Modeling Of Transport Phenomena Research Articles

Pyrolysis of industrial hemp biomass from contaminated soil phytoremediation: Kinetics, modelling transport phenomena and biochar-based metal reduction

Phytoremediation is the use of vegetation for the in situ treatment of contaminated environments. After plants have been used for phytoremediation of soils, their biomass can be used for example as value-added products or converted by thermochemical processes. Large-scale application of pyrolysis technology for phytoremediation biomass requires accurate predictive kinetic models and a characterization of the toxicity of the materials produced. The pyrolysis of industrial hemp (Cannabis sativa L.) was investigated on a laboratory scale by varying the process conditions and accurately modelled by considering four pseudo-components with first reaction order. The average value of the coefficients of determination is 0.9980. Biomass and biochar were characterized and the main components of the gas phase were monitored. We found Cd, Pb, and Zn in the roots, although in lower amounts than in the soil. Especially the leaves and stems showed negligible traces of these elements, so that these parts can be used directly, even if the hemp was grown on the polluted soil. After pyrolysis, the concentration of pollutants in the solid fraction decreased, which could be attributed to the reduction of metal oxides (or salts) to elemental form and subsequent evaporation. This pyrolysis process has the potential to treat heavy metal-rich biomass, with gas phase purification via condensation, yielding agricultural-grade biochar, CO-rich gas and a highly concentrated heavy metal stream in absorbent material.

A one-field fluid/meso-structure coupling approach for multiscale transport in heterogeneous porous media

Modeling transport phenomena within heterogeneous porous media poses considerable challenges, particularly on account of the complexity of the involved geometries combined with nonlinear transport interactions. In the present study, a novel one-field modeling approach for multiscale fluid–solid interactions is proposed that does not need any a priori information on permeability. This approach implicitly considers the existence of multiscale structures through a penalization function that encompasses merely one single effective parameter. The definition, determination, as well as the response of the effective parameter to influencing factors are elaborated in detail. It is demonstrated that this approach is effective in representing properly the heterogeneity of solids. The method has been successfully applied to both nonlinear porous media flows and Darcian transport problems, exhibiting comparable accuracy but substantial computational savings as opposed to pore-scale simulations. It leads to more accurate interphase mass transfer predictions and lower computational cost in comparison with the Darcy–Brinkmann–Stokes approach. Overall, this method appears to be highly effective in forecasting realistic, industrial-scale porous media transport problems.

A comprehensive review of the modeling of transport phenomenon in the flow channels of polymer electrolyte membrane fuel cells

A comprehensive review of the modeling of transport phenomenon in the flow channels of polymer electrolyte membrane fuel cells

Flow modeling and structural characterization in fungal pellets

Fungal pellets are hierarchical systems that can be found in an ample variety of applications. Modeling transport phenomena in this type of systems is a challenging but necessary task to provide knowledge-based processes that improve the outcome of their biotechnological applications. In this work, an upscaled model for total mass and momentum transport in fungal pellets is implemented and analyzed, using elements of the volume averaging and adjoint homogenization methods departing from the governing equations at the microscale in the intracellular and extracellular phases. The biomass is assumed to be composed of a non-Newtonian fluid and the organelles impervious to momentum transport are modeled as a rigid solid phase. The upscaled equations contain effective-medium coefficients, which are predicted from the solution of adjoint closure problems in a three-dimensional periodic domains representative of the microstructure. The construction of these domains was performed for Laccaria trichodermophora based on observations of actual biological structures. The upscaled model was validated with direct numerical simulations in homogeneous portions of the pellets core. It is shown that no significant differences are observed when the dolipores are open or closed to fluid flow. By comparing the predictions of the average velocity in the extracellular phase resulting from the upscaled model with those from the classical Darcy equation (i.e., assuming that the biomass is a solid phase) the contribution of the intracellular fluid phase was evidenced. This work sets the foundations for further studies dedicated to transport phenomena in this type of systems.

