**5.2 Tridimensional models using CAD tools**

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

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


**Table 1.**

*Computational Fluid Dynamics Simulations*

The basic dimensions defined for the reaction zone container are 300 x 40 x 25 mm.

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

*V* ρ Lc

For the geometry employed in the reactor, characteristic length may be calcu-

*Lc* = \_ 4 × *A*

) \_\_\_\_\_\_\_\_\_\_\_\_\_\_ 0.056 *<sup>m</sup>* = 0.00535 *<sup>m</sup>*

= 133.10

*<sup>m</sup>*⁄*<sup>s</sup>* <sup>×</sup> 998.2 *kg*⁄*m*<sup>3</sup> <sup>×</sup> 0.00535 *<sup>m</sup>* \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_0.001003 *kg*⁄*<sup>m</sup>* <sup>−</sup> *<sup>s</sup>*

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

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

*A* = 0.25 *m* × 0.003 *m* = 75 × 10−6 *m*<sup>2</sup>

0.025

.

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

*Lc* = <sup>4</sup> × (75 × 10−6 *m*<sup>2</sup>

μ (5)

*<sup>I</sup>* (6)

Reynolds number can be calculated with the next equation:

*Re* = \_

lated with the next equation (for rectangular ducts):

*V* = velocity in m/s. ρ = density in kg/m3.

*Re*=

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.

Lc = characteristic length in m. μ = dynamic viscosity in Pa-s.

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.

**92**

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

**Figure 2.** *Photocatalytic reactor proposed. (a) Reactor assembly isometric view and (b) reactor assembly side view.*

#### **Figure 3.**

*Reaction zone, (a) isometric view of reaction zone, (b) top view of reaction zone, and (c) lateral view of reaction zone including LEDs.*

CFD calculations because the methodology used is finite volume. For that purpose, the domain will be processed using the software by first discretizing the domain in small control volumes where the governing equations will be resolved with the help of numerical methods to obtain valuable results.

Finite volume methodology is based in dividing the domain in a number of control volumes (cells or elements), the elements should not overlap among them, and the variable of interest is located at the centroid of each element. If the nodes in the border wall of each consecutive region are unidentical, the mesh is nonconformed. The walls should connect through their interphase, and calculated flows through these walls may be assigned from a mesh to the other.

Conformed mesh is the most precise connectivity between regions. Nonconformed mesh may reduce the complexity of the meshing process but would increase the error, at least the local error. In this work, there is an effort to obtain the conformed mesh during the discretization process.

#### **5.3 Photocatalytic reactor general operation**

The reactor operation is simple; the design intent is having an inlet circular port with a diameter of 6 mm and arrives into a rectangular cavity which is filled until reaching the reaction zone level. Then the fluid circulates through the reaction zone under a laminar flow regime. The fluid reaches the outlet and finally goes

**95**

**Figure 4.**

*Definition of reaction zone for CFD simulations.*

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

out through a 6-mm-diameter outlet port. The reaction zone has the dimensions of 3 mm x 25 mm x 250 mm, and from there the calculated volume is 18,750 mm3. With these dimensions the reactor complies with one of its purposes since it is intended for laboratory testing. **Figure 4** shows an image of the domain.

The reactor has a cover made of a transparent material that allows light to pass through; in this case we selected Pyrex glass with dimensions of 40 x 300 mm, and it will be fastened to the main block using ten fasteners and two fixing devices made

The light source will not be analyzed in this chapter, but initial estimations will be mentioned in this section. The distance to locate the light source from the reaction zone is adjustable. For the light source, it is intended to use 10 lamps which will be UV LED devices with 365 nm mounted in a bench that will have dimensions of 25 x 300 mm. LEDs are distributed along the reaction zone in 250 mm of the total length. Light source selection is based in some of the advantages this device offer such as low electric consumption, long life cycle, and easy control of light intensity

The inlet and outlet have a 6 mm diameter with a threaded connection. The centerline of the inlet is located at a height of 18 mm with respect to the reactor base. The outlet is located at a height of 10 mm with respect to the reactor base with

An initial mesh of *m* (0.75 mm) hexahedral-type cubic cells was used considering the geometry is simple enough, applying a meshing method known as hexadominant within the native options within ANSYS® Mesh. The initial meshing process generated 52,615 cells. This is the first step in an iterative process where the cell count increases in order to find the optimal cell count where the effect of the number of cells in the calculation is minimized. This is done comparing the iterative residual values in a simple calculation; when the difference between one experiment and the subsequent is minimum, then the cell count may be considered irrelevant,

and this may be considered the optimum cell count for the problem.

