Pressure-Loss Coefficient of 90 deg Sharp-Angled Miter Elbows

The pressure drop across $90deg$ sharp-angled miter elbows connecting straight circular pipes is studied in a bespoke experimental facility by using water and air as working fluids flowing in the range of bulk Reynolds number $500<Re<60,000$⁠. To the best of our knowledge, the dependence on the Reynolds number of the pressure drop across the miter elbow scaled by the dynamic pressure, i.e., the pressure-loss coefficient $K$⁠, is reported herein for the first time. The coefficient is shown to decrease sharply with the Reynolds number up to about $Re=20,000$ and, at higher Reynolds numbers, to approach mildly a constant $K=0.9$⁠, which is about 20% lower than the currently reported value in the literature. We quantify this relation and the dependence between $K$ and the straight-pipe friction factor at the same Reynolds number through two new empirical correlations, which will be useful for the design of piping systems fitted with these sharp elbows. The pressure drop is also expressed in terms of the scaled equivalent length, i.e., the length of a straight pipe that would produce the same pressure drop as the elbow at the same Reynolds number.