Mixing Dynamics

FLOW-3D can be used as an effective tool for modeling the droplet/bubble dynamics in microfluidic devices, including simulating a novel device called the Hong Chamber. The Hong Chamber is an innovative in-plane passive micromixer using modified Tesla structures, which are used as passive valves. This has been designed, simulated, fabricated and successfully characterized by Hong et al.[3].

Hong chamber simulations
Multiphase FLOW-3D simulation of Hong Chamber using conformal mesh to accurately capture entrapped bubble phase.

This novel micromixer has shown excellent mixing performance over a wide range of flow conditions in the micro scale. We simulated the Hong Chamber with two fluids coming in from the inlet, to look at the mixing patterns as a function of time. The series above shows the mixing pattern as a function of time. The two streams represent two water-based reagents.

The fluid fraction varies from 0 to 1, where 0 indicates a region completely occupied by fluid one and 1 indicates a region completely occupied by the second fluid. Fixed velocities were used at the inlet and an outflow boundary condition was used at the outlet. The initial region was filled with the blue fluid. Figure 10 shows results from the filling simulation. Here no fluid was defined in the initial region. Fixed velocities were used at the inlet boundary conditions and the adiabatic bubble model was used to trap bubbles. What is notable is that at each Tesla valve unit, the flow in the reverse direction is prevented, which leads to the formation of bubbles.

Simulation Setup

The simulation below shows the mixing of blood plasma and water as the fluids come in from the two inlets. The flow rates for both streams are 1e-8 m3/sec. The simulation is colored by fluid fraction. Red is water.

Hong chamber CFD simulation
The mixing pattern as a function of time at 0.04s, 0.2s, 0.5s, and 0.65s. Courtesy of Stanford University.