Use Of CFD Model Research Articles

Modeling and optimizing gas solid distribution in fluidized beds

In fluidized bed reactors, uniform distribution of gas and solids is critical to achieve the desired hydrodynamic and kinetic performance. For FCC units, Technip Energies uses a proprietary distributor design to terminate both reactor risers and spent catalyst lift lines to distribute the exiting gas-solid stream into a fluidized bed.In Technip Energies' Resid FCC unit, air and spent catalyst are distributed from an upward flowing stream into a catalyst bed for coke combustion on catalyst. Proper distribution is key to achieve a uniform coke burn and an even temperature profile throughout the bed. In PropyleneMax™ Catalytic Cracking (PMcc™) technology, the reactor riser also terminates in a fluidized bed, requiring proper distribution of the hydrocarbon vapor and solid mixture into the reactor bed, which is key to providing adequate contact for further cracking to valuable products. This paper discusses Technip Energies' gas-solid distribution technology and the recent work performed to develop an improved distributor for use as a riser termination device in both the PMcc reactor and the RFCC regenerator to achieve improved performance. The use of CFD modeling to screen and evaluate the initial concepts and optimize the final selected concept are presented here. The performance matrices used to quantify the benefits of the optimized distributor design with respect to the existing one in the reactor application are highlighted, showing the benefits of improved gas solid distribution on hydrodynamic and kinetic performance. The paper presents a systematic approach to develop a novel industrial device using physics-based computational tools.

CFD-mass transfer model process in a vertical sedimentation tank

Currently, the world is actively developing a logical course to create hypothetical strategies for the calculation of tanks for sewage sump. At the same time, engineers usually use balance models and one-dimensional kinematic models. These models do not take into account the hydrodynamics of the flow inside the sump and its complex geometric shape. This can be a serious deterrent to the widespread use of Navier-Stokes conditions when refining a regular plan. The use of CFD models based on the formulation of Navier-Stokes conditions requires the use of a really thin network, which leads to critical computer time spent on obtaining predictive information. To this conclusion, it is fundamental to form an successful CFD show to think about the method of wastewater treatment in vertical settling tanks, taking into consideration their geometric shape and plan highlights. The plans of individual parts, carried out by the strategy of the current count, are used. A 2-D-CFD demo was created that allows a vertical settler to be calculated in a few seconds, taking into account its geometric shape, the proximity of the central pipe, its parameters, and the proximity of a divider that has recently exited the pipe. The application of the strategy for checking the calculated space in the constructed show makes it possible to carry out coordinate numerical simulation of the flow hydrodynamics and mass transfer in settling tanks without limiting their shape. Creation of CFD models that allow, on the one hand, to require into consideration the geometric shape of the sump, the most physical forms of mass exchange within the structure, and on the other hand - requiring small time to get comes about. The created CFD demonstrate and the code based on it permit, with a little consumption of computer time - approximately the same as when calculating a one-dimensional demonstrate, to illuminate complex multiparametric issues that emerge at the plan arrange of vertical settling tanks, considering their shape and design features.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ СПОСОБОВ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ СЖИГАНИЯ ТОПЛИВА В ТОПОЧНЫХ УСТРОЙСТВАХ ЭНЕРГЕТИЧЕСКИХ КОТЛОВ

The conditions of combustion reactions determine the nature of combustion and its results. An uninterrupted operation of combustion devices is required to ensure a complete combustion of fuel by the influence of heat mass transfer and aerodynamics on the ongoing chemical reactions since power plants are the main sources of hazardous emissions. Therefore, the study of furnace process efficiency by means of mathematical modeling is getting more significant. This study allows to determine the dynamic performance of a power plant, to investigate the effectiveness of security measures, the use of combined fuels and low-emission burners. Based on the review of works on the research topic, it can be concluded that the study of furnace processes requires the use of CFD modeling. The article considers a mathematical model and methodology for the numerical study of the methane-air mixture combustion in STAR-CCM+, and describes the choice of mesh and combustion model. The results of numerical study with the influence of recirculation degree changing the ratio of combustion gas from 0 to 15% to reduce the hazardous emissions are presented. Based on the results of simulation, a technical solution was developed to improve the effectiveness of fuel combustion in power plants, and its scheme is presented. The article is intended for graduate and doctoral students interested in numerical study and development of methods for suppressing the formation of thermal nitrogen oxides in the combustion products of boilers of thermal power plants.

