Redefined Hydraulic Diameter for Laminar Flow

摘要

For laminar, steady flow in ducts, the current definition of hydraulic diameter, Dh, does not accurately depict the non-uniform wall shear stress distribution around the perimeter of non-circular duct shapes. In this investigation, a new hydraulic diameter Dh(1), was empirically determined. It correlated friction factor data for many non-circular shapes to within approximately 2.4 % of the circular duct value. An experiment, using the AFIT oil Flow Rig Set-Up, was run to determine the effect of transition Reynolds number, Re(tr), and hydrodynamic entrance length, L(+), of replacing Dh with Dh(1). Transition Reynolds number and L(+) were determined, based on Dh and Dh(1) for a circular, square, and concentric annular duct. Transition Reynolds numbers, based on Dh, for the square and concentric annular ducts were approximately 12.5% lower than the circular duct Re(tr). The Re(tr), based on Dh(1), did not correlate well for the concentric annulus, but did correlate for the square duct. Keywords: Hydrodynamic length. (Theses)