A Surrogate Integrated Production Modeling Approach to Long-Term Gas-Lift Allocation Optimization

The conventional static gas-lift allocation optimization approaches are not appropriate for long-term gas-lift projects. A good choice for long-term optimization should predict gas-lift performance dynamically as a function of production time and other variables. A good solution approach for problem is a hybrid of surrogate integrated production modeling and genetic algorithm (GA). Hybrid GAs have received significant interest in recent years and are being increasingly used to solve real-world problems. GA incorporates other techniques within its framework to produce a hybrid that reaps the best from the combination. This study discusses a new method known as surrogate integrated production modeling that uses an artificial neural network to predict gas-lift performance based on a database of oil production. Then, a hybrid of the neural network and GA is used for long-term gas-lift allocation optimization in a group of wells under real constraints.     

Modified equilibrium modelling of coal gasification with in situ CO2 capture using sorbent CaO: Assessment of approach temperature

Gasification process has become more attractive around the globe due to the energy crisis and environmental issues. An equilibrium model based on minimization of Gibbs energy is developed to predict the product gas composition of an air-blown coal gasifier. This paper further proposes a method for modifying the thermodynamic equilibrium model. The presented method includes the introduction of an approach temperature which corresponds to the deviation from equilibrium condition. The major components in produced gas, H₂, H₂O, CH₄, CO, CO₂, and N₂ have been determined and compared with the pure equilibrium modelling as well as the experimental data. Comparison with experimental measurements revealed that the modification of the equilibrium model has significantly reduced the error in predicting the product gas composition. In situ CO₂ capture using sorbent (CaO) is also investigated in order to enhance the hydrogen production and also to address the environmental regulations on Green House Gas (GHG) emissions. The effect of important process parameters on the product gas composition is studied and the temperature of 1200 K, pressure of 1 bar, air ratio of 0.4, and sorbent to feed ratio of 2.2 have been predicted as the optimum operating conditions for the purpose of maximum hydrogen production.     

Toughening mechanisms of rubber modified thin film epoxy resins

An epoxy terminated polybutadiene (ETPB) was synthesized and utilized to enhance the toughening of an epoxy system, in both bulk and coating states. In the first step, the fracture energy of the modified samples was determined using a single edge notched type specimen in a three point bending (SEN3PB) geometry. The effective toughening mechanisms of bulk epoxy specimens were examined using scanning electron microscopy (SEM). The results showed that plastic void growth, cavitation and shear yielding mechanisms were the main toughening mechanisms of the bulk epoxy systems. In the next step, mechanical properties (i.e. impact resistance, flexibility, cupping resistance and hardness) and adhesion of the thin film specimens were evaluated in accordance to the amount of synthesized ETPB. The results showed that the mechanical properties of the ETPB modified epoxy resins considerably improved. In all cases, it was found that the improvement of the mechanical properties reached a maximum at 7.5 wt.% and then began to decrease with further increase in ETPB content. The effective toughening mechanisms in the modified thin films were also examined using SEM and compared to the bulk types. In contrast to the bulk types, the results showed that crack arresting and shear yielding were active mechanisms in thin films. The contribution of these mechanisms led to the improvement of adhesion and mechanical properties by energy dissipation.     

Sensitivity analysis pertaining to effective parameters on electrohydrodynamic drying of porous shrinkable materials

Abstract

A phenomenological computational fluid dynamics model was developed to simulate drying process of a porous body using electric field corona discharge. The set of coupled nonlinear partial differential equations were solved simultaneously and compared with the experimental findings in the literature. The relative error of the corona wind velocity compared to the experiments was less than 1%. The main gradients of the EHD volume force and corona wind were close to the discharge electrode. Moreover, for no inlet air, the corona wind velocity and field distribution indicated the existence of vortices as the main factor for enhancing mass transfer during the drying process. At a constant air velocity, increase in the voltage caused increasing the corona velocity. In addition, by increasing the air velocity to some extent, the corona velocity first increased and then started to drop. As a result, for any voltage and electrode distance from the surface, an optimum air velocity could be determined. Due to the sweep impact of the primary air flow and moving the ionized molecules to the outside, the drying rates at air velocity of 1?m s^?1 were higher than those for air velocity of 1.5?m s^?1. Applying an intake air flow also altered the optimal electrode velocity from the surface due to the occurred change in the corona discharge. Therefore, is concluded that the severity of mass humidity changes is affected by the applied voltage, electrode distances from the surface, temperature, and the intake air velocity.     

