Expansion and Contraction of Capillary Jets of Newtonian Liquids

Abstract

Laminar jets of Newtonian liquids are found to contract or to expand upon ejection from a capillary nozzle depending upon conditions of ejection and fluid properties. The ratio of final jet diameter to nozzle diameter is a function of Reynolds number Re and a weak function of Weber number. At Re < 16 the jets expand, above 16 they contract. At Re < 6 expansion becomes independent of Re at a diameter ratio of 1.06, if the Weber number dependence is removed. At Re > 150 contraction becomes independent of Reynolds number at a diameter ratio of 0.87. These results are explained by means of the momentum and energy equations for the motion. The terms in the equations leading to expansion are comparable to relaxing normal stress terms. The existence of relaxing normal stresses in Newtonian liquid jets leads to some questions concerning the origin of normal stresses which are thought to be responsible for the more common observation of expansion in viscoelastic liquid jets.