Browsing by Subject "Flow of fluids"

Now showing 1 - 6 of 6

Open Access
Boundary element method for optical force calibration in microfluidic dual-beam optical trap
(SPIE, 2015) Solmaz, Mehmet E.; Çetin, Barbaros; Baranoglu, B.; Serhatloglu, Murat; Bıyıklı, Necmi
The potential use of optical forces in microfluidic environment enables highly selective bio-particle manipulation. Manipulation could be accomplished via trapping or pushing a particle due to optical field. Empirical determination of optical force is often needed to ensure efficient operation of manipulation. The external force applied to a trapped particle in a microfluidic channel is a combination of optical and drag forces. The optical force can be found by measuring the particle velocity for a certain laser power level and a multiplicative correction factor is applied for the proximity of the particle to the channel surface. This method is not accurate especially for small microfluidic geometries where the particle size is in Mie regime and is comparable to channel cross section. In this work, we propose to use Boundary Element Method (BEM) to simulate fluid flow within the micro-channel with the presence of the particle to predict drag force. Pushing experiments were performed in a dual-beam optical trap and particlea's position information was extracted. The drag force acting on the particle was then obtained using BEM and other analytical expressions, and was compared to the calculated optical force. BEM was able to predict the behavior of the optical force due to the inclusion of all the channel walls. © 2015 SPIE.
Open Access
Experimental characterization of capacitive micromachined ultrasonic transducers
(IEEE, 2007) Ölçüm, Selim; Atalar, Abdullah; Köymen, Hayrettin; Oğuz, Kağan; Şenlik, Muhammed N.
In this paper, capacitive micromachined ultrasonic transducers are fabricated using a sacrificial surface micromachining process. A testing procedure has been established in order to measure the absolute transmit and receive sensitivity spectra of the fabricated devices. The experiments are performed in oil. Pulse-echo experiments are performed and the results are compared to the pitch-catch measurements using calibrated transducers.
Open Access
Finite element modeling of micro-particle separation using ultrasonic standing waves
(ASME, 2014) Büyükkoçak, S.; Çetin, Barbaros; Özer, M. B.
Acoustophoresis which means separation of particles and cells using acoustic waves is becoming an intensive research subject. The method is based on inducing an ultrasonic compression standing wave inside a microchannel. A finite element approach is used to model the acoustic and electro-mechanical behavior of the piezoelectric material, the micro-channel geometry as well as the fluid inside the channel. The choices of silicon and PDMS materials are investigated as the chip materials for the resonator. A separation channel geometry which is commonly used in the literature is implemented in this study and the fluid flow inside the microchannel geometry is simulated using computational fluid dynamics. The acoustic field inside the fluid channel is also be simulated using the finite element method. For the separation process to be successful micro-particles of different diameter groups should end up in different channels of the micro-separator. In order to simulate real life scenarios, each particle size group have a size distribution within themselves. For realistic simulation results the particles will be released into the micro separator from a different starting locations (starting location distribution). The results of this Monte-Carlo based finite element simulation approach will be compared with the reported experimental results.
Open Access
Numerical analysis of mixing performance in sinusoidal microchannels based on particle motion in droplets
(Springer Verlag, 2015) Özkan, A.; Erdem, E. Y.
This numerical study was conducted to analyze and understand the parameters that affect the mixing performance of droplet-based flow in sinusoidal microfluidic channels. Finite element analysis was used for modeling fluid flow and droplet formation inside the microchannels via tracking interface between the two heterogeneous fluids along with multiple particle trajectories inside a droplet. The solutions of multiphase fluid flow and particle trajectories were coupled with each other so that drag on every single particle changed in every time step. To solve fluid motion in multiphase flow, level set method was used. Parametric study was repeated for different channel dimensions and different sinusoidal channel profiles. These results were compared with mixing in droplets inside a straight microchannel. Additionally, tracking of multiple particles inside a droplet was performed to simulate the circulating flow profile inside the droplets. Based on the calculation of the dispersion length, particle trajectories, and velocities inside droplets, it is concluded that having smaller channel geometries increases the mixing performance inside the droplet. This also shows that droplet-based fluid flow in microchannels is very suitable for performing chemical reactions inside droplets as it will occur faster. Moreover, narrower and sinusoidal microchannels showed better dispersion length difference compared to straight and wider microchannels.
Open Access
Numerical modeling of ultrasonic particle manipulation for microfluidic applications
(Springer Verlag, 2014) Büyükkoçak S.; Özer, M. B.; Çetin B.
A numerical simulation methodology for ultrasonic particle/cell separation and cell washing processes is introduced and validated by comparing with the results from the literature. In this study, a finite element approach is used for modeling fluid flow in a microchannel and analytical relations are utilized for the calculation of the ultrasonic radiation forces. The solutions in acoustic and fluidic domains are coupled, and the particle separation under the influence of ultrasonic waves is numerically simulated. In order to simulate the cell washing process, diffusion and fluid dynamics solutions are coupled and solved. A Monte Carlo approach is chosen where statistical distributions are implemented in the simulations. Uniform distributions for the starting locations of particles/cells in the microchannel and normal distributions for the size of the particles are used in numerical simulations. In each case, 750 particles are used for the simulation, and the performance of separation process is evaluated by checking how many microparticles resulted in the targeted outlet channels. Channel geometries for the numerical simulations are adapted from the experimental studies in literature, and comparison between the reported experimental results and the numerical estimations is performed. It has been observed that the numerical estimations and experimental results from the literature are in good agreement, and the proposed methodology may be implemented as a design tool for ultrasonic particle manipulation for microfluidic applications. © 2014, Springer-Verlag Berlin Heidelberg.
Open Access
A versatile plug microvalve for microfluidic applications
(Elsevier, 2017-10) Guler, M. T.; Beyazkilic, P.; Elbuken, C.
Most of the available microvalves include complicated fabrication steps and multiple materials. We present a microvalve which is inspired from macroplug valves. The plug microvalve is fabricated by boring a hole through a rigid cylindrical rod and inserting it through a microfluidic chip. It simply functions by rotating the rod which aligns or misaligns the valve port with the microchannel. The rod is made up of a rigid material for applying the valve to an elastic polydimethylsiloxane (PDMS) microchannel. The valve can also be used for a rigid channel by inserting the rod into an elastic tubing. Therefore, the presented microvalve can be used for both elastomeric and thermoplastic channels. The plug microvalve can be applied to a prefabricated microchannel and does not require modification of the mold design. We have verified the repeatability and robustness of the valve by repetitive operation cycles using a servo motor. The plug microvalve is adaptable to numerous microfluidic applications. We have shown three modes of operation for the microvalve including fluid flow control across multiple intersecting channels. Integrating the microvalve to some commonly used microfluidic designs, we demonstrated the versatility and the practicality of the microvalve for controlling flow focusing, microdroplet sorting and rapid chemical agent detection. This low-cost microvalve significantly minimizes the prototyping time for microfluidic systems.