Termodinâmica estatística de líquidos com o método de Monte Carlo. I. Metodologia

Statistical mechanics Monte Carlo simulation is reviewed as a formalism to study thermodynamic properties of liquids. Considering the importance of free energy changes in chemical processes, the thermodynamic perturbation theory implemented in the Monte Carlo method is discussed. The representation of molecular interaction by the Lennard-Jones and Coulomb potential functions is also discussed. Charges derived from quantum molecular electrostatic potential are also discussed as an useful methodology to generate an adequate set of partial charges to be used in liquid simulation.

Termodinâmica estatística de líquidos com o método de Monte Carlo. II. O líquido clorofórmio

Thermodynamic properties and radial distribution functions for liquid chloroform were calculated using the Monte Carlo method implemented with Metropolis algorithm in the NpT ensemble at 298 K and 1 atm. A five site model was developed to represent the chloroform molecules. A force field composed by Lennard-Jones and Coulomb potential functions was used to calculate the intermolecular energy. The partial charges needed to represent the Coulombic interactions were obtained from quantum chemical ab initio calculations. The Lennard-Jones parameters were adjusted to reproduce experimental values for density and enthalpy of vaporization for pure liquid. All thermodynamic results are in excelent agreement with experimental data. The correlation functions calculated are in good accordance with theoretical results avaliable in the literature. The free energy for solvating one chloroform molecule into its own liquid at 298 K and 1 atm was computed as an additional test of the potential model. The result obtained compares well with the experimental value. The medium effects on cis/trans convertion of a hypotetical solute in water TIP4P and chloroform solvents were also accomplished. The results obtained from this investigation are in agreement with estimates of the continuous theory of solvation.

Simulation of the energy performance of maize production integrated to pig farming

The study evaluated the energy performance of pig farming integrated with maize production in mechanized no-tillage system. In this proposed conception of integration, the swine excrement is used as fertilizers in the maize crop. The system was designed involving the activities associated to the pig management and maize production (soil management, cultivation and harvest). A one-year period of analysis was considered, enabling the production of three batches of pigs and two crops of maize. To evaluate the energy performance, three indicators were created: energy efficiency, use of non-renewable resources efficiency and cost of non-renewable energy to produce protein. The energy inputs are composed by the inputs and infrastructure used by the breeding of pigs and maize production, as well as the solar energy incident on the agroecosystem. The energy outputs are represented by the products (finished pigs and maize). The results obtained in the simulation indicates that the integration improves the energy performance of pig farms, with an increase in the energy efficiency (186%) as well as in the use of the non-renewable energy resources efficiency (352%), while reducing the cost of non-renewable energy to produce protein (‑58%).

Modeling and simulation of forced-air cooling of strawberries using variable convective coefficient

In the forced-air cooling process of fruits occurs, besides the convective heat transfer, the mass transfer by evaporation. The energy need in the evaporation is taken from fruit that has its temperature lowered. In this study it has been proposed the use of empirical correlations for calculating the convective heat transfer coefficient as a function of surface temperature of the strawberry during the cooling process. The aim of this variation of the convective coefficient is to compensate the effect of evaporation in the heat transfer process. Linear and exponential correlations are tested, both with two adjustable parameters. The simulations are performed using experimental conditions reported in the literature for the cooling of strawberries. The results confirm the suitability of the proposed methodology.

Performance of small wind turbines: simulation of electricity supply to loads connected to the public or isolated grid

ABSTRACT The successful in the implementation of wind turbines depends on several factors, including: the wind resource at the installation site, the equipment used, project acquisition and operational costs. In this paper, the production of electricity from two small wind turbines was compared through simulation using the computer software HOMER - a national model of 6kW and an imported one of 5kW. The wind resources in three different cities were considered: Campinas (SP/BR), Cubatão (São Paulo/BR) and Roscoe (Texas/ USA). A wind power system connected to the grid and a wind isolated system - batteries were evaluated. The results showed that the energy cost ($/kWh) is strongly dependent on the windmill characteristics and local wind resource. Regarding the isolated wind system – batteries, the full supply guarantee to the simulated electrical load is only achieved with a battery bank with many units and high number of wind turbines, due to the intermittency of wind power.