The option facing was used to standardize the cell size and its orthogonality (these are native options within ANSYS® Mesh). During the mesh analysis,

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

of metal with dimensions of 7.5 x 300 mm.

using low-cost electronic devices.

the intention of helping out the fluid.

**5.4 Mesh details**

*Hydrodynamic Analysis on a Photocatalytic Reactor Using ANSYS Fluent® DOI: http://dx.doi.org/10.5772/intechopen.89782*

out through a 6-mm-diameter outlet port. The reaction zone has the dimensions of 3 mm x 25 mm x 250 mm, and from there the calculated volume is 18,750 mm3. With these dimensions the reactor complies with one of its purposes since it is intended for laboratory testing. **Figure 4** shows an image of the domain.

The reactor has a cover made of a transparent material that allows light to pass through; in this case we selected Pyrex glass with dimensions of 40 x 300 mm, and it will be fastened to the main block using ten fasteners and two fixing devices made of metal with dimensions of 7.5 x 300 mm.

The light source will not be analyzed in this chapter, but initial estimations will be mentioned in this section. The distance to locate the light source from the reaction zone is adjustable. For the light source, it is intended to use 10 lamps which will be UV LED devices with 365 nm mounted in a bench that will have dimensions of 25 x 300 mm. LEDs are distributed along the reaction zone in 250 mm of the total length. Light source selection is based in some of the advantages this device offer such as low electric consumption, long life cycle, and easy control of light intensity using low-cost electronic devices.

The inlet and outlet have a 6 mm diameter with a threaded connection. The centerline of the inlet is located at a height of 18 mm with respect to the reactor base. The outlet is located at a height of 10 mm with respect to the reactor base with the intention of helping out the fluid.

### **5.4 Mesh details**

*Computational Fluid Dynamics Simulations*

**94**

**Figure 3.**

*reaction zone including LEDs.*

of numerical methods to obtain valuable results.

these walls may be assigned from a mesh to the other.

conformed mesh during the discretization process.

**5.3 Photocatalytic reactor general operation**

*Reaction zone, (a) isometric view of reaction zone, (b) top view of reaction zone, and (c) lateral view of* 

CFD calculations because the methodology used is finite volume. For that purpose, the domain will be processed using the software by first discretizing the domain in small control volumes where the governing equations will be resolved with the help

Finite volume methodology is based in dividing the domain in a number of control volumes (cells or elements), the elements should not overlap among them, and the variable of interest is located at the centroid of each element. If the nodes in the border wall of each consecutive region are unidentical, the mesh is nonconformed. The walls should connect through their interphase, and calculated flows through

Conformed mesh is the most precise connectivity between regions.

Nonconformed mesh may reduce the complexity of the meshing process but would increase the error, at least the local error. In this work, there is an effort to obtain the

The reactor operation is simple; the design intent is having an inlet circular port with a diameter of 6 mm and arrives into a rectangular cavity which is filled until reaching the reaction zone level. Then the fluid circulates through the reaction zone under a laminar flow regime. The fluid reaches the outlet and finally goes

An initial mesh of *m* (0.75 mm) hexahedral-type cubic cells was used considering the geometry is simple enough, applying a meshing method known as hexadominant within the native options within ANSYS® Mesh. The initial meshing process generated 52,615 cells. This is the first step in an iterative process where the cell count increases in order to find the optimal cell count where the effect of the number of cells in the calculation is minimized. This is done comparing the iterative residual values in a simple calculation; when the difference between one experiment and the subsequent is minimum, then the cell count may be considered irrelevant, and this may be considered the optimum cell count for the problem.

The option facing was used to standardize the cell size and its orthogonality (these are native options within ANSYS® Mesh). During the mesh analysis,

**Figure 4.** *Definition of reaction zone for CFD simulations.*

AANSYS® version 19.2 was also used. For this analysis, the cell count was increased until reaching 500,000 cells. The simulation was performed in the reaction zone which has a simple geometry that facilitates all the meshing process and in general reduces the problem complexity. The results of the mesh analysis are displayed in **Tables 2** and **3**, and the best choices for the meshing process are marked \*.

