Search

In this paper, we have investigated the possibility of implementation of three solar chimney systems in the two Algeria regions (Constantine, Tamanrasset). Numerical simulations were performed for ...

If transport is an essential means for the development of the economy, society and its mobility, it has the drawback of leading to significant atmospheric pollution. As traffic density is very high in large cities, air pollution is amplified by the various means of transport resulting from the combustion of fossil fuels. Urban air pollution is mainly caused by vehicles generating emissions harmful to human health. Our objective of this work is to analyze a strategy to eliminate or reduce the emission of these pollutants (NOx, CO, CO2) during combustion. This strategy aims to explore a clean energy source alternative to fossil fuels. This approach consists of completely replacing the internal combustion scalar with the engine powered by fuel cells using hydrogen. This motivates decision makers to choose hydrogen as an alternative fuel to protect the urban environment and the health human from air pollution. This study shows that it is possible to perfectly mitigate pollutants from urban transport systems by using a PEMFC as an alternative clean energy source. Analyze a strategy to eliminate or reduce the emissions of these pollutants (NOx, CO, CO2) during the combustion of full fossil fuel in vehicle engines. This strategy aims to exploit the energy vector represented by hydrogen in order to save human life in more populated areas and protect the environment. The pressure, temperature and concentration of each species (O2, H2 and H2O) are obtained from the resolution of the electrochemical model coupled to the dynamic model, which we do not present here.

The use of biofuels in applications of interest requires knowledge of behavior of their flames under various working conditions. This paper aims at demonstrating the effect of strain rate and ambient pressure on laminar diffusion flames structure and extinction temperature limits of biogas-syngas mixtures. Opposed-flow configuration is adopted over a wide interval of strain rate (nearly from ignition to extinction) and ambient pressure (from 1 to 10 atm). Chemical kinetics is described by GRI-Mech 3.0 mechanism and Chemkin program used to solve the problem. Results revealed that increase of hydrogen volume in syngas highly enlarges strain rate extinction limits and keeps extinction temperature nearly constant. On the other hand, methane volume augmentation in biogas preserves approximately extinction strain rate and improves extinction temperature. Besides, it has been observed that increasing strain rate enhances non-equilibrium effects and radical production; whereas, it reduces temperature and final combustion products. It has been established that ambient pressure has opposite role of strain rate except for flame thickness. Results showed that in this kind of flames, for the cases of low strain rate and pressure or high strain rate and pressure, the NO species production is governed by the NO2 route. For the other cases, the prompt route is preferred and the thermal path is the least favored and disabled at elevated pressures. Reaction zone thickness is almost constant for all compositions; however, it is reduced by pressure and strain rate augmentations.

The influence of the addition of hydrogen on the formation of soot in an ethylene-gas/air mixture of a counter-current laminar diffusion flame in the flameless regime and at atmospheric pressure has been studied. A detailed gas phase reaction mechanism, including aromatic chemistry up to four cycles and complex thermal and transport properties, was used. The soot is modeled by the moments method. The interactions between soot and gas phase chemistry have been taken into account. Losses by thermal radiation (from CO2, CO, H2O from CH4 and soot) modeled by a thin body. Adding hydrogen to the fuel eliminates the formation of soot. The calculations further suggest that the effect of the addition of hydrogen on soot formation is due to the absence of the concentration of hydrogen atoms in the surface growth regions of soot (stagnation plane) and at a higher concentration of molecular hydrogen in the flame zone. It also reduces the concentrations of C3H3, C6H6 as well as PAHs (for example, pyrene) which all suppress the process of soot formation.

Energy conversion through combustion is one of main energy production processes. The research related to combustion has progressed enormously, leading to an improvement in energy performance in industrial combustion systems. Relative to strong growth in global energy demand, gradual depletion of fossil resources is reported. The latter generates an improvement in combustion processes and makes energy optimization a major challenge for researchers. On the other hand, the combustion emissions to the atmosphere are considered as one of main environmental and climate change concerns. This work analyzes the non-premixed flameless combustion of CH4-syngaz mixture in opposed jet configuration. Kinetics of combustion is described by Grimech 3.0 mechanism, calculations are achieved by Chemkin code. Several ratio values were considered, fuel injection temperature is T = 300 K, that of oxidant is 1200 K with a constant pressure equals to one atmosphere. It has been found that increasing H2/CO ratio does not affect combustion temperature and consequently NO emission. Furthermore, a large reduction in NO2 has been depicted. The replacement of N2 by CO2 in the oxidizer has a significant impact on the thermal field and species.

