Ana Jacinta Soares

A relaxation kinetic model for transport phenomena in a reactive flow

A gaseous mixture of four constituents undergoing a reversible bimolecular reaction is modeled by means of a Bhatnagar, Gross, and Krook (BGK)-type equation in a flow regime close to chemical equilibrium. In the proposed relaxation method, elastic and chemistry collision terms are approximated separately, introducing different reference distribution functions which assure the correct balance laws. A Chapman-Enskog procedure is applied in order to provide explicitly the transport coefficients of diffusion, shear viscosity and thermal conductivity in dependence on elastic and reactive collision frequencies, mass concentrations of each species and temperature of the whole mixture. The closure of the balance equations is performed at the Navier-Stokes level and plane wave solutions are characterized. For the (H2,Cl,HCl,H) system, transport coefficients, as well as the Prandtl number of the mixture, are represented as functions of the temperature and compared with the inert case in order to discuss the influen...

A Customized Evolutionary Algorithm for Multiobjective Management of Residential Energy Resources

Dynamic tariffs are expected to become a relevant pricing scheme in the context of smart grids. In this framework, active management of residential loads can play an important role to optimize the usage of end-use energy resources while minimizing energy cost. This paper presents an evolutionary algorithm to optimize the integrated usage of multiple residential energy resources (local generation, shiftable loads, thermostatically controlled loads, and storage systems) considering a large set of management strategies. Customized solution encoding and operators are developed for different groups of loads. The multiobjective model considers as objective functions the minimization of the energy cost and the minimization of end-users dissatisfaction associated with management strategies. Results have shown that significant savings can be achieved mainly through demand response actions implemented over thermostatically controlled loads. Savings are also dependent on the end-users preferences and degree of willingness to accept automated control.

Domestic load characterization for demand-responsive energy management systems

The final goal of our research is to design a methodology to be implemented in a demand-responsive energy management system for controlling domestic energy resources in a smart grid scenario, taking into account the existence of dynamic tariffs and quality of service constraints. This paper aims at fulfilling an essential step towards that goal: evaluating the manageable demand available at the residential sector and assess the impacts of automated demand response actions in the domestic aggregated load diagram. Domestic energy resources comprise typical manageable loads, energy storage systems, plugin electric vehicles and micro-generation systems. The management strategy must consist of real time local energy monitoring and load control assuring the quality of the energy service provided and the end-users comfort requirements and preferences while optimizing the operation of power systems, contributing to maximize the integration of renewables and minimizing the electricity bill.

Endothelial progenitor cells in diabetic patients with myocardial infarction – Can statins improve their function?

The effect of statins on endothelial progenitor cells (EPCs) function derived from diabetic patients (DMpts) with acute myocardial infarction (AMI) is unknown. In this study we assess the response of early and late EPCs from diabetic versus non-diabetic patients (NDMpts) with AMI to statins. EPCs were obtained from 10 diabetic and 10 age-matched non-diabetic male patients with AMI. For each patient, cultures of early and late EPCs were performed under 4 different conditions: normal glucose concentration (control); high glucose concentration; normal glucose concentration with atorvastatin supplementation and normal glucose concentration with pravastatin supplementation. To compare the effect of these treatments on EPC function in DMpts versus NDMpts, we performed in vitro: EPC colony-forming units (CFU) assay; cell cycle analysis; viability assessment and expression of the surface markers CXCR4, CD133, CD34 and KDR. Under control conditions, CFU numbers were reduced in DMpts-derived EPCs when compared to those of NDMpts (1.4±0.8 vs 2.6±1.2 CFU/well, P=0.021). When early EPCs from DMpts were cultured in the presence of statins, CFU capacity was restored, surmounting that of NDMpts under control conditions. Statins significantly improved viability of early EPCs and delayed the onset of late EPCs senescence, even in cells from DMpts. In addition, statins induced approximately a 2-fold increase in the proportion of late EPCs in S-phase of the cell cycle (P<0.05). Statins have a beneficial effect on both early and late EPCs from DMpts with AMI. Despite the functional impairment of EPCs from DMpts, they exhibit similar responsiveness to statins as equivalent cells from NDMpts.

BGK-type models in strong reaction and kinetic chemical equilibrium regimes

A BGK-type procedure is applied to multi-component gases undergoing chemical reactions of bimolecular type. The relaxation process towards local Maxwellians, depending on mass and numerical densities of each species as well as common velocity and temperature, is investigated in two different cases with respect to chemical regimes. These cases are related to the strong reaction regime characterized by slow reactions, and to the kinetic chemical equilibrium regime where fast reactions take place. The consistency properties of both models are stated in detail. The trend to equilibrium is numerically tested and comparisons for the two regimes are performed within the hydrogen–air and carbon–oxygen reaction mechanism. In the spatial homogeneous case, it is also shown that the thermodynamical equilibrium of the models recovers satisfactorily the asymptotic equilibrium solutions to the reactive Euler equations.

