VANAM multi-compartment aerosol depletion test M4 with mixed aerosol material (soluble and insoluble), and resuspension by hydrogen burn

This report presents the experimental data of VANAM experiment M4 which was performed in two parts: as the M4 main test, and the add-on resuspension test. The M4 main test covers the first three of the above items. This test was performed under the same thermodynamic conditions as the two previous experiments, M2' and M3, but with a mixed aerosol consisting of a soluble, hygroscopic component (NaOH) and an insoluble SnO2 component. The aim of the add-on resuspension test is to investigate to which extent settled aerosol material can be resuspended by an H2 deflagration. The most important results of the two tests are: The hygroscopic component of the aerosol material, NaOH, enhances condensation of water vapour at the aerosol particles, resulting in faster aerosol depletion. The depletion rates of the mixed NaOH-SnO2 aerosol in the M4 main test were at least as high as the depletion rates of the single-component NaOH aerosol in experiment M3 and much higher than those of the SnO2 aerosol in experiment M2'. Locally different thermal-hydraulic conditions in the various zones of the multi-compartment containment geometry result in a non-uniform aerosol depletion process. From this, differences in local aerosol concentration develop during the M4 main test, coming up to 2.5 orders of magnitude (i.e. factor 1:300). Hydrogen deflagrations in a branched multi-compartment geometry proceed significantly slower and produce only negligible local pressure differentials compared to the deflagration effects (jet ignition) observed in basic multi-compartment deflagration tests using a simple chain of compartments. Even a moderate H2 deflagration (see above) still yields a pronounced resuspension of settled aerosol material. The aerosol resuspended shows a very wide size distribution with a remarkably high fine fraction remaining suspended over a very long period of time. (orig.)