The flow of polymer thickened motor oils in convergent jet thrust nozzles

Jet nozzles are described in which liquids are subjected to uniaxial and biaxial stretching motions, shear also being present near the nozzle walls. Jet thrust measurements show that the behaviour of polymer-thickened oils can best be studied by comparison with the behaviour of Newtonian base oils at equivalent Reynolds numbers. These data compare well with measurements previously made in long, straight tubes.Jet thrusts for polymer-thickened oils are lower than those of base oils and show evidence of a threshold point at which the two forms of behaviour deviate. The axial stress in the oil is almost independent of the strain rate, at high strain rates, but is related to axial strain in a simple manner. For 3.5 per cent polymer dissolved in Iranian light base oil, the axial stress is shown to be τ₁₁ = 2000 γ_G dyn cm^?2 for uniaxial strain and τ₁₁ = 2800 γ^1.30_G dyn cm^?2 for biaxial strain, where γ_G is the measure of strain defined by Green. For a standard Shell Multigrade 20W/50 motor oil the equivalent equation for biaxial strain is τ₁₁ = 3200 γ^1.02_G dyn cm^?2. The stresses developed during biaxial extension are higher than those developed during uniaxial extension.The presence of fully elastic behaviour in polymer-thickened oils at extensional strain rates of the order 500 s^?1 and principal extension ratios of only 8 is of potential significance to lubrication technology. The stress rises with the square of the extension ratio and should become large as lubricated surfaces approach. Polymer degradation will commence as the stress rises; it is suggested that further tests be carried out at higher stresses and temperatures.