Laws of thermodynamics

Summary

The laws of thermodynamics are a set of scientific laws which define a group of physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems in thermodynamic equilibrium. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. They state empirical facts that form a basis of precluding the possibility of certain phenomena, such as perpetual motion. In addition to their use in thermodynamics, they are important fundamental laws of physics in general and are applicable in other natural sciences. Traditionally, thermodynamics has recognized three fundamental laws, simply named by an ordinal identification, the first law, the second law, and the third law. A more fundamental statement was later labelled as the zeroth law after the first three laws had been established. The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature: If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. The first law of thermodynamics states that, when energy passes into or out of a system (as work, heat, or matter), the system's internal energy changes in accordance with the law of conservation of energy. The second law of thermodynamics states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems never decreases. A common corollary of the statement is that heat does not spontaneously pass from a colder body to a warmer body. The third law of thermodynamics states that a system's entropy approaches a constant value as the temperature approaches absolute zero. With the exception of non-crystalline solids (glasses), the entropy of a system at absolute zero is typically close to zero. The first and second laws prohibit two kinds of perpetual motion machines, respectively: the perpetual motion machine of the first kind which produces work with no energy input, and the perpetual motion machine of the second kind which spontaneously converts thermal energy into mechanical work.

Official source

https://en.wikipedia.org/wiki/Laws_of_thermodynamics

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Three quarters of the thesis will be devoted to the discussion of non equilibrium systems. We show how certain biological systems cannot be described by standard thermodynamics. The reason is that the energy consumption due to the hydrolysis of ATP imposes to the systems a directionality and therefore a chemical flux that is different from zero. More specifically, we will apply the formalism to molecular chaperones, that are proteins involved in a plethora of biological processes, with a particular in-depth analysis on the mechanisms of protein unfolding and refolding mediated by the two families of chaperones Hsp70 and GroEL. Moreover, with the same mathematical tools, we will provide a qualitative description of some phenomena regarding the Atp-binding cassette transporters, that are important membrane protein complexes used to translocate small molecules in and out of the cell. In the remaining quarter we will analyze the deformation of a polymer chain when it is pulled by an external force. We will explain how it is possible to quantify the orientation along the force and the shrinking along the other directions. It will be also shown that the transverse section shrinks isotropically once the orientation along the force is complete. The main quantities that are used to identify the shape and the orientation of a polymer chain can all be written as a function of a universal quantity that is independent, in first ap- proximation, by the number of monomers, by the rigidity, and even by the volume exclusion.

EPFL2018

The development of multinary nitrides materials has revolutionised the hard coatings industry over the last 20 years. Especially important materials systems in this matter have been TiAlN and CrAlN which shows higher hardness, better oxidation resistance and can perform at higher temperatures as compared to TiN. When synthesised through physical vapour deposition techniques these system form cubic rock salt structured Ti1-xAlxN and Cr1-xAlxN solid solutions as a metastable phase over a large part of the concentration range. One of the main objectives during the optimisation of the coatings has been to increase the amount of Al in the coating while still keeping the rock salt structure, avoiding phase separation and the formation of hexagonal wurtzite AlN. However, in Al-rich TiAlN coatings it was found that isostructural decomposition within the cubic phase was in fact beneficial for the coatings performance at working temperatures just below 1000 °C. The reason was that the formation of strained coherent c-AlN domains within the grains initiated a age-hardening of the coating. In the CrAlN coatings it is possible to solve a larger amount of Al in the cubic phase. Possibly connected to this fact is that no isostructural decomposition and in principle no age hardening has been observed in rock salt structured Cr1-xAlxN. Although large series of experimental investigations have been performed on these systems, no systematic theoretical study has yet been undertaken. This theoretical work is an attempt by means of first-principles calculations together with thermodynamics considerations within the framework of alloy theory, to close or decrease the knowledge gap between experimental observations of cutting performance of various coatings and the fundamental quantum mechanical and thermodynamics processes that governs it. We first consider the structural properties of the treated mixed nitride systems. The concept of atomic misfit or volume difference, which is well known in the community is studied and the physics that leads to a positive deviation from Vegard's rule is revealed. Then the TiAlN and CrAlN systems are studied in detail. A clear connection between the development of the electronic structure with composition and the mixing enthalpy of the alloys, and thus the tendency for decomposition, is found for TiAlN. The importance of magnetic effects on the thermodynamics of mixing in CrAlN is established leading to a qualitative lower tendency for decomposition. Since the nitrogen composition can deviate substantially from perfect stoichiometry in these systems, a study of the influence of nitrogen vacancies on the decomposition pattern of TiAlN in the cubic phase is performed. The results imply that a presence of nitrogen sub-stoichiometry in Al-rich TiAlN will enhance the tendency for isostructural decomposition. The achieved results including those for the systems ScAlN and HfAlN are compared and discussed especially by considering volume misfit and electronic bandstructure effects as driving forces for coherent and incoherent decomposition.

EPFL2009

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In the pulp and paper industry, multi-effect evaporators are used to evaporate water from black liquor solutions to allow its recycle as chemicals and fuel for the process. The thermodynamic principle of the multi-effect evaporator consists in a serie of reboilers operating at different pressures; the water evaporated at one stage is condensed and used as the heat source for another stage. Due to its strong integration with the process, it is worth to analyse the integration of the multi-effect evaporator with the rest of the process. To do so a thermo-economic analysis model of the evaporation system has been developped. The example is based on the evaporation system of a calcium bisulfite pulp manufacturing mill located in Switzerland. This system involves 3 multi-effect evaporators fed at different concentrations of black liquor. A systematic analysis of the system Grand composite curve has been developed to identify pertinent process modifications. From this analysis, several modifications like decreasing the deltaTmin of a stream, increasing or decreasing pressures of evaporation effects have been evaluated. For each of these measures, we have analysed the thermo-economic aspects, adapting the pinch analysis rules to account for the thermo-econmic benefit of integration. By these measures, the minimum energy requirement of the multi-effect evaporation system can be reduced by up to 20%. Resulting from the integration of the utility system, the related utility cost can be diminished of up to 23% from the base case model. The integration of heat pumping system and the utilities has then been analysed in order to reduce the exergy degradation in the energy conversion system. A thermoeconomic analysis including operating and investment cost estimation, evaluation of the Net Present Value and Payback Time of different process configurations corresponding to different energy savings scenarios has been performed. The integration of a heat pump system shows a reduction of the Net Present Value and an acceptable Payback Time compared to the base case model. A sensitivity analysis on electricity and natural gas prices has then been performed in order to better understand the economic condition of the integration.

2008

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EPFL2009

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2008