Thermodynamic, Transport, and Chemical Properties of “Reference ...

Figure 12: A photograph of the viscometer used for the measurement of methyl- andpropylcyclohexane.The instrument allows viscosity measurements relative to liquids with well knownviscosities. Calibrations were performed with certified viscosity standards to determinethe constants C and E of the working equation: = C·t - E / t 2 . (7)The first term on the right hand side of this equation is the reformulated Hagen-Poiseuilleexpression for laminar flow in a circular tube whereas the second term is the Hagenbach-1correction for kinetic energy losses. Symbol denotes the kinematic viscosity in mm2·sand t the efflux time in seconds of a known volume of liquid through the capillary. Effluxtimes are measured with three thermistor sensors on the outside of the capillary aboveand below the two measuring bulbs. The thermistors detect the passing of the liquidmeniscus at their locations and trigger an internal stopwatch. Depending on the viscosityrange the two upper or the two lower thermistors are used to time the efflux of the testliquid through the respective measuring bulb of known volume.25