COMPUTATIONAL PREDICTION ON DROPLETS FORMATION IN MICROCHANNELS Catalin MARCULESCU, Catalin Mihai BALAN, Andrei AVRAM and Marioara AVRAM L10 - Micro and Nano Fluidics Laboratory, National Institute for Research and Development in Microtechnologies - IMT-Bucharest, corresponding e-mail address: catalin.marculescu@imt.ro Abstract The present microfluidic study is emphasizing the flow behavior of two immiscible fluids within a Y shape micro-bifurcation with two inlets and one outlet. We report here a numerical investigation on the interface shape dynamics manifested at different capillary numbers ( Ca), by a variation of the flow rate ratios (FRR) over the inlets. The experimental data were compared with numerical simulations performed with commercial computational code FLUENT™ in a 3D geometry with the same dimensions as the experimental one. The numerical flow patterns are found to be in good agreement with the experimental manifestations. We demonstrated numerically that the Ca variation has an important impact on the droplet frequency formation. Changing only the FRR of the inlets, the droplets behavior modifies drastically. From the numerical point of view, the interface shape is used to characterize the manifestation of droplet formation. Keywords: CFD, droplet behavior, immiscible fluids, interfacial tension, capillary number, microchannel. 1. Introduction Liposomes are quasi-spherical structures formed from lipid bilayer membranes that encapsulate an aqueous volume. Liposome size and size distribution are tailored for each particular application and are inherently important for in-vivo applications such as drug delivery and transfection across nuclear membranes in gene therapy [1]. In conventional methods, lipids are spontaneously assembled into heterogeneous bilayers in a bulk phase. Additional processing by extrusion or sonication is required in order to obtain small size liposomes with narrow size distribution. Jahn et al. [2] were amongst the first to develop a microfluidic hydrodynamic focusing (MHF) method for controlled liposome formation.. Through the current study, we propose to create a similarity between the liposome sizing and droplet formation using two well-known Newtonian fluids: mineral oil and deionized water. This procedure does not intend to be an alternative to the MHF method, but more of an enhancement to the mentioned method. Of course, the study is in an early stage development, the scales being a bit larger, due to experimental set-up constrains. The future investigations will try to match the scales that liposome work involves. The test geometry was a commercial microchannel with a “Y” shape that presented a squared cross-section of 300x300 μm. It had two separate inlets for each fluid and one outlet. An important feature from the physical characterization of the working fluids is represented by the interfacial tension, value measured with a goniometer and taken into consideration in the numerical model. The main purpose of the study was to make a numerical determination of the interface shape dynamics manifested at different capillary numbers (Ca), by slight variations of the flow rate ratios (FRR) applied at the inlets.