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Novel Design of Laboratory Scale Photocatalytic Reactor for Degradation of Dyes
Niraj S Topare, Sunita J Raut, Yogesh Kode, Nilesh Inamdar. In a photocatalytic reactor, the major elements required for the Photocatalytic Oxidation (PCO) process are combined to form a unit, within which the pollutants are neutralised. The aim of reactor design is to obtain the greatest reaction yield, i.e., neutralise as much pollutants as possible, whilst expending the least amount of energy. To achieve this, reactor should provide effective contact among catalyst, reactants and photons. The study gives insight into the design aspects of photocatalytic reactor construction based on the modelling and simulation.

The commercialisation of TiO2 photocatalysis and other Advanced Oxidation Technologies (AOTs), for the destruction of pollutants in water and air, has been the subject of much research recently. Photocatalysis has been a subject of increasing interest during the last many years. It has indeed various potential applications such as metal recovery, abatement of NOx, synthesis of ammonia but the recent developments have been induced mainly by the application to the abatement of organic pollutants both in the aqueous and the gaseous phase1,2. This development participates to the general concern about the environment and the increasing constraints on the toxicity of wastes2. The academic studies have been much developed in the fields of organic chemistry, physical chemistry, chemical kinetics and catalyst preparation, but few studies have been dedicated to chemical engineering and the development of reactors. Concomitantly, few industrial processes have been developed3. In our laboratories, we have developed a novel photocatalytic reactor. In this reactor, the degradation of toxic compounds can be carried out in a batch manner. Mixing of the solution is achieved by magnetic starrier while the photocatalytic reactions occur on the UV. The aim of this study is to give some design aspects of photocatalytic reactor construction based on the modelling and simulation.

Photocatalysis
With the discovery of photoinduced water cleavage on titanium dioxide (TiO2) semiconductor electrodes by Fujishima and Honda in the early 1970Ês4, it was soon realised that this phenomenon could be applied for environmental remediation. Photocatalytic Oxidation (PCO) first saw use as a technique for water purification, following from Frank and BardÊs investigation into the decomposition of cyanide using an aqueous TiO2 suspension in 1977. Aqueous suspensions of catalysts, such as TiO2, were found to be effective at breaking down organic pollutants. However, due to the inherent inefficiency of the process (the need to filter out the TiO2 after purification), techniques had to be developed to immobilise TiO2 onto support surfaces. This has lead to a technology that lends itself to air purification.

Photocatalytic Reactors
The versatility of PCO technology has seen many commercial applications such as in glazing, paving stones, wall paper, and paint to name but a few, where the PCO effect is secondary to their main function. These products are typically activated solely by sunlight with photocatalytic air purification tending to be given less significance than the Âself-cleaningÊ aspect of these products. Non-the-less this marks a major shift from conventional air purifying systems. An air purifying capability can be incorporated into construction materials, surface finishes, even clothes. Devices solely intended for purification purposes are still an important technology required to meet the need for clean air. Immobilised TiO2 is being employed in place of conventional purifying units, or incorporated to form hybrid devices. These are typically not activated by sunlight but by UV lamps, so achieving greater efficiencies, and can be located in areas where natural light is minimal if not non-existent.

Principles of Reactor Design
In a photocatalytic reactor, the major elements required for the PCO process are combined to form a unit, within which the pollutants are neutralised. The aim of reactor design is to obtain the greatest reaction yield, i.e., neutralise as much pollutants as possible, whilst expending the least amount of energy. To achieve this reactor should provide effective contact among catalyst, reactants, and photons. For the catalyst to be effective it must have a high surface area, to allow contact with as large a volume of reactants as possible. Extremely large surface areas are possible when using powder form TiO2. However, the need to immobilise TiO2 on to a substrate results in a significant reduction of surface area. Unless using sunlight, due to electricity charges and bulb replacement, the light source will tend to be the most costly component of any photo-reactor. So, photons are expensive, it is essential to utilise them effectively and ensure that few are emitted that do not contact the catalyst and initiate oxidation. As well as this, efforts must be made to ensure that all reactor surfaces receive adequate irradiation from the light source, so that no flow paths through the reactor exist where the catalyst is not illuminated. Effective design is therefore essential to maximise surface area when using immobilised TiO2, and to ensure that it is properly irradiated. The method of immobilisation also demands careful consideration to ensure an adequate coating on the substrate surface. Factors to consider include: thickness, coverage, and robustness, as well as simplicity, cost, and repeatability for commercial application. Several existing reactor designs as used for research and some commercial applications are described below.

