The combined effect of ∆P and φ on clog dimension and location is readily seen in the scatter plots in Fig. . Each data point represents a clog. Normalized clog length l is plotted versus clog centroid position x. x represents the direction of clog growth: the origin x = 0 cm is the location of the channel outlets; the inlet area is located at x = 4 cm. That is, data points to the left within each figure represent clogs nearer the outlet, downstream, while data points to the right within each figure represent clogs nearer the inlet, upstream. The y axis location of each data point represents clog length. Each row of plots represents a constant ∆P condition while φ is varied in each column. The top two rows in Fig. show For each φ , there seems to be a critical ∆P around 900 mbar, beyond which the average l increases by a factor of 2. Note that the ∆P axis is not on a linear scale.