Eliseu Monteiro

Computational fluid dynamics analysis of greenhouse microclimates by heated underground tubes

One of the main problems of Mediterranean climates is the large diurnal amplitude of temperature, with too low temperature during winter nights and too high temperatures during summer days. This is particularly felt in the north of Portugal, where the low temperature during winter nights can be compensated by the introduction of a heat source. The objective of this is work is to simulate the effects in the temperature and velocity fields by the introduction of hot water tubes along a greenhouse in night conditions. Three different situations are simulated: natural convective heating (case A), artificial heating tubes (case B), artificial heating tubes, and natural ventilation (case C). The commercial CFD package ANSYS® (FLOTRAN module) is used for this propose.The turbulence is modelled by the RNG turbulence model. The numerical results are compared with experimental values, the procedure for which is also presented.The average increase in air temperature for cases A, B and C was 2.2°C, 6.7°C and 3.5°C, respectively. Turbulence is lower in case A, increases slightly when the heating system is introduced (case B), and increases significantly in case C due to the effect of natural ventilation. A very good agreement between experimental and numerical temperature values was verified. This allows validating the RNG turbulence model as suitable to simulate arch-shaped greenhouse microclimates. Some improvements can be done to this work: introduction of night-time crop transpiration, 3D simulations, or optimizing the size of the element mesh in order to reduce the computation time.

The feasibility of biomass pellets production in Portugal.

Abstract The production of pellets represents the possibility of using different biomass residues in a standardized fuel. In this article, the economic feasibility of pellets production is analyzed in the Portuguese scenario according to the key indicators of biomass availability, costs, and legal framework. The potential of biomass residues in Portugal is significant and mainly from forestry. However, several limitations to its utilization for pellets production may arise since they are already put to other uses, such as biomass power plants. The combination of the biomass power plants with pellet production plants seems to be the best option for pellet production in the actual Portuguese scenario. The main constrains for the pellets market has been to convince small-scale customers that pellets are a good alternative fuel, mainly due to the investment needed and the strong competition in terms of fuel price with natural gas. These market problems need incentives at a political level bringing the value added tax for the same level of natural gas.

Heat Transfer Simulation in the Mold With Generalized Curvilinear Formulation

The production of a part by foundry techniques is influenced by its complex geometry configuration, which affects the solidification conditions and subsequent cooling. For example certain pipes, some vessels and most valves are produced by casting. To model the solidification of the complex shapes such as valves is difficult if Cartesian coordinates are used. Even simpler parts like pipes may become difficult to model because they usually are not orthogonally ruled shapes. The main objective of this paper is to describe the development of a finite volume method intended to simulate the heat transfer phenomena during the phase change process. Because of the mold design complexity, the finite volume is described using the generalized curvilinear formulation.

Syngas Application to Spark Ignition Engine Working Simulations by Use of Rapid Compression Machine

© 2012 Monteiro et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Syngas Application to Spark Ignition Engine Working Simulations by Use of Rapid Compression Machine

Characterization of Municipal, Construction and Demolition Wastes for Energy Production Through Gasification - A Case Study for a Portuguese Waste Management Company

Gasification of wastes is considered a promising alternative for energy generation due to its lower environmental impacts when compared with conventional landfilling and incineration. Valorisation of such wastes improves sustainability of resource management and of energy production. However, an appropriate characterisation of wastes in terms of physical and chemical properties is essential for the prediction of their behaviour during gasification, allowing to identify possible problems for the environment and installed equipment and also to define which materials present a greater energy potential. This study aimed to characterise 10 different fractions from municipal, construction and demolition wastes received in different fluxes by a Portuguese waste management company. These fractions included wood (44.83 wt%), plastic (22.15 wt%), paper/card (0.04 wt%), mixtures of paper and plastic (14.67 wt%) and sewage sludge (18.31 wt%). For this purpose, determination of density, proximate and ultimate analysis, higher heating value (HHV), thermogravimetric profiles and inorganic composition of ashes were performed for each fraction. Analysis revealed that plastics and their mixtures with paper/card possess the highest HHV’s (25–45 MJ/kg db), thus exhibiting a greater capacity for energy production. High levels of ashes found in dried sewage sludge (50 wt% db) indicate that a lot of by-product will be generated after gasification, possibly increasing the treatment costs. A gasification unit operating at 50 kg/h and admitting a mixture of all these wastes would generate 109.7 kW of total power, having capacity to receive more waste fluxes along the year.

