Flow Patterns of Liquid in a Cylindrical Mixing Vessel without Baffles

Abstract

The velocity distribution of agitated liquid in a cylindrical mixing vessel was measured by using a set of pitot tubes, the construction of which is shown in Fig. 2. Some of the experimental results are shown in Figs. 4, 5, 6, 7, 8, 9 and 10. As a result, the flow patterns in an agitated vessel were made clear and it was ascertained that, in addition to the primary circulation flow around the impeller axis, there was a secondary circulation of liquid ensued by the discharge flow from the tip of an impeller as shown in Figs. 8 and 10. Integrating the measured velocity distributions, the discharge flow rates of impellers were determined and the discharging performance of various impellers (refer to Table 1) was compared in connection with the power consumption. Dimensionless factor, Nq₁, was defined and was called the coefficient of discharge. The ratio, Np/Nq₁ in Table 3, corresponds to the relative power required for a unit quantity of discharge. Furthermore, the power consumption in the neighbourhood of an impeller (Nᴘᵢₘₚ), in other words, in the cylindrical domain (refer to hatched region in Fig. 14) was calculated and compared with that consumed in the outer region of the vessel as shown in Table 4. It is concluded that the improvement in the discharging capacity can be accomplished to some extent by the proper design of an impeller ; however, the fundamental improvement must rely upon some other method.