Screening of Metal Reduction Potential for Thermochemical Hydrogen Storage

The screening of all non-radioactive metals without lanthanides for thermochemical hydrogen storage was performed based on physical chemistry calculations. The thermodynamic data were collected from the NIST (National Institute of Standards and Technology) public data repository, which was followed by calculations regarding the change in enthalpy, entropy, Gibbs free energy and equilibrium reaction temperature. The results were critically evaluated based on thermodynamic parameters, viable metals were identified, and their hydrogen storage densities and energy–enthalpy ratios were evaluated. The elements viable for controlled thermochemical hydrogen storage via the reversible reduction and oxidation of metal oxides and metals are manganese (Mn), iron (Fe), molybdenum (Mo) and tungsten (W). Manganese has the largest theoretical potential for hydrogen storage with reversible reduction and oxidation of metal oxides and metals. The second candidate is iron, while the other two (Mo and W) have much lower potential. More research efforts should be dedicated to experimental testing of the identified metals (Mn, Fe, Mo and W) and their different oxides for thermochemical hydrogen storage capabilities both on laboratory and pilot scales. Ferromanganese alloy(s) might also prove itself as an efficient and affordable thermochemical hydrogen storage material. Our theoretical investigation expanded the knowledge on thermochemical hydrogen storage and is accompanied with a brief literature review revealing the lack of experimental studies, especially on oxidation of metals with water vapor occurring during the hydrogen release phase of the cycle. Consequently, accurate modelling of transport, kinetics and other phenomena during hydrogen storage and release is scarce.

Integrative Probabilistic Design of River Jetties by 3D Numerical Models of Transport Phenomena: The Case Study of Kabakoz River Jetties

Various methods are employed to investigate the effects of coastal structures in coastal areas on marine environments and transport phenomena. These methods can be categorized into physical models and numerical simulations. Due to the lack of long-term wave height data in Türkiye, numerical models are utilized to estimate wave heights generated by wind based on long-term measured wind speeds. These wave heights generated in deep sea conditions can be transported to the coast by wave transformation and interactions between coastal structures and waves, turbulence, currents induced by wind and breaking waves, coastal sediment transport rates, and changes in the coastline can be successfully predicted with the assistance of numerical models. In the scope of this study, the new “Integrative Probabilistic Design Approach of River Jetties” was developed. 3D numerical models were used for the optimum design, considering the sediment transport near the jetties and aiming to protect the coastal environment in the long term. 3D numerical modeling has been conducted to investigate the transport phenomena occurring at the outlet of the Kabakoz River in the Şile District of İstanbul Province to acquire the optimum layout and design of the coastal structures. The study presents the “Integrative Probabilistic Design Approach” for coastal protection structures by wind and wave climate, wave transformation, coastal sediment transport, shoreline change, and coastal structure probabilistic design sub-models. Monte Carlo Simulation of Hudson Limit State function conducts probabilistic design for the jetties. The greatest advantage of probabilistic design (Monte Carlo Simulation) is the prediction of uncertainties, such as wave height changes under design conditions. Following the completion of the construction of groins, the effect of probabilistic design on both design and coastal morphology can be evaluated precisely. In conclusion, in the study area, 146,237.55 m3 of sediment is transported annually from west to east and 221,043.49 m3 from east to west. In the absence of coastal structures, sediment transport from east to west is approximately 1.5 times greater than from west to east. The annual net coastal sediment transport from east to west is approximately 74,805.94 m3, while the total transport is estimated to be 367,281.04 m3. The coastline is expected to reach sediment balance within approximately two years. In this study, the coastal structure of a jetty is designed from an innovative probabilistic design perspective. The aim is to ensure the reliability of the structure and, at the same time, protect the morphology of the coastline where the structure will be constructed. The region’s wind and wave climate were initially determined using Hydrotam 3D software. Following this procedure, the length of the jetty is predicted considering the closure depth. The model parameters were calibrated from coastline morphology using satellite images and Google Earth over the past twenty years. These parameters are defined to Hydrotam 3D as input data; a trial-and-error model application procedure calibrates the coastline’s accumulation and erosion. Finally, the probabilistic design is conducted with Monte Carlo Simulation using the Hudson Equation as the limit state function. Det Norske Veritas developed a design code for marine structures in 1992, where the target reliability is 10-3 for structures with less serious failure consequences. This reliability level validated the Level IV model presented in this paper. The class of failure depends on the possibility of timely warning, and these standards can be revised by the model presented to address the effects of climate change on the design of maritime structures.

Computer simulation of a nonlinear wave model of transport phenomena in media with non-local effects

The main contribution of the presented article is that sufficient assumptions have been established for the modified Witham equation describing nonlinear wave propagation for transport phenomena in physicochemical systems. It is shown that when deriving Witham-type equations, the presence of spatial nonlocality of the medium can play a fundamental role. The article also discusses the issues of physical interpretation of the model under study. The principal presence of non-local effects in the studied systems can be justified and obtained as a result of the presence of domains with a complexly organized spatial structure, as well as the presence of heat and mass sources. Computer modeling was carried out and the results were obtained using the Java programming language.

