Extensional viscosity measurements are being made at increasingly high strain rates. The behaviour of semi-solid materials and molten polymers was generally studied at extensional strain rates well below one reciprocal second (1–4); some tests on polymer solutions were also carried out at low strain rates (5). These experiments showed that the Trouton ratio (extensional viscosity divided by shear viscosity) sometimes rose above the value 3 predicted by Newtonian theory. At higher rates of strain, for polymer solutions, the Trouton ratio rises rapidly and novel experimental methods are required (6). The orifice jet thrust technique of Metzner and Metzner (7) has been used independently by the present authors (8), confirming that the Trouton ratio for dilute polyacrylamide solutions is in excess of 103 for extensional strain rates of 103–104 sec−1. Precise knowledge of the flow pattern upstream of the orifice is essential for the accurate use of this method.



Constant defining extensional strain rate (see Appendix)


Extensional strain rate in axial direction


Effective length of central jet, covering region of constant extensional strain rate


Initial radius of central jet just outside orifice, corresponding to velocity R 0


Final radius of central jet, corresponding to velocity V 1


Radius of central jet at point distant x from tube exit


Radius of orifice in orifice jet thrust experiment


Time for which fluid has been subjected to extensional flow


Reduction of thrust on central capillary following jet attachment


Mean velocity of fluid in central jet before extensional flow commences


Mean velocity of fluid in central jet at point distant “L” from tube exit


Mean velocity of fluid in central jet at point distant “x” from tube exit


Mean velocity of fluid through orifice (in orifice jet thrust experiment)


Axial distance from central tube exit


Axial stress in fluid


Initial axial stress in fluid in central jet


Time-average axial stress in fluid in central jet


Extensional viscosity i.e. (τ11) av /d 11


Shear viscosity


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Copyright information

© Springer-Verlag Berlin Heidelberg 1975

Authors and Affiliations

  • D. R. Oliver
    • 1
  • R. Bragg
    • 1
  1. 1.Chemical Engineering DepartmentUniversity of BirminghamEngland

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