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Numerical investigations on electric field characteristics with respect to capacitive detection of free-flying droplets.

Ernst A, Mutschler K, Tanguy L, Paust N, Zengerle R, Koltay P - Sensors (Basel) (2012)

Bottom Line: The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+.The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL.The simulation results are validated by experiments which exhibit good agreement.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany. andreas.ernst@imtek.de

ABSTRACT
In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM), including calculations of an electric field which changes according to the presence of a liquid droplet. The volume of fluid (VOF) method is applied for the simulation of the ejection process of a liquid droplet out of a dispenser nozzle. The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+. The investigated capacitive sensing principle enables to determine the volume of a micro droplet passing the sensor capacitor due to the induced change in capacity. It could be found that single droplets in the considered volume range of 5 nL < V(drop) < 100 nL lead to a linear change of the capacity up to ΔQ < 30 fC. The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.

No MeSH data available.


Computational domain as used for the CFD simulations.
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f3-sensors-12-10550: Computational domain as used for the CFD simulations.

Mentions: The numerical multi-physics model to study the electrical field of the droplet sensor is based on a structured 3D grid consisting of the droplet generator, implemented by a liquid column, and the capacitor electrodes embedded in the sensor support material (bulk material). The computational domain, shown in Figure 3, consists mainly of half shell shaped electrodes, like used for the experimental realisation of the sensor prototype [9] and some air space above and below the capacitor. The liquid column at the top side of the domain represents the liquid phase inside the nozzle of a droplet generator and enables to simulate a droplet dispensing process. The nozzle diameter (w) is 500 μm corresponding to the experimentally used PipeJet™ dispensing system [9]. The variable nozzle length (l) enables to study the capacitive coupling effect in detail and was initially set to 500 μm. The capacitor electrodes are centred underneath the nozzle at a variable distance hvar with an initial height of 2 mm. The geometry of the capacitor featured an inner diameter (d) of 1.2 mm and a trench width (s) of 400 μm, separating the electrodes. The electrodes' height (z) set to 1.6 mm reflecting the prototype's geometry. The electrodes are embedded in bulk material made of FR4 (εr = 4.8). In order to save computation time the mirror symmetry of the problem has been exploited and only half of the spatial geometry was modelled as shown in Figure 3.


Numerical investigations on electric field characteristics with respect to capacitive detection of free-flying droplets.

Ernst A, Mutschler K, Tanguy L, Paust N, Zengerle R, Koltay P - Sensors (Basel) (2012)

Computational domain as used for the CFD simulations.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472843&req=5

f3-sensors-12-10550: Computational domain as used for the CFD simulations.
Mentions: The numerical multi-physics model to study the electrical field of the droplet sensor is based on a structured 3D grid consisting of the droplet generator, implemented by a liquid column, and the capacitor electrodes embedded in the sensor support material (bulk material). The computational domain, shown in Figure 3, consists mainly of half shell shaped electrodes, like used for the experimental realisation of the sensor prototype [9] and some air space above and below the capacitor. The liquid column at the top side of the domain represents the liquid phase inside the nozzle of a droplet generator and enables to simulate a droplet dispensing process. The nozzle diameter (w) is 500 μm corresponding to the experimentally used PipeJet™ dispensing system [9]. The variable nozzle length (l) enables to study the capacitive coupling effect in detail and was initially set to 500 μm. The capacitor electrodes are centred underneath the nozzle at a variable distance hvar with an initial height of 2 mm. The geometry of the capacitor featured an inner diameter (d) of 1.2 mm and a trench width (s) of 400 μm, separating the electrodes. The electrodes' height (z) set to 1.6 mm reflecting the prototype's geometry. The electrodes are embedded in bulk material made of FR4 (εr = 4.8). In order to save computation time the mirror symmetry of the problem has been exploited and only half of the spatial geometry was modelled as shown in Figure 3.

Bottom Line: The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+.The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL.The simulation results are validated by experiments which exhibit good agreement.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany. andreas.ernst@imtek.de

ABSTRACT
In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM), including calculations of an electric field which changes according to the presence of a liquid droplet. The volume of fluid (VOF) method is applied for the simulation of the ejection process of a liquid droplet out of a dispenser nozzle. The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+. The investigated capacitive sensing principle enables to determine the volume of a micro droplet passing the sensor capacitor due to the induced change in capacity. It could be found that single droplets in the considered volume range of 5 nL < V(drop) < 100 nL lead to a linear change of the capacity up to ΔQ < 30 fC. The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.

No MeSH data available.