1. Optimizing Optical Dielectrophoretic (ODEP) Performance: Position- and Size-Dependent Droplet Manipulation in an Open-Chamber Oil Medium
Abstract: An optimization study is presented to enhance optical dielectrophoretic (ODEP) performance for effective manipulation of an oil-immersed droplet in the floating electrode optoelectronic tweezers (FEOET) device. This study focuses on understanding how the droplet’s position and size, relative to light illumination, affect the maximum ODEP force. Numerical simulations identified the characteristic length (Lc) of the electric field as a pivotal factor, representing the location of peak field strength. Utilizing 3D finite element simulations, the ODEP force is calculated through the Maxwell stress tensor by integrating the electric field strength over the droplet’s surface and then analyzed as a function of the droplet’s position and size normalized to Lc. Our findings reveal that the optimal position is xopt = Lc + r, (with r being the droplet radius), while the optimal droplet size is ropt = 5Lc, maximizing light-induced field perturbation around the droplet. Experimental validations involving the tracking of droplet dynamics corroborated these findings. Especially, a droplet sized at r = 5Lc demonstrated the greatest optical actuation by performing the longest travel distance of 13.5 mm with its highest moving speed of 6.15 mm/s, when it was initially positioned at x0 = Lc + r = 6Lc from the light’s center. These results align well with our simulations, confirming the criticality of both the position (xopt) and size (ropt) for maximizing ODEP force. This study not only provides a deeper understanding of the position- and size-dependent parameters for effective droplet manipulation in FEOET systems, but also advances the development of low-cost, disposable, lab-on-a-chip (LOC) devices for multiplexed biological and biochemical analyses.
2. EFFECT OF ORIENTATION AND FILLING RATIO ON THERMAL PERFORMANCE FOR A CLOSED LOOP PULSATING HEAT PIPE USING DIFFERENT NANOFLUIDS ( Conference proceedings: ICMIME 2019)
One of the main problem faced in the thermal management of modern small-scale electronic devices have very
high power density resulting in higher heat dissipation rate..Traditional fan-cooling method can remove up to
50 W of the dissipated heat and thus is very inefficient. Pulsating heat pipes (PHP) can be installed inside the
motherboard which can remove almost 100% of the dissipated heat. Using PHPs instead of fan not only make
the motherboard more compact but also reduces noise. This study focuses on the effect of the inclination angle
(gravity) and the filling ratio at different heat input levels on the heat transfer characteristics of a Closed Loop
Pulsating Heat Pipe (CLPHP) using both conventional working fluids and nanofluids. In this investigation,
seven different working fluids have been used namely distilled water, ethanol, methanol, Acetone, Zinc Oxide-
Water, Copper Oxide-Water and Aluminum Oxide-water. A closed-loop pulsating heat pipe is designed and
fabricated with proper facility to change the angle of inclination (orientation), filling ratio and heat input.
Experiments are then conducted with different filling ratios ranging from 20%-80%, heat input ranging from
10W to 90W and angle of inclination varying between 30° to 90°. The main target of this study was to find out
an optimum value for filling ratio and inclination angle for which heat transfer from evaporator section to
condenser section is maximum. Heat transfer capability of different working fluids is also compared Among all
the fluids used, heat transfer capability of the nanofluids was better than the conventional heat transfer fluid
and among the three nanofluids used, Aluminum Oxide-water based nanofluid showed the best performance.
The optimum value for filling ratio is found to lie between 45%-50% and the optimum angle of inclination is
within 40°-50°.