Defect and Diffusion Forum Vol. 427

Abstract: In this work, we propose a stochastic wind field based on the Bayesian dynamic linear model to account for the wind flow field in the transient advection-diffusion partial differential equation (PDE). The resulting dispersion model accounts for the time variation in the wind field and meteorological variables, allowing the simulation of a transient regime. The main advantage of using such a wind field model over a Fourier series to fit wind time series is its potential to make predictions. In addition, a suitable methodology is necessary to solve the resulting dispersion model. In this work, we use a finite element formulation appropriate to solve transient advection-diffusion PDEs. We verify the accuracy of the proposed methodology by reproducing a case study considering a field tracer experiment. The model evaluation against experimental data shows the good performance of the proposed dispersion model.

Abstract: This paper presents a landscape evolution model based on physical processes – hillslope processes and fluvial erosion, transport, and deposition – solved by numerical methodology. That is, through the solution of differential equations approximated by numerical methods. In this case, hillslope processes are modeled through the classical diffusion equation, discretized by the finite volume method. Fluvial erosion, transport, and deposition are modeled by the fluvial potential equations (stream power law). For this, the approximation is performed by the finite difference method. The topography – initial condition – is set by digital elevation models, obtained from satellite images. These are Raster datasets, that each cell contains a representative elevation value. The drainage is determined through the classical algorithm D8, which performs a scan on the digital elevation model, tracing routes of greater slopes between the cells. The algorithm execution flowchart is presented, and the model is validated. Finally, a geomorphological study is presented in the Piratini river basin, showing thar developed model mimics largescale natural phenomena of watershed processes.

Abstract: This work aimed to analyze the atmospheric dispersion of ammonia gas (NH₃) caused by a hypothetical leak in a tanker truck due to an accident during its transport. These accidents with dangerous products in road transport are unpredictable and can generate severe impacts on communities' borders and the environment close to the accident site. With the use of mathematical models, it is possible to estimate, assuming that there was an accidental release, how far, from the point of leakage to the cloud formed in the atmosphere will move until it is diluted in a way that does not pose a danger of toxicity. In this work, the ALOHA software and Google Earth will be used to estimate the dispersion of this toxic gas in different scenarios, varying the stability class and the height of the leak orifice. Among the proposed and analyzed scenarios, the results show that the plume with the greatest reach was 948 m in the red zone (AEGL 3 - 1100 ppm or 769 mg/m³), 1900 meters in the orange zone (AEGL 2 - 160 ppm or 112 mg /m³) and 3600 meters in the yellow zone (AEGL 1 - 30 ppm or 21 mg/m³).

Abstract: This article deals with an analysis of uncertainties applied to a bioheat transfer problem containing a deep brain stimulation lead. The classic two-dimensional bioheat transfer equation in cylindrical coordinates was considered in the mathematical formulation. The electric potential was solved with a Laplace equation to incorporate the DBS lead effects. Thus, the solution for the electric potential was coupled to the temperature problem, considering an external heat transfer rate. The analysis under uncertainties was performed by the Monte Carlo method considering different types of uncertainties for all parameters of the mathematical model. The uncertainties were chosen according to the information available in the literature in order to analyze the problem more realistically. The solutions showed a significant variation in the temperature profile over time when considering the random variations in the parameters.

Abstract: This work investigates how the configuration of the geometric parameters of a radial crystallizer influences the results of the crystallization of lovastatin by antisolvent and using a multi-scale computational fluid dynamics (CFD) model. The OPENFOAM open-source software uses macro and micromixing expressions for flow, and complete energy and population equilibrium equations during nucleation and crystal growth. The model is based on the Reynolds-Averaged-Navier-Stokes (RANS) equation, along with a multi-environment probability density function (PDF) model and the spatially semi-discretized population equilibrium equation, operating a high-resolution finite volume method. The variation crystallizer construction parameters provided another crystallizer design, and analyses demonstrated improved performance and effects on crystal distribution.