Recent Advances in Computational Convective Heat Transfer Study in a Sub-Channel for Nuclear Power Reactor and Future Directions

A nuclear power reactor's primary use is to generate thermal energy, which in turn produces electricity. The primary heat source is a nuclear fission event occurring inside the fuel rod. The convection heat is transmitted through the coolant by the heat energy generated at the fuel rod wall boundary. Better heat transfer is produced in the flow area by turbulence and irregularity. As a result, turbulent flow heat transfer may present a significant challenge when predicting and assessing the thermal performance of nuclear power reactors. Computational techniques in convective heat transfer have become indispensable for solving challenging issues in the fields of science and engineering thanks to the development of current sophisticated numerical methods and high-performance computer hardware. The development of novel computational techniques and models for complicated transport and multi-physical phenomena is constantly in demand throughout applicable disciplines. This chapter's objective is to provide some recent developments in computational techniques for convective heat transfer, taking into account research interests in the community of mass and heat transfer, and to showcase relevant applications in nuclear power plant engineering domains including future directions. This study describes the most recent advancements in nuclear reactor convective heat transfer research utilizing the computational fluid dynamics (CFD) method, particularly at Ansys Fluent. This work examines the convective heat transfer and fluid dynamics fluid dynamics for turbulent flows across three rod bundle sub-channels that are typical of those employed in the PWR-based VVER type reactor. In this paper, CFD analysis is carried out using the software tool Ansys Fluent. Temperature distribution profile, velocity profile, pressure drop, and turbulence properties were investigated in this study. Boundary conditions i.e. temperature, velocity, pressure, heat flux, and heat generation rate were applied in the sub-channel domain. The main obstacles and bright spots for the CFD methods in nuclear reactor engineering are discussed, which helps to further its further uses. We intend to research a full-length fuel bundle model for VVER-1200 in the future to gather specific fluid characteristic data and use the findings to analyze safety and operate nuclear power facilities in Bangladesh. This paper presents a thorough analysis of the sub-channel thermal hydraulic codes used in nuclear reactor core analysis. This review discusses several facets of previous experimental, analytical, and computational work on rod bundles and identifies potential future directions based on those earlier studies.

Ab initio modelling of transport phenomena in multi-component mixtures of rarefied gases

The direct simulation Monte Carlo method based on ab initio potentials is applied to model transport phenomena in binary, ternary and quaternary mixtures of noble gases. To this end, the Couette and Fourier problems are solved over the whole range of the rarefaction parameter spanning the near free-molecular, transitional, and slip flow regimes. Moreover, analytical solutions are obtained in the limits of the free-molecular and continuous medium regimes of flow. As a result, the shear stress, heat flux through multi-component mixtures, distributions of velocity, temperature, and mole fractions of each species are calculated as a function of the gas rarefaction. An analysis of these data points out the properties which are strongly affected by the chemical composition. It is found that the largest deviations of characteristics of mixtures from those of a single gas are observed for the binary mixture of helium and krypton, while their deviations for the ternary and quaternary mixtures are smaller. A temperature variation in a mixture leads to non-uniform distributions of chemical composition due to the thermal diffusion phenomenon. Such redistributions are analyzed in both problems and their effect on the heat and momentum transfer is evaluated. The reported results can be used to evaluate the main factors determining transport phenomena in practical applications such as vacuum systems, microfluidics, gas separation technology, space research etc.

Modeling of transport phenomena in a hybrid forward osmosis-directional freeze crystallization process for clean water recovery from hydrometallurgical effluents.

Sustainable water recovery and reuse are critical yet challenging, especially from industrial effluents in cold regions. This work presents a robust numerical model of the transport phenomena in a hybrid two-step forward osmosis (FO)-directional freeze crystallization (DFC) desalination process, whose application in areas with cold climates is advantageous. Deionized (DI) water and a hydrometallurgical effluent were considered as the feed solution in the FO step, while three aqueous solutions of inorganic salts were considered as the draw solutions (DS): NaCl, CaCl2, and MgCl2. The effects of temperature and initial DS concentration were investigated on water flux, reverse solute flux, and specific water flux using computational fluid dynamics (CFD). Based on the simulation results, the highest water flux (18 L/m2/h for DI water and 5 L/m2/h for the hydrometallurgical effluent) and lowest reverse solute flux (consistently below 0.3 mol/m2/h) were obtained when MgCl2 was used as the DS. The effect of solute type in the DS on both water recovery yield and purity was in turn studied in the subsequent DFC step, allowing to visualize the solute distribution during the freezing process.

