Converging flow and stretching flow: a compilation

As fluids flow from a reservoir through a constriction they are subject to a complex deformation history which may be considered to contain a strong stretching flow component. A number of workers have studied such flows with the objective of elucidating the stretching flow rheology of the material under test. A wide range of polymeric materials has been investigated in this way including solutions, melts and pastes. As yet there is no general acceptance that converging flow may be interpreted as a dominantly stretching flow and each author who has taken this course has approached it from a different route generating different equations which have, to some extent, obscured the picture. Thus there is, at present, no consensus view on the interpretation of converging flow : however, the differences between different authors are in fact relatively small compared to the magnitude of the problem under investigation. This paper reviews the approaches that have been adopted, and compares the theories and experiences that have been recorded. The objective is to provide an empirical basis upon which practical rheologists may act, from which theoreticians may develop a more fundamental understanding, and as a result of which a more definitive method of measurement may be deduced.