Abstract
IN a previous communication1 an error in pressure measurement was pointed out, which might lead to spurious results in measuring the viscosity of certain anomalous liquids. Reference was also made to viscosity determinations recently carried out on rubber solutions and the like, using a viscometer in which the true pressure-drop along the capillary was measured directly. The measurements indicated the existence of an end effect, the ratio of the length, L, to the diameter, D, of the capillary, being a significant factor. A typical family of flow curves for one rubber solution, plotted in the conventional manner, is indicated in Fig. 1. These clearly show that if the L/D ratio is sufficiently large, the curves approximate closely to a line which is independent of capillary bore. Smaller L/D ratios give curves diverging from this, indicating a higher apparent viscosity, the divergence increasing as L/D decreases. These curves emphasize the importance of using long tubes, particularly at high stresses, if the results are to be assumed to apply to an equilibrium condition.
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References
Merrington, A. C., NATURE, 152, 214 (1943).
Peek and Ericson, J. Rheol., 2, 351 (1931).
Scott Blair, G. W., "An Introduction to Industrial Rheology" (London: Churchill Ltd., 1938).
Barus phenomenon, Amer. J. Sci., (3), 45, 87 (1893).
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MERRINGTON, A. Flow of Visco-Elastic Materials in Capillaries. Nature 152, 663 (1943). https://doi.org/10.1038/152663a0
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DOI: https://doi.org/10.1038/152663a0
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