Mechanism for clogging of microchannels

We investigate clogging of microchannels at the single-pore level using microfluidic devices as model porous media. The process of clogging is studied at low volume fractions and high flow rates, a technologically important regime. We show that clogging is independent of particle flow rate and volume fraction, indicating that collective effects do not play an important role. Instead, the average number of particles that can pass through a pore before it clogs scales with the ratio of pore to particle size. We present a simple model that accounts for the data.

Figure 1

(Color online) (a) Microscope image of a microfluidic device during a clogging experiment. A particle suspension of volume fraction $\varphi =4\times {10}^{-2}$ is pumped from left to right through a series of channels in the device. The pressure difference between inlet and outlet is held constant at $\Delta p=2\mathrm{psi}$; the total length of the channels is $1.2\mathrm{mm}$. The particle diameter is $D=2.9\mu \mathrm{m}$; the height of the device is $H=25\mu \mathrm{m}$. Inset: close-up of the channel exit zone; the smallest width at the bottleneck of each channel is $W=20\mu \mathrm{m}$. (b) Close-up of three channels in the device as a time series, $t=0\mathrm{s},8\mathrm{s},38\mathrm{s}$. (c) Dependence on applied pressure for the same geometry. The ratio of clogged channels as a function of time at different applied pressures. $\Delta p=2\mathrm{psi}$ (red diamonds, results of experiment shown on top); $\Delta p=4\mathrm{psi}$ (blue circles). Inset: plot of the same data with time normalized by the relative pressure difference $\Delta p∕\Delta p_0$ $(\Delta p_0=2\mathrm{psi})$.

Figure 2

(Color online) Dependence of the average clogging time $t^{*}$ and the number $N^{*}$ of particles required to clog a channel on the particle volume fraction $\varphi$. Clogging times of experiments taken at pressure differences $\Delta p\ne \Delta p_0=2\mathrm{psi}$ are normalized by the relative pressure difference $\Delta p∕\Delta p_0$. The dotted line is a power-law fit to the data with a resulting slope of $-1$. The solid line is a constant value.

Figure 3

(Color online) (a) Number of particles, $N^{*}$, that pass through a pore before clogging as a function of $W∕D$ (circles). The same data rescaled according to the prediction of our simple model (diamonds). Solid symbols: $D=5.2\mu \mathrm{m}$. Open symbols: $D=2.9\mu \mathrm{m}$. Inset: schematic pore cross section. Shown in blue are the “sticking areas” of width $ϵ$ and height $H$. (b) Schematic illustration of fluid streamlines (blue) and a particle trajectory (red) at a constriction.

Figure 4

(Color online) Characteristic clogging time scale $t^{*}$ of single pores versus the NaCl concentration. The error bars represent the standard deviation of $t^{*}$.