Investigation of the Flow Behavioral Dynamics of Ammonia Component Gases in a Microreactor via Computational Fluid Dynamics (CFD) Approach

Ammonia (NH3) synthesis has been among the most favorable production process in the industry, especially for its application as synthetic urea. As the current conventional system of synthesizing NH3 poses some disadvantages in terms of its operating conditions and production cost, yet producing low conversion and product yield; this project offers a new technique to enhance NH3 synthesis through channeling the reactants in a microreactor consisting of supported catalyst at ambient operating condition. Prior to the process of constructing the rigs for experimental work to investigate NH3 production in the said condition, a computer simulation via the utilization of computational fluid dynamics (CFD) approach will be conducted. This is to examine the flow behavior of the reactant gases in a microfluidic environment, particularly their mixing characteristics, which would assist in optimizing the localization of the catalyst for the reaction to take place. The results of the simulation will lead to the design of the overall microreactor itself, which will be used in the experimental approach of the NH3 synthesis in the next step of the project. CFD is preferred as parametric studies in determining optimal design could be varied without the need to construct the real rig, which thus could reduce cost, time and material wastage

Mixing Improvement in a T-Shaped Micro-Junction through Small Rectangular Cavities

The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration

Investigation of the Flow Behavioral Dynamics of Ammonia Component Gases in a Microreactor via Computational Fluid Dynamics (CFD) Approach

Ammonia (NH3) synthesis has been among the most favorable production process in the industry, especially for its application as synthetic urea. As the current conventional system of synthesizing NH3 poses some disadvantages in terms of its operating conditions and production cost, yet producing low conversion and product yield; this project offers a new technique to enhance NH3 synthesis through channeling the reactants in a microreactor consisting of supported catalyst at ambient operating condition. Prior to the process of constructing the rigs for experimental work to investigate NH3 production in the said condition, a computer simulation via the utilization of computational fluid dynamics (CFD) approach will be conducted. This is to examine the flow behavior of the reactant gases in a microfluidic environment, particularly their mixing characteristics, which would assist in optimizing the localization of the catalyst for the reaction to take place. The results of the simulation will lead to the design of the overall microreactor itself, which will be used in the experimental approach of the NH3 synthesis in the next step of the project. CFD is preferred as parametric studies in determining optimal design could be varied without the need to construct the real rig, which thus could reduce cost, time and material wastage

CFD Modelling of the Microreactor for the Ammonia Synthesis

This project is related to the microreaction technology under the microengineering field. The development of microreactors has been researched worldwide due to their better performance over conventional reactors. Mixing is one of the key components in chemical process especially in microreactors. With good mixing, a better control on the quality of the final product and its properties are ascertained to comply with the specification of the product. However, poor mixing will result in a non-homogenous distribution of the product that certainly lacks consistency with the specification desired. The study of mixing behaviour in microreactors is crucial due to the laminar behavioural of the flow in microchannels. Together with the advancement in technology, the study of mixing can be done through Computational Fluid Dynamics (CFD) simulations. With CFD simulations, the design for the optimum mixing in a microreactor can be made based on a trial-and-error method. Through simulation, the best location of the catalyst placement can be predicted according to the mixing behaviour in the microreactor. This project involves the investigation of the effect of the micromixer geometric design and the inflow configuration for the micromixer on the mixing performance using CFD

Novel reactors for multiphase processes

Process intensification tools, such as the capillary reactor, offer several benefits to the chemical process industries due to the well-defined high specific interfacial area available for heat and mass transfer, which increases the transfer rates, and due to low inventories, they also enhance the safety of the process. This has provided motivation to investigate three such tools, namely the capillary microreactor, spinning disc and rotating tube reactors, in this study.The gas-liquid slug flow capillary microreactor intensifies reactor performance through internal circulation caused by the shear between the continuous phase/wall surface and the slug axis, which enhances the diffusivity and consequently increases the reaction rates. However, integrating the complex hydrodynamics of this reactor with its chemical kinetics is a mathematically challenging task. Therefore, in this study, a simple-to-complex approach, using a set of state-of-the-art computational fluid dynamic tools, has been used. Firstly, simulations were performed without any chemical reaction to ascertain the extent of slug flow regime. The model also clearly captured the slug flow generation mechanism which can be used to structurally optimize the angle of entry in these reactors. Finally, the hydrodynamic model was also capable of estimating the pressure drop and slug lengths. After successfully simulating the hydrodynamics of the system, a reaction model was incorporated to study the chemical reaction kinetics. The results were compared with the published experimental work and were found to be in good agreement.The spinning disc reactor utilizes the centrifugal and shear forces to generate thin liquid films characterized with intense interfering waves. This enables a very high heat transfer coefficients to be realized between the disc and liquid, as well as very high mass transfer between the liquid and the bulk gas phase. The waves formed also produce an intense local mixing with very little back mixing. This makes a spinning disc reactor an ideal contactor for multiphase processes. The focus of this study has been to elucidate the hydrodynamic behaviour of the liquid film flow over the horizontal spinning disc. Investigations were also performed to elaborate the local and overall hydrodynamic characteristics of a fully developed spinning disc reactor. Simulation results showed a continuous linear liquid film on the horizontal spinning disc and intense mixing performance in the annulus of the reactor around the disc surface. Finally, the film thickness data from the simulations were compared with the limited amount of data available for this novel process.Rotating tube reactor also uses centrifugal forces to generate the liquid film and a high degree of mixing along with an improved control over the reactant retention times. In this work we have conducted a CFD analysis to understand the hydrodynamics of this new technology for future developments