On the dynamics and linear stability of one-dimensional steady detonation waves

A detailed analysis of the dynamics and linear stability of a steady one-dimensional detonation wave propagating in a binary reactive system with an Arrhenius chemical kinetics of type is carried out. Starting from the frame of the kinetic theory, the binary reactive mixture is modelled at the mesoscopic scale by the reactive Boltzmann equation (BE), assuming hard sphere cross sections for elastic collisions and step cross sections with activation energy for reactive interactions. The corresponding hydrodynamic limit is based on a second-order non-equilibrium solution of the BE obtained in a previous paper, using the Chapman–Enskog method in a chemical regime for which the reactive interactions are less frequent than the elastic collisions. The resulting hydrodynamic governing equations are the reactive Euler equations, including a rate law which exhibits an explicit dependence on the reaction heat and forward activation energy of the chemical reaction. These equations are used to describe the spatial structure of the steady detonation wave solution and investigate how this structure varies with the reaction heat. The response of the steady solution to one-dimensional disturbances is studied using a normal-mode linear approach which leads to an initial-value problem for the state variable disturbances in the reaction zone. The stability problem is treated numerically, using an iterative shooting technique to determine the unstable modes. The analysis developed here emphasizes the influence of the chemical reaction heat and activation energy on the linear stability spectra.

Effect of reaction heat on Maxwellian distribution functions and rate of reactions

A binary gaseous mixture undergoing a reversible reaction of type is modeled with the chemical kinetic Boltzmann equation, assuming hard sphere cross sections for elastic collisions, and two different models with activation energy for reactive interactions, namely the line-of-centers and step cross-section models. The Chapman–Enskog method and Sonine polynomial representation of the distribution functions are used to obtain the solution of the Boltzmann equation in a chemical regime for which the reactive interactions are less frequent than the elastic collisions, i.e. in the early stage of the reaction when the constituent A is in a large amount with respect to B and the affinity of the reaction tends to infinity. The aim of this paper is twofold: (i) to evaluate the effect of the reaction heat on the Maxwellian distribution functions and on the production terms of both particle number densities and mixture energy density; (ii) to analyze spatially homogeneous solutions for the particle number density and temperature of the reactants when the chemical reaction advances. It is shown that the reaction heat changes the Maxwellian distribution functions, the production terms and hence the trend to equilibrium of the particle number density and temperature of the reactants. Moreover, these changes differ for exothermic and endothermic reactions.

Analysis of the trend to equilibrium of a chemically reacting system

In this present paper, a quaternary gaseous reactive mixture, for which the chemical reaction is close to its final stage and the elastic and reactive frequencies are comparable, is modelled within the Boltzmann equation extended to reacting gases. The main objective is a detailed analysis of the non-equilibrium effects arising in the reactive system A1 + A2 A3 + A4, in a flow regime which is considered not far away from thermal, mechanical and chemical equilibrium. A first-order perturbation solution technique is applied to the macroscopic field equations for the spatially homogeneous gas system, and the trend to equilibrium is studied in detail. Adopting elastic hard-spheres and reactive line-of-centres cross sections and an appropriate choice of the input distribution functions—which allows us to distinguish the two cases where the constituents are either at same or different temperatures—explicit computations of the linearized production terms for mass, momentum and total energy are performed for each gas species. The departures from the equilibrium states of densities, temperatures and diffusion fluxes are characterized by small perturbations of their corresponding equilibrium values. For the hydrogen–chlorine system, the perturbations are plotted as functions of time for both cases where the species are either at the same or different temperatures. Moreover, the trend to equilibrium of the reaction rates is represented for the forward and backward reaction H2 + Cl HCl + H.

Kinetic Theory of Simple Reacting Spheres I

We consider physical and mathematical aspects of the model of simple reacting spheres (SRS) in the kinetic theory of chemically reacting fluids. The SRS, being a natural extension of the hard‐sphere collisional model, reduces itself to the revised Enskog theory when the chemical reactions are turned off. In the dilute‐gas limit, it provides an interesting kinetic model of chemical reactions that has not been considered before. In contrast to other reactive kinetic theories (e.g., line‐of‐centers models), the SRS has built‐in detailed balance and microscopic reversibility conditions. The mathematical analysis of the work consists of global existence result for the system of partial differential equations for the model of SRS.

Impacts of demand side management and micro-generation units on low voltage distribution radial networks

The increasing dissemination of micro-generation systems, interest in demand-side management actions as a tool potentially contributing for increasing the operational efficiency of power systems operation and higher penetration of renewables will originate scenarios in which these issues co-exist in the same low voltage distribution network. The impacts of these scenarios, namely on power quality, should be properly assessed. This paper presents a case study in which the impacts on voltage fluctuation and unbalance are assessed in a low voltage radial distribution network in which some micro-generation units are installed.