Abstract

Flow field measurements behind pipe entrance inserts called as flow conditioners in a mean flow Reynolds number range 547≤Re≤9000 are presented herein. A tube bundle, a Laws’ perforated plate and an etoile were located at the entrance of a smooth circular pipe of inner diameter, D=26.6 mm. The covered ranges of open area ratio, β and non-dimensional length, L/D were 0.49≤β≤0.74 and 0.123≤L/D≤2 respectively. The cross-sectional axial velocity (r) profiles at the downstream stations of X/D=75, X/D=375, X/D=680 together with pressure losses  are referred to determine the influence of utilized designs.

The flow conditioners have a single performance characteristics expressed through a relationship of pressure loss coefficient K=K(Reβ) which provides a practical method for the calculation of time-averaged pressure loss, ∆P̅ in an average error margin of ±18%. The laminar flow inside the pipe without an insert in the range of Re<2450 is not fully-developed sensed with u=u(r) profiles having a ±20% deviation from the Blasius profile for the lengths X/D<680.  Meanwhile flow conditioners provide a fully-developed laminar flow independent of Re and X observed in terms of downstream u=u(r) profiles with a better fit to the Blasius profile in a mean error margin of ±10%.

The laminar flow control via flow conditioners is analyzed through a discussion in terms of the introduced local non-dimensional velocity parameters. The used methodology is based on the definition of entrance length Reynolds Number; Re_x=(X/D)Re. The proposed equations “Re_x β =C” (where C is a constant) can be used for the estimation of settling distance of the flow conditioners and laminar entrance length. The experimental data are in conformity with the magnitudes of C=2.87×10⁴ and C=3×10⁵ with the corresponding error margins of ±4% and ±6% respectively.