Flow visualisation investigation of water in a channel with flat plate obstruction geometry at the entry

The flow of water in a test channel placed within another wider channel with an obstruction at the entry is seen to be stagnant, forward or reverse depending on the position of the obstruction. This interesting flow phenomenon has potential benefit in process industry. The flow behaviour with a flat plate obstruction at the entry is investigated in this study. A set of different test channel lengths (200, 300, 400 and 500 mm) was used in the experiment. A Pitot-static tube, calibrated against another velocity measurement technique, was used to measure the fluid velocity inside and outside the test channel. It is observed that the flow inside the test channel vary with the position of the obstruction, Reynolds number and lengths of the test channel. The flow visualisation photographs are presented for a range of gaps between the obstruction and the test channel in order to investigate the effect of the gap to width (g/w) ratio on the magnitude of the velocity ratio (Vi/Vo: inside/outside velocity of the test channel). The influence of the Reynolds numbers on the value of the velocity ratio is discussed. The effect

of the te~ channel length on the velocity ratio is investigated at the Reynolds number of 4000 for different g/w ratios. Flow visualisation photographs were taken by a Nikon broadways high-speed digital camera and are presented here to explain the fluid motion in details.