Simulation Of Transport Phenomena Research Articles

Lattice Boltzmann method for simulating transport phenomena avoiding the use of lattice units

Lattice Boltzmann method for simulating transport phenomena avoiding the use of lattice units

Finite Volume Method: An Efficient Tool for Transport Equation Solutions

A strong and flexible numerical method for solving transport equations encountered in various scientific and engineering applications is the Finite volume method (FVM). The free-volume model (FVM) provides a strong basis for modeling the advection-dominated transport phenomena by partitioning the domain into control volumes and applying the conservation rules here. Focusing on its efficiency and accuracy, this paper delves into the basic concepts of the FVM and how it is applied to solve transport equations. Topics covered include numerical flux formulas, consideration of boundary conditions, spatial and temporal discretization techniques, and other important details. We prove that the technique can capture both continuous and discrete solutions to complicated transport phenomena by thoroughly analyzing its benefits. Our numerical findings show that the Finite Volume Method is useful in solving many kinds of transport equations, and they come from real-world applications. We highlight the method's flexibility to handle various problem situations and its ability to improve computational performance through parallel computing. While exploring the Finite Volume Method's potential, we take into account the factors that could affect its implementation. We go over current innovations and those on the horizon, pointing out places where things could be optimized and improved. In order to help researchers, engineers, and practitioners in their fields who are looking for efficient computational methods to simulate transport phenomena with reliable results, this study aims to give a brief but thorough overview of the FVM.

Impact of thermodynamic hypotheses on the calculation of the quantity of CO2 stored in a saline aquifer

The aim of this paper is to study the impact of thermodynamics models on the CO2 storage capacity of an aquifer, by using modelling and simulation of transport phenomena in porous media. The aquifer is represented here by a simplified three phase isothermal non-reacting medium composed by an inert solid phase and two binary (CO2 and H2O) fluid phases. The mathematical description is classically developed by the volume averaging method. For each phase, the conservation equations of mass, momentum and energy alongside thermodynamic laws and boundary conditions are first written. They are then integrated over a representative elementary volume in order to establish the description at the local scale. In a thermodynamic point of view, two kinds of models have been implemented and compared. The first one assumes that the gas and liquid phases are ideal. On the contrary, in the second approach, non-ideal thermodynamics is taken into account by calculating an activity coefficient (γ-φ approach) for the liquid phase and a fugacity coefficient (PengRobinson approach) for the gas phase. Results show, among other things, that the amount of CO2 dissolved in the liquid phase is significantly reduced with the non-ideal approach compared to the ideal case. These results highlight the interest of considering non-ideal phases in more complex models.

On the performance study of a hybrid indirect evaporative cooling and latent-heat thermal energy storage system under commercial operating conditions

In this paper, a hybrid evaporatively-enhanced cooling system is proposed under commercial operating conditions. The indirect evaporative cooler (IEC) is first employed as a pre-cooling equipment to treat ambient air by recovering energy from the indoor exhaust air. The pre-cooled air is then treated to achieve the required thermal condition by employing the latent-heat thermal energy storage (LHTES) containing spherical balls encapsulated with a synthesized phase change material (PCM). Such a novel hybrid process takes full advantage of the IEC’s high cooling efficiency and LHTES’s power peak load shifting capability. Experimental system comprising the IEC integrated with the LHTES is designed and tested under various air conditions. Additionally, mathematical models are developed to simulate transport phenomena behind the system. Employing experimentally-validated models, thermodynamic analyses are conducted to study the system's performance. Results indicate that (1) the proposed hybrid system is able to pre-cool and dehumidify the ambient air in the tropics simultaneously; (2) the ambient air temperature and humidity ratio can be respectively reduced by 6–10 °C and 2–11 g/kg dry air under specific operating ranges; (3) the evaporative cooling technology facilitates the use of a higher chilled water supply temperature which results in an improvement on the chiller efficiency; and (4) a higher water flow rate leads to faster cold energy storage and release rates during the respective charging and discharging periods.

