The shape function of a laminar liquid jet issuing from a circular orifice and falling vertically in air under gravity is analyzed. The diameter of the jet is observed to decrease with the axial distance from the nozzle. The governing equation for variation of the jet radius with the axial coordinate is derived from a modified Bernoulli's law, including the interfacial energy density and viscous losses. The analytical solution found in terms of dimensionless group numbers agrees well with experimental data.
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