CFD simulation of an industrial steam methane reformer: Effect of burner fuel distribution on hydrogen production

Simulation of the steam methane reformer serves as a launching pad to investigate the optimal amount of hydrogen production. In this study, a 3D-CFD simulation is implemented to model transport phenomena for a turbulent fluid flow with chemical reactions within the reformer. Accordingly, the realizable k-ɛ turbulence model and discrete ordinates (DO) radiation model have been employed to simulate the kinetic mechanism of the SMR process and hydrogen/methane combustion. In addition, the REV-scale approach is considered to model the flow in the porous catalyst bed. Numerical results show that 3D-CFD simulation can accurately model such complex flows in comparison to 2D simulation. In the following, 3D numerical simulations have been performed to investigate the effect of fuel distribution between burners on the amount of heat provided, which affects the amount of hydrogen production and the tube wall temperature. Results indicate that the burner feed flow without purge gas and vent gas streams has the highest efficiency in hydrogen production and leads to a ca. 10% increase in hydrogen production compared to industrial case. Although feeding the burner with purge gas and without vent gas increases hydrogen production by about 7% compared to industrial data, it may be a more suitable option due to lower natural gas consumption and economic savings.

Determination of Heat and Mass Transport Correlations for Hollow Membrane Distillation Modules

Development and optimization of the membrane distillation (MD) process are strongly associated with better understanding of heat and mass transport across the membrane. The current state-of-the-art on heat and mass transport in MD greatly relies upon the use of various empirical correlations for the Nusselt number (Nu), tortuosity factor (τ), and thermal conductivity (κm) of the membrane. However, the current literature lacks investigations about finding the most representative combination of these three parameters for modeling transport phenomena in MD. In this study, we investigated 189 combinations of Nu, κm, and τ to assess their capability to predict the experimental flux and outlet temperatures of feed and permeate streams for hollow fiber MD modules. It was concluded that 31 out of 189 tested combinations could predict the experimental flux with reasonable accuracy (R2 > 0.95). Most of the combinations capable of predicting the flux reasonably well could predict the feed outlet temperature well; however, the capability of the tested combinations to predict the permeate outlet temperatures was poor, and only 13 combinations reasonably predicted the experimental temperature. As a generally observed tendency, it was noted that in the best-performing models, most of the correlations used for the determination of κm were parallel models. The study also identified the best-performing combinations to simultaneously predict flux, feed, and permeate outlet temperatures. Thus, it was noted that the best model to simultaneously predict flux, feed, and permeate outlet temperatures consisted of the following correlations for τ, Nu, and κm: =ε1−1−ε1/3, Nu=0.13Re0.64Pr0.38, κm=1−εκpol+εκair where ε, Re, Pr, κpol, and κair represent membrane porosity, Reynolds number, Prandtl number, thermal conductivities of polymer and air, respectively.

Modeling of the transport and diffusion phenomena for petroleum aromatic hydrocarbons from spilled crude oil in a stagnant mangrove water body

In water, oil spill constitutes serious environmental concern. When impacted water is flowing, it can be self-cleansed by waves. Turbulent water bodies have attracted huge research attention with many models available. However, it becomes different with non-turbulent and stagnant water as in the case with mangrove swamps. This paper reports the development of mathematical models for monitoring transport and diffusion phenomena of aromatics through water column using equations of transport and mass transfer. The models were validated using results from a simulated stagnant water polluted with crude oil. From the result, aromatics transported through water at 0.25 m and 1 m for month 1 is 12.988 µg/l and 0.081 µg/l for experiment and 9.215 µg/l, and 0.0781 µg/l for model, respectively. While month 5, was 48.982 µg/l and 1.890 µg/l for experiment and 39.850 µg/l and 1.650 µg/l for model, respectively. These and others reported show that the models can adequately predict the transport of aromatics through such water body.

Minimal model of drag in one-dimensional crystals

Using a nonperturbative classical approach, we study the dynamics of a mobile particle interacting with an infinite one-dimensional (1D) chain of harmonic oscillators. This minimal system is an effective model for many 1D transport phenomena, such as molecular motion in nanotubes and ionic conduction through solid-state materials. As expected, coupling between the mobile particle and the chain induces dissipation of the mobile particle's energy. However, both numerical and analytic results demonstrate an unconventional nonmonotonic dependence of the drag on particle speed. In addition, when this system is subjected to a constant bias, it supports multiple steady-state drift velocities.

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.

