Measuring shear stress at lowest possible shear rates and improving viscosity determination of fat suspensions, for example chocolates

摘要

In industrial practice, flow property results are frequently discussed due to deviations caused by the measurement method. This project intended to improve preciseness of measuring fat suspensions like chocolate masses at very low shear using a rotary viscosimeter. Results showed no impreciseness at continuous shear rates of 0.03 s~(-1) and above. A new measurement profile including constant shear of 0.05 s~(-1) and flow curve evaluation according to Windhab and Casson models was created. Measuring seventeen different chocolates and comparing with a previous method showed changes in numerical results. Shear stress at constant 0.05 s~(-1) approximated to Casson and Windhab yield values; they were brought into agreement. Linear correlation between the various data sets at low and high shear rates gave acceptable results, thus allowing any of the models to be used in laboratory practice. Finally, repeatability at low shear was further improved after fine tuning and avoiding wall slip effects.