Multi-component Numerical Model Research Articles

Effects of size and composition of bitumen drops on intra-oil diffusion and dissolution of hydrocarbon solvents in froth treatment tailings ponds

The rate of mass transfer of lower molecular weight hydrocarbons (naphtha) from bitumen drops in mature fine tailings of oil sand tailings ponds (OSTPs) may control their bioavailability and the associated rate of GHG production. Experiments were conducted using bitumen drops spiked with o-xylene and 1-methylnaphthalene to determine the mass transfer rate of these naphtha components from bitumen drops. The results were compared to simulations using a multi-component numerical model that accounted for transport in the drop and across the oil-water interface. The results demonstrate rate-limited mass transfer, with aqueous concentrations after 60 days of dissolution that were different than those in equilibrium with the initial drop composition (less for o-xylene and greater for 1-methylnaphthalene). The simulations suggest that mole fractions were unchanged at the center of the drop, resulting in concentration gradients out to the oil-water interface. Numerical simulations conducted using different drop sizes and bitumen viscosities also suggest the potential for persistent naphtha dissolution, where the time required to deplete 80% of the o-xylene and 1-methylnaphthalene mass from an oil drop was estimated to be on the order of months to years for mm-sized drops, and years to decades for cm-sized drops assuming instantaneous biodegradation in the aqueous phase surrounding the bitumen.

Multiphase Multicomponent Transport Modeling of Cyclic Solvent Injection in Shale Reservoirs

Summary A thorough understanding of fluid transport in ultratight shale reservoirs is crucial for designing and optimizing cyclic solvent injection processes, known as huff ’n’ puff (HnP). We develop a two-phase multicomponent numerical model to investigate hydrocarbon and solvent transport and species mixing during HnP. Unlike the conventional modeling approaches that rely on bulk fluid (advective) transport frameworks, the proposed model considers species transport within nanopores. The chemical potential gradient is considered the driving force for the movement of nonideal fluid mixtures. A binary friction concept is adopted that considers friction between different fluid molecules and between fluid molecules and pore walls. After validating the developed model against analytical solutions and experimental data, the model examines solvent HnP enhanced oil recovery (EOR) mechanisms by considering four-component oil and Eagle Ford crude oil systems. The impacts of injection pressure, primary production duration, soaking time, and solvent type on the oil recovery are examined. The results reveal that the formation of a solvent-oil mixing zone during the huff period and oil swelling and vaporization of oil components during the puff period are key mechanisms for enhancing oil recovery. Furthermore, the incremental recovery factor (RF) increases with injection pressure, even when the injection pressure exceeds the minimum miscibility pressure (MMP), implying that MMP may not play a critical role in the design of HnP in ultratight reservoirs. The results suggest that injecting solvents after a sufficient primary production period is more effective, allowing reservoir pressure depletion. Injecting the solvent without enough primary production may result in significant production of the injected solvent. The results show that the solvent-oil mixing zone expands, and the solvent recycling ratio decreases as soaking time increases. However, short soaking periods with higher HnP cycles are recommended for improving oil recovery at a given time frame. Finally, CO2 HnP outperforms CH4 or N2 HnP due to the higher ability of CO2 to extract a larger amount of intermediate and heavy components into the vapor phase, which has higher transmissibilities as compared with the liquid phase.

Multicomponent numerical model for heat pump control with low-temperature heat storage: A benchmark in the conditions of Central Europe

This paper presents a computational parametric study on increasing the Seasonal Coefficient of Performance for residential heat pumps, utilizing an enhanced computational model and comparing it to previous research. The model computes a system that consists of a heat pump, low-temperature heat storage, heat exchanger and circulation pump, and a control unit which allows the heat pump to choose either low-temperature heat storage or ambient air as the favorable heat source. A parametric study is conducted to obtain results from a numerical model describing in detail the heat storage, surrounding soil, and the behavior of a water tank with and without temperature stratification and with two different geometries. These are combined into three different systems. Each system uses an algorithm for heat pump control that combines equithermal regulation and deferred heat storage discharging based on long-term temperature trends. Python is used to transform the numerical model into a computational model, and the assessment of heat pump operation is made based on meteorological data from the years 2012–2021 recorded in the city of Brno, Czech Republic, Central Europe. Previous studies have suggested that this combination for heat pump control and a more detailed numerical model of the system should result in a SCOP increase. In this study, heat losses of an actual occupied building with floor area of 140 m2 without considering heat radiation are used. The results show that stratification cannot be omitted for numerical modelling, and that the geometry of the storage influences how the storage should be designed. For a wide and shallow storage, it is better to insulate the system and increase the SCOP from 3.8 to 4.65, but non-insulated deep and narrow storage can increase the from 3.8 to 4.95. Flow rate is also an important parameter with a local maximum between 0.01 and 0.02 kg/s for every cubic meter of the storage. When a system consisting of parts readily available on the market is used at optimal conditions, the resulting increase can be from 11.8% up to as high as 25.7% with low-temperature heat storage ranging from 9 to 25 cubic meters.

