José Helvecio Martins

Methodology for evaluation of grid-tie connection of distributed energy resources - Case study with photovoltaic and energy storage

The availability of reliable energy sources for all people, especially electricity, indicates an imbalance in the living conditions of a society. Therefore, new systems must be implemented to couple energy storage and renewable energy generation for the grid reliability improvement and increase access to electricity. This paper proposes a methodology to establish a general index focused on the insertion of distributed photovoltaic generation and energy storage using batteries. This methodology was applied in the IEEE 14-bus electric power system with load variation from different energy providers for the period of one year. The simulation results allow of the best performance evaluation to add distributed photovoltaic generation and/or energy storage in a real electric power system in different buses. The proposed methodology will allow planners to at the same time visualize different aspects by means of a single index that includes technical, economic and environmental aspects.

Three-Dimensional Modeling and Simulation of Heat and Mass Transfer Processes in Porous Media: An Application for Maize Stored in a Flat Bin

If the relative humidity and temperature of the air inside a granular mass of stored grain exceeds a certain threshold value, microorganism activity is likely to increase. Lower relative humidity and temperature, when uniformly distributed inside the grain mass, prevent moisture migration and an increase in microorganism activity. To cool down or maintain the temperature of the grain mass below a threshold value, forced ventilation with an appropriate airflow can be used to remove excess moisture or heat generated by grain or microorganism respiration. The objective of this work was to solve the equations that describe the conservation of heat, mass, and momentum in order to predict heat and mass transfer processes in the environment inside a grain mass of maize, stored in a flat bin. Three-dimensional computational fluid dynamics was used to solve the equations. The analysis of heat and mass transfer was performed considering the geometry of a two-ton-capacity bin prototype using a hexahedral mesh for the finite volume analysis. The numerical grid was defined to discretize the physical flow domain of interest to calculate velocity, temperature, and moisture distribution in the bulk of stored grain. The predicted results were compared with experimental data, and the agreement between them was very good.

Convective Drying Analysis of a Single Wheat Kernel Based on an Irreversible Thermodynamics Model

The application of irreversible thermodynamics offers a formal treatment for drying analysis that allows the evaluation of intra-particle or intra-medium temperature and moisture profiles, and enthalpy, liquid, and vapor fluxes. However, researchers have claimed that its implementation is complex. This work presents a simple methodology for modeling, solving, and validating the drying equations, as applied to wheat kernels, and for obtaining the inherent and usually unavailable transport coefficients. To clarify and simplify the ensuing physical analysis, a spherical shape and isotropy were assumed. Additionally, solutions obtained with both Dirichlet and convective boundary conditions were analyzed and compared against experimental data. The thermal and hydro-stresses depend heavily on internal vapor and liquid fluxes and on the respective drying evaporation fronts, all of which were evaluated and compared.

Reflectometria no domínio do tempo na determinação do conteúdo de água no solo

This study had as objective the determination of the correlation between the apparent dielectric constant and water content for a clay-textured soil and a sandy-textured soil by fitting a cubic polynomial type model. To measure the soil water content a TDR system was proposed, which consists of: oscilloscope; electromagnetic pulse generator; coaxial cable of 50 W; TV antenna cable; impedance matching; probes (paralleled metallic guides) with 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35 m lengths and with two diameters (d1 = 3.2 and d2 = 6.5 mm). For the sandy soil, the best fit was obtained with a 0.30 m-long probe with 3.2 mm-diameter guides, an adjusted determination coefficient, R2, of 0.954. For the clay soil, the best fit was obtained with a 0.30 m-long probe with a 3.2 mm-diameter guides, and an adjusted determination coefficient, R2, of 0.923. The TDR system, proposed for determination of the soil water content within the range between the field capacity and the wilting point, provided the best determination coefficients for the 0.30 m probe in both soils and the studied probe lengths. The proposed TDR system estimated the clay-soil water content with mean relative error of 6.6%, for the 0.30 m probe.

A novel low-cost instrumentation system for measuring the water content and apparent electrical conductivity of soils.

The scarcity of drinking water affects various regions of the planet. Although climate change is responsible for the water availability, humanity plays an important role in preserving this precious natural resource. In case of negligence, the likely trend is to increase the demand and the depletion of water resources due to the increasing world population. This paper addresses the development, design and construction of a low cost system for measuring soil volumetric water content (θ), electrical conductivity (σ) and temperature (T), in order to optimize the use of water, energy and fertilizer in food production. Different from the existing measurement instruments commonly deployed in these applications, the proposed system uses an auto-balancing bridge circuit as measurement method. The proposed models to estimate θ and σ and correct them in function of T are compared to the ones reported in literature. The final prototype corresponds to a simple circuit connected to a pair of electrode probes, and presents high accuracy, high signal to noise ratio, fast response, and immunity to stray capacitance. The instrument calibration is based on salt solutions with known dielectric constant and electrical conductivity as reference. Experiments measuring clay and sandy soils demonstrate the satisfactory performance of the instrument.

