A corotating two-roll mill for studies of two-dimensional elongational flows with vorticity

A closed-form analytical solution for the Stokes flow generated by a corota ting two-roll mill is used to generate two-dimensional elongational flows w ith well-defined amounts of vorticity. These flow devices can generate cond itions found between simple shear and purely elongational flows, and are am ong the few systems that can take into account the presence of nearby bound aries. In the laboratory, these devices have been used for studies of the m icrostructural dynamics of complex fluids such as polymeric solutions, coll oids, bubbles and drops, etc., and allow pointwise optical studies of the f low parameters. Hence, a comparison is presented of available experimental and numerical results for the stagnation point versus the analytical soluti on presented here. Based upon this solution, a new design for the two-roll mill is presented for the purpose of minimizing the disadvantages of curren t mills. (C) 2000 American Institute of Physics. [S1070- 6631(00)00510-9].