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The development of a compact mechanism has made a great contribution to work on the combustion of hydrocarbon species and facilitates the investigations on chemical kinetics and computational fluid dynamics (CFD) studies. N-propylcyclohexane (NPCH) is one of the important components for jet, diesel, and gasoline fuels which needs a reliable compact reaction kinetics mechanism. This study aims to investigate the construction of a well-validated mechanism for NPCH with a simplified chemical kinetics model that delivers a good prediction ability for the key combustion parameters in a wide range of conditions (temperatures, pressures, and equivalence rates). The NPCH reaction kinetic mechanism was constructed with the aid of a coupling process, simplification process, rate modification, and a combination of standard reduction methods. The model includes a simplified sub-mechanism with 16 species and 58 reactions and a semi-detailed core mechanism with 56 species and 390 reactions. Two key parameters including ignition delay time and laminar flame speed are simulated by the use of ANSYS Chemkin-Pro. The simulation results for these parameters are validated against the available data in the literature, and the results show a good agreement compared to the experimental data over a wide range of conditions covering low to high temperatures at different pressures and equivalence ratios. [ABSTRACT FROM AUTHOR]

Highlights: [•] A CFD model is developed to simulate the flame produced in thermal cracking furnaces. [•] This flame is produced by the ESP low NO x burner with internal FGR. [•] Different combustion models are used to simulate the ESP burner and the flame D case. [•] The EDC-GRI2.11 model is the most accurate model to predict CO and NO concentrations. [•] The EDC-GRI2.11 is the only model which predicts the flame length quite accurately. [Copyright &y& Elsevier]

• The twist angle has the most significant effect on the winglet of VAWTs. • The winglet's influence increases along the blade span towards the tip. • A winglet can weaken the tip vortex and enhance the power coefficient of the VAWT. Vertical axis wind turbines (VAWTs) have been attracting an increasing attention in recent years because of their potential for effectively using wind energy. The tip vortices from the VAWT blades have a negative impact on the power efficiency. Since a winglet has been proved to be effective in decreasing the tip vortex in the aerospace field, this paper numerically studies the aerodynamic effect of appending a winglet on the blade of a VAWT. Based on the theoretical motion pattern of the VAWT blade, this paper simplifies the three-dimensional full-scale rotor simulation to a one-blade oscillating problem in order to reduce the computational cost. The full rotor model simulation is also used in validating the result. The numerical approach has been validated by the experimental data that is available in the open literature. Six parameters are applied in defining the configuration of the winglet. The orthogonal experimental design (OED) approach is adopted in this paper to determine the significance of the design parameters that affect the rotor's power coefficient. The OED results show that the twist angle of the winglet is the most significant factor that affects the winglet's performance. A range analysis of the OED results produces an optimal variable arrangement in the current scope, and the winglet's performance in this variable arrangement is compared with the blade without a winglet. For the single blade study, the comparison result shows that the optimal winglet can decrease the tip vortices and improve the blade's power performance by up to 31% at a tip speed ratio of 2.29. However, for the full VAWT case, the relative enhancement in the power coefficient is about 10.5, 6.7, and 10.0% for TSRs of 1.85, 2.29, and 2.52, respectively. The winglet assists in maintain the pressure difference between the two sides of the blade, thus weakening the tip vortex and improving the aerodynamic efficiency of the surface near the blade tip. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new mesoscale 3D CFD model is proposed to predict the liquid flow in an RPB. • Detailed liquid flow patterns in the RPB are obtained. • Liquid holdup, percentage of droplets and interfacial area in the RPB are analysed. • New correlations for liquid holdup and effective interfacial area are developed. • Parametric sensitivity analyses of the RPB for influencing CO 2 capture are performed. Abstract Rotating packed beds (RPBs), as a type of process intensification technology, are promising to be employed as high-efficiency CO 2 absorbers. However, the detailed understanding of the liquid flow in the RPB is still very limited. The complex and dense packing of the bed and the multiscale of the RPB make it very difficult to perform numerical simulations in detail, in particular for full 3D simulations. In this paper, a mesoscale 3D CFD modelling approach is proposed which can be used to investigate the liquid flow in both laboratory- and large-scale RPBs in detail and accuracy. A 3D representative elementary unit of the RPB has been built and validated with experimental observations, and then it is employed to investigate the gas–liquid flows at different locations, across a typical RPB, so that the overall characteristics of the liquid flow in the RPB can be assembled. The proposed approach enables the detailed prediction of the liquid holdup, droplets formation, effective interfacial area, wetted packing area and specific surface area of the liquid within real 3D packing structures throughout the bed. New correlations to predict the liquid holdup, effective interfacial area, and specific surface area of the liquid are proposed, and the sensitivities of these quantities to the rotational speed, liquid flow rate, viscosity and contact angle have been investigated. The results have been compared with experimental data, previous correlations and theoretical values and it shows that the new correlations have a good accuracy in predicting these critical quantities. Further, recommendations for scale-up and operation of an RPB for CO 2 capture are provided. This proposed model leads to a much better understanding of the liquid flow behaviours and can assist in the RPB optimisation design and scaling up. [ABSTRACT FROM AUTHOR]

