ISSN:
1435-1528
Keywords:
Slit die viscometer
;
viscous heating correction
;
Weissenberg-Rabinowitch operator
;
time-temperature superposition principle
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract If the viscosity can be expressed in the formη = α (T)f(σ), the walls are at a constant temperatureT 0, and the extra stress, velocity and temperature fields are fully developed, then the wall shear rate $$\dot \gamma _w$$ can be calculated by applying the Weissenberg-Rabinowitsch operator toF c Q instead of to the flow rateQ, whereF c is a correction factor which differs from 1 when the temperature field is non-uniform; the isothermal equation relating the wall shear stress and pressure gradient is still valid. For the case in whcihη = η 0|σ| n /(1 +β(T−T 0)), wheren, η 0, andβ are independent of shear stressσ and temperatureT, an exact analytical expression forF c in terms of the Nahme-Griffith numberNa andn is obtained. Use of this expression gives agreement with data obtained for degassed decalin (η = 2.5 mPa s) from a new miniature slit-die viscometer at shear rates $$\dot \gamma$$ up to 5 × 106s−1; here, the correction is only 7%,Na is 1.3, andGz, the Graetz number at the die exit, is 119. For a Cannon standard liquidS6 (η = 9 mPa s), agreement extends up to 5 × 105s−1; at 2×106s−1 (whereNa = 7.2 andGz = 231), the corrections are 11% (measured) and 36% (calculated).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01332917
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