During the 3D printing of graphene platelet inclusion in resin, residual stresses due to thermal loading can cause wrinkle/distortion of final part. This paper presents a multi-scale modeling approach to reduce the residual thermal stress at the interphase between inclusion and resin. Material characterization is performed utilizing an integrated multi-scale modeling approach: (a) nano modeling examines effect of defects such as void shape/size/distribution, platelet orientation, etc.); (b) micro-mechanics examines constituents (platelet/matrix/interphase, residual stress); (c) macro-mechanics examines the delamination and debonding. De-homogenized multi-scale modeling approach provides detailed stiffness/strength to Finite Element Model (FEM) for full structural/thermal progressive failure analysis to address wrinkling/distortion, damage and delamination evolution via cohesive traction separation.

An ICME (Integrated Computational Material Engineering) and lifing model/method is developed for optimizing multifunctional coatings Atmospheric Plasma Spray (APS) process of metallic TBC (Thermal Barrier Coating) system. Optimized TBC performance was achieved by minimizing thermal conductivity and residual stresses/strains during APS utilizing multiphysics-based multi-objective topology optimization methodology, and virtual design of experiment (DOE), surrogate meta modeling methodology. Thermal conductivity and residual strains were minimized 41% and 27%, respectively, for APS 8YSZ TBC with MCrAlY bond over Waspaloy substrate considering as variables yttria (mol.%), number of layers, total thickness, substrate initial temperature, and coating initial temperature. Durability and Damage Tolerance (D&DT) analysis of Metallic bonded TBC dogbone specimen was performed using Multi-Scale Progressive Failure Analysis (MS-PFA). The objective was to determine the Remaining Useful Life (RUL) of Metal/TBC (8YSZ, Bond, Inconel-718) system under Low Cycle Fatigue (LCF) in-service loading at 900°C. The multi-scale multi-layer TBC modeling considered Thermal Growth Oxidation (TGO) in bond coat, and recession of top coat. Prediction was validated by Rig testing; TGO measurement Progressive damage analysis revealed that failure is due to tension and out of plane shear, delamination growth due to when recession penetrates bond. The results showed that predicted fatigue life compared well to experimental observations.

A mathematical model of a fixed-bed reactor for Fischer–Tropsch Synthesis (FTS) over 37% Co/SiO2 catalyst was developed to investigate the performance of the whole process for products’ selectivity and syngas conversion. The model was capable of calculating the changes of reactant and products’ concentrations, partial pressures, conversion and selectivity. In the previous study, a series of combined novel FT and water gas shift (WGS) reaction mechanisms (eight elementary FT reaction pathways along with seven WGS kinetics models) were developed in order to calibrate and validate the mathematical model along with reaction kinetics at different experimental conditions. Such mathematical model with reaction networks can be used as a key tool to emphasise the most significant facts of FTS catalysis and chemistry. Integration of the Global Search optimization algorithm with the developed model was explained for estimation of kinetics parameters. Data analyses were carried out to assure that the predicted model results as well as kinetic parameters are significantly relevant and physically meaningful. Parametric studies were performed to numerically investigate the effects of operating conditions (e.g. reaction temperature, total pressure, space velocity and H2/CO molar ratio) on products’ selectivity and reactant conversion. These parameters were then included in a multi-objective optimization in MATLAB using NSGA–II to optimize the CO2 and HC products’ selectivity and syngas conversion. The optimization process gives rise to a set of trade-off optimal solutions (Pareto-optimal solutions) which is used as a dynamic database depending on the specific requirement. A different operating condition can be selected from such database which privileges the optimization of a particular output (e.g. conversion and selectivity).

