A Comparison of Extensional Rheometers

Cai, Jiannan; Mendes, Paulo R. Souza; Macosko, Christopher W.; Scriven, L. E.; Secor, R. B.

doi:10.1016/b978-0-444-89007-8.50456-1

Cited by 4 publications

(4 citation statements)

References 5 publications

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“…At vanishing extension rates, the output extensional viscosity is T/E = 4.9r/o, as opposed to the theoretical limit η Ε = 3τ/ο· This is in excellent agreement with experimental findings for Newtonian fluids [4], for which the opposed nozzle device always gives a Trouton ratio 885 T R = VE/^O between 4 . 5 and 5.0.…”

Section: Opposed-nozzle Methodssupporting

confidence: 84%

“…Although the behav ior of viscoelastic liquids in shear can usually be mea sured with a reasonable degree of reliability, the same is not true for the measurement of extensional proper ties. Experimental re sults using these techniques suggest that many process liquids exhibit extensional properties that dramatically differ from the ones observed for Newtonian liquids [3,4]-Normal usage of constitutive equations in flow sim ulations requires that the related material functions be experimentally determined a priori. Therefore, techniques now available for measuring extensional viscosity should only be regarded as indexing methods, especially for low viscosity liquids [2].…”

Section: Introductionmentioning

confidence: 99%

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Remarks on Two Available Extensional Viscosity Measurement Techniques

Mendes¹,

Padmanabhan²,

Macosko³

et al. 1993

Experimental Heat Transfer, Fluid Mechanics and Thermodynamics 1993

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A B S T R A C TTwo different experimental methods for measuring extensional viscosity are examined, the entrance pressure drop method and the opposed-nozzle approach. The ve locity and stress fields for the flows that occur in these geometries have been obtained by integrating the cor responding governing equations. The Galerkin method with finite element basis functions was employed in the integration. An inelastic constitutive relation with a new viscosity function was used to relate the extra stress with the flow field. The pressure drop and force that are mea sured in the experimental techniques are evaluated here by using the calculated pressure and stress fields. These quantities are then used in conjunction with the work ing equations of each technique to determine apparent extension viscosities and extension rates. The thus ob tained extensional viscosity-functions are compared with the ones used in the constitutive equation, to give an as sessment of the accuracy of each technique. Results show that the entrance pressure drop method underestimates the extension viscosity of extension-thinning fluids and overestimates this material function when the fluid dis plays extension-thickening. The opposed-nozzle method is quite reliable at low to moderate extension rates. At high rates, shear thinning becomes important and affects the measured force.

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Section: Opposed-nozzle Methodssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Remarks on Two Available Extensional Viscosity Measurement Techniques

Mendes¹,

Padmanabhan²,

Macosko³

et al. 1993

Experimental Heat Transfer, Fluid Mechanics and Thermodynamics 1993

Self Cite

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show abstract

“…The third is the small-deformation-rate assumption along the side wall in Eqs. (23) and (24). The first and third turn out to be insignificant; the Reynolds number is low (10 −4 to 10 −3 ), and the shear and normal stresses at the side wall are indeed negligible (about 0.1% of g (H − h)).…”

Section: Force Balancementioning

confidence: 94%

“…The latter would be inaccurate since the polymers are unlikely to reach steady stretching at such a small strain. Even for Newtonian fluids, the opposed-nozzle device gives a Trouton ratio that deviates much from 3 [3,20]; typical values range from 2 to 4 [19] to order 10 [23] and even 100 [24]. As a result, Dontula et al [20] recommended using the device as an "indexer" rather than rheometer.…”

Section: Introductionmentioning

confidence: 95%