Effect of down-stream processing parameters on the mechanical properties of bacterial cellulose

Bacterial cellulose (BC), a biodegradable polymer with high degree of crystallinity, produced by Gluconacetobacter xylinus, was used as reinforcement in biocomposites. The downstream process parameters involved in the preparation process of BC have important influence on its mechanical properties. The effect of some key processing parameters such as treatment temperature, drying stages, type of treatment solvent and pressure on biocellulose sheets was investigated during drying in order to modify the parameters responsible in mechanical properties. The rise in treatment temperature and drying processes of BC sheets showed about 8 and 11 % reduction in tensile strength, respectively. The addition of NaOH solutions during the treatment reduced the tensile strength of BC sheets sharply, though an increase in NaOH concentration produced treated samples with higher tensile modulus. The use of optimum NaClO solution as a cheap treatment solvent led to an increase of about 10–11 % in the mechanical properties of BC. A pressure increase during drying stage improved the tensile strength of biocellulose sheets by 7 % and resulted in highly enhanced tensile modulus of BC samples. The production process (microbial fermentation) and structural features (porous web-shaped structure) provide an ideal scenario for synthesis of BC composites. A number of schemes have been introduced to synthesize BC composites with different materials. Among these schemes, the initial addition of materials to BC culture media, the treatment of BC with solutions and suspensions, and the dissolution of BC in solvents are the most commonly used techniques.     

Role of core‐shell rubber particle cavitation resistance on toughenability of epoxy resins

The role of rubber particle cavitation resistance on toughening of epoxy resins is still unresolved. In this research, the role of rubber particle cavitation resistance was exclusively studied. Two types of core‐shell rubber (CSR) particles with different cavitation resistances were utilized for modifying epoxy resin. Matrix crosslink density (XLD) was varied by using nonstoichiometric amounts of hardener. Fracture toughness values of neat and CSR‐modified epoxy samples decreased with lowering of XLD via deviation from stoichiometric point. It was resulted by higher modulus and lower elongation at break of the nonstoichiometric samples, and also antiplasticization of epoxy networks resulted from suppression of β‐transition relaxation motions. In all XLDs, the CSR particles with higher core T_g and modulus yielded higher fracture energy. Results showed that core properties such as T_g and modulus of CSR particles had a significant effect on toughening of the epoxy networks. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of Al addition on pressureless sintering of B4C

The effect of Al addition on pressureless sintering of B₄C ceramic was analyzed in the present work. Different amounts of Al, from 0 to 5 wt.% were added to the base material and pressureless sintering was conducted at 2050 and 2150 °C under argon atmosphere. Microstructure, crystal phases and density evolution were studied and correlated to Al additions and firing temperature. Density and grain size of sintered samples, increased significantly with Al load while less evidence is the effect of sintering temperature; 94% dense material was obtained by adding 4 wt.% Al regardless of the maximum firing temperature.     

Effect of poly(vinyl pyrrolidone) concentration and coagulation bath temperature on the morphology,permeability, and thermal stability of asymmetric cellulose acetate membranes

Cellulose acetate (CA) is widely used in membrane processes. In this study, CA (weight‐average molecular weight = 52,000) was mixed with poly(vinyl pyrrolidone) (PVP; weight‐average molecular weight = 15,000) as an additive in 1‐methyl‐2‐pyrrolidone as a solvent. The phase‐inversion method was used for the preparation of flat‐sheet membranes. The effects of PVP concentration and coagulation bath temperature (CBT) on the morphology, pure water permeation flux, and thermal stability of the prepared membranes were studied and are discussed in this article. The solute rejection of the developed CA membranes was quantified with an insulin protein solution. The results showed that an increase in the CBT levels from 0 to 23°C along with an increase in the PVP concentration in the cast film from 0 to 1.5 wt % resulted in an increase in the macrovoid formation in the membrane sublayer, an increase in the pure water flux (PWF), and a decrease in insulin rejection. Further increases in the PVP concentration from 1.5 to 3, 6, and 9 wt % resulted in gradual suppression of the macrovoid formation, a decrease in PWF, and an increase in insulin rejection. Higher PVP concentrations and lower CBT levels also appeared to result in higher glass‐transition temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009