Experimental Investigation of the Transverse Size of a Viscous Jet Flowing Out of a Capillary Channel

The radii of the orifice of a capillary channel and a jet flowing out of it are generally different. Fluid friction on the channel walls leads to the parabolic velocity distribution, while small shear stresses at the free jet boundary are responsible for the velocity profile equalization. Dissipation has an effect on both the length of the region, where the velocity profile is settled, and its radius-average value, as well as on the steady-state jet radius. Previously, the corresponding problem was theoretically solved in the axisymmetric approximation. However, the symmetry condition is not fulfilled in the case of small Reynolds numbers, owing to the occurrence of a bend flow region. Moreover, in the jets flowing out at a low velocity there occur the phenomena of global and boundary instability of the capillary flow. The totality of the nonlinear, mutually-agreed effects leads to velocity profile deformation, such that it becomes asymmetric with respect to the axis in the region, where its value is settled, and the non-uniqueness of the Reynolds-number dependence of the jet radius. The results of an experimental investigation of the dependence of the steady radius of highly viscous jets on the outflow velocity are for the first time presented for the case in which the bend flow region arises.