Accelerated Heat Transfer Simulations Using Coupled CFD and DEM

This work presents an accelerated simulation of heat and mass transfer by coupling Discrete Element Methodologies (DEMs) and Computational Fluid Dynamics (CFD), utilising Graphics Processing Unit (GPU) technology. The presented model is a continuation of previous work[1] and focuses on demonstrating the capabilities and effectiveness of implementing the GPU combined with the Central Processing Unit (CPUs) technologies to run a complex industrial simulation. A model of an aggregate drum dryer was used to produce hot mix asphalt and different configurations have been implemented to investigate the effect of GPU-CPU technology in such a complex simulation. Commercial codes from ANSYS and DEM-Solutions were coupled to simulate heat transfer from the hot gases to the aggregate particles. Fluid flow and particle-fluid interactions are solved by the CFD solver which exchanges information at regular intervals. The results showed that the coupled model captures accurately the convective heat transfer from the fluid to the solid phase and demonstrated significant improvement in terms of simulation time. The proposed model will have a significant impact in industrial applications as it describes a methodology to simulate large-scale applications rapidly and accurately

Effectiveness of CFD simulation for the performance prediction of phase change building boards in the thermal environment control of indoor spaces

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2013 ElsevierThis paper reports on a validation study of CFD models used to predict the effect of PCM clay boards on the control of indoor environments, in ventilated and non-ventilated situations. Unlike multi-zonal models, CFD is important in situations where localised properties are essential such as in buildings with complex and large geometries. The employed phase change model considers temperature/enthalpy hysteresis and varying enthalpy-temperature characteristics to more accurately simulate the phase change behaviour of the PCM boards compared to the standard default modelling approach in the commercial CFD codes. Successful validation was obtained with a mean error of 1.0 K relative to experimental data, and the results show that in addition to providing satisfactory quantitative results, CFD also provides qualitative results which are useful in the effective design of indoor thermal environment control systems utilising PCM. These results include: i) temperature and air flow distribution within the space resulting from the use of PCM boards and different night ventilation rates; ii) the fraction of PCM experiencing phase change and is effective in the control of the indoor thermal environment, enabling optimisation of the location of the boards; and iii) the energy impact of PCM boards and adequate ventilation configurations for effective night charging.This work was funded through sponsorship from the UK Engineering and Physical Sciences Research Council (EPSRC), Grant No: EP/H004181/1

Experimental and numerical investigations of particle/air flows in dustiness testers

Dust is generated from bulk materials during handling, free fall and through belt conveyor transfers, creating air pollutants which can affect human communities, industrial equipment and the environment. A greater understanding of the generation of dust from bulk material requires knowledge of the mechanisms of bulk material flows. The purpose of this research was to investigate the mechanisms of bulk material flow in dustiness testers by using numerical simulations and by comparing these results with experimental data. The experiments were carried out using three types of bulk materials with different properties, namely, polyethylene pellets, iron ore and coal. In these experiments, the flow of bulk materials are measured in rotating drums using two types of standard dustiness testers. The two standard dustiness testers that were chosen in this study are the International Standard (IS) dustiness tester and the Australian Standard (AS) dustiness tester. Even though both of these dustiness testers are very similar in their operations, they differ in terms of: (i) the air flow and velocity of the drum rotations and, (ii) the volume of materials used in the experiments. Four types of particle heaps were considered in this work, namely, particles that are: spread from the front to the back of the drum, in the middle, at the front and at the back of the drum. This study investigated the mechanisms of bulk materials movement in both dustiness testers by varying the types of materials, contact force, particle velocity and the collision of materials as the particles flow in both dustiness testers

CFD-DEM modelling of particle ejection by a sensor-based automated sorter

© 2015 Elsevier Ltd. Abstract The efficiency of sensor-based automated sorting depends on both correct identification and separation of different types of particles. It is known that the distribution of particles fed to the sorter will affect both of these. When different particles are in close proximity, they can be "agglomerated" or seen as a single particle during identification and also have an increased probability of being unintentionally co-ejected. Both factors will have a negative effect on separation efficiency. The aim of this work was to model the air ejection manifold of a sensor-based automated sorter and to investigate the relationship between particle proximity and unintentional co-ejections. The airflow from a single air ejection valve of a sorter was modelled using computational fluid dynamics (CFD) software and calibrated against a Tomra Sorting Solutions optical sorter. It was found that the air ejection manifold could be accurately represented in CFD code. Particles were modelled using the discrete element method (DEM) software and the effect of particle position, relative to an air ejection valve, on accurate ejection was examined using an integrated CFD-DEM model. The results of these models matched reasonably well with physical measurements. The models created can be used as a basis for the prediction of sorter efficiency

