Jalal Abedi

Comparison of finite element and pendulum models for simulation of sloshing

Abstract The pendulum model is a cost effective tool for the simulation of sloshing. However, the accuracy and applicability of the model has not been well established. In this article, we compare the simulation results obtained from the pendulum model and a more complicated finite element model for sloshing of liquids in tanker trucks. In the pendulum model, we assume that the liquid in the tanker is a point mass oscillating like a frictionless pendulum subjected to an external acceleration. In the finite element model, we solve the full Navier–Stokes equations written for two fluids to obtain the location and motion of the free surface. Stabilized finite element formulations are used in these complex 3D simulations. These finite element formulations are implemented in parallel using the message-passing interface libraries. The numerical example includes the simulation of sloshing in tanker trucks during turning.

Advective–diffusive mass transfer in fractured porous media with variable rock matrix block size

Traditional dual porosity models do not take into account the effect of matrix block size distribution on the mass transfer between matrix and fracture. In this study, we introduce the matrix block size distributions into an advective-diffusive solute transport model of a divergent radial system to evaluate the mass transfer shape factor, which is considered as a first-order exchange coefficient between the fracture and matrix. The results obtained lead to a better understanding of the advective-diffusive mass transport in fractured porous media by identifying two early and late time periods of mass transfer. Results show that fractured rock matrix block size distribution has a great impact on mass transfer during early time period. In addition, two dimensionless shape factors are obtained for the late time, which depend on the injection flow rate and the distance of the rock matrix from the injection point.

Adsorption of naphthenic acids on high surface area activated carbons

In oil sands mining extraction, water is an essential component; however, the processed water becomes contaminated through contact with the bitumen at high temperature, and a portion of it cannot be recycled and ends up in tailing ponds. The removal of naphthenic acids (NAs) from tailing pond water is crucial, as they are corrosive and toxic and provide a substrate for microbial activity that can give rise to methane, which is a potent greenhouse gas. In this study, the conversion of sawdust into an activated carbon (AC) that could be used to remove NAs from tailings water was studied. After producing biochar from sawdust by a slow‐pyrolysis process, the biochar was physically activated using carbon dioxide (CO2) over a range of temperatures or prior to producing biochar, and the sawdust was chemically activated using phosphoric acid (H3PO4). The physically activated carbon had a lower surface area per gram than the chemically activated carbon. The physically produced ACs had a lower surface area per gram than chemically produced AC. In the adsorption tests with NAs, up to 35 mg of NAs was removed from the water per gram of AC. The chemically treated ACs showed better uptake, which can be attributed to its higher surface area and increased mesopore size when compared with the physically treated AC. Both the chemically produced and physically produced AC provided better uptake than the commercially AC.

Onset of Convection in CO Sequestration in Deep Inclined Saline Aquifers

CO2-sequestration in deep geological formations has been suggested as an option to reduce greenhouse gas emissions. Saline aquifers are one of the most promising options for carbon dioxide storage. It has been investigated that if the layer of aquifer is deep enough, at depths more than 800 meters, dissolution of CO2 into brine causes density of the mixture to increase. If the corresponding Rayleigh number of the porous medium is enough to initiate convection currents, the rate of dissolution will increase. Early time dissolution of CO2 in brine is mainly dominated by molecular diffusion while the late time dissolution is predominantly governed by convective mixing mechanism. In this paper, linear stability analysis of densitydriven miscible flow for carbon dioxide sequestration in deep inclined saline aquifers is presented. The effect of inclination and its influence on the pattern of convection cells has been investigated and the results are compared with the horizontal layer. The current analysis provides approximations for initial wavelength of the convective instabilities and onset of convection that help in selecting suitable candidates for geological CO2 sequestration sites.

Removal of naphthenic acids using adsorption process and the effect of the addition of salt

In this study, various types of adsorbents were examined for the removal of Naphthenic acids (NAs) in the preliminary stage of this study. Among them, activated carbon and nickel (Ni) based alumina (Ni-Al2O3) possess relatively high adsorption capacity of NAs. The removal of NAs was evaluated comparing the total organic carbon (TOC) of the solution before and after the adsorption process. The effect of Ni loading was investigated using Ni-Al2O4 with various nickel loadings. The highest adsorption capacity (20 mg of TOC/1 mg of adsorbent) was belong to Ni-Al2O4 with 10.7% Ni loading. By the addition of salt (1500 ppm NaCl) to NAs solutions having concentrations from of 15 to 38 ppm, it was observed that the adsorption decreased dramatically (up to 80%) depending on the concentration of TOC. The kinetics of the adsorption of TOC on Ni-based alumina was also investigated. The decrease of TOC was more that 40% in the first half hour, indicating that adsorption was very rapid in the beginning. The adsorption increased slightly for up to 5 h and then leveled off when the TOC reached to 50% of initial TOC concentration. However, when sodium chloride (NaCl) was added to the solution, the adsorption decreased to almost 9% within the first half hour, reaching to almost 5% after 3 h. These phenomena suggest that the effectiveness of adsorbents may be improved by decreasing the total dissolved salts in tailings pond wastewater.