A comprehensive model for analysis of turbulent natural convection flow in rectangular and trapezoidal enclosures at high Rayleigh numbers > 109

Turbulent natural convection is dominant mechanism of heat transfer in enclosed cavities. The simulation of transport phenomena in different enclosures is of paramount importance in industrial design and operation. The present research aimed to find the proper model for prediction of heat transfer mechanisms in rectangular and trapezoidal enclosures filled with air (Pr 0.71) in wide range of Five Reynolds averaged Navier-Stokes equations (SA, standard k-ɛ, RNG k-ɛ, standard k-ω, SST k-ω) were solved numerically with finite volume method. The simulation results were fitted to the experimental data so as to reach the proper model for analysis of turbulent natural convection. It was concluded that the kε and kω models can well describe the heat transfer at low and high Ra numbers, respectively, for both enclosures. For prediction of transport phenomena in the entire range of Ra, it is proposed to develop two-equation eddy-viscosity models.

Spectral Numerical Study of Entropy Generation in Magneto-Convective Viscoelastic Biofluid Flow Through Poro-Elastic Media With Thermal Radiation and Buoyancy Effects

Abstract Electromagnetic high-temperature therapy is popular in medical engineering treatments for various diseases including tissue damage ablation repair, hyperthermia, and oncological illness diagnosis. The simulation of transport phenomena in such applications requires multi-physical models featuring magnetohydrodynamics, biorheology, heat transfer, and deformable porous media. Motivated by investigating the fluid dynamics and thermodynamic optimization of such processes, in the present article, a mathematical model is developed to study the combined influence of thermal buoyancy, magnetic field and thermal radiation on the entropy generation, and momentum and heat transfer characteristics in electrically conducting viscoelastic biofluid flow through a vertical deformable porous medium. It is assumed that heat is generated within the fluid by both viscous and Darcy (porous matrix) dissipations. The governing equations for fluid velocity, solid displacement, and temperature are formulated. The boundary value problem is normalized with appropriate transformations. The nondimensional biofluid velocity, solid displacement, and temperature equations with appropriate boundary conditions are solved computationally using a spectral method. Verification of accuracy is conducted via monitoring residuals of the solutions. The effects of various parameters on flow velocity, solid displacement, temperature, and entropy generation are depicted graphically and discussed. Increasing magnetic field and drag parameters are found to reduce the field velocity, solid displacement, temperature, and entropy production. Entropy production is enhanced with an increase in buoyancy parameter and volume fraction of the fluid. The novelty of the work is the simultaneous inclusion of multiple thermophysical phenomena, and the consideration of thermodynamic optimization in coupled thermal/fluid/elastic media. The computations provide an insight into multiphysical transport in electromagnetic radiative tissue ablation therapy and a good benchmark for more advanced simulations.

High-performance hybrid modeling chemical reactors using differential evolution based fuzzy inference system

Bubbly flow behavior simulation in two-phase chemical reactors such bubble column type reactors is widely employed for chemical industry purposes. The computational fluid dynamics (CFD) approach has been employed by engineers and researchers for modeling these types of chemical reactors. In spite of the CFD robustness for simulating transport phenomena and chemical reactions in these reactors, this approach has been known as expensive for modeling such turbulent complex flows. Artificial intelligence (AI) algorithm of the adaptive network-based fuzzy inference system (ANFIS) are largely understood and utilized for the CFD approach optimization. In this hybrid approach, the CFD findings are learned by AI algorithms like ANFIS to save computational time and expenses. Once the pattern of the CFD results have been captured by the AI model, this hybrid model can be then used for process simulation and optimization. As such, there is no need for further simulations of new conditions. The objective of this paper is to obviate the need for expensive CFD computations for two-phase flows in chemical reactors via coupling CFD data to an AI algorithm, i.e., differential evolution based fuzzy inference system (DEFIS). To do so, air velocity as the output and the values of the x, and y coordinates, water velocity, and time step as the inputs are inputted the AI model for learning the flow pattern. The effects of cross over as the DE parameter and also the number of inputs on the best intelligence are investigated. Indeed, DEFIS correlates the air velocity to the nodes coordinates, time, and liquid velocity and then after the CFD modeling could be replaced with the simple correlation. For the first time, a comparison is made between the ANFIS and the DEFIS performances in terms of the prediction capability of the gas (air) velocity. The results released that both ANFIS and DEFIS could accurately predict the CFD pattern. The prediction times of both methods were obtained to be equal. However, the learning time of the DEFIS was fourfold of ANFIS.

