Microfluidics and Nanofluidics

, Volume 18, Issue 4, pp 599–612

Investigations on the characterization of laminar and transitional flow conditions after high pressure homogenization orifices

  • Katharina Kelemen
  • F. E. Crowther
  • C. Cierpka
  • L. L. Hecht
  • C. J. Kähler
  • H. P. Schuchmann
Research Paper

DOI: 10.1007/s10404-014-1457-0

Cite this article as:
Kelemen, K., Crowther, F.E., Cierpka, C. et al. Microfluid Nanofluid (2015) 18: 599. doi:10.1007/s10404-014-1457-0

Abstract

High pressure homogenization is a well-established technique to achieve droplets in the submicron range. However, droplet breakup mechanisms are still not completely understood, since studies to characterize the flow are limited due to very small dimensions (typically several micrometers) and very large velocity ranges (from almost stagnant flow to 300 m/s and more). Furthermore, cavitation can occur resulting in multiphase flow. So far, experiments were performed only via integral measurements of, for example, the pressure drop or the droplet size distribution at the outlet. In the current study, this gap shall be closed using Particle Image Velocimetry measurements to analyze the flow field. In addition, an overall method, the characteristic correlation between the discharge coefficient (CD) and Re0.5 is used to distinguish between laminar, transitional and turbulent flow conditions at Reynolds numbers based on the channel width (d = 200 µm) between 250 and 22,500. The investigated orifices of this study had different positions of the constriction: coaxial and next to the wall. For both orifices, the CD measurement was applicable and showed different characteristic regions which can be associated with laminar, transitional and turbulent flow conditions. Mean velocity fields and fluctuations were measured quantitatively at the outlet and 50 diameters downstream using Micro Particle Image Velocimetry (µ-PIV) in an optically accessible orifice. Increased velocity fluctuations were found in the shear layers when the flow turns from laminar into unstable transitional conditions. The combination of both measurement techniques will help to optimize these systems for the future.

Keywords

High pressure homogenization Discharge coefficient Orifice µPIV 

List of Symbols

A [–]

Cross-sectional area of the orifice

B [mm]

Width of the squared orifice

B [mm]

Width of the squared inlet and outlet of the orifice unit

CD [–]

Discharge coefficient

CD,const [–]

Constant discharge coefficient

D [mm]

Diameter of the orifice

D [mm]

Diameter of the inlet and outlet of the orifice unit

d/D [–]

Ratio of orifice diameter to outlet diameter

h [mm]

Step height of a backward facing step

H [mm]

Outlet height of a backward facing step

L [mm]

Length of the orifice

Ntotal [–]

Number of images

NVector [–]

Number of vectors accounting for calculation

Δp [bar]

Homogenization pressure

Δp1 [bar]

Pressure loss after the first orifice unit

Δpideal [bar]

Frictionless pressure loss

Δpmax [bar]

Maximum pressure loss

Δpreal [bar]

Real pressure loss

Δptotal [bar]

Total homogenization pressure

Re [–]

Reynolds number

Δt [s]

Interframing time between two images

u [m/s]

Mean axial velocity

ub [m/s]

Mean bulk velocity

uexit,c [m/s]

Mean exit centerline velocity

um,c [m/s]

Mean centerline velocity

u2/um,c2 [–]

Normalized Reynolds shear stresses axial direction

v2/um,c2 [–]

Normalized Reynolds shear stresses radial direction

\(\dot{V}\) [m3/s]

Volume flow rate

x [mm]

Streamwise or axial coordinate

x/d or x/b resp.

Normalized distance after the orifice

y [mm]

Lateral or radial coordinate

y/d or y/b resp.

Normalized diameter of the orifice

z

Height coordinate

Greek letters

η [mPa s]

Dynamic viscosity of the fluid

ρ [kg/m3]

Density of the fluid

cp

Counter pressure

µ-PIV

Micro Particle Image Velocimetry

PEG

Polyethylene glycol

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Katharina Kelemen
    • 1
  • F. E. Crowther
    • 1
  • C. Cierpka
    • 2
  • L. L. Hecht
    • 1
  • C. J. Kähler
    • 2
  • H. P. Schuchmann
    • 1
  1. 1.Institute of Process Engineering in Life Sciences Section I: Food Process EngineeringKarlsruhe Institute of TechnologyKarlsruheGermany
  2. 2.Institute of Fluid Dynamics and AerodynamicsUniversität der Bundeswehr MünchenNeubibergGermany