Modelling the throttle effect in a mine drift

The throttle effect is a phenomenon, which may occur during a fire underground, causing unforeseen smoke spread. This paper focuses on the modelling of the throttle effect in a mine drift, using a CFD software. The aim of the paper is to investigate whether the CFD tool is able to predict and reproduce the throttle effect for fire scenarios underground. Experimental data from fire experiments in a model-scale mine drift and modelling results from a CFD model were used during the analysis. It was found that the CFD model was not able to fully reproduce the throttle effect for fire scenarios in a mine drift. The inability was due to the under prediction of the fire gas temperature at the ceiling level and the over prediction of the temperatures at the lower levels. The difficulties occurred foremost during transient periods with high fire growth rates. Given the difficulties in modelling the thermal stratification and the throttle effect, the use of CFD models should be mainly for qualitative analysis. Qualitative analysis could possibly be performed for non-transient and low intensity fires.

ОСОБЕННОСТИ ОБРАБОТКИ ЭКСПЕРИМЕНТАЛЬНЫХ ДАННЫХ ПРИ ОПРЕДЕЛЕНИИ КОЭФФИЦИЕНТА ТЕПЛООТДАЧИ В МАСЛЯНОЙ ПОЛОСТИ ОПОРЫ ГТД

The development of gas turbine technology is accompanied by an increase in temperatures, pressures, and airflow velocity in the gas path. Increasing operating cycle parameters for gas turbine engine complicates the tasks of ensuring the permissible temperature state of engine parts, requires improving the methods of their calculation and design. This fact fully applies bearing assemblies, especially those operating in a hot environment, and causes interest in the study of thermohydraulic processes in the bearing chamber, which determines the temperature state of the rotor parts. The necessity of pressurizing the seals leads to the presence of the oil-air mixture in the bearing chamber. A wide range of operating parameters, flow inhomogeneity, phase disequilibrium, and phase separation significantly complicate the mathematical description of processes in the bearing chamber, including the use of CFD-modeling. Therefore, considerable attention is paid to experimental research. The experimental results are used not only to verify mathematical models but also to obtain generalizing dependencies. Most often, the desired value is the heat transfer coefficient in the oil cavity of the support. The article deals with the heat transfer features in the near-wall zone of the gas-turbine engine bearing chamber which were associated with the presence of oil-air flow. Also, approaches to the experimental determination of the heat transfer coefficient were analyzed and an appropriate system for measuring the local temperatures of the media was formed. The values of the error of the experimental heat transfer coefficient and the degree of influence of the determining factors were estimated. The contribution of the non-uniformity of the temperature field in the walls of the chamber and the uncertainty in the value of the temperature of the flow core was determined. The advantages of using the averaged heat transfer coefficient for engineering calculations and the significant influence of the averaging method on its value were also shown. Averaging over the heat flux density corresponds most accurately to the tasks of such calculations, at which the total heat flux through the chamber walls does not change.

Numerical Study of Temperature and Air Velocity Distribution In Oil Filling Factory

This paper describes the use of CFD modeling to analyze the thermal comfort in the oil filling factory which has an area of 3000 m 2. the need for this analysis comes from an uncomfortable condition that is felt by the workers of the factory. A 3D simulation using FLUENT software 6.3.26 conducted to analyze the temperature and velocity distribution in the plant room. The water is assumed as an incompressible ideal gas, steady flow, turbulence models used k-e standard, the SIMPLE algorithm and second order upwind discretisation. Analysis was conducted on existing models and propose models, whereby on a model propose, the diffuser is installed above the workers with a height of 4,2 m above the floor, the velocity of supply air diffuser is varied from 1,5 m/s, 2 m/s, and 2,5 m/s. The simulation results show that the temperature distribution in the existing conditions in the range of about 34-36 ° C, this value exceeds the thermal comfort standards specified by ASHRAE. The simulation results show that the proposed model better temperature distribution, where the temperature is generated in the range of ASHRAE thermal comfort criteria, ranging from 24-26 °C, and the supply air velocity at the diffuser inlet of 1,5 m/s recommended for use in AHU system. For the 20 units of the diffuser with inlet velocity of 1,5 m / s, the mass flow rate that should be handled by a cooling device is 9 kg/s and require a cooling capacity of 0,128 MW. This is 58% more efficient than cooling the entire room factory.

