The flow of polymer-thickened oils in convergent jet-thrust nozzles at a temperature of 84°C

It is shown that an existing form of jet-thrust device may be modified for satisfactory use at elevated temperatures. Jets are produced from a straight capillary tube and from three nozzles designed to provide different rates of uniaxial extension in the flowing oil, with shear present near the nozzle walls.The behaviour of three simulated multigrade motor oils with additives of different chemical type is compared with that of Newtonian oils at temperature of 84°C. In straight-tube flow, no measurable normal stress is detected in one of the oils (that with an alkylmethacrylate as polymer additive), but the other two oils give stresses which are measurable and, in one case, as high as those obtained at ambient temperature (that with the styrene-butadiene copolymer additive). For these oils the normal stresses measured in tubes are much closer to the axial stresses measured in nozzles than was the case at ambient temperature.In nozzle flow, axial stresses are detected in each oil which are rather lower than those measured at ambient temperature, the deviation increasing with increased jet velocity. The relative importance of axial stress, compared with shear stress, is shown to increase with increasing temperature and shear rate. The ration of axial stress to shear may reach a value of 3 or 4 at a shear rate of 10⁵set^?1, the oils with styrene-butadiene and styrene-isoprene copolymer additives being somewhat better performers than that with the alkylmethacrylate copolymer additive.It is suggested that the presence of normal, or axial, stresses might improve lubrication performance in those situations where normal load is applied with little relative movement of the bearing surfaces.