1,720,997 research outputs found
The influence of multiple tubes on the tube-to-bed heat transfer in a fluidised bed
Full text linkThere have been few studies modelling both flow and heat transfer in fluidised beds. The kinetic theory of granular flow (KTGF) has been used for flow prediction in the past without heat transfer modelling. In the present study, a two-fluid Eulerian-Eulerian formulation incorporating the KTGF was applied first to a tube-to-bed reactor with one immersed tube and compared with the results in the literature. The bed was then modified to introduce two and three heated tubes. The effects on the flow and temperature distribution, local heat transfer coefficients and averaged heat transfer coefficients over a 3.0s time period were carried out. Results showed that increasing the number of tubes promotes heat transfer from tubes to the particles and flow. The heat transfer coefficients extracted from the single-tube to three-tube cases were analyzed in detail, confirming the importance of linking flow/particle and heat transfer calculation
CFD modelling of the co-gasification of biomass and coal particles in fluidised beds
No full textThe rapid depletion of oil and the environmental impact of combustion has motivated the search for clean combustion technologies. Fluidised bed technology (FBT) works by suspending a fuel over a fast air inlet whilst sustaining the required temperatures. Using biomass or a mixture of coal/biomass as the fuel, FBC provides a low-carbon combustion technology whilst operating at low temperatures. Computational modelling has shown great advancement in its predictive capability and reliability over recent years. Two-fluid modelling (TFM) has become a viable tool for the modelling of the hydrodynamic and heat transfer processes in fluidised beds yet the inclusion of reaction kinetics is still in the early stages due to their complexity. Such reaction kinetics need to be implemented by means of a user defined function (UDF) into the commercial software ANSYS 12.0 as current built in models are not available. In this paper, two-fluid modelling is used to model a bubbling fluidised bed gasifier (BFBG) using four solid phases namely, biomass, coal and two types of char. The devolatilisation model and heterogeneous reactions are implemented and the simulated gases produced are compared to experimental results from the literatur
Effect of tube shape on the hydrodynamics and tube-to-bed heat transfer in fluidized beds
No full textGas-liquid flow on smooth and textured inclined planes
No full textCarbon Capture & Storage (CCS) is one of the various methods that can be used to reduce the carbon footprint of the energy sector. This paper focuses on the absorption of CO2 from flue gas using packed columns, whose efficiency is highly dependent on the structure of the liquid films within the column. To study the characteristics of liquid films a CFD solver, OpenFOAM is utilised to solve two-phase, isothermal film flow using the volume-of-fluid (VOF) method. The model was validated using existing experimental data and the Nusselt theory. It was found that smaller plate inclination angles, with respect to the horizontal plane, resulted in larger wetted areas on smooth plates. However, only a slight improvement in the wetted area was observed. Simulations were also performed using a ridged plate and it was observed that these surface textures significantly increase the wetted area of the plate. This was mainly attributed to the channelling effect of the ridges, which helped to oppose the surface tension forces trying to minimise the surface area. Rivulet formations on the ridged plate were also flattened out and spread across a larger proportion of the plate widt
Parametric study of gasification processes in a BFB coal gasifier
No full textAn Eulerian-Eulerian computational fluid dynamics (CFD) model of the gasification processes in a coal bubblingfluidized bed (BFB) is presented based on the experimental setup taken from the literature. The base model is modified to account for different parameter changes in the model setup. The exiting gas compositions for the base model have been averaged over time and validated with experimental data and compared to the exiting results for the different parameter models. An extensive study is also carried out which considers the variation of different parameters such as bed temperatures, bed height, bed material, heat transfer coefficients, and devolatilization models influenced the gasification processes in different ways. Such an extensive parametric study has yet to be carried out for an Eulerian-Eulerian coal gasification model
Study of wall-to-bed heat transfer in a bubbling fluidised bed using the kinetic theory of granular flow
No full textResearch into heat transfer modelling in fluidised beds is very limited due to its complexity. The kinetic theory of granular flow (KTGF) has been applied successfully to hydrodynamic modelling in the past but its application in heat transfer modelling has not been tested extensively. A two-fluid Eulerian–Eulerian model has been carried out applying the KTGF to a wall-to-bed reactor. The local heat transfer coefficients are compared against experimental data for two drag models, namely the Gidaspow and the Syamlal–O’Brien drag models. Furthermore, a parametric study is carried out for a variety of coefficients of restitution, particle diameter sizes and inlet velocities. Near wall analysis is carried out in both dense and dilute regions. Both drag models detect the passage of the bubble reasonably well but they predict the complete transition of the bubble past the sensors occurs at slightly different times. The heat transfer coefficients obtained with the Syamlal–O’Brien model showed more local fluctuations than the Gidaspow model because the Syamlal–O’Brien models was developed based on the particle terminal velocities which would indicate a slight sensitivity to a microscopic scale. Extension of the simulation for a longer period makes it possible to reveal that a periodic distribution occurred after 1.5 s and the local heat transfer coefficients gradually reduced to agree better with the experimental results which were previously over estimated. The study shows that a regular dynamic pattern is established in the bubbling fluidised bed only after 1.5–2 s
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Operando infrared spectroscopy to probe the importance of framework selection in silicon-doped aluminophosphates, SAPO-5, SAPO-11, SAPO-18, and SAPO-34, for acid catalysed dimethyl ether formation
No full textMethanol dehydration chemistry is heavily reliant on solid acid catalysts for the formation of a wide range of hydrocarbons. Whilst olefins are routinely formed on strong Brønsted acid sites, there is a growing interest in dimethyl ether production, due to its potential as a sustainable fuel alternative, which is compatible with current petroleum infrastructure. The effective formation of dimethyl ether over extended time periods typically favours weaker acid sites. Here, two methanol molecules can couple together, reducing the formation of larger aromatic products that facilitate the methanol-to-olefin process, but which can also facilitate catalyst deactivation. In this manuscript, we use operando diffuse reflectance infrared Fourier transform spectroscopy to probe methanol dehydration on a range of microporous silicon-doped aluminophosphates (SAPO-5, SAPO-11, SAPO-18, and SAPO-34), correlating the findings with catalytic data to highlight the key parameters for an effective methanol-to-dimethyl ether catalyst. In doing so, we demonstrate that weaker acid sites play a key role in the production of dimethyl ether by permitting bound methoxy species and unbound methanol molecules to co-exist, triggering dimethyl ether formation
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