Waste heat recovery of low-to-medium grade heat sources such as solar energy or biomass using Organic Rankine Cycle (ORC) technology has received growing attention recently. Few manufacturer of biomass (wood logs) stoves utilizes silicon-carbide as the material for manufacturing of their stoves to facilitate slow-heat-release for a long period of time for up to twelve hours. Despite good performance of these stoves, there is still significant amount of heat that is wasted through exhaust at the temperature of between 240 degrees C to 270 degrees C. This paper investigated various strategies to minimize heat losses to the environment by introducing an ORC system that can capture the waste heat and convert it into useful power. The stove's temperature distribution as well as identification of potential location for the ORC evaporator were obtained using experimental testing. Such results were then employed for validation of a CFD model and it was shown that this CFD model can fairly accurately predict both temperature distribution and recovered heat on the ORC evaporator coils. Among investigated scenarios, "Modification 2" proved to be most effective as it not only preserved the heating functionality of the stove but also improved the stove's efficiency by about 20% while generating 1.113 kW of electricity.

The ever-increasing demand for energy, scarcity of traditional energy sources and severe environmental issues are, perhaps, the biggest global challenges that need immediate actions. In this regard, harnessing the renewable energies and waste heat recovery are considered as potential solutions that can effectively address these issues. Organic Rankine cycle (ORC) is proved to be reliable technology that can efficiently convert these low to medium-grade heat sources into useful power. This paper is a comprehensive review of literature about the ORC that contains the ORC configurations, ORC applications, ORC working fluid selection and modelling and experimental study of the ORC expansion devices. (C) 2016 Elsevier Ltd. All rights reserved.

A comprehensive kinetics study of Fischer-Tropsch (FT) synthesis mechanism was investigated over an in-house 37% Co-based catalyst on a SiO2 support. A series of combined FT and water gas shift (WGS) reaction mechanisms were developed in order to calibrate the model at twelve different operating conditions. Two different approaches were used to develop a model for the FT synthesis reaction network. The first was based on an empirical approach; whereas the second approach explained the novel mechanistic details of FT kinetics. In the former, the rate equations were derived by power-law rate expressions, while in the latter the rate equations were derived by the Langmuir-Flinshelwood-Houge n-Watson (LHHW) rate theory. The limitations of power-law rate model were highlighted for the applications that wider range of operating conditions has to be selected. In contrast the advantages of LHHW for predicting a wider range of operating conditions were underlined. A comprehensive plausible mechanism-derived FT kinetics models with eight elementary reaction pathways along with seven WGS kinetics models were developed. Such reaction networks were investigated to fit and validate against the newly obtained experimental results which can be used as a key tool to emphasise the most significant facts of FT synthesis catalysis and chemistry. Model validation was carried out subsequent to completion of the model calibration and the estimation of proper kinetic parameters. The overall purpose of the validation study was to ensure that the model provides a robust and realistic assessment of all the parameters. In order to ensure model is precise to an appropriate level, the model was assessed against experimental data at four different operating conditions. The results obtained from kinetic study were compared to the most recent findings that have been reported in literature. It was shown that the novel developed kinetic model based on a combination of allcylialkenyl mechanism for FT reactions (for production of n-paraffins and a-olefins) along with formate mechanism for WGS reaction can provide the most accurate predictions. (C) 2017 Elsevier Ltd. All rights reserved.

With ever increasing demand on energy, disturbed power generation utilizing efficient technologies such as compressed air energy storage (CAES) and organic Rankine cycle (ORC) are receiving growing attention. Expander for such systems is a key component and its performance has substantial effects on overall system efficiency. This study addresses such component by proposing an effective and comprehensive methodology for developing a small-scale radial inflow turbine (RIT). The methodology consists of 1-D modelling, 3-D aerodynamic investigation and structural analysis, manufacturing with pioneering technique and experimental testing for validation. The proposed 1-D modelling was very effective in determining the primary geometry and performance of turbine based on parametric studies of turbine input design variables. However with CFD analysis, it was shown that more efficient turbine geometry can be achieved that not only provides more realistic turbine performance by capturing the 3-D fluid flow behaviour but also improves turbine efficiency with the aid of parametric studies of turbine geometry parameters. Turbine efficiency was improved from 81.3% obtained from 1-D modelling to 84.5% obtained by CFD. Accuracy of the CFD model was assessed by conducting experiments on the RIT manufactured with stereolithography technique. The CFD model can predict turbine efficiency and power with accuracy of 16% and 13% respectively for a wide range of tested operating conditions. Such results highlights the effectiveness of the proposed methodology and the CFD model can be used as benchmarkirig model for analyses of small-scale RITs. Besides, it was shown that for such applications, the novel manufacturing technique and employed material are very effective for producing prototypes that assist design decisions and validation of CFD model with reasonable accuracy at reasonable cost and in timely manner. (C) 2017 Elsevier Ltd. All rights reserved.