CFD will resolve governing equations for mass, momentum, and energy. The discretization process is also known as the meshing process. In this process ANSYS Fluent® has improved a lot, and since the geometry was simple for this reactor, meshing was resolved easily. There are two meshing types: structured mesh and nonstructured mesh. Examples of structured and nonstructured cases are shown in **Figure 5**.

In the former the mesh is identified by a triple index (i, j, k), in three dimensions. The cell borders form continuous lines of meshing with the adjacent cells which help a lot in the subsequent steps. In nonstructured meshing, cells and nodes do not have an exact match and cannot identify easily between neighboring cells.

Meshing has been regarded as the most difficult process in a CFD simulation. The latest versions of ANSYS® incorporate new tools that have enhanced the program capabilities and make the job easier for the users. Among the different tools incorporated, the known tools have been improved. An important factor to consider while meshing the domain is the cell shape. For this case, the geometry is a regular shape, so the cell shape was resolved easily. Conformed mesh is the desired status for the mesh because the nodes and boundaries will work smoothly if the individual cells are conformed.

In this way, the user needs to consider the interphase interaction, for example, interaction between the walls and the fluid and others. Discretized domain is shown in **Figure 6**.

Different scenarios were calculated with variants in the mesh, so the results can be compared in search for the optimum mesh as shown in **Tables 2**–**4**. Results such as velocity, pressure, and mainly the residuals were used to reach a conclusion on which mesh and how many cells are the best choice for this work.


*\* Optimized value for elements quantity.*

**Table 2.**

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


**97**

**Table 4.**

**Figure 5.**

**Figure 6.**

**Inlet velocity (m/s)**

**Maximum pressure absolute (Pa)**

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

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

*Mesh examples: (a) non-structured mesh and (b) structured mesh.*

*Discretized domain using tools incorporated in ANSYS fluent® version 19.2.*

**Outlet pressure at central zone**

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

**Minimum pressure absolute (Pa)**

0.1 27.906 11.310 0.245 1 0.103 0.151 1.00E-05 0.1 27.906 11.310 0.245 1 0.103 0.151 1.00E-06 0.1 29.802 11.265 0.007 2 0.100 0.160 1.00E-05 0.1 30.481 12.218 0.004 3 0.101 0.154 1.00E-05 0.1 29.804 11.265 0.007 2 0.100 0.160 1.00E-06 0.1 30.482 12.218 0.004 3 0.101 0.154 1.00E-06

**Mesh variant**

**Inlet velocity (m/s)**

**Outlet velocity (m/s)**

**Residuals**

**Table 3.**

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

*Hydrodynamic Analysis on a Photocatalytic Reactor Using ANSYS Fluent® DOI: http://dx.doi.org/10.5772/intechopen.89782*

#### **Figure 5.**

*Computational Fluid Dynamics Simulations*

cells are conformed.

in **Figure 6**.

**Inlet velocity (m/s)**

**Table 2.**

AANSYS® version 19.2 was also used. For this analysis, the cell count was increased until reaching 500,000 cells. The simulation was performed in the reaction zone which has a simple geometry that facilitates all the meshing process and in general reduces the problem complexity. The results of the mesh analysis are displayed in **Tables 2** and **3**, and the best choices for the meshing process are marked \*.

CFD will resolve governing equations for mass, momentum, and energy. The discretization process is also known as the meshing process. In this process ANSYS Fluent® has improved a lot, and since the geometry was simple for this reactor, meshing was resolved easily. There are two meshing types: structured mesh and nonstructured mesh. Examples of structured and nonstructured cases are shown in **Figure 5**. In the former the mesh is identified by a triple index (i, j, k), in three dimensions. The cell borders form continuous lines of meshing with the adjacent cells which help a lot in the subsequent steps. In nonstructured meshing, cells and nodes do not have an exact match and cannot identify easily between neighboring cells. Meshing has been regarded as the most difficult process in a CFD simulation. The latest versions of ANSYS® incorporate new tools that have enhanced the program capabilities and make the job easier for the users. Among the different tools incorporated, the known tools have been improved. An important factor to consider while meshing the domain is the cell shape. For this case, the geometry is a regular shape, so the cell shape was resolved easily. Conformed mesh is the desired status for the mesh because the nodes and boundaries will work smoothly if the individual

In this way, the user needs to consider the interphase interaction, for example, interaction between the walls and the fluid and others. Discretized domain is shown