Mathematical modeling of transport phenomena in compressible multicomponent flows

The present article proposes a diffuse interface model for compressible multicomponent flows with transport phenomena of mass, momentum and energy (i.e., mass diffusion, viscous dissipation and heat conduction). The model is reduced from the seven-equation Baer-Nuziato type model with asymptotic analysis in the limit of instantaneous mechanical relaxations. The main difference between the present model and the Kapila's five-equation model consists in that different time scales for pressure and velocity relaxations are assumed, the former being much smaller than the latter. Thanks to this assumption, the velocity disequilibrium is retained to model the mass diffusion process. Aided by the diffusion laws, the final model still formally consists of five equations. The proposed model satisfy two desirable properties: (1) it respects the laws of thermodynamics, (2) it is free of the spurious oscillation problem in the vicinity of the diffused interface zone. For solution of the model governing equations, we implement the fractional step method to split the model into five physical steps: the hydrodynamic step, the viscous step, the heat transfer step, the heat conduction step and the mass diffusion step. The split governing equations for the hydrodynamic step formally coincide with the Kapila's five-equation model and are solved with the Godunov finite volume method. The mass diffusion, viscous dissipation and heat conduction processes contribute parabolic partial differential equations that are solved with the Chebyshev method of local iterations. Numerical results show that the proposed model maintains pressure, velocity and temperature equilibrium near the diffused interface. Convergence tests demonstrate that the numerical methods achieve second order in space and time. The proposed model and numerical methods are applied to simulate the hydrodynamic instability problems in the inertial confinement fusion. Good agreement with experimental results is observed.

Numerical calculation of temperature, velocity, and species concentration distributions in a hot filament chemical vapor deposition in a reactor using a CH4/H2 mixture

This study is a numerical modeling of transport phenomena occurring in the reaction chamber during diamond or amorphous hydrogenated carbon films growth by a hot filament chemical vapor deposition (HFCVD) technique. A two-dimensional model was adopted to study the HFCVD reactor. The equations of heat, momentum, and mass transfer were solved numerically; the simulation was performed using a program in FORTRAN language. All temperature, velocity, and species concentration distributions were similar at the filaments and they were also similar between the filaments. The results show that the gas temperature increases when the number of filaments increases from three to four filaments. We also noted an increase in the production of CH3 and C2H5 radicals near the surface; there was also an increase in the growth rate of the thin film. The concentrations of C2H6, C2H4, and C2H5 were very high. Temperature and concentrations were affected by the distance between filaments and the distance filaments-substrates.

Coupled Process Modeling of Flow and Transport Phenomena in LCM Processing

Coupled Process Modeling of Flow and Transport Phenomena in LCM Processing

Modeling transport phenomena in the shrimp drying process

In this paper, a three-dimensional mathematical model is used to investigate the distribution of the temperature and moisture content in the shrimp through two different approaches as two modes of simulation. The governing equations, including heat and mass transfer, are discretized utilizing the finite element method and solved numerically by applying initial as well as boundary conditions and employing COMSOL Multiphysics® software (version 5.4). At the beginning of the drying, the heat is transferred from the hot air to the shrimp quickly, then follows a slower trend, leading to only moisture transfer. The numerical results of the two modes are presented and compared against experimental data from a natural convection type of shrimp dryer. The simulation results in the first and second modes show 39.7% and 4.41% deviation compared to the experimental results, respectively. In addition, the effect of the moisture diffusion coefficient on the moisture content is investigated.

Microstructural Classification and Reconstruction of the Computational Geometry of Steamed Bread Using Descriptor-Based Approach

Microstructures affect the properties of food products; accurate and relatively less complex microstructural representations are thus needed for modelling of transport phenomena during food processing. Hence, the present study aimed at developing computational microstructures of steamed bread using descriptor-based approach. Relevant information was extracted from the scanning electron microscope (SEM) images of the steamed bread and evaluated using seven classifiers. For the automatic classification and using all descriptors, bagged trees ensembles (BTE) had the highest accuracy of 98.40%, while Gaussian Naïve Bayes was the least with 92.10% accuracy. In the “step forward” analysis, five descriptors had higher classification accuracy (98.80%) than all descriptors, implying that increase in descriptors might or might not increase classification accuracy. Microstructural validation revealed that the ellipse fitting method with a p value of 0.7984 for the area was found to be superior to the Voronoi method with a corresponding p value of 1.4554 × 10−5, confirming that the ellipse developed microstructure was more suitable for microscale modelling of transport phenomena in steamed bread.