Classification was made of the equipments employed to measure the power requirement of mixing impellers used by previous investigators. The causes of errors made with the measuring equipments were discussed. As the result, it was concluded that static friction would be a serious cause of error and the correction term for Froude number proposed by Rushton contained the errors that could be traced back to this source.

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Using Radio Isotope as a means of measuring liquid velocity, flow patterns of liquid in a mixing tank were studied.
The gist of this method was as follows: A set of device, consisting of a miniature GM counter shielded in an aluminium tube and a steel ball (dia. 5-7mm), containing an appropriate amount of ⁶⁰Co, and hung with platinum wire (dia. 30 micron), was immersed in a mixing tank. In order to compute the liquid velocity by using Eq. (1), the transposition of the ball from P to P', expected from the balance of moments around A, presented in Fig. 3, was determined with fairly good accuracy, by measuring the intensity of gamma radiation. Paying no less attentions to the stability of GM counter and the preparation of a calibrated curve as shown in Fig. 2, the measurement of liquid velocity in each of the experiments was made.
Experimental conditions were as follows:
Tank diameter: 28cm
Liquid used: water
Liquid depth: 26cm
Impeller used: paddle type: length 12cm
width 1.6cm
Dimensions of baffle plates employed to study the flow pattern under fully baffled condition were:
width 3cm
length 30cm; number of plates 4
Since the liquid used was water, the flow patterns thus studied pertain to those of so-called turbulent flow region.
Experimental results are shown in Figs. 4, 5, 6 and 7. In these Figures, marked differences between flow patterns when baffled and those when unbaffled are revealed: decrease of tangential velocity and marked appearance of vertical velocity was noted in fully baffled agitation.
Further, the turbulent state which has been defined by the interrelation between the Power number and the Reynolds number in agitation was experimentally described as the following: Flow patterns are independent of rotational speed of impeller (See Figs. 6 and 7).
In the last section, some considerations on the relationship between flow pattern and power consumption in agitation are given.

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Effects of liquid viscosity on flow patterns were experimentally studied and so far as flow patterns of paddle type impeller were concerned, more concrete explanations were given on the correlation between N_P and Re, which is considered to be an over-all reflection of flow pattern. In the second place, the relation between flow patterns and scale-up was studicd, followed by the study concerning those of geometrically dissimilar impellers.
Experimental conditions were as follows:
Experiment 1: (effect of liquid viscosity)
Tank diameter: 28cm
Liquid (water and glycerine solution) viscosity: 1-108c.p.
Liquid depth: 13cm; Paddle (L=12cm, W=1.6cm)
Experiment 2: (scale-up)
Tank diameter: 15.5-50.0cm
Liquid (water) depth: approximately equal to tank dia. Geometrical ratios relating to paddles, tanks (including baffle plates) and so on were the same as those in Ex. 1.
Experiment 3: (geometrical dissimilarity)
Tank diameter: 28cm
Liquid (water) depth: 26cm
Paddles: dimensions employed are shown in Table 1.
The procedure of measuring liquid velocity reported here is the same as that which was reported in the previous paper.¹⁾
The effect of liquid viscosity on flow patterns is apparent as shown in Fig. 6 (c), in which the pattern is no longer independent of rotational speed of the impeller. This figure corresponds to that of the experimental region (c) described in Fig. 5. Flow patterns expected from the curves in Fig. 5 are checked in Figs. 6 and 7.
Figs. 8 and 9 show flow patterns in geometrically similar mixing systems. Each figure indicates that the pattern remains unchanged, irrespective of dimensions of apparatuses and rotational speed of impellers, so far as the turbulent state is concerned, provided the depression of liquid surface when unbaffled is not taken into consideration.
Flow patterns, particularly tangential velocity distributions in Fig. 4, indicate marked differences among geometrically dissimilar impellers, but a rather simple correlation between C^* and Re^* was observed as presented in Fig. 10, covering a considerably wide range of experimental conditions.
The procedure through which the correlation was made is also described in the previous paper¹⁾.

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