Studies on the Cone Type Rotational Viscometer

Abstract

In order to eliminate the end effect of the ordinary rotational viscometer, we designed a new viscometer which was constructed of a conical vessel with a concentrically situated inner cone as shown in Fig.1. The outer cone was rotated by a motor. By comparing the experimental data on the operation of this viscometer with the theoretically calculated values, we obtained a good stable agreement between the two. By means of this viscometer, we were able to measure more accrately even low viscosity as well as high viscosity than by any other rotational viscometer.
The experimental apparatus is shown in Fig.2. A general equation for the torque of the rotational viscometer (with outer cylinder rotated) may be expressed with the aid of Eqs.(3), (4)and (5)as in Eq.(21). From this, a theoretical equation for the cone type rotational viscometer may be derived using Fig.6, which will be expressed as shown in Eq. (28),
By introducing the constants of this apParatus, (t₁, t₀, H, r₀) and (h, M, N) into Eq. (28), we obtained the coeffcient of viscosity η of the sample liquid. Eq. (31) shows the relation between the moment M and the angle of deflection θ of torsion wire.
The experimental data are shown in Figs.7, 8 and 9. In Figs.7 and 8, we find the sample liquids having the quality of the Newtonian liquid, and the data represented by linear lines through the origin. As seen from these results, the end effect was completely eliminated from this apparatus, and the experimental data obtained with it were well ordered and had good reproductivity. Fig. 10 shows the relation between torque M and the dipped height of the inner cone into liquid, it having been proved that M is proportional to h³ and that there is a good agreement between Eq. (33) and the experimental results.
The comparison of the experimental data on this cone type rotational viscometer and those of the other viscometers is shown in Fig.12. For water, the difference between the two was about 50%. It may be considered somewhat greater than ususal, but such is common with ordinary viscometers. The data on other oils and resin varnishes obtained with this viscometer were approximately equal to those obtained with other viscometers, measurements being always stable and having good reproductivity.