Reverse roll coating of non‐Newtonian liquids
作者:
D. J. Coyle,
C. W. Macosko,
L. E. Scriven,
期刊:
Journal of Rheology
(AIP Available online 1990)
卷期:
Volume 34,
issue 5
页码: 615-636
ISSN:0148-6055
年代: 1990
DOI:10.1122/1.550145
出版商: The Society of Rheology
关键词: Reverse roll coating;Flow field in cylinder gap;Flow instabilities;Capillary number;NON−NEWTONIAN FLUIDS;COATINGS;SHEAR FLOW;DEPOSITION;STEADY FLOW;FLOW RATE;SOLUTIONS;ORGANIC POLYMERS;FILM FLOW
数据来源: AIP
摘要:
The essence of reverse roll coating is the rapid high‐shear flow in a small gap between two rigid cylinders rotating with opposed surface speeds. The flow field established in this gap, including the free surface locations and flow rate, is determined mainly by the balance of viscous and surface tension forces, as measured by the capillary number. Non‐Newtonian rheological behavior can strongly affect both the steady, uniform flow and the instabilities to which it is susceptible. Computed solutions of the governing equations indicate that flows of purely viscous liquids differ little from those of Newtonian liquids at the same capillary number, provided that the dimensionless force ratio is defined with the viscosity at the appropriate shear rate. Experiments with shear thinning but relatively inelastic algin solutions confirm this, with the exception that ribbing is strongly exaggerated, presumably by slight elasticity of the liquid. Experiments with highly elastic polyacrylamide solutions show that the coating thickness and the nature of the instabilities can be dramatically altered.
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