**5. Case of study**

In this case, an academic example of a photocatalytic reactor design process is included. More specifically, the intention is to develop the hydrodynamic simulation of the photocatalytic reactor. The data that can be obtained from hydrodynamic simulation permits a detailed definition of the flow motion features, for example, fluid speed in the reaction zone, fluid pressure distribution, and the use of these data as input for further calculations such as distribution of energy from light source, photocatalytic reaction, etc. To achieve these calculations, literature and operational basic requirements were studied in order to define fundamental criteria to assign basic dimensions to the reactor geometry.

With the definition of basic dimensions, it is possible to start using CAD tools to build 3D models that will provide the reactor geometric features that will be needed during CFD simulations. Creo 4.0 and SolidWorks 2016 were used to develop the 3D models of the proposed reactor. For hydrodynamic calculations ANSYS Fluent® versions 18.2 and 19 were used [6, 7].

#### **5.1 Initial calculations**

To be able to grow an understanding of the basic reactor design criteria, it was needed to consult the bibliography in different functional areas. The design intent is to build a photochemical reactor of an appropriate size to support laboratory capabilities for testing of nanoparticles after those are synthetized by our research group. It is important for this design to simplify as much as possible the reactor operation.

The basic dimensions defined for the reaction zone container are 300 x 40 x 25 mm. From these dimensions everything else was defined until a 3D model was ready for each component of the reactor including a file with the part assembly that contains the whole reactor. Also, the basic dimensions allow fundamental initial calculations such as volume, inlet/outlet diameter, Reynolds number, etc. Some of the initial assumptions made for this reactor relate to the shape of the reaction zone container which was defined as cuboid (a rectangular hexahedron or a polyhedron bounded by six quadrilateral faces) as will be displayed in the next pages. Within this reaction zone, polluted water will be subject to a chemical reaction to degrade the pollutant into harmless components. So, the fluid chosen is water with a pollutant in low concentration.

Another criterion that needs to be covered in this initial part is the pollutant that will be considered during the design procedures. For this case hydrogen peroxide (H2O2) at very low concentrations (20 mg/L) was selected, so for hydrogen calculations the effects of the pollutant may be ignored, and the fluid may be considered as water. Inlet velocity is considered completely axial to the inlet face, and this face is considered exposed to the atmospheric pressure (Pabs = 1 atm). All the walls in the domain are considered steady nonslip conditions. The analysis was performed in steady state (nondependent of time) and in laminar regime considering that Reynolds number can be calculated with the next equation: *Re* = \_

$$Re = \frac{V \rho \text{ Lc}}{\mu} \tag{5}$$

*V* = velocity in m/s.

ρ = density in kg/m3.

Lc = characteristic length in m.

μ = dynamic viscosity in Pa-s.

For the geometry employed in the reactor, characteristic length may be calculated with the next equation (for rectangular ducts): *Lc* = \_

$$L\_c = \frac{4 \times A}{I} \tag{6}$$

**93**

**Figure 2.**

**Table 1.**

*Hydrodynamic Analysis on a Photocatalytic Reactor Using ANSYS Fluent®*

With the initial parameters mainly in the reaction zone, the CAD 3D models were developed to continue further building the rest of the components. After designing each one of the components, the assembly of the whole reactor was built, and engineering prints were also generated to complete the CAD development. In this chapter the reaction zone will be the main focus for calculations. The rest of the assembly will be displayed to complement the reactor context. Engineering prints will be mentioned only, but the information within the prints which is intended to manufacture the components falls out of the scope of this chapter. The assembly of

Once the geometry definition of the reactor is completed, then it is needed to define the domain where the hydrodynamic calculations will be performed. The reaction zone was defined from the beginning and is considered the central part of the reactor. From the reaction zone, the volume that will be used for hydrodynamic calculations is extracted using CAD software and ANSYS Fluent® tools. The geometry of the reaction zone is shown in **Figure 3**. This domain is the central part of

**Item Inlet velocity (m/s) Reynolds number Residence time in the reaction zone (s)**

 0.05 266.2 5.00 0.10 532.4 2.50 0.15 798.6 1.33 0.20 1064.8 1.25 0.25 1331.0 1.00

*Photocatalytic reactor proposed. (a) Reactor assembly isometric view and (b) reactor assembly side view.*

*Effects of cell count for an experiment under V = 0.05 m/s during the mesh analysis.*

*DOI: http://dx.doi.org/10.5772/intechopen.89782*

**5.2 Tridimensional models using CAD tools**

the reactor design is displayed in **Figure 2**.

So, we can calculate for a velocity with the next value: *V* = 0.025 m/s:

$$A = 0.25 \, m \times 0.003 \, m = 75 \times 10^{-6} \, m^2$$

*P* = (2 × 0.025 *m*) + (2 × 0.003 *m*) = 0.056 *m*

$$L\_c = \frac{4 \times \left(75 \times 10^{-6} \,\mathrm{m}^2\right)}{0.056 \,\mathrm{m}} = 0.00535 \,\mathrm{m}$$

$$L\_c = \frac{\frac{\frac{\pi}{4}}{4} \frac{\pi}{0.056} \frac{m}{m}}{0.056 \, m} = \text{0.002532 } \,\text{m}$$

$$Re = \frac{0.025 \,\text{m/s} \times 998.2 \,\text{kg/m} \times 0.00535 \, m}{0.001003 \,\text{kg/m} \, ^\circ \text{s}} = 133.10 \,\text{J}$$

Then, the values for Re may be calculated for different inlet velocities (**Table 1**).

For the hydrodynamic simulation, the inferior face to work as the reaction surface as well as the inlet and outlet flow face was defined. The liquid selected will be water, and the properties are defined as explained in prior pages. The properties that will be used for water are:

Density = 998.2 kg/m3 . Viscosity = 0.001003 kg/(m-s). Inlet velocity = 0.05 m/s. Temperature = 288.16 K = 15.01 C.
