A comparative study of the performance of selected in-line viscometers on Newtonian and shear-thinning fluids

Three commercial instruments for in-line process Measurement of fluid visco sity (an oscillating sphere viscometer, a tube viscometer and a coaxial cyl inder viscometer) were evaluated using a Newtonian (60% sucrose) and two sh ear-thinning fluids (0.5 % xanthan gum and 2 % hydroxypropyl methylcellulos e). The oscillating sphere viscometer required little or no calibration to measure the viscosity of Newtonian fluids. Otherwise, when compared to resu lts given by analytical off-line rheometry, the in-line viscometers were fo und to be grossly inaccurate in predicting viscosity. A methodology is pres ented to correct the flow curves generated by each in-line instrument such that the output measurements are consistent with that given by off-line rhe ometry. Additional characteristics of each instrument that should be consid ered when choosing an instrument for in-line process application are presen ted.