Volume 41, Issue 1 - Special Issue: The 13th Joint European Thermodynamics Conference JETC2015, Guest Editors: Michel Feidt and Daniel Tondeur

Mass flux occurring when a substance evaporates from an open surface is proportional to its saturated vapor pressure at a given temperature. The proportionality coefficient that relates this flux to the vapor pressure shows how far a system is from equilibrium and is called the accommodation coefficient. Under vacuum, when a system deviates from equilibrium to the greatest extent possible, the accommodation coefficient equals unity. Under finite pressure, however, the accommodation coefficient is no longer equal to unity, and in fact, it is much less than unity. In this article, we consider the isothermal evaporation or sublimation of low-volatile individual substances under conditions of thermogravimetric analysis, when the external pressure of the purging gas is equal to the atmospheric pressure and the purging gas rate varies. When properly treated, the dependence of sample mass over time provides us with various information on the properties of the examined compound, such as saturated vapor pressure, diffusion coefficient, and density of the condensed (liquid or solid) phase at the temperature of experiment. We propose here the model describing the accommodation coefficient as a function of both substance properties and experimental conditions. This model gives the final expression for evaporation rate, and thus for mass dependence over time, with approximation parameters resulting in the properties being sought.

The traditional connection between rate constants and free energy landscapes is extended to define effective free energy landscapes relevant on any chosen timescale. Although the Eyring–Polanyi transition state theory specifies a fixed timescale of τ=h/kBT${\tau =h/k_{\mathrm {B}}T}$, we introduce instead the timescale of interest for the system in question, e.g. the observation time. The utility of drawing such landscapes using a variety of timescales is illustrated by the example of Holliday junction resolution. The resulting free energy landscapes are easier to interpret, clearly reveal observation time dependent effects like coalescence of short-lived states, and reveal features of interest for the specific system more clearly.

In the present article, an endoreversible Curzon–Ahlborn engine is studied by considering a non-linear heat transfer law, particularly the Dulong–Petit heat transfer law, using the `componendo and dividendo' rule as well as a simple differentiation to obtain the Curzon–Ahlborn efficiency as proposed by Agrawal in 2009. This rule is actually a change of variable that simplifies a two-variable problem to a one-variable problem. From elemental calculus, we obtain an analytical expression of efficiency and the power output. The efficiency is given only in terms of the temperatures of the reservoirs, such as both Carnot and Curzon–Ahlborn cycles. We make a comparison between efficiencies measured in real power plants and theoretical values from analytical expressions obtained in this article and others found in literature from several other authors. This comparison shows that the theoretical values of efficiency are close to real efficiency, and in some cases, they are exactly the same. Therefore, we can say that the Agrawal method is good in calculating thermal engine efficiencies approximately.

This article presents the results obtained from an energy-exergy analysis of a vapor compression refrigeration system during induced transient regimes. Using experimental data, exergy destruction as a function of time under the influence of some factors that perturb the stationary regime, such as deactivation of piston, variation of mass flow rate and initial temperature of cooled fluid, and diminution of the compressor rotation speed, was calculated. Under the perturbation, an antagonistic increase in the coefficient of performance and a decrease in exergy efficiency were noted.

We report heat pulse experiments at room temperature that cannot be described by Fourier's law. The experimental data are modeled properly by the Guyer–Krumhansl equation, in its over-diffusion regime. The phenomenon may be due to conduction channels with differing conductivities and parallel to the direction of the heat flux.

The process of bone remodeling includes a cycle of repair, renewal, and optimization. This adaptation process, in response to variations in external loads and chemical driving factors, involves three main types of bone cells: osteoclasts, which remove the old pre-existing bone; osteoblasts, which form the new bone in a second phase; osteocytes, which are sensing cells embedded into the bone matrix, trigger the aforementioned sequence of events. The remodeling process involves mineralization of the bone in the diffuse interface separating the marrow, which contains all specialized cells, from the newly formed bone. The main objective advocated in this contribution is the setting up of a modeling and simulation framework relying on the phase field method to capture the evolution of the diffuse interface between the new bone and the marrow at the scale of individual trabeculae. The phase field describes the degree of mineralization of this diffuse interface; it varies continuously between the lower value (no mineral) and unity (fully mineralized phase, e.g. new bone), allowing the consideration of a diffuse moving interface. The modeling framework is the theory of continuous media, for which field equations for the mechanical, chemical, and interfacial phenomena are written, based on the thermodynamics of irreversible processes. Additional models for the cellular activity are formulated to describe the coupling of the cell activity responsible for bone production/resorption to the kinetics of the internal variables. Kinetic equations for the internal variables are obtained from a pseudo-potential of dissipation. The combination of the balance equations for the microforce associated to the phase field and the kinetic equations lead to the Ginzburg–Landau equation satisfied by the phase field with a source term accounting for the dissipative microforce. Simulations illustrating the proposed framework are performed in a one-dimensional situation showing the evolution of the diffuse interface separating new bone from marrow.