• Energy Research

Abstract Liquid solid fluidized beds are widely applicable two-phase contactors by which solid and liquid phase constantly exchange energy/mass at the interface. In this paper, a new DEM simulation approach to analyse the hydrodynamic behaviour of fluidized beds has been introduced and validated. In this approach, a random liquid fluctuating velocity following a Gaussian distribution is used to simulate the fluid phase. The mean and standard deviation of the distribution were functions of the liquid velocity and bed concentration. The liquid fluctuating velocity was able to produce a random motion of the particle across the entire bed. This new methodology can predict bed expansion and porosity, particle mixing time and velocity as a function of liquid velocity. The simulation results revealed that using DEM only along with the simulation methodology presented in this study suffices to predict the hydrodynamics of a fluidized bed to a reasonable accuracy.

Abstract Liquid solid fluidized beds are widely applicable two-phase contactors by which solid and liquid phase constantly exchange energy/mass at the interface. In this paper, a new DEM simulation approach to analyse the hydrodynamic behaviour of fluidized beds has been introduced and validated. In this approach, a random liquid fluctuating velocity following a Gaussian distribution is used to simulate the fluid phase. The mean and standard deviation of the distribution were functions of the liquid velocity and bed concentration. The liquid fluctuating velocity was able to produce a random motion of the particle across the entire bed. This new methodology can predict bed expansion and porosity, particle mixing time and velocity as a function of liquid velocity. The simulation results revealed that using DEM only along with the simulation methodology presented in this study suffices to predict the hydrodynamics of a fluidized bed to a reasonable accuracy.

Abstract In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ∼ 2.77–3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.

Abstract In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ∼ 2.77–3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.

Abstract Natural gas is an important energy source for power generation, a chemical feedstock and residential usage. It is important to analyse the future production of conventional and unconventional natural gas. Analysis of the literature determined conventional URR estimates of 10,700–18,300 EJ, and the unconventional gas URR estimates were determined to be 4250–11,000 EJ. Six scenarios were assumed, with three static where demand and supply do not interact and three dynamic where it does. The projections indicate that world natural gas production will peak between 2025 and 2066 at 140–217 EJ/y (133–206 tcf/y). Natural gas resources are more abundant than some of the literature indicates.

Abstract Natural gas is an important energy source for power generation, a chemical feedstock and residential usage. It is important to analyse the future production of conventional and unconventional natural gas. Analysis of the literature determined conventional URR estimates of 10,700–18,300 EJ, and the unconventional gas URR estimates were determined to be 4250–11,000 EJ. Six scenarios were assumed, with three static where demand and supply do not interact and three dynamic where it does. The projections indicate that world natural gas production will peak between 2025 and 2066 at 140–217 EJ/y (133–206 tcf/y). Natural gas resources are more abundant than some of the literature indicates.

This paper briefly describes the various stages used to perform the life cycle analysis (LCA) of a product or process. The analysis is simplified in its outputs in that it focuses only on energy usage and carbon and sulfur dioxide emissions. The main point however, is to provide examples to first year engineering and science students that illustrate the principle of LCA without the need for extensive spreadsheet analysis that is so often required. Two examples are given and are staged in their complexity. Firstly, the task of choosing which option for drying hands after washing is explored. Air drying, washable cloth towel and disposable paper towels are assessed based on their carbon dioxide emission. This example provides a quantitative approach to determining impacts as well as an introduction to creating flowsheets and manipulation of unit equations. The second example, dealing with the location of a manufacturing plant, extends the LCA approach to sulfur dioxide impacts at both a local and global scale. It introduces the not-in-my-back-yard (NIMBY) concept and how this might be overcome by an optimisation (minimisation) of impacts at both local and global scales.

This paper briefly describes the various stages used to perform the life cycle analysis (LCA) of a product or process. The analysis is simplified in its outputs in that it focuses only on energy usage and carbon and sulfur dioxide emissions. The main point however, is to provide examples to first year engineering and science students that illustrate the principle of LCA without the need for extensive spreadsheet analysis that is so often required. Two examples are given and are staged in their complexity. Firstly, the task of choosing which option for drying hands after washing is explored. Air drying, washable cloth towel and disposable paper towels are assessed based on their carbon dioxide emission. This example provides a quantitative approach to determining impacts as well as an introduction to creating flowsheets and manipulation of unit equations. The second example, dealing with the location of a manufacturing plant, extends the LCA approach to sulfur dioxide impacts at both a local and global scale. It introduces the not-in-my-back-yard (NIMBY) concept and how this might be overcome by an optimisation (minimisation) of impacts at both local and global scales.

Abstract Turbulence modulation of a nearly isotropic flow field due to the presence of single glass particles, with diameters in the range of 1−8 mm (~10–77 times the Kolmogorov scale), was studied experimentally in an oscillating grid apparatus. Particle image velocimetry (PIV) was used to obtain the instantaneous, two-dimensional velocity field for grid Reynolds number, Re g , varying from 1080 to 10,800. Fluctuating velocity components, flow field length scales, energy dissipation rates, turbulence intensity modulation and energy spectra were determined. An apparent increase of ~2–25% in the turbulence fluctuating velocity in the inertial subrange was noted compared with the fluid-only system. Presence of the particle led to enhancement in the flow field isotropy ratio and this ratio was found to be more dependent on the particle size compared with grid Reynolds number. The integral length scale for both fluid-only and fluid–particle systems exhibited a decreasing power law dependency on the grid Reynolds number. A critical ratio (0.41) of particle size to integral length scale was obtained which demarcated the regime of attenuation and enhancement of turbulence intensity and found to be valid for general grid turbulence in multiparticle systems as well. Energy dissipation rate was observed to increase with increase in particle size. Both longitudinal and transverse energy spectrum exhibited less steep slope than −5/3 in the presence of particle which was reasoned to the production of turbulence in the inertial subrange region. Energy enhancements from large scale to smaller scale were explained by the dissipative spectrum which showed maximum energy enhancement in the inertial subrange followed by a decaying trend. In general, the role of a particle in modulating turbulence was explained through possible wake oscillation and vortex shedding due to boundary layer separation on the particle surface and interaction with bulk eddies.