Different scenarios were calculated with variants in the mesh, so the results can be compared in search for the optimum mesh as shown in **Tables 2**–**4**. Results such as velocity, pressure, and mainly the residuals were used to reach a conclusion on

**Item Mesh size (m) Adjustments used Cells generated** 7.5 e-4 54,615 1e-3, 1e-4, 1e-5 y 1e-6 5.00E-04 200000\* 1e-3, 1e-4, 1e-5 y 1e-6 4.00E-04 385020\* 1e-3, 1e-4, 1e-5 y 1e-6

> **Likeliness between values**

0.1 27.906 91.6 11.310 92.6 0.1 27.906 91.6 11.310 92.6 0.1 29.802 97.8 11.265 92.2 0.1 29.804 97.8 11.265 92.2 0.1 30.481 100.0 12.218 100.0 0.1 30.482 100.0 12.218 100.0

**Outlet pressure at central zone (Pa)**

**Likeliness between values**

which mesh and how many cells are the best choice for this work.

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

**Maximum pressure absolute (Pa)**

*\* Optimized value for elements quantity.*

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

**96**

**Table 3.**

*Mesh examples: (a) non-structured mesh and (b) structured mesh.*


#### **Table 4.**

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

#### **5.5 Processing and resolution of governing equations**

As mentioned in prior sections, flow dynamics is the first step during the design development of a photocatalytic reactor. A good velocity field with an appropriate distribution will be important for the photocatalyst distribution and to avoid possible nonuniform zones. Since the estimated operational parameters indicate Reynolds will oscillate between 266.2 and 1331.0, calculations will be carried on under laminar flow regime. Since the regime and the fluid conditions may be considered homogeneous, calculations can be performed in steady state and assume one can proceed on to resolve the continuity equation (Eq. 7) and the tridimensional classical equation of Navier–Stokes (Eq. 8):

$$\nabla \left( \rho \boldsymbol{\sigma} \right) = \mathbf{0} \tag{7}$$

$$
\nabla \cdot (\rho \nabla \sigma) = (-\nabla P) + (\nabla \cdot \overline{\mathbf{r}}) + \left(\rho \overline{\mathbf{g}}\right) \tag{8}
$$

where ∇ is the delta operator and ρ, *v*̅, P, τ̿, and are the fluid density, velocity vector, pressure, stress tensor, and gravity acceleration, respectively. These equations and Newton's viscosity law as a constitutive equation to relate the stress tensor with the continuous fluid motion will enable the user to calculate the velocity field for this reactor. Since we are interested only in fluid dynamics, we will skip energy equation. The resolution of these equations keeps representing one of the most complicated problems analytically and numerically in fluid mechanics for complex geometries. An analytical solution is unavailable, but a reasonably accurate solution may be reached numerically using methodologies such as finite volume as it was described briefly in prior sections.

In this case the resolution algorithm semi-implicit, linked equations (SIMPLE) was used. In this algorithm an initial value for pressure from there calculates the velocity and verifies that the outlet flow is identical to the inlet value and increases or decreases the input according to the best option. The program will resolve numerically for each of the finite volumes created during the discretization process or in other words will resolve the equations in the centroid for each cell in the mesh. This step may be considered a numerical solution for the discrete volumes but need an integration to display global results. The integration is done by producing an algebraic version of the differential equations, and the solution for this version is reached with a matrix. The processing means the software will resolve the governing equations according to the inputs provided. The inputs include the geometry, the mesh, fluid properties, boundary conditions, the algorithm to be used, and other details that the software will require if following its natural sequence as coded by ANSYS Fluent®.

#### **5.6 Result analysis and postprocessing**

When the processing step completes its respective work cycle, the governing equations are resolved for the centroid of each cell, and the integration process was also completed for global results.

From these results the program offers a module to create views of the domain geometry that facilitate the analysis by the users or the presentation of the results to a specific audience. In this problem, the results obtained relate to the reactor zone hydrodynamics. A useful tool generates contours of the domain for the desired parameters such as velocity, pressure, drag force, residuals, mass imbalances, etc.

