32
3 Simulating Droplet Microfluidic Networks
frames. This switch uses the effect that the presence of a droplet at the input
of a narrow channel causes a blocking of the flow into this channel (i.e., the
droplet clogs the channel). Figure 3.5a shows a state where the droplet in the
“Control region” clogs the flow into the channel downwards. This cut of the flow
controls the second droplet in the “Switching region,” i.e., this cut of the flow
routes this droplet into the channel to the east, which is depicted by the arrow
in Fig. 3.5a. In contrast, Fig. 3.5b shows another state where the droplet in the
“Control region” does not clog the flow into the channel downwards. This causes
the second droplet in the “Switching region” to enter the channel to the north,
which again is depicted by the arrow in Fig. 3.5b. All details how this switch
exploits the clogging of the flow in order to route droplets are described in [11].
However, in order to simulate these operations, the simulation of further physical
phenomena is required, namely whether droplets
• are trapped in the microfluidic network,
• are squeezed through any gap, or
• are clogging a channel.
Using the “basic” framework introduced in the previous section, none of these
phenomena and, hence, none of the operations can properly be simulated. Since
also all related works proposed thus far (i.e., the ones mentioned above [4, 7, 21, 37,
40, 67, 101, 105, 106, 109]) do not provide support for that, the practically relevant
applications discussed in [11, 13] cannot be simulated on the 1D analysis model
thus far.
3.3.3 Simulation Support for New Phenomena
In order to support these physical phenomena and, by this, allow for the simulation
of practically relevant applications such as those discussed above, the introduced
framework is extended with new equations and events. These new events demonstrate how the presented framework allows for easy extensions—here in the form of
the following three events:
Droplet Trapped Event
A droplet is trapped in the microfluidic network when it stops in an edge. As long as
a trapped droplet is not pushed further (e.g., by a change of the pressure), it stays in
the edge (potentially until the end of the simulation). In the framework, this event is
triggered when a droplet is contained in an edge (i.e., a channel or module), which
does not have a successor edge through which the droplet can leave this edge (cf. the
next event implements the check whether a droplet is pushed out of an edge).
3 Simulating Droplet Microfluidic Networks
frames. This switch uses the effect that the presence of a droplet at the input
of a narrow channel causes a blocking of the flow into this channel (i.e., the
droplet clogs the channel). Figure 3.5a shows a state where the droplet in the
“Control region” clogs the flow into the channel downwards. This cut of the flow
controls the second droplet in the “Switching region,” i.e., this cut of the flow
routes this droplet into the channel to the east, which is depicted by the arrow
in Fig. 3.5a. In contrast, Fig. 3.5b shows another state where the droplet in the
“Control region” does not clog the flow into the channel downwards. This causes
the second droplet in the “Switching region” to enter the channel to the north,
which again is depicted by the arrow in Fig. 3.5b. All details how this switch
exploits the clogging of the flow in order to route droplets are described in [11].
However, in order to simulate these operations, the simulation of further physical
phenomena is required, namely whether droplets
• are trapped in the microfluidic network,
• are squeezed through any gap, or
• are clogging a channel.
Using the “basic” framework introduced in the previous section, none of these
phenomena and, hence, none of the operations can properly be simulated. Since
also all related works proposed thus far (i.e., the ones mentioned above [4, 7, 21, 37,
40, 67, 101, 105, 106, 109]) do not provide support for that, the practically relevant
applications discussed in [11, 13] cannot be simulated on the 1D analysis model
thus far.
3.3.3 Simulation Support for New Phenomena
In order to support these physical phenomena and, by this, allow for the simulation
of practically relevant applications such as those discussed above, the introduced
framework is extended with new equations and events. These new events demonstrate how the presented framework allows for easy extensions—here in the form of
the following three events:
Droplet Trapped Event
A droplet is trapped in the microfluidic network when it stops in an edge. As long as
a trapped droplet is not pushed further (e.g., by a change of the pressure), it stays in
the edge (potentially until the end of the simulation). In the framework, this event is
triggered when a droplet is contained in an edge (i.e., a channel or module), which
does not have a successor edge through which the droplet can leave this edge (cf. the
next event implements the check whether a droplet is pushed out of an edge).