Application and function

For the dust measurement by means of cascade impactors the different inertia of particles is used. Thereby several combinations of nozzle plates and deflectors are switched successively. If the dust loaded gas flow meets the deflector the bigger (inerter) particles are separated, whereas the smaller onces follow the gas flow. The nozzle diameter reducing from stage to stage leads to an increase of the gas velocity and therefore to separation of the single corn fractions. Before the exit there is an absoulte filter which absorbs the remaining dust content of the gas. Similar to the gravimetric measurement the cascade impactor has to be pretreated before executing the measurement in order to get respective faultless measuring values (see also DMS 01). The absolute filter is dried, equilibrised (exsiccator) and weighed. In addition it must be secured that before the measurement all elements are cleaned. Then the net weight of the nozzle plates and deflectors belonging together of each stage should be determined and documented. The structure of the sampling can be basically compared with the gravimetric dust measurement. The cascade impactor FIF 7 is a device with 7 separation stages. In the single stages there are hole circles (nozzles) which have per stage the same diameter reducing towards the flow direction. By that the gas velocity increases from separation stage to separation stage in a defined way. A circular dust collecting room formed as blind hole on the deflector is assigned to each opening of the nozzle exit. There the particles are deposited according to their separation characteristics. The decisive advantage of the device construction is not only the low wall losses whereby the collection of dust separated in total is relieved. A use of filter or adhesive mediums is not necessary so that no material changes occur during the measurements. In addition the device features a simple and handy, but robust design. So it is especially suitable for the measurement directly in the exhaust gas stream (In-stack-arrangement). The FIF 7 can be combined with common measuring technology for the gravimetric dust measurement. In order to meet the different measuring gas conditions, different materials e.g. stainless steel of titan are available. The suction rate of the FIF 7 is limited by a critical nozzle at max. 3 m³/h. The sampling times to be realised with the device orientate at conventional dust measuring devices. The evaluation of the measurements is done according to VDI 2066 page 5.

Specifications