A mathematical model of a fixed-bed reactor for Fischer-Tropsch synthesis (FTS) over 37% Co/SiO2 catalyst was developed to investigate the performance of the whole process for products' selectivity and syngas conversion. The model was capable of calculating the changes of reactant and products' concentrations, partial pressures, conversion, and selectivity. In a previous study, a series of combined novel FT and water gas shift (WGS) reaction mechanisms (eight elementary FT reaction pathways along with seven WGS kinetics models) were developed in order to calibrate and validate the mathematical model along with reaction kinetics at different experimental conditions. Such mathematical models with reaction networks can be used as a key tool to emphasize the most significant facts of FTS catalysis and chemistry. Integration of the global search optimization algorithm with the developed model was explained for estimation of kinetics parameters. Data analyses were carried out to ensure that the predicted model results as well as kinetic parameters are significantly relevant and physically meaningful. Parametric studies were performed to numerically investigate the effects of operating conditions (e.g., reaction temperature, total pressure, space velocity, and H-2/CO molar ratio) on products' selectivity and reactant conversion. These parameters were then included in a multiobjective optimization in MATLAB using NSGA-II to optimize the CO2 and HC products' selectivity and syngas conversion. The optimization process gives rise to a set of trade-off optimal solutions (Pareto-optimal solutions) which is used as a dynamic database depending on the specific requirement. A different operating condition can be selected from such a database which privileges the optimization of a particular output (e.g., conversion and selectivity).

Organic Rankine cycle is one of the most efficient technologies that can utilize low-to-medium grade heat sources and generate useful power. Radial inflow turbine (RIT) is the key component of the ORC and its efficiency has significant effect on the overall cycle performance. Obtaining high cycle thermal efficiency requires large pressure difference (expansion ratio) across the cycle. With the low speed of sound of organic fluids and the high expansion ratios, RIT becomes chocked with supersonic flow regime and shock waves that deteriorate the turbine efficiency and hence reduce the cycle performance. Therefore, developing highly efficient RIT that can both preserve the high expansion ratio requirements of the ORC and maintain the turbine isentropic efficiency is crucial. This paper proposed the complete 1-D and 3D numerical optimization of two different configurations as single stage supersonic and dual-stage transonic RITs. Initially, the integrated 1-D modelling of the ORC with RIT coupled with genetic algorithm optimization technique was conducted to maximize the cycle thermal efficiency. The results showed that the dual-stage RIT exhibited considerably higher turbine efficiency in both stages and hence higher cycle efficiency compared to the single-stage supersonic one. Both configurations were further optimized using the 3-D CFD optimization procedure to maximize the turbine efficiency. The CFD results showed that the optimization of each stage individually was successful as the turbine performance increased significantly. The results revealed that the optimizations were more effective for the dual-stage transonic turbine compared to the single-stage supersonic due to the presence of shock waves. Comparison of the optimized single stage supersonic RIT and complete dual-stage transonic RIT showed that about 15.7%, 10.63kW and 16.08% higher turbine isentropic efficiency, turbine power and cycle thermal efficiency were achieved respectively with the latter configuration.

This paper presents the integrated modelling and multi objective optimization of ORC based on radial inflow turbine. With this approach it is possible to replace the constant turbine efficiency with a dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. This allows overcoming any arbitrary assumption of the turbine efficiency, unlike the previous literature, and providing a more realistic estimation of the cycle performance. Parametric studies were conducted utilizing the developed model to identify the key input variables that have significant effects on the critical turbine-ORC performance indicators. These variables were then included in the optimization process using DIRECT algorithm to optimize two objective functions as the cycle thermal efficiency and the turbine overall size for five organic fluids. Optimization results predicted that isobutane exhibited the best performance with the maximum cycle thermal efficiency of 13.21% and turbine overall size of 0.1434m while having relatively high turbine isentropic efficiency of 77.03%.

