions are used to disperse liquids, which is often also referred to as atomizing or misting .

While pure substances are usually used to generate liquid particles, the drops obtained from solutions, emulsions and suspensions are dried in a drying section, at the end of which an aerosol consisting of solid particles is present. Due to the polarity of most of the liquids used, the particles produced carry electrical charges.

The droplets can be generated by means of ultrasound , among other things , or by means of an oscillating diaphragm - a perforated diaphragm that is made to vibrate via a piezo crystal . Another method is the atomization of liquids with the help of a two-substance nozzle (e.g. Laskin nozzle ), in which a gas volume flow entrains drops from the liquid to be dispersed through shear forces . The electrostatic atomization of solutions, emulsions or suspensions takes place by means of an electrospray aerosol generator .

condensation

Condensation processes are divided into processes with controlled and uncontrolled condensation.

  • When condensation process with controlled condensation are separated from each condensation nuclei generated and a liquid with a low vapor pressure evaporates. Then condensation nuclei and evaporated liquid are brought together and cooled down together.
A condensation process for the production of test aerosols is the process according to Sinclair and La Mer. With common salt, which is frequently used as the basic substance for the production of condensation nuclei, there is the problem that these usually occur as cubic crystals , which are difficult to control by measurement.
  • In the condensation process with uncontrolled condensation, a saturated vapor mixture is cooled from the inside or outside, so that a large number of tiny particles are created that coagulate within fractions of a second . In this way, solid particles can also be produced from platinum oxide .

Chemical reaction

During the production of test aerosols by means of a chemical reaction , a product is produced in the gas phase, the vapor pressure of which is lower than that of its starting materials , so that the substance produced condenses.

Organosilicon compounds are burned to produce nanoparticles from silicon dioxide . The same procedure can be used for the production of nanoparticles from titanium dioxide .

Dilution systems

Dilution systems are used to reduce the concentration of a test aerosol . Reasons for this can, for example, be the avoidance of coagulation or the adaptation to the measuring range of a measuring method. In the dilution system, the aerosol is mixed with a particle-free gas in a defined manner; Common dilution systems filter a partial flow of the aerosol and then recombine it with the unfiltered partial flow, or they mix the aerosol with particle-free air.

The dilution factor is used to describe the dilution process; it is the ratio of the concentrations of the undiluted aerosol and the diluted aerosol. Dilution factors are usually between 5 and 100. However, higher dilution factors can also be achieved by connecting them in series. The dilution factor depends on the particle size.

literature

  • VDI 3491 Part 1: 2016-07 Measurement of particles; Manufacturing process for test aerosols; Basics and overview (Measurement of particles; Methods for generating test aerosols; Principles and overview) . Beuth Verlag, Berlin, ( summary and table of contents online )