A comparative study of flux-limiting methods for numerical simulation of gas–solid reactions with Arrhenius type reaction kinetics

Abstract Heterogeneous gas–solid reactions play an important role in a wide variety of engineering problems. Accurate numerical modeling is essential in order to correctly interpret experimental measurements, leading to developing a better understanding and design of industrial scale processes. The exothermic nature of gas–solid reactions results in large concentration and temperature gradients, leading to steep reaction fronts. Such sharp reaction fronts are difficult to capture using traditional numerical schemes unless by means of very fine grid numerical simulations. However, fine grid simulations of gas–solid reactions at large scale are computationally expensive. On the other hand, using coarse grid block simulations leads to excessive front dissipation/smearing and inaccurate results. In this study, we investigate the application of higher-order and flux-limiting methods for numerically modeling one-dimensional coupled heat and mass transfer accompanied with a gas–solid reaction. A comparative study of different numerical schemes is presented. Numerical simulations of gas–solid reactions show that at low grid resolution which is of practical importance Superbee, MC, and van Albada-2 flux limiters are superior as compared to other schemes. Results of this study will find application in numerical modeling of gas–solid reactions with Arrhenius type reaction kinetics involved in various industrial operations.

Stability Analysis of Coupled Heat and Mass Transfer Boundary Layers During Steam–Solvent Oil Recovery Process

Convective mixing at the edge of the steam chamber enhances heat and mass transfer rates, which increases oil mobility and production rate. A linear stability analysis is performed under transient concentration and steady-state temperature boundary layers with temperature and concentration dependent fluid density and viscosity. It is found that the critical Rayleigh number depends on coefficients of the mixture viscosity and density function. Results show that the onset of instability is delayed as the concentration and temperature dependency of the solvent–oil mixture viscosity increases. Different potential solvents for heavy oil recovery are compared based on the critical time of instability. It is shown that intermediate molecular weight solvents lead to stronger convection, which is in agreement with experimental observations reported in the literature. These results are applicable for optimum design of laboratory experiments and selection of appropriate additives to steam for design of field- scale heavy oil recovery process.

Experimental and modeling study of residual liquid recovery from spent sand in bitumen extraction processes from oil sands.

Disposing solid residue with high liquid content into the environment may impact the immediate ecosystem and its surroundings. In bitumen recovery process from oil sands, it is environmentally and economically desirable to effectively recover as much of the liquid trapped in the spent solids as possible, prior to releasing it into the environment. An experiment was designed to investigate the effect of capillary force to enhance liquid recovery by using a thin, semipermeable layer as the membrane. The results indicate that by employing a membrane at the outlet, and pressurizing the air above the sand bed, the average liquid saturation can be decreased by 50%; however, the maximum pressure applied is restricted by the physical characteristics of the membrane. A mathematical model is developed to predict the liquid saturation profile along the sand pack during transient and steady-state conditions, and results are validated against measured average saturation using two different sand types. Results suggest that more liquid can be recovered from the spent sand bed by increasing the height of the bed; however, the required time to achieve the maximum recovery is increased as well. This method can be applied to reduce the liquid content of spent sand from any process before it is disposed of, thereby reducing possible hazards which may affect the environment.

Modelling Mass Transfer Boundary Layer Instability in the CO-Based VAPEX Process

Vapex (vapor extraction) is a promising technique for the recovery of heavy oil and bitumen reservoirs, especially for cases where steam-assisted gravity drainage and other thermal recovery methods are not economical. In the Vapex process, a solvent is injected into the reservoir to reduce the oil viscosity and mobilize it towards the production well. CO2-based Vapex is an attractive option from both economical and environmental perspectives. In CO2-based Vapex, unlike other hydrocarbon solvents, the dissolution of CO2 in oil can result in a density increase of the diluted oil. As a consequence, the diluted oil has a higher density than the immobile oil beneath and a gravitationally unstable diffusive boundary layer is induced, which may lead to natural convection. In this paper, a mathematical model for the diffusive boundary layer in the CO2-oil contact region is developed; and, the possibility of convective mixing is examined using linear stability analysis, based on the amplification of the initial perturbations. It is found that in most experimental cases, depending on the Rayleigh number of the porous medium, convective mixing occurs, which results in higher dissolution of CO2 in oil and thus a higher oil production rate than what is expected from theoretical analysis. This would explain the unexpected higher oil production rate of some experiments in Vapex when CO2 was used as a solvent. In field-scale operations, the results are different. In field cases, since it is almost impossible for the Rayleigh number to exceed the critical Rayleigh number (Rac), convection does not happen.

A Review of Single-Phase Liquid Flow and Heat Transfer in Microchannels

Fluid flow and heat transfer in microchannels have been important research area during the past decade. The understanding and explanation of the fundamental mechanisms of flow and heat transfer are critical to the application of microchannel systems to many important industrial and research projects. We present a review of the literatures on fluid flow and heat transfer of single-phase liquid in microchannels. Recent experimental and theoretical studies are both covered. The emphasis has been on studies on single-phase liquid flows. As a conclusion, although further work needs to be done, carefully designed experiments have obtained data that agree well with the conventional theory developed for larger channels. The theoretical explanation of some experimental results, which deviate the conventional theory for larger channels, is still under development.Copyright