Coupled bio-hydro-thermo-mechanical interactions of landfilled MSW based on a multi-phase, multi-component numerical model

A clear understanding of long-term bio-hydro-thermo-mechanical (BHTM) behaviors of landfilled Municipal Solid Waste (MSW) is essential to better design and manage landfills, which requires the development of both analytical and numerical models that can represent typical behaviors of MSW. In this study, a novel multi-phase, multi-component numerical model, which incorporated the diffusion of landfill gas components, changes in the pH of leachate, and its solute migration as well as phase changes, was presented and adopted to investigate long-term coupled behaviors of MSW and the spatial and temporal variations of MSW properties. The numerical simulations were conducted on a typical landfill column and a landfill slope with relatively clear initial and boundary conditions to explore the coupled BHTM interactions of landfilled MSW. Based on the simulation results, the coupled mechanisms of MSW biodegradation, leachate and gas flows, MSW deformation, and heat transfer were revealed, and some significant insights on qualities of both leachate and landfill gas were also given. It has been found that the coupled model associated with its numerical code successfully predicted the long-term behaviors of landfilled MSW and qualities of leachate and landfill gas.

Three-Dimensional Numerical Modeling of Internal Ballistics for Solid Propellant Combinations

The processes that take place within the Internal Ballistics cycle of an artillery round are highly influenced by geometric effects. They are also highly affected by the presence of a combination of energetic materials, such as the propellant, igniter, primer, and the combustible cartridge cases. For a more realistic simulation of these phenomena, a multidimensional and multicomponent numerical model is presented, based on adaptations and improvements of previous models of conservation equations, maintaining a two-phase, Eulerian–Eulerian approximation. A numerical method based on Finite Volumes and conservative flux schemes (Rusanov and AUSM+), with the ability to predict detonation effects, is proposed. As a result, a versatile 3D numerical code was obtained that was tested in the simulation of artillery firing with conventional and modular charges (MACS). Results show the code is able to characterize the heat and mass transfer of the different energetic materials during the combustion of the propellant and the cartridge cases, the gas expansion, and the projectile acceleration.

Vacuum membrane distillation multi-component numerical model for ammonia recovery from liquid streams

In this work, a modelling research on the separation of ammonia gas from liquid streams via vacuum membrane distillation (VMD) is conducted. An experimentally validated multi-component simulation model of a flat sheet VMD module is developed by implementing heat and mass balances through the feed, membrane and permeate channels. Continuous removal of the gases transferred through the membrane at a constant pressure in the permeate channel is assumed. The transport mechanisms through the pores under VMD conditions for both volatiles are discussed. Under studied VMD conditions and the typical concentration range in waste waters (i.e. 1-10 g TAN l-1), it is observed that none of the two volatile components (ammonia and water) is preferentially transported. The resulting VMD performance is simulated and evaluated in terms of total transmembrane flux, ammonia flux, ammonia selectivity and thermal energy consumption. The model was validated experimentally and showed good agreement, with an average relative error <10%. The experiments were performed with a solution of (NH4)2SO4 in a laboratory set up under controlled conditions. The simulation, as well as the experimental results, emphasize the existing trade-off between the flux (JNH3) and selectivity (SNH3) of ammonia. Increasing feed temperature and decreasing vacuum pressure results in higher JNH3 but lower SNH3. Moreover, those parameters that enhance the heat transfer through the membrane (i.e. feed temperature, pore size, porosity, vacuum pressure, etc.) promote the water flux over ammonia. While those parameters that enhance mixing and the ammonia mass transfer in the feed (i.e. feed velocity, spacer geometry, pH, ammonia feed concentration, etc.) promote the ammonia flux over water. The only operating parameter which enhances simultaneously the JNH3 and SNH3 is the feed velocity, indicating that the spacer geometry can play an important role in designing VMD modules for ammonia separation. VMD can extract and concentrate ammonia on the permeate side at a low specific thermal energy consumption. However, the JNH3 is greatly limited by the feed ammonia concentration which will ultimately determine the cost-effectiveness of the recovery. The trends described by the model are in agreement with other authors’ observations and give insight into the mechanisms dominating ammonia separation via VMD and its performance limits.