Control of a one-legged robot with energy savings

This paper presents a new strategy to control an one-legged robot aiming to reduce the energy expended by the system. To validate this algorithm, a classic method as benchmark was used. This method has been extensively validated by simulations and experimental prototypes in the literature. For simplicity reasons, the work is restricted to the two dimensional case due to simplicity reasons. This new method is compared to the classic one with respect to performance and energy expended by the system. The model consists on a springy leg, a simple body, and an actuated hinge-type hip. The new control strategy is composed of three parts, considering the hopping height, the forward speed, and the body orientation separately. The method exploits the system passive dynamics, defined as non-forced response of the system. In this case, the model is modified adding a spring to the hip. The method defines a desired leg trajectory close to the passive hip swing movement. Simulation results for both methods are analyzed and compared.

Fluid dynamic modelling and simulation of circulating fluidized bed reactors: importance of the interface turbulence transfer

The main objective of this work is to analyze the importance of the gas-solid interface transfer of the kinetic energy of the turbulent motion on the accuracy of prediction of the fluid dynamic of Circulating Fluidized Bed (CFB) reactors. CFB reactors are used in a variety of industrial applications related to combustion, incineration and catalytic cracking. In this work a two-dimensional fluid dynamic model for gas-particle flow has been used to compute the porosity, the pressure, and the velocity fields of both phases in 2-D axisymmetrical cylindrical co-ordinates. The fluid dynamic model is based on the two fluid model approach in which both phases are considered to be continuous and fully interpenetrating. CFB processes are essentially turbulent. The model of effective stress on each phase is that of a Newtonian fluid, where the effective gas viscosity was calculated from the standard k-epsilon turbulence model and the transport coefficients of the particulate phase were calculated from the kinetic theory of granular flow (KTGF). This work shows that the turbulence transfer between the phases is very important for a better representation of the fluid dynamics of CFB reactors, especially for systems with internal recirculation and high gradients of particle concentration. Two systems with different characteristics were analyzed. The results were compared with experimental data available in the literature. The results were obtained by using a computer code developed by the authors. The finite volume method with collocated grid, the hybrid interpolation scheme, the false time step strategy and SIMPLEC (Semi-Implicit Method for Pressure Linked Equations - Consistent) algorithm were used to obtain the numerical solution.

Chinese multinational corporations in Brazil: strategies and implications in energy and telecom sectors

This study aims to understand how Chinese enterprises acted in Brazilian energy and telecommunication sectors in the past ten years and whether they would be leading to an increase in the asymmetries between Brazil and China. It argues that the asymmetries presented in the relations are due in large part to successful Chinese enterprises' strategies.

Chinese energy policy progress and challenges in the transition to low carbon development, 2006-2013

If the world is not to jeopardize the chances for human life on Earth, climate change must be mitigated; therefore, achieving low carbon development is crucial. China is the world's greatest GHG emitter, energy producer and energy consumer; investigating its energy-climate policy developments and international positions are of utmost importance to understand and tackle current stumbling blocks of the global energy and climate governance.

Public hearings as a tool to improve participation in regulatory policies: case study of the National Agency of Electric Energy

The participation of citizens in public policies is an opportunity not only to educate them, but also to increase their empowerment. However, the best way for deploying participatory policies, defining their scope and approach, still remains an open and continuous debate. Using as a case study the Brazilian National Agency of Electric Energy (Aneel), with its public hearings about tariff review, this paper aims at analyzing the democratic aspects of these hearings and challenges the hypothesis of many scholars about the social participation bias in this kind of procedure. This study points out a majority participation of experts, contrasting with the political content of discussions. And, this way, it contributes to a critical analysis of the public hearings as a participatory tool, indicating their strengths and their aspects which deserve a special attention.