| Nowadays,people put forward higher requirements for lubricants in the industrial application scenarios.Lubricants should not only adapt to various extreme conditions,but also have good wear reduction and anti-wear performance.In order to improve the performance of lubricants,it is increasingly common to use synthetic oils,mineral oils,greases and lubricants containing various additives.These lubricants often exhibit various properties of nonNewtonian fluids.However,the lubrication characteristics of non-Newtonian fluids are very complicated,and it is often difficult to obtain ideal results either in theoretical calculation or in experimental study.In the extreme working conditions of high temperature and high pressure,lubrication failure will occur to all kinds of lubricants.In this article,influencing factors of nonNewtonian properties of fluids are analyzed theoretically and experimentally.The main contents are as follows:1.The one-dimensional energy equation is reasonably simplified at the plate lubrication interface,and the temperature effect equation in the form of non-Newtonian fluid constitutive equation is obtained by integrating the Reynolds viscosity equation and shear strain rate expression.The properties of the temperature effect equation were analyzed by selecting the 1%polyvinyl oxide aqueous solution as the research object,and the actual working conditions were set.The following conclusion was drawn: the temperature effect equation obtained from the average temperature showed that with the increase of the shear strain rate,the shear thinning phenomenon would occur,but the whole contact area could be effectively lubricated;the temperature effect equation of the temperature at the outlet position shows that there is a shear stress limit,exceeding which lubrication failure will occur;the outlet position is the most dangerous point in the contact zone.2.Based on the flow velocity separation method,the universal fluid lubrication equation is derived,then the temperature effect equation is applied to it.The specific steps of numerical solution are given,and a numerical solution is obtained by selecting a working condition.Compared with Newtonian fluid the results showed that: under the effect of temperature,the bearing capacity of the fluid is not like a Newtonian fluid,which can always increase with the decrease of the film thickness.However,the bearing capacity can be improved by decreasing the film thickness within a certain range.After decreasing the film thickness beyond this range,the bearing capacity decreases instead of increasing;In addition,with the decrease of film thickness,when the fluid reaches the shear stress limit,the maximum pressure will shift towards the inlet position.3.Taking polyvinyl oxide aqueous solution as the research object,six different solutions were respectively prepared.The rheological properties of polyvinyl oxide aqueous solution were measured in detail by using Haake Rheowin MARS40 rheometer under different temperature and range of shear strain rate.The results show that in the range of higher shear strain rate,the high concentration of polyvinyl oxide solution shows the characteristic of shear thinning.With the increase of shear strain rate,the viscosity of the solution gradually decreases and tends to a fixed value,and the higher the temperature is,the more obvious this characteristic is.However,in the range of low shear strain rate,the high concentration of polyvinyl oxide solution shows the characteristic of shear thickening followed by shear thinning,and the higher the temperature is,the more the solution tends to be Newtonian fluid,while the lower the temperature is,the more the solution tends to be non-Newtonian fluid.In addition,the following experimental phenomena were observed: with the increasing of shear strain rate,the high viscosity solution was easy to climb the rod at low temperature;low viscosity solution is easy to be thrown out at high temperature.4.The viscosity-temperature characteristics of the six solutions configured previously were measured in detail and fitted using the Reynolds viscosity equation.The results show that the viscosity of high concentration of polyvinyl oxide solution decreases with the increase of temperature.Under the condition of the same shear strain rate,the higher the concentration of the solution,the more obvious this characteristic is.The higher the shear strain rate is,the less obvious this characteristic is.In addition,the ratio of ethylene glycol added to the base solution has little effect on the trend of viscose-temperature characteristics. |
