Laboratory vessel

The laboratory CSTR is a vessel with torospherical bottom, equipped with a retreated curved blade impeller. Figure 4.1 shows the computational model of this reactor, for which the domain is discretized into 116106 finite volumes. The impeller is in the curved part of the tank, near the bottom. A single beaver-tail baffle is placed near the wall of the tank to improve the flow circulation and the stirring. Dimensions of the reactor are reported in Table 4.1.

Table 4.1: Geometrical dimensions of laboratory vessel.

Vessel diameter	D	0.308 m
Vessel height	H	0.400 m
Baffle width	$B_w$	0.025 m
Number of baffles	$n_B$	1
Impeller diameter	d	0.180 m
Blade width	b	0.021 m
Number of blades	$n_b$	3

In Figure 4.1, it is possible to observe the baffle, in blue, which is assumed to be of zero-thickness in the finite volume model. A regular meshing was used for the discretization of the cylindrical body of the tank as shown in Figure 4.2, while a deformed grid was used for the round bottom of the vessel (purple part in Figure 4.1) to reproduce the curvature and to model the shape of the impeller. A three dimensional view of the impeller is shown in Figure 4.3. The impeller rotation is counter-clockwise.

Figure 4.1: Front view of laboratory reactor.

Figure 4.2: Top view of laboratory reactor.

Figure 4.3: Impeller shape for laboratory reactor.

Figure 4.4: Boundary conditions for simulations.

Simulations made on this model of the laboratory vessel are aimed at validating the computational code against available experimental data. For this reason, the same fluid and angular velocity examined in the experimental work have been considered for the simulations. The characteristics of all simulations are gathered in Table 4.2. As discussed, all simulations started from still fluid and the flow field was let to evolve until a pseudo-steady state was reached. This procedure is based on the sliding mesh approach (see Appendix A for details) and the coupling between the static and rotating regions is made through the sliding boundary shown in red in Figure 4.4.

Table 4.2: Simulations made for the laboratory reactor.

Ref	Density $[kg/m^3]$	Viscosity $[Pa \cdot s]$	RPM
S1	1200.	0.5	84
S2	1259.	0.825	200
S3	1181.	0.025	80
S4	1181.	0.025	180
S5	1000.	0.001	80
S6	1000.	0.001	200

No-slip condition is used for the wall of the vessel ($\bf {v}=0$), and for the surface of the impeller ( $v_{\theta}(r)=\omega r$). Free shear condition is used at the top of the vessel to simulate a flat free surface.