A one-dimensional pseudo-homogeneous mathematical model of a fixed bed reactor for Fischer–Tropsch (FT) synthesis was developed for the flow of simulated N2-rich syngas over an in-house cobalt–silica catalyst. This study aims at improving the efficiency of FT synthesis by maximizing the liquid productivities and selectivity, as well as maximizing the syngas conversion and minimizing the methane formation. The developed model predicts the fraction of the reactants and products along the reactor bed length. The rate of syngas conversion and the rate of CO2, H2O, CH4, C2H4, C2H6, C3H8, n-C4H10, i-C4H10 and C6.05H12.36 (C5+) formation were calculated by developing advanced codes in MATLAB. The reaction equations were proposed as a number of lumped chemical reactions (8 reactions, including water gas shift reaction) by means of the molar coefficients of reaction molecules (11 reactive species). The kinetic parameters were estimated by global optimization in MATLAB using the global search method. Optimum values were achieved during the search process. The results predicted by the model were in very good agreement with those measured experimentally at different operating conditions, with respect to conversion and the FT products׳ selectivity. The rates of production and consumption were derived from a modified power-law rate expression. This study shows that the adapted rate model can deliver a better prediction of final conversion and selectivity. The accuracy of the fitted model relative to the experimental data was determined by a quantitative analysis method using the mean absolute relative residual percentage (MARR %) for the total of 35 data points. It was found that the model based on the modified equation provided a better fit to the experimental data with a MARR of 6.57%, compared to the classic equation with a MARR of 12.24%.

This study presents an optimized modelling approach for ORC based on radial turbo-expander, where the constant expander efficiency is replaced by dynamic efficiency and is unique for each set of cycle operating conditions and working fluid properties. The model was used to identify the key variables that have significant effects on the turbine overall size. These parameters are then included in the optimization process using genetic algorithm to minimize the turbine overall size for six organic fluids. Results showed that, dynamic efficiency approach predicted considerable differences in the turbine efficiencies of various working fluids at different operating conditions with the maximum difference of 7.3% predicted between the turbine efficiencies of n-pentane and R245fa. Also, the optimization results predicted that minimum turbine overall size was achieved by R236fa with the value of 0.0576m. Such results highlight the potential of the optimized modeling technique to further improve the performance estimation of ORC and minimize the size.

Organic Rankine Cycle converts low grade heat sources into power utilizing organic fluids with low boiling temperature and pressure. In this cycle the design and performance of the expander has a significant impact on the cycle's overall efficiency. This work presents an integrated mathematical approach for the development of an efficient and compact small-scale radial turbine. This mathematical approach integrates the mean-line modelling with real gas formulation and GA(genetic algorithm) optimisation technique. In this methodology, the mean-line modelling coupled with real gas formulation is employed to perform parametric studies to identify the key variables that have significant effect on the turbine efficiency. Such variables are then used in the GA to optimise the turbine performance. Eight organic fluids are investigated to optimise the performance of the small-scale radial turbine in terms of efficiency. Results showed that the achieved radial turbine efficiencies vary from 82.9% to 84%; which is higher than the reported efficiency values of other types of expanders. R152a showed the highest efficiency of 84% with seven degrees (K) of superheating. However, if the superheating is to be avoided, isobutane exhibited the most favourable characteristics in terms of efficiency (83.82%), rotor size (66.3 mm) and inlet temperature (89.2 degrees C). (C) 2015 Elsevier Ltd. All rights reserved.

