Énergie thermique | EPFL Graph Search

L'énergie thermique est l'énergie cinétique d'agitation microscopique d'un objet, qui est due à une agitation désordonnée de ses molécules et de ses atomes. L'énergie thermique est une partie de l'énergie interne d'un corps. Les transferts d'énergie thermique entre corps sont appelés transferts thermiques et jouent un rôle essentiel en thermodynamique. Ils atteignent un équilibre lorsque la température des corps est égale. Énergie et équilibre thermiques Transfert thermique L'énergie thermique a tendance à se diffuser uniformément dans l'espace. Ce mécanisme naturel d'équilibre est un des mécanismes énoncés dans le principe zéro de la thermodynamique, qui comprend aussi l'équilibre mécanique (des pressions s'équilibrent) et l'équilibre chimique (les fluides se mélangent). Les mécanismes de répartition de l'énergie thermique se font :

par contact direct : ** la conduction thermique (transfert de l'énergie cinétique des molécules sans échange de matière) ; ** la conve

Preliminary Study of a Solar Trough/Tower Power Plant

Jorge López Moreno

The possibility of combining both the advantages of a solar tower thermal power plant and of a solar parabolic trough power plant could be interesting from an energetic point of view as well from an economic point of view. The preliminary study of this combination feasibility is the goal of this project. The study of the project viability consist first of all on the modeling of the trough system, the energy balance of the parabolic troughs will be established at first. Secondly, and choosing a perfect solar day simulating a day when the solar radiation is rather stable, with no cloudy periods along the day, the power available from the trough plant can be calculated. Once we have estimated the power that we can introduce into the cycle of the tower plant, the main issue consists on how and where it is better to use this energy in the cycle. Several possibilities seem to be interesting a priori, however a more detailed study of each one is to be done in order to get to the most economic and efficient layout. The work related to the tower thermal power plant will be done taking as starting point the master thesis of James Spelling, who did an incredible work in this field and whose work will be a valuable help to continue the research on the proposed concept in this project of combining two plants, tower and trough. The main advantage of the tower design compared to the parabolic trough design is the higher temperature. As it will be explained further, thermal energy at higher temperature can be converted more efficiently, the exergy efficiency is better. In terms of storage, the high temperature results in a cheaper and a more efficient storage system. Nevertheless, the set up of the field of heliostats is more complex than the set up of the parabolic trough lines even though the area for a trough plant must be previously flattened. The lower temperature level that entails an inconvenient itself for a parabolic trough power plant may become an advantage when combining both types of concentrating solar power plants. If the results are positive enough that it seems interesting to combine both types of power plants, another step forward will be done towards the use of the sun energy as a renewable source thus making it a more interesting choice for power generation. Sun potential has already shown as an important technology not only at the present time but also in the future. Commercial solar plants have already achieved levelized energy costs around 12-15 UScts/kWh, and the potential for cost reduction is expected to follow this trend even further, to costs as low as 5 UScts/kWh. In addition the taxes imposed for the non-green power should make even more interesting the use of concentrating solar power plants. The requirements of high beam normal radiation lead to a limited amount of suitable places where the implantation of this technology is possible. However many places exist on Earth where the conditions are perfectly adapted, we talk about regions such as United States (the country with more carbon dioxide emissions in the world), some regions in Mexico, North Africa, India, Australia, northeastern Brazil and some locations around the Mediterranean, especially in the south of Spain. The challenge is therefore set for a change in our energy production scheme.

2010

Optimisation of integrated energy systems for remote communities considering economic, LCA factors and gaseous emissions with evolutionary algorithm

Xavier Pelet

Nowadays the methods of design, planning and managing of integrated energetic systems which allow an overall view of all possibilities are still embryonic. However, this first phase of the design is crucial if we want to aim at a better resources management and at the decrease of energy consumption togheter with reduced pollution. Dealing with energetic energy integrated systems implies dealing with complex systems exploiting the synergy between the various components (for example the thermal energy of a diesel engine produced during the night is valorised by the Rankine Organic Cycle of a solar thermal plant). The context of the isolated communities further increases the difficulties and the needs for a more rational energy use considering the long distance of transportation linked to the supply of fossil fuels. These sites are often located in very precarious environments, with limited or inexistent resources, and with additional requirements for desalination (arid zones). ...........

2004

Monte Carlo Modeling of Crystal Channeling at High Energies

Philippe Jean Schoofs

Charged particles entering a crystal close to some preferred direction can be trapped in the electromagnetic potential well existing between consecutive planes or strings of atoms. This channeling effect can be used to extract beam particles if the crystal is bent beforehand. Crystal channeling is becoming a reliable and efficient technique for collimating beams and removing halo particles. At the European Organization for Nuclear Research (CERN), the installation of silicon crystals in the Large Hadron Collider (LHC) is under scrutiny by the UA9 collaboration with the goal of investigating if they are a viable option for the collimation system upgrade. This thesis describes a new Monte Carlo model of planar channeling which has been developed from scratch in order to be implemented in the FLUKA code simulating particle transport and interactions. Crystal channels are described through the concept of continuous potential taking into account thermal motion of the lattice atoms and using Moliere screening function. The energy of the particle transverse motion determines whether or not it is trapped between the crystal planes while single Coulomb scattering on lattice atoms can lead to dechanneling. The volume capture and reflection applying to quasi-channeled particles are also modeled. Analogously to dechanneling, single scattering is used to determine the occurrence of volume capture. The parameters of the crystals, such as torsion or miscut, are described as well. For channeled particles, the suppression of electromagnetic and nuclear collisions is implemented. It is stronger for particles oscillating close to the center of the channel and is crucial for a correct evaluation of the rate of dechanneling without having recourse to the use of a macroscopic dechanneling length. The UA9-H8 experiment conducted at CERN aims at investigating new crystal physics as well as characterizing crystals that can be of interest in view of the implementation of crystal collimation at CERN, including in the LHC. This experiment uses silicon strip detectors situated on both sides of the crystal. Putting together upstream and downstream tracks in coincidence and matching at an identical fitted location on the crystal, it yields information about the deflections given to the beam population. Several runs from the UA9-H8 experiment are analyzed and compared to the model results. Channeling and dechanneling rates, as well as angular distributions at crystal exit are shown to be in a very encouraging agreement both for strip and quasi-mosaic crystals.

EPFL2014