The experimental observation and modeling of an “Ovaici” necklace and stick–spurt instability arising during the cold extrusion of chocolate
作者:
H. Ovaici,
M. R. Mackley,
G. H. McKinley,
S. J. Crook,
期刊:
Journal of Rheology
(AIP Available online 1998)
卷期:
Volume 42,
issue 1
页码: 125-157
ISSN:0148-6055
年代: 1998
DOI:10.1122/1.550885
出版商: The Society of Rheology
关键词: Chocolate;Instability;Slip;Spurt flow;Stability
数据来源: AIP
摘要:
This paper reports experimental results and modeling relating to the ambient temperature, cold extrusion of chocolate. In particular, extrusion conditions are given where two different modes of instability are described and modeled. In the first case, at low flow rates, a stick–spurt instability is observed, which leads to large amplitude fluctuations in the extrusion pressure and extrudate velocity. This instability is modeled as a modified relaxation oscillation process in which the combined nonlinear plastic flow behavior of the chocolate and the compressibility of the material in the reservoir control the instability mechanism. The second mode of instability, observed for a specific thermal history, concerns the unusual extrusion of a “necklace” structure consisting of beads regularly spaced on a narrow extrudate core. This instability is explained in terms of the steady core–annular coextrusion of two Bingham-plastic chocolate components having different yield stresses.
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