Highlights • The paper proposes a fast and accurate method for the angle of attack calculation. • This method could be used during the simulations without extensive post-processing. • The estimated lift and drag are very useful for understanding the power coefficient. • This method may be applied to analyse a variable pitch VAWT for design optimisation. Abstract The Angle of Attack (AOA) of the Vertical Axis Wind Turbines (VAWTs) blades has a dominant role in the generation of the aerodynamic forces and the power generation of the turbine. However, there is a significant uncertainty in determining the blade AOAs during operation due to the very complex flow structures and this limits the turbine design optimization. The paper proposes a fast and accurate method for the calculation of the constantly changing AOA based on the velocity flow field data at two reference points upstream the turbine blades. The new method could be used to calculate and store the AOA data during the CFD simulations without the need for extensive post-processing for efficient turbine aerodynamic analysis and optimisation. Several single reference-points and pair of reference-points criteria are used to select the most appropriate locations of the two reference points to calculate the AOA and It is found that using the flow data from the two reference points at the locations 0.5 aerofoil chord length upstream and 1 chord away from each side of the aerofoil can give most accurate estimation across a range of tested AOAs. Based on the proposed AOA estimation method, the performance of a fixed pitch and the sinusoidal variable pitch VAWT configurations are analysed and compared with each other. The analysis illustrates how the sinusoidal variable pitch configuration could enhance the overall performance of the turbine by maintaining more favourable AOAs, and lift and drag distributions. [ABSTRACT FROM AUTHOR]

Rotating packed beds (RPBs) have been proposed as an emerging technology to be used for post-combustion CO 2 capture (PCC) from the flue gas. However, due to the complex structure of the packing in RPBs, characteristics of the liquid flow within RPBs are very difficult to be fully investigated by experimental methods. Therefore, in this paper, a two-dimensional (2D) CFD model has been built for analysing the characteristics of liquid flow within an RPB. The volume of fluid (VOF) multiphase flow model is implemented to calculate the flow field and capture the interface between the gas and liquid phases in the RPB. The simulation results show good agreement with the experimental data. The distinct liquid flow patterns in different regions of an RPB are clearly observed. The simulation results indicate that increasing the rotational speed dramatically decreases the liquid holdup and increases the degree of the liquid dispersion. The increasing liquid jet velocity decreases the liquid residence time but slightly increases the liquid holdup. In addition, the liquid holdup increases and the degree of the liquid dispersion decreases with increasing MEA concentration, but the effects are weaker at a higher rotational speed. With the increasing of the contact angle, both the liquid holdup and the degree of the liquid dispersion are reduced. This proposed model leads to a much better understanding of the liquid flow characteristics within RPBs. [ABSTRACT FROM AUTHOR]

A dynamic CFD model, which is based on the inertia impaction, the thermophoresis and the direct alkali vapour condensation incorporating the influence of the heat transfer to the tube, has been developed for predicting the ash deposition formation in Zhundong lignite combustion in a pilot-scale furnace. The results show that particle deposition from the inertia impaction and the thermophoresis dictates the ash deposition formation under high furnace temperatures. The deposition caused by the direct alkali vapour condensation is less significant. As deposition time increases, particle impaction efficiency decreases and sticking efficiency increases due to the thermophoresis and the local temperature conditions, which result in the time-dependent behaviour of the deposition growth. In addition, the ash deposition characteristics are influenced under different furnace temperatures, due to the change in the particle impaction and sticking behaviours. Qualitative agreement is obtained between the predicted results and the measurements for the heat flux to the tube and the ash deposition growth. [ABSTRACT FROM AUTHOR]

The aim of this paper is to numerically investigate the effects of CO 2 dilution on the operation of an industrial micro gas turbine combustor in order to assess the possible application of exhaust gas recirculation (EGR) for post-combustion CO 2 capture. A complete 3D model of the combustion chamber has been developed, taking into account the conjugate heat transfer (CHT) and radiation effects, and a detailed chemical mechanism has been employed in the framework of the Flamelet Generated Manifolds approach to model the combustion process. The importance of including the effects of conjugate heat transfer in the model has been demonstrated for both air-fired and EGR conditions. Also, combustion with EGR resulted in lower temperature levels with respect to the air-fired case and thus in reduced NO x production. Further, the increased presence of carbon dioxide has been observed to have an impact on both the flame speed and the flame stabilization mechanism. According to the numerical results, EGR can be a viable way to increase the CO 2 content in the flue gas of dry low-emissions (DLE) combustors, and therefore enhance the efficiency of post-combustion carbon separation. At the same time, due to the reduced temperature levels within the combustion chamber, it is possible to attain lower NO x emissions without compromising the combustion efficiency under the considered EGR levels. [ABSTRACT FROM AUTHOR]

