Energy efficiency in rotating equipment

Abstract: This paper reports the findings of the first stage of a study on how the efficiency of a centrifugal pump depends on the eccentricity of the impeller (rotor). The geometry of the pump is based on the ERCOFTAC centrifugal pump that has been used to validate computational fluid dynamics software with laboratory measurements. The pump is modelled using the CFD-code Comsol multi physics (tm) in order to get the pressure and velocity field. From the pressure and velocity field the efficiency and output power for the pump is calculated. The energy efficiency of the same pump with different static eccentricities is then compared, showing the effect of eccentricity To validate the CFD-model the velocity and pressure field for the pump is compared to results from another simulation of the same pump and an experiment. The comparison shows that the results are comparable and shows good agreement with experimental data. It is showed that the energy losses of the pump increase with increased static eccentricity of the impeller. The losses at 10% eccentricity are about 0.5% of the produced energy. The main contribution to the losses is the introduced asymmetry, eccentricity, of the pump, which causes an unsteady flow and also increases the total unbalance force on the rotor. It is further noted that rotor-stator interactions of the impeller and the stator blades have small influence on the energy losses. It is concluded that rotordynamic design can improve the energy efficiency of the process that the rotating equipment is involved in. Further research is suggested on whirling eccentric motion, experimental verification and more detailed simulation models.