Review of Microfluidic Devices and Imaging Techniques for Fluid Flow Study in Porous Geomaterials.

Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely “fluid flow in porous media”, “flow in heterogeneous rocks and fractures”, “reactive transport, solute and colloid transport”, and finally “porous media characterization”. In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media.

An investigation of nonlinear time-fractional anomalous diffusion models for simulating transport processes in heterogeneous binary media

In this work, we consider two of the most frequently used two-dimensional nonlinear time-fractional anomalous sub-diffusion models for simulating transport phenomena in heterogeneous binary media—a variable-order model and a generalised transport equation based on the Riemann-Liouville fractional operator. Our computational modelling framework uses a second order modified weighted shifted Grünwald-Letnikov scheme with correction terms to approximate the time-fractional derivative and nonlinear source term, together with an unstructured mesh control volume method for the spatial discretisation that accommodates the heterogeneous model properties. The resulting nonlinear system of algebraic equations is then stepped in time using an efficient Jacobian-free, Newton-Krylov solver to determine the set of discrete solution unknowns. We derive a semi-analytical solution and mass balance equation for a class of two-layered problems to evaluate the accuracy of the different computational models. A key contribution of our work is to identify the correct form of the interfacial boundary conditions to impose for the flux terms within the time-fractional framework and to illustrate the significant impact that the time-fractional indices have on the mass transfer. We show that the generalised transport model not only exhibits the correct physical solution behaviour, it produces a more accurate overall mass balance in comparison to the variable-order time-fractional model which is unable to resolve the abrupt changes in the solution behaviour at the interface between two different media having contrasting diffusivity, fractional index and source term. This finding indicates that this generalised model is an effective tool for characterising anomalous transport processes in heterogeneous systems. Finally, a series of numerical examples are presented to verify the theoretical analysis and to highlight the capability of the generalised transport model.

Existence of the solitary wave solutions supported by the modified FitzHugh–Nagumo system

We study a system of nonlinear differential equations simulating transport phenomena in active media. The model we are interested in is a generalization of the celebrated FitzHugh–Nagumo system describing the nerve impulse propagation in axon. The modeling system is shown to possesses soliton-like solutions under certain restrictions on the parameters. The results of theoretical studies are backed by the direct numerical simulation.

From tumour perfusion to drug delivery and clinical translation of in silico cancer models

In silico cancer models have demonstrated great potential as a tool to improve drug design, optimise the delivery of drugs to target sites in the host tissue and, hence, improve therapeutic efficacy and patient outcome. However, there are significant barriers to the successful translation of in silico technology from bench to bedside. More precisely, the specification of unknown model parameters, the necessity for models to adequately reflect in vivo conditions, and the limited amount of pertinent validation data to evaluate models' accuracy and assess their reliability, pose major obstacles in the path towards their clinical translation. This review aims to capture the state-of-the-art in in silico cancer modelling of vascularised solid tumour growth, and identify the important advances and barriers to success of these models in clinical oncology. Particular emphasis has been put on continuum-based models of cancer since they - amongst the class of mechanistic spatio-temporal modelling approaches - are well-established in simulating transport phenomena and the biomechanics of tissues, and have demonstrated potential for clinical translation. Three important avenues in in silico modelling are considered in this contribution: first, since systemic therapy is a major cancer treatment approach, we start with an overview of the tumour perfusion and angiogenesis in silico models. Next, we present the state-of-the-art in silico work encompassing the delivery of chemotherapeutic agents to cancer nanomedicines through the bloodstream, and then review continuum-based modelling approaches that demonstrate great promise for successful clinical translation. We conclude with a discussion of what we view to be the key challenges and opportunities for in silico modelling in personalised and precision medicine.

