The literature review on rarefied gas flow through microchannels with

The pressure variation along the inner and outer walls is shown in Fig. 2 for the 8 mm diameter tube with 90° bend (Re = 0.67 and 83.7 with Kno = 0.0355 and 0.002 respectively). Here (and in the subsequent plots), the tube is unfolded so that AGN 205728 points before and after the bend can be plotted as a function of a single coordinate X (where X is the distance along the centerline from the first pressure tap; see Fig. 1b). The distance is normalized by the tube length (L); as the lengths upstream and downstream of the bend are equal, the bend plane always lies at X/L = 0.5. Pi is the measured pressure at the first tap (X/L = 0) and (Po) is the measured pressure at the last tap (X/L = 1). Note Pleistocene on the whole, pressure reduces with distance along the tube as expected. However the pressure variation is non-monotonic, rising at the outer wall upstream of the bend. The unequal pressure drops can be noted from the figure for equal upstream and downstream lengths from the bend plane, which is unlike incompressible flows. Similar trend in pressure variation is observed in the case of bend tubes of other diameters for different Reynolds number cases. The adverse pressure gradient region indicates the presence of secondary flow near the bend. These observations are analyzed further in the discussion section.