CHEME 7160 Fluid Flow in Process Units Project

CHEM-E 7160 - Fluid Flow in Process Units, Project Work Flow Through a Pipe Elbow (Comsol) Shahid Sarfraz James Kabugo May 15, 2017

Contents Ø Introduction Ø Model geometry (in Comsol) Ø Results and validation Ø Conclusions

Highlighted part was not included in this study!! Introduction: Pipe elbows Ø Commonly applied pipe elbows include: o 45° bends, 90° bends and 180°bends Ø Mainly applied to purposely to change the direction of flow in the pipe (e. g. in pipe connections, cooling coils, e. t. c) Ø Shortcomings: o Notable pressure losses or head losses in the pipe line o In somes cases pipe elbows are more susceptible to corrosion or erosion than equivalent straight pipes. Ø In this study, a 90° pipe elbow (circular) based on the given Figure (on the right) was studied. Ref. Homicz (2004)

Introduction: Flow through a 90° Pipe elbow o Dean’ vortices o Flow separation o Pressure losses Ref. Homicz (2004) Ref. Jayanti (Thermopedia)

Parameters& Assumptions •

Modeling methodology •

Pipe Elbow Model Geometry &Mesh Geometry of the 90° pipe elbow. Ref. (Comsol) Meshed geometry of the 90° pipe elbow.

Results: Wall Resolution Study 1: wall lift-off in viscous units (below 11. 06 units!) Study 1: Turbulent viscosity along the symmetry axis (constant before the inlet!) Study 2: wall lift-off in viscous units (below 100 units!)

Results: Velocity field & pressure at 45° cutplane

Results: effect of coarser mesh Wall lift-off in viscous units is above 100 units! Flow at the walls not well resolved!

Results: effect of changes in the average inlet velocity Study 1: Wall resolution for 10 m/s (above 11. 06 units!) Study 1: Wall resolution for 2. 5 m/s ( acceptable at 11. 06 units)

Results: other turbulence models &Discretization •

Validation of numerical results Ref. Homicz (2004)

Validation of numerical results • Note: evaluated at half way through the bend i. e. at 45°! Correlation for friction factor through a curved pipe (noted accuracy of ± 15%!).

Conclusions • Higher pressure development on the outer wall of the curvature • Increase in flow velocity and maximum velocity observed along the centerline • Formation of two counteracting vortices (swirling behaviour) • Separation of the flow as it leaves the pipe elbow • Pressure or head losses are experienced in the pipe elbow • With a coarser grid, flow near the walls was poorly modeled