1,720,999 research outputs found
Enabling Dynamic Process Simulators to Perform Alternative Tasks: A Time-Stepper-Based Toolkit for Computer-Aided Analysis
No full textComputational Issues in Hybrid Multizonal/CFD modelling
No full textHybrid multizonal/computational fluid dynamics (CFD) models provide a means of
introducing a more realistic description of fluid mechanics and mixing phenomena within
process models. The solution of the CFD submodel implicitly defines a function relating
one or more of the variables in the multizonal model (the function outputs) in terms of
another subset of the variables (the function inputs). This paper is concerned with the
accurate and efficient evaluation of this function using local approximate models (LAMs)
that may have a general mathematical structure, or be based on physical correlations.
Practical issues relating to the robustness of the solution of hybrid models are also
considered, and a general architecture for the software interface between the multizonal
and CFD submodels is presented. The effectiveness and efficiency of the overall approach
are tested by two applications relating, respectively, to a stirred-tank chemical reactor
fitted with a cooling jacket and to a stirred-tank bioreactor
A General Framework for the Integration of Computational Fluid Dynamics and Process Simulation
No full textComputational fluid dynamics (CFD) and process simulation are widely used in the process industry. The two technologies are
largely complementary, each being able to capture and analyse some of the important process characteristics. Their combined
application can, therefore, lead to significant industrial benefits. This is especially true for systems, such as chemical reactors, in
which steady-state performance, dynamics and control strategy depend on mixing and fluid flow behaviour. This paper presents
a new approach for the integration of the capabilities of CFD technology and process simulation via a general interface that
allows the automatic exchange of critical variables between the two packages, leading to a simultaneous solution of the overall
problem. The approach applies to both steady-state and dynamic problems. The feasibility of the approach and its first practical implementation are demonstrated by integrating a widely used CFD package (Fluent 4.5, by Fluent Inc.) within a general-purpose advanced process simulator (gPROMS 1.7, by Process Systems Enterprise Ltd. (1999)). One case study involving a batch reactor is used to illustrate the ability of the combined tool to provide information on the detailed interactions between fluid mechanics, heat transfer, reaction and control strategy, and to provide insights on important design and operational decisions.
heat transfer, reaction and control strategy, and to provide insights on important design and operational decisions
implementation are demonstrated by integrating a widely used CFD package (Fluent 4.5, by Fluent Inc.) within a general-purpose
advanced process simulator (gPROMS 1.7, by Process Systems Enterprise Ltd. (1999)). One case study involving a batch reactor
is used to illustrate the ability of the combined tool to provide information on the detailed interactions between fluid mechanics,
heat transfer, reaction and control strategy, and to provide insights on important design and operational decisions
A General Hybrid Multizonal/CFD Approach for Bioreactor Modeling
No full textA critical issue in the modeling of aerobic bioreactors is the close interaction between
fluid flow and the biological reactions. In particular, shear rate has a large effect on the
broth viscosity which, in turn, affects the rate of mass transfer of oxygen from the gas to
the liquid phase. We demonstrate how a generic hybrid multizonalrcomputational fluid
dynamics (CFD) modeling approach can be applied to take account of these interactions.
The approach to multizonal modeling presented characterizes the flow rates between
adjacent zones, and also the fluid mechanical quantities, such as the shear stress,
that have important effects on the process behavior within each zone, by means of
steady-state CFD calculations. An unstructured model for xanthan gum production in a
batch aerobic bioreactor is used for this purpose. The hybrid modeling approach is also
applied to structured models involving distributions of cell mass within each zone
A General Methodology for Hybrid Multizonal/CFD Models: Part I: Theoretical Framework
No full textMultizonal models have been widely used for modelling the effects of mixing non-idealities in process equipment, presenting a realistic
trade-off of computational efficiency and predictive accuracy between simple models based on idealised descriptions of mixing and full
computational fluid dynamics (CFD) computations. However, a key weakness of multizonal models has been the difficulty of characterisation
of the flow-rates between adjacent zones, and also of fluid mechanical quantities, such as the turbulent energy dissipation rate, that have
important effects on the process behaviour within each zone. This paper presents a formal framework for addressing the above difficulties via
a multiscale modelling approach based on hybrid multizonal/CFD models. The framework is applicable to systems where the fluid dynamics
operate on a much faster time-scale than other phenomena, and can be described in terms of steady-state CFD computations involving a
(pseudo) homogeneous fluid, the physical properties of which are relatively weak functions of intensive properties. Such processes include
crystallisation and a wide variety of liquid-phase chemical and biological reactions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Accurate and efficient representation of intramolecular energy in ab initio generation of crystal structures. I. Adaptive local approximate models
Get PDFThe global search stage of Crystal Structure Prediction (CSP) methods requires a fine balance between accuracy and computational cost, particularly for the study of large flexible molecules. A major improvement in the accuracy and cost of the intramolecular energy function used in the CrystalPredictor II (Habgood, M., Sugden, I. J., Kazantsev, A. V., Adjiman, C. S. & Pantelides, C. C. (2015). J Chem Theory Comput 11, 1957-1969) program is presented, where the most efficient use of computational effort is ensured via the use of adaptive Local Approximate Model (LAM) placement. The entire search space of relevant molecule’s conformations is initially evaluated using a coarse, low accuracy grid. Additional LAM points are then placed at appropriate points determined via an automated process, aiming to minimise the computational effort expended in high energy regions whilst maximising the accuracy in low energy regions. As the size, complexity, and flexibility of molecules increase, the reduction in computational cost becomes marked. This improvement is illustrated with energy calculations for benzoic acid and the ROY molecule, and a CSP study of molecule XXVI from the sixth blind test (Reilly et al., (2016). Acta Cryst. B, 72, 439-459), which is challenging due to its size and flexibility. Its known experimental form is successfully predicted as the global minimum. The computational cost of the study is tractable without the need to make unphysical simplifying assumptions
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