Laminar flow control via utilization of pipe entrance inserts (a comment on entrance length concept)

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=26.6mm. The covered ranges of open area ratio, ββ and non-dimensional length, L/DL/D were 0.49≤β≤0.740.49≤β≤0.74 and 0.123≤L/D≤20.123≤L/D≤2 respectively. The cross-sectional axial velocity u=u(r)u=u(r) profiles at the downstream stations of X/D=75,X/D=375,X/D=680X/D=75,X/D=375,X/D=680 together with pressure losses ΔPΔP are referred to determine the influence of utilized designs.The flow conditioners have a single performance characteristic expressed through a relationship of pressure loss coefficient  K=K(Reβ) which provides a practical method for the calculation of time-averaged pressure loss, ΔP̄ 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)u=u(r) profiles having a ±20% deviation from the Blasius profile for the lengths X/D<680X/D<680. Meanwhile flow conditioners provide a fully developed laminar flow independent of Re and XX observed in terms of downstream u=u(r)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; ReX=(X/D)Re. The proposed equations “ReXβ=C” (where CC 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=2.87×104C=2.87×104 and C=3×105C=3×105 with the corresponding error margins of ±4% and ±6% respectively.

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► The laminar flow control via flow conditioners is analyzed experimentally.
► The used methodology is based on the definition of entrance length Reynolds Number.
► Equations are proposed for pipe insert settling distance and laminar entrance length.
► Significance of pipe inserts for flow development is also verified.