Parametric Study with Simulation of Transport Phenomenon of a Solid Oxide Fuel Cell

The Solid oxide fuel cells (SOFC) have the potential to become one of the efficient and cost-effective direct management systems for converting a wide variety of fuels into electricity. In this study, we developed a three-dimensional model with a single phase of a solid oxide fuel cell (SOFC) planar fueled with hydrogen to improve the fundamental understanding of transport phenomena and performance in the SOFC. The simulations were carried out using COMSOL Multiphysics software (version 5.4) based on the finite element method for solving the continuity equation (mass transport), the conservation equation (transport of the moment of transport). gas, ordinary diffusion transport of chemical species, heat transfer, charge transport), a parametric study was done to examine the effect of certain parameters such as the operating pressure, the temperature and porosity the porosity of the electrodes) the gas diffusion layer (GDL) on the performance of the SOFC stack for boundary conditions.

Hybridized method of pseudopotential lattice Boltzmann and cubic-plus-association equation of state assesses thermodynamic characteristics of associating fluids.

It is crucial to properly describe the associating fluids in terms of phase equilibrium behaviors, which are needed for design, operation, and optimization of various chemical and energy processes. Pseudopotential lattice Boltzmann method (LBM) appears to be a reliable and efficient approach to study thermodynamic behaviors and phase transition of complex fluid systems. However, when cubic equations of state (EOSs) are incorporated into single-component multiphase LBM, simulation results are not well matched with experimental data. This study presents the utilization of cubic-plus-association (CPA) EOS in the LBM structure to obtain more accurate modeling results for associating fluids. An approach based on the global search optimization algorithm is introduced to find the optimal association parameters of CPA EOS for water and primary alcohols in the lattice units. The thermodynamic consistency is verified by the Maxwell construction and is also improved by the forcing scheme of [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 86, 016709 (2012)10.1103/PhysRevE.86.016709]. The spurious velocity is reduced with increasing isotropy in the gradient operator. Furthermore, an extended version of CPA EOS is introduced, which increases the system stability at low reduced temperatures. There is a very good match between the LBM results and experimental data, confirming the reliability of the model developed in the present study. The introduced approach has potential to be employed for simulating transport phenomena and interfacial characteristics of associating fluids in porous systems.

New insights on modeling of evaporation phenomena in thin films

Thin film evaporation modeling is commonly used to simulate transport phenomena in two phase capillary cooling devices and microchannels. However, one of the difficulties faced in the application of such models is the absence of consensus in the implementation of boundary conditions. In the present work, different methods available in the literature are analyzed for their capability to model the physics of the problem. Both their strengths and shortcomings are highlighted. Hence, a novel method for estimation of the film thickness at the onset of evaporation is presented. It is tested for a wide range of superheats and is found to give physically realistic results. A new thin film evaporation model is also presented, consisting of the velocity slip boundary condition at the wall and a disjoining pressure consisting of both retarded and nonretarded terms. It is found that the heat flux decreases monotonically throughout the thin film region.

Modeling of mass transfer enhancement in a magnetofluidic micromixer

The use of magnetism for various microfluidic functions such as separation, mixing, and pumping has been attracting great interest from the research community as this concept is simple, effective, and of low cost. Magnetic control avoids common problems of active microfluidic manipulation such as heat, surface charge, and high ionic concentration. The majority of past works on micromagnetofluidic devices were experimental, and a comprehensive numerical model to simulate the fundamental transport phenomena in these devices is still lacking. The present study aims to develop a numerical model to simulate transport phenomena in microfluidic devices with ferrofluid and fluorescent dye induced by a nonuniform magnetic field. The numerical results were validated by experimental data from our previous work, indicating a significant increase in mass transfer. The model shows a reasonable agreement with experimental data for the concentration distribution of both magnetic and nonmagnetic species. Magnetoconvective secondary flow enhances the transport of nonmagnetic fluorescent dye. A subsequent parametric analysis investigated the effect of the magnetic field strength and nanoparticle size on the mass transfer process. Mass transport of the fluorescent dye is enhanced with increasing field strength and size of magnetic particles.