Assessment of Municipal Solid Wastes Gasification Through CFD Simulation

A two dimensional CFD model for MSW gasification has been used to predict and analyze the viability of the hydrogen generation from MSW gasification. The model is based in an Eulerian-Eulerian approach to describe the transport of mass, momentum and energy for the solid and gas phases. The model is applied to a fluidized bed gasifier to full predict and analyze the viability of the hydrogen generation from MSW gasification taking into account the equivalence ratio and steam-to-waste ratio. Conclusion could be drawn that the increase of equivalence ratio has a negative effect on hydrogen production because the oxidation reactions are favored. The introduction of steam to MSW gasification is favorable for improving hydrogen yield, because it increases the partial pressure of steam inside the reactor which favors the gas-phase reactions.

Fluid dynamics model on fluidized bed gasifier using agro-industrial biomass as fuel

The present study shows the experimental and numerical results of thermal gasification of biomass, on the energy potential of agro-industrial waste from the Portalegre region. Gasification tests were performed in a pilot-scale fluidized bed gasifier, in order to study the behavior of peach stones and miscanthus to investigate the effect of gasification temperatures at 750°C, 800°C and 850°C at a constant biomass flow rate of 45kg/h. In order to optimize the operating conditions of the biomass gasification process, a numerical model is developed namely COMMENT code. This model is a computer model of two dimensions describing the biomass gasification processes in a fluidized bed gasifier using peach stone and miscanthus as fuel. Both phases, solid and gaseous, were described using an Eulerian-Eulerian approach exchanging mass, energy, and momentum. The numerical model results are then compared with experimental results. The produced results show the impact of the increased temperature in the calorific value of the syngas. The tests carried out at 750°C shown an increase in CO2 and N2 and a decrease of CO in the range of 5% comparing to the tests carried out at 850°C. In addition, increased temperature favors a decrease in tar production in thermal gasification process. Numerical results shows to be in good agreement with the experimental data.

Analysis of Combustion Flame of Syngas-Air Mixtures

In the proposed paper for this conference, three typical mixtures of H2 , CO, CH4 , CO2 and N2 have been considered as representative of the producer gas (syngas) resulting from biomass gasification. Syngas is being recognized worldwide as a viable energy source, particularly for stationary power generation. However, there are gaps in the fundamental understanding of syngas combustion characteristics, particularly at elevated pressures that are relevant to practical combustors. In this work, constant volume spherical expanding flames of three typical syngas compositions have been employed to measure the laminar burning velocity for pressures ranges between 1.0 and 20 bar. Over the ranges studied, the burning velocities are fitted by the functional formula of Metghalchi and Keck. Conclusion can be drawn that the burning velocity decreases with the increase of pressure. In opposite, the increase of temperature induces the increase of burning velocity. The higher burning velocity value is obtained for the downdraft syngas. This result is endorsed to the higher heat value, lower dilution and higher volume percentage of hydrogen in the downdraft syngas.Copyright

Advantages of Using a Block Unstructured Grid in a Casting Scenario

Numerical modeling of heat transfer during solidification has become widespread in the foundry industry. This is because it is possible to investigate the effects of adjustment to the casting variables on final casting quality, without having to do costly trial‐and‐error experiments. After selecting a suitable mathematical model, one has to choose an appropriate discretization method. If the grid is very fine, each type of method yields the same solution. However, some methods are more suitable to some classes of problems than others. The main objective of this paper is to demonstrate the advantages of using a block unstructured grid in combination with a generalized curvilinear formulation in a casting scenario and compare the performance of two discretization methods, finite differences (FD) and finite volume (FV). The validation of the numerical procedure is done by comparison with measurements which experimental set up is also described. A very good agreement of both numerical methods were verified wi...

Syngas Laminar Burning Velocity: Comparison Between the Schlieren Photography and Spherical Bomb Methods

Gasification is a thermochemical process which can be defined as the conversion of an organically derived, carbonaceous feedstock by partial oxidation[1]. Typical gas product (syngas) includes mainly H2, CO, CO2, CH4 and N2, when air is used as oxidizing agent.Copyright