Microtech2010 2010

Drop Formation and Control of Non-Newtonian Fluid

J. Gao, K. Ng
Eastman Kodak Company, US

Keywords: jet break up, non-newtonian fluid, satellite drops, jet stability, inkjet, printing


It is well known that fluid jets tend to break up into droplets of multiple sizes. However, the ability to make and control individual droplets from arrays of such jets in speed, number, and size has become reality only recently in new generation Micro-Electro-Mechanical Systems (MEMS) technology. The talk will begin with an overview of MEMS based microfluidic technology. The devices from this technology are capable of stimulating drop breakup of jets of complex fluids with unprecedented precision, speed, and selectivity. The instability of non-Newtonian liquid jets and drop formation from the MEMS-based microfluidic device is the main topic of the presentation. The governing equation for the surface profile of the liquid jet is derived in the forms of a partial differential equation (PDE). The PDE is solved for various cases of Carreau-Yasuda fluid to study the effect of fluid properties on jet breakup. The Carreau-Yasuda fluid has a power law viscosity bounded by an upper bound at zero strain rate, and a lower bound at the infinite strain rate. The effects of various parameters on the instability behavior are studied in comparison with two Newtonian jets with upper and lower bound viscosities. A number of quantitative conclusions and sensitivities on the instability behavior of non-Newtonian jets are investigated. It is found that the jet breakup mechanism depends on the properties of the fluid as well as the wave number of the thermal disturbance that causes the surface tension gradient. In contrast to the Newtonian liquid where the jet surface profile has the same frequency as the surface tension gradient, the nonlinear nature of the non-Newtonian constitutive behavior may tend to enable the jet surface profile at frequencies higher than that of the surface tension gradient. This leads to significant surface profile oscillation within one wavelength of the surface tension gradient and the generation of small satellite drops. The present work can provide a good foundation for further investigations of the instability and breakup of non-Newtonian fluid jets under the situation where the surface tension gradient exits. The applications of such a phenomenon include a microfluidic inkjet printhead with thousands of nozzles that are thermally modulated near the nozzle orifice to produce steady streams of picoliter-sized droplets at kilohertz frequency rates.
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