Design And Manufacture For Strong Shear Rheometer And Experimental Study Of Shear Flow Cavitation

Cavitation often appears in hydraulic pressure system. The influence of liquid temperature and pressure and surface tension and tensile strength is obvious. Bubble inception and grow and collapse is a particularly important process. As for the film rupture in the sliding solid wall, the influence of shearing cavitation is obvious. Of course, shearing cavitation has highly important effects on the hydraulic pressure system efficiency and the lubricating performance of film oil and rheology measurement. The former researcher had only used highly viscous liquid. Furthermore, they had not considered carefully the influence of the solubility of air in the solution. The researcher had explained the shearing cavitation by the principal normal stress cavitation criterion or the shear stress nucleation or the shear energy nucleation. The research by us indicated that the influence of the solubilities of air in the solution and the film stability is obvious.The experimental system principle and its structure and its function are indicated in this paper. Base on the techniques of high-precision designing and machining, a new Couette apparatus where its outer cylinder rotating with flow visualization and pressure control has been made. Utilizing the well-known viscosity-temperature formula and approximate adiabatic surroundings, the viscosities of water and 10cSt silicone oil and 16500cSt silicone oil at high shear rates measured by this apparatus agree well with that obtained the computed viscosities at various temperatures. At a certain shear stress, cavitation occurred for fresh water and two silicone oils with low and medium viscosities. After the thermocouple is located in the stationary cylindrical layer, in a Cylindrical coordinate system, with the experimental shearing torque and transient heat transfer differential equation, the transient computed temperature of high shearing flow are calculated by numerical equation. The transient computed temperature was consistent with the experimental temperature. It shows that the shearing torque and the symmetrical gap and the transient temperature of pressure fitting Couette flow apparatus where its outer cylinder rotating is transparent are precise. The elevated transient temperature of high shearing flow is calculated by the computed methods in the simple calculation. It indicated that the transient computed temperature by the transient heat transfer differential equation is precise and the accuracy verification way can be well fitted by many applications.Overcoming some drawbacks of previous methods measuring gas-solubility, a new piston apparatus was established in which the state equation of ideal gas is used to determine the amount of gas-dissolution. An expression of the Bunsen solubility of air in 500cSt silicone at temperature of 293.2 and 353.2 K and in the gas-pressure range of 0-350 kPa has been determined. Also measured is the Bunsen solubility of air in 20cSt silicone and Chinese 32# hydraulic oil at 298.2 K under various gas-pressures. Reliability and accuracy analyses indicate that the error range of the experimental data is about 6%. The Bunsen solubility and gas-pressure exhibit good linearity while the relationship between the molar fraction and the pressure in the experimental range is nonlinear but can be well fitted by the Krichevsky-Ilinskaya equation. It was discovered that the Bunsen solubilities of air in silicone with quite different molecular mass are closed with each other. We suggest that the molar fraction based on the monomer mass is more appropriate than that based on the molecular weight for engineering extrapolation of the solubility data of small and non-polar solutes in polymer solvents. At last, for the solvent containing much different or uncertain molecular weight, the commonplace in engineering applications, the Bunsen solubility is appropriate to give the dissolved gas concentration.There are two categories of nucleation about classical nucleation, i.e. homogeneous nucleation and heterogeneous nucleation. Four possible types of nucleation are described from gas cavities. Considering influence of liquid surface tension, equilibrium of a spherical nucleus has been discussed based on mechanical equilibrium of the interface. We analyzed the thermal behavior of the gas content. Gas diffusion and nucleus stability has been discussed based on diffusive equilibrium of the interface. The critical nucleus radii where the ratio of the dissolved concentration of air in 500cSt silicone is different have been calculated. The experiment about heterogeneous nucleation has been carried by us in supersaturated still solution. It is clear that the small crevices in solid alls or in solid particles carried by the liquid flow can shelter stable heterogeneous nuclei. Of course, gas cavities can not be formed in still liquid unless there is shearing flow.It is highly important to remove visible small air bubble and to get lighting and to control air in the solution and to select appropriate distinguishing cavitation inception ways in shearing cavitation experiment. This apparatus has been used in the cavitation inception experiment after the saturation ratio of air has been changed. We had given an empirical relationship between the saturation ratio and Peclet number and the Capillary number and the cavitation index. We found that critical shear stress of cavitation inception is roughly proportional to the applied pressure, but it is less than results of PNSCC. The critical shear stress of cavitation inception is roughly inversely proportional to the saturation. The transient temperature of shearing flow will decrease when the cavitation is appearing because quantity of heat is decreasing by shearing torque. The decrease of temperature is consistent with the shearing torque. But the torque is not sensitive. We think that the change of temperature is one of the effective ways about identification shearing cavitaion. According to the classical nucleation theory, the probability of occurrence of nuclei is determined from the free energy required for the formation of a critical bubble formation, the more high the saturation ratio of air in solution is, the more easily the shearing cavitation has been formed. In the gas-undersaturated liquid, shearing cavitation can be formed by increasing the shear rate.