A PLEXIGLAS RESEARCH PUMP WITH CALIBRATED MAGNETIC BEARINGS/LOAD CELLS FOR RADIAL AND AXIAL HYDRAULIC FORCE MEASUREMENT

摘要

A research pump intended for both flow visualization studiesrnand direct measurement of hydraulically induced radial andrnaxial forces has been developed. The impeller and the voluterncasing are constructed from Plexiglas which facilitates opticalrnaccess for laser velocimetry measurements of the flow fieldrnboth inside the impeller and in the volute casing. The pumprnhousing is designed for flexibility allowing for easy interchangernof impellers and volute configurations. The rotor of the pumprnis supported by three radial magnetic bearings and a singlerndouble acting magnetic thrust bearing. The magnetic bearingsrnhave been calibrated to characterize the force versus coilrncurrent and air gap relationship for each bearing type. Linearrncalibration functions valid for rotor eccentricities of up to 2/3 ofrnthe nominal bearing clearances and force level of ± 55.6 Nrn(12.5 lbf) and ± 267 N (60 lbf) for the radial and axial bearingsrnrespectively were found. A detailed uncertainty analysis of thernforce calibration functions was conducted such that meaningfulrnuncertainty bounds can be applied to in situ forcernmeasurements. Hysteresis and eddy current effects werernquantified for each bearing such that their effect on the in siturnforce measurements could be assessed. By directly measuringrnthe bearing reaction forces it is possible to determine the radialrnand axial hydraulic loads acting on the pump impeller. Torndemonstrate the capability of the magnetic bearings as activernload cells representative hydraulic force measurements for arncentered 4 vane 16 degree log spiral radial flow impellerrnoperating in a single tongue spiral volute casing were made. Atrnshut-off a non-dimensional radial thrust of 0.072 was measured.rnA minimum non-dimensional radial thrust of about 0.017 wasrnobserved in the range of 80% to 90% of design flow. Aboverndesign flow the non-dimensional radial thrust increased to aboutrn0.03 at 120 % of design flow. The non-dimensional axial thrustrnhad a maximum at shut-off of 0.335 and decreased steadily tornapproximately 0.175 at 120 % of design flow. A region ofrnincreasing axial thrust, in the flow range 80 % to 90 % of designrnflow, was observed. The measurements are compared to radialrnand axial force predictions using classical force models. Therndirect radial force measurements are compared to arnrepresentative set of radial force measurements from thernliterature. In addition, the directly measured radial force atrndesign flow is compared to a single representative radial forcernmeasurement (obtained from the literature) calculated from therncombination of static pressure and net momentum fluxrndistribution at the impeller exit.