Pedestrian level wind assessment through city development: A study of the financial district in Toronto

In the future, cities will be defined by super tall buildings due to an increase in population growth and urbanization. Although there are many benefits to living in dense urban centers, the interactions between buildings and wind affect the comfort and safety of pedestrians at street level. In a few notable instances, tall buildings have directed high speed winds to street levels that have affected outdoor spaces of businesses, the balance of pedestrians or in severe cases the safety of pedestrians when a car flipped over and fatally injured an individual in Leeds, England. The Financial District in Toronto has been selected as a case study, as dense development of the area over the last 70 years has fostered increasingly noticeable high winds at pedestrian level. The stages of development in this district have been divided into six significant construction periods and the changes in wind effects have been assessed with the use of CFD models, water flume and wind tunnel tests. The results demonstrated that tall buildings can alter the flow in unexpected ways and that the effects caused by the buildings in the urban environment are interconnected. The safety and comfort (along with other parameters associated with wind) of pedestrians are factors that must be incorporated into the design of the city. Through visualizing the decade long changes in wind due to the growth of cities, it is possible to create strategies that can incorporate the knowledge of wind issues into the design of future cities. By using accessible methods, whether through visualization or computational means, the highly complex relationships between the built environment, wind and people can be shared with engineers, architects and other designers of cities, to enable a collaborative design of future cities that will reduce wind-related discomfort.

Modelling and parametric study of an efficient Alpha type Stirling engine performance based on 3D CFD analysis

As an externally heated engine the Stirling engine has the advantage of being able to efficiently exploit various waste heat sources. Computational fluid dynamic simulation (CFD) for the thermodynamic performance of such engines can provide a powerful tool to predict and improve the design and performance. Despite the advantages of alpha type Stirling engines, there has been very limited published work regarding the use of CFD modelling to improve its performance. This paper, proposed a new methodology combining the thermodynamic model with 3D CFD analysis to investigate the performance of a V-Alpha Type Stirling engine under various operating conditions and design parameters. The thermodynamic model of an alpha type Stirling engine has been developed using non-ideal adiabatic analysis and validated against experimental measurements of the engine prototype. A 3D CFD model was then developed and the results, compared to the those of the thermodynamic model, showed good agreement in predicting the indicated power.The CFD model was used to carry out a parametric study to investigate the effects of various design parameters and operating conditions such as, regenerator porosity, charge pressure, matrix wire diameter, dead volume and hot/cold ends temperatures on the engine performance in terms of power output through predicting the PV diagram of the engine. Results showed that maximum power can be achieved by increasing the porosity up to 80% and the wire matrix diameter to 0.02mm at a temperature of the hot and cold sides at 600°C and 20°C respectively. Further decreasing of the cold end temperature to −20°C can produce 162W. For the heater and the cooler volumes, it was found that a height of 140mm produced the highest engine power output of 170W. This work highlights the potential of using CFD modelling to improve the design parameters and operating conditions to enhance the performance of alpha type Stirling engines.

Use of CFD Modeling for Designing Permanent Canal Closures and Pump Stations

Use of CFD Modeling for Designing Permanent Canal Closures and Pump Stations

Optimization of Secondary Air Distribution in Biomass Boiler by CFD Analysis

This paper deals with a use of CFD modelling for optimization of supply of secondary combustion air in the two-chamber biomass boiler combusting very wet biomass (capacity ca. 200 kW). Objective of the analyse is to observe the impact of diameter of a secondary air supply pipe and air flow velocity on mixing of the secondary air with flue gas in the combustion chamber. The numerical model of the experimental boiler was build up for subsequent utilizing of CFD computation based on finite element method. The commercial code STAR-CD was used for carried out parametrical studies. Series of calculations were carried out for four different diameters of air distribution pipes and for 3 different air velocities in distribution orifice. Quality of air dispersion in flue gas flow was assessed in the vertical cross section lead in the end of the combustion chamber. The results of calculation were verified on the experimental installation of the boiler. Influence of secondary air mixing on emission production was measured and analysed. Emissions of pollutants for recommended air distribution comply with emission limits stipulated in the most stringent class 5 according to ČSN-EN 303-5 as well as with emission limits under Regulation No. 405/2012 Sb.

Maximization of performance of a PCM latent heat storage system with innovative fins

Latent heat thermal energy storage (LHTES) based on phase change material (PCMs) is an interesting solution to be used for mitigating the mismatch between energy demand and supply that affects various kinds energy systems. The advance of LHTES technology requires to overcome the limitations posed by the poor thermal conductivity of most of the PCMs. Thus, a large scale utilization of LHTES system strongly depends on the development of efficient heat transfer enhancement techniques. In this paper the use of tree shaped fins is proposed to enhance the performance of a shell-and-tube LHTES unit. The study is performed through a numerical model that takes into account of the thermal behaviour of the system. The geometry of Y-shaped fins with one and two bifurcations are optimized through the combined use of CFD modelling and response surface method. The results show that an increase of 24% of the system efficiency can be achieved by the optimized unit. Another relevant result arises from the analysis: the optimal fin design depends on the operating time of the LHTES unit. For short operating times Y-shaped fins with wide angles between branches are preferable. On the contrary, smaller angles are necessary for long operating times.To summarize, this work presents for the first time a shape optimization strategy for the improvement of a system involving transient operating conditions. This is a key feature of the paper and an innovative effort to tackle optimization problems involving energy systems that show unsteady state behaviour.