A CFD model that simulates particle impaction and sticking has been developed for predicting the ash deposition characteristics for the co-combustion of South African Coal (SAC) and palm kernel expeller (PKE) in an entrained flow reactor. The numerical related errors, caused by interception and the improper resolving of the flow-field within the boundary layer near the deposition surface, are investigated. In order to minimize the numerical related errors without excessive meshing, a new revised particle impaction model has been developed and accomplished using an impaction correction factor. The particle sticking is predicted based on the molten fraction results that have been obtained from the chemical equilibrium calculations using the chemical fractionation data in order to consider the short residence time of fly ash particles. The simulation results show that a reasonable coarse mesh, coupled with the revised particle impaction model, is suitable to accurately resolve the particle impaction without using a prohibitive meshing size. The ash deposition behaviour is determined by the particle impaction and sticking properties. Good agreements are obtained between the predicted results and the experimental data for the ash deposition behaviour. [ABSTRACT FROM AUTHOR]

This study evaluates the use of large eddy simulation (LES) and Reynolds-averaged Navier Stokes (RANS) models for the prediction of turbulent coal combustion under air and oxyfuel environments in a pilot-scale 250 kW th furnace. The furnace is part of the UKCCSRC Pilot-scale Advanced Capture Technology (PACT) facilities and was designed for detailed analysis of the combustion process. The prediction of thermal radiation is validated against experimental measurements under both air- and oxy-firing regimes. Two radiation models were evaluated during the RANS calculations, the widely used weighted sum of grey gases (WSGG) and the full-spectrum correlated k (FSCK) model, while the LES case was calculated using the FSCK radiation model. The results show that the choice in gas radiation model demonstrates only a small change in the temperature and heat flux predictions in the RANS calculations, while the LES solutions are able to achieve better agreement with measured values than the RANS predictions for both air-fired and oxyfuel coal combustion. [ABSTRACT FROM AUTHOR]

Oxyfuel is a promising technology for carbon capture and storage (CCS) applied to combustion processes. It would be highly advantageous in the deployment of CCS to be able to model and optimise oxyfuel combustion, however the increased concentrations of CO 2 and H 2 O under oxyfuel conditions modify several fundamental processes of combustion, including radiative heat transfer. This study uses benchmark narrow band radiation models to evaluate the influence of assumptions in global full-spectrum k-distribution (FSK) models, and whether they are suitable for modelling radiation in computational fluid dynamics (CFD) calculations of oxyfuel combustion. The statistical narrow band (SNB) and correlated-k (CK) models are used to calculate benchmark data for the radiative source term and heat flux, which are then compared to the results calculated from FSK models. Both the full-spectrum correlated k (FSCK) and the full-spectrum scaled k (FSSK) models are applied using up-to-date spectral data. The results show that the FSCK and FSSK methods achieve good agreement in the test cases. The FSCK method using a five-point Gauss quadrature scheme is recommended for CFD calculations in oxyfuel conditions, however there are still potential inaccuracies in cases with very wide variations in the ratio between CO 2 and H 2 O concentrations. [ABSTRACT FROM AUTHOR]

Abstract: This study describes an investigation into predicting the major flow properties in wake-stabilised jet flames in a cross flow of air using first- and second-order turbulence models, applied within a RANS (Reynolds-averaged Navier–Stokes) modelling framework. Standard and RNG (re-normalisation group) versions of the k-ε turbulence model were employed at the first-order level and the results compared with a second-moment closure, or RSM (Reynolds stress model). The combustion process was modelled using the laminar flamelet approach together with a thermal radiation model using the discrete ordinate method. The ability of the various turbulence models to reproduce experimentally established flame appearance, profiles of velocity and turbulence intensity, as well as the combustion efficiency of such flames is reported. The results show that all the turbulence models predict similar velocity profiles over the majority of the flow domain considered, except in the wake region, where the predictions of the RSM and RNG k-ε models are in closer agreement with experimental data. In contrast, the standard k-ε model over-predicts the peak turbulence intensity. Also, it is found that the RSM provides superior predictions of the planar recirculation and flame zones attached to the release pipe in the wake region. [Copyright &y& Elsevier]