**99**

**Figure 7.**

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

The analysis of pressure for the system and in specific regions of the reaction zone may be an interesting contour to start with the analysis procedures. **Figure 7** shows the results obtained for pressure within the domain by generating an image at the inlet and outlet. In **Figure 8**, one may see another interesting vector graphic to display the velocity profile at the inlet and outlet considering an inlet velocity of 0.1 m/s. The maximum pressure calculated at the inlet is 29.8 Pa, while the minimum pressure at the outlet is 0.0742 Pa. Then, with this data the designer has an idea of the pump dimensions considering the inlet pressure is needed, so the flow can pass through the reaction zone under the selected conditions. Pressure losses due to the interaction of the fluid with pipes and other reactor components in its way to the inlet in the reaction zone will not be included within this chapter but can easily be

Reaction zone pressure in addition with pressure losses will provide the minimum value needed to dimension the appropriate pump for a correct operation of this reactor. An interesting tool that helps to know the exact value in a specific location within the domain may be completed with the help of the probe tool. With this tool the software is capable of calculating this parameter on a specific location, for example, if the user would like to know the average velocity, the probe tool should indicate the specific region and the desired parameter, and, in this case, the average

*Postprocessing contour for pressure distribution in the reaction zone in (a) isometric view and (b) lateral view.*

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

resolved by the designer.

*Hydrodynamic Analysis on a Photocatalytic Reactor Using ANSYS Fluent® DOI: http://dx.doi.org/10.5772/intechopen.89782*

*Computational Fluid Dynamics Simulations*

**5.5 Processing and resolution of governing equations**

sional classical equation of Navier–Stokes (Eq. 8):

∇∙

(ρ*<sup>v</sup>*¯*v*¯) = (−∇*P*) <sup>+</sup> (∇<sup>∙</sup>

where ∇ is the delta operator and ρ, *v*̅, P, τ̿, and are the fluid density, velocity vector, pressure, stress tensor, and gravity acceleration, respectively. These equations and Newton's viscosity law as a constitutive equation to relate the stress tensor with the continuous fluid motion will enable the user to calculate the velocity field for this reactor. Since we are interested only in fluid dynamics, we will skip energy equation. The resolution of these equations keeps representing one of the most complicated problems analytically and numerically in fluid mechanics for complex geometries. An analytical solution is unavailable, but a reasonably accurate solution may be reached numerically using methodologies such as finite volume as it was

In this case the resolution algorithm semi-implicit, linked equations (SIMPLE) was used. In this algorithm an initial value for pressure from there calculates the velocity and verifies that the outlet flow is identical to the inlet value and increases or decreases the input according to the best option. The program will resolve numerically for each of the finite volumes created during the discretization process or in other words will resolve the equations in the centroid for each cell in the mesh. This step may be considered a numerical solution for the discrete volumes but need an integration to display global results. The integration is done by producing an algebraic version of the differential equations, and the solution for this version is reached with a matrix. The processing means the software will resolve the governing equations according to the inputs provided. The inputs include the geometry, the mesh, fluid properties, boundary conditions, the algorithm to be used, and other details that the software will require if following its natural sequence as coded

When the processing step completes its respective work cycle, the governing equations are resolved for the centroid of each cell, and the integration process was

From these results the program offers a module to create views of the domain geometry that facilitate the analysis by the users or the presentation of the results to a specific audience. In this problem, the results obtained relate to the reactor zone hydrodynamics. A useful tool generates contours of the domain for the desired parameters such as velocity, pressure, drag force, residuals, mass imbalances, etc.

‗ τ) + (ρ →

∇

described briefly in prior sections.

by ANSYS Fluent®.

**5.6 Result analysis and postprocessing**

also completed for global results.

As mentioned in prior sections, flow dynamics is the first step during the design development of a photocatalytic reactor. A good velocity field with an appropriate distribution will be important for the photocatalyst distribution and to avoid possible nonuniform zones. Since the estimated operational parameters indicate Reynolds will oscillate between 266.2 and 1331.0, calculations will be carried on under laminar flow regime. Since the regime and the fluid conditions may be considered homogeneous, calculations can be performed in steady state and assume one can proceed on to resolve the continuity equation (Eq. 7) and the tridimen-

(ρ*<sup>v</sup>*¯) = 0 (7)

*g*) (8)

**98**

The analysis of pressure for the system and in specific regions of the reaction zone may be an interesting contour to start with the analysis procedures. **Figure 7** shows the results obtained for pressure within the domain by generating an image at the inlet and outlet. In **Figure 8**, one may see another interesting vector graphic to display the velocity profile at the inlet and outlet considering an inlet velocity of 0.1 m/s. The maximum pressure calculated at the inlet is 29.8 Pa, while the minimum pressure at the outlet is 0.0742 Pa. Then, with this data the designer has an idea of the pump dimensions considering the inlet pressure is needed, so the flow can pass through the reaction zone under the selected conditions. Pressure losses due to the interaction of the fluid with pipes and other reactor components in its way to the inlet in the reaction zone will not be included within this chapter but can easily be resolved by the designer.