Development of capacitive sensor for measuring soil water content

The irrigation management based on the monitoring of the soil water content allows for the minimization of the amount of water applied, making its use more efficient. Taking into account these aspects, in this work, a sensor for measuring the soil water content was developed to allow real time automation of irrigation systems. This way, problems affecting crop yielding such as irregularities in the time to turn on or turn off the pump, and excess or deficit of water can be solved. To develop the sensors were used stainless steel rods, resin, and insulating varnish. The sensors measuring circuit was based on a microcontroller, which gives its output signal in the digital format. The sensors were calibrated using soil of the type “Quartzarenic Neosoil”. A third order polynomial model was fitted to the experimental data between the values of water content corresponding to the field capacity and the wilting point to correlate the soil water content obtained by the oven standard method with those measured by the electronic circuit, with a coefficient of determination of 93.17%, and an accuracy in the measures of ±0.010 kg kg-1. Based on the results, it was concluded that the sensor and its implemented measuring circuit can be used in the automation process of irrigation systems.

Remote environmental monitoring and management of data systems.

As instrumentation and measurement system technology develop, the demand for faster and more reliable data transfer increases. At the same time, data collection in field research is becoming more expensive given the necessity of the researcher’s on-site presence. This requires that researchers invest significant amounts of time on the acquisition of data, especially when points of collection are geographically stratified. The utilization of communication networks in instrumentation systems enables remote analysis of data in real-time, allowing researchers to explore more diverse uses for the data. Such systems can be easily utilized by multiple users, regardless of their location. The objective of this project was to develop a system for remote management of data transmission over diverse communication interfaces. This goal was achieved by developing a protocol system that allows remote storage, access, and transmission of data. In this case, the data used was obtained from previously implemented projects. With a standardized method of data storage, collected data takes a consistent form. Databanks created facilitate the inclusion and recuperation of information in an unequivocal format, allowing researchers to integrate the information efficiently in their research projects. Project activities can be easily and reliably managed, making possible a more organized execution of field studies and eliminating problematic manual registers.

Efeito das condições de colheita, pré-processamento e armazenamento na qualidade do milho-pipoca

Aiming to identify parameters of popcorn quality decreases, the effects of harvest and shelling methods, initial moisture contents, drying air temperature and storage time on the expansion capacity of the Zelia and CMS 43 cultivars were evaluated. The harvest was performed when both popcorn varieties reached moisture contents of 19% w.b. and, further, 15% w.b. Manual harvest and shelling and mechanic harvest with different speeds of the shelling cylinder were used. The product was submitted to artificial drying process in thin layers and also to natural drying. Periodically a quality pattern-test related to the popcorn expansion capacity was performed. The grain quality was significantly affected by mechanical harvest and by increase in the drying air temperature; there was no decrease on the physiological quality of the popcorn during the storage; the best values of expansion capacity, for most of the treatments, were obtained after 270 days of storage. The popcorn of Zelia variety showed superior commercial quality compared to the variety CMS 43. However, it is necessary to stress the fact that the latter is still in stage of development and genetic breeding.

Grapsi_Draw Digital Psychrometric Chart

Knowledge of psychrometric properties is the basic requirement for environmental measurements and drying processes. The software GRAPSI_DRAW is capable of calculating the psychrometric properties and simulating the basic psychrometric processes with the precision of analytical methods, also showing the results in charts plotted on the computer screen.

Avaliação do deslocamento de minhocas (Eudrilus Eugeniae) submetidas a pulsos elétricos controlados

Realizou-se este trabalho com o objetivo de determinar, em laboratorio, os indices de deslocamento e de separacao de minhocas gigante africana (Eudrilus eugeniae) do humus, e definir as caracteristicas eletricas dos pulsos eletricos que permitam melhor eficiencia na separacao de minhocas em escala piloto. Os testes realizados apresentavam as seguintes caracteristicas: (i) tensao de 100 a 500 V; (ii) patamar de pulso de 2, 3 e 4 ms; (iii) frequencia de 1 e 5 Hz; e (iv) tempo de exposicao de 1, 2, 3 e 4 h. Verificou-se que as minhocas submetidas aos pulsos eletricos se deslocam, preferencialmente, no sentido do catodo. Nas situacoes estudadas o maior valor de indice de deslocamento obtido foi de 78,18% e o indice de separacao, de 62,37%. A utilizacao de pulsos eletricos controlados, para a separacao de minhocas do humus, gera um ganho medio, ao longo da vida util estimada, de cerca de 26% de economia financeira.