Browsing by Author "Atay, Atakan"

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Open Access
DC-electrokinetic motion of colloidal cylinder(s) in the vicinity of a conducting wall
(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-06) Atay, Atakan; Beşkök, A.; Çetin, Barbaros
The boundary effects on DC-electrokinetic behavior of colloidal cylinder(s) in the vicinity of a conducting wall is investigated through a computational model. The contribution of the hydrodynamic drag, gravity, electrokinetic (i.e., electrophoretic and dielectrophoretic), and colloidal forces (i.e., forces due to the electrical double layer and van der Waals interactions) are incorporated in the model. The contribution of electrokinetic and colloidal forces are included by introducing the resulting forces as an external force acting on the particle(s). The colloidal forces are implemented with the prescribed expressions from the literature, and the electrokinetic force is obtained by integrating the corresponding Maxwell stress tensor over the particles' surfaces. The electrokinetic slip-velocity together with the thin electrical double layer assumption is applied on the surfaces. The position and velocity of the particles and the resulting electric and flow fields are obtained and the physical insight for the behavior of the colloidal cylinders are discussed in conjunction with the experimental observations in the literature.
Open Access
DC-electrokinetic motion of colloidal cylinder(s) in the vicinity of a wall
(2021-07) Atay, Atakan
DC-electrokinetic behavior of colloidal particles in the vicinity of a conducting/non-conducting planar boundary is investigated using an inhouse boundary element method (BEM) based solver in MATLAB R􀀁 environment. In the model, contribu-tion of hydrodynamic drag, electrokinetic (electrophoretic and dielectrophoretic), and colloidal forces (van der Waals and EDL) to over-all particle velocity is com-puted. The electrokinetic and colloidal forces are calculated using prescribed relations obtained from the literature. These forces are then included in the model as external forces acting on the particles. The electrokinetic (EK) forces are obtained by integrating Maxwell stress tensor (MST) over particles’ surfaces. Throughout this work, a thin EDL assumption is made. Position and velocities of the particles along with resulting ﬂow and electric ﬁelds are computed. Over-all, results are compared with experimental observations and a general discussion regarding colloidal behavior is made.
Open Access
Flow rate-controlled pipetting for microfluidics: second-generation flexible hydraulic reservoir (FHRv2)
(Springer, 2021-01-04) Atay, Atakan; Topuz, Alper; Sarıarslan, Büşra; Yıldırım, E.; Charmet, J.; Couling, K.; Çetin, Barbaros
A critical component of microfluidic technology is the fluid pumping mechanism. Syringe and pressure pumps are typically used in the lab environment; however, their operations generate considerable dead volume that is often larger than the volume of the chip itself, leading to considerable waste of precious sample. As an alternative, pipetting allows for precise liquid dispensing with zero dead volume; however, it has a limited flow control. Recently, we have introduced a low-cost sample loading interface with zero dead-volume named flexible hydraulic reservoir (FHR). In this study, we present a second-generation FHRv2 that combines continuous pumping, zero-dead volume and the versatility of pipetting. The performance of FHRv2 is tested against a syringe pump at flow rates ranging between 20 and 60 μL/min. It demonstrated smoother operation and identical transient time to reach steady flow rate as confirmed by a mathematical model developed for the occasion. Importantly, we also demonstrate that the FHRv2 prevents sedimentation-induced artifacts typically encountered in typical syringe pumps when dispensing particles. Finally, we demonstrate the fabrication of the FHRv2 concept with injection molding using a 3D-printed mold. Overall, our FHRv2 offers a low-cost and versatile solution for zero-volume liquid handling in microfluidic devices.
Open Access
Performance assessment of commercial heat pipes with sintered and grooved wicks under natural convection
(TIBTD, 2019) Atay, Atakan; Sarıarslan, Büşra; Kuşçu, Yiğit F.; Saygan, S.; Akkuş, Y.; Gürer, A. T.; Çetin, Barbaros; Dursunkaya, Z.
Heat pipes are widely used in thermal management of high heat flux devices due to their ability of removing high heat loads with small temperature differences. While the thermal conductivity of standard metal coolers is approximately 100–500 W/m.K, effective thermal conductivities of heat pipes, which utilize phase-change heat transfer, can reach up to 50,000 W/m.K. In industrial applications, commercially available heat pipes are commonly preferred by thermal engineers due to their low cost and versatility. Thermal performance of a heat pipe is functions of heat pipe type and operating conditions. Selection of the appropriate heat pipe complying with the operating conditions is critical in obtaining satisfactory thermal management. One key point for the utilization of heat pipes is to avoid dryout operation condition in which heat pipes operate no more at the desired heat transport capacity. In the current study, the performance of cylindrical heat pipes with sintered and grooved wick structures, which are among the most commonly used types, is experimentally tested at different heat loads, gravitational orientations and ambient temperatures. Dryout limits of the heat pipes are determined and the relationship between the dryout onset and operating conditions is elucidated. The results reported in the present study are expected to guide thermal engineers for the proper selection and operation of conventional heat pipes.
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Polatlı'nın Kurtuluş Savaşındaki rolü
(Bilkent University, 2014) Yiğit, Aykut; Atay, Atakan; İsen, Berkay Emre; Kuşçu, Yiğit Fırat; Özcan, Doğanay