Reaction zone pressure in addition with pressure losses will provide the minimum value needed to dimension the appropriate pump for a correct operation of this reactor. An interesting tool that helps to know the exact value in a specific location within the domain may be completed with the help of the probe tool. With this tool the software is capable of calculating this parameter on a specific location, for example, if the user would like to know the average velocity, the probe tool should indicate the specific region and the desired parameter, and, in this case, the average

#### **Figure 7.**

*Postprocessing contour for pressure distribution in the reaction zone in (a) isometric view and (b) lateral view.*

#### **Figure 8.**

*(a) The graph showing velocity vectors at the inlet in the reaction zone considering an inlet velocity of 0.1 m/s and (b) velocity profile at the outlet considering the case of an inlet fluid velocity of 0.1 m/s.*

velocity at central region is 0.1000459 m/s. In this measurement it is interesting to observe that the expected value was 0.1 m/s for the inlet speed at the central region and the software calculated 0.1000459 m/s instead. The difference is very small, so a conclusion that may be reached is that the calculation accuracy is acceptable for the case of the velocity in this location. The minimum pressure obtained was 0.0742 Pa, for a velocity of 0.1 m/s in the reaction zone. **Figure 9** shows the velocity contour.

ANSYS® in its latest version offers a whole module to carry on with the postprocessing procedures. This module facilitates a lot the designer work and allows the user to generate a great deal of graphics, charts, animations, etc. which will be of great help for the presentation of results. In this example the graphics generated so far will be considered enough to illustrate the analysis done but represent only a few of the potential analysis tools that can be obtained.

**101**

**6. Conclusions**

**Figure 9.**

great deal in the meshing process.

*the reaction zone with an inlet velocity of 0.1 m/s.*

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

In conclusion, CFD codes are becoming common tools used in chemical reactor design development. The simulation possibilities are quite interesting and include resolving the governing equations for fluid dynamics but also may include chemical species and multiphase, among other, additional possibilities for the simulation of the chemical reactor operation under different scenarios. CAD tools complement the CFD code because the geometry is the central piece of information required to carry on with CFD simulation. Discretization process required a formidable amount of efforts in the past, in particular for complex geometries, but this problem has decreased in the latest versions of CFD codes. In particular, ANSYS® has incorporated a series of tools at different stages of the simulation process that facilitate in a

*(a) Contour graphic for pressure obtained at the outlet of the reaction zone. (b) Contour graphic for velocity in* 

In the case of study, a simple geometry was used for the reaction zone of the chemi-

cal reactor proposed for a laboratory scale, and a mesh with 385,020 elements was

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

*Hydrodynamic Analysis on a Photocatalytic Reactor Using ANSYS Fluent® DOI: http://dx.doi.org/10.5772/intechopen.89782*

#### **Figure 9.**

*Computational Fluid Dynamics Simulations*

velocity at central region is 0.1000459 m/s. In this measurement it is interesting to observe that the expected value was 0.1 m/s for the inlet speed at the central region and the software calculated 0.1000459 m/s instead. The difference is very small, so a conclusion that may be reached is that the calculation accuracy is acceptable for the case of the velocity in this location. The minimum pressure obtained was 0.0742 Pa, for a velocity of 0.1 m/s in the reaction zone. **Figure 9** shows the velocity

*(a) The graph showing velocity vectors at the inlet in the reaction zone considering an inlet velocity of 0.1 m/s* 

*and (b) velocity profile at the outlet considering the case of an inlet fluid velocity of 0.1 m/s.*

ANSYS® in its latest version offers a whole module to carry on with the postprocessing procedures. This module facilitates a lot the designer work and allows the user to generate a great deal of graphics, charts, animations, etc. which will be of great help for the presentation of results. In this example the graphics generated so far will be considered enough to illustrate the analysis done but represent only a few

of the potential analysis tools that can be obtained.

**100**

contour.

**Figure 8.**

*(a) Contour graphic for pressure obtained at the outlet of the reaction zone. (b) Contour graphic for velocity in the reaction zone with an inlet velocity of 0.1 m/s.*
