The Performance Study On Lubricant Gas Film Of The Spiral Grooved Dry Gas Seal Based On The Second Order Slip Boundary Conditions

With spiral grooved dry gas seal performance researched unceasingly, its applicationscope is from the high peed and pressure expanded to low speed and pressure. At low speedand pressure, the dynamic pressure effect of dry gas seal face is weaked, which make gas filmthickness thinner and make end face produce dry friction and serious wear, because it isdifficult to establish stable gas film. It results in the research of dry gas seal face sliding flowproblem at low speed and pressure. In this paper, the second-order nonlinear sliding boundaryconditions of the gas flow in dry gas seal slots is constructed on the first-order linear slipboundary condition and theoretical analysis. Then it measures the quantitative relationship ofthe parameters influencing nonlinear sliding boundary conditions by the experiment andconstructs the nonlinear dynamical equation of the rarefied gas flow, which analyse howparameters influence the sealing performance and reveals the complex nonlinear dynamicbehaviorin of the dry gas seal system. The main contents and conclusion are summarized asfollow:To address this issue, a modified generalized Reynolds equation is derived with thesecond-order nonlinear slip boundary condition, and the approximate analytic leakage isobtained by solving the nonlinear Reynolds equation with the linear PH method and iterativemethod. Maple program developed with this proposed method was used to compute theleakage values under the different rotational speed and pressure of an engineering instance,and it is compared to the results obtained with the first-order linear slip boundary conditionand the experimental measurements. The results demonstrate that the leakage valuesestimated with the second-order nonlinear slip boundary condition are closer to theexperimental values than that estimated with the first-order linear slip boundary condition.Especially in low-speed and low-pressure conditions, the estimated values with second-ordernonlinear slip boundary condition are significant better than with the first-order linear slipboundary condition.To address this issue, a modified generalized Reynolds equation is derived with thesecond-order nonlinear slip boundary condition, and the approximate analytic gas film thrustis obtained by solving the nonlinear Reynolds equation with the linear PH method anditerative method. Then, the approximate analytic gas film stiffness is obtained by gas filmthrust derivativing of the gas film thickness. Maple program developed with this proposedmethod is used to compute the gas film stiffness values under the different rotational speedand pressure of an engineering instance, and it is compared to the results obtained with the first-order linear slip boundary conditions and the experimental measurements. The resultsdemonstrate that the gas film stiffness values estimated with the second-order nonlinear slipboundary condition decreases with the gas film thickness increasing, and it is the nonlinearrelationship between the stiffness and thickness of gas, and the gas film stiffness increaseswith the pressure and rotate speed of the medium increasing, and it is the linear relationshipbetween the gas film stiffness and the pressure and rotate speed of the medium, and the gasfilm stiffness values estimated with the second-order nonlinear slip boundary condition arecloser to the experimental values than that estimated with the first-order linear slip boundarycondition, and it has the higher calculation accuracy. Especially in low-speed andlow-pressure conditions, the estimated values with second-order nonlinear slip boundarycondition are significant better than with the first-order linear slip boundary condition. Theoptimization design by hydromechanics theory with the second-order nonlinear slip boundarycondition in shaft dry gas seal of the low-speed and low-pressure conditions can guideengineering application.The modified generalized Reynolds equation was derived under the second ordernonlinear slip boundary conditions. The nonlinear Reynolds equation was solved to obtain theapproximate solution of gas film thrust by using the PH linearization method, iterative method.Then, gas film stiffness approximate solution was obtained by derivativing gas film thickness.And a trade-off function of rigidity-to-spillage ratio was derived and the optimized geometricparameters were acquired by solving the objective function. Then the gas film stiffness valuesand Leakage values were calculated under the different media pressure and rotational speedby using Maple Program according to an engineering instance, which were compared with theexperimental values. The results show that: Testing values of dry gas seal prototype under theoptimized geometric parameters closed to theoretical numerical calculation. It explained thattheoretical numerical values of the second order nonlinear slip boundary conditions had goodprecision.The spiral groove dry gas seal system was studied in the dry gas seal test bench, andshowed real figure of the dry gas seal test bench. In order to ensure the accuracy of the testresults, it takes the necessary anti-interference measures system. The experimental values ofmicroscale end flow parameters are obtained by optimization of the spiral groove dry gasseals prototype.Through the experimental data and the theoretical data contrasted, thetheoretical data on the second-order linear slip boundary conditions is closer to theexperimental value, especially at high speed and high pressure, which verify the correctnessof the theory in this paper.