Experimental and numerical study on thermal performance of Li(NixCoyMnz)O2 spiral-wound lithium-ion batteries

A clear understanding of thermal properties of lithium-ion batteries and their effects on battery performance is vital to design thermal management systems. The thermal characteristics of a commercial 18,650 Li(NixCoyMnz)O2 Lithium-ion battery is studied under constant current discharge rates of 1 C, 2 C, 3 C, 4 C, and 5 C. Infra-red (IR) images are captured during experiments with a Tix520 Thermal imager at various discharge rates. And temperature variations at different position of the battery surface at different discharge C-rates are investigated. In addition, the internal resistances of the battery cap, jelly roll and their influence on the heat generation are also discussed. The results show that the variation of the surface temperature of the battery at high rates (3 C, 4 C, 5 C) is different from low rates (1 C, 2 C) during discharging. The temperature difference at high rates is up to 6 °C. The volumetric heat generation rate of the cap is much higher than the jelly-roll’s, which is up to 2.2 × 105 W/m3 at 1 C. At last, a 3D multi-component thermal model is present to simulate the thermal behaviors of the battery. The multi-component numerical model can present the thermal characteristics of different battery parts at different discharge rates and thus good consistence with experiment data.

Numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well

AbstractMethane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with a multiphase flow and multicomponent numerical model. The conceptual model used for the simulations assumes that the target shale formation is 200 m thick, overlain by a 750 m thick caprock, which is in turn overlain by a 50 m thick surficial sand aquifer, the 1000 m geological sequence being intersected by a fully penetrating borehole. This succession of geological units is representative of the region targeted for shale gas exploration in the St. Lawrence Lowlands (Québec, Canada). The simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer. The leakage of fluids can subsequently lead to the contamination of groundwater resources and/or, in the case of methane migration to ground surface, to an increase in greenhouse gas emissions. The minimum reported surface casing vent flow (measured at ground level) for shale gas wells in Quebec (0.01 m3/d) is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration. The simulations suggest that an adequately cemented borehole (with a casing annulus permeability kc 1 mD) can prevent methane and brine leakage over a time scale of up to 100 years. However, a poorly cemented borehole (kc 10 mD) could yield methane leakage rates at the base of an aquifer ranging from 0.04 m3/d to more than 100 m3/d, depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation. These values are compatible with surface casing vent flows reported for shale gas wells in the St. Lawrence Lowlands (Quebec, Canada). The simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years, depending on cementation quality and hydrodynamic properties of the casing annulus. Simulated long‐term brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10−5 m3/d (10 mL/d) to 10−3 m3/d (1 L/d). Based on scoping calculations with a well‐mixed aquifer model, these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration in a pristine aquifer to 1 mg/L, which is significantly below the commonly recommended aesthetic objective of 250 mg/L for chloride.

Numerical modeling of cemented wellbore leakage from storage reservoirs with secondary capture due to thief zones

Abstract A 3D, multi-phase, multi-component numerical model of injection into a storage reservoir with an abandoned wellbore is developed. A shallow aquifer is modeled above the storage reservoir separated by a caprock layer. An intermediate permeable layer assumed to be a thief zone is modeled. The abandoned wellbore penetrates the entire model from the surface, through shallow aquifer and thief zone to the bottom of the primary storage reservoir. The amount of CO 2 captured within the thief zone and released to the shallow aquifer and atmosphere is assessed. A Latin Hypercube sample evaluates the effects of variations in CO 2 injection rate, depth of the reservoir, relative depth of the thief zone, and permeability of the wellbore, thief zone, and shallow aquifer. In addition, full factorial design parameter studies evaluate the effect of differing wellbore permeabilities above and below the thief zone. Analyses of the Latin Hypercube sample and parameter studies provide indications of the necessary conditions for secondary capture in thief zones and potential for leakage to the shallow aquifer and atmosphere.

