Numerical Analysis On Performance Of Outwardly Pumping Spiral Groove Mechanical Seal With Gas-liquid Film Lubrication

There are a lot of pumps in petrochemical industry, used for conveying easily vaporized,highly toxic, high-temperature, flammable and combustible liquid medium. In recent years,outwardly pumping spiral groove gas seal whose spiral groove is located at the inner diameterof seal end face, has been applied to seal such liquid medium pumps, to achieve an effect ofzero leakage and even zero emission of sealed medium, because the ordinary mechanical sealsof these pumps can not meet the sealing requirements. However, when the blocking gaspressure of outwardly pumping spiral groove gas film seal is lower than the design pressure,the sealed liquid medium may enter the seal end clearance, and thus the flow field and thesealing performance of outwardly pumping spiral groove gas film seal will be affected.In this paper, the fluid film between outwardly pumping spiral groove seal end clearancewas studied, and the flow field of fluid film in the clearance was obtained by using Fluentsoftware to solve three-dimensional N-S equations. Firstly, the fluid flow was simulated whenthe fluid between outwardly pumping spiral groove seal end clearance was pure gas, and thepressure distribution, the velocity distribution and the path lines of fluid film were obtainedunder the condition of hydrodynamic action. Secondly, by using the VOF model, the fluidflow was simulated when sealed liquid medium entered the clearance, and the phasedistribution of gas and liquid would change because the gas-liquid film flow was transientstate. Thirdly, surface tension’s influence on gas-liquid two-phase flow process was studied,discriminated by film pressure, opening force, phase distribution of gas and liquid, and so on.Finally, critical value of the blocking gas pressure was solved, and the gas-liquid film flowfield was analyzed when the blocking gas pressure was zero. The conclusions are as followed:the hydrodynamic effect can be enhanced by sealed liquid medium and surface tension; thepumping rate will reduce when the flow resistance of gas medium increases; mixture of gas and liquid will change the sealing performances of pressure distribution, opening force, phasedistribution of gas and liquid, and will make the fluid flow in seal end clearance change froma laminar flow state into a turbulent flow state; the critical value of the blocking gas pressureis solved out, and so are the times needed for sealed liquid medium to flow into spiral grooveand to flow to inner diameter boundary when the blocking gas pressure is zero. The studyprovides data to the design of sealing auxiliary system.