The term isokinetic sampling or Isokinetic sampling ( English Isokinetic sampling ) refers to a method for sampling of flowing fluids , in which the current flowing in the sample collector fluid comprises the same speed as the fluid in the immediate vicinity. This method, which is used both for gases and liquids, is intended to ensure that the number of particles in the fluid to be sampled is not falsified during sampling.
In emission measurement technology , a partial flow is extracted from the exhaust gas flows of larger systems using a sampling probe and fed to the dust measuring device . In order to prevent fractionation from taking place and the measurement result being falsified, the suction must be isokinetic (i.e. at the same speed). In practice this is the ideal case. In order to ensure suction at the same speed, the static pressures in the gas flow and in the sampling line are compared and regulated with one another during suction using a so-called zero pressure probe .
If during sampling the suction is carried out at a speed greater than the flow velocity ( hyperkinetic sampling ), exhaust gas is sucked in that should have flowed around the sampling probe. Due to their inertia , the particles contained in the exhaust gas can not follow the change in flow direction that is forced on them. The measured dust content is too low. When aspirating at a speed less than the flow rate ( hypokinetic sampling ), exhaust gas that should have been sucked in flows around the sampling probe. Due to their inertia, particles cannot follow the deflection and get into the probe. The measured dust content is too high. The error if the suction speed is too high is smaller than if the suction speed is lower to the same extent. Accordingly, the isokinetic ratio permissible for dust emission measurements - the ratio of the gas velocities of the extracted partial flow to the main volume flow - is between 95% and 115%.
In measurement technology, the term isokinetic ratio is used as a parameter for compliance with isokinetic sampling.
The same applies to liquids to be sampled.
- ↑ DIN EN ISO 29461-1: 2014-03 Air filter inlet systems of rotary machines; Test procedure; Part 1: Static filter elements (ISO 29461-1: 2013); German version EN ISO 29461-1: 2013. Beuth Verlag, Berlin. P. 13.
- ↑ VDI 2066 sheet 1: 2006-11 measurement of particles; Dust measurements in flowing gases; Gravimetric determination of dust load (Particulate matter measurement; Dust measurement in flowing gases; Gravimetric determination of dust load). Beuth Verlag, Berlin. P. 7.
- ↑ DIN 38402-15: 2010-04 German standard methods for water, waste water and sludge testing; General information (group A); Part 15: Sampling from rivers (A 15). Beuth Verlag, Berlin. P. 7.
- ↑ James H. Vincent: Aerosol Sampling - Science, Standards, Instrumentation and Applications . John Wiley & Sons, Chichester 2007, ISBN 978-0-470-02725-7 , p. 237.
- ↑ Jens Linnenberg, Georg Schwedt, Klaus Broschinski: Long-term sampling of particle-bound and filter-permeable heavy metal emissions in pure gases from technical furnaces. In: Hazardous substances - cleanliness. Air . 60, No. 5, 2000, ISSN 0949-8036 , pp. 223-227.
- ↑ J. H. Vincent: Aerosol Sampling - Science and Practice, Wiley & Sons, Chichester 1989.
- ^ Günter Baumbach: Air pollution control. Springer-Verlag Berlin, Heidelberg, New York, 2nd edition 1992, ISBN 3-540-55078-X , p. 206.
- ↑ a b VDI 2066 sheet 1: 2006-11 measurement of particles; Dust measurements in flowing gases; Gravimetric determination of dust load (Particulate matter measurement; Dust measurement in flowing gases; Gravimetric determination of dust load) . Beuth Verlag, Berlin. P. 9.