3.3 Advanced Simulation Framework
31
3.3.2 Unsupported Phenomena
The basic working principle described in the previous section only allows for
simulating droplets flowing through networks consisting of channels which branch
and merge (exploiting the fact that a droplet always flows into the branch with
the highest instantaneous volumetric flow rate). But this approach does not yet
allow to simulate important operations as therefore used physical phenomena are
unsupported. In the following, two operations are presented, which cannot be
simulated thus far because they are based on unsupported phenomena:
• Trapping of droplets is an important operation in experiments because trapped
droplets allow to precisely control the reaction time or to observe particle–
particle interactions [13, 124]. Figure 3.4 shows a passive realization (i.e., only
hydrodynamic effects and no external components for control are used) of two,
connected trapping wells, which have been proposed in [13]. If this trapping
well does not yet contain a droplet, the first arriving droplet is trapped. As soon
as it contains a droplet, all following droplets do not enter the trapping well
anymore and are bypassed. Therefore, the design ensures that the trapped droplet
clogs the two narrow channels so that the flow into the bypass channel is higher.
Additionally, in order to analyze the trapped droplet, it must not be squeezed
through the narrow channels.
• Droplet switching allows to control the path of droplets. In [11], the switch shown
in Fig. 3.5 has recently been proposed, which is capable to route multi-droplet
Fig. 3.4 Realization of a passive trapping well [13]
(a) The droplet in the “Control region” clogs
the flow into the “Control channel”, which
routes the droplet in the “Switching region”
into the channel to the east
(b) The droplet in the “Control region” does
not clogs the flow into the “Control channel”,
which routes the droplet in the “Switching
region” into the channel to the north
Fig. 3.5 Multi-droplet switch proposed in [11]
31
3.3.2 Unsupported Phenomena
The basic working principle described in the previous section only allows for
simulating droplets flowing through networks consisting of channels which branch
and merge (exploiting the fact that a droplet always flows into the branch with
the highest instantaneous volumetric flow rate). But this approach does not yet
allow to simulate important operations as therefore used physical phenomena are
unsupported. In the following, two operations are presented, which cannot be
simulated thus far because they are based on unsupported phenomena:
• Trapping of droplets is an important operation in experiments because trapped
droplets allow to precisely control the reaction time or to observe particle–
particle interactions [13, 124]. Figure 3.4 shows a passive realization (i.e., only
hydrodynamic effects and no external components for control are used) of two,
connected trapping wells, which have been proposed in [13]. If this trapping
well does not yet contain a droplet, the first arriving droplet is trapped. As soon
as it contains a droplet, all following droplets do not enter the trapping well
anymore and are bypassed. Therefore, the design ensures that the trapped droplet
clogs the two narrow channels so that the flow into the bypass channel is higher.
Additionally, in order to analyze the trapped droplet, it must not be squeezed
through the narrow channels.
• Droplet switching allows to control the path of droplets. In [11], the switch shown
in Fig. 3.5 has recently been proposed, which is capable to route multi-droplet
Fig. 3.4 Realization of a passive trapping well [13]
(a) The droplet in the “Control region” clogs
the flow into the “Control channel”, which
routes the droplet in the “Switching region”
into the channel to the east
(b) The droplet in the “Control region” does
not clogs the flow into the “Control channel”,
which routes the droplet in the “Switching
region” into the channel to the north
Fig. 3.5 Multi-droplet switch proposed in [11]