Abstract: Oscillating water column (OWC) wave energy converters can be integrated in harbor protection structures, such as vertical, rubble mound and piled breakwaters. The interaction between the incident wave and the structure, in which the OWC device is integrated, is significantly different, since the structure of the vertical breakwater is impermeable, while that of the rubble mound breakwater is porous. The performance of the OWC device for the three configurations is analyzed for a range of wave periods from 6 to 12 s and a wave height of 1 m. The OWC device integrated into the vertical breakwater shows the best performance (maximum mean pneumatic power of 70 kW), and the mean pneumatic power is globally 3 % higher than that of the OWC device integrated into the rubble mound breakwater (maximum mean pneumatic power of 67.4 kW). The performance of the OWC device integrated into the piled breakwater shows a similar trend to the OWC device integrated into the vertical breakwater for wave periods lower than 9 s, but it has a significant loss of performance for higher wave periods.

Abstract: Earth-air heat exchangers (EAHE) consist of buried ducts and a ventilation system, which require minimal electricity, making them a cost-effective and sustainable solution for improving the thermal conditions of built environments. To enhance the efficiency of the EAHE system and optimize its use of the soil's thermal potential, we employed a galvanized block with a cross-sectional area of 1.5 m² around the duct. The simulations conducted in this study used climatic data from Viamão, a city in southern Brazil, and demonstrated the effectiveness of this strategy. The galvanized block increased the thermal conductivity of the soil region and enabled the EAHE system to utilize higher quantities of thermal energy. The first part of the work highlights the importance of block coupling in improving thermal efficiency and the two potentials of EAHE systems. We also introduce a new method for calculating EAHE efficiency throughout the year. We name it maximum efficiency because it measures how much thermal potential an EAHE installation can extract from the highest amount available in the soil during the year. Subsequently, we conducted simulations of ducts at different depths to evaluate their performance. Our results showed that annual efficiencies increased significantly with the addition of the galvanized block. We also found how the installation depth impacts the thermal potentials. Specifically, we obtained almost 4.0°C and 3.8°C for the (annual RMS) soil and EAHE thermal potentials, respectively, at 3.5m.

Abstract: The earth-air heat exchanger (EAHE) is a sustainable option that allows the electrical energy consumption reduction in buildings. The objective of this study is to evaluate the influence of the incorporation of the thermal energy storage principle based on phase change materials (PCM) into the EAHE on its thermal potential. For this, a three-dimensional numerical model of the PCM coupled to the EAHE (EAHE-PCM) was developed based on the effective heat capacity method and adapted to the climatic conditions and soil characteristics of the Viamão city, Rio Grande do Sul State, Brazil. It was found that for a duct diameter and length of 0.11 m and 25.77 m, the incorporation of PCM to EAHE improved by 8.90% and 3.97% in the average annual thermal potential of heating and cooling, respectively. In addition, the average monthly thermal potential increased 19.70% (heating) and 8.48%(cooling), for the months of May and December, respectively, when the PCM was integrated into the system.

Abstract: This work presents the development of a computational model for the simulation of an Oscillating Water Column device that converts wave flow into electrical energy. The device is placed into a wave channel and a Savonius turbine is inserted in the inlet/outlet duct of the converter. The modeling of the turbine is performed with a rotational moving mesh that simulates the turbine movement in stabilized operating conditions. This coupling provides the minimization of simplifying assumptions, addressing in a single problem the two phenomena inherent to the device approach: the two-phase, incompressible and turbulent flow of air and water in a wave channel containing the oscillating water column device and the incompressible and turbulent airflow passing through a rotational turbine. The computational model was verified/validated for a free stream turbulent flow over a Savonius turbine and verified for the case of wave flow over a converter without the inserted turbine. Results showed that the coupled model allowed obtaining not only available power but also mechanical power in the turbine. For the rotation imposed in the domain, the turbine did not affect the behavior of the wave flow that impinges on the chamber of the OWC device. An augmentation of the power coefficient of the turbine in comparison with turbines subjected to free stream flows was obtained, showing that the fairing of turbine can led to increased power takeoff.