Droplet actuation

The threshold voltage for droplet actuation, Vj, occurs when V = Vj and U = 0 in Eq. (2). Thus, at the threshold of droplet actuation ... 

Walker S, Shapiro B (2005) A control method for steraing individual particles inside liquid droplets actuated by electrowetting. Lab Chip 12 1404-1407... 

Digitized Heat Transfer, Table 1 Eorces and velocity for various droplet actuation methods. P is the applied voltage, c is the capacitance per unit area, d is the thickness of the dielectric layer, R is the radius, p is the viscosity, h is the channel height, L is the droplet length, q is the charge per unit area. A is the potential difference, is the dielectric constant, y is the surface tension, T is the temperature, and 0 is the contact angle. For additional information, please refer to Ref. [7]... 

Im DJ, Noh J, Moon D, Kang IS (2011) Electrophoresis of a charged droplet in a dielectric liquid for droplet actuation. Anal Chem 83 5168-5174... 

Another application of laser-driven thermocapiUary flows is dedicated to droplet actuation in digital microfluidics. By moving the fluid around a flowing droplet, it becomes possible to move or stop it, to change its direction, to sample it, or to force coalescence in a contactless manner. The actuation process can easily be understood from the mechanism of... 

Zengerle, R., and Koltay, P. (2008) Passive water removal in fuel cells by capillary droplet actuation. Sens. Actuators A Phys., 143 (1), 49—57. 

Bahadur V, Garimella SVJ (2006) An energy-based model for electrowetting-induced droplet actuation. J Micromech Microeng 16 1494-1503... 

Percin, G. Levin, L. Khuri-Yakub, B. 1997. Piezoelectrically actuated droplet ejector. Rev. Sci. Instr. 68 4561—4563. 

The core components of a complete microsystem are the integrated sensing, acting or passive micromechanical devices. In most cases, a naked chip manufactured in bulk or surface micromachining is used for the detection of a physical or chemical quantity or some actuation principle, like the dosage of ink droplets in inkjet printheads. A complete microsystem can consist of a complex set of these devices. 

M. Pollack, R.B. Fair, and A.D. Shenderov Electrowetting-Based Actuation of Liquid Droplets for Microfluidic Applications. Appl. Phys. Lett. 77(11), 1725... 

Liquid fuel was seldom utilized in the previous ACC studies because it was not only difficult to actuate liquid-fuel injection at high frequencies, but the combustion delays associated with liquid-fuel atomization, droplet heating, vaporization, and burning processes made such a control extremely slow for fast-response in situ type controllers. As a result, the use of liquid fuel was confined to either steady injection process ]13] or upstream addition of prevaporized fuel ]4, 7] which limited the ACC flexibility associated with temporal responsiveness. The goal of this project is to make ACC more practical for propulsion systems by studying direct liquid-fueled ACC in a closed-loop controller setting. 

The injector, when used directly, was not suitable for ACC at high frequencies as it produced very large droplets. To reduce droplet size, a swirl-based atomizer with 300 pm exit diameter [29] was fitted at the fuel jet exit. In this close-coupled configuration, the automotive fuel injector was used as a high-frequency solenoid valve for the fuel line. This new combination actuator improved the overall atomization characteristics while maintaining good frequency... 

The formulation of combustion dynamics can be constructed using the same approach as that employed in the previous work for state-feedback control with distributed actuators [1, 4]. In brief, the medium in the chamber is treated as a two-phase mixture. The gas phase contains inert species, reactants, and combustion products. The liquid phase is comprised of fuel and/or oxidizer droplets, and its unsteady behavior can be correctly modeled as a distribution of time-varying mass, momentum, and energy perturbations to the gas-phase flowfield. If the droplets are taken to be dispersed, the conservation equations for a two-phase mixture can be written in the following form, involving the mass-averaged properties of the flow ... 

Flow and mixing visualization were achieved by means of fluorescence dilution imaging [97]. A fluorescent droplet (1 mM fluorescein, 0.125 M KC1,0.125 M sodium hydroxide) was merged with a non-fluorescent droplet (0.125 M KC1, 0.125 M sodium hydroxide). The volume of the droplet in passive mixing was 1.75 pi, while 1.32 pi droplets were applied for active mixing. The actuation voltage was 30 V. The fluidic properties of the filler and droplet fluids were closely matched. The interfacial tension between the two liquids was 36 and 37 dyn cm4 for the non-fluorescent and the fluorescent droplets, respectively. 

Dielectrophoretic forces depend on the polarizibility of species, rather than on movement of charges [99]. This allows the movement of any type of droplet being immersed by a dielectrically distinct immiscible carrier medium. Since dielectric forces are generated by spatially inhomogeneous fields, no mechanical actuation is required. In addition to this, dielectrophoretic droplet movement benefits from the general advantages given by droplet microfluidic, i.e. discrete, well-known very small volumes, no need for channels, avoidance of dead volumes and more. 

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