Flat Plate Reactors: The flat plate reactor (Fig 1) designed and tested by Brandi et al5 is composed of two flat glass plates with a certain gap between them, through which the fluid to be cleaned is passed. The catalyst is coated on the interior surface of each plate, with an external light source irradiating the catalyst. The thickness of the catalyst layer is thin enough to allow the entire catalyst surface to be illuminated by the light. The light sources have a reflector behind them to help utilise all the available radiation by directing it onto the catalyst. Flat plate reactors are the most basic reactor type offering low surface area, and generally, poor utilisation of available light.

Honeycomb Monolith Reactors: The honeycomb monolith (Fig 2) configuration is the type commonly found in automobile exhaust systems for emission control. They contain a number of channels with typical internal dimensions of around 1 mm. A very thin layer of catalyst is coated onto the walls of the channels. The benefits of this type of design are that there is a low-pressure-drop and high surface area to volume ratio6. Raupp has investi-gated reactors using various monolith formations; square channelled monoliths of various dimensions as well as porous cylindrical ceramic monoliths.

Fluidised Bed Reactors: The advantages of a fluidised bed reactor, as claimed by Dibble and Raupp, include a low pressure drop, high throughput, and very high catalyst surface area, thus efficient reactant-catalyst contact. In Fig 3, the catalyst bed consists of silica gel impregnated with the catalyst, using a sol gel technique.

The silica gel particle size is 250??450 nm in diameter, which resulted in the particles exhibiting smooth and smooth/bubbling fluidisation. Fluidised bed reactors have seen further developments made by researchers such as Nam et al. who placed the light source at the centre of the catalyst bed, and six inlet nozzles at the base of the reactor to provide a uniform air distribution in the catalyst bed. Lim et al combined features of a tubular and a fluidised bed reactor, forming and tubular bed with the light source in the centre. A quartz filter was used to distribute light evenly and a mirror box surrounded the reactor to minimise loss of light6.

Solidworks Software The Solid Works CAD software is a mechanical design automation application that lets designers quickly sketch out ideas, experiment with features and dimensions, and produce models, simulation and detailed drawings. A Solid Works model consists of 3D solid geometry in a part or assembly document. Drawings are created from models, or by drafting views in a drawing document. Typically, you begin with a sketch, create a base feature, and then add more features to your model. (You can also begin with an imported surface or solid geometry.) You can refine your design by adding, editing, or reordering features. Associatively between parts, assemblies, and drawings assures that changes made to one document or view is automatically made to all other documents and views. You can generate drawings or assemblies at any time in the design process. With a Real View-compatible graphics card installed, you can display photo-realistic models and environments. The SolidWorks software saves your work for you with auto-recover. You can also choose to be reminded to save your work. Parts are the basic building blocks in the Solid Works software. Assemblies contain parts or other assemblies, called subassemblies. A Solid Works model consists of 3D geometry that defines its edges, faces, and surfaces. The Solid Works software lets you design models quickly and precisely. The design process usually involves the following steps:

• Identify the model requirements.
• Conceptualise the model based on the identified needs.
• Develop the model based on the concepts.
• Analyse the model.
• Prototype the model.
• Construct the model.
• Edit the model, if needed.

What Is Solidworks Simulation?
SolidWorks Simulation is a design analysis system fully integrated with SolidWorks. SolidWorks Simulation provides one screen solution for stress, frequency, buckling, thermal, and optimisation analyses. Powered by fast solvers, SolidWorks Simulation enables you to solve large problems quickly using your personal computer. SolidWorks Simulation comes in several bundles to satisfy your analysis needs. SolidWorks Simulation shortens time to market by saving time and effort in searching for the optimum. Here discusses some basic concepts and terminology used throughout the SolidWorks Simulation software. It provides an overview of the following topics:

Benefits of Analysis: After building your model, you need to make sure that it performs efficiently in the field. In the absence of analysis tools, this task can only be answered by performing expensive and time-consuming product development cycles. A product development cycle typically includes the following steps:

• Building your model.
• Building a prototype of the design.
• Testing the prototype in the field.
• Evaluating the results of the field tests.
• Modifying the design based on the field test results.

