• Energy Research

Abstract Conventional steam power cycles have their limitations on recovering low grade waste heat, therefore other alternatives are required in these cases. Organic Rankine Cycle (ORC) is suitable for power generation based on various heat sources including solar, geothermal, biomass or waste heat. ORC working fluids can be characterized as wet, dry or isentropic. The aim of this paper is to give a method to find novel dry or isentropic working fluids based on simple physical properties, like degree of freedom and isochoric heat capacity.

Adiabatic processes in the liquid–vapor two-phase region were studied with several equations of state. The comparison of the resulting isentropes, particularly their patterns in quality (fraction of vapor phase) vs temperature diagrams, indicates that there are two different classes of fluids: One class shows a simple pattern where isentropes entering the two-phase region never leave it again; the other shows a more complicated pattern with reentrant isentropes, which may either cross the entire two-phase region or exhibit a retrograde behavior. The existence of these two classes can be related to the shapes of entropy–volume or temperature–entropy curves, and these in turn to the temperature dependence of ideal-gas heat capacities. The two-phase isentrope that runs to the critical point approaches it with an infinite slope in the quality–temperature diagram. The slope is positive for reference equations of state, but negative for all other equations of state used in this work.

To have a sustainable society, the need to use renewable sources to produce electricity is inevitable [...]

Abstract Power generation from low-temperature heat sources (80–300 °C) like thermal solar, geothermal, biomass or waste heat has been becoming more and more significant in the last few decades. Organic Rankine Cycle (ORC) uses organic working fluids, obtaining higher thermal efficiency than with water used in traditional Rankine Cycles, because of the physical (thermodynamic) properties of these fluids. The traditional classification of pure (one-component) working fluids is based on the quality of the expanded vapour after an isentropic (adiabatic and reversible) expansion from saturated vapour state, and distinguishes merely three categories: wet, dry and isentropic working fluids. The purpose of this paper is to show the deficiencies of this traditional classification and to introduce novel categorisation mostly to help in finding the thermodynamically optimal working fluid for a given heat source.

This study proposes an innovative system for recovering waste heat from exhaust air after a regenerative thermal oxidiser process, integrating a Carnot battery and photovoltaic (PV) modules. The Carnot battery incorporates an organic Rankine cycle (ORC) with a recuperator, thermal energy storage (TES), and heat pump. Waste heat is initially captured in TES, with additional energy extracted by a heat pump to increase the temperature of a secondary fluid, effectively charging TES from both direct and indirect sources. The stored heat enables electricity generation via ORC. The result of this study shows a heat pump COP between 2.55 and 2.87, the efficiency of ORC ranging from 0.125 to 0.155, and the power-to-power of the Carnot battery between 0.36 and 0.40. Moreover, PV generates 1.35 GWh annually, primarily powering the heat pump and ORC system pump. The proposed system shows a total annual net generation of 4.30 GWh. Economic evaluation across four configurations demonstrates favourable outcomes, with a return on investment between 25% and 160%. The economic evaluation examined configurations with and without the PV system and recuperation process in the ORC. Results indicate that incorporating the PV system and recuperator significantly increases power output, offering a highly viable and sustainable energy solution.

Abstract In this paper the most important properties of the lattice Boltzmann methods are reviewed with focus on two-phase flow modeling. The lattice methods are compared with the conventional computational fluid dynamics methods, their advantages and disadvantages are highlighted. Necessary improvements for practical applications are summarized.

In order to lessen reliance on fossil fuels, a rise in interest in the utilization of fluctuating and intermittent heat sources derived from renewable energy (such as solar thermal, ocean thermal, and geothermal) and waste heat has been observed. These heat sources could be used to generate electricity at relatively low and medium temperatures, for example, through the organic Rankine cycle (ORC). In some case studies, various approaches have been developed to deal with and design ORCs in the desired operating condition utilizing suitable working fluids. This article aims to review some designs and integrated systems of ORC with thermal energy storage (TES) and a two-phase expansion system focusing on the utilization of medium- and low-temperature heat sources in which some subcritical ORCs are presented. Moreover, several possible control systems (both conventional and advanced ones) of ORC with TES and a two-phase expansion system are reported and compared. At the end of this article, the possible future developments of design and control systems are discussed to describe advanced ORC for utilizing low-grade heat sources. This study aims to provide researchers and engineers with an insight into the challenges involved in this process, making industrialization of ORC technology more extensive, in particular when combined with TES and a two-phase expansion system.