Simulation of an innovative flow-field design based on a bio inspired pattern for PEM fuel cells

Proton exchange membrane (PEM) fuel cell performance is directly related to the bipolar plate design and their channels pattern. Power enhancements can be achieved by optimal design of the type, size, or patterns of the channels. It has been realized that the bipolar plate design has significant role on reactant transport as well as water management in a PEM Fuel cell. Present work concentrates on improvements in the fuel cell performance by optimization of flow-field design and channels configurations. A three-dimensional, multi-component numerical model of flow distribution based on Navier–Stokes equations using individual computer code is presented. The simulation results showed excellent agreement with the experimental data in the previous publications. In this paper, a new bipolar plate design inspired from the existed biological fluid flow patterns in the leaf is presented and analyzed. The main design criteria in this research are based on more uniform velocity distribution and more homogeneous molar spreading of species along the flow channels and also higher voltage and power density output in different current densities. By developing a numerical code it was found that the velocity and pressure profiles on catalyst surface are much more uniform, reactant concentration on catalyst surface is very more homogeneous and the power density is higher than parallel and serpentine flow channels up to 56% and 26% respectively.

Integrated 3D physical-numerical modelling for simulating bioremediation of petroleum contamination in heterogeneous subsurface environment

This study presents physical-numerical modelling of petroleum contaminant transport and enhanced in situ bioremediation in heterogeneous subsurface environment. The approach is based on development of a three-dimensional multi-layered physical model coupled with a three-dimensional multiphase multi-component numerical model. An experimental scheme was designed to conduct 40-day benzene transport, followed by 17-day enhanced bioremediation. The results show a significant reduction in benzene levels in the enhanced process, demonstrating that the physical model was effective in facilitating the realisation of the remediation technology. Moreover, the results indicate that numerical model was capable of predicting the bioremediation process and supporting decisions of groundwater remediation.

Numerical studies on an air-breathing proton exchange membrane (PEM) fuel cell

The objective of this article is to investigate the performance of an air-breathing proton exchange membrane (PEM) fuel cell operating with hydrogen fed at the anode and air supplied by natural convection at the cathode. Considering a dual-cell cartridge configuration with a common anode flow chamber, a comprehensive two-dimensional, non-isothermal, multi-component numerical model is developed to simulate the mass transport and electrochemical phenomena governing the cell operation. Systematic parametric studies are presented to investigate the effects of operating conditions, cell orientation and cell geometry on the performance. Temperature and species distributions are also studied to assist the understanding of the single cell performance for different conditions. It is shown that the cell orientation affects the local current density distribution along the cell and the average current density, particularly at lower cell voltages. The cell performance is shown to improve with increase of temperature, anode flow rate, anode pressure and anode relative humidity.

Numerical studies on an air-breathing proton exchange membrane (PEM) fuel cell stack

Air-breathing proton exchange membrane (PEM) fuel cells provide for fully or partially passive operation and have gained much interest in the past decade, as part of the efforts to reduce the system complexity. This paper presents a detailed physics-based numerical analysis of the transport and electrochemical phenomena involved in the operation of a stack consisting of an array of vertically oriented air-breathing fuel cells. A comprehensive two-dimensional, nonisothermal, multi-component numerical model with pressurized hydrogen supply at the anode and natural convection air supply at the cathode is developed and validated with experimental data. Systematic parametric studies are performed to investigate the effects of cell dimensions, inter-cell spacing and the gap between the array and the substrate on the performance of the stack. Temperature and species distributions and flow patterns are presented to elucidate the coupled multiphysics phenomena. The analysis is used to determine optimum stack designs based on constraints on desired performance and overall stack size.

Transport of a Mixture of Chlorinated Solvent Vapors in the Vadose Zone of a Sandy Aquifer: Experimental Study and Numerical Modeling

Experimental and modeling studies were performed to investigate the simultaneous transport of trichloroethylene (TCE) and perchloroethylene (PCE) in the vadose zone of a large (25 by 12 by 3 m) well‐instrumented artificial aquifer called SCERES. The experimental facility, made up of a 1‐m‐thick saturated zone and a 2‐m‐thick unsaturated zone, allowed direct measurements of the contaminants in both the liquid and gas phases. Main objectives of the study were to obtain a better understanding of the fate and transport of chlorinated solvents in the subsurface and, more specifically, to compare simultaneously measured TCE and PCE volatilization rates from the soil surface with predictions obtained with both a comprehensive multiphase multicomponent numerical model (SIMUSCOPP) and a quasianalytical approach based on Fick's first law. The numerical and quasianalytical results generally agreed very well with the observed data. Transient PCE and TCE vapor phase concentrations calculated with the numerical model were found to be close to the observations, which indicated applicability of Raoult's Law. A comparison of observed and calculated TCE and PCE concentrations in the capillary fringe showed more impact of water infiltration on the simulations as compared with the observed data, which may reflect a lack of equilibrium between the gaseous and aqueous phase during leaching for the given experimental flow conditions. A sensitivity analysis showed that the adopted source boundary condition (a fixed nonaqueous phase liquid [NAPL] saturation distribution instead of an injected DNAPL source) did not have much influence on the concentration breakthrough curves, but that temperature can be an important factor influencing the results.

