A new three-control-volume theory for circumferentially-grooved liquid seals

Abstract

Circumferentially-grooved seals are used in centrifugal pumps to reduce leakage flow. Florjancic (1990) developed an analysis using a partition of the seal into three control volumes, bulk-flow theory and Hirs' lubrication equations. This thesis presents a new theory based on Florjancic's work to predict leakage flow and rotordynamic coefficients for circumferentially-grooved liquid seals, through a perturbation analysis of the pressure and velocity governing equations. We assume a single-vortex flow pattern in seal cavity, and account for the penetration of main flow streamlines inside cavities and a first order flow leaving the main flow. Validation of the new analysis is achieved through a comparison with existing experimental data taken from Kilgore (1988), lwatsubo (1990), and Florjancic (1990). Theoretical results are fair and consistent, i.e., a modification in the seal parameters always induces evolution of the rotordynamic coefficients according to the right expected trend. Direct and cross-coupled stiffness coefficients are slightly underpredicted, whereas direct damping coefficient is undetpredicted within 40%. Leakage flow predictions are very good.