Design optimization and field demonstration of natural ventilation for high-rise residential buildings

Natural ventilation in residential buildings has a great potential for conserving energy and improving the health of occupants. This paper first presents a design strategy for optimizing natural ventilation in high-rise residential buildings in Chongqing, China, a region with unfavorably low wind speed. Through the use of CFD modeling, building orientation and spacing were adjusted, wind paths were created into internal zones, and two windows were constructed in each bedroom. The optimized design reduced the age of air to less than 6min in 90% of the rooms, as compared to an age of greater than 30min in 50% of the rooms in a conventional design. Natural ventilation was found to be effective in the Chongqing area with the optimized design. This investigation also measured the local age of air and air change rate in a building with the optimized design using a tracer-gas method. The measurements confirmed the reliability of the CFD results.

CFD-model of the mass transfer in the vertical settler

Purpose. Nowadays the mathematical models of the secondary settlers are intensively developed. As a rule the engineers use the 0-D models or 1-D models to design settlers. But these models do not take into account the hydrodynamics process inside the settler and its geometrical form. That is why the CFD-models based on Navier - Stokes equations are not widely used in practice now. The use of CFD-models based on Navier - Stokes equations needs to incorporate very refine grid. It is very actually now to develop the CFD-models which permit to take into account the geometrical form of the settler, the most important physical processes and needs small computer time for calculation. That is why the development of the 2-D numerical model for the investigation of the waste waters transfer in the vertical settlers which permits to take into account the geometrical form and the constructive features of the settler is essential. Methodology. The finite - difference schemes are applied. Findings. The new 2-D-CFD-model was developed, which permits to perform the CFD investigation of the vertical settler. This model takes into account the geometrical form of the settler, the central pipe inside it and others peculiarities. The method of «porosity technique» is used to create the geometrical form of the settler in the numerical model. This technique permits to build any geometrical form of the settler for CFD investigation. Originality. Making of CFD-model which permits on the one hand to take into account the geometrical form of the settler, basic physical processes of mass transfer in construction and on the other hand requiring the low time cost in order to obtain results. Practical value. CFD-model is designed and code which is constructed on its basis allows at low cost of computer time and about the same as in the calculation of the 1-D model to solve complex multiparameter problems that arise during the design of vertical settlers with their shape and design features.

A comparative study for nanoparticle production with passive mixers via solvent-displacement: Use of CFD models for optimization and design

Active and passive mixers, including a considerable variety of micro-devices, are nowadays widely used for the production of nanoparticles. Polymer nanoparticles for controlled drug delivery applications are investigated in this work with two specific objectives. The first one is to experimentally quantify the efficiency of confined impinging jets reactors and Tee-mixers in the production of nanoparticles constituted by two polymers: poly-ɛ-caprolactone and poly(methoxypolyethyleneglycolcyanoacrylate- co-hexadecylcyanoacrylate). The second objective is the development of a simple and reliable mathematical model to be used for the design, optimization and scale up of mixers for polymer nanoparticle production. Although the behaviour of the polymers investigated is quite different, it is possible to conclude that confined impinging jets reactors are more efficient than Tee-mixers, in converting the pressure drop into turbulent kinetic energy and as a consequence in producing smaller particles. The very simple modelling approach proposed here (based on the evaluation of the mixing time) seems to be able to correlate well experimental data obtained under different operating conditions, independently on the type of device used. Moreover, in the case of poly-ɛ-caprolactone it was also possible to successfully quantify the particle formation time with a simple power law, further exploiting the model.

Use of CFD Modelling to Optimise the Design of Upper-room UVGI Disinfection Systems for Ventilated Rooms

The installation of upper-room ultraviolet germicidal irradiation (UVGI) devices in ventilated rooms has the potential to reduce transmission of infections by an airborne route. However, the performance of such devices is dependant on several factors including the location of the lamp and the ventilation airflow in the room. This study uses a CFD model to evaluate the performance of UVGI devices by considering the cumulative UV-C dose received by the bulk room air in a ventilated room. By evaluating the UV dose rather than the resulting micro-organism inactivation the methodology can be used to optimise UVGI systems at the design stage, particularly when the source location of bioaerosol contaminants is not known. The study investigates the relationships between the lamp location, lamp power, ventilation system and room heating in a small, ventilated room. The results show that with ventilation air supplied at low level and extracted at high level the UVGI system performs better than with the air supplied at high level and extracted close to the floor. In addition the results show the presence of a heater in the room is unlikely to have a detrimental effect on performance and may promote mixing to increase the extent of disinfection.