Simulating the Effect of Aerobic Biodegradation on Soil Vapor Intrusion into Buildings: Influence of Degradation Rate, Source Concentration, and Depth

Steady-state vapor intrusion scenarios involving aerobically biodegradable chemicals are studied using a three-dimensional multicomponent numerical model. In these scenarios, sources of aerobically biodegradable chemical vapors are placed at depths of 1-14 m beneath a 10 m x 10 m basement or slab-on-grade construction building, and the simultaneous transport and reaction of hydrocarbon and oxygen vapors are simulated. The results are presented as Johnson and Ettinger attenuation factors alpha (predicted indoor air hydrocarbon concentration/source vapor concentration), and normalized contour plots of hydrocarbon and oxygen concentrations. In addition to varying the vapor source depth, the effects of source concentration (2-200 mg chemical/L vapor) and oxygen-limited first-order reaction rates (0.018-1.8 h(-1)) are studied. Hydrocarbon inputs were specific to benzene, although the relevant properties are similar to those for a range of hydrocarbons of interest. Overall, the results suggest that aerobic biodegradation could play a significant role in reducing vapor intrusion into buildings (decreased alpha-values) relative to the no-biodegradation case, with the significance of aerobic biodegradation increasing with increasing vapor source depth, decreasing vapor source concentration, and increasing first-order biodegradation rate. In contrast to the no-biodegradation case, differences in foundation construction can be significant in some settings. The significance of aerobic biodegradation is directly related to the extent to which oxygen is capable of migrating beneath the foundation. For example, in the case of a basement scenario with a 200 mg/L vapor source located at 3 m bgs, oxygen is consumed before it can migrate beneath the foundation, so the attenuation factors for simulations with and without aerobic biodegradation are similar for all first-order rates studied. For the case of a 2 mg/L vapor source located at 8 m bgs, the oxygen is widely distributed beneath the foundation, and the attenuation factor for the biodegradation case ranges from about 3 to 18 orders-of-magnitude less than that for the no-biodegradation case.

Controlling transport processes during NAPL removal by soil venting

Soil venting is a widely used technique to remediate unsaturated soils contaminated with organic contaminants. A fundamental concern in the remedial design is to predict the performance of the venting system in terms of the contaminant vapor removal rates and the clean-up limits that can be achieved at a site. In this paper, a mass transport model to simulate the evaporation of non-aqueous phase contaminants from the unsaturated soil during venting is presented. In particular, the dependence of NAPL evaporation on the resistance due to diffusional transport within the liquid phase is discussed in detail. Various limiting mechanisms that control the contaminant removal from NAPL phase have been identified. Results from numerical simulations have indicated that interfacial concentration can be overpredicted by models employing complete mixing assumption when the mass transfer coefficients are high and the interface transfer rates are limited by the diffusional transport within the liquid layer. Venting scenarios were simulated using a multi-component numerical model in which diffusional resistance in the liquid layer was included. The predicted vapor concentrations in the outlet air have been found to be in good comparison with experimental data.

Hydrogeological and numerical analysis of CO 2 disposal in deep aquifers in the Alberta sedimentary basin

For landlocked large sources of CO 2, the best approaches for reducing CO 2 emissions into the atmosphere are its utilization and deep disposal into deep sedimentary aquifers or depleted oil and gas reservoirs. A number of coal-based power plants (total capacity of more than 4000 MW) are located near Lake Wabamun in central Alberta, Canada. A hydrogeological study of the sedimentary succession at the site was undertaken to identify and select aquifers which meet various requirements for CO 2 disposal, particularly with respect to depth and confinement. The multi-phase, multi-component numerical model STARS was used to study the ability of the selected aquifers to accept and retain for long periods of time large quantities of CO 2 injected in a supercritical state. The CO 2 injectivity of the selected aquifers was examined for a whole series of parameters, including aquifer depth and thickness, rock and formation water properties, and injection characteristics. The numerical simulations indicate that even generally low-permeability aquifers can accept and retain large quantities of CO 2, showing that injection of CO 2 in a supercritical state into deep aquifers in sedimentary basins is a viable option and may be the best short-to-medium term solution for reducing CO 2 emissions into the atmosphere. The CO 2 injectivity is enhanced by the existence of ‘sweet’ zones of high permeability.