The solar chimney power plant (SCPP) is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated ...

The aim of our study is to project an optimized wind turbine Darrieus type capable to start at low wind speeds. This type of the turbine is characterized by a low starting torque compared with the Savonius rotor. To allow them, to operate for a long period, we consider a system enabling a self-start at low wind speeds. The study consist in three parts: first, a system of monitoring and control of the angle of attack that allows a self-starting at low wind speeds is presented, second part presents a general method for obtaining a profile with good starting torque and third part presents experimental study of the impacts of the angle of attack, the solidity and the wind velocity on the lift, grad forces and torque. The study continues to extend to other configurations namely that parabolic shape.

The environmental and economic objectives for the reduction of fuel consumption and reduction in the polluting emissions are always of crucial news. Thus, the elucidation of new techniques of combustion using the diffusion flame (more secure) in a confined environment and the comprehension of the involved physical phenomena remains of capital challenge. The dilution of the combustion air by CO 2 has confirmed its technological interest; the objective of this work is to quantify numerically the polluting emissions in a turbulent diffusion flame. The air is diluted by CO 2 and attention has been paid to its thermal and chemical effects on the internal structure of the flame. It is found that CO 2 addition reduces flame temperature by both thermal and chemical effects. Most of the emissions are also reduced by CO 2 increasing in the air.

The solar chimney power plant (SCPP) is a power generator which uses solar radiation to increase the internal energy of the air circulating in the system, thereby transforming the useful gain of th...

The aim of this work is to present a two-dimensional transient model, of heat and mass transfer in a proton exchange membrane fuel cell (PEMFC). The model includes various conservation equations such as mass (hydrogen, oxygen, water concentration), Momentum and energy equations this model is combined with the electrochemical model. The objective of this work is to know the hydrogen, oxygen water concentration, temperature and pressure to determine the performance conditions of the fuel cell under the current density and permeability effect. A program based on the finite volume method was performed to simulate these equations system. The numerical results show that the gas distribution in the assembly membrane electrode (MEA) and the power density is affected by the nature of porous middle (permeability).

We develop the natural iteration method (NIM) in the cluster variation method (CVM) using the congruence between input and output maximum cluster probabilities in the procedure of iteration. In this method, the effective chemical potential $$ \upmu_{i}^{*} $$ is not necessarily fixed, and one can calculate the equilibrium in a certain grand potential Ω. This property is absent in the cluster variation method using the natural iteration method or the Newton-Raphson (N-R) method. When the new method is used, the calculations of binary phase diagrams for first-order transitions are easy, and one can obtain high precision results for CVM calculations in a short period of time using ordinary micro-computers. We illustrate this development by its application in $$ {\text{A1/L1}}_{ 0} / {\text{L1}}_{ 2} $$ binary phase diagram.

The aim of the present study is to examine the Dufour influence and Soret effects on entropy generation in convective heat and mass transfer for the case of a binary gas mixture with a single diffusive species in a square cavity. We numerically investigate the thermosolutal convection in a square cavity, where a binary mixture of incompressible fluid is confined under the conditions of both thermal and solutal gradients. Furthermore, we analyze the effect of Dufour and Soret on entropy generation. We find that, according to Grashof number values, the entropy generation could be mainly due to heat transfer or to fluid friction irreversibility and that the Soret and Dufour effects have great impact on the production of entropy.

The purpose of this work is to present a two-dimensional transient model of the gas flow in the fuel cell (PEMFC). The model includes various conservation equations such movement and energy equations. The governing equations were resolved by the finite volume method. The objective of this work is to know the maximum temperature and its location in PEMFC and to determine the performance conditions of the fuel cell under the current density and velocity inlet effect. The polarization curve obtained numerically is compared with much numerical work. The numerical results show the regime flow effect and the nature of porous middle on the gas distribution in the membrane electrode assembly (MEA).

Natural convection flow past a vertical porous plate in a porous medium is studied numerically, by taking into account the Dufour and Soret effects. The similarity equations of the problem considered are obtained by using usual similarity technique. This system of ordinary differential equations, which are solved numerically by using the Nachtsheim -Swigerst hooting iteration technique together with a sixth order Runge-Kutta integrations scheme. The results show that Soret and Dufour effects do not appreciably influence the velocity, temperature and concentration fields, but rather only tend to increase the mass and energy flux due to the added contributions.