Improved system for measuring rheological properties of thickened liquid using an inclined parallel plate and optical sensor

The purpose of this study was to improve the method of using an inclined parallel plate (IPP) in directly estimating the yield stress ${\tau }_{\mathrm{iy}}$ and evaluating the properties of a thickened liquid. The flow curve of the relationship between the shear rate and shear stress of a liquid thickened with a xanthan gum agent was predicted using the Herschel–Bulkley fluid model ($\tau ={\tau }_y+k{\dot{\gamma }}^{n-1}$). We supposed that the yield stress ${\tau }_y$ and the result of a line spread test (LST) indicate the deformation state and the flow state of shear stress ($k{\dot{\gamma }}^{n-1}$), respectively. ${\tau }_{\mathrm{iy}}$, the yield stress ${\tau }_{\mathrm{ry}}$ estimated adopting a rotational viscometer and LST, was investigated for three liquids thickened with xanthan gum at four concentrations (C) at intervals of 0.5 wt% within the range 0.5–2.0 wt%. Linear plots of the relations of $C$ versus ${\tau }_{\mathrm{iy}}$ and ${\tau }_{\mathrm{ry}}$ and the LST show that with an increase in $C$, the resistance force (${\tau }_{\mathrm{ry}}$ and ${\tau }_{\mathrm{iy}}$) increases until flow starts, after which viscosity increases. We suggest that yield stress ${\tau }_{\mathrm{iy}}$ estimated with the IPP method effectively indicates the rheological properties of thickened liquids.