Individual evidence

  1. ↑ Achim Breidenbach, Frank Schmidt, Hartmut Finger, Stefan Haep: Testing of motor vehicle cabin filters - diesel soot as test and loading aerosol . In: Hazardous substances - cleanliness. Air. 69, No. 5, 2009, ISSN  0949-8036 , pp. 189-193.
  2. ↑ Frank Schmidt, Achim Breidenbach, Thomas Engelke, Eckhard Däuber: The efficiency of filters for air conditioning systems with increasing load - comparison of filters from operation and laboratory tests. In: Hazardous substances - cleanliness. Air. 76, No. 3, 2016, ISSN  0949-8036 , pp. 92-96.
  3. ↑ VDI 3491 sheet 1: 2016-07 Measurement of particles; Manufacturing process for test aerosols; Basics and overview (Measurement of particles; Methods for generating test aerosols; Principles and overview) . Beuth Verlag, Berlin, p. 2.
  4. ↑ VDI 3677 sheet 2: 2004-02 Filtering separators; Depth fiber filters (filtering separators). Beuth Verlag, Berlin. P. 6.
  5. ↑ VDI 3491 sheet 9: 1989-09 measurement of particles; Production of test aerosols by means of a brush dispenser (Particulate matter measurement; generation of test aerosols with a rotating brush generator). Beuth Verlag, Berlin, p. 3.
  6. ↑ VDI 3491 sheet 8: 1989-09 measurement of particles; Production of test aerosols from powdery heaps using a belt feeder (Particulate matter measurement; generation of test aerosols from powders using a belt feed unit). Beuth Verlag, Berlin, p. 3.
  7. ^ A b William C. Hinds: Dry-Dispersion Aerosol Generators. In: Klaus Willeke (Ed.): Generation of Aerosols and Facilities for Exposure Experiments. Ann Arbor Science Publishers, Michigan 1980, ISBN 0-250-40293-9 , pp. 171-189.
  8. ↑ VDI 3491 sheet 10: 1990-01 measurement of particles; Production of test aerosols from heaps of fibrous particles using a vibrating bed aerosol generator (Particulate matter measurement; generation of test aerosols from fibrous powders using a vibrating bed aerosol generator). Beuth Verlag, Berlin, p. 2.
  9. ↑ VDI 3491 sheet 3: 2018-03 measurement of particles; Manufacturing process for test aerosols; Dispersion of piles and solids (Measurement of particles; Methods for generating test aerosols; Dispersing solid materials). Beuth Verlag, Berlin, p. 7.
  10. ↑ Dirk Dahmann: The dustiness of nanomaterials - a criterion for safe handling. In: Hazardous substances - cleanliness. Air . 73, No. 7/8, 2013, ISSN  0949-8036 , pp. 307-310.
  11. ↑ VDI 3491 sheet 11: 1996-06 measurement of particles; Production of test aerosols using ultrasonic atomizers (Particulate matter measurement; generation of test aerosols using ultrasonic atomizers). Beuth Verlag, Berlin, p. 2.
  12. ↑ VDI 3491 sheet 13: 1990-01 measurement of particles; Production of test aerosols using a vibrating orifice aerosol generator (Particulate matter measurement; Generation of test aerosols using a vibrating-orifice generator). Beuth Verlag, Berlin, p. 2.
  13. ↑ VDI 3491 sheet 2: 2017-01 measurement of particles; Manufacturing process for test aerosols; Dispersion of liquids (Measurement of particles; Methods for generating test aerosols; Dispersing liquids). Beuth Verlag, Berlin, pp. 9-10.
  14. ↑ VDI 3491 sheet 2: 2017-01 measurement of particles; Manufacturing process for test aerosols; Dispersion of liquids (Measurement of particles; Methods for generating test aerosols; Dispersing liquids). Beuth Verlag, Berlin, pp. 14-16.
  15. ↑ VDI 3491 sheet 4: 1980-12 measurement of particles; Manufacturing process for test aerosols; Aerosol generator according to Sinclair and La Mer . VDI publishing house, Düsseldorf. P. 2.
  16. ↑ Gerhard Kasper, Axel Berner: A generator for producing extremely monodisperse table salt aerosols. In: Dust - cleanliness. Air . 38, No. 5, 1978, ISSN  0949-8036 , pp. 183-186.
  17. ↑ VDI 3491 sheet 6: 1980-12 measurement of particles; Manufacturing process for test aerosols; Platinum oxide aerosol generator. VDI publishing house, Düsseldorf. P. 1.
  18. ↑ a b c Leander Mölter, Martin Schmidt: Dilution systems for test aerosols: Basics and possible applications. In: Hazardous substances - cleanliness. Air. 78, No. 3, 2018, ISSN  0949-8036 , pp. 88-94.
  19. ↑ a b c d e VDI 3491 sheet 15 Measurement of particles; Manufacturing process for test aerosols; Dilution systems with continuous volumetric flow (Particulate matter measurement; Generation of test aerosols; Dilution systems with continuous volumetric flow). Beuth Verlag, Berlin, pp. 2–3.