This process continues until a satisfactory solution is reached. Analysis can help you accomplish the following tasks:

• Reduce cost by simulating the testing of your model on the computer instead of expensive field tests.
• Reduce time to market by reducing the number of product development cycles.
• Improve products by quickly testing many concepts and scenarios before making a final decision, giving you more time to think of new designs.

Basic Concepts of Analysis: The software uses the Finite Element Method (FEM). FEM is a numerical technique for analysing engineering designs. FEM is accepted as the standard analysis method due to its generality and suitability for computer implementation. FEM divides the model into many small pieces of simple shapes called elements effectively replacing a complex problem by many simple problems that need to be solved simultaneously. The software offers the following types of studies:

• Static (or Stress) Studies.
• Frequency Studies.
• Dynamic Studies.
• Buckling Studies.
• Thermal Studies.
• Nonlinear Studies.
• Drop Test Studies.
• Fatigue Studies.

3D Model Design of Photocatalytic Reactor The photocatalytic reactor consists of cylindrical vessels 330 mm length and 70 mm diameter with the condensation system, along with the inside tube of 330 mm length and 30 mm diameter and closing cap of 335 mm diameter. The following Figure 4 shows the 3D model of each part with assembly of Photo catalytic reactor.



Simulation of Photocatalytic Reactor (Fig 5) Assumptions:
• No heat losses
• Heat source constant
• Temperature variations along the diameter of reactor

Study Properties:
• Analysis type = Thermal(Steady state)
• Mesh type = Solid Mesh
• Solution type = Steady state
• Contact resistance defined = No Units:
• Unit system = SI (MKS)
• Length/Displacement = mm
• Temperature = Kelvin
• Angular velocity = Rad/sec
• Pressure/Stress = N/m2

Material Properties:
• Name = Glass
• Model Type = Linear Elastic Isotropic
• Thermal Conductivity = 0.74976 W/(m.K)
• Specific Heat = 834.61 J/(kg.K)
• Mass density = 2457.6 kg/m3

Thermal Loads
Thermal analysis calculates the temperature distribution in a body due to some or all of these mechanisms. In all three mechanisms, heat energy flows from the medium with higher temperature to the medium with lower temperature. Heat transfer by conduction and convection requires the presence of an intervening medium while heat transfer by radiation does not. Consider different thermal load conditions on different parts of reactor. The following Table 1 shows the Thermal load data.

Mesh Information
Finite Element Analysis (FEA) provides a reliable numerical technique for analysing engineering designs. The process starts with the creation of a geometric model. Then, the program subdivides the model into small pieces of simple shapes called elements connected at common points called nodes. The process of subdividing the model into small pieces is called meshing. Finite element analysis programs look at the model as a network of interconnected elements. Meshing is a crucial step in design analysis. The software automatically creates a mixed mesh of solid, shell and beam elements. The solid mesh is appropriate for bulky or complex 3D models. Shell elements are suitable for thin parts (like sheet metals). Beam elements are suitable for structural members. The accuracy of the solution depends on the quality of the mesh.

Result and Discussion
From the given thermal condition temperature (min 25 degree Celsius and max 80 degree Celsius) applied to the photocatalytic reactor we get that the following result which is the final output of software.

Conclusion
Modelling photocatalytic reactors is of importance in order to get true intrinsic kinetic parameters and to carry out the simulation of reactors so as to select or to improve the reactor design. Many phenomena are involved in the modeling which results in the need for effective parameters and in the complexity of the solving of the problem by numerical methods. As the operating condition of reactor i.e temperature (min 25 degree Celsius and max 80 degree Celsius)and 1 atm. Pressure. Thermal analysis shows that, on this operating condition our design of reactor is feasible. A reactor was designed and constructed based on the modelling results, and when experiments were conducted showed very promising results.