3.5 Comparison of pressure drop for flow from settling chamber and without settling chamber
To confirm that settling chamber has no effect on the measurement of pressure drop, the data collected from 2 and 4 mm pipes (non-coated) with and without settling chamber. Figure 9 present the data of pressure drop collected from the experiments. The results confirm that there is no effect of using settling chamber on pressure measurements.
Figure 10 present a summary of the results from all coated and non-coated pipes. The results offer an increased perspective and quantification of drag variations in hydrophobic small pipes. When the results are graphically inspected together, a common trend of the effect of coating on pressure drop is recognised. As the Reynolds number increases past values of laminar flow seen in the 1 and 2mm pipes, Cassie Baxter air trapping reduces drag allowing the flow to enter the transition / turbulent flow regime which in turn creates a Wenzel wetting state leading to a drag increase.