Fig. 6.

An average ${\tau }_{1/2}$ value was calculated for five different flow speeds from the 100 scans taken at each dial setting. The log of the average ${\tau }_{1/2}$ value was plotted against its corresponding flow speed as listed in the legend. The uncertainty associated with the ${\tau }_{1/2}$ values ranged between 5% and 6%. A linear model was fitted (dashed line) from the five data points that show a linear relation ($R^2=0.99$) between the flow speed and $\log ({\tau }_{1/2})$. The subplot of the average autocorrelation curves for five different flow speeds further show this relation qualitatively. An immediate leftward shift in the autocorrelation curve is observed when moving from a no-flow state (maroon curve) to a flow state (red, orange, and blue curves). A gradual shift is observed when increasing the speed of the flow state. These results indicate that the device can differentiate between a flow and no-flow state with some sensitivity to changing flow rates.