On the Measurement of Flow Patterns of Liquid in a Mixing Tank, Applying Radio Isotope

Abstract

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: 28cmLiquid used: waterLiquid depth: 26cmImpeller used: paddle type: length 12cmwidth 1.6cmDimensions of baffle plates employed to study the flow pattern under fully baffled condition were:width 3cmlength 30cm; number of plates 4Since 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.