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

Abstract

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.

Water–air flow in straight pipes and across 90∘ sharp-angled mitre elbows

“…The flow recovery length was 60D * downstream of the bend and the upstream perturbation distance was 32.5D * upstream of the elbow. Like for the single-phase study documented in our paper [35], the pressure produced by the water-air flow was axisymmetric around the pipe periphery at all the tested positions. These measurements agree with the result by Lima and Thome for the two-phase refrigerant flow through horizontal 180 • round elbows [12].…”

“…This research work continues our research investigation on flows across mitre elbows, i.e., the study of the pressure drop for single-phase flow [35] and the flow visualization and pressure-loss measurements in two-phase flow conditions [37]. The present paper differs from the latter because in [37] we only used a pipe with one diameter in the horizontal configuration and employed the Lockhart-Martinelli model to scale the pressure drop, while in the present work pipes with three different diameters were used for both horizontal and vertical orientations and novel correlations for the scaled pressure drops in all the configurations were obtained.…”

“…The rig is shown schematically in Fig. 1 and described in further detail in two papers of ours [35,37]. It was composed of air and water lines, a mixer of the two fluids, and the test section equipped with the 90 • sharp-angled mitre elbow.…”

“…Furthermore, the models for flows across pipe fittings predict the frictional pressure drop without considering the effect of the flow separation, which is the main cause of the losses in sharp-angled mitre elbows. Despite a few investigations on single-phase flow across 90 • sharp-angled elbows for laminar [30,31,32] and turbulent flows [33,34,35], to the best of our knowledge, no study in the literature has examined the pressure drop and flow patterns of the two-phase flow in this type of fittings. Mitre bends are widely used in many industrial applications, especially those requiring large-diameter piping in the chemical, nuclear, and oil industries [36].…”

Improving flow efficiency in curved pipes during multi-phase, immiscible fluid flow using edge-tailored guide vanes

“…The pressure loss coefficient was relayed to decrease steeply at approximately Re = 20,000, and going upward. On the other hand, at lower Re, a linear dependence of pressure coefficient and Re was postulated (Al-Tameemi and Ricco, 2018). It could infer that high Re does not necessarily mean high-pressure loss.…”