Advanced Computational Fluid Dynamics for Emerging Engineering Processes

As researchers deal with processes and phenomena that are geometrically complex and phenomenologically coupled the demand for high-performance computational fluid dynamics (CFD) increases continuously. The intrinsic nature of coupled irreversibility requires computational tools that can provide physically meaningful results within a reasonable time. This book collects the state-of-the-art CFD research activities and future R&D directions of advanced fluid dynamics. Topics covered include in-depth fundamentals of the Navier-Stokes equation, advanced multi-phase fluid flow, and coupling algorithms of computational fluid and particle dynamics. In the near future, true multi-physics and multi-scale simulation tools must be developed by combining micro-hydrodynamics, fluid dynamics, and chemical reactions within an umbrella of irreversible statistical physics

A novel approach for integrating concentrated solar energy with biomass thermochemical conversion processes

Concentrated solar energy provides thermal energy that can be utilised for thermochemical conversion of biomass to produce liquid fuel and gases. This creates an efficient and a carbon-free process. The fast pyrolysis of biomass is an endothermic thermal process that occurs within 400-550oC at fast heating rates of >300 oC/second in the absence of oxygen. This temperature is within the range produced in a parabolic trough arrangement. The process of biomass gasification is the conversion of biomass fuels to non-condensable gases usually for chemical feedstock or as fuel using a fluidising medium. Solar intermittence is a major issue; this can be resolved by proposing a continuous process from concentrated solar energy to fuels or chemical feedstock. Computational fluid dynamics has proven to be a tool for design and optimisation of reactors. The Eulerian-Eulerian multiphase model using ANSYS Fluent has shown to be cost-effective at describing the characteristics of complex processes. The project entails using parabolic trough for fast pyrolysis of biomass; it is integrated with a gasification process with utilities produced entirely from solar energy. The scope of the project are: (i) A Computational fluid dynamic (CFD) model analysis of the novel reactor is to be developed to model biomass pyrolysis (ii) Investigate the potentials of integrating the proposed solar reactor with a conventional circulating fluidised bed (CFB) gasifier to create a highly efficient and sustainable closed loop thermo-solar process (iii) Validate the circulating fluidised bed model with an experimental scale Circulating fluidised bed (CFB) gasifier at Aston University’s European Bioenergy Research Institute. The report studied the use of CFD modelling to investigate fast pyrolysis of switch grass biomass using a solar parabolic trough receiver/reactor equipped with a novel gas-separation system. The separator controls the effect of tar-cracking reactions and achieves high separation efficiency compared to other gas-solid separation methods. The study assumes an average heat flux concentrated along the receiver/reactor. Pyrolysis reaction was represented as a single global first order Arrhenius type reaction with volatiles separated into condensable (bio-oil) and non-condensable products. The drying of moisture of the switch grass was represented as a mass transfer process. The separation efficiency achieved by the conical deflector was about 99%. The proposed reactor at the considered operating conditions can achieve overall energy efficiency of 42%; the product yield consist of 51.5% bio-oil, 43.7% char and 4.8% non-condensable gases. The average reactor temperature, gas residence time, and maximum devolatilisation efficiency were 450 °C, 1.5 s, and 60% respectively. There was good agreement in comparison with experimental findings from literature. A sensitivity analysis was conducted to study the effect of heat flux conditions, heat transfer, sweeping gas temperature, and particle size. The heat flux distribution showed that non-homogeneous provides a greater heating rate and temperature compared to the homogeneous flux. Radiation negligibly affects the final product composition; the radiation heats the biomass mainly rather than cause devolatilisation. The larger the biomass diameter the more bio-oil is produced, when a uniform particle temperature is assumed. An experimental study was conducted for the validation of the hydrodynamic model of a circulating fluidised bed. The experiment measured the pressure profiles and the solid recirculation rate. The experiment result showed that particle size has a negative correlation to the ease of fluidisation. High fluidising gas flowrate has a positive impact on the fluidising regime and pressure in the riser. The following parameters were compared with experimental results: grid size, turbulence model, drag laws, wall treatment, and wall shear properties (specularity coefficient and restitution coefficient). The results proved the optimum hydrodynamic model through comparison of pressure profiles of the model with experimental results. The gasification of char in a circulating fluidised was studied using the optimum hydrodynamic model validated from experiment. The model considered the effect of turbulence on the species evolution and tar reforming with char. Over the range of operating conditions, the results looked into the hydrodynamics and product yield of the gasifier. The product yields obtained for the base case was CO (12%), CO2 (19%), H2 (6%), CH4 (0.7%), and N2 (63%). The results proved that for smaller particles the evolution of species are dominated by kinetics. The catalytic effect of char showed improvement in tar yield and CGE to 15.12g/Nm3 and 67.74%. The product yields showed improvement with the compositions of CO2 and H2 due to reforming reactions. The yields and efficiency were in qualitative agreement with results from literature. The proposed models described will provide details on the procedures for future design of integrated solar biomass thermochemical conversion systems

