YAN XIAO
M.S. in Mechanical Engineering, August, 2006
Advanced Materials and Technologies Laboratory
University of Connecticut

Now at The Florida International University

 

THEORETICAL ANALYSIS OF CAPILLARY-DRIVEN FLOWS IN MICROCHANNELS.

Motion of a fluid in capillary geometries is a classical problem and one that’s of much significance now in light of the many microscale applications being investigated. Based on different types of fluids, geometric configurations, and model assumptions, theoretical analyses in the literature have led to a number of problem-specific first or second-order nonlinear ordinary differential equations, which are usually solved by numerical methods. In this thesis, the theories for capillary flow are generalized to a unified nonlinear second-order differential equation which accounts for the effects of the entrance, the inertial forces, and the dynamic contact angle. Applying the generalized formulation to flow in vertical microchannels, an analytical solution is obtained in terms of a double Dirichlet series. The readily evaluated analytical solution is compared with several experimental and numerical results in the literature, which shows a good agreement and demonstrates that the analytical approach can be used to predict capillary flows for a wide range of fluids and vertical parallel-plate and tube geometries in a unified manner. Further, capillary-driven flow in horizontal microchannels is studied by considering an application to a microcasting process for the fabrication of ceramic and metallic microdevices, which involves flow of a nanoparticulate slurry in a micromold. A comprehensive theoretical model is developed to account for the capillary-driven flow and simultaneous particle settling behavior. Numerical simulations are performed over a wide range of parameters to illustrate the effects of four nondimensional groups on the fill time and particle distribution, and to develop design windows, which serve as guidelines in the design of nanoparticle properties, slurry composition, and microchannel dimensions to maintain a desired level of uniformity in particle distribution. Overall, the thesis provides the theoretical basis for investigation of capillary-driven flows in microgeometries for a number of applications of emerging importance.

 

Publications

J-06-02: [Abstract | Request Reprint] Y. Xiao, F. Yang, and R. Pitchumani, “ A Generalized Analysis of Capillary Flows in Channels,” Journal of Colloid and Interface Science, 298(2), pp. 880-888, 2006.

C-06-01: Y. Xiao, A. Mawardi, and R. Pitchumani, “Theoretical Model of Micromold Filling by Nanoparticulate Slurries,” International Heat Transfer Conference, Sydney , Australia , August 2006.

J-08-01: [Abstract | Request Reprint] A. Mawardi, Y. Xiao, and R. Pitchumani, “Theoretical Analysis of Capillary-driven Nanoparticulate Slurry Flow During a Micromold Filling Process,” International Journal of Multiphase Flow, 34, pp. 227-240, 2008.