Estimation of Friction and Inlet Loss Coefficient in Stationary Annulus

The wear rings are annular flow path provided in pumps, which offer significant resistance to the leakage flow. The pressure loss in annulus is composed of inlet loss at the entrance of annulus and friction loss in the annulus. The loss coefficients for annulus with lower R/C (mean radius of annulus to radial clearance) of ~ 10 to 70 were estimated and available in literature, whereas the wear rings have R/C ratio of about 250–700. CFD analysis of annulus with entrance region is carried out in ANSYS FLUENT. The friction coefficient is estimated for lower R/C ratio and the results obtained from CFD analysis matches well with correlations available. For annulus with larger R/C ratio (250–700), the friction loss coefficient estimated for stationary annulus found to match well with correlations developed for annulus with smaller R/C ratio. The behaviour of inlet loss coefficients for annulus is estimated. Inlet loss coefficient is estimated to be ~ 0.4 in turbulent regime for all the annulus studied. In laminar regime, the inlet loss coefficient was much higher than 0.4, which is found to decrease with increase in Reynolds number.