A numerical investigation of air-core formation and particle separation in a hydrocyclone

Abstract: Process equipment is widely used in industry today and applies complex physical interactions when used in simulations. A need has emerged to obtain a fully working and accurate simulation of process equipment involved with multiphase flows. Through research and application of various numerical theories to multiphase flow simulations this can be achieved. Thus, the aim of this study is to achieve a fully developed and stable air-core model with particle separation whilst implementing the Eulerian-Eulerian multiphase model and the Reynolds Stress Model (RSM). Focus will be placed on ensuring model accuracy when compared to experiment as well as aircore formation and stability. A brief literature study was conducted in order to gain insight into the most recent stage of development in hydrocyclone modelling. A physical experiment was conducted in order to obtain the boundary and input conditions for the simulation such that the results obtained from the simulation can be experimentally validated against the experimental results. Silicon (MQ 15 Crystalline Quartz) particulates and a hydrocyclone barrel diameter of 50mm were used in the experiment. These conditions remained the same when the simulations were conducted. Two air-core models were constructed with different turbulent models and the particulates model was constructed as a continuation from the air-core models. The first air-core model utilised the Eulerian-Eulerian approach coupled with the Renormalization Group (RNG, k-ϵ) model theory. The second air-core model also utilised the Eulerian-Eulerian approach but with the RSM. These models were conducted first in order to reduce computational instabilities that may occur when adding particulates to the system. Comparisons between the two models were made and were also validated against experimental results. Both achieved fully developed and stable air-cores and accurate results of predicted mass flow rate at the overflow in comparison to experiment. Both models did not produce accurate results when predicting the mass flow rate at the underflow. The particulates model was analysed regarding air-core formation, particle separation and particle physics. The results from simulation produced a partially developed aircore with accurate results in predicting the mass flow rate at the overflow in comparison to experiment. The predicted mass flow rate at the underflow was noticeably over-predicted in comparison to experimental results. The particle separation efficiency was found to be fairly accurate in comparison to experimental results. The challenges experienced with the particle simulation results were deemed to be the result of insufficient run time and the lack of an adequate particle interactions model. The results from the study showed that a fully developed and accurate Eulerian- Eulerian based air-core model can be achieved although difficulties arise when incorporating particles into the system due to the complex physical interactions taking place especially at the underflow. Incorporating more complex numerical models such as the coupled Computational Fluid Dynamics (CFD) – Direct Element Method (DEM) model with the Dense Discrete Phase Model (DDPM) for additional granular interactions may improve the mentioned problem areas.M.Ing. (Mechanical engineering science

Modelling Tremie Concrete Placement in Deep Foundations

Cast-in-place foundations are typically constructed using the Tremie Method of concrete emplacement. A pipe and hopper system is used to fill an excavation from the base up with a specialised, highly workable concrete called Tremie Concrete. In this thesis, numerical modelling and experimental analysis are employed to define what conditions encourage the occurrence of defects in cast-in-place foundations. Two numerical methods were chosen to simulate concrete: Computational Fluid Dynamics (CFD) and the Material Point Method (MPM). A new thixotropic model integrating the Papanastasiou-Bingham model with thixotropy equations was developed, enabling the simulation of thixotropic behaviour of Tremie Concrete in the Material Point Method framework. The novel model revealed a decline in concrete workability during simulations of the Slump-flow and L-box tests after a period of rest which the physical version of the test fails to capture. A classification system of flow behaviours which relies on a scale of flow restriction was developed based on CFD simulations of concrete flow in a novel apparatus designed to represent conditions closer to those found in cast-in-place foundations. Additional simulations of the same apparatus in MPM found the effect of thixotropy and the addition of a support fluid represent further restrictions to flow that can lead to defective foundations. In summary, defects within deep foundations associated with the flow behaviour of concrete during the Tremie Method can be predicted based on the level of restriction to flow the concrete will experience.EPSRC ICASE (ref: 1769998