Experimental facility

The experimental set-up is shown in Figure 2.1. An open, torospherical bottom, cylindrical, glass vessel equipped with baffles of different type and spaced $180^o$, and a liquid height-to tank diameter equal to 1.62 is used. Table 2.1 gives the dimensions of the vessel.

Table 2.1: Geometrical dimensions of the laboratory vessel.

Vessel diameter	D	0.308 m
Vessel height	H	0.500 m
$H/D$ ratio	$H/D$	1.62
Baffle width	$B_w$	0.025 m
$B_w/D$ ratio	$B_w/D$	$8.11~\%$
Number of baffles	$n_B$	1
Impeller diameter	d	0.180 m
$d/D$ ratio	$d/D$	$0.584~\%$

Agitation is provided by a $2~kW$ variable speed motor with a maximum angular velocity of $1100~RPM$. The angular velocity is measured with a digital tachometer with a photoelectric pick-up sensor, accurate within $\pm 1~RPM$. The vessel is equipped with a retreated curved blade impeller having diameter equal to $0.18~m$. The ratio between the clearance of the impeller and the vessel diameter is 0.049.

The shaft of the impeller is coupled to an instrumented shaft equipped with two strain gauges. The strain gauges are connected by insulated wires to a slip ring assembly, which, in turn, is connected to a signal conditioner and amplifier system. A data acquisition system board connected to a computer is used to analyze all the signals and extract the data. The vessel can be moved vertically to vary the impeller off-bottom clearance. Experiments are performed at room temperature using tap water and solutions of glycerol to vary the fluid properties. Table 2.2 gives the physical properties of the working fluids taken at $25^o~C$.

Table 2.2: Physical properties of the working fluids.

Liquid	Density	Viscosity
	$[kg/m^3]$	$[Pa \cdot s]$
Water	1000.	0.001
Glycerol ($98\%$)	1259.	0.825
Water-Glycerol solution	1181.	0.025

Three different experimental sets are performed corresponding to the following setups: single beaver-tail baffle, two beaver-tail baffles spaced $180^o$, single finger baffle.