Evaluation and estimation of the inside greenhouse temperature, numerical study with thermal and optical aspect

To evaluate the microclimate inside an agricultural greenhouse, the Ansys Fluent R16.0 Computational Fluid Dynamic (CFD) code was used for a 2D simulation of transport phenomena like heat transfer and radiation for three Rayleigh number values using the finite volumes method. The daily variation of external solar radiation was introduced via User Defined Functions (UDF) to modulate solar radiation using the Discrete Ordinates (DO) model. In the current study, the flow was simulated in the steady case and the plants were not considered. During simulation, both cases were tested day and night. The obtained results corroborate with the literature and its confrontation was satisfactory. This work should make it possible to improve the thermal performances of greenhouses by a better positioning of heating and ventilation systems.

Developing micro-scale heterogeneous numerical simulation of a solid oxide fuel cell anode

In this article a fully three dimensional, multiphase, meso-scale Solid Oxide Fuel Cell (SOFC) anode transport phenomena model is described. The Butler-Volmer model is combined with empirical relations for conductivity and diffusivity - notably the Fuller-Shetler-Giddings equation - for transport of gas reagents. Numerical simulation is used to obtain partial pressure and electric potential fields for each phase, accounting for activation and concentration overpotential as well as ohmic losses. Mesh generator and a solver have been developed to provide an in-house code for the computations. The findings are presented alongside a parametric study of a specific YSZ electrolyte-based SOFC anode microstructure. Despite high dependence of SOFC anode performance on the geometry of its anisotropic, three-phase microstructure, meso-scale numerical models simulating transport phenomena within these electrodes are not very common.

Modeling of Epitaxial Silicon Growth From the DCS-H2-HCl System in a Large Scale CVD Reactor

Multi-wafer planetary type chemical vapor deposition (CVD) reactors are widely used in thin film growth and suitable for large scale production. In this paper, numerical modeling has been carried out to simulate transport phenomena and epitaxial silicon growth in a planetary CVD reactor for the SiH2Cl2–H2–HCl system. A chemical reaction model using temperature dependent reaction rate is proposed and validated using experimental data. Based on the model, the effect of various operation conditions such as satellite rotational speed, species concentration, operating temperature and pressure is considered to determine the key factor influencing the growth rate and uniformity. The results reveal that the growth rate and uniformity are strongly related to total flow rate, species concentration and operating pressure, but are not affected by rotational speed of the satellite in case of high flow rates. Growth rates are found to be increased from 0.02 $\mu \text{m}$ /min at operating pressure of 10 torr to approximately 0.16 $\mu \text{m}$ /min at 150 torr. Growth deposition non-uniformity decreases from 80% for total flow rate of 460 slm to 13% for total flow rate of 46 slm.

A three-dimensional heterogeneity analysis of electrochemical energy conversion in SOFC anodes using electron nanotomography and mathematical modeling

In this paper a fully three dimensional, multiphase, micro-scale solid oxide fuel cell anode transport phenomena numerical model is proposed and verified. The Butler-Volmer model was combined with empirical relations for conductivity and diffusivity - notably the Fuller-Shetler-Giddings equation, and the Fickian model for transport of gas reagents. FIB-SEM tomography of a commercial SOFC stack anode was performed and the resulting images were processed to acquire input data. A novel method for estimating local values of Triple Phase Boundary length density for use in a three-phase, three-dimensional numerical mesh was proposed. The model equations are solved using an in-house code and the results were verified by comparison to an analytical solution within the range of its applicability. A limited parametric study was performed to qualitatively assess simulation performance and impact of heterogeneity. Despite the high dependence of the SOFC anode performance on the geometry of its anisotropic, three-phase microstructure there are very few micro-scale numerical models simulating transport phenomena within these electrodes.

A unified framework for heat and mass transport at the atomic scale

We present a unified framework to simulate heat and mass transport in systems of particles. The proposed framework is based on kinematic mean field theory and uses a phenomenological master equation to compute effective transport rates between particles without the need to evaluate operators. We exploit this advantage and apply the model to simulate transport phenomena at the nanoscale. We demonstrate that, when calibrated to experimentally-measured transport coefficients, the model can accurately predict transient and steady state temperature and concentration profiles even in scenarios where the length of the device is comparable to the mean free path of the carriers. Through several example applications, we demonstrate the validity of our model for all classes of materials, including ones that, until now, would have been outside the domain of computational feasibility.