A numerical one-dimensional pseudo-homogeneous mathematical model of a fixed bed reactor for Fischer-Tropsch (FT) synthesis was developed over a simulated nitrogen-rich syngas (33% hydrogen, 17% carbon monoxide and 50% nitrogen (volume basis)), on a cobalt-silica catalyst. An algorithm was developed and the MATLAB codes were written in order to predict the product selectivity (H 2 O, CO 2 and hydrocarbons i.e. CH 4 , C 2 , C 3 , C 4 and C 5+ ) and syngas conversion (CO and H 2 ). In order to predict the kinetic parameters, the global search optimization subroutine (from MATLAB Global Optimization) was used. The model was fitted with experimental data at five different operating conditions with respect to conversion and selectivity. Discrimination between the model and the experiments was determined by the mean absolute relative residuals percentage (MARR %) and the value was 13.29%. The Effects of operating conditions such as reaction temperature, total pressure, flow rate and H 2 /CO molar ratio were investigated on the catalytic performance of the cobalt-silica for synthesis of liquid fuel. The model was studied in the range of 200-260 °C, 1-25 bar, reduced gas flow rate (per unit mass of catalyst) of 2.4-3.6 NL g cat-1 h -1 and H 2 /CO = 1.75-2.75 (mole basis)

A numerical pseudo-homogeneous one-dimensional mathematical model of a mini-scale laboratory fixed bed reactor for Fischer-Tropsch (FT) synthesis was developed. FT synthesis was modelled for simulated N-2-rich syngas (17%Vol CO, 33%Vol H-2, and 50%Vol N-2) on a cobalt-silica (i.e. Co/SiO2) catalyst/support. The performance of the reactor model for gas/liquid fuel production was studied at different operating conditions i.e. temperature of 503-543 K, pressure of 10-25 bar and gas hourly space velocity (GHSV) of 1800-3600 Nml g(cat)(1)h (1). An algorithm was written in order to calculate the conservation of species, pressure drop, reaction rate equations and physicochemical and thermodynamic properties' relationships along the axial dimension i.e. in the flow direction. The program code was executed in a MATLAB environment to describe the profiles of concentration of each individual component in the gas phase along the reactor. The model was capable of predicting the selectivity of different product species and conversion of CO and H-2 in the flow direction.The power law rate expression was chosen for the rate of reaction and the dominating FT and Water Gas Shift (WGS) reaction equations were considered in accordance with the literature. After the mechanisms and rate equations were derived, the kinetic data (e.g. rate constant (k(j)), for reaction 'j') for the proposed reaction equations were obtained as "integral reactor data'' where the total conversion is measured as a function of: catalyst weight to flow rate ratio (i.e. W/F), inlet pressure, final conversion obtained by experiment, and inlet fluid temperature. The pre-exponential factors (A(j)) were calculated by the classic Arrhenius equation using the predicted k(j) and literature-derived activation energies (E-j). Finally, the partial order of reactions with regard to CO (m(j)) and H-2 (n(j)) were calculated for the power law rate equation using MATLAB Global Optimization Toolbox with additional in-house procedures according to the results acquired from experiments with the Co/SiO2 catalyst.The predicted results of the model were validated successfully against 16 experimental conditions with respect to conversion of CO and selectivity of products species such as CO2, CH4, C-2, C-3, C-4, and C5+. The error between the predicted and experimental results was negligible. Finally, the influence of the GHSV, temperature and inlet pressure of fluid mixture on components' selectivity and conversion, were also investigated and the conclusions were in agreement with the literature. (C) 2015 The Authors. Published by Elsevier Ltd.

In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered for a wide range of cycle operating conditions and for various working fluids. This study presents an optimized modelling approach for the ORC based on radial inflow turbine, where the constant expander efficiency is replaced by dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. Considering the size and performance of the ORC, the model was used to identify the key input variables that have significant effects on the turbine overall size and the cycle net electric power output. These parameters were then included in the optimization process using the DIRECT algorithm to maximize the ratio of cycle net electric power output to the turbine overall size (objective function) for six organic fluids. Results showed that, dynamic efficiency approach predicted considerable differences in the turbine efficiencies of various working fluids. The maximum difference of 6.13% between the turbine efficiencies of R245fa and isobutane was predicted. Also the optimization results showed that, the maximum objective function of 0.5748 kW/mm was achieved by isobutane with the cycle net electric power output and the turbine overall size of 90.3 kW and 157.2 mm respectively. Such results are better than the other studies and highlight the potential of the optimization technique to further improve the performance and reduce the size of the ORC based on small-scale radial turbines. (C) 2014 Elsevier Ltd. All rights reserved.