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D. Markauskas and H. Kruggel-Emden
lower bulk mass is used. This results in a more steadily decreasing retained mass on
the screen allowing for more accurate modeling by the screening process models as
a consequence. For both cases, a varying stroke angle and a mass variation, models
β and θ show particularly suitable results due to their functional forms, which can
take varying mass depletions into account.
4.3 Discontinuous Screening with Moisture
To reliably go the step from DEM modelling of dry screening to screening under
moist conditions requires the validation of the model extensions described in Sect. 2.4
under real screening conditions. Therefore, a validation of the used DEM model under
these conditions has been performed shading light on the related subprocesses and
their linkage to liquid bridge formation, stressing and rupture (see [29]). Results on
this are presented in Sect. 4.3.2 by comparing insights obtained from batch screening
experiments and simulations. The investigated setup is outlined in Sect. 4.3.1. The
successful validation allows the application of the extended screening models from
Sect. 3.2.4 (see [123]) in the final Sect. 4.3.3.
4.3.1 Experimental and Numerical Setup
A batch screening apparatus, which can be applied for dry and wet screening
(see Fig. 19), is used for the experiments and the modelling in this study. The screen
apparatus is a modified “Haver and Boecker EML digital plus” batch screen tower
with a circular screen surface, which is on top additionally equipped with a feed bin to
ensure that the particles in experiments and simulations reach the screen surface at the
same time and to ensure that the screen excitation is already in a continuous motion
when particles get into the contact with the screening surface. In addition, there is an
outlet below the screen to measure the particle passage through the apertures when
they reach the collecting bin placed on a balance. Above the outlet various screens
with different aperture sizes can be places. In the study performed here, one screen
surface is applied in each case with the aperture sizes adjusted to the particle sizes
as presented in Table 6. The screen is operated with a fixed frequency of 50.6 Hz;
two amplitudes of A = 1 mm and A = 0.8 mm are considered. For details on the
elliptical stroke motion of the screen surface see [29].
In the investigation, POM and glass spheres are applied in three different size
classes. They are assumed to be ideal spheres of d 1 = 5 mm, d 2 = 7 mm, d 3 = 10 mm
in a first and d 1 = 3 mm, d 2 = 5 mm and d 3 = 7 mm in a second configuration.
In both configurations, the particles and the aperture size are related as d 1 < d 2 < a
< d 3 , where a is the size of an aperture. To perform the experiments POM spheres
are filled into the feed bin with a mass of m p = 3m pi = 3 × 250 g = 750 g. The
amount of glass spheres is chosen to be volume equivalent with the POM spheres
giving a mass of m p ≈ 1410 g (see Table 6). For both materials, three different liquid
D. Markauskas and H. Kruggel-Emden
lower bulk mass is used. This results in a more steadily decreasing retained mass on
the screen allowing for more accurate modeling by the screening process models as
a consequence. For both cases, a varying stroke angle and a mass variation, models
β and θ show particularly suitable results due to their functional forms, which can
take varying mass depletions into account.
4.3 Discontinuous Screening with Moisture
To reliably go the step from DEM modelling of dry screening to screening under
moist conditions requires the validation of the model extensions described in Sect. 2.4
under real screening conditions. Therefore, a validation of the used DEM model under
these conditions has been performed shading light on the related subprocesses and
their linkage to liquid bridge formation, stressing and rupture (see [29]). Results on
this are presented in Sect. 4.3.2 by comparing insights obtained from batch screening
experiments and simulations. The investigated setup is outlined in Sect. 4.3.1. The
successful validation allows the application of the extended screening models from
Sect. 3.2.4 (see [123]) in the final Sect. 4.3.3.
4.3.1 Experimental and Numerical Setup
A batch screening apparatus, which can be applied for dry and wet screening
(see Fig. 19), is used for the experiments and the modelling in this study. The screen
apparatus is a modified “Haver and Boecker EML digital plus” batch screen tower
with a circular screen surface, which is on top additionally equipped with a feed bin to
ensure that the particles in experiments and simulations reach the screen surface at the
same time and to ensure that the screen excitation is already in a continuous motion
when particles get into the contact with the screening surface. In addition, there is an
outlet below the screen to measure the particle passage through the apertures when
they reach the collecting bin placed on a balance. Above the outlet various screens
with different aperture sizes can be places. In the study performed here, one screen
surface is applied in each case with the aperture sizes adjusted to the particle sizes
as presented in Table 6. The screen is operated with a fixed frequency of 50.6 Hz;
two amplitudes of A = 1 mm and A = 0.8 mm are considered. For details on the
elliptical stroke motion of the screen surface see [29].
In the investigation, POM and glass spheres are applied in three different size
classes. They are assumed to be ideal spheres of d 1 = 5 mm, d 2 = 7 mm, d 3 = 10 mm
in a first and d 1 = 3 mm, d 2 = 5 mm and d 3 = 7 mm in a second configuration.
In both configurations, the particles and the aperture size are related as d 1 < d 2 < a
< d 3 , where a is the size of an aperture. To perform the experiments POM spheres
are filled into the feed bin with a mass of m p = 3m pi = 3 × 250 g = 750 g. The
amount of glass spheres is chosen to be volume equivalent with the POM spheres
giving a mass of m p ≈ 1410 g (see Table 6). For both materials, three different liquid