Two Phase Flow Analysis on Filling Processes of Microfluidic/Microarray Integrated Systems

For the last decade, most applications of microfluidics for "lab-on-a-chip" (LOC) technology have focused on the successful transfer of established technologies from conventional lab-bench methodologies to a chip-based format. Because of the unique environments offered within microfluidic networks, a variety of integration processes can be performed in a continuous format, on one platform. The Lab-on-a-Chip Application Development (LOCAD) team at NASA's Marshall Space Flight Center is utilizing LOC to support technology development specifically for Exploration. This paper will describe the design and operation of an integrated micro-channel/micro-array configuration. Specifically, the filling processes of a liquid inside a circular chamber hosting the micro-array, subjected to a specific inlet pumping velocity at various geometrical and/or operational parameters will be examined. Numerical simulations are performed for the movement of a liquid-gas two-phase flow inside the microchannel and the circular disk-shaped well. The numerical simulations were conducted using the free surface Volume of Fluid (VOF) method which allows for the interface between two immiscible fluids to be simulated while incorporating the effects of surface tension. The results are presented in terms of the movement of the gas-liquid interface. During the filling processes the two-phase flow patterns result from the competition among the inertia, adhesion and surface tension. The numerical results indicate that air bubble entrapment cannot be avoided by continuous pumping of the liquid. A pressure "pulse" in descending increments is necessary to eliminate air entrapment. Only by carefully "tuning" the appropriate balanced pressure drop across the microchannel at the last stage of pulsation, the liquid was able to contract into the small channel.