Unsteady Flow Regimes in a T-Shaped Micromixer: Mixing and Characteristic Frequencies

Experiments and direct numerical simulations are used jointly to study the asymmetric and symmetric time-periodic regimes occurring in a T-shaped micro mixer for larger Reynolds numbers than those of steady regimes. The first is characterized by a large mixing degree, whereas the flow in the second regime Always exhibits a nearly double mirror symmetry in the mixing channel, which strongly hampers mixing. The characteristic nondimensional frequency, calculated using the hydraulic diameter of the mixing channel and the bulk velocity, augments with the Reynolds number in both periodic regimes, but a large discontinuity is observed at the transition between the two regimes. A detailed description of the main flow features is given to provide a physical explanation on the Strouhal number variation. The present analysis can be exploited in practice to design active control strategies, e.g., by exciting the flow at the frequencies typical of the asymmetric unsteady regime

Multi-objective optimisation methods applied to aircraft techno-economic and environmental issues

Engineering methods that couple multi-objective optimisation (MOO) techniques with high fidelity computational tools are expected to minimise the environmental impact of aviation while increasing the growth, with the potential to reveal innovative solutions. In order to mitigate the compromise between computational efficiency and fidelity, these methods can be accelerated by harnessing the computational efficiency of Graphic Processor Units (GPUs). The aim of the research is to develop a family of engineering methods to support research in aviation with respect to the environmental and economic aspects. In order to reveal the non-dominated trade-o_, also known as Pareto Front(PF), among conflicting objectives, a MOO algorithm, called Multi-Objective Tabu Search 2 (MOTS2), is developed, benchmarked relative to state-of-the-art methods and accelerated by using GPUs. A prototype fluid solver based on GPU is also developed, so as to simulate the mixing capability of a microreactor that could potentially be used in fuel-saving technologies in aviation. By using the aforementioned methods, optimal aircraft trajectories in terms of flight time, fuel consumption and emissions are generated, and alternative designs of a microreactor are suggested, so as to assess the trade-offs between pressure losses and the micro-mixing capability. As a key contribution to knowledge, with reference to competitive optimisers and previous cases, the capabilities of the proposed methodology are illustrated in prototype applications of aircraft trajectory optimisation (ATO) and micromixing optimisation with 2 and 3 objectives, under operational and geometrical constraints, respectively. In the short-term, ATO ought to be applied to existing aircraft. In the long-term, improving the micro-mixing capability of a microreactor is expected to enable the use of hydrogen-based fuel. This methodology is also benchmarked and assessed relative to state-of-the-art techniques in ATO and micro-mixing optimisation with known and unknown trade-offs, whereas the former could only optimise 2 objectives and the latter could not exploit the computational efficiency of GPUs. The impact of deploying on GPUs a micro-mixing _ow solver, which accelerates the generation of trade-off against a reference study, and MOTS2, which illustrates the scalability potential, is assessed. With regard to standard analytical function test cases and verification cases in MOO, MOTS2 can handle the multi-modality of the trade-o_ of ZDT4, which is a MOO benchmark function with many local optima that presents a challenge for a state-of-the-art genetic algorithm for ATO, called NSGAMO, based on case studies in the public domain. However, MOTS2 demonstrated worse performance on ZDT3, which is a MOO benchmark function with a discontinuous trade-o_, for which NSGAMO successfully captured the target PF. Comparing their overall performance, if the shape of the PF is known, MOTS2 should be preferred in problems with multi-modal trade-offs, whereas NSGAMO should be employed in discontinuous PFs. The shape of the trade-o_ between the objectives in airfoil shape optimisation, ATO and micro-mixing optimisation was continuous. The weakness of MOTS2 to sufficiently capture the discontinuous PF of ZDT3 was not critical in the studied examples … [cont.]