Entropy: Thermodynamics – Energy – Environment – Economy

Entropie - ISSN 2634-1476 - © ISTE Ltd

Journal issues

Recent articles

The much-needed energy transition brings special focus on fuel cell micro-combined Heat and Power (mCHP or micro-CHP) systems for residential uses, one of which is a Solid Oxide Fuel Cell (SOFC), fed by natural gas, designed to provide continuously 1.5 kWel with an associated amazingly high expected Low heating Value (LHV) electrical efficiency of 60%. This power output can be modulated as desired down to 500 Wel and heat can also be recovered to partially contribute to the heat demand of the household. This system has been installed in a laboratory environment and has been specifically instrumented in order to evaluate its performance with different thermal loads and electrical output power settings. In this paper, focus is brought on the resulting thermal output and efficiencies, both thermal and electrical, which have also been modelled with great goodness of fit. With several electrical power outputs between the 500-1500 Wel range, this study shows total High Heating Value (HHV) total efficiencies up to 88-89% at minimal return temperatures (around 20°C) in the heat recovery circuit. Maximum LHV electrical efficiency has been found to be equal to 57% at nominal output power (regardless of the thermal loads), which is close to the manufacturer’s target of 60%.

This article is dedicated to the analysis of the magnetic induction effects on the iron loss and the equivalent diagrams elements of a ferromagnetic domain subjected to this induction by using a parallelepipedic ferromagnetic domain subjected to a uniaxial magnetic flux. Induction B produced by an interdependent known source with the domain causes the domain saturation. This domain increases its consumption and sees the decrease of the resistances and the reactances values of its equivalent diagrams vis-a-vis the induction producing source. The increase in the iron loss and the reduction in the passive elements values of the equivalent diagrams are confirmed by the reduction in the resistivity and the permeability of the domain in Voltage Model where elements RL are in parallel as in Current Model where elements RL are in series. This phenomenon is visible during the duality parallel-series checking of the domain equivalent diagrams vis-a-vis the inductive source.

Bioeconomics is a new approach to the relationship between the economy and the environment developed by N. Georgescu-Roegen (1906-1994), a great economist of the 20th century who was also a mathematician, philosopher and historian of science. The economy, as a sub-system of the biosphere, is understood in a global ecological context. It is also inseparable from the historical dimension of the development of societies, given the limited access to a stock of resources (energy and matter) taken from the environment. The ultimate aim of this original approach is to reconcile economic development with ecological constraints and to lead the economy towards sufficiency.

The so-called “water vapor pump” cycle is defined by the selective recycling of the water vapor carried by the combustion products at the outlet of the thermal machine by exchange of mass and heat between the exiting combustion products and the incoming atmospheric air. With hydrogen fuel, this form of wet combustion is capable of very high energy and ecological performance. In this context, we present here the Hydrometric Combustion Diagram (HCD) of hydrogen and apply this tool to anticipate the energy performance of this new fuel whose PCS exceeds its PCI by 18%. These expectations also concern the case of gas turbines in the case of wet combustion which, moreover, are, a priori, highly consuming additional water. The formation of atmospheric water plumes, the "cost" of its elimination, the possible residual pollution due to NOx are also presented, this concerning the use of hydrogen fuel in all thermal combustion machines, including in fuel cells. All applications combined and in a cogeneration context, wet combustion, of which the so-called “water vapor pump” cycle is part, increases the dew point temperature of the combustion products by approximately 10°C and promotes useful energy recovery. approaching 100% of the higher calorific value of the fuel (100% of the PCS). What is to be emphasized with hydrogen fuel.

The exponential growth in the use of digital technology is forcing changes in the engineering of material and energy transformation processes, not only in terms of training, but also in terms of inventions of various origins, to revitalize this discipline, which is subject to strong environmental constraints. This near-breakthrough situation needs to be translated into greater creativity before we can achieve breakthrough or incremental innovations. To achieve this objective, it is sometimes useful to bring together two normally disjoint fields to generate ideas that are robust enough to be applied. This article discusses this method, based on biomimicry. Can taking advantage of nature’s ingenuity foster the emergence of anthropocentric inventions and thus accelerate innovation in the field of process engineering? This is the question posed by the authors in their quest to illustrate the opportunities and advantages of such an approach, as well as its current limitations.

Le Congrès de la Société Française de Thermique a lieu pour la première fois à Strasbourg. A la fois capitale européenne et capitale alsacienne, Strasbourg est une grande ville universitaire s’appuyant sur le dynamisme de son université et de ses nombreux laboratoires de recherche pour asseoir sa réputation d’excellence. La 32ème Congrès Français de Thermique s’est déroulé du 4 au 7 juin 2024 à l’INSA Strasbourg. Le thème scientifique choisi pour cette édition est "Thermique et Architecture".

The objective of this study is to develop a transient CFD model representing the dynamic behavior of Trombe walls. The current model takes into consideration variable solar radiation as well as the presence of occupants and their activities. The temperature and velocity profiles at different locations are plotted. The moisture’s impact on the hygrothermal behavior is then investigated. The results show that the relative humidity distribution inside the system is mainly influenced by the ventilation strategy in which the moisture is accelerated and transported by the flow in the case of vents opening. The finding revealed that the maximum relative humidity (RH) reached in the system doesn’t exceed 22%. However, due to the lower temperature values observed in the system during overcast winter nights, there is a potential condensation risk on glass and wall surfaces.

Flows within solar receivers are turbulent and highly anisothermal, as they are subjected to significant temperature gradients. These conditions generate a strong coupling between heat transport and flow dynamics, requiring specific modeling to account for the effects of anisothermy on flow dynamics. In this article, we focus in particular on energy transfers between turbulent scales and thermal scales. A spectral analysis is developed and presented.

This article deals with the contribution of reduced models in the context of estimating the thermal diffusivity of liquid metals. The identification of this property is carried out using an experimental setup suitable for high temperatures, combined with an inverse process involving a numerical model that describes the transient thermal conduction and advection phenomena within the molten metal. A modal reduction technique of the numerical model is proposed here, in which temperature and velocity are decomposed on a POD basis. This double reduction procedure allows for a significant reduction in the order of the numerical model used in the inverse procedure, and thus in the identification computational time compared to classical finite element models. Initial results demonstrate the benefits of the technique in terms of results accuracy and computational speed.

Thermochemical heat storage is a promising technology: it enables long-term heat storage with negligible heat loss and high energy densities. Composite sorbents based on silica, polyethylene glycol (PEG) and a thermochemical salt were developed for a transport application and studied in an open fixed-bed reactor. These composites were cycled to assess their stability and to evaluate